We present new calculations of transit spectra of super-Earths that allow for atmospheres with arbitrary proportions of common molecular species and haze. We test this method with generic spectra, reproducing the expected systematics and absorption features, then apply it to the nearby super-Earth GJ 1214b, which has produced conflicting observational data, leaving the questions of a hydrogen-rich versus hydrogen-poor atmosphere and the water content of the atmosphere ambiguous. We present representative transit spectra for a range of classes of atmosphere models for GJ 1214b. Our analysis supports a hydrogen-rich atmosphere with a cloud or haze layer, although a hydrogen-poor model with less than 10% water is not ruled out. Several classes of models are ruled out, however, including hydrogen-rich atmospheres with no haze, hydrogen-rich atmospheres with a haze of about 0.01-micron tholin particles, and hydrogen-poor atmospheres with major sources of absorption other than water. We propose an observational test to distinguish hydrogen-rich from hydrogen-poor atmospheres and make predictions for the spectral features of HD 97658b based on our best fits for GJ 1214b. Finally, we provide a library of theoretical transit spectra for super-Earths with a broad range of parameters to facilitate future comparison with anticipated data.
We investigate the stability of super Earth atmospheres around M stars using a 7-parameter, analytical framework. We construct stability diagrams in the parameter space of exoplanetary radius versus semi-major axis and elucidate the regions in which stable atmospheres may exist. We find that super Earth atmospheres with higher mean molecular weights and enhanced metallicities occupy a smaller region of allowed parameter space, because of the dual effects of diminished advection and enhanced radiative cooling. Furthermore, many super Earths which reside within the habitable zones of M stars may not possess stable, Earth-like atmospheres. We apply our stability diagrams to GJ 436b and GJ 1214b, and demonstrate that Earth-like elemental compositions for their atmospheres are disfavoured if these exoplanets possess solid surfaces and shallow atmospheres. Finally, we construct stability diagrams tailored to the Kepler dataset, for G and K stars, and predict that about half of the exoplanetary candidates are expected to habour stable atmospheres if Earth-like conditions are assumed. We include 55 Cancri e and CoRoT-7b in our stability diagram for G stars.
The majority of the extragalactic sources yet detected at TeV photon energies belong to the class of "high frequency peaked BL Lacs" (HBLs) that exhibit a spectral energy distribution with a lower peak in the X-ray band. Such spectra are well described in terms of a log-parabolic shape with a considerable curvature, and widely interpreted as synchrotron emission from ultrarelativistic electrons outflowing in a relativistic jet; these are expected to radiate also in gamma-rays by the inverse Compton process. Recently we have compared the X-ray spectral parameter distributions of TeV detected HBLs (TBLs) with those undetected (UBLs), and found that the distributions of the peak energies E_p are similarly symmetric around a value of a few keVs for both subclasses, while the X-ray spectra are broader for TBLs than for UBLs. Here we propose an acceleration scenario to interpret both the E_p and the spectral curvature distributions in terms of a coherent and a stochastic acceleration mechanisms, respectively. We show how the curvature parameter b< 0.3 - 0.7 of the synchrotron X rays, that depends only on the latter acceleration component, can be related to the inverse Compton luminosity in gamma-rays, so introducing a link between the X-ray and the TeV observations of HBLs.
ABRIGED Herschel/SPIRE has provided confusion limited maps of deep fields at
250, 350, and 500um, as part of the HerMES survey. Due to confusion, only a
small fraction of the Cosmic Infrared Background can be resolved into
individually-detected sources. Our goal is to produce deep galaxy number counts
and redshift distributions below the confusion limit, which we then use to
place strong constraints on the origins of the cosmic infrared background and
on models of galaxy evolution.
We individually extracted the bright SPIRE with a method using the positions,
the flux densities, and the redshifts of the 24um sources as a prior, and
derived the number counts and redshift distributions of the bright SPIRE
sources. For fainter SPIRE sources, we reconstructed the number counts and the
redshift distribution below the confusion limit using the deep 24um catalogs
associated with photometric redshift and information provided by the stacking
of these sources into the deep SPIRE maps. Finally, by integrating all these
counts, we studied the contribution of the galaxies to the CIB as a function of
their flux density and redshift.
Through stacking, we managed to reconstruct the source counts per redshift
slice down to ~2 mJy in the three SPIRE bands, which lies about a factor 10
below the 5sigma confusion limit. None of the pre-existing population models
are able to reproduce our results at better than 3sigma. Finally, we
extrapolate our counts to zero flux density in order to derive an estimate of
the total contribution of galaxies to the CIB, finding 10.1, 6.5, and 2.8
nW/m2/sr at 250, 350, and 500um, respectively. These values agree well with
FIRAS absolute measurements, suggesting our number counts and their
extrapolation are sufficient to explain the CIB. Finally, combining our results
with other works, we estimate the energy budget contained in the CIB between 8
and 1000um: 26 nW/m2/sr.
We present a quantitative study on the properties at death of fast-rotating massive stars evolved at low-metallicity, objects that are proposed as likely progenitors of long-duration gamma-ray bursts (LGRBs). We perform 1D+rotation stellar-collapse simulations on the progenitor models of Woosley & Heger (2006) and critically assess their potential for the formation of a black hole and a Keplerian disk (namely a collapsar) or a proto-magnetar. We note that theoretical uncertainties in the treatment of magnetic fields and the approximate handling of rotation compromises the accuracy of stellar-evolution models. We find that only the fastest rotating progenitors achieve sufficient compactness for black-hole formation while the bulk of models possess a core density structure typical of garden-variety core-collapse supernova (SN) progenitors evolved without rotation and at solar metallicity. Of the models that do have sufficient compactness for black-hole formation, most of them also retain a large amount of angular momentum in the core, making them prone to a magneto-rotational explosion, therefore preferentially leaving behind a proto-magnetar. A large progenitor angular-momentum budget is often the sole criterion invoked in the community today to assess the suitability for producing a collapsar. This simplification ignores equally important considerations such as the core compactness, which conditions black-hole formation, the core angular momentum, which may foster a magneto-rotational explosion preventing black-hole formation, or the metallicity and the residual envelope mass which must be compatible with inferences from observed LGRB/SNe. Our study suggests that black-hole formation is non trivial, that there is room for accommodating both collapsars and proto-magnetars as LGRB progenitors, although proto-magnetars seem much more easily produced by current stellar-evolutionary models.
Fluctuations in the cosmic microwave background (CMB) contain information which has been pivotal in establishing the current cosmological model. These data can also be used to test well-motivated additions to this model, such as cosmic textures. Textures are a type of topological defect that can be produced during a cosmological phase transition in the early universe, and which leave characteristic hot and cold spots in the CMB. We apply Bayesian methods to carry out an optimal test of the texture hypothesis, using full-sky data from the Wilkinson Microwave Anisotropy Probe. We conclude that current data do not warrant augmenting the standard cosmological model with textures. We rule out at 95% confidence models that predict more than 6 detectable cosmic textures on the full sky.
We have obtained VIMOS/VLT optical integral field spectroscopy (IFS) data for a sample of 4 LIRGs which have been selected at a similar distance ($\sim$ 70 Mpc) to avoid relative resolution effects. They have been classified in two groups (isolated disk and post-coalescence mergers) according to their morphology. The $kinemetry$ method (developed by Krajnovic and coworkers) is used to characterize the kinematic properties of these galaxies and to discuss new criteria for distinguishing their status. We present and discuss new kinematic maps (i.e., velocity field and velocity dispersion) for these four galaxies. The morphological and kinematic classifications of these systems are consistent, with disks having lower kinematic asymmetries than post-coalescence mergers. We then propose and discuss a new kinematic criterion to differentiate these two groups. This criterion distinguishes better these two categories and has the advantage of being less sensitive to angular resolution effects. According to the previous criteria,the present post-coalescence systems would have been classified as disks. This indicates that the separation of disks from mergers is subjective to the definition of `merger'. It also suggests that previous estimates of the merger/disk ratio could have been underestimated, but larger samples are necessary to establish a firmer conclusion.
Context: It is crucial to develop a method for classifying objects detected in deep surveys at infrared wavelengths. We specifically need a method to separate galaxies from stars using only the infrared information to study the properties of galaxies, e.g., to estimate the angular correlation function, without introducing any additional bias. Aims. We aim to separate stars and galaxies in the data from the AKARI North Ecliptic Pole (NEP) Deep survey collected in nine AKARI / IRC bands from 2 to 24 {\mu}m that cover the near- and mid-infrared wavelengths (hereafter NIR and MIR). We plan to estimate the correlation function for NIR and MIR galaxies from a sample selected according to our criteria in future research. Methods: We used support vector machines (SVM) to study the distribution of stars and galaxies in the AKARIs multicolor space. We defined the training samples of these objects by calculating their infrared stellarity parameter (sgc). We created the most efficient classifier and then tested it on the whole sample. We confirmed the developed separation with auxiliary optical data obtained by the Subaru telescope and by creating Euclidean normalized number count plots. Results: We obtain a 90% accuracy in pinpointing galaxies and 98% accuracy for stars in infrared multicolor space with the infrared SVM classifier. The source counts and comparison with the optical data (with a consistency of 65% for selecting stars and 96% for galaxies) confirm that our star/galaxy separation methods are reliable. Conclusions: The infrared classifier derived with the SVM method based on infrared sgc- selected training samples proves to be very efficient and accurate in selecting stars and galaxies in deep surveys at infrared wavelengths carried out without any previous target object selection.
Type Ia supernovae are thought to be caused by thermonuclear explosions of a carbon-oxygen white dwarf in close binary systems. In the single-degenerate scenario (SDS), the companion star is non-degenerate and can be significantly affected by the explosion. We explore this interaction by means of multi-dimensional adaptive mesh refinement simulations using the FLASH code. We consider several different companion types, including main-sequence-like stars (MS), red giants (RG), and helium stars (He). In addition, we include the symmetry-breaking effects of orbital motion, rotation of the non-degenerate star, and Roche-lobe overflow. A detailed study of a sub-grid model for Type Ia supernovae is also presented. We find that the dependence of the unbound stellar mass and kick velocity on the initial binary separation can be fitted by power-law relations. By using the tracer particles in FLASH, the process leading to the unbinding of matter is dominated by ablation, which has usually been neglected in past analytical studies. The level of Ni/Fe contamination of the companion that results from the passage of the supernova ejecta is found to be a $\sim 10^{-5} M_{\odot}$ for the MS star, $\sim 10^{-4} M_{\odot}$ for the He star, and $\sim 10^{-8} M_{\odot}$ for the RG. The spinning MS companion star loses about half of its initial angular momentum during the impact, causing the rotational velocity to drop to a quarter of the original rotational velocity, suggesting that the Tycho G star is a promising progenitor candidate in the SDS.
We present observations of the Type Ic supernova (SN Ic) 2011bm spanning a period of about one year. The data establish that SN 2011bm is a spectroscopically normal SN Ic with moderately low ejecta velocities and with a very slow spectroscopic and photometric evolution (more than twice as slow as SN 1998bw). The Pan-STARRS1 retrospective detection shows that the rise time from explosion to peak was 40 days in the R band. Through an analysis of the light curve and the spectral sequence, we estimate a kinetic energy of 7-17 foe and a total ejected mass of 7-17 Mo, 5-10 Mo of which is oxygen and 0.6-0.7 Mo is 56Ni. The physical parameters obtained for SN 2011bm suggest that its progenitor was a massive star of initial mass 30-50 Mo. The profile of the forbidden oxygen lines in the nebular spectra show no evidence of a bi-polar geometry in the ejected material.
We present a new library of synthetic spectra based on the stellar atmosphere code PHOENIX. It covers the wavelength range from 500{\AA} to 55000{\AA} with a resolution of R=500000 in the optical and near IR, R=100000 in the IR and {\Delta}{\lambda}=0.1{\AA} in the UV. The parameter space covers 2300K<=Teff<=8000K, 0.0<=log(g)<=6.0, -4.0<=[Fe/H]<=+1.0 and -0.3<=[{\alpha}/Fe]<=+0.8. The library is work-in-progress and going to be extended to at least Teff=25000K. We use a new self-consistent way of describing the microturbulence for our model atmospheres. The entire library of synthetic spectra will be available for download. Futhermore we present a method for fitting spectra, especially designed to work with the new 2nd generation VLT instrument MUSE. We show that we can determine stellar parameters (Teff, log(g), [Fe/H] and [{\alpha}/Fe]) and even single element abundances.
We have developed the "S_IX" statistic to identify bright, highly-likely
Active Galactic Nucleus (AGN) candidates solely on the basis of WISE, 2MASS and
Rosat all-sky survey data. This statistic was optimized with SDSS data and
tested with Lick 3-m Kast spectroscopy. We find that sources with S_IX < 0 have
a >~95% likelihood of being an AGN (defined in this paper as a Seyfert 1,
quasar or blazar). Application to the currently available WISE/2MASS/RASS data
yields the "W2R" sample of 1,924 sources with S_IX < 0, only 831 of which are
currently in the Veron-Cetty and Veron (VCV) catalog of spectroscopically
confirmed AGN. This indicates that the W2R sample contains ~1,000 new,
relatively bright (J <~ 16) AGN.
We utilize the W2R sample to quantify biases and incompleteness in the VCV
catalog. We find it is highly complete for bright (J < 14), northern
(declination > -20^o) AGN, but the completeness drops below 50% for fainter,
southern samples. Once the full WISE dataset is released, it will be possible
to use the S_IX and similar statistics to identify AGN in any (sufficiently
large) region of sky. This approach has also led to the spectroscopic
identification of 10 new AGN in the Kepler field, more than doubling the number
of AGN being monitored by Kepler.
We report the discovery of a systematic constant time lag between the X-ray and radio flares of the gamma-ray binary LSI +61 303, persistent over long, multi-year, time scale. Using the data of monitoring of the system by RXTE we show that the orbital phase of X-ray flares from the source varies from $\phi_X\simeq 0.35$ to $\phi_X\simeq 0.75$ on the superorbital 4.6 yr time scale. Simultaneous radio observations show that periodic radio flares always lag the X-ray flare by $\Delta\phi_{X-R}\simeq 0.2$. We propose that the constant phase lag corresponds to the time of flight of the high-energy particle filled plasma blobs from inside the binary to the radio emission region at the distance ~10 times the binary separation distance. We put forward a hypothesis that the X-ray bursts correspond to the moments of formation of plasma blobs inside the binary system.
We show that the evolutionary track of a low-mass red giant should make an extended zigzag on the Hertzsprung-Russel diagram just after the bump luminosity, if fast internal rotation and enhanced extra mixing in the radiative zone bring the temperature gradient close to the adiabatic one. This can explain both the location and peculiar surface chemical composition of Li-rich K giants studied by Kumar, Reddy, & Lambert (2011). We also discuss a striking resemblance between the photometric and composition peculiarities of these stars and giant components of RS CVn binaries. We demonstrate that the observationally constrained values of the temperature gradient in the Li-rich K giants agree with the required rate of extra mixing only if the turbulence which is believed to be responsible for this extra mixing is highly anisotropic, with its associated transport coefficients in the horizontal direction strongly dominating over those in the vertical direction.
Measurements conducted with the ASPERA-4 instrument and the magnetometer of the Venus Express spacecraft show that the dynamic pressure of planetary O+ ion fluxes measured in the Venus wake can be significantly larger than the local magnetic pressure and, as a result, those ions are not being driven by magnetic forces but by the kinetic energy of the solar wind. Beams of planetary O+ ions with those properties have been detected in several orbits of the Venus Express through the wake as the spacecraft traverses by the noon-midnight plane along its near polar trajectory. The momentum flux of the O+ ions leads to superalfvenic flow conditions. It is suggested that such O+ ion beams are produced in the vicinity of the magnetic polar regions of the Venus ionosphere where the solar wind erodes the local plasma leading to plasma channels that extend downstream from those regions.
DEBRIS is a flux-limited survey of nearby stars (spectral types A-M) for evidence of debris disks with the Herschel Space Observatory. One goal of the survey is to determine disk incidence as a function of various stellar parameters. Understanding debris disk evolution depends on knowledge of the precise age of stars around which these debris disks are found. However, finding ages for field stars is notoriously difficult. Furthermore, in an unbiased sample like DEBRIS, one is working with stars across many spectral types. This requires a multi-method approach to age determination. In this paper, we outline several methods of age determination broken down by spectral type, including some strengths and limitations of each method. In total, we were able to calculate ages for 263 of 274 F, G, and K-type stars, and all 83 A-type stars in the DEBRIS sample.
Optical observations of the low mass X-ray binary 4U 1735-44 were obtained during 1997-2007 and combined with earlier published observations from 1984-1993 to refine the ephemeris for the system. The linear fit for the time of maximum optical light has the ephemeris HJD = 2445904.0494(90) + [ N x 0.19383222(29)] with a value of chi^2 = 253.5$ for 16 dof and a scatter about phase zero of sigma = 0.061. The new data reconciles the discrepancy between the previous ephemeris and the more recent spectral ephemeris based on emission from the companion star which defined the systems true dynamical phase zero. The optical maximum for 4U 1735-44 now occurs at spectral phase 0.47 \pm 0.05 and thus supports the classic model for an LMXB system. Our data further supports the standard model in several ways. The mean optical flux shows a positive correlation with the RXTE ASM X-ray flux, the relative increases suggesting that the non-X-ray induced optical flux from the companion is < 14 percent of the total optical light from the system. There is no apparent trend in the optical modulation percentage with increasing X-ray flux. The X-ray flux for various ASM energy bands shows no evidence of orbital modulation, eclipses or dips when folded using the new ephemeris.
We examine the distribution of young stars associated with the spiral arms of a simulated L* cosmological disk galaxy. We find age patterns orthogonal to the arms which are not inconsistent with the predictions of classical density wave theory, a view further supported by recent observations of face-on Grand Design spirals such as M51. The distribution of metals within a simulated ~0.1L* disk is presented, reinforcing the link between star formation, the age-metallicity relation, and the metallicity distribution function.
Context: We analyze the NGC 2024 HII region and molecular cloud interface using [12CII] and [13CII] observations. Aims: We attempt to gain insight into the physical structure of the interface layer between the molecular cloud and the HII region. Methods. Observations of [12CII] and [13CII] emission at 158 {\mu}m with high spatial and spectral resolution allow us to study the detailed structure of the ionization front and estimate the column densities and temperatures of the ionized carbon layer in the PDR. Results: The [12CII] emission closely follows the distribution of the 8 mum continuum. Across most of the source, the spectral lines have two velocity peaks similar to lines of rare CO isotopes. The [13CII] emission is detected near the edge-on ionization front. It has only a single velocity component, which implies that the [12CII] line shape is caused by self-absorption. An anomalous hyperfine line-intensity ratio observed in [13CII] cannot yet be explained. Conclusions: Our analysis of the two isotopes results in a total column density of N(H)~1.6\times10^23 cm^-2 in the gas emitting the [CII] line. A large fraction of this gas has to be at a temperature of several hundred K. The self-absorption is caused by a cooler (T<=100 K) foreground component containing a column density of N(H)~10^22 cm^-2.
An update on recent methods for automated stellar parametrization is given. We present preliminary results of the ongoing program for rapid parametrization of field stars using medium resolution spectra obtained using Vainu Bappu Telescope at VBO, Kavalur, India. We have used Artificial Neural Network for estimating temperature, gravity, metallicity and absolute magnitude of the field stars. The network for each parameter is trained independently using a large number of calibrating stars. The trained network is used for estimating atmospheric parameters of unexplored field stars.
Context: As revealed by high-resolution spectral investigations in the wavelength range between 300 and 400 nm, the interstellar extinction curve does not display any sharp electronic absorption bands characteristic for large polyatomic molecules, like polycyclic aromatic hydrocarbons (PAHs), which belong to the most abundant interstellar molecules. Aims: We try to verify whether the absorption curves of mixtures of medium-sized PAHs produced in the laboratory can explain the astronomical observations. Methods: The PAH mixtures were synthesized by infrared laser pyrolysis and subsequent chemical extraction and size separation. The matrix isolation technique was used to study the absorption spectra of isolated molecules at low temperature. Results: Our experimental results demonstrate that the UV-visible absorption curves of PAH mixtures can be very smooth, displaying no sharp bands, if the molecular diversity is sufficiently high. Conclusions: In view of the absence of sharp electronic features on the interstellar extinction curve for 300 < lambda < 400 nm, we conclude from our experimental findings that the interstellar PAH population must be very diverse. The low fractional abundances of individual species prevent their detection on the basis of spectral fingerprints in the UV.
We derive the relativistic kinetic equation for Compton scattering of polarized radiation in strong magnetic field using the Bogolyubov method. The induced scattering and the Pauli exclusion principle are taken into account. The electron polarization is also considered in the general form of the kinetic equation. The special forms of the equation for the cases of the non-polarized electrons, the rarefied electron gas and the two polarization mode description of radiation are found. The derived equations are valid for any photon and electron energies and the magnetic field strength below about 10^{16} G. These equations provide the basis for formulation of the equation for polarized radiation transport in atmospheres and magnetospheres of strongly magnetized neutron stars.
Burst oscillations, a phenomenon observed in a significant fraction of Type I (thermonuclear) X-ray bursts, involve the development of highly asymmetric brightness patches in the burning surface layers of accreting neutron stars. Intrinsically interesting as nuclear phenomena, they are also important as probes of dense matter physics and the strong gravity, high magnetic field environment of the neutron star surface. Burst oscillation frequency is also used to measure stellar spin, and doubles the sample of rapidly rotating (above 10 Hz) accreting neutron stars with known spins. Although the mechanism remains mysterious, burst oscillation models must take into account thermonuclear flame spread, nuclear processes, rapid rotation, and the dynamical role of the magnetic field. This review provides a comprehensive summary of the observational properties of burst oscillations, an assessment of the status of the theoretical models that are being developed to explain them, and an overview of how they can be used to constrain neutron star properties such as spin, mass and radius.
We review the effects of source size in interferometric observations and focus on the cases of very compact sources. If a source is extremely compact and/or weak (so it is not possible to detect signature of source structure in the visibilities) we describe a test of hypothesis that can be used to set a strong upper limit to the size of the source. We also estimate the minimum possible size of a source whose structure can still be detected by an interferometer (i.e., the maximum theoretical over-resolution power of an interferometer), which depends on the overall observing time, the compactness in the array distribution, and the sensitivity of the receivers. As a result, and depending on the observing frequency, the over-resolution power of forthcoming ultra-sensitive arrays, like the Square Kilometer Array (SKA), may allow us to study details of sources at angular scales down to a few micro-as.
In this work, the linear and gauge-invariant theory of cosmological perturbations in a class of anisotropic and shear-free spacetimes is developed. After constructing an explicit set of complete eigenfunctions in terms of which perturbations can be expanded, we identify the effective degrees of freedom during a generic slow-roll inflationary phase. These correspond to the anisotropic equivalent of the standard Mukhanov-Sasaki variables. The associated equations of motion present a remarkable resemblance to those found in perturbed Friedmann-Robertson-Walker spacetimes with curvature, apart from the spectrum of the Laplacian, which exhibits the characteristic frequencies of the underlying geometry. In particular, it is found that the perturbations cannot develop arbitrarily large super-Hubble modes.
In the present work we derive a Differential Emission Measure (DEM) dis- tribution from a region dominated by spicules. We use spectral data from the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) spectrometer on-board the Solar Heliospheric Observatory (SoHO) covering the entire SUMER wavelength range taken off-limb in the Northern polar coronal hole to construct this DEM distribution using the CHIANTI atomic database. This distribution is then used to study the thermal properties of the emission contributing to the 171 {\AA} channel in the Atmospheric Imaging Assembly (AIA) on-board the Solar Dynamics Observatory (SDO). From our off-limb DEM we found that the radiance in the AIA 171 {\AA} channel is dominated by emission from the Fe ix 171.07 {\AA} line and has sparingly little contribution from other lines. The product of the Fe ix 171.07 {\AA} line contribution function with the off-limb DEM was found to have a maximum at logTmax (K) = 5.8 indicating that during spicule observations the emission in this line comes from plasma at transition region temperatures rather than coronal. For comparison, the same product with a quiet Sun and prominence DEM were found to have a maximum at logT max (K) = 5.9 and logTmax (K) = 5.7, respectively. We point out that the interpretation of data obtained from the AIA 171 {\AA} filter should be done with foreknowledge of the thermal nature of the observed phenomenon. For example, with an off-limb DEM we find that only 3.6% of the plasma is above a million degrees, whereas using a quiet Sun DEM, this contribution rises to 15%.
Small and elongated, cool and dense blob-like structures are being reported with high resolution telescopes in physically different regions throughout the solar atmosphere. Their detection and the understanding of their formation, morphology and thermodynamical characteristics can provide important information on their hosting environment, especially concerning the magnetic field, whose understanding constitutes a major problem in solar physics. An example of such blobs is coronal rain, a phenomenon of thermal non- equilibrium observed in active region loops, which consists of cool and dense chromospheric blobs falling along loop-like paths from coronal heights. So far, only off-limb coronal rain has been observed and few reports on the phenomenon exist. In the present work, several datasets of on-disk H{\alpha} observations with the CRisp Imaging SpectroPolarimeter (CRISP) at the Swedish 1-m Solar Telescope (SST) are analyzed. A special family of on-disk blobs is selected for each dataset and a statistical analysis is carried out on their dynamics, morphology and temperatures. All characteristics present distributions which are very similar to reported coronal rain statistics. We discuss possible interpretations considering other similar blob-like structures reported so far and show that a coronal rain interpretation is the most likely one. Their chromospheric nature and the projection effects (which eliminate all direct possibility of height estimation) on one side, and their small sizes, fast dynamics, and especially, their faint character (offering low contrast with the background intensity) on the other side, are found as the main causes for the absence until now of the detection of this on-disk coronal rain counterpart.
We present results of the optical spectral and photometric observations of the nucleus of Markarian 6 made with the 2.6-m Shajn telescope at the Crimean Astrophysical Observatory. The continuum and emission Balmer line intensities varied more than by a factor of two during 1992-2008. The lag between the continuum and Hbeta emission line flux variations is 21.1+-1.9 days. For the Halpha line the lag is about 27 days but its uncertainty is much larger. We use Monte-Carlo simulation of the random time series to check the effect of our data sampling on the lag uncertainties and we compare our simulation results with those obtained by random subset selection (RSS) method of Peterson et al. (1998). The lag in the high-velocity wings are shorter than in the line core in accordance with the virial motions. However, the lag is slightly larger in the blue wing than in the red wing. This is a signature of the infall gas motion. Probably the BLR kinematic in the Mrk 6 nucleus is a combination of the Keplerian and infall motions. The velocity-delay dependence is similar for individual observational seasons. The measurements of the Hbeta line width in combination with the reverberation lag permits us to determine the black hole mass, M_BH=(1.8+-0.2)x10^8 M_sun. This result is consistent with the AGN scaling relationships between the BLR radius and the optical continuum luminosity (R_BLR is proportional to L^0.5) as well as with the black-hole mass-luminosity relationship (M_BH-L) under the Eddington luminosity ratio for Mrk 6 to be L_bol/L_Edd ~ 0.01.
We present a new methodology which can determine magnetic helicity transport by the passage of helical magnetic field lines from sub-photosphere and the shuffling motions of foot-points of preexisting coronal field lines separately. It is well known that only the velocity component which is perpendicular to the magnetic field ($\upsilon_{\perp B}$) has contribution to the helicity accumulation. Here, we demonstrate that $\upsilon_{\perp B}$ can be deduced from horizontal motion and vector magnetograms, under a simple relation of $\upsilon_t = \mu_t + \frac{\upsilon_n}{B_n} B_t$ as suggested by D$\acute{e}$moulin & Berger (2003). Then after dividing $\upsilon_{\perp B}$ into two components, as one is tangential and the other is normal to the solar surface, we can determine both terms of helicity transport. Active region (AR) NOAA 10930 is analyzed as an example during its solar disk center passage by using data obtained by the Spectro-Polarimeter and the Narrowband Filter Imager of Solar Optical Telescope on board Hinode. We find that in our calculation, the helicity injection by flux emergence and shuffling motions have the same sign. During the period we studied, the main contribution of helicity accumulation comes from the flux emergence effect, while the dynamic transient evolution comes from the shuffling motions effect. Our observational results further indicate that for this AR, the apparent rotational motion in the following sunspot is the real shuffling motions on solar surface.
We present a model that attempts to fuse the inflationary era and the subsequent radiation dominated era under a unified framework so as to provide a smooth transition between the two. The model is based on a modification of the generalized Chaplygin gas. We constrain the model observationally by mapping the primordial power spectrum of the scalar perturbations to the latest data of WMAP7. We compute as well the spectrum of the primordial gravitational waves as would be measured today.
Observations of chromospheric spectral lines near and beyond the solar limb provide information on the solar chromosphere without any photospheric contamination. For ground-based observations near and off the limb with real-time image correction by adaptive optics (AO), some technical requirements have to be met, such as an AO lock point that is independent of the location of the field of view observed by the science instruments, both for 1D and 2D instruments. We show how to obtain simultaneous AO-corrected spectra in Ca II H, Ha, Ca II IR at 854 nm, and He I at 1083 nm with the instrumentation at the German Vacuum Tower Telescope in Izana, Tenerife. We determined the spectral properties of an active-region macrospicule inside the field of view in the four chromospheric lines, including its signature in polarization in He I at 1083 nm. Compared to the line-core intensities, the Doppler shifts of the lines change on a smaller spatial scale in the direction parallel to the limb, suggesting the presence of coherent rotating structures or the passage of upwards propagating helical waves on the surfaces of expanding flux tubes.
It is widely accepted that supersonic, magnetised turbulence plays a fundamental role for star formation in molecular clouds. It produces the initial dense gas seeds out of which new stars can form. However, the exact relation between gas compression, turbulent Mach number, and magnetic field strength is still poorly understood. Here, we introduce and test an analytical prediction for the relation between the density variance and the root-mean-square Mach number in supersonic, isothermal, magnetised turbulent flows. We approximate the density and velocity structure of the interstellar medium as a superposition of shock waves. We obtain the density contrast considering the momentum continuity equation for a single magnetised shock and extrapolate this result to the entire cloud. Depending on the field geometry, we then make three different assumptions based on observational and theoretical constraints: B independent of density, B proportional to the root square of the density and B proportional to the density. We test the analytically derived density variance--Mach number relation with numerical simulations, and find that for B proportional to the root square of the density, the variance in the logarithmic density contrast, $\sigma_{\ln \rho/\rho_0}^2=\ln[1+b^2\mathscr{M}^2\beta_0/(\beta_0+1)]$, fits very well to simulated data with turbulent forcing parameter b=0.4, when the gas is super-Alfv\'enic. However, this result breaks down when the turbulence becomes trans-Alfv\'enic or sub-Alfv\'enic, because in this regime the turbulence becomes highly anisotropic. Our density variance--Mach number relations simplify to the purely hydrodynamic relation as the ratio of thermal to magnetic pressure $\beta_0$ approaches infinite.
Context. Photon orbital angular momentum (POAM) is normally invoked in a
quantum mechanical context. It can, however, also be adapted to the classical
regime, which includes observational astronomy.
Aims. I explain why POAM quantities are excellent metrics for describing the
end-to-end behavior of astronomical systems. To demonstrate their utility, I
calculate POAM probabilities and torques from holography measurements of EVLA
antenna surfaces.
Methods. With previously defined concepts and calculi, I present generic
expressions for POAM spectra, total POAM, torque spectra, and total torque in
the image plane. I extend these functional forms to describe the specific POAM
behavior of single telescopes and interferometers.
Results. POAM probabilities of spatially uncorrelated astronomical sources
are symmetric in quantum number. Such objects have zero intrinsic total POAM on
the celestial sphere, which means that the total POAM in the image plane is
identical to the total torque induced by aberrations within propagation media &
instrumentation. The total torque can be divided into source- independent and
dependent components, and the latter can be written in terms of three
illustrative forms. For interferometers, complications arise from discrete
sampling of synthesized apertures, but they can be overcome. POAM also
manifests itself in the apodization of each telescope in an array. Holography
of EVLA antennas observing a point source indicate that ~ 10% of photons in the
n = 0 state are torqued to n != 0 states.
Conclusions. POAM quantities represent excellent metrics for characterizing
instruments because they are used to simultaneously describe amplitude and
phase aberrations. In contrast, Zernike polynomials are just solutions of a
differential equation that happen to ~ correspond to specific types of
aberrations and are typically employed to fit only phases.
The weak lensing signal (cosmic shear) has been shown to be strongly contaminated by the various types of galaxy intrinsic alignment (IA) correlations, which poses a barrier to precision weak lensing measurements. The redshift dependence of the IA signal has been used at the 2-point level to reduce this contamination by only measuring cross-correlations between large redshift bins, which significantly reduces the galaxy intrinsic ellipticity - intrinsic ellipticity (II) correlation. A self-calibration technique based on the redshift dependences of the IA correlations has also been proposed as a means to remove the 2-point IA contamination from the lensing signal. We explore here the redshift dependences of the IA and lensing bispectra in order to propose a self-calibration of the IA auto-correlations at the 3-point level (i.e. GGI, GII, and III), which can be well understood without the assumption of any particular IA model. We find that future weak lensing surveys will be able to measure the distinctive IA redshift dependence over ranges of $|\Delta z^P|\le 0.2$. Using conservative estimates of photo-z accuracy, we describe the 3-point self-calibration technique for the total IA signal, which can be accomplished through lensing tomography of photo-z bin size $\sim 0.01$. We find that the 3-point self-calibration can function at the accuracy of the 2-point technique with modest constraints in redshift separation. This allows the 3-point IA auto-correlation self-calibration technique proposed here to significantly reduce the contamination of the IA contamination to the weak lensing bispectrum.
We review the status and results of the high energy neutrino telescopes in the Northern Hemisphere, namely ANTARES and Baikal (NT200+).
A laboratory prototype spectral/spatial interferometer has been constructed to demonstrate the feasibility of the double Fourier technique at Far Infrared (FIR) wavelengths (0.15 - 1 THz). It is planned to use this demonstrator to investigate and validate important design features and data processing methods for future astronomical FIR interferometer instruments. In building this prototype we have had to address several key technologies to provide an end-end system demonstration of this double Fourier interferometer. We report on the first results taken when viewing single slit and double slit sources at the focus of a large collimator used to simulate real sources at infinity. The performance of the prototype instrument for these specific field geometries is analyzed to compare with the observed interferometric fringes and to demonstrate image reconstruction capabilities.
We identify 51 blue horizontal branch (BHB) stars, 12 possible BHB stars and 58 RR Lyrae stars in Anticentre fields. Their selection does not depend on their kinematics. Light curves and ephemerides are given for 7 previously unknown RR Lyrae stars. All but 4 of the RR Lyrae stars are of Oosterhoff type I. Our selection criteria for BHB stars give results that agree with those used by Smith et al. (2010) and Ruhland et al. (2011). We use 5 methods to determine distances for the BHB stars and 3 methods for the RR Lyrae stars to get distances on a uniform scale. Absolute proper motions (largely derived from the GSCII and SDSS (DR7) databases) are given for these stars; radial velocities are given for 31 of the BHB stars and 37 of the RR Lyrae stars. Combining these data for BHB and RR Lyrae stars with those previously found in fields at the North Galactic Pole, we find that retrograde orbits dominate for galactocentric distances greater than 12.5 kpc. The majority of metal-poor stars in the solar neighbourhood are known to be concentrated in a Lperp vs. Lz angular momentum plot. We show that the ratio of the number of outliers to the number in the main concentration increases with galactocentric distance. The location of these outliers with Lperp and Lz shows that the halo BHB and RR Lyrae stars have more retrograde orbits and a more spherical distribution with increasing galactocentric distance. Six RR Lyrae stars are identified in the H99 group of outliers; the small spread in their [Fe/H] suggests that they could have come from a single globular cluster. Another group of outliers contains two pairs of RR Lyrae stars; the stars in each pair have similar properties.
This work provides a statistical analysis of the massive star binary characteristics in the Cygnus OB2 Association using radial velocity information of 114 B3-O3 primary stars and orbital properties for the 24 known binaries. We compare these data to a series of Monte Carlo simulations to infer the intrinsic binary fraction and distributions of mass ratios, periods, and eccentricities. We model the distribution of mass ratio, log-period, and eccentricity as power-laws and find best fitting indices of alpha=0.1+/-0.5, beta=0.2+/-0.4, and gamma=-0.6+/-0.3 respectively. These distributions indicate a preference for massive companions, short periods, and low eccentricities. Our analysis indicates that the binary fraction of the cluster is 44+/-8% if all binary systems are (artificially) assumed to have P<1000 days; if the power-law period distribution is extrapolated to 10^4 years, a plausible upper limit for bound systems, the binary fraction is ~90+/-10%. Of these binary (or higher order) systems, ~45% will have companions close enough to interact during pre- or post-main-sequence evolution (semi-major axis ~/<4.7 AU). The period distribution for P<27 days is not well reproduced by any single power-law owing to an excess of systems with periods around 3-5 days (0.08-0.31 AU) and a relative shortage of systems with periods around 7-14 days (0.14-0.62 AU). We explore the idea that these longer-period systems evolved to produce the observed excess of short-period systems. The best fitting binary parameters imply that secondaries generate, on average, ~16% of the V-band light in young massive populations. This means that photometrically based distance measurements for young massive clusters & associations will be systematically low by ~8% (0.16 mag in the distance modulus) if the luminous contributions of unresolved secondaries are not taken into account.
The characterisation of dark energy is one of the primary goals in cosmology especially now that many new experiments are being planned with the aim of reaching a high sensitivity on cosmological parameters. It is known that if we move away from the simple cosmological constant model then we need to consider perturbations in the dark energy fluid. This means that dark energy has two extra degrees of freedom: the sound speed $\cs$ and the anisotropic stress $\sigma$. If dark energy is inhomogenous at the scales of interest then the gravitational potentials are modified and the evolution of the dark matter perturbations is also directly affected. In this paper we add an anisotropic component to the dark energy perturbations. Following the idea introduced in \cite{Sapone:2009mb}, we solve analytically the equations of perturbations in the dark sector, finding simple and accurate approximated solutions. We also find that the evolution of the density perturbations is governed by an effective sound speed which depends on both the sound speed and the anisotropic stress parameter. We then use these solutions to look at the impact of the dark energy perturbations on the matter power spectrum and on the Integrated Sachs-Wolfe effect in the Cosmic Microwave Background.
Broad Absorption Line (BAL) trough variability is predominantly due to cloud motion transverse to our line of sight. The rate at which the variability occurs indicates the velocity of the cloud, which can provide constraints on the cloud's distance from the central source. This requires detailed spectroscopy during a variability event. Such spectra have proven elusive, suggesting either the timescale of variability is too short to be caught, or too long to notice until a sufficient amount of time has passed. Photometric monitoring of BAL quasar colours may potentially be used as an early warning system to trigger time resolved spectroscopic monitoring of BAL variability. Towards this end, we are analyzing both BAL and non-BAL colour variability using time series photometry from Stripe 82 in the Sloan Digital Sky Survey.
The reflectionless filter cell described in this article alleviates many system problems associated with excess out-of-band gain, impedance mismatches, and component interactions. The simplest filter cell exhibits a third-order Inverse Chebyshev response with 14.47 dB peak stopband attenuation, and several can be cascaded for additional attenuation as needed. They are simple to design and easy to use - for much like small fixed attenuators ("pads"), they can be placed anywhere in the signal path desired without fear of causing unwanted standing waves, and instead reducing them where they already exist beyond the intended frequency range. Compared to conventional filter topologies with similar cutoff frequencies, they exhibit an order of magnitude greater amplitude and phase stability, ensuring accurate and repeatable complex gain in calibrated systems. Finally, the component requirements are moderate in value and minimal in number, easing their implementation while improving design yield, and extending the applicability of a given component technology beyond the normal range, both above and below.
We demonstrate the Sunyaev-Zel'dovich (SZ) effect imaging capabilities of the Combined Array for Research in Millimeter-wave Astronomy (CARMA) by presenting an SZ map of the galaxy cluster RXJ1347.5-1145. By combining data from multiple CARMA bands and configurations, we are able to capture the structure of this cluster over a wide range of angular scales, from its bulk properties to its core morphology. We find that roughly 9% of this cluster's thermal energy is associated with sub-arcminute-scale structure imparted by a merger, illustrating the value of high-resolution SZ measurements for pursuing cluster astrophysics and for understanding the scatter in SZ scaling relations. We also find that the cluster's SZ signal is lower in amplitude than suggested by a spherically-symmetric model derived from X-ray data, consistent with compression along the line of sight relative to the plane of the sky. Finally, we discuss the impact of upgrades currently in progress that will further enhance CARMA's power as an SZ imaging instrument.
In two recent papers (arXiv:1106.4546, arXiv:1107.0721), we introduced "dynamical dark matter" (DDM), a new framework for dark-matter physics in which the requirement of stability is replaced by a delicate balancing between lifetimes and cosmological abundances across a vast ensemble of individual dark-matter components whose collective behavior transcends that normally associated with traditional dark-matter candidates. We also presented an explicit model involving axions in large extra spacetime dimensions, and demonstrated that this model has all of the features necessary to constitute a viable realization of the general DDM framework. In this paper, we complete our study by performing a general analysis of all phenomenological constraints which are relevant to this bulk-axion DDM model. Although the analysis in this paper is primarily aimed at our specific DDM model, many of our findings have important implications for bulk axion theories in general. Our analysis can also serve as a prototype for phenomenological studies of theories in which there exist large numbers of interacting and decaying particles.
We derive an equation whose solutions describe self-consistent states of marginal stability for a proton-electron plasma interacting with parallel-propagating ion cyclotron waves. Ion cyclotron waves propagating through this marginally stable plasma will neither grow nor damp. The dispersion relation of these waves, {\omega} (k), smoothly rises from the usual MHD behavior at small |k| to reach {\omega} = {\Omega}p as k \rightarrow \pm\infty. The proton distribution function has constant phase-space density along the characteristic resonant surfaces defined by this dispersion relation. Our equation contains a free function describing the variation of the proton phase-space density across these surfaces. Taking this free function to be a simple "box function", we obtain specific solutions of the marginally stable state for a range of proton parallel betas. The phase speeds of these waves are larger than those given by the cold plasma dispersion relation, and the characteristic surfaces are more sharply peaked in the v\bot direction. The threshold anisotropy for generation of ion cyclotron waves is also larger than that given by estimates which assume bi-Maxwellian proton distributions.
On behalf of the International Women Day, the Sun gave a hot kiss to our mother Earth in a form of a full halo CME generated by the yesterday's double X-class flare. The resulting geomagnetic storm gives a good opportunity to compare the performance of space weather forecast models operating in near-real-time. We compare the forecasts of most major models and identify some common problems. We also present the results of our own near-real-time forecast models.
Asymptotically safe theories of gravitation have received great attention in recent times. In this framework an effective action embodying the basic features of the renormalized flow around the non-gaussian fixed point is derived and its implications for the early universe are discussed. In particular, a "landscape" of a countably infinite number of cosmological inflationary solutions characterized by an unstable de Sitter phase lasting for a large enough number of e-folds is found.
Dark energy models with various scenarios of evolution are considered from the viewpoint of the formalism for the equation of state. It is shown that these models are compatible with current astronomical data. Some of the models presented here evolve arbitrarily close to $\Lambda$CDM up to the present, but diverge in the future into a number of different possible asymptotic states, including asymptotic de-Sitter (pseudo-rip) evolution, little rips with disintegration of bound structures, and various forms of finite-time future singularities. Therefore it is impossible from observational data to determine whether the universe will end in a future singularity or not. We demonstrate that the models under consideration are stable for a long period of time (billions of years) before entering a Little Rip/Pseudo-Rip induced dissolution of bound structures or before entering a soft finite-time future singularity. Finally, the physical consequences of Little Rip, Type II, III and Big Crush singularities are briefly compared.
We investigate Holographic Dark Energy Correspondence of Interacting Generalized Chaplygin Gas model in the framework of compact Kaluza-Klein cosmology. The evolution of the modified holographic dark energy and the equation of state parameter is obtained here.Using the present observational value of density parameter a stable configuration is formed which accommodates Dark Energy. we note a connection between Dark Energy and Phantom field and have shown that Dark Energy might have evolved from a Phantom state in the past.
Einstein's equation is rewritten in an equivalent form, which remains valid at the singularities in some major cases. These cases include the Schwarzschild singularity, the Friedmann-Lemaitre-Robertson-Walker Big Bang singularity, isotropic singularities, and a class of warped product singularities. This equation is constructed in terms of the Ricci part of the Riemann curvature (as the Kulkarni-Nomizu product between Einstein's equation and the metric tensor).
A summary of noncommutative spectral geometry as an approach to unification is presented. The role of the doubling of the algebra, the seeds of quantization and some cosmological implications are briefly discussed.
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Temporal changes of X-ray to very-high-energy gamma-ray emissions from the pulsar-Be star binary PSR B1259-63/LS 2883 are studied based on 3-D SPH simulations of pulsar wind interaction with Be-disk and wind. We focus on the periastron passage of the binary and calculate the variation of the synchrotron and inverse-Compton emissions using the simulated shock geometry and pressure distribution of the pulsar wind. The characteristic double-peaked X-ray light curve from observations is reproduced by our simulation under a dense Be disk condition (base density ~10^{-9} g cm^{-3}). We interpret the pre- and post-periastron peaks as being due to a significant increase in the conversion efficiency from pulsar spin down power to the shock-accelerated particle energy at orbital phases when the pulsar crosses the disk before periastron passage, and when the pulsar wind creates a cavity in the disk gas after periastron passage, respectively. On the contrary, in the model TeV light curve, which also shows a double peak feature, the first peak appears around the periastron phase. The possible effects of cooling processes on the TeV light curve are briefly discussed.
We find that if we live at the center of an inhomogeneity with density contrast of roughly 0.1, dark energy is not a cosmological constant at 95% confidence level. Observational constraints on the equation of state of dark energy, w, depend strongly on the local matter density around the observer. We model the local inhomogeneity with an exact spherically symmetric solution which features a pressureless matter component and a dark-energy fluid with constant equation of state and negligible sound speed, that reaches a homogeneous solution at finite radius. We fit this model to observations of the local expansion rate, distant supernovae and the cosmic microwave background. We conclude that the possible bias from large-scale structure has to be taken into account if one wants to progress towards not just precision but also accurate cosmology.
Bipolar outflows constitute some of the best laboratories to study shock chemistry in the interstellar medium. A number of molecular species have their abundance enhanced by several orders of magnitude in the outflow gas, likely as a combined result of dust mantle disruption and high temperature gas chemistry, and therefore become sensitive indicators of the physical changes taking place in the shock. Identifying these species and understanding their chemical behavior is therefore of high interest both to chemical studies and to our understanding of the star-formation process. Here we review some of the recent progress in the study of the molecular composition of bipolar outflows, with emphasis in the tracers most relevant for shock chemistry. As we discuss, there has been rapid progress both in characterizing the molecular composition of certain outflows as well as in modeling the chemical processes likely involved. However, a number of limitations still affect our understanding of outflow chemistry. These include a very limited statistical approach in the observations and a dependence of the models on plane-parallel shocks, which cannot reproduce the observed wing morphology of the lines. We finish our contribution by discussing the chemistry of the so-called extremely high velocity component, which seems different from the rest of the outflow and may originate in the wind from the very vicinity of the protostar.
The mixing of photons with axion-like particles (ALPs) in the large-scale magnetic field $B$ changes the polarization angle of a linearly polarized photon beam from active galactic nuclei in radio galaxies as it propagates over cosmological distances. Using available ultraviolet polarization data concerning these sources we derive a new bound on the product of the photon-ALP coupling $g_{a\gamma}$ times $B$. We find $g_{a\gamma} B \lesssim 10^{-11}$ GeV$^{-1}$ nG for ultralight ALPs with $m_a \lesssim 10^{-15}$ eV. We compare our new bound with the ones present in the literature and we comment about possible improvements with observations of more sources.
The quiet Sun internetwork is permeated by weak and highly inclined magnetic fields whose physical properties, dynamics, and magnetic interactions are not fully understood. High spatial resolution magnetograms show them as discrete magnetic elements that appear/emerge and disappear/cancel continuously over the quiet Sun surface. The 4-m European Solar Telescope (EST) and the Advanced Technology Solar Telescope (ATST) will obtain two-dimensional, high cadence, high precision polarimetric measurements at the diffraction limit (30 km). Here, we compile the basic requirements for the observation of internetwork fields with EST and ATST (field of view, cadence, instrument configuration, etc). More specifically, we concentrate on the field-of-view requirements. To set them we analyze the proper motion of internetwork magnetic elements across the solar surface. We use 13 hours of magnetograms taken with the Hinode satellite to identify and track thousands of internetwork magnetic element in an isolated supergranular cell. We calculate the velocity components of each element and the mean distance they travel. The results show that, on average, magnetic elements in the interior of supergranular cells move toward the network. The radial velocity is observed to depend on the distance to the center of the supergranule. Internetwork magnetic elements travel 400 on average. These results suggest that ATST and EST should cover, at least, one supergranular cell to obtain a complete picture of the quiet Sun internetwork.
We present a detailed auto-consistent study of the nearest blue compact dwarf
galaxy NGC 6789 by means of optical and UV archive photometry data and optical
long-slit ISIS-WHT spectroscopy observations of the five brightest star-forming
knots. The analysis of the spectra in all knots allowed the derivation of ionic
chemical abundances of oxygen, nitrogen, sulphur, argon and neon using measures
of both the high- and low-excitation electron temperatures, leading to the
conclusion that NGC 6789 is chemically homogeneous with low values of the
abundance of oxygen in the range 12+log(O/H) = 7.80-7.93, but presenting at the
same time higher values of the nitrogen-to-oxygen ratio than expected for its
metal regime.
We used archival HST/WFPC2 F555W and F814W observations of NGC 6789 to
perform a photometric study of the colour-magnitude diagram (CMD) of the
resolved stellar populations and derive its star formation history (SFH), which
is compatible with the presence of different young and old stellar populations
whose metallicities do not necessarily increase with age. We fit the observed
optical spectrum in all the five knots using the STARLIGHT code and a
combination of single stellar populations following the SFH obtained from the
CMD. We compare the resulting stellar masses and the relative fractions of the
ionising populations with a non-constrained SFH case. The properties of the
younger populations were obtained using CLOUDY photoionisation models, giving
similar ages in all the knots in the range 3-6 Myr and the estimation of the
dust absorption factor, which correlates with the observed GALEX FUV-NUV colour
indices. The total photometric extinction and dust-absorption corrected
H\alpha\ fluxes were finally used to derive the star formation rates.
The X-ray and near-IR emission from Sgr A* is dominated by flaring, while a quiescent component dominates the emission at radio and sub-mm wavelengths. The spectral energy distribution of the quiescent emission from Sgr A* peaks at sub-mm wavelengths and is modeled as synchrotron radiation from a thermal population of electrons in the accretion flow, with electron temperatures ranging up to $\sim 5-20$\,MeV. Here we investigate the mechanism by which X-ray flare emission is produced through the interaction of the quiescent and flaring components of Sgr A*. The X-ray flare emission has been interpreted as inverse Compton, self-synchrotron-Compton, or synchrotron emission. We present results of simultaneous X-ray and near-IR observations and show evidence that X-ray peak flare emission lags behind near-IR flare emission with a time delay ranging from a few to tens of minutes. Our Inverse Compton scattering modeling places constraints on the electron density and temperature distributions of the accretion flow and on the locations where flares are produced. In the context of this model, the strong X-ray counterparts to near-IR flares arising from the inner disk should show no significant time delay, whereas near-IR flares in the outer disk should show a broadened and delayed X-ray flare.
We present spectroscopic follow-up observations of Lyman Break Galaxies (LBGs) selected in the field surrounding the radio galaxy MRC0316-257 at z~3.13 (0316). Robust spectroscopic redshifts are determined for 20 out of 24 objects. Three of the spectroscopically confirmed galaxies have 3.12<z<3.13 indicating that these objects reside in a protocluster structure previously found around the radio galaxy. An additional 5 objects are found 1600 km/s blue-shifted with respect to the main protocluster structure. This is in addition to three [OIII] emitters found at this redshift in a previous study. This is further evidence that a structure exists directly in front of the 0316 protocluster. We estimate that the foreground structure is responsible for half of the surface overdensity of LBGs found in the field as a whole. The foreground structure is associated with a strong surface density peak 1.4 Mpc to the North-West of the radio galaxy and a 2D Kolmogorov-Smirnov test indicates that the spatial distributions of the 0316 and foreground galaxies differ at the 3 sigma level. In addition, we compare the properties of protocluster, foreground structure and field galaxies, but we find no significant differences. In terms of the nature of the two structures, a merger scenario is a possible option. Simple merger dynamics indicates that the observed relative velocity of 1600 km/s can be reproduced if the two structures have masses of ~5x10^14 Msun and have starting separations of around 2.5 to 3 Mpc. It is also possible that the foreground structure is unrelated to the 0316 protocluster in which case the two structures will not interact before z=0.
We investigate the effects of plasma interactions on resonance-enhanced fusion rates in stars. Starting from basic principles we derive an expression for the fusion rate that can serve as a basis for discussion of approximation schemes. The present state-of-the-art correction algorithms, based on the classical correlation function for the fusing particles and the classical energy shift for the resonant state, do not follow from this result, even as an approximation. The results of expanding in a perturbation solution for the case of a weakly coupled plasma are somewhat enlightening. But at this point we are at a loss as to how to do meaningful calculations in systems with even moderate plasma coupling strength. Examples where this can matter are: the effect of a possible low energy $^{12}$ C +$^{12}$ C resonance on X-ray bursts from accreting neutron stars or on supernova 1A simulations; and the calculation of the triple $\alpha$ rate in some of the more strongly coupled regions in which the process enters, such as accretion onto a neutron star.
We study the linear $m=1$ counter-rotating instability in a two-component, nearly Keplerian disc. Our goal is to understand these \emph{slow} modes in discs orbiting massive black holes in galactic nuclei. They are of interest not only because they are of large spatial scale--and can hence dominate observations--but also because they can be growing modes that are readily excited by accretion events. Self-gravity being nonlocal, the eigenvalue problem results in a pair of coupled integral equations, which we derive for a two-component softened gravity disc. We solve this integral eigenvalue problem numerically for various values of mass fraction in the counter-rotating component. The eigenvalues are in general complex, being real only in the absence of the counter-rotating component, or imaginary when both components have identical surface density profiles. Our main results are as follows: (i) the pattern speed appears to be non negative, with the growth (or damping) rate being larger for larger values of the pattern speed; (ii) for a given value of the pattern speed, the growth (or damping) rate increases as the mass in the counter-rotating component increases; (iii) the number of nodes of the eigenfunctions decreases with increasing pattern speed and growth rate. Observations of lopsided brightness distributions would then be dominated by modes with the least number of nodes, which also possess the largest pattern speeds and growth rates.
Because of the Herschel and Planck satellite missions, there is strong interest in the interpretation the sub-millimetre dust spectra from interstellar clouds. Much work has been done to understand the dependence between the spectral index beta_Obs and the colour temperature T_C that is partly caused by the noise. The (T_C, beta_Obs) confidence regions are elongated, banana-shaped structures. We studied under which conditions these exhibit anomalous, strongly non-Gaussian behaviour that could affect the interpretation of the observed (T_C, beta_Obs) relations. We examined modified black body spectra and spectra calculated from radiative transfer models of filamentary clouds at wavelengths 100um-850um. We performed modified black body fits and examined the structure of the chi^2(T_, beta_Obs) function. We show cases where, when the signal-to-noise ratio is low, the chi^2 has multiple local minima in the (T_C, beta_Obs) plane. A small change in the weighting of the data points can cause the solution to jump to completely different values. In particular, noise can lead to the appearance of a separate population of solutions with low colour temperatures and high spectral indices. The anomalies are caused by the noise but the tendency to show multiple chi^2 minima depends on the model and the wavelengths analysed. Deviations from the assumed single modified black body spectrum are not important. The presence of local minima implies that the results obtained from the chi^2 minimisation depend on the starting point of the optimisation and may correspond to non-global minima. The (T_C,beta_Obs) distributions may be contaminated by a few solutions with unrealistically low colour temperatures and high spectral indices. Proper weighting must be applied to avoid the determination of the beta_Obs(T_C) relation to be unduly affected by these measurements.
In the past two decades, the complex nature of sunspots has been disclosed with high-resolution observations. One of the most important findings is the "uncombed" penumbral structure, where a more horizontal magnetic component carrying most of Evershed Flows is embedded in a more vertical magnetic background (Solanki & Montavon 1993). The penumbral bright grains are locations of hot upflows and dark fibrils are locations of horizontal flows that are guided by nearly horizontal magnetic field. On the other hand, it was found that flares may change the topology of sunspots in $\delta$ configuration: the structure at the flaring polarity inversion line becomes darkened while sections of peripheral penumbrae may disappear quickly and permanently associated with flares (Liu et al. 2005). The high spatial and temporal resolution observations obtained with Hinode/ SOT provide an excellent opportunity to study the evolution of penumbral fine structure associated with major flares. Taking advantage of two near-limb events, we found that in sections of peripheral penumbrae swept by flare ribbons, the dark fibrils completely disappear, while the bright grains evolve into faculae that are signatures of vertical magnetic flux tubes. The corresponding magnetic fluxes measured in the decaying penumbrae show stepwise changes temporally correlated with the flares. These observations suggest that the horizontal magnetic field component of the penumbra could be straightened upward (i.e., turning from horizontal to vertical) due to magnetic field restructuring associated with flares, which results in the transition of penumbrae to faculae.
The renormalization group framework can be applied to Quantum Field Theory on curved space-time, but there is no proof whether the beta-function of the gravitational coupling indeed goes to zero in the far infrared or not. In a recent paper we have shown that the amount of dark matter inside spiral galaxies may be negligible if a small running of the General Relativity coupling G is present. Here we extend the proposed model to elliptical galaxies and present a detailed analysis on the modeling of NGC 4494 (an ordinary elliptical) and NGC 4374 (a giant elliptical). In order to compare our results to a well known alternative model to the standard dark matter picture, we also evaluate NGC 4374 with MOND. In this galaxy MOND leads to a significative discrepancy with the observed velocity dispersion curve and has a significative tendency towards tangential anisotropy. On the other hand, the approach based on the renormalization group and general relativity (RGGR) could be applied with good results to these elliptical galaxies and is compatible with lower mass-to-light ratios (of about the Kroupa IMF type).
The analysis of the 21 cm signature of cosmic string wakes is extended in several ways. First we consider the constraints on $G\mu$ from the absorption signal of shock heated wakes laid down much later than matter radiation equality. Secondly we analyze the signal of diffuse wake, that is those wakes in which there is a baryon overdensity but which have not shock heated. Finally we compare the size of these signals compared to the expected thermal noise per pixel which dominates over the background cosmic gas brightness temperature and find that the cosmic string signal will exceed the thermal noise of an individual pixel in the Square Kilometre Array for string tensions $G\mu > 5 \times 10^{-9}$.
We present a pair of 3-d magnetohydrodynamical simulations of intermittent jets from a central active galactic nucleus (AGN) in a galaxy cluster extracted from a high resolution cosmological simulation. The selected cluster was chosen as an apparently relatively relaxed system, not having undergone a major merger in almost 7 Gyr. Despite this characterization and history, the intra-cluster medium (ICM) contains quite active "weather". We explore the effects of this ICM weather on the morphological evolution of the AGN jets and lobes. The orientation of the jets is different in the two simulations so that they probe different aspects of the ICM structure and dynamics. We find that even for this cluster that can be characterized as relaxed by an observational standard, the large-scale, bulk ICM motions can significantly distort the jets and lobes. Synthetic X-ray observations of the simulations show that the jets produce complex cavity systems, while synthetic radio observations reveal bending of the jets and lobes similar to wide-angle tail (WAT) radio sources. The jets are cycled on and off with a 26 Myr period using a 50% duty cycle. This leads to morphological features similar to those in "double-double" radio galaxies. While the jet and ICM magnetic fields are generally too weak in the simulations to play a major role in the dynamics, Maxwell stresses can still become locally significant.
We present a detailed comparison between the 2-10 keV hard X-ray and infrared (IR) luminosity function (LF) of active galactic nuclei (AGN). The composite X-ray to IR spectral energy distributions (SEDs) of AGN used for connecting the hard X-ray LF (HXLF) and IR LF (IRLF) are modeled with a simple but well tested torus model based on the radiative transfer and photoionization code CLOUDY. Four observational determinations of the evolution of 2-10 keV HXLF and six evolution models of the obscured type-2 AGN fraction ($f_2$) have been considered. The 8.0 and 15 \micron LFs for the total, unobscured type-1 and obscured type-2 AGN are predicted from the HXLFs, and then compared with the measurements currently available. We find that the IRLFs predicted from HXLFs tend to underestimate the number of the most IR-luminous AGN. This is independent of the choices of HXLF and $f_2$, and even more obvious for the HXLFs recently measured. We show that the discrepancy between the HXLFs and IRLFs can be largely resolved when the anticorrelation between the UV to X-ray slope $\alpha_{\mathrm{ox}}$ and UV luminosity $L_{\rm UV}$ is appropriately considered. We also discuss other possible explanations for the discrepancy, such as the missing population of Compton-thick AGN and possible contribution of star-formation in the host to the mid-IR. Meanwhile, we find that the HXLFs and IRLFs of AGN can be more consistent with each other if the obscuration mechanisms of quasars and Seyferts are assumed to be different, corresponding to their different triggering and fueling mechanisms. More accurate measurements of the IRLFs of AGN, especially that determined at smaller redshift bins and more accurately separated to that for type-1 and type-2, are very helpful for clarifying these interesting issues.
Well-sampled optical lightcurves of 146 GRBs are complied from the literature. Fitting the lightcurves with the superposition of multiple broken power law functions, we identify eight possible emission components that may have distinct physical origins. We summarize the results in a "synthetic" optical lightcurve. In this paper we focus on a statistical analysis of optical flares and an early optical shallow-decay component, both are likely related to a long-term central engine activity. Twenty-four optical flares are obtained from 19 GRBs. The isotropic flare peak luminosity is correlated with that of gamma-rays. The flares peak at from tens of seconds to several days post the GRB trigger. Later flares tend to be wider and dimmer. The fraction of GRBs with detected optical flares is much smaller than that of X-ray flares. Associated X-ray flares are observed for 4 optical flares, and the optical flares usually lag behind the corresponding X-ray flares. An optical shallow decay segment is observed in 39 GRBs. Their break times range from tens of seconds to several days post the GRB trigger. The break luminosity is anti-correlated, similar to that derived from X-ray flares. The detection fraction of the optical shallow decay component is comparable to that in the X-ray band. The X-ray and optical breaks are usually chromatic, but a tentative correlation is found. We suggest that similar to the prompt optical emission that tracks the gamma-rays, the optical flares are also related to the erratic behavior of the central engine. The shallow decay component, on the other hand, is likely due to energy injection into the blastwave, possibly related to a long-lasting spinning-down central engine or piling up of flare materials onto the blastwave. Mixing of different emission components may be the reason of the diverse chromatic afterglow behaviors as observed for Swift GRBs.
A previously undetected X-ray source (L_X<10**36 erg/s) in the strongly star-forming galaxy M83 entered an ultraluminous state between August 2009 and December 2010. It was first seen with Chandra on 23 December 2010 at L_X ~ 4 10**39 ergs/s, and has remained ultraluminous through our most recent observations in December 2011, with typical flux variation of a factor of two. The spectrum is well fitted by a combination of absorbed power-law and disk black-body models. While the relative contributions of the models varies with time, we have seen no evidence for a canonical state transition. The luminosity and spectral properties are consistent with accretion powered by a black hole with M_BH ~ 40-100 solar masses. In July 2011 we found a luminous, blue optical counterpart which had not been seen in deep HST observations obtained in August 2009. These optical observations suggest that the donor star is a low-mass star undergoing Roche-lobe overflow, and that the blue optical emission seen during the outburst is coming from an irradiated accretion disk. This source shows that ultraluminous X-ray sources (ULXs) with low-mass companions are an important component of the ULX population in star-forming galaxies, and provides further evidence that the blue optical counterparts of some ULXs need not indicate a young, high-mass companion, but rather that they may indicate X-ray reprocessing.
Using linear Vlasov theory of plasma waves and quasi-linear theory of resonant wave-particle interaction, the dispersion relations and the electromagnetic field fluctuations of fast and Alfven waves are studied for a low-beta multi-ion plasma in the inner corona. Their probable roles in heating and accelerating the solar wind via Landau and cyclotron resonances are quantified. We assume that (1) low-frequency Alfven and fast waves have the same spectral shape and the same amplitude of power spectral density; (2) these waves eventually reach ion cyclotron frequencies due to a turbulence cascade; (3) kinetic wave-particle interaction powers the solar wind. The existence of alpha particles in a dominant proton/electron plasma can trigger linear mode conversion between oblique fast-whistler and hybrid alpha-proton cyclotron waves. The fast-cyclotron waves undergo both alpha and proton cyclotron resonances. The alpha cyclotron resonance in fast-cyclotron waves is much stronger than that in Alfven-cyclotron waves. For alpha cyclotron resonance, an oblique fast-cyclotron wave has a larger left-handed electric field fluctuation, a smaller wave number, a larger local wave amplitude, and a greater energization capability than a corresponding Alfven-cyclotron wave at the same wave propagation angle \theta, particularly at $80^\circ$ < \theta < $90^\circ$. When Alfven-cyclotron or fast-cyclotron waves are present, alpha particles are the chief energy recipient. The transition of preferential energization from alpha particles to protons may be self-modulated by differential speed and temperature anisotropy of alpha particles via the self-consistently evolving wave-particle interaction. Therefore, fast-cyclotron waves as a result of linear mode coupling is a potentially important mechanism for preferential energization of minor ions in the main acceleration region of the solar wind.
The origin of equilibrium gravitational configurations is sought in terms of the stability of their trajectories, as described by the curvature of their Lagrangian configuration manifold. We focus on the case of spherical systems, which are integrable in the collisionless (mean field) limit despite the apparent persistence of local instability of trajectories even as $N \rightarrow \infty$. It is shown that when the singularity in the potential is removed, a null scalar curvature is associated with an effective, averaged, equation of state describing dynamically relaxed equilibria with marginally stable trajectories. The associated configurations are quite similar to those of observed elliptical galaxies and simulated cosmological halos. This is the case because a system starting far from equilibrium finally settles in a state which is integrable when unperturbed, but where it can most efficiently wash out perturbations. We explicitly test this interpretation by means of direct simulations.
We study the long-term dynamics of a planetary system composed of a star and a planet. Both bodies are considered as extended, non-spherical, rotating objects. There are no assumptions made on the relative angles between the orbital angular momentum and the spin vectors of the bodies. Thus, we analyze full, spatial model of the planetary system. Both objects are assumed to be deformed due to their own rotations, as well as due to the mutual tidal interactions. The general relativity corrections are considered in terms of the post-Newtonian approximation. Besides the conservative contributions to the perturbing forces, there are also taken into account non-conservative effects, i.e., the dissipation of the mechanical energy. This dissipation is a result of the tidal perturbation on the velocity field in the internal zones with non-zero turbulent viscosity (convective zones). Our main goal is to derive the equations of the orbital motion as well as the equations governing time-evolution of the spin vectors (angular velocities). We derive the Lagrangian equations of the second kind for systems which do not conserve the mechanical energy. Next, the equations of motion are averaged out over all fast angles with respect to time-scales characteristic for conservative perturbations. The final equations of motion are then used to study the dynamics of the non-conservative model over time scales of the order of the age of the star. We analyze the final state of the system as a function of the initial conditions. Equilibria states of the averaged system are finally discussed.
We propose an innovative demodulation scheme for coherent detectors used in cosmic microwave background polarization experiments. Line removal of detector noise is one of the key requirements for the experiments. In experiments that use coherent detectors, a combination of modulation and demodulation is used to extract polarization signals as well as to suppress line noise. Traditional demodulation, which is based on the two- point numerical differentiation, works as a first-order high pass filter for such non-white noise. The proposed demodulation is based on the three-point numerical differentiation. It works as a second-order high pass filter. We evaluated its impact by applying it to data collected from a real coherent detector. Line noise is significantly suppressed as expected. We also found improvement of the noise floor in the demodulated data. This improvement results from minimization of 1/f noise contamination at around the modulation frequency.
The Spitzer GLIMPSE survey has revealed a number of "Extended Green Objects" (EGOs) which display extended emission at 4.5 micron. These EGOs are potential candidates for high mass protostellar outflows. We have used high resolution (< 1") H2 1-0 S(1) line, K, and H-band images from the United Kingdom Infrared Telescope to study 34 EGOs to investigate their nature. We found that 12 EGOs exhibit H2 outflows (two with chains of H2 knotty structures; five with extended H2 bipolar structures; three with extended H2 lobes; two with pairs of H2 knots). In the 12 EGOs with H2 outflows, three of them exhibit similar morphologies between the 4.5 micron and H2 emission. However, the remaining 9 EGOs show that the H2 features are more extended than the continuum features, and the H2 emission is seldom associated with continuum emission. Furthermore, the morphologies of the near-infrared continuum and 4.5 micron emission are similar to each other for those EGOs with K-band emission, implying that at least a part of the IRAC-band continuum emission of EGOs comes from scattered light from the embedded YSOs.
The Quintuplet, one of three massive stellar clusters in the Galactic center, is located about 30pc in projection from Sagittarius A*. Based on near-infrared K-band spectra we determine temperatures and luminosities for all stars in our sample and construct the Herztsprung-Russell diagram. We find two distinct groups: early-type OB stars and late-type KM stars, well separated from each other. By comparison with Geneva stellar evolution models we derive initial masses exceeding 8 solar masses for the OB stars, that are located along an isochrone corresponding to a cluster age of about 4 million years. In addition, we derive number ratios (e. g. N_WR/N_O) and compare them with predictions of population synthesis models. We find that an instantaneous burst of star formation at about 3.3 to 3.6\,Myr ago is the most likely scenario to form the Quintuplet cluster. The late-type stars in the sample are red giant branch (RGB) stars or red supergiants (RSGs) according to their spectral signatures. It is discussed if they could physically belong to the Quintuplet cluster. Furthermore, we apply a mass-luminosity relation to construct the initial mass function (IMF) of the cluster. We find indications for a slightly top-heavy IMF.
SH2 has been described as an isolated HII-region, located about 6.5 arcmin south of the nucleus of NGC 1316 (Fornax A), a merger remnant in the the outskirts of the Fornax cluster of galaxies. We give a first, preliminary description of the stellar content and environment of this remarkable object. We used photometric data in the Washington system and HST photometry from the Hubble Legacy Archive for a morphological description and preliminary aperture photometry. Low-resolution spectroscopy provides radial velocities of the brightest star cluster in SH2 and a nearby intermediate-age cluster. SH2 is not a normal HII-region, ionized by very young stars. It contains a multitude of star clusters with ages of approximately 0.1 Gyr. A ring-like morphology is striking. SH2 seems to be connected to an intermediate-age massive globular cluster with a similar radial velocity, which itself is the main object of a group of fainter clusters. Metallicity estimates from emission lines remain ambiguous. The present data do not yet allow firm conclusions about the nature or origin of SH2. It might be a dwarf galaxy that has experienced a burst of extremely clustered star formation. We may witness how globular clusters are donated to a parent galaxy.
Recently, there has been an interest in inflation and modified gravity with a Weyl term added to the general-relativistic action (N. Derulle, M. Sasaki, Y. Sendouda and A. Youssef, JCAP, 3, 040 (2011)). In this paper we study empirical constraint on this modified gravity from solar-system experiments/observations. We first derive linearized equation of motion in the weak field limit and solve it for isolated system in the slow motion limit. We then use it to derive the light propagation equations, and obtain the relativistic Shapiro time delay and the light deflection in one-body central problem. Applying these results to the solar-system measurements, we obtain constraints on the Weyl term parameter {\gamma}_W; the most stringent constraint, which comes from the Cassini relativistic time delay experiment, is for {\gamma}_W to be less than 0.0015 AU^2, or |{\gamma}_W|^(1/2) less than 0.039 AU (19 s). Analysis of precision laboratory gravity experiments put further limit on the Weyl term parameter {\gamma}_W to below the laboratory scale.
Measuring radio waves at low frequencies offers a new window to study cosmic magnetism, and LOFAR is the ideal radio telescope to open this window widely. The LOFAR Magnetism Key Science Project (MKSP) draws together expertise from multiple fields of magnetism science and intends to use LOFAR to tackle fundamental questions on cosmic magnetism by exploiting a variety of observational techniques. Surveys will provide diffuse emission from the Milky Way and from nearby galaxies, tracking the propagation of long-lived cosmic-ray electrons through magnetic field structures, to search for radio halos around spiral and dwarf galaxies and for magnetic fields in intergalactic space. Targeted deep-field observations of selected nearby galaxies and suspected intergalactic filaments allow sensitive mapping of weak magnetic fields through Rotation Measure (RM) grids. High-resolution observations of protostellar jets and giant radio galaxies reveal structures on small physical scales and at high redshifts, whilst pulsar RMs map large-scale magnetic structures of the Galactic disk and halo in revolutionary detail. The MKSP is responsible for the development of polarization calibration and processing, thus widening the scientific power of LOFAR.
We study the average X-ray and soft gamma-ray spectrum of Cyg X-1 in the hard
spectral state, using data from INTEGRAL. We compare these results with those
from CGRO, and find a good agreement. Confirming previous studies, we find the
presence of a high-energy MeV tail beyond a thermal-Comptonization spectrum;
however, the tail is much softer and weaker than that recently published by
Laurent et al. In spite of this difference, the observed high-energy tail could
still be due to the synchrotron emission of the jet of Cyg X-1, as claimed by
Laurent et al.
To test this possibility, we study optically-thin synchrotron and
self-Compton emission from partially self-absorbed jets. We develop formalisms
for calculating both emission of the jet base (which we define here as the
region where the jet starts its emission) and emission of the entire jet. We
require the emission to match that observed at the turnover energy. The
optically thin emission is dominated by that from the jet base, and it has to
become self-absorbed within it at the turnover frequency. We find this implies
the magnetic field strength at the jet base of B_0 prop. to z_0^4, where z_0 is
the distance of the base from the black-hole centre. The value of B_0 is then
constrained from below by the condition that the self-Compton emission is below
an upper limit in the GeV range, and from above by the condition that the
Poynting flux does not exceed the jet kinetic power. This yields B_0 of the
order of ~10^4 G and the location of the jet base at ~10^3 gravitational radii.
Using our formalism, we find the MeV tail can be due to jet synchrotron
emission, but this requires the electron acceleration at a rather hard
power-law index, p~1.3-1.6. For acceleration indices of p> 2, the amplitude of
the synchrotron component is much below that of MeV tail, and its origin is
likely to be due to hybrid Comptonization in the accretion flow.
Recent results of Milagro, Tibet, ARGO-YBJ and IceCube experiments on the small-scale anisotropy of Galactic cosmic rays (CRs) with energies from units up to a few hundred TeV arise a question on a possible nature of the observed phenomenon, as well as on the anisotropy of CRs at higher energies. An analysis of a small-scale anisotropy of CRs with energies at around PeV registered with the EAS MSU array presented in the article, reveals a number of regions with an excessive flux. A typical size of the regions varies from 3 up to 12 degrees. We study correlation of these regions with positions of potential astrophysical sources of CRs and discuss a possible origin of the observed anisotropy.
Tadpole galaxies have a giant star-forming region at the end of an elongated intensity distribution. Here we use SDSS data to determine the ages, masses, and surface densities of the heads and tails in 14 local tadpoles selected from the Kiso and Michigan surveys of UV-bright galaxies, and we compare them to tadpoles previously studied in the Hubble Ultra Deep Field. The young stellar mass in the head scales linearly with restframe galaxy luminosity, ranging from ~10^5 M_solar at galaxy absolute magnitude U=-13 mag to 10^9 M_solar at U=-20 mag. The corresponding head surface density increases from several M_solar pc^{-2} locally to 10-100 M_solar pc^{-2} at high redshift, and the star formation rate per unit area in the head increases from ~0.01 M_solar yr^{-1} kpc^{-2} locally to ~1 M_solar yr^{-1} kpc^{-2} at high z. These local values are normal for star-forming regions, and the increases with redshift are consistent with other cosmological star formation rates, most likely reflecting an increase in gas abundance. The tails in the local sample look like bulge-free galaxy disks. Their photometric ages decrease from several Gyr to several hundred Myr with increasing z, and their surface densities are more constant than the surface densities of the heads. The far outer intensity profiles in the local sample are symmetric and exponential. We suggest that most local tadpoles are bulge-free galaxy disks with lopsided star formation, perhaps from environmental effects such as ram pressure or disk impacts, or from a Jeans length comparable to half the disk size.
We have analyzed the long period, double-lined eclipsing binary system OGLE SMC113.3 4007 (SC10 137844) in the SMC. The binary lies in the north-eastern part of the galaxy and consists of two evolved, well detached, non-active G8 giants. The orbit is eccentric with e = 0.311 and the orbital period is 371.6 days. Using extensive high-resolution spectroscopic and multi-color photometric data we have determined a true distance modulus of the system of m-M=18.83 +/- 0.02 (statistical) +/- 0.05 (systematic) mag using a surface brightness - color relation for giant stars. This method is very insensitive to metallicity and reddening corrections and depends only very little on stellar atmosphere model assumptions. Additionally, we derived very accurate, at the level of 1%-2%, physical parameters of both giant stars, particularly their masses and radii, making our results important for comparison with stellar evolution models. Our analysis underlines the high potential of late-type, double-lined detached binary systems for accurate distance determinations to nearby galaxies.
Context. Observing supernova remnants (SNRs) and modelling the shocks they are associated with is the best way to quantify the energy SNRs re-distribute back into the Interstellar Medium (ISM). Aims. We present comparisons of shock models with CO observations in the F knot of the W28 supernova remnant. These comparisons constitute a valuable tool to constrain both the shock characteristics and pre-shock conditions. Methods. New CO observations from the shocked regions with the APEX and SOFIA telescopes are presented and combined. The integrated intensities are compared to the outputs of a grid of models, which were combined from an MHD shock code that calculates the dynamical and chemical structure of these regions, and a radiative transfer module based on the 'large velocity gradient' (LVG) approximation. Results. We base our modelling method on the higher J CO transitions, which unambiguously trace the passage of a shock wave. We provide fits for the blue- and red-lobe components of the observed shocks. We find that only stationary, C-type shock models can reproduce the observed levels of CO emission. Our best models are found for a pre-shock density of 104 cm-3, with the magnetic field strength varying between 45 and 100 {\mu}G, and a higher shock velocity for the so-called blue shock (\sim25 km s-1) than for the red one (\sim20 km s-1). Our models also satisfactorily account for the pure rotational H2 emission that is observed with Spitzer.
Supernova remnants (SNRs) are widely considered to be accelerators of cosmic rays (CR). They are also expected to produce very-high-energy (VHE; $E > 100$ GeV) gamma rays through interactions of high-energy particles with the surrounding medium and photon fields. They are, therefore, promising targets for observations with ground-based imaging atmospheric Cherenkov telescopes like the H.E.S.S. telescope array. VHE gamma-ray emission has already been discovered from a number of SNRs, establishing them as a prominent source class in the VHE domain. Of particular interest are the handful of SNRs whose X-ray spectra are dominated by non-thermal synchrotron emission, such as the VHE gamma-ray emitters RX J0852.0-4622 (Vela Jr.) and RX J1713-3946. The shell-type SNRs G1.9+0.3 and G330.2+1.0 also belong to this subclass and are further notable for their young ages ($\leq 1$ kyr), especially G1.9+0.3, which was recently determined to be the youngest SNR in the Galaxy ($\sim100$ yr). These unique characteristics motivated investigations with H.E.S.S. to search for VHE gamma rays. The results of the H.E.S.S. observations and analyses are presented, along with implications for potential particle acceleration scenarios.
MERLIN phase-referenced polarimetric observations towards the W51 complex were carried out in March 2006 in the Class II methanol maser transition at 6.668 GHz and three of the four excited OH maser hyperfine transitions at 6 GHz. Methanol maser emission is found towards both W51 Main and South. We did not detect any emission in the excited OH maser lines at 6.030 and 6.049 GHz down to a 3 sigma limit of ~20 mJy per beam. Excited OH maser emission at 6.035 GHz is only found towards W51 Main. This emission is highly circularly polarised (typically 45% and up to 87%). Seven Zeeman pairs were identified in this transition, one of which contains detectable linear polarisation. The magnetic field strength derived from these Zeeman pairs ranges from +1.6 to +6.8 mG, consistent with the previously published magnetic field strengths inferred from the OH ground-state lines. The bulk of the methanol maser emission is associated with W51 Main, sampling a total area of ~3"x2.2" (i.e., ~16200x11900 AU), while only two maser components, separated by ~2.5", are found in the W51 South region. The astrometric distributions of both 6.668-GHz methanol and 6.035-GHz excited-OH maser emission in the W51 Main/South region are presented here. The methanol masers in W51 Main show a clear coherent velocity and spatial structure with the bulk of the maser components distributed into 2 regions showing a similar conical opening angle with of a central velocity of ~+55.5 km/s and an expansion velocity of =<5 km/s. The mass contained in this structure is estimated to be at least 22 solar masses. The location of maser emission in the two afore-mentioned lines is compared with that of previously published OH ground-state emission. Association with the UCHII regions in the W51 Main/South complex and relationship of the masers to infall or outflow in the region are discussed.
Supernova Remnants (SNRs) are believed to be acceleration sites of Galactic cosmic rays. Therefore, deep studies of these objects are instrumental for an understanding of the high energy processes in our Galaxy. \velajr, also known as Vela Junior, is one of the few (4) shell-type SNRs resolved at Very High Energies (VHE; $E > 100 \GeV$). It is one of the largest known VHE sources ($\sim 1.0^\circ$ radius) and its flux level is comparable to the flux level of the Crab Nebula in the same energy band. These characteristics allow for a detailed analysis, shedding further light on the high-energy processes taking place in the remnant. In this document we present further details on the spatial and spectral morphology derived with an extended data set. The analysis of the spectral morphology of the remnant is compatible with a constant power-law photon index of $2.11 \pm 0.05_{\rm stat} \pm 0.20_{\rm syst}$ from the whole SNR in the energy range from 0.5 TeV to 7 TeV. The analysis of the spatial morphology shows an enhanced emission towards the direction of the pulsar \psr, however as the pulsar is lying on the rim of the SNR, it is difficult to disentangle both contributions. Therefore, assuming a point source, the upper limit on the flux of the pulsar wind nebula (PWN) between 1 TeV and 10 TeV, is estimated to be $\sim 2%$ of the Crab Nebula flux in the same energy range.
We report an intriguing debris disk towards the F3V star HD 15407A, in which an extremely large amount of warm fine dust (~ 10^(-7) Msun) is detected. The dust temperature is derived as ~ 500--600 K and the location of the debris dust is estimated as 0.6--1.0 AU from the central star, a terrestrial planet region. The fractional luminosity of the debris disk is ~ 0.005, which is much larger than those predicted by steady-state models of the debris disk produced by planetesimal collisions. The mid-infrared spectrum obtained by Spitzer indicates the presence of abundant micron-sized silica dust, suggesting that the dust comes from the surface layer of differentiated large rocky bodies and might be trapped around the star.
Investigating the properties of magnetic flux emergence is one of the most important problems of solar physics. In this study we present a newly developed deep-focus time-distance measurement scheme which is able to detect strong emerging flux events in the deep solar interior, before the flux becomes visible on the surface. We discuss in detail the differences between our method and previous methods, and demonstrate step-by-step how the signal-to-noise (S/N) ratio is increased. The method is based on detection of perturbations in acoustic phase travel times determined from cross-covariances of solar oscillations observed on the surface. We detect strong acoustic travel-time reductions of an order of 12 - 16 seconds at a depth of 42 - 75 Mm. These acoustic anomalies are detected 1 - 2 days before high peaks in the photospheric magnetic flux rate implying that the average emerging speed is 0.3 - 0.6 km/s. The results of this work contribute to our understanding of solar magnetism and benefit space weather forecasting.
The use of integral field units is now commonplace at all major observatories offering efficient means of obtaining spectral as well as imaging information at the same time. IFU instrument designs are complex and spectral images have typically highly condensed formats, therefore presenting challenges for the IFU data reduction pipelines. In the case of the VLT VIMOS-IFU, a fringe-like pattern affecting the spectra well into the optical and blue wavelength regime as well as artificial intensity variations, require additional reduction steps beyond standard pipeline processing. In this research note we propose an empirical method for the removal of the fringe-like pattern in the spectral domain and the intensity variations in the imaging domain. We also demonstrate the potential consequences for data analysis if the effects are not corrected. Here we use the example of deriving stellar velocity, velocity dispersion and absorption line-strength maps for early-type galaxies. We derive for each spectrum, reduced by the ESO standard VIMOS pipeline, a correction-spectrum by using the median of the eight surrounding spectra as a proxy for the unaffected, underlying spectrum. This method relies on the fact that our science targets (nearby ETGs) cover the complete FoV of the VIMOS-IFU with slowly varying spectral properties and that the exact shape of the fringe-like pattern is nearly independent and highly variable between neighboring spatial positions. We find that the proposed correction methods for the removal of the fringe-like pattern and the intensity variations in VIMOS-IFU data-cubes are suitable to allow for meaningful data analysis in our sample of nearby early-type galaxies. Since the method relies on the scientific target properties it is not suitable for general implementation in the pipeline software for VIMOS.
The Herschel Multi-tiered Extragalactic Survey, HerMES, is a legacy program
designed to map a set of nested fields totalling ~380 deg^2. Fields range in
size from 0.01 to ~20 deg^2, using Herschel-SPIRE (at 250, 350 and 500 \mu m),
and Herschel-PACS (at 100 and 160 \mu m), with an additional wider component of
270 deg^2 with SPIRE alone. These bands cover the peak of the redshifted
thermal spectral energy distribution from interstellar dust and thus capture
the re-processed optical and ultra-violet radiation from star formation that
has been absorbed by dust, and are critical for forming a complete
multi-wavelength understanding of galaxy formation and evolution.
The survey will detect of order 100,000 galaxies at 5\sigma in some of the
best studied fields in the sky. Additionally, HerMES is closely coordinated
with the PACS Evolutionary Probe survey. Making maximum use of the full
spectrum of ancillary data, from radio to X-ray wavelengths, it is designed to:
facilitate redshift determination; rapidly identify unusual objects; and
understand the relationships between thermal emission from dust and other
processes. Scientific questions HerMES will be used to answer include: the
total infrared emission of galaxies; the evolution of the luminosity function;
the clustering properties of dusty galaxies; and the properties of populations
of galaxies which lie below the confusion limit through lensing and statistical
techniques.
This paper defines the survey observations and data products, outlines the
primary scientific goals of the HerMES team, and reviews some of the early
results.
This project uses the 2MASS all-sky image database to study the structure of galaxies over a range of luminosities, sizes and morphological types. This first paper in this series will outline the techniques, reliability and data products to our surface photometry program. Our program will analyze all acceptable galaxies (meeting our criteria for isolation from companions and bright stars) from the Revised Shapley-Ames and Uppsala galaxy catalogs. Resulting photometry and surface brightness profiles are released using a transparent scheme of data storage which includes not only all the processed data but knowledge of the processing steps and calibrating parameters.
We have analyzed the available spectra of WW And and for the first time obtained a reasonably well defined radial velocity curve of the primary star. Combined with the available radial velocity curve of the secondary component, these data led to the first determination of the spectroscopic mass ratio of the system at q-spec = 0.16 +/- 0.03. We also determined the radius of the accretion disc from analysis of the double-peaked H-alpha emission lines. Our new, high-precision, Johnson VRI and the previously available Stromgren vby light curves were modelled with stellar and accretion disc models. A consistent model for WW And - a semidetached system harbouring an accretion disc which is optically thick in its inner region, but optically thin in the outer parts - agrees well with both spectroscopic and photometric data.
We examined 134 Chandra observations of the population of X-ray sources associated with globular clusters (GCs) in the central region of M31. These are expected to be X-ray binary systems (XBs), consisting of a neutron star or black hole accreting material from a close companion. We created long term lightcurves for these sources, correcting for interstellar absorption and instrumental effects. We tested for variability by examining the goodness of fit for the best fit constant intensity. We found significant variability in 27 out of 33 GCs and GC candidates; the other 6 sources had 0.3--10 keV luminosities fainter than ~2E+36 erg/s, limiting our ability to detect similar variability. We identify 3 new black hole candidates (BHCs), bringing the total number of M31 GC BHCs to 9, with 8 covered in this survey. The variable GC XBs either exhibited substantially higher amplitudes than expected from ensemble studies of AGN, or exhibited fluxes expected for <1 AGN per square degree. The two AGN in our sample did vary, but less often, and with smaller amplitudes, than the GC XBs. These encouraging results suggest that examining the long term lightcurves of other X-ray sources in the field may provide an important distinction between X-ray binaries and background galaxies, as the X-ray emission spectra from these two classes of X-ray sources are similar. We also identify a possible transient HMXB associated with a H{\sc ii} region that was previously identified as a GC; its outbursts are consistent with a ~120 day period.
Supergranules are convection cells seen at the Sun's surface as a space filling pattern of horizontal flows. While typical supergranules have diameters of about 35 Mm, they exhibit a broad spectrum of sizes from ~10 Mm to ~100 Mm. Here we show that supergranules of different sizes can be used to probe the rotation rate in the Sun's outer convection zone. We find that the equatorial rotation rate as a function of depth as measured by global helioseismology matches the equatorial rotation as a function of wavelength for the supergranules. This suggests that supergranules are advected by flows at depths equal to their wavelengths and thus can be used to probe flows at those depths. The supergranule rotation profiles show that the surface shear layer, through which the rotation rate increases inward, extends to depths of ~50 Mm and to latitudes of at least 70 degrees. Typical supergranules are well observed at high latitudes and have a range of sizes that extend to greater depths than those typically available for measuring subsurface flows with local helioseismology. These characteristics indicate that probing the solar convection zone dynamics with supergranules can complement the results of helioseismology.
The blackbody spectrum of CMB was created behind the blackbody surface at redshifts $z\gtrsim 2\times 10^6$. At earlier times, the Universe was dense and hot enough that complete thermal equilibrium between baryonic matter (electrons and ions) and photons could be established. Any perturbation away from the blackbody spectrum was suppressed exponentially. New physics, for example annihilation and decay of dark matter, can add energy and photons to CMB at redshifts $z\gtrsim 10^5$ and result in a non-zero chemical potential ($\mu$) of CMB. Precise evolution of the CMB spectrum around the critical redshift of $z\gtrsim 2\times 10^6$ is required in order to calculate the $\mu$-type spectral distortion. Although numerical calculation of important processes involved (double Compton process, comptonization and bremsstrahlung) is not difficult, analytic solutions are much faster and easier to calculate and provide valuable physical insights. We provide precise (better than 1%) analytic solutions for the decay of $\mu$, created at an earlier epoch, including all three processes, double Compton, Compton scattering on thermal electrons and bremsstrahlung in the limit of small distortions. This is a significant improvement over the existing solutions with accuracy $\sim 10%$ or worse. We also give a census of important sources of energy injection into CMB in standard cosmology. In particular, calculations of distortions from electron-positron annihilation and primordial nucleosynthesis illustrate in a dramatic way the strength of the equilibrium restoring processes in the early Universe. Finally, we point out the triple degeneracy in standard cosmology, i.e., the $\mu$ and $y$ distortions from adiabatic cooling of baryons and electrons, Silk damping and annihilation of thermally produced WIMP dark matter are of similar order of magnitude ($\sim 10^{-8}-10^{-10}$).
Gauge-flation, non-Abelian gauge field inflation, which was introduced in arXiv:1102.1513 and analyzed more thoroughly in arXiv:1102.1932, is a model of inflation driven by non-Abelian gauge fields minimally coupled to Einstein gravity. In this model certain rotationally invariant combination of gauge fields play the role of inflaton. Recently, the chromo-natural inflation model was proposed arXiv:1202.2366 which besides the non-Abelian gauge fields also involve an axion field. In this short note we show that the model involving axions, indeed allows for various slow-roll trajectories for different values of its parameters: A specific trajectory discussed in arXiv:1202.2366 starts from a "small axion" region, while the trajectory considered in arXiv:1102.1513 corresponds to a "large axion" region.
We employ the effective field theory approach for multi-field inflation which is a generalization of Weinberg's work. In this method the first correction terms in addition to standard terms in the Lagrangian have been considered. These terms contain up to the fourth derivative of the fields including the scalar field and the metric. The results show the possible shapes of the interaction terms resulting eventually in non-Gaussianity in a general formalism. In addition generally the speed of sound is different but almost unity. Since in this method the adiabatic mode is not discriminated initially so we define the adiabatic as well as entropy modes for a specific two-field model. It has been shown that the non-Gaussianity of the adiabatic mode and the entropy mode are correlated in shape and amplitude. It is shown that even for speed close to unity large non-Gaussianities are possible in multi-field case. The amount of the non-Gaussianity depends on the curvature of the classical path in the phase-space in the Hubble unit such that it is large for the large curvature. In addition it is emphasized that the time derivative of adiabatic and entropy perturbations do not transform due to the shift symmetry as well as the original perturbations. Though two specific combinations of them are invariant under such a symmetry and these combinations should be employed to construct an effective field theory of multi-field inflation.
In this paper, we give a possible solution to the cosmological constant problem. It is shown hat the traditional approach, based on volume weighting of probabilities, leads to an incoherent onclusion: the probability that a randomly chosen observer measures $\Lambda=0$ is exactly equal to 1. Using an alternative, volume averaging measure, instead of volume weighting can explain why the osmological constant is non-zero.
In this report, we present a dynamical systems' approach to study the exact nonlinear wave-particle interaction in relativistic regime. We give a particular attention to the effect of wave obliquity on the dynamics of the orbits by studying the specific cases of parallel ($\theta=0$) and perpendicular ($\theta=-\pi/2$) propagations in comparison to the general case of oblique propagation $\theta=]-\pi/2, 0[$. We found that the fixed points of the system correspond to Landau resonance, and that the dynamics can evolve from trapping to surfatron acceleration for propagation angles obeying a Hopf bifurcations condition. Cyclotron-resonant particles are also studied by the construction of a pseudo-potential structure in the Lorentz factor $\gamma$. We derived a condition for which Arnold diffusion results in relativistic stochastic acceleration. Hence, two general conclusions are drawn : 1) The propagation angle $\theta$ can significantly alter the dynamics of the orbits at both Landau and cyclotron-resonances. 2) Considering the short-time scales upon which the particles are accelerated, these two mechanisms for Landau and cyclotron resonant orbits could become potential candidates for problems of particle energization in weakly collisional space and cosmic plasmas.
A formula is derived for the combined motional and gravitational Doppler effect in general stationary axisymmetric metrics for a photon emitted parallel or antiparallel to the assumed circular orbital motion of its source. The same formula is derived from eikonal approximation and Killing vector approaches to elucidate connections between observational astronomy and modern Relativity. The formula yields expected results in the limits of a moving or stationary source in the exterior Kerr and Schwarzschild metrics and a moving source in flat space.
Dark matter with mass below about a GeV is essentially unobservable in conventional direct detection experiments. However, newly proposed technology will allow the detection of single electron events in semiconductor materials with significantly lowered thresholds. This would allow detection of dark matter as light as an MeV in mass. Compared to other detection technologies, semiconductors allow enhanced sensitivity because of their low ionization energy around an eV. Such detectors would be particularly sensitive to dark matter with electric and magnetic dipole moments, with a reach many orders of magnitude beyond current bounds. Observable dipole moment interactions can be generated by new particles with masses as great as 1000 TeV, providing a window to scales beyond the reach of current colliders.
Weakly Interacting Massive Particles (WIMPs), are a leading candidate for the dark matter that is observed to constitute ~25% of the total mass-energy density of the Universe. The direct detection of relic WIMPs (those produced during the early moments of the Universe's expansion) is at the forefront of active research areas in particle astrophysics with a numerous international experimental collaborations pursuing this goal. This paper presents an overview of the theoretical and practical considerations common to the design and operation of direct detection experiments, as well as their unique features and capabilities.
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Context: The discovery and chemical analysis of extremely metal-poor stars permit a better understanding of the star formation of the first generation of stars and of the Universe emerging from the Big Bang. aims: We report the study of a primordial star situated in the centre of the constellation Leo (SDSS J102915+172027). method: The star, selected from the low resolution-spectrum of the Sloan Digital Sky Survey, was observed at intermediate (with X-Shooter at VLT) and at high spectral resolution (with UVES at VLT). The stellar parameters were derived from the photometry. The standard spectroscopic analysis based on 1D ATLAS models was completed by applying 3D and non-LTE corrections. results: An iron abundance of [Fe/H]=--4.89 makes SDSS J102915+172927 one of the lowest [Fe/H] stars known. However, the absence of measurable C and N enhancements indicates that it has the lowest metallicity, Z<= 7.40x10^{-7} (metal-mass fraction), ever detected. No oxygen measurement was possible. conclusions: The discovery of SDSS J102915+172927 highlights that low-mass star formation occurred at metallicities lower than previously assumed. Even lower metallicity stars may yet be discovered, with a chemical composition closer to the composition of the primordial gas and of the first supernovae.
A growing number of low luminosity and low surface brightness astronomical objects challenge traditional notions of both galaxies and star clusters. To address this challenge, we propose a definition of galaxy that does not depend on a cold dark matter model of the universe: A galaxy is a gravitationally bound collection of stars whose properties cannot be explained by a combination of baryons and Newton's laws of gravity. We use this definition to critically examine the classification of ultra-faint dwarfs, globular clusters, ultra-compact dwarfs, and tidal dwarfs. While kinematic studies provide an effective diagnostic of the definition in many regimes, they can be less useful for compact or very faint systems. To explore the utility of using the [Fe/H] spread as a diagnostic, we use published spectroscopic [Fe/H] measurements of 16 Milky Way dwarfs and 24 globular clusters to uniformly calculate their [Fe/H] spreads and associated uncertainties. Our principal results are: (i) no known, old star cluster with M_V > -10 has a significant (~> 0.1 dex) spread in its iron abundance; (ii) most known ultra-faint dwarfs can be unambiguously classified with a combination of kinematic and [Fe/H] observations; (iii) the observed [Fe/H] spreads in massive (~> 10^6 M_sun) globular clusters do not necessarily imply that they are the stripped nuclei of dwarfs, nor a need for dark matter; and (iv) if ultra-compact dwarf galaxies reside in dark matter halos akin to those of ultra-faint dwarfs of the same half-light radii, then they will show no clear dynamical signature of dark matter. We suggest several measurements that may assist the future classification of massive globular clusters, ultra-compact dwarfs, and ultra-faint galaxies.
The source counts of galaxies discovered at sub-millimetre and millimetre wavelengths provide important information on the evolution of infrared-bright galaxies. We combine the data from six blank-field surveys carried out at 1.1 mm with AzTEC, totalling 1.6 square degrees in area with root-mean-square depths ranging from 0.4 to 1.7 mJy, and derive the strongest constraints to date on the 1.1 mm source counts at flux densities S(1100) = 1-12 mJy. Using additional data from the AzTEC Cluster Environment Survey to extend the counts to S(1100) ~ 20 mJy, we see tentative evidence for an enhancement relative to the exponential drop in the counts at S(1100) ~ 13 mJy and a smooth connection to the bright source counts at >20 mJy measured by the South Pole Telescope; this excess may be due to strong lensing effects. We compare these counts to predictions from several semi-analytical and phenomenological models and find that for most the agreement is quite good at flux densities > 4 mJy; however, we find significant discrepancies (>3sigma) between the models and the observed 1.1 mm counts at lower flux densities, and none of them are consistent with the observed turnover in the Euclidean-normalised counts at S(1100) < 2 mJy. Our new results therefore may require modifications to existing evolutionary models for low luminosity galaxies. Alternatively, the discrepancy between the measured counts at the faint end and predictions from phenomenological models could arise from limited knowledge of the spectral energy distributions of faint galaxies in the local Universe.
We model the formation of Auriga's Wheel - a recently discovered collisional ring galaxy. Auriga's Wheel has a number of interesting features including a bridge of stars linking the neighbouring elliptical to the ring galaxy, and evidence for components of expansion and rotation within the ring. Using N-body/SPH modelling, we study collisions between an elliptical galaxy and a late-type disk galaxy. A near direct collision, with a mildy inclined disk, is found to reasonably reproduce the general system morphology ~50 Myr following the collision. The collision must have a relatively low velocity (initially ~150 km s^{-1}) in order to form the observed bridge, and simultaneously match the galaxies separation. Our best-match model suggests the total disk galaxy is ~5 times more massive than the elliptical. We find that the velocity of expansion of the ring is sensitive to the mass of the elliptical, while insensitive to the encounter velocity. We evolve our simulation beyond the current epoch to study the future destiny of the galaxy pair. In our model, the nucleus moves further away from the plane of the ring in the direction of the stellar bridge. The nucleus eventually merges with the elliptical galaxy ~100 Myr after the present time. The ring continues to expand for ~200 Myr before collapsing back. The low initial relative velocity of the two galaxies will eventually result in a complete merger.
We perform a detailed analysis of the resolved colors and stellar populations of a complete sample of 323 star-forming galaxies at 0.5 < z < 1.5, and 326 star-forming galaxies at 1.5 < z < 2.5 in the ERS and CANDELS-Deep region of GOODS-South. Galaxies were selected to be more massive than 10^10 Msun and have specific star formation rates above 1/t_H. We model the 7-band optical ACS + near-IR WFC3 spectral energy distributions of individual bins of pixels, accounting simultaneously for the galaxy-integrated photometric constraints available over a longer wavelength range. We analyze variations in rest-frame color, stellar surface mass density, age, and extinction as a function of galactocentric radius and local surface brightness/density, and measure structural parameters on luminosity and stellar mass maps. We find evidence for redder colors, older stellar ages, and increased dust extinction in the nuclei of galaxies. Big star-forming clumps seen in star formation tracers are less prominent or even invisible on the inferred stellar mass distributions. Off-center clumps contribute up to ~20% to the integrated SFR, but only 7% or less to the integrated mass of all massive star-forming galaxies at z ~ 1 and z ~ 2, with the fractional contributions being a decreasing function of wavelength used to select the clumps. The stellar mass profiles tend to have smaller sizes and M20 coefficients, and higher concentration and Gini coefficients than the light distribution. Our results are consistent with an inside-out disk growth scenario with brief (100 - 200 Myr) episodic local enhancements in star formation superposed on the underlying disk. Alternatively, the young ages of off-center clumps may signal inward clump migration, provided this happens efficiently on the order of an orbital timescale.
The early Universe had a chemical composition consisting of hydrogen, helium and traces of lithium1, almost all other elements were created in stars and supernovae. The mass fraction, Z, of elements more massive than helium, is called "metallicity". A number of very metal poor stars have been found some of which, while having a low iron abundance, are rich in carbon, nitrogen and oxygen. For theoretical reasons and because of an observed absence of stars with metallicities lower than Z=1.5E-5, it has been suggested that low mass stars (M<0.8M\odot, the ones that survive to the present day) cannot form until the interstellar medium has been enriched above a critical value, estimated to lie in the range 1.5E-8\leqZ\leq1.5E-6, although competing theories claiming the contrary do exist. Here we report the chemical composition of a star with a very low Z\leq6.9E-7 (4.5E-5 of that of the Sun) and a chemical pattern typical of classical extremely metal poor stars, meaning without the enrichment of carbon, nitrogen and oxygen. This shows that low mass stars can be formed at very low metallicity. Lithium is not detected, suggesting a low metallicity extension of the previously observed trend in lithium depletion. Lithium depletion implies that the stellar material must have experienced temperatures above two million K in its history, which points to rather particular formation condition or internal mixing process, for low Z stars.
Direct collapse of supermassive stars (SMSs) is a possible pathway for generating supermassive black holes in the early universe. It is expected that an SMS could form via very rapid mass accretion with Mdot ~ 0.1 - 1 Msun/yr during the gravitational collapse of an atomic-cooling primordial gas cloud. In this paper we study how stars would evolve under such extreme rapid mass accretion, focusing on the early evolution until the stellar mass reaches 1000 Msun. To this end we numerically calculate the detailed interior structure of accreting stars with primordial element abundances. Our results show that for accretion rates higher than 0.01 Msun/yr, stellar evolution is qualitatively different from that expected at lower rates. While accreting at these high rates the star always has a radius exceeding 100 Rsun, which increases monotonically with the stellar mass. The mass-radius relation for stellar masses exceeding ~ 100 Msun follows the same track with R_* \propto M_*^0.5 in all cases with accretion rates > 0.01 Msun/yr; at a stellar mass of 1000 Msun the radius is about 7000 Rsun (~= 30 AU). With higher accretion rates the onset of hydrogen burning is shifted towards higher stellar masses. In particular, for accretion rates exceeding Mdot > 0.1 Msun/yr, there is no significant hydrogen burning even after 1000 Msun have accreted onto the protostar. Such "supergiant" protostars have effective temperatures as low as Teff ~= 5000 K throughout their evolution and because they hardly emit ionizing photons, they do not create an HII region or significantly heat their immediate surroundings. Thus, radiative feedback is unable to hinder the growth of rapidly accreting stars to masses in excess of 1000 Msun, as long as material is accreted at rates Mdot > 0.01 Msun/yr.
We investigate the gravitational lensing properties of lines of sight containing multiple cluster-scale halos, motivated by their ability to lens very high-redshift (z ~ 10) sources into detectability. We control for the total mass along the line of sight, isolating the effects of distributing the mass among multiple halos and of varying the physical properties of the halos. Our results show that multiple-halo lines of sight can increase the magnified source-plane region compared to the single cluster lenses typically targeted for lensing studies, and thus are generally better fields for detecting very high-redshift sources. The configurations that result in optimal lensing cross sections benefit from interactions between the lens potentials of the halos when they overlap somewhat on the sky, creating regions of high magnification in the source plane not present when the halos are considered individually. The effect of these interactions on the lensing cross section can even be comparable to factor of ~3 changes in the total mass of the lens. The gain in lensing cross section increases as the mass is split into more halos, provided that the lens potentials are projected close enough to interact with each other. A nonzero projected halo angular separation, equal halo mass ratio, and high projected halo concentration are the best mass configurations, whereas projected halo ellipticity, halo triaxiality, and the relative orientations of the halos are unimportant. We have identified high mass, multiple-halo lines of sight in the SDSS.
As the only directly imaged multiple planet system, HR 8799 provides a unique opportunity to study the physical properties of several planets in parallel. In this paper, we image all four of the HR 8799 planets at H-band and 3.3 microns with the new LBT adaptive optics system, PISCES, and LBTI/LMIRCam. Our images offer an unprecedented view of the system, allowing us to obtain H and 3.3$ micron photometry of the innermost planet (for the first time) and put strong upper-limits on the presence of a hypothetical fifth companion. We find that all four planets are unexpectedly bright at 3.3 microns compared to the equilibrium chemistry models used for field brown dwarfs, which predict that planets should be faint at 3.3 microns due to CH4 opacity. We attempt to model the planets with thick-cloudy, non-equilibrium chemistry atmospheres, but find that removing CH4 to fit the 3.3 micron photometry increases the predicted L' (3.8 microns) flux enough that it is inconsistent with observations. In an effort to fit the SED of the HR 8799 planets, we construct mixtures of cloudy atmospheres, which are intended to represent planets covered by clouds of varying opacity. In this scenario, regions with low opacity look hot and bright, while regions with high opacity look faint, similar to the patchy cloud structures on Jupiter and L/T transition brown-dwarfs. Our mixed cloud models reproduce all of the available data, but self-consistent models are still necessary to demonstrate their viability.
We formulate the concept of non-linear and stochastic galaxy biasing in the framework of halo occupation statistics. Using two-point statistics in projection, we define the galaxy bias function, b_g(r_p), and the galaxy-dark matter cross-correlation function, R_{gm}(r_p), where r_p is the projected distance. We use the analytical halo model to predict how the scale dependence of b_g and R_{gm}, over the range 0.1 Mpc/h < r_p < 30 Mpc/h, depends on the non-linearity and stochasticity in halo occupation models. In particular we quantify the effect due to the presence of central galaxies, the assumption for the radial distribution of satellite galaxies, the richness of the halo, and the Poisson character of the probability to have a certain number of satellite galaxies in a halo of a certain mass. Overall, brighter galaxies reveal a stronger scale dependence, and out to a larger radius. In real-space, we find that galaxy bias becomes scale independent, with R_{gm} = 1, for radii r > 1 - 5 Mpc/h, depending on luminosity. However, galaxy bias is scale-dependent out to much larger radii when one uses the projected quantities defined in this paper. These projected bias functions have the advantage that they are more easily accessible observationally and that their scale dependence carries a wealth of information regarding the properties of galaxy biasing. To observationally constrain the parameters of the halo occupation statistics and to unveil the origin of galaxy biasing we propose the use of the bias function Gamma_{gm}(r_p)=b_g(r_p)/R_{gm}(r_p). This function is obtained via a combination of weak gravitational lensing and galaxy clustering, and it can be measured using existing and forthcoming imaging and spectroscopic galaxy surveys.
Estimates of the mass of super-massive black holes (BHs) in distant active galactic nuclei (AGNs) can be obtained efficiently only through single-epoch spectra, using a combination of their broad emission-line widths and continuum luminosities. Yet the reliability and accuracy of the method, and the resulting mass estimates, M_BH, remain uncertain. A recent study by Croom using a sample of SDSS, 2QZ and 2SLAQ quasars suggests that line widths contribute little information about the BH mass in these single-epoch estimates and can be replaced by a constant value without significant loss of accuracy. In this Letter, we use a sample of nearby reverberation-mapped AGNs to show that this conclusion is not universally applicable. We use the bulge luminosity (L_Bulge) of these local objects to test how well the known M_BH - L_Bulge correlation is recovered when using randomly assigned line widths instead of the measured ones to estimate M_BH. We find that line widths provide significant information about M_BH, and that for this sample, the line width information is just as significant as that provided by the continuum luminosities. We discuss the effects of observational biases upon the analysis of Croom and suggest that the results can probably be explained as a bias of flux-limited, shallow quasar samples.
We calculate the "observed at infinity" image and spectrum of the accretion structure in Sgr A*, by modelling it as an optically thin, constant angular momentum ion torus in hydrodynamic equilibrium. The physics we consider includes a two-temperature plasma, a toroidal magnetic field, as well as radiative cooling by bremsstrahlung, synchrotron and inverse Compton processes. Our relativistic model has the virtue of being fully analytic and very simple, depending only on eight tunable parameters: the black hole spin and the inclination of the spin axis to our line of sight, the torus angular momentum, the polytropic index, the magnetic to total pressure ratio, the central values of density and electron temperature and the ratio of electron to ion temperatures. The observed image and spectrum are calculated numerically using the ray-tracing code GYOTO. Our results demonstrate that the ion torus model is able to account for the main features of the accretion structure surrounding Sgr A*.
We present diffraction-limited \ks band and \lprime adaptive optics images of the edge-on debris disk around the nearby F2 star HD 15115, obtained with a single 8.4 m primary mirror at the Large Binocular Telescope. At \ks band the disk is detected at signal-to-noise per resolution element (SNRE) \about 3-8 from \about 1-2\fasec 5 (45-113 AU) on the western side, and from \about 1.2-2\fasec 1 (63-90 AU) on the east. At \lprime the disk is detected at SNRE \about 2.5 from \about 1-1\fasec 45 (45-90 AU) on both sides, implying more symmetric disk structure at 3.8 \microns . At both wavelengths the disk has a bow-like shape and is offset from the star to the north by a few AU. A surface brightness asymmetry exists between the two sides of the disk at \ks band, but not at \lprime . The surface brightness at \ks band declines inside 1\asec (\about 45 AU), which may be indicative of a gap in the disk near 1\asec. The \ks - \lprime disk color, after removal of the stellar color, is mostly grey for both sides of the disk. This suggests that scattered light is coming from large dust grains, with 3-10 \microns -sized grains on the east side and 1-10 \microns dust grains on the west. This may suggest that the west side is composed of smaller dust grains than the east side, which would support the interpretation that the disk is being dynamically affected by interactions with the local interstellar medium.
[abridged] We report simulations of the formation of a star cluster similar to the Orion Nebula Cluster (ONC), including both radiative transfer and protostellar outflows, and starting from both smooth and self-consistently turbulent initial conditions. Our calculations form hundreds of stars and brown dwarfs, yielding a stellar mass distribution that is well-sampled from <0.1 Msun to >10 Msun. We show that a simulation that begins with turbulent density and velocity fields embedded in a larger turbulent volume, and that includes protostellar outflows, produces an excellent fit to the observed initial mass function (IMF) of the ONC. This is the first simulation published to date that reproduces the observed IMF in a cluster large enough to contain massive stars, and where the peak of the mass function is determined by a fully self-consistent calculation of gas thermodynamics rather than a hand-imposed equation of state. This simulation also produces a star formation rate that, while still too high, is much closer to observed values than in any other case. Moreover, we show that the combination of outflows and turbulence yields an IMF that is invariant with time, resolving the "overheating" problem in which simulations without these features have an IMF peak that shifts to progressively higher masses over time as more and more of the gas is heated, inconsistent with the observed invariance of the IMF. The simulation that matches the observed IMF also reproduces the observed trend of stellar multiplicity strongly increasing with mass. This simulation produces massive stars from distinct massive cores whose properties are consistent with those of observed massive cores. However, the stars formed in these cores also undergo dynamical interactions as they accrete that naturally produce Trapezium-like hierarchical multiple systems of massive stars.
We investigate the evolution of galactic disks in N-body Tree-SPH simulations. We find that disks, initially truncated at three scale-lengths, can triple their radial extent, solely driven by secular evolution. Both Type I (single exponential) and Type II (down-bending) observed disk surface-brightness profiles can be explained by our findings. We relate these results to the strong angular momentum outward transfer, resulting from torques and radial migration associated with multiple patterns, such as central bars and spiral waves of different multiplicity. We show that even for stars ending up on cold orbits, the changes in angular momentum exhibit complex structure as a function of radius, unlike the expected effect of transient spirals alone. Focussing on one of our models, we find evidence for non-linear coupling among m=1, 2, 3 and 4 density waves, where m is the pattern multiplicity. We suggest that the naturally occurring larger resonance widths at galactic radii beyond four scale-lengths may have profound consequences on the formation and location of breaks in disk density profiles, provided spirals are present at such large distances. We also consider the effect of gas inflow and show that when in-plane smooth gas accretion of ~5 M_sun/yr is included, the outer disks become more unstable, leading to a strong increase in the stellar velocity dispersion. This, in turn, causes the formation of a Type III (up-bending) profile in the old stellar population. We propose that observations of Type III surface brightness profiles, combined with an up-turn in the stellar velocity dispersions beyond the disk break, could be a signature of ongoing gas-accretion. The results of this study suggest that disk outskirts comprised of stars migrated from the inner disk would have relatively large radial velocity dispersions, and significant thickness when seen edge-on. [Abridged]
The statistical uncertainty in measuring the primordial density perturbations on a given comoving scale is dictated by the number of independent regions of that scale that are accessible to an observer. This number varies with cosmic time and diminishes per Hubble volume in the distant past or future of the standard cosmological model. We show that the best constraints on the initial power spectrum of linear density perturbations are accessible (e.g. through 21-cm intensity mapping) at redshifts z~10-50, and that the ability to constrain the cosmological initial conditions will deteriorate quickly in our cosmic future.
We characterize the kinematics, morphology, stellar populations and star formation histories of a sample of massive compact galaxies in the nearby Universe, which might provide a closer look to the nature of their high redshift (z > 1.0) massive counterparts. We find that nearby compact massive objects show elongated morphologies and are fast rotators. New high-quality long-slit spectra show that they have young mean luminosity-weighted ages (< 2Gyr) and solar metallicities or above ([Z/H]> 0.0). No significant stellar population gradients are found. The analysis of their star formation histories suggests that these objects have experienced recently enormous bursts which, in some cases, represent unprecedented large fractions of their total stellar mass. These galaxies seem to be truly unique, as they do not follow the characteristic kinematical and stellar population patterns of present-day massive ellipticals, spirals or even dwarfs.
We investigate the spectral variability of the Seyfert galaxy Fairall 9 using almost 6 years of monitoring with the Rossi X-ray Timing Explorer (RXTE) with an approximate time resolution of 4 days. We discover the existence of pronounced and sharp dips in the X-ray flux, with a rapid decline of the 2--20 keV flux of a factor 2 or more followed by a recovery to pre-dip fluxes after ~10 days . These dips skew the flux distribution away from the commonly observed log-normal distribution. Dips may result from the eclipse of the central X-ray source by broad line region (BLR) clouds, as has recently been found in NGC 1365 and Mrk 766. Unlike these other examples, however, the clouds in Fairall 9 would need to be Compton-thick, and the non-dip state is remarkably free of any absorption features. A particularly intriguing alternative is that the accretion disk is undergoing the same cycle of disruption/ejection as seen in the accretion disks of broad line radio galaxies (BLRGs) such as 3C120 but, for some reason, fails to create a relativistic jet. This suggests that a detailed comparison of Fairall 9 and 3C120 with future high-quality data may hold the key to understanding the formation of relativistic jets in AGN.
Sagittarius A*, the super-massive black hole at the center of the Milky Way, is surrounded by a small cluster of high velocity stars, known as the S-stars. We aim at constraining the amount and nature of the stellar and dark mass associated with the cluster in the immediate vicinity of Sagittarius A*. We use near-infrared imaging to determine the $K_s$-band luminosity function of the S-star cluster members, and use the distribution of the diffuse background emission and the stellar number density counts around the central black hole. This allows us to determine the stellar light and mass contribution that we can expect from the faint members of the cluster. We then use post-Newtonian N-body techniques to investigate the effect of stellar perturbations on the motion of S2, as a means of detecting the number and masses of the perturbers. We find that the stellar mass derived from the $K_s$-band luminosity extrapolation is much smaller than the amount of mass that might be present considering the uncertainties in the orbital motion of the star S2. Also the amount of light from the fainter S-cluster members is below the amount of residual light at the position of the S-star cluster after removing the bright cluster members. If the distribution of stars and stellar remnants is strongly enough peaked near Sagittarius A*, observed changes in the orbital elements of S2 can be used to constrain both their masses and numbers. Based on simulations of the cluster of high velocity stars we find that at a wavelength of 2.2 $\mu$m close to the confusion level for 8 m class telescopes blend stars will occur (preferentially near the position of Sagittarius A*) that last for typically 3 years before they dissolve due to proper motions.
High-velocity clouds (HVC), fast-moving ionized and neutral gas clouds found at high galactic latitudes, may play an important role in the evolution of the Milky Way. The extent of this role depends sensitively on their distances and total sky covering factor. We search for HVC absorption in HST high resolution ultraviolet spectra of a carefully selected sample of 133 AGN using a range of atomic species in different ionization stages. This allows us to identify neutral, weakly ionized, or highly ionized HVCs over several decades in HI column densities. The sky covering factor of UV-selected HVCs with |v_LSR|>90 km/s is 68%+/-4% for the entire Galactic sky. We show that our survey is essentially complete, i.e., an undetected population of HVCs with extremely low N(H) (HI+HII) is unlikely to be important for the HVC mass budget. We confirm that the predominantly ionized HVCs contain at least as much mass as the traditional HI HVCs and show that large HI HVC complexes have generally ionized envelopes extending far from the HI contours. There are also large regions of the Galactic sky that are covered with ionized high-velocity gas with little HI emission nearby. We show that the covering factors of HVCs with 90<|v_LSR|<170 km/s drawn from the AGN and stellar samples are similar. This confirms that these HVCs are within 5-15 kpc of the sun. The covering factor of these HVCs drops with decreasing vertical height, which is consistent with HVCs being decelerated or disrupted as they fall to the Milky Way disk. The HVCs with |v_LSR|>170 km/s are largely associated with the Magellanic Stream at b<0 and its leading arm at b>0 as well as other large known HI complexes. Therefore there is no evidence in the Local Group that any galaxy shows a population of HVCs extending much farther away than 50 kpc from its host, except possibly for those tracing remnants of galaxy interaction.
Numerical calculations of the linear Rossby wave instability (RWI) in global three-dimensional (3D) disks are presented. The linearized fluid equations are solved for vertically stratified, radially structured disks with either a locally isothermal or polytropic equation of state. It is confirmed that the RWI operates in 3D. There is little difference in growth rates between 3D and two-dimensional (2D) calculations. Comparison between 2D and 3D solutions suggest the RWI is fundamentally a 2D instability and that three-dimensional effects, such as vertical motion, to be interpreted as a perturbative consequence of the dominant 2D flow. The vertical flow around co-rotation, where vortex-formation is expected, is examined. In locally isothermal disks the expected vortex center remains in approximate vertical hydrostatic equilibrium. For polytropic disks the vortex center has positive vertical velocity, whose magnitude increases with decreasing polytropic index $n$.
We apply a von Zeipel gravity darkening model to corotating binaries to obtain a simple, analytical expression for the emergent radiative flux from a tidally distorted primary orbiting a point-mass secondary. We adopt a simple Roche model to determine the envelope structure of the primary, assumed massive and centrally condensed, and use the results to calculate the flux. As for single rotating stars, gravity darkening reduces the flux along the stellar equator of the primary, but, unlike for rotating stars, we find that gravity brightening enhances the flux in a region around the stellar poles. We identify a critical limiting separation beyond which hydrostatic equilibrium no longer is possible, whereby the flux vanishes at the point on the stellar equator of the primary facing the companion. For equal-mass binaries, the total luminosity is reduced by about 13 % when this limiting separation is reached.
A pressing problem in comparing inflationary models with observation is the accurate calculation of correlation functions. One approach is to evolve them using ordinary differential equations ("transport equations"), analogous to the Schwinger-Dyson hierarchy of in-out quantum field theory. We extend this approach to the complete set of momentum space correlation functions. A formal solution can be obtained using raytracing techniques adapted from geometrical optics. We reformulate inflationary perturbation theory in this language, and show that raytracing reproduces the familiar "delta N" Taylor expansion. Our method produces ordinary differential equations which allow the Taylor coefficients to be computed efficiently. We use raytracing methods to express the gauge transformation between field fluctuations and the curvature perturbation, zeta, in geometrical terms. Using these results we give a compact expression for the nonlinear gauge-transform part of fNL in terms of the principal curvatures of uniform energy-density hypersurfaces in field space.
The new 8.4m LBT adaptive secondary AO system, with its novel pyramid wavefront sensor, was used to produce very high Strehl (75% at 2.16 microns) near infrared narrowband (Br gamma: 2.16 microns and [FeII]: 1.64 microns) images of 47 young (~1 Myr) Orion Trapezium theta1 Ori cluster members. The inner ~41x53" of the cluster was imaged at spatial resolutions of ~0.050" (at 1.64 microns). A combination of high spatial resolution and high S/N yielded relative binary positions to ~0.5 mas accuracies. Including previous speckle data, we analyse a 15 year baseline of high-resolution observations of this cluster. We are now sensitive to relative proper motions of just ~0.3 mas/yr (0.6 km/s at 450 pc) this is a ~7x improvement in orbital velocity accuracy compared to previous efforts. We now detect clear orbital motions in the theta1 Ori B2/B3 system of 4.9+/-0.3 km/s and 7.2+/-0.8 km/s in the theta1 Ori A1/A2 system (with correlations of PA vs. time at >99% confidence). All five members of the theta1 Ori B system appear likely as a gravitationally bound "mini-cluster". The very lowest mass member of the theta1 Ori B system (B4; mass ~0.2 Msun) has, for the first time, a clearly detected motion (at 4.3+/-2.0 km/s; correlation=99.7%) w.r.t B1. However, B4 is most likely in an long-term unstable (non-hierarchical) orbit and may "soon" be ejected from this "mini-cluster". This "ejection" process could play a major role in the formation of low mass stars and brown dwarfs.
Bright submm-selected galaxies have been found to be a rich source of strong gravitational lenses. However, strong gravitational lensing of extended sources leads inevitably to differential magnification. In this paper I quantify the effect of differential magnification on simulated far-infrared and submm surveys of strong gravitational lenses, using a foreground population of Navarro-Frenk-White plus de Vaucouleurs' density profiles, with a model source resembling the Cosmic Eyelash and QSO J1148+5251. Some emission line diagnostics are surprisingly unaffected by differential magnification effects: for example, the bolometric fractions of [C II] 158um and CO(J=1-0), often used to infer densities and ionisation parameters, have typical differential magnification effects that are smaller than the measurement errors. However, the CO ladder itself is significantly affected. Far-infrared lensed galaxy surveys (e.g. at 60um) strongly select for high-redshift galaxies with caustics close to AGN, boosting the apparent bolometric contribution of AGN. The lens configuration of IRAS F10214+4724 is naturally explained in this context. Conversely, submm/mm-wave surveys (e.g. 500-1400um) strongly select for caustics close to knots of star formation boosting the latter's bolometric fraction. In general, estimates of bolometric fractions from spectral energy distributions of strongly lensed infrared galaxies are so unreliable as to be useless, unless a lens mass model is available to correct for differential magnification.
The long-period Cepheid RS Pup is surrounded by a large dusty nebula reflecting the light from the central star. Due to the changing luminosity of the central source, light echoes propagate into the nebula. This remarkable phenomenon was the subject of Paper I.The origin and physical properties of the nebula are however uncertain: it may have been created through mass loss from the star itself, or it could be the remnant of a pre-existing interstellar cloud. Our goal is to determine the 3D structure of the nebula, and estimate its mass. Knowing the geometrical shape of the nebula will also allow us to retrieve the distance of RS Pup in an unambiguous manner using a model of its light echoes (in a forthcoming work). The scattering angle of the Cepheid light in the circumstellar nebula can be recovered from its degree of linear polarization. We thus observed the nebula surrounding RS Pup using the polarimetric imaging mode of the VLT/FORS instrument, and obtained a map of the degree and position angle of linear polarization. From our FORS observations, we derive a 3D map of the distribution of the dust, whose overall geometry is an irregular and thin layer. The nebula does not present a well-defined symmetry. Using a simple model, we derive a total dust mass of M(dust) = 2.9 +/- 0.9 Msun for the dust within 1.8 arcmin of the Cepheid. This translates into a total mass of M(gas+dust) = 290 +/- 120 Msun, assuming a dust-to-gas ratio of 1.0 +/- 0.3 %. The high mass of the dusty nebula excludes that it was created by mass-loss from the star. However, the thinness nebula is an indication that the Cepheid participated to its shaping, e.g. through its radiation pressure or stellar wind. RS Pup therefore appears as a regular long-period Cepheid located in an exceptionally dense interstellar environment.
We present a catalog of over 6.2 million stars with measured proper motions. All these stars are observed in the direction of the Magellanic Clouds within the brightness range 12 < I < 19 mag. Based on these proper motions around 440 000 Galactic foreground stars can be selected. Because the proper motions are based on a few hundred epochs collected during eight years, their statistical uncertainties are below 0.5 mas/yr for stars brighter than I = 18.5 mag. The parallaxes are derived with uncertainties down to 1.6 mas. For above 13 000 objects parallaxes are derived with significance above 3\sigma, which allows selecting around 270 white dwarfs (WDs). The search for common proper motion binaries among stars presented was performed resulting in over 500 candidate systems. The most interesting ones are candidate halo main sequence star-WD and WD-WD systems. The application of the catalog to empirically bound the Cepheid instability strip is also discussed.
The bright southern star Delta Vel is a multiple system comprising at least three stars. Its brightest component, Delta Vel A, was identified in 2000 as one of the brightest eclipsing system in the sky. Its eclipses are easily observable with the unaided eye, a remarkable property shared only by Algol, Beta Aur, Alpha CrB and Psi Cen. We determined dynamical masses from a combination of spectroscopy, high-precision astrometry of the orbits of Aab-B and Aa-Ab using adaptive optics (VLT/NACO) and optical interferometry (VLTI/AMBER). The main eclipsing component is a pair of A-type stars in rapid rotation. We modeled the photometric and radial velocity measurements of the eclipsing pair Aa-Ab using a self consistent method based on physical parameters (mass, radius, luminosity, rotational velocity). From this modeling, we derive the fundamental parameters of the eclipsing stars with a typical accuracy of 1%. We find that they have similar masses, respectively 2.43 +/- 0.02 and 2.27 +/- 0.02 Msun. The physical parameters of the tertiary component (Delta Vel B) are also derived, although to a lower accuracy, as well as the parallax of the system, 39.8 +/- 0.4 mas. This value is in satisfactory agreement (-1.2 sigma) with the Hipparcos parallax of the system (pi_Hip =40.5 +/- 0.4 mas).
Though the bulk of the observed optical flux from the discs of intermediate-redshift lensed quasars is formed well outside the region of strong relativistic boosting and light-bending, relativistic effects have important influence on microlensing curves. The reason is in the divergent nature of amplification factors near fold caustics increasingly sensitive to small spatial size details. Higher-order disc images produced by strong light bending around the black hole may affect the amplification curves, making a contribution of up to several percent near maximum amplification. In accordance with theoretical predictions, some of the observed high-amplification events possess fine structure. Here we consider three putative caustic crossing events, one by SBS1520+530 and two events for individual images of the Einstein's cross (QSO J2237+0305). Using relativistic disc models allows to improve the fits, but the required inclinations are high, about 70deg or larger. Such high inclinations apparently contradict the absence of any strong absorption that is likely to arise if a disc is observed edge-on through a dust torus. Still, the high inclinations are required only for the central parts of the disc, that allows the disc itself to be initially tilted by 60-90deg with respect to the black hole and aligned toward the black hole equatorial plane near the last stable orbit radius. For SBS1520+530, an alternative explanation for the observed amplification curve is a superposition of two subsequent fold caustic crossings. While relativistic disc models favour black hole masses ~10^10 solar (several times higher than the virial estimates) or small Eddington ratios, this model is consistent with the observed distribution of galaxies over peculiar velocities only if the black hole mass is about 3 10^8 solar.
Effects of the non-Newtonian gravity on properties of finite nuclei are studied by consistently incorporating both the direct and exchange contribution of the Yukawa potential in the Hartree-Fock approach using a well-tested Skyrme force for the strong interaction. It is shown for the first time that the strength of the Yukawa term in the non-Newtonian gravity is limited to $\log(|\alpha|)<1.75/[\lambda(\rm fm)]^{0.54} + 33.6$ within the length scale of $\lambda=1-10$ fm in order for the calculated properties of finite nuclei not to be in conflict with accurate experimental data available.
In the early Universe, energy stored in small-scale density perturbations is quickly dissipated by Silk-damping, a process that inevitably generates mu- and y-type spectral distortions of the cosmic microwave background (CMB). These spectral distortions depend on the shape and amplitude of the primordial power spectrum at wavenumbers k < 10^4 Mpc^{-1}. Here we study constraints on the primordial power spectrum derived from COBE/FIRAS and forecasted for PIXIE. We show that measurements of mu and y impose strong bounds on the integrated small-scale power, and we demonstrate how to compute these constraints using k-space window functions that account for the effects of thermalization and dissipation physics. We show that COBE/FIRAS places a robust upper limit on the amplitude of the small-scale power spectrum. This limit is about three orders of magnitude stronger than the one derived from primordial black holes in the same scale range. Furthermore, this limit could be improved by another three orders of magnitude with PIXIE, potentially opening up a new window to early Universe physics. To illustrate the power of these constraints, we consider several generic models for the small-scale power spectrum predicted by different inflation scenarios, including running-mass inflation models and inflation scenarios with episodes of particle production. PIXIE could place very tight constraints on these scenarios, potentially even ruling out running-mass inflation models if no distortion is detected. We also show that inflation models with sub-Planckian field excursion that generate detectable tensor perturbations should simultaneously produce a large CMB spectral distortion, a link that could potentially be established by PIXIE.
The quantum contributions to the gravitational action are relatively easy to calculate in the higher derivative sector of the theory. However, the applications to the post-inflationary cosmology and astrophysics require the corrections to the Einstein-Hilbert action and to the cosmological constant, and those we can not derive yet in a consistent and safe way. At the same time, if we assume that these quantum terms are covariant and that they have relevant magnitude, their functional form can be defined up to a single free parameter, which can be defined on the phenomenological basis. It turns out that the quantum correction may lead, in principle, to surprisingly strong and interesting effects in astrophysics and cosmology.
(Abridged abstract) We investigate the lithium plateau in the context of primordial dual-shock quark novae (dsQNe; i.e. a QN occurring a few days to a few weeks following the preceding SN explosion) going off in the wake of Pop. III stars. The neutron-rich relativistic QN ejecta leads to spallation of 56Ni processed in the ejecta of the preceding SN ejecta and thus to "iron impoverishment" of the primordial gas swept by dsQNe. We show that the generation of stars formed from fragmentation of pristine clouds swept-up by dsQNe acquire a metallicity with -7.5 < [Fe/H] < -1.5 for dsQNe with 2 < t_delay (days) < 30. Spallation in dsQNe naturally lead to the depletion of 56Ni and formation of sub-Ni elements such as Ti, V, Cr, and Mn providing a reasonable account of the trends observed in galactic halo metal-poor stars. CEMP stars with [C/Fe] > 2 (and up to [C/Fe] ~ 5) can be accounted for in our model for dsQNe with t_delay < 5 days (i.e. [Fe/H] < -4). These dsQNe lead to important destruction of 56Ni (and thus to a drastic reduction of the amount of Fe in the swept up cloud) while preserving the C processed in the outer layers of the SN ejecta. NEMP stars are also accounted for in our model. Neutron-capture of the spallated neutrons in the inner SN shell leads to production of s-process elements; CEMP-s and CEMP-r stars can form without involving accretion from a binary companion. Lithium is produced from the interaction of the neutron-rich QN ejecta with the outer (oxygen-rich) layers of the SN ejecta. A 7Li plateau with 2 < A(Li) < 2.4 is naturally produced in our model from dsQNe with t_delay > 10-11 days (i.e. [Fe/H] > -3). For shorter delays the temperature of the SN shell is too hot (> 2.5x10^6 K) for the spallated 7Li to survive. We find a corresponding 6Li plateau with 6Li/7Li < 0.3.
We benchmark the reliability of the Rotation Measure (RM) synthesis algorithm
using the 1005 Centaurus A field sources of Feain et al. (2009). The RM
synthesis solutions are compared with estimates of the polarization parameters
using traditional methods. This analysis provides verification of the
reliability of RM synthesis estimates. We show that estimates of the
polarization parameters can be made at lower S/N if the range of RMs is
bounded, but reliable estimates of individual sources with unusual RMs require
unconstrainted solutions and higher S/N.
We derive from first principles the statistical properties of the
polarization amplitude associated with RM synthesis in the presence of noise.
The amplitude distribution depends explicitly on the amplitude of the
underlying (intrinsic) polarization signal. Hence it is necessary to model the
underlying polarization signal distribution in order to estimate the
reliability and errors in polarization parameter estimates. We introduce a
Bayesian method to derive the distribution of intrinsic amplitudes based on the
distribution of measured amplitudes.
The theoretically-derived distribution is compared with the empirical data to
provide quantitative estimates of the probability that an RM synthesis solution
is correct as a function of S/N. We provide quantitative estimates of the
probability that any given RM synthesis solution is correct as a function of
measured polarized amplitude and the intrinsic polarization amplitude compared
to the noise.
The multi-object fibre-fed spectrograph AAOmega at the Anglo-Australian Telescope has been used to establish and measure accurate (<1 kms-1) radial velocities for a new sample of members in the outer parts of the stellar system omega Centauri. The new sample more than doubles the number of known members with precise velocities that lie between 25' and 45' from the cluster center. Combining this sample with earlier work confirms that the line-of-sight velocity dispersion of omega Cen remains approximately constant at ~6.5 kms-1 in the outer parts of the cluster, which contain only a small fraction of the total cluster stellar mass. It is argued that the approximately constant velocity dispersion in the outer regions is most likely a consequence of external influences, such as the tidal shock heating that occurs each time omega Cen crosses the Galactic plane. There is therefore no requirement to invoke dark matter or non-standard gravitational theories.
We present multi-wavelength observations of the radio magnetar PSR J1622-4950 and its environment. Observations of PSR J1622-4950 with Chandra (in 2007 and 2009) and XMM (in 2011) show that the X-ray flux of PSR J1622-4950 has decreased by a factor of ~50 over 3.7 years, decaying exponentially with a characteristic time of 360 +/- 11 days. This behavior identifies PSR J1622-4950 as a possible addition to the small class of transient magnetars. The X-ray decay likely indicates that PSR J1622-4950 is recovering from an X-ray outburst that occurred earlier in 2007, before the 2007 Chandra observations. Observations with the Australia Telescope Compact Array show strong radio variability, including a possible radio flaring event at least one and a half years after the 2007 X-ray outburst that may be a direct result of this X-ray event. Radio observations with the Molonglo Observatory Synthesis Telescope reveal that PSR J1622-4950 is 8' southeast of a diffuse radio arc, G333.9+0.0, which appears non-thermal in nature and which could possibly be a previously undiscovered supernova remnant. If G333.9+0.0 is a supernova remnant then the estimates of its size and age, combined with the close proximity and reasonable implied velocity of PSR J1622-4950, suggests that these two objects could be physically associated.
We discuss the possibility of observing the transient formation event of an accretion disk from the tidal destruction process of an asteroid near a white dwarf (WD). This scenario is commonly proposed as the explanation for dusty disks around WDs. We find that the initial formation phase lasts for about a month and material that ends in a close orbit near the WD forms a gaseous disk rather than a dusty disk. The mass and size of this gaseous accretion disk is very similar to that of Dwarf Novae (DNe) in quiescence. The bolometric luminosity of the event at maximum is estimated to be 0.001-0.1Lsun. Based on the similarity with DNe we expect that transient outburst events such as discussed here will be observed at wavelengths ranging from visible to the X-ray, and be detected by present and future surveys.
We have performed H and Ks band observations of the planetary system around HR 8799 using the new AO system at the Large Binocular Telescope and the PISCES Camera. The excellent instrument performance (Strehl ratios up to 80% in H band) enabled detection the inner planet HR8799e in the H band for the first time. The H and Ks magnitudes of HR8799e are similar to those of planets c and d, with planet e slightly brighter. Therefore, HR8799e is likely slightly more massive than c and d. We also explored possible orbital configurations and their orbital stability. We confirm that the orbits of planets b, c and e are consistent with being circular and coplanar; planet d should have either an orbital eccentricity of about 0.1 or be non-coplanar with respect to b and c. Planet e can not be in circular and coplanar orbit in a 4:2:1 mean motion resonances with c and d, while coplanar and circular orbits are allowed for a 5:2 resonance. The analysis of dynamical stability shows that the system is highly unstable or chaotic when planetary masses of about 5 MJup for b and 7 MJup for the other planets are adopted. Significant regions of dynamical stability for timescales of tens of Myr are found when adopting planetary masses of about 3.5, 5, 5, and 5 Mjup for HR 8799 b, c, d, and e respectively. These masses are below the current estimates based on the stellar age (30 Myr) and theoretical models of substellar objects.
We investigate the possibility of constraining the dark energy equation of state by measuring the ratio of Einstein radii in a strong gravitational lens system with two source planes. This quantity is independent of the Hubble parameter and directly measures the growth of angular diameter distances as a function of redshift. We investigate the prospects for a single double source plane system and for a forecast population of systems discovered by re-observing a population of single source lenses already known from a photometrically selected catalogue such as CASSOWARY or from a spectroscopically selected catalogue such as SLACS. We find that constraints comparable to current data-sets (15% uncertainty on the dark equation of state at 68%CL) are possible with a handful of double source plane systems. We also find that the method's degeneracy between Omega_M and w is almost orthogonal to that of CMB and BAO measurements, making this method highly complimentary to current probes.
The Large Binocular Telescope (LBT) is a unique telescope featuring two co-mounted optical trains with 8.4m primary mirrors. The telescope Adaptive Optics (AO) system uses two innovative key components, namely an adaptive secondary mirror with 672 actuators and a high-order pyramid wave-front sensor. During the on-sky commissioning such a system reached performances never achieved before on large ground-based optical telescopes. Images with 40mas resolution and Strehl Ratios higher than 80% have been acquired in H band (1.6 micron). Such images showed a contrast as high as 10e-4. Based on these results, we compare the performances offered by a Natural Guide Star (NGS) system upgraded with the state-of-the-art technology and those delivered by existing Laser Guide Star (LGS) systems. The comparison, in terms of sky coverage and performances, suggests rethinking the current role ascribed to NGS and LGS in the next generation of AO systems for the 8-10 meter class telescopes and Extremely Large Telescopes (ELTs).
We present estimates of magnetic field in a number of AGNs from the Spectropolarimetric atlas of Smith, Young & Robinson (2002) from the observed degrees of linear polarization and the positional angles of spectral lines (H-alpha) (broad line regions of AGNs) and nearby continuum. The observed polarization is lower than the Milne value in a non-magnetized atmosphere. We hypothesize that the polarized radiation escapes from optically thick magnetized accretion discs and is weakened by the Faraday rotation effect. This effect is able to explain both the value of the polarization and the position angle. We estimate the required magnetic field in the broad line region by using simple asymptotic analytical formulas for Milne's problem in magnetized atmosphere, which take into account the last scattering of radiation before escaping from the accretion disc. The polarization of a broad spectral line escaping from disc is described by the same mechanism. The characteristic features of polarization of a broad line is the minimum of the degree of polarization in the center of the line and continuous rotation of the position angle from one wing to another. These effects can be explained by existence of clouds in the left (velocity is directed to an observer) and the right (velocity is directed from an observer) parts of the orbit in a rotating keplerian magnetized accretion disc. The base of explanation is existence of azimuthal magnetic field in the orbit. The existence of normal component of magnetic field makes the picture of polarization asymmetric. The existence of clouds in left and right parts of the orbit with different emissions also give the contribution in asymmetry effect. Assuming a power-law dependence of the magnetic field inside the disc, we obtain the estimate of the magnetic field strength at first stable orbit near the central SMBH for a number of AGNs.
We review the conformal equivalence in describing the background expansion of the universe by $f(R)$ gravity both in the Jordan frame and the Einstein frame. In the Jordan frame, we present the general analytic expression for $f(R)$ models that have the same expansion history as the $\Lambda$CDM model. This analytic form can provide further insights on how cosmology can be used to test the $f(R)$ gravity at the largest scales. Moreover we present a systematic and self-consistent way to construct the viable $f(R)$ model in Jordan frame using the mass dilation rate function from the Einstein frame through the conformal transformation. In addition, we extend our study to the linear perturbation theories and we further exhibit the equivalence of the $f(R)$ gravity presented in the Jordan frame and Einstein frame in the perturbed space-time. We argue that this equivalence has solid physics root.
Forthcoming experiments will enable us to determine high precision tomographic shear spectra. Matter density fluctuation spectra, at various $z$, should then be worked out of them, in order to constrain the model and determine the DE state equation. Available analytical expressions, however, do the opposite, enabling us to derive shear spectra from fluctuation spectra. Here we find the inverse expression, yielding density fluctuation spectra from observational tomographic shear spectra. The procedure involves SVD techniques for matrix inversion. We show in detail how the approach works and provide a few examples.
We present Very Long Baseline Array observations of the radio galaxy 3C120 at 5, 8, 12, and 15 GHz designed to study a peculiar stationary jet feature (hereafter C80) located ~80 mas from the core, which was previously shown to display a brightness temperature ~600 times lager than expected at such distances. The high sensitivity of the images -- obtained between December 2009 and June 2010 -- has revealed that C80 corresponds to the eastern flux density peak of an arc of emission (hereafter A80), downstream of which extends a large (~20 mas in size) bubble-like structure that resembles an inverted bow shock. The linearly polarized emission closely follows that of the total intensity in A80, with the electric vector position angle distributed nearly perpendicular to the arc-shaped structure. Despite the stationary nature of C80/A80, superluminal components with speeds up to ~3 c have been detected downstream from its position, resembling the behavior observed in the HST-1 emission complex in M87. The total and polarized emission of the C80/A80 structure, its lack of motion, and brightness temperature excess are best reproduced by a model based on synchrotron emission from a conical shock with cone opening angle \eta=10 degrees, jet viewing angle \theta=16 degrees, a completely tangled upstream magnetic field, and upstream Lorentz factor \gamma=8.4. The good agreement between our observations and numerical modeling leads us to conclude that the peculiar feature associated with C80/A80 corresponds to a conical recollimation shock in the jet of 3C120 located at a de-projected distance of ~140 pc downstream from the nucleus.
Aims. We investigate the properties of hydrocarbon grains in the galactic superwind of M 82. Methods. With AKARI, we performed near-infrared (2.5 - 4.5 um) spectroscopic observations of 34 regions in M 82 including its northern and southern halos. Results. Many of the spectra show strong emission at 3.3 um due to polycyclic aromatic hydrocarbons (PAHs) and relatively weak features at 3.4 - 3.6 um due to aliphatic hydrocarbons. In particular, we clearly detect the PAH 3.3 um emission and the 3.4 - 3.6 um features in halo regions, which are located at a distance of 2 kpc away from the galactic center. We find that the ratios of the 3.4 - 3.6 um features to the 3.3 um feature intensity significantly increase with distance from the galactic center, while the ratios of the 3.3 um feature to the AKARI 7 um band intensity do not. Conclusions. Our results clearly confirm the presence of small PAHs even in a harsh environment of the halo of M 82. The results also reveal that the aliphatic hydrocarbons emitting the 3.4 - 3.6 um features are unusually abundant in the halo, suggesting that small carbonaceous grains are produced by shattering of larger grains in the galactic superwind.
We describe inhomogeneities in a \Lambda CDM universe with a gradient series expansion and show that it describes the gravitational evolution far into the non-linear regime and beyond the capacity of standard perturbation theory at any order. We compare the gradient expansion with exact inhomogeneous \Lambda LTB solutions (Lema\^itre-Tolman-Bondi metric with the inclusion of a cosmological constant) describing growing structure in a \Lambda CDM universe and find that the expansion approximates the exact solution well, following the collapse of an over-density all the way into a singularity.
The common approach to compute the cosmic-ray distribution in an starburst galaxy or region is equivalent to assume that at any point within that environment, there is an accelerator inputing cosmic rays at a reduced rate. This rate should be compatible with the overall volume-average injection, given by the total number of accelerators that were active during the starburst age. These assumptions seem reasonable, especially under the supposition of an homogeneous and isotropic distribution of accelerators. However, in this approach the temporal evolution of the superposed spectrum is not explicitly derived; rather, it is essentially assumed ab-initio. Here, we test the validity of this approach by following the temporal evolution and spatial distribution of the superposed cosmic-ray spectrum and compare our results with those from theoretical models that treat the starburst region as a single source. In the calorimetric limit (with no cosmic-ray advection), homogeneity is reached (typically within 20%) across most of the starburst region. However, values of center-to-edge intensity ratios can amount to a factor of several. Differences between the common homogeneous assumption for the cosmic-ray distribution and our models are larger in the case of two-zone geometries, such as a central nucleus with a surrounding disc. We have also found that the decay of the cosmic-ray density following the duration of the starburst process is slow, and even approximately 1 Myr after the burst ends (for a gas density of 35 cm-3) it may still be within an order of magnitude of its peak value. Based on our simulations, it seems that the detection of a relatively hard spectrum up to the highest gamma-ray energies from nearby starburst galaxies favors a relatively small diffusion coefficient (i.e., long diffusion time) in the region where most of the emission originates.
Well-sampled optical lightcurves of 146 gamma-ray bursts (GRBs) are complied from the literature. Multiple optical emission components are extracted with power-law function fits to these lightcurves. We present a systematical analysis for statistical properties and their relations to prompt gamma-ray emission and X-ray afterglow for each component. We show that peak luminosity in the prompt and late flares are correlated and the evolution of the peak luminosity may signal the evolution of the accretion rate. No tight correlation between the shallow decay phase/plateau and prompt gamma-ray emission is found. Assuming that they are due to a long-lasting wind injected by a compact object, we show that the injected behavior favors the scenarios of a long-lasting wind after the main burst episode. The peak luminosity of the afterglow onset is tightly correlated with Eiso, and it is dimmer as peaking later. Assuming that the onset bump is due to the fireball deceleration by the external medium, we examine the Gamma_0-Eiso relation and find that it is confirmed with the current sample. Optical re-brightening is observed in 30 GRBs in our sample. It shares the same relation between the width and the peak time as found in the onset bump, but no clear correlation between the peak luminosity and Eiso as observed in the onset bumps is found. Although its peak luminosity also decays with time, the slope is much shallower than that of the onset peak. We get L t^{-1}_{p}$, being consistent with off-axis observations to an expanding external fireball in a wind-like circum medium. The late re-brightening may signal another jet component. Mixing of different emission components may be the reason for the observed chromatic breaks in different energy bands.
We present a multi-wavelength observational study towards the high-mass young stellar object G8.68-0.37. A single massive gas-and-dust core is observed in the (sub)millimeter continuum and molecular line emissions. We fitted the spectral energy distribution (SED) from the dust continuum emission. The best-fit SED suggests the presence of two components with temperature of $T_{\rm d}=20$ K and 120 K, respectively. The core has a total mass of up to $1.5\times10^3$ $M_{\odot}$ and bolometric luminosity of $2.3\times10^4 L_{\odot}$. Both the mass and luminosity are dominated by the cold component ($T_{\rm d}=20$ K). The molecular lines of C$^{18}$O, C$^{34}$S, DCN, and thermally excited CH$_3$OH are detected in this core. Prominent infall signatures are observed in the $^{12}$CO $(1-0)$ and $(2-1)$. We estimated an infall velocity of 0.45 km s$^{-1}$ and mass infall rate of $7\times10^{-4} M_{\odot}$ year$^{-1}$. From the molecular lines, we have found a high DCN abundance and relative abundance ratio to HCN. The overabundant DCN may originate from a significant deuteration in the previous cold pre-protostellar phase. And the DCN should now be rapidly sublimated from the grain mantles to maintain the overabundance in the gas phase.
Chromospheric brighten and H$\alpha$ surge are the evident and common phenomena along sunspot light bridge. In this paper, a coronal jet ejects from sunspot light bridge is presented. Using the data from the Solar Dynamics Observatory (SDO) and Hinode satellites, it is confirmed that the jet has the root near light bridge, this suggests that the jet may be a result of reconnection between main sunspot and light bridge. Due to the processing of jet ejects, the intensity and width of light bridge have some changes at some extent. This also suggests that jet is related to the interaction between light bridge and umbra, possibly magnetic reconnection or heat plasma trapped in light bridge escaping and moving along field line.
The current standard model of cosmology, the LambdaCDM model, is based on the homogeneous FLRW solutions of the Einstein equations to which some perturbations are added to account for the CMB features and structure formation at large scales. This model fits rather well the observations provided 95% of the energy density budget of the Universe should be of an unknown physical nature, i.e. dark matter and dark energy. Now, the aim of a cosmological model is not merely to reproduce the observations, but also to give a physical understanding of the Universe we live in. Moreover, even if the assumption of homogeneity seems to be more or less valid at large scales, it appears to be in contradiction with observations at intermediate scales (between the scale of non linear structure formation and that where structures virialize). This is the reason why, during the last decade, a community of researchers formed whose aim was to look for the best way to take into account the influence of the inhomogeneities seen in the Universe and to construct accurate cosmological models which could possibly get rid of the dark components. This task, which is still in its infancy, is currently progressing towards promising results. Two types of methods can be found in the literature: spatial averaging of scalar quantities and use of exact inhomogeneous solutions of General Relativity. We will give here a brief report of the second one.
Although water is an essential and widespread molecule in star-forming regions, its chemical formation pathways are still not very well constrained. Observing the level of deuterium fractionation of OH, a radical involved in the water chemical network, is a promising way to infer its chemical origin. We aim at understanding the formation mechanisms of water by investigating the origin of its deuterium fractionation. This can be achieved by observing the abundance of OD towards the low-mass protostar IRAS16293-2422, where the HDO distribution is already known. Using the GREAT receiver on board SOFIA, we observed the ground-state OD transition at 1391.5 GHz towards the low-mass protostar IRAS16293-2422. We also present the detection of the HDO 111-000 line using the APEX telescope. We compare the OD/HDO abundance ratio inferred from these observations with the predictions of chemical models. The OD line is detected in absorption towards the source continuum. This is the first detection of OD outside the solar system. The SOFIA observation, coupled to the observation of the HDO 111-000 line, provides an estimate of the abundance ratio OD/HDO ~ 17-90 in the gas where the absorption takes place. This value is fairly high compared with model predictions. This may be reconciled if reprocessing in the gas by means of the dissociative recombination of H2DO+ further fractionates OH with respect to water. The present observation demonstrates the capability of the SOFIA/GREAT instrument to detect the ground transition of OD towards star-forming regions in a frequency range that was not accessible before. Dissociative recombination of H2DO+ may play an important role in setting a high OD abundance. Measuring the branching ratios of this reaction in the laboratory will be of great value for chemical models.
Context. High-contrast imaging is currently the only available technique for the study of the thermodynamical and compositional properties of exoplanets in long-period orbits. The SPICES project is a coronagraphic space telescope dedicated to the spectro-polarimetric analysis of gaseous and icy giant planets as well as super-Earths at visible wavelengths. So far, studies for high-contrast imaging instruments have mainly focused on technical feasibility because of the challenging planet/star flux ratio of 10-8-10-10 required at short separations (200 mas or so) to image cold exoplanets. However, the analysis of planet atmospheric/surface properties has remained largely unexplored. Aims. The aim of this paper is to determine which planetary properties SPICES or an equivalent direct imaging mission can measure, considering realistic reflected planet spectra and instrument limitation. Methods. We use numerical simulations of the SPICES instrument concept and theoretical planet spectra to carry out this performance study. Results. We find that the characterization of the main planetary properties (identification of molecules, effect of metallicity, presence of clouds and type of surfaces) would require a median signal-to-noise ratio of at least 30. In the case of a solar-type star \leq 10 pc, SPICES will be able to study Jupiters and Neptunes up to ~5 and ~2 AU respectively. It would also analyze cloud and surface coverage of super-Earths of radius 2.5 RE at 1 AU. Finally, we determine the potential targets in terms of planet separation, radius and distance for several stellar types. For a Sun analog, we show that SPICES could characterize Jupiters (M \geq 30 ME) as small as 0.5 Jupiter radii at ~2 AU up to 10 pc, and super-Earths at 1-2 AU for the handful of stars that exist within 4-5 pc. Potentially, SPICES could perform analysis of a hypothetical Earth-size planet around alpha Cen A and B.
We have developed a method for analyzing the kinematic association of isolated relativistic objects - possible remnants of disrupted close binary systems. We investigate pairs of fairly young radio pulsars with known proper motions and estimated distances (dispersion measures) that are spaced no more than 2-3 kpc apart. Using a specified radial velocity distribution for these objects, we have constructed 100-300 thousand trajectories of their possible motion in the Galactic gravitational field on a time scale of several million years. The probabilities of their close encounters at epochs consistent with the age of the younger pulsar in the pair are analyzed. When these probabilities exceed considerably their reference values obtained by assuming a purely random encounter between the pulsars under consideration, we conclude that the objects may have been gravitationally bound in the past. As a result, we have detected six pulsar pairs (J0543+2329/J0528+2200, J1453-6413/J1430-6623, J2354+6155/J2321+6024, J1915+1009/J1909+1102, J1832-0827/J1836-1008, and J1917+1353/J1926+1648) that are companions in disrupted binary systems with a high probability. Estimates of their kinematic ages and velocities at binary disruption and at the present epoch are provided.
We describe the design and construction of GREAT, the German REceiver for
Astronomy at Terahertz frequencies operated on the Stratospheric Observatory
for Infrared Astronomy (SOFIA). GREAT is a modular dual-color heterodyne
instrument for highresolution far-infrared (FIR) spectroscopy. Selected for
SOFIA's Early Science demonstration, the instrument has successfully performed
three Short and more than a dozen Basic Science flights since first light was
recorded on its April 1, 2011 commissioning flight.
We report on the in-flight performance and operation of the receiver that -
in various flight configurations, with three different detector channels -
observed in several science-defined frequency windows between 1.25 and 2.5 THz.
The receiver optics was verified to be diffraction-limited as designed, with
nominal efficiencies; receiver sensitivities are state-of-the-art, with
excellent system stability. The modular design allows for the continuous
integration of latest technologies; we briefly discuss additional channels
under development and ongoing improvements for Cycle 1 observations.
GREAT is a principal investigator instrument, developed by a consortium of
four German research institutes, available to the SOFIA users on a
collaborative basis.
We study the dynamics of the 3-D three-body problem of a small body moving under the attractions of a star and a giant planet which orbits the star on a much wider and elliptic orbit. In particular, we focus on the influence of an eccentric orbit of the outer perturber on the dynamics of a small highly inclined inner body. Our analytical study of the secular perturbations relies on the classical octupole hamiltonian expansion (third-order theory in the ratio of the semi-major axes), as third-order terms are needed to consider the secular variations of the outer perturber and potential secular resonances between the arguments of the pericenter and/or longitudes of the node of both bodies. Short-period averaging and node reduction (Laplace plane) reduce the problem to two degrees of freedom. The four-dimensional dynamics is analyzed through representative planes which identify the main equilibria of the problem. As in the circular problem (i.e. perturber on a circular orbit), the "Kozai-bifurcated" equilibria play a major role in the dynamics of an inner body on quasi-circular orbit: its eccentricity variations are very limited for mutual inclination between the orbital planes smaller than ~40^{\deg}, while they become large and chaotic for higher mutual inclination. Particular attention is also given to a region around 35^{\deg} of mutual inclination, detected numerically by Funk et al. (2011) and consisting of long-time stable and particularly low eccentric orbits of the small body. Using a 12th-order Hamiltonian expansion in eccentricities and inclinations, in particular its action-angle formulation obtained by Lie transforms in Libert & Henrard (2008), we show that this region presents an equality of two fundamental frequencies and can be regarded as a secular resonance. Our results also apply to binary star systems where a planet is revolving around one of the two stars.
We describe the consistency testing of a new code for gravitational wave signal parameter estimation in known pulsar searches. The code uses an implementation of nested sampling to explore the likelihood volume. Using fake signals and simulated noise we compare this to a previous code that calculated the signal parameter posterior distributions on both a grid and using a crude Markov chain Monte Carlo (MCMC) method. We define a new parameterisation of two orientation angles of neutron stars used in the signal model (the initial phase and polarisation angle), which breaks a degeneracy between them and allows more efficient exploration of those parameters. Finally, we briefly describe potential areas for further study and the uses of this code in the future.
LISA will use quadrant photoreceivers as front-end devices for the phasemeter measuring the motion of drag-free test masses in both angular orientation and separation. We have set up a laboratory testbed for the characterization of photoreceivers. Some of the limiting noise sources have been identified and their contribution has been either measured or derived from the measured data. We have built a photoreceiver with a 0.5 mm diameter quadrant photodiode with an equivalent input current noise of better than $1.8\,\mathrm{pA}/\sqrt{\mathrm{Hz}}$ below 20\,MHz and a 3\,dB bandwidth of 34\,MHz.
The very high energy (VHE) \gamma-ray source HESS J0632+057 has recently been confirmed to be a \gamma-ray binary. The optical counterpart is the Be star MWC 148, and a compact object of unknown nature orbits it every ~321 d with a high eccentricity of ~0.8. We monitored HESS J0632+057 with the stereoscopic MAGIC telescopes from 2010 October to 2011 March and detected significant VHE \gamma-ray emission during 2011 February, when the system exhibited an X-ray outburst. We find no \gamma-ray signal in the other observation periods when the system did not show increased X-ray flux. Thus HESS J0632+057 exhibits \gamma-ray variability on timescales of the order of one to two months possibly linked to the X-ray outburst that takes place about 100 days after the periastron passage. Furthermore our measurements provide for the first time the \gamma-ray spectrum down to about 140 GeV and indicate no turnover of the spectrum at low energies. We compare the properties of HESS J0632+057 with the similar \gamma-ray binary LS I +61 303, and discuss on the possible origin of the multi-wavelength emission of the source
Weak gravitational lensing has become a common tool to constrain the cosmological model. The majority of the methods to derive constraints on cosmological parameters use second-order statistics of the cosmic shear. Despite their success, second-order statistics are not optimal and degeneracies between some parameters remain. Tighter constraints can be obtained if second-order statistics are combined with a statistic that is efficient to capture non-Gaussianity. In this paper, we search for such a statistical tool and we show that there is additional information to be extracted from statistical analysis of the convergence maps beyond what can be obtained from statistical analysis of the shear field. For this purpose, we have carried out a large number of cosmological simulations along the {\sigma}8-{\Omega}m degeneracy, and we have considered three different statistics commonly used for non-Gaussian features characterization: skewness, kurtosis and peak count. To be able to investigate non-Gaussianity directly in the shear field we have used the aperture mass definition of these three statistics for different scales. Then, the results have been compared with the results obtained with the same statistics estimated in the convergence maps at the same scales. First, we show that shear statistics give similar constraints to those given by convergence statistics, if the same scale is considered. In addition, we find that the peak count statistic is the best to capture non-Gaussianities in the weak lensing field and to break the {\sigma}8-{\Omega}m degeneracy. We show that this statistical analysis should be conducted in the convergence maps: first, because there exist fast algorithms to compute the convergence map for different scales, and secondly because it offers the opportunity to denoise the reconstructed convergence map, which improves non-Gaussian features extraction.
Using ultraviolet spectra obtained with the Cosmic Origins Spectrograph on the Hubble Space Telescope, we extend our previous ground-based optical determinations of the composition of the extrasolar asteroids accreted onto two white dwarfs, GD 40 and G241-6. Combining optical and ultraviolet spectra of these stars with He-dominated atmospheres, 13 and 12 polluting elements are confidently detected in GD 40 and G241-6, respectively. For the material accreted onto GD 40, the volatile elements C and S are deficient by more than a factor of 10 and N by at least a factor of 5 compared to their mass fractions in primitive CI chondrites and approach what is inferred for bulk Earth. A similar pattern is found for G241-6 except that S is undepleted. We have also newly detected or placed meaningful upper limits for the amount of Cl, Al, P, Ni and Cu in the accreted matter. Extending results from optical studies, the mass fractions of refractory elements in the accreted parent bodies are similar to what is measured for bulk Earth and chondrites. Thermal processing, perhaps interior to a snow line, appears to be of central importance in determining the elemental compositions of these particular extrasolar asteroids.
The Blazhko-phenomenon, the modulation of the pulsation of RR Lyrae stars remains one of the most stubborn unsolved problems of stellar pulsation. The recent idea of Stothers proposes that periodic variations in the properties of the convective envelope may be behind the amplitude and phase modulation. In this work we approximated the mechanism by introducing variations in the convective parameters of the Florida-Budapest hydrodynamic code and also by means of amplitude equations. We found that the process is only effective for long modulation periods, typically for more than hundred days, in agreement with the thermal time scales of the pulsation in RR Lyrae stars. Due to the slow response of the pulsation to the structure changes, short period, high amplitude Blazhko-modulation cannot be reproduced with this mechanism or would require implausible variations in the convective parameters on short time scales. We also found that the modulation of the mixing length results in strong differences between both the luminosity and radius variations and the respective phase modulations of the two quantities, suggesting notable differences between the energy output of the photosphere and the mechanical variations of the layers. The findings suggest that the convective cycle model is not well suited as a standalone mechanism behind the Blazhko-effect.
Physical collisions and close approaches between stars play an important role in the formation of exotic stellar systems. Standard theories suggest that collisions are are, occurring only via random encounters between stars in dense clusters. We present a different formation pathway, the triple evolution dynamical instability (TEDI), in which mass loss in an evolving triple star system causes orbital instability. The subsequent chaotic orbital evolution of the stars triggers close encounters, collisions, exchanges between the stellar components, and the dynamical formation of eccentric compact binaries like Sirius. We demonstrate that the rate of stellar collisions due to the TEDI is ~10^(-4) yr^(-1) per Milky-Way Galaxy, which is ~30 times higher than the collision rate due to random encounters in globular clusters. Moreover, we find that the dominant type of stellar collisions is qualitatively different; most collisions involve asymptotic giant branch stars, rather than main sequence, or slightly evolved stars, which dominate collisions in globular clusters. The TEDI mechanism should lead us to revise our understanding of collisions and the formation of compact, eccentric binaries in the field.
The Daya Bay Collaboration has recently reported its first \bar{\nu}_e \to \bar{\nu}_e oscillation result which points to \theta_{13} \simeq 8.8^\circ \pm 0.8^\circ (best-fit \pm 1\sigma range) or \theta_{13} \neq 0^\circ at the 5.2\sigma level. The fact that this smallest neutrino mixing angle is not strongly suppressed motivates us to look into the underlying structure of lepton flavor mixing and CP violation. Two phenomenological strategies are outlined: (1) the lepton flavor mixing matrix U consists of a constant leading term U_0 and a small perturbation term \Delta U; and (2) the mixing angles of U are associated with the lepton mass ratios. Some typical patterns of U_0 are reexamined by constraining their respective perturbations with current experimental data. We illustrate a few possible ways to minimally correct U_0 in order to fit the observed values of three mixing angles. We point out that the structure of U may exhibit an approximate \mu-\tau permutation symmetry in modulus, and reiterate the geometrical description of CP violation in terms of the leptonic unitarity triangles. The salient features of nine distinct parametrizations of U are summarized, and its Wolfenstein-like expansion is presented by taking U_0 to be the democratic mixing pattern.
We provide a detailed discussion of the multi-field trajectories and inflationary dynamics of the recently proposed model of Chromo-Natural inflation, which allows for slow roll inflation on a steep potential with the aid of classical non-Abelian gauge fields. We show that slow roll inflation can be achieved across a wide range of the parameter space. We demonstrate that Chromo-Natural Inflation includes trajectories that match those found in Gauge-flation and describe how the theories are related.
We have developed a method to equip homodyne interferometers with the capability to operate with constant high sensitivity over many fringes for continuous real-time tracking. The method can be considered as an extension of the "$J_1...J_4$" methods, and its enhancement to deliver very sensitive angular measurements through Differential Wavefront Sensing is straightforward. Beam generation requires a sinusoidal phase modulation of several radians in one interferometer arm. On a stable optical bench, we have demonstrated a long-term sensitivity over thousands of seconds of 0.1\,mrad$/\sqrt{\rm Hz}$ that correspond to 20\,pm$/\sqrt{\rm Hz}$ in length, and 10\,nrad$/\sqrt{\rm Hz}$ in angle at millihertz frequencies.
The cosmological behavior of modified gravity theories with additional degrees of freedom (DOFs) is typically complex and can give rise to non-intuitive results. A possible way of exploring such theories is to consider appropriate parameterizations of these new DOFs. Here I suggest using the algebraic structure of trivial identities, which typically occur at the level of the perturbed field equations, for defining such parameterizations. Choosing the example of Bekenstein's tensor-vector-scalar theory (TeVeS) and considering perturbations in the conformal Newtonian gauge, this parameterization is then used to study several aspects of the cosmological evolution in an Einstein-de Sitter universe. As a main result, I conclude that perturbations of the scalar field take a key role in generating enhanced growth if this enhancement is primarily associated with a gravitational slip. From this point of view, the previously found modified growth in TeVeS is truly a result of the complex interplay between both the scalar and the vector field. Since the occurrence of trivial identities of the above kind appears as a generic feature of modified gravity theories with extra DOFs, these parameterizations should generally prove useful to investigate the cosmological properties of other proposed modifications. As such parameterizations capture the full nature of modifications by construction, they also provide a suitable framework for developing semi-analytic models of cosmologically interesting quantities like, for instance, the growth factor, leading to various applications. Supplementary to numerical analysis, parameterizations based on trivial identities are thus an interesting tool to approach modified gravity theories with extra DOFs.
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Monte Carlo approaches to radiation transport have several attractive properties compared to deterministic methods. These include simplicity of implementation, high accuracy, and good parallel scaling. Moreover, Monte Carlo methods can handle complicated geometries and are relatively easy to extend to multiple spatial dimensions, which makes them particularly interesting in modeling complex multi-dimensional astrophysical phenomena such as core-collapse supernovae. The aim of this paper is to explore Monte Carlo methods for modeling neutrino transport in core-collapse supernovae. We generalize the implicit Monte Carlo photon transport scheme of Fleck & Cummings and gray discrete-diffusion scheme of Densmore et al. to energy-, time-, and velocity-dependent neutrino transport. Using our 1D spherically-symmetric implementation, we show that, similar to the photon transport case, the implicit scheme enables significantly larger timesteps compared with explicit time discretization, without sacrificing accuracy, while the discrete-diffusion method leads to significant speed-ups at high optical depth. Our results suggest that a combination of spectral, velocity-dependent, implicit Monte Carlo and discrete-diffusion Monte Carlo methods represents an attractive approach for use in neutrino radiation-hydrodynamics simulations of core-collapse supernovae. Our velocity-dependent scheme can easily be adapted to photon transport.
Comparing the ejecta velocities at maximum brightness and narrow circumstellar/interstellar Na D absorption line profiles of a sample of 23 Type Ia supernovae (SNe Ia), we determine that the properties of SN Ia progenitor systems and explosions are intimately connected. As demonstrated by Sternberg et al. (2011), half of all SNe Ia with detectable Na D absorption at the host-galaxy redshift in high-resolution spectroscopy have Na D line profiles with significant blueshifted absorption relative to the strongest absorption component, which indicates that a large fraction of SN Ia progenitor systems have strong winds. In this study, we find that SNe Ia with blueshifted circumstellar/interstellar absorption systematically have higher ejecta velocities and redder colors at maximum brightness relative to the rest of the SN Ia population. This result is robust at a 98.9 - 99.8% confidence level, providing the first link between the progenitor systems and properties of the explosion. This finding is further evidence that the wind scenario is the correct interpretation of the blueshifted Na D absorption, adding additional confirmation that some SNe Ia are produced from a single-degenerate progenitor channel. An additional implication is that either SN Ia progenitor systems have highly asymmetric winds that are also aligned with the SN explosion or SNe Ia come from a variety of progenitor systems where SNe Ia from systems with strong winds tend to have more kinetic energy per unit mass than those from systems with weak or no winds.
Mass transfer from an evolved donor star to its binary companion is a standard feature of stellar evolution in binaries. In wide binaries, the companion star captures some of the mass ejected in a wind by the primary star. The captured material forms an accretion disk. Here, we study the evolution of wind-accretion disks, using a numerical approach which allows us to follow the long term evolution. For a broad range of initial conditions, we derive the radial density and temperature profiles of the disk. In most cases, wind-accretion leads to long-lived stable disks over the lifetime of the AGB donor star. The disks have masses of a few times 10^(-5)-10^(-3) Msun, with surface density and temperature profiles that follow broken power-laws. Roughly 50% to 80% of the mass falling into the disk accretes onto the central star; the rest flows out through the outer edge of the disk into the stellar wind of the primary. For systems with large accretion rates, the secondary accretes as much as 0.1 Msun. When the secondary is a white dwarf, accretion naturally leads to nova and supernova eruptions. For all types of secondary star, the surface density and temperature profiles of massive disks resemble structures observed in protoplanetary disks, suggesting that coordinated observational programs might improve our understanding of uncertain disk physics.
Context. Recently the discovery of PSR J1719-1438, a 5.8 ms pulsar with a companion in a 2.2 hr orbit, was reported. The combination of this orbital period and the very low mass function is unique. The discoverers, Bailes et al., proposed an ultracompact X-ray binary (UCXB) as the progenitor system. However, the standard UCXB scenario would not produce this system as the time required to reach this orbital period exceeds the current estimate of the age of the Universe. The detached state of the system aggravates the problem. Aims. We want to understand the evolutionary history of PSR J1719-1438, and determine under which circumstances it could have evolved from an UCXB. Methods. We model UCXB evolution varying the donor size and investigate the effect of a wind mass loss from the donor, and compare the results with the observed characteristics of PSR J1719-1438. Results. An UCXB can reach a 2.2 hr orbit within the age of the Universe, provided that 1) the millisecond pulsar can significantly heat and expand the donor by pulsar irradiation, or 2) the system loses extra orbital angular momentum, e.g. via a fast wind from the donor. Conclusions. The most likely scenario for the formation of PSR J1719-1438 is UCXB evolution driven by angular momentum loss via the usual gravitational wave emission, which is enhanced by angular momentum loss via a donor wind of ~3x10^-13 Msun/yr. Depending on the size of the donor during the evolution, the companion presently probably has a mass of ~1-3 Jupiter masses, making it a very low mass white dwarf as proposed by Bailes et al. Its composition can be either helium or carbon-oxygen. A helium white dwarf companion makes the long (for an UCXB) orbital period easier to explain, but the required inclination makes it a priori less likely than a carbon-oxygen white dwarf.
Recent numerical relativity simulations have shown that the final black hole produced in a binary merger can recoil with a velocity as large as 5,000 km/s. Because of enhanced gravitational-wave emission in the so-called "hang-up" configurations, this maximum recoil occurs when the black-hole spins are partially aligned with the orbital angular momentum. We revisit our previous statistical analysis of post-Newtonian evolutions of black-hole binaries in the light of these new findings. We demonstrate that despite these new configurations with enhanced recoil velocities, spin alignment during the post-Newtonian stage of the inspiral will still significantly suppress (or enhance) kick magnitudes when the initial spin of the more massive black hole is more (or less) closely aligned with the orbital angular momentum than that of the smaller hole. We present a preliminary study of how this post-Newtonian spin alignment affects the ejection probabilities of supermassive black holes from their host galaxies with astrophysically motivated mass ratio and initial spin distributions. We find that spin alignment suppresses (enhances) ejection probabilities by ~ 40% (20%) for an observationally motivated mass-dependent galactic escape velocity, and by an even greater amount for a constant escape velocity of 1,000 km/s. Kick suppression is thus at least a factor two more efficient than enhancement.
Molecular line polarization is a unique source of information about the magnetic fields and anisotropies in the circumstellar envelopes of evolved stars. Here we present the first detection of thermal CO(J=2-1) and SiO(J=5-4, v=0) polarization, in the envelope of the asymptotic giant branch star IK Tau. The observed polarization direction does not match predictions for circumstellar envelope polarization induced only by an anisotropic radiation field. Assuming that the polarization is purely due to the Goldreich-Kylafis effect, the linear polarization direction is defined by the magnetic field as even the small Zeeman splitting of CO and SiO dominates the molecular collisional and spontaneous emission rates. The polarization was mapped using the Submillimeter Array (SMA) and is predominantly north-south. There is close agreement between the CO and SiO observations, even though the CO polarization arises in the circumstellar envelope at ~800 AU and the SiO polarization at <250 AU. If the polarization indeed traces the magnetic field, we can thus conclude that it maintains a large-scale structure throughout the circumstellar envelope. We propose that the magnetic field, oriented either east-west or north-south is responsible for the east-west elongation of the CO distribution and asymmetries in the dust envelope. In the future, the Atacama Large Millimeter/submillimeter Array will be able to map the magnetic field using CO polarization for a large number of evolved stars.
The structure function of opacity fluctuations is a useful statistical tool to study tiny scale structures of neutral hydrogen. Here we present high resolution observation of HI absorption towards 3C 138, and estimate the structure function of opacity fluctuations from the combined VLA, MERLIN and VLBA data. The angular scales probed in this work are ~ 10-200 milliarcsec (about 5-100 AU). The structure function in this range is found to be well represented by a power law S_tau(x) ~ x^{beta} with index beta ~ 0.33 +/- 0.07 corresponding to a power spectrum P_tau(U) ~ U^{-2.33}. This is slightly shallower than the earlier reported power law index of ~ 2.5-3.0 at ~ 1000 AU to few pc scales. The amplitude of the derived structure function is a factor of ~ 20-60 times higher than the extrapolated amplitude from observation of Cas A at larger scales. On the other hand, extrapolating the AU scale structure function for 3C 138 predicts the observed structure function for Cas A at the pc scale correctly. These results clearly establish that the atomic gas has significantly more structures in AU scales than expected from earlier pc scale observations. Some plausible reasons are identified and discussed here to explain these results. The observational evidence of a shallower slope and the presence of rich small scale structures may have implications for the current understanding of the interstellar turbulence.
The pressure exerted by the radiation of young stars may be an important feedback mechanism that drives turbulence and winds in forming star clusters and the disks of starburst galaxies. However, there is great uncertainty in how efficiently radiation couples to matter in these high optical depth environments. In particular, it is unclear what levels of turbulence the radiation can produce, and whether the infrared radiation trapped by the dust opacity can give rise to heavily mass-loaded winds. In this paper we report a series of numerical experiments performed with the radiation-hydrodynamics code ORION in which we drive strong radiation fluxes through columns of dusty matter confined by gravity in order to answer these questions. We consider both systems where the radiation flux is sub-Eddington throughout the gas column, and those where it is super-Eddington at the midplane but sub-Eddington in the atmosphere. In the latter, we find that the radiation-matter interaction gives rise to radiation-driven Rayleigh-Taylor instability, which drives supersonic turbulence at a level sufficient to fully explain the turbulence seen in Galactic protocluster gas clouds, and to make a non-trivial contribution to the turbulence observed in starburst galaxy disks. However, the instability also produces a channel structure in which the radiation-matter interaction is reduced compared to time-steady analytic models because the radiation field is not fully trapped. This effect reduces the net momentum deposition rate in the dusty gas, and in steady state the Eddington ratio reaches unity and there are no strong winds. We provide an approximation formula, appropriate for implementation in analytic models and non-radiative simulations, for the force exerted by the infrared radiation field in this regime.
Galaxy-galaxy interactions are expected to be responsible for triggering massive star formation and possibly accretion onto a supermassive black hole, by providing large amounts of dense molecular gas down to the central kiloparsec region. Several scenarios to drive the gas further down to the central ~100 pc, have been proposed, including the formation of a nuclear disk around the black hole, where massive stars would produce supernovae. Here, we probe the radial distribution of supernovae and supernova remnants in the nuclear regions of the starburst galaxies M82, Arp 299-A, and Arp 220, by using high-angular resolution (< 0."1) radio observations published in the literature (for M82 and Arp 220), or obtained by ourselves from the European VLBI Network (Arp 299-A). Our main goal was to characterize the nuclear starbursts in those galaxies and thus test scenarios that propose that nuclear disks of sizes ~100 pc form in the central regions of starburst galaxies. We obtained the radial distribution of supernovae (SNe) in the nuclear starbursts of M82, Arp 299-A, and Arp 220, and derived scale-length values for the putative nuclear disks powering the bursts in those central regions. The scale lengths for the (exponential) disks range from ~20-30 pc for Arp 299-A and Arp 220, up to ~140 pc for M82. The radial distribution of SNe for the nuclear disks in Arp 299-A and Arp 220 is also consistent with a power-law surface density profile of exponent gamma=1, as expected from detailed hydrodynamical simulations of nuclear disks. Our results support scenarios where a nuclear disk of size ~100 pc is formed in (U)LIRGs, and sustained by gas pressure, in which case the accretion onto the black hole could be lowered by supernova feedback.
We present updated calculations of stellar evolutionary sequences and detailed nucleosynthesis predictions for the brightest asymptotic giant branch (AGB) stars in the Galaxy with masses between 5Msun to 9Msun, with an initial metallicity of Z =0.02 ([Fe/H] = 0.14). In our previous studies we used the Vassiliadis & Wood (1993) mass-loss rate, which stays low until the pulsation period reaches 500 days after which point a superwind begins. Vassiliadis & Wood noted that for stars over 2.5Msun the superwind should be delayed until P ~ 750 days at 5Msun. We calculate evolutionary sequences where we delay the onset of the superwind to pulsation periods of P ~ 700-800 days in models of M = 5, 6, and 7Msun. Post-processing nucleosynthesis calculations show that the 6 and 7Msun models produce the most Rb, with [Rb/Fe] ~ 1 dex, close to the average of most of the Galactic Rb-rich stars ([Rb/Fe] ~ 1.4 plus or minus 0.8 dex). Changing the rate of the 22Ne + alpha reactions results in variations of [Rb/Fe] as large as 0.5 dex in models with a delayed superwind. The largest enrichment in heavy elements is found for models that adopt the NACRE rate of the 22Ne(a,n)25Mg reaction. Using this rate allows us to best match the composition of most of the Rb-rich stars. A synthetic evolution algorithm is then used to remove the remaining envelope resulting in final [Rb/Fe] of ~ 1.4 dex although with C/O ratios > 1. We conclude that delaying the superwind may account for the large Rb overabundances observed in the brightest metal-rich AGB stars.
We have performed Smoothed Particle Magnetohydrodynamics (SPMHD) simulations demonstrating the production of collimated jets during collapse of 1 solar mass molecular cloud cores to form the `first hydrostatic core' in low mass star formation. Recently a number of candidate first core objects have been observed, including L1448 IRS2E, L1451-mm and Per Bolo 58, although it is not yet clear that these are first hydrostatic cores. Recent observations of Per Bolo 58 in particular appear to show collimated, bipolar outflows which are inconsistent with previous theoretical expectations. We show that low mass first cores can indeed produce tightly collimated jets (opening angles <~ 10 degrees) with speeds of ~2-7 km/s, consistent with some of the observed candidates. We have also demonstrated, for the first time, that such phenomena can be successfully captured in SPMHD simulations.
The environment near super massive black holes (SMBHs) in galactic nuclei contain a large number of stars and compact objects. A fraction of these are likely to be members of binaries. Here we discuss the binary population of stellar black holes and neutron stars near SMBHs and focus on the secular evolution of such binaries, due to the perturbation by the SMBH. Binaries with highly inclined orbits in respect to their orbit around the SMBH are strongly affected by secular Kozai processes, which periodically change their eccentricities and inclinations (Kozai-cycles). During periapsis approach, at the highest eccentricities during the Kozai-cycles, gravitational wave emission becomes highly efficient. Some binaries in this environment can inspiral and coalesce at timescales much shorter than a Hubble time and much shorter than similar binaries which do not reside near a SMBH. The close environment of SMBHs could therefore serve as catalyst for the inspiral and coalescence of binaries, and strongly affect their orbital properties. Such compact binaries would be detectable as gravitational wave (GW) sources by the next generation of GW detectors (e.g. advanced- LIGO). About 0.5% of such nuclear merging binaries will enter the LIGO observational window while on orbit that are still very eccentric (e>~0.5). The efficient gravitational wave analysis for such systems would therefore require the use of eccentric templates. We also find that binaries very close to the MBH could evolve through a complex dynamical (non-secular) evolution leading to emission of several GW pulses during only a few yrs (though these are likely to be rare). Finally, we note that the formation of close stellar binaries, X-ray binaries and their merger products could be induced by similar secular processes, combined with tidal friction rather than GW emission as in the case of compact object binaries.
Recent theories suggest planetesimal formation via streaming and/or gravitational instabilities may be triggered by localized enhancements in the dust-to-gas ratio, and one hypothesis is that sufficient enhancements may be produced in the pile-up of small solid particles inspiralling under aerodynamic drag from the large mass reservoir in the outer disc. Studies of particle pile-up in static gas discs have provided partial support for this hypothesis. Here, we study the radial and temporal evolution of the dust-to-gas ratio in turbulent discs, that evolve under the action of viscosity and photoevaporation. We find that particle pile-ups do not generically occur within evolving discs, particularly if the introduction of large grains is restricted to the inner, dense regions of a disc. Instead, radial drift results in depletion of solids from the outer disc, while the inner disc maintains a dust-to-gas ratio that is within a factor of ~2 of the initial value. We attribute this result to the short time-scales for turbulent diffusion and radial advection (with the mean gas flow) in the inner disc. We show that the qualitative evolution of the dust-to-gas ratio depends only weakly upon the parameters of the disc model (the disc mass, size, viscosity, and value of the Schmidt number), and discuss the implications for planetesimal formation via collective instabilities. Our results suggest that in discs where there is a significant level of midplane turbulence and accretion, planetesimal formation would need to be possible in the absence of large-scale enhancements. Instead, trapping and concentration of particles within local turbulent structures may be required as a first stage of planetesimal formation.
A three dimensional parallel Monte Carlo (MC) dust radiative transfer code is presented. To overcome the huge computing time requirements of MC treatments, the computational power of vectorized hardware is used, utilizing either multi-core computer power or graphics processing units. The approach is a self-consistent way to solve the radiative transfer equation in arbitrary dust configurations. The code calculates the equilibrium temperatures of two populations of large grains and stochastic heated polycyclic aromatic hydrocarbons (PAH). Anisotropic scattering is treated applying the Heney-Greenstein phase function. The spectral energy distribution (SED) of the object is derived at low spatial resolution by a photon counting procedure and at high spatial resolution by a vectorized ray-tracer. The latter allows computation of high signal-to-noise images of the objects at any frequencies and arbitrary viewing angles. We test the robustness of our approach against other radiative transfer codes. The SED and dust temperatures of one and two dimensional benchmarks are reproduced at high precision. We utilize the Lucy-algorithm for the optical thin case where the Poisson noise is high, the iteration free Bjorkman & Wood method to reduce the calculation time, and the Fleck & Canfield diffusion approximation for extreme optical thick cells. The code is applied to model the appearance of active galactic nuclei (AGN) at optical and infrared wavelengths. The AGN torus is clumpy and includes fluffy composite grains of various sizes made-up of silicates and carbon. The dependence of the SED on the number of clumps in the torus and the viewing angle is studied. The appearance of the 10 micron silicate features in absorption or emission is discussed. The SED of the radio loud quasar 3C 249.1 is fit by the AGN model and a cirrus component to account for the far infrared emission.
In AGN spectra, a series of FeII multiplets form a pseudo-continuum that extends from the ultraviolet to the near-infrared (NIR). This emission is believed to originate in the Broad Line Region (BLR), and it has been known for a long time that pure photoionization fails to reproduce it in the most extreme cases, as does the collisional-excitation alone. The most recent models by Sigut & Pradhan (2003) include details of the FeII ion microphysics and cover a wide range in ionization parameter log U_ion= (-3.0 -> -1.3) and density log n_H = (9.6 -> 12.6). With the aid of such models and a spectral synthesis approach, we study for the first time in detail the NIR emission of I Zw 1. The main goals are to confirm the role played by Ly\alpha-fluorescence mechanisms in the production of the FeII spectrum and to construct the first semi-empirical NIR FeII template that best represents this emission and can be used to subtract it in other sources. A good overall match between the observed FeII+MgII features with those predicted by the best fitted model is obtained, corroborating the Ly\alpha-fluorescence as a key process to understand the FeII spectrum. The best model is then adjusted by applying a deconvolution method on the observed FeII+MgII spectrum. The derived semi-empirical template is then fitted to the spectrum of Ark 564, suitably reproducing its observed FeII+MgII emission. Our approach extends the current set of available FeII templates into the NIR region.
We report the discovery of a bipolar nebula around the peculiar emission-line star MWC 349A using archival Spitzer Space Telescope 24 um data. The nebula extends over several arcminutes (up to 5 pc) and has the same orientation and geometry as the well-known subarcsecond-scale (~400 times smaller) bipolar radio nebula associated with this star. We discuss the physical relationship between MWC 349A and the nearby B0 III star MWC 349B and propose that both stars were members of a hierarchical triple system, which was ejected from the core of the Cyg OB2 association several Myr ago and recently was dissolved into a binary system (now MWC 349A) and a single unbound star (MWC 349B). Our proposal implies that MWC 349A is an evolved massive star (likely a luminous blue variable) in a binary system with a low-mass star. A possible origin of the bipolar nebula around MWC 349A is discussed.
Dwarf spheroidal galaxies compose one of the most dark matter dominated classes of objects, making them a set of targets to search for signals of dark matter annihilation. The recent developments in gamma-ray astronomy, most importantly the launch of the Fermi-LAT instrument, have brought those targets into attention. Yet, no clear excess of gamma-rays has been confirmed from these targets, resulting in some of the tightest limits on dark matter annihilation from indirect searches. In extracting limits from dwarf spheroidal galaxies, it is of great importance, to properly take into account all relevant uncertainties, which include the dark matter distribution properties of the dwarf spheroidals, and the uncertainties on the underlying background. We revisit the limits on dark matter annihilation, from gamma-rays studying a set of close-by dwarf spheroidal galaxies, for which, we have good understanding of the uncertainties in the dark matter distribution. For those targets, we perform and compare results for alternative methods in extracting the background gamma-ray flux; which provides a method to discriminate among the dark matter annihilation targets, those that can give robust constraints. We finally present our tightest limits on dark matter annihilation, coming only from the targets that ensure accurate understanding of both the gamma-ray background and the dark matter distribution uncertainties.
Assuming that giant planets are formed in thin protoplanetary discs, a '3D' system can form, provided that the mutual inclination is excited by some dynamical mechanism. Resonant interactions and close planetary encounters are thought to be the primary inclination-excitation mechanisms, resulting in a resonant and non-resonant system, respectively. Here we propose an alternative formation scenario, starting from a system composed of three giant planets in a nearly coplanar configuration. As was recently shown for the case of the Solar system, planetary migration in the gas disc (Type II migration) can force the planets to become trapped in a multiply resonant state. We simulate this process, assuming different values for the planetary masses and mass ratios. We show that such a triple resonance generally becomes unstable as the resonance excites the eccentricities of all planets and planet-planet scattering sets in. One of the three planets is typically ejected from the system, leaving behind a dynamically 'hot' (but stable) two-planet configuration. The resulting two-planet systems typically have large values of semimajor axial ratios (a1/a2 < 0.3), while the mutual inclination can be as high as 70{\deg}, with a median of \sim30{\deg}. A small fraction of our two-planet systems (\sim5 per cent) ends up in the stability zone of the Kozai resonance. In a few cases, the triple resonance can remain stable for long times and a '3D' system can form by resonant excitation of the orbital inclinations; such a three-planet system could be stable if enough eccentricity damping is exerted on the planets. Finally, in the single-planet resulting systems, which are formed when two planets are ejected from the system, the inclination of the planet's orbital plane with respect to the initial invariant plane -presumably the plane perpendicular to the star's spin axis- can be as large as \sim40{\deg}.
It is widely recognized that nucleosynthetic output of the first, Population III supernovae was a catalyst defining the character of subsequent stellar generations. Most of the work on the earliest enrichment was carried out assuming that the first stars were extremely massive and that the associated supernovae were unusually energetic, enough to completely unbind the baryons in the host cosmic minihalo and disperse the synthesized metals into the intergalactic medium. Recent work, however, suggests that the first stars may in fact have been somewhat less massive, with a characteristic mass scale of a few tens of solar masses. We present a cosmological simulation following the transport of the metals synthesized in a Population III supernova assuming that it had an energy of 10^51 ergs, compatible with standard Type II supernovae. A young supernova remnant is inserted in the first star's relic HII region in the free expansion phase and is followed for 40 Myr, all with the help of adaptive mesh refinement and Lagrangian tracer particle techniques. The supernova remnant remains partially trapped within the minihalo and the thin snowplow shell develops pronounced instability and fingering. Roughly half of the ejecta turn around and fall back toward the center of the halo, with 1% of the ejecta reaching the center in ~30 kyr and 10% in ~10 Myr. The average metallicity of the combined returning ejecta and the pristine filaments feeding into the halo center from the cosmic web is ~ 0.001-0.01 Z_sun, but the two remain unmixed until accreting onto the central hydrostatic core that is unresolved at the end of the simulation. We conclude that if Population III stars had less extreme masses, they promptly enriched the host minihalos with metals and triggered Population II star formation.
We study the establishment of three-planet resonances -similar to the Laplace resonance in the Galilean satellites- and their effects on the mutual inclinations of the orbital planes of the planets, assuming that the latter undergo migration in a gaseous disc. In particular, we examine the resonance relations that occur, by varying the physical and initial orbital parameters of the planets (mass, initial semi-major axis and eccentricity) as well as the parameters of the migration forces (migration rate and eccentricity damping rate), which are modeled here through a simplified analytic prescription. We find that, in general, for planetary masses below 1.5 M_J, multiple-planet resonances of the form n3:n2:n1=1:2:4 and 1:3:6 are established, as the inner planets, m1 and m2, get trapped in a 1:2 resonance and the outer planet m3 subsequently is captured in a 1:2 or 1:3 resonance with m2. For mild eccentricity damping, the resonance pumps the eccentricities of all planets on a relatively short time-scale, to the point where they enter an inclination-type resonance (as in Libert & Tsiganis 2011); then mutual inclinations can grow to ~35{\deg}, thus forming a "3-D system". On the other hand, we find that trapping of m2 in a 2:3 resonance with m1 occurs very rarely, for the range of masses used here, so only two cases of capture in a respective three-planet resonance were found. Our results suggest that trapping in a three-planet resonance can be common in exoplanetary systems, provided that the planets are not very massive. Inclination pumping could then occur relatively fast, provided that eccentricity damping is not very efficient so that at least one of the inner planets acquires an orbital eccentricity higher than e=0.3.
NGC 1333 IRAS 4A and IRAS 4B sources are among the best studied Stage 0 low-mass protostars which are driving prominent bipolar outflows. Most studies have so far concentrated on the colder parts (T<30K) of these regions. The aim is to characterize the warmer parts of the protostellar envelope in order to quantify the feedback of the protostars on their surroundings in terms of shocks, UV heating, photodissociation and outflow dispersal. Fully sampled large scale maps of the region were obtained; APEX-CHAMP+ was used for 12CO 6-5, 13CO 6-5 and [CI] 2-1, and JCMT-HARP-B for 12CO 3-2 emissions. Complementary Herschel-HIFI and ground-based lines of CO and its isotopologs, from 1-0 upto 10-9 (Eu/k 300K), are collected at the source positions. Radiative-transfer models of the dust and lines are used to determine temperatures and masses of the outflowing and UV-heated gas and infer the CO abundance structure. Broad CO emission line profiles trace entrained shocked gas along the outflow walls, with typical temperatures of ~100K. At other positions surrounding the outflow and the protostar, the 6-5 line profiles are narrow indicating UV excitation. The narrow 13CO 6-5 data directly reveal the UV heated gas distribution for the first time. The amount of UV-heated and outflowing gas are found to be comparable from the 12CO and 13CO 6-5 maps, implying that UV photons can affect the gas as much as the outflows. Weak [CI] emission throughout the region indicates a lack of CO dissociating photons. Modeling of the C18O lines indicates the necessity of a "drop" abundance profile throughout the envelope where the CO freezes out and is reloaded back into the gas phase, thus providing quantitative evidence for the CO ice evaporation zone around the protostars. The inner abundances are less than the canonical value of CO/H_2=2.7x10^-4, indicating some processing of CO into other species on the grains.
We study a model of fast magnetic reconnection in the presence of weak turbulence proposed by Lazarian and Vishniac (1999) using three-dimensional direct numerical simulations. The model has been already successfully tested in Kowal et al. (2009) confirming the dependencies of the reconnection speed $V_{rec}$ on the turbulence injection power $P_{inj}$ and the injection scale $l_{inj}$ expressed by a constraint $V_{rec} \sim P_{inj}^{1/2} l_{inj}^{3/4}$ and no observed dependency on Ohmic resistivity. In Kowal et al. (2009), in order to drive turbulence, we injected velocity fluctuations in Fourier space with frequencies concentrated around $k_{inj}=1/l_{inj}$, as described in Alvelius (1999). In this paper we extend our previous studies by comparing fast magnetic reconnection under different mechanisms of turbulence injection by introducing a new way of turbulence driving. The new method injects velocity or magnetic eddies with a specified amplitude and scale in random locations directly in real space. We provide exact relations between the eddy parameters and turbulent power and injection scale. We performed simulations with new forcing in order to study turbulent power and injection scale dependencies. The results show no discrepancy between models with two different methods of turbulence driving exposing the same scalings in both cases. This is in agreement with the Lazarian and Vishniac (1999) predictions. In addition, we performed a series of models with varying viscosity $\nu$. Although Lazarian and Vishniac (1999) do not provide any prediction for this dependence, we report a weak relation between the reconnection speed with viscosity, $V_{rec}\sim\nu^{-1/4}$.
A number of relaxed, cool-core galaxy clusters exhibit diffuse, steep-spectrum radio sources in their central regions, known as radio mini-halos. It has been proposed that the relativistic electrons responsible for the emission have been reaccelerated by turbulence generated by the sloshing of the cool core gas. We present a high-resolution MHD simulation of gas sloshing in a galaxy cluster coupled with subgrid simulations of relativistic electron acceleration to test this hypothesis. Our simulation shows that the sloshing motions generate turbulence on the order of $\delta{v} \sim$ 100-200 km s$^{-1}$ on spatial scales of $\sim$50-100 kpc and below in the cool core region within the envelope of the sloshing cold fronts, whereas outside the cold fronts, there is negligible turbulence. Our simulations show that this turbulence is potentially strong enough to reaccelerate relativistic electron seeds ($\gamma \sim 100-500$) that could remain in the cluster from e.g., past AGN activity, but are too old to emit in the radio band. In combination with the magnetic field amplification in the core, these electrons then produce diffuse radio synchrotron emission that is coincident with the region bounded by the sloshing cold fronts, as indeed observed in X-rays and the radio. The result holds for different initial spatial distributions of preexisting relativistic electrons. The power and the steep spectral index ($\alpha \approx 1-2$) of the resulting radio emission are consistent with observations of minihalos. We also produce simulated maps of inverse-Compton hard X-ray emission from the same population of relativistic electrons.
We investigate the scale-dependence, or the runnings, of linear and second order density perturbations generated in various curvaton scenarios. We argue that the second order perturbations, i.e. non-Gaussianity, can strongly depend on the scale, even when the linear perturbations are nearly scale-invariant. We present analytic formulae for the runnings from curvatons with general energy potentials, and clarify the conditions under which fNL becomes strongly scale-dependent. From the point of view of the fNL running, curvaton potentials can be classified into roughly two categories by whether the potential flattens or steepens compared to a quadratic one. As such examples, we study pseudo-Nambu-Goldstone curvatons, and self-interacting curvatons, respectively. The dynamics of non-quadratic curvatons and the behaviors of the resulting density perturbations are clarified by analytical methods. Then we also study models where multiple source can be responsible for density perturbations such as the multi-curvaton, and mixed curvaton and inflaton models where the running of fNL can also be large due to their multi-source nature. We make quantitative analysis for each curvaton scenario and discuss in what cases the scale-dependence, in particular, of fNL can be large enough to be probed with future CMB experiments.
A deep Spitzer Infrared Spectrograph map of the PKS 1138-26 galaxy protocluster reveals ultraluminous PAH emission from obscured star formation in three protocluster galaxies, including Halpha-emitter (HAE) 229, HAE 131, and the central Spiderweb Galaxy. Star formation rates of 500-1100 Msun/yr are estimated from the 7.7 micron PAH feature. At such prodigious formation rates, the galaxy stellar masses will double in 0.6-1.1 Gyr. We are viewing the peak epoch of star formation for these protocluster galaxies. However, it appears that extinction of Halpha is much greater (factor of 40) in the two ULIRG HAEs compared to the Spiderweb. This may be attributed to different spatial distributions of star formation--nuclear star formation in the HAEs versus extended star formation in accreting satellite galaxies in the Spiderweb. We find extremely luminous mid-IR rotational line emission from warm molecular hydrogen in the Spiderweb Galaxy, with L(H2 0-0 S(3))= 1.4E44 erg/s (3.7E10 Lsun), 20 times more luminous than any previously known H2 emission galaxy (MOHEG). Depending on temperature, this corresponds to a very large mass of >9E6-2E9 Msun of T>300 K molecular gas, heated by the PKS 1138-26 radio jet, acting to quench nuclear star formation. There is >8 times more warm H2 at these temperatures in the Spiderweb than what has been seen in low-redshift (z<0.2) radio galaxies, indicating that the Spiderweb may have a larger reservoir of molecular gas than more evolved radio galaxies. This is the highest redshift galaxy yet in which warm molecular hydrogen has been directly detected.
We used archival Hubble Space Telescope WFC3 images to obtain the Luminosity Function of the remote globular cluster NGC2419 from two magnitudes above the Horizontal Branch level down to \sim3.0 magnitudes below the Turn Off point (to M_I\sim6.4), approximately covering the range of initial stellar masses 0.5 M_sun<= m <= 0.9 M_sun. The completeness-corrected Luminosity Function does not display any change of shape over the radial range covered by the WFC3 data, out to ~6 core radii (r_c), or, equivalently, to ~2 half-light radii. The Luminosity Function in this radial range is also identical to that obtained from ground based data at much larger distances from the cluster centre (12r_c<= R<= 22r_c), in the magnitude range in which the two distributions overlap (M_I<= 4.0). These results support the conclusion by Dalessandro et al. that there is no significant mass segregation among cluster stars, hence the stellar mass-to-light ratio remains constant with distance from the cluster centre. We fitted the observed Luminosity Function with theoretical counterparts with the proper age and metallicity from different sets of stellar evolution models and we consistently derive a total V band mass-to-light ratio 1.2<= M/L_V<= 1.7, by extrapolating to the Hydrogen burning limit, with a best-fit value M/L_V=1.5 +/- 0.1. On the other hand, assuming that there are no cluster stars with m<= 0.3 M_sun, we establish a robust lower limit M/L_V> 0.8. These estimates provide useful constraints for dynamical models of the cluster that were forced to consider the stellar mass-to-light ratio as a (nearly) free parameter.
The collapse of an isolated, uniform and spherical cloud of self-gravitating particles represents a paradigmatic example of a relaxation process leading to the formation of a quasi-stationary state in virial equilibrium. We consider several N-body simulations of such a system, with the initial velocity dispersion as a free parameter. We show that there is a clear difference between structures formed when the initial virial ratio is b_0 < b_0^c \approx -1/2 and b_0>b_0^c. These two sets of initial conditions give rise respectively to a mild and violent relaxation occurring in about the same time scale: however in the latter case the system contracts by a large factor, while in the former it approximately maintains its original size. Correspondingly the resulting quasi equilibrium state is characterized by a density profile decaying at large enough distances as 1/r^4 or with a sharp cut-off. While the case b_0<b_0^c can be well described by the Lynden-Bell theory of collisionless relaxation, for b_0>b_0^c the relevant feature is the ejection of particles and energy, which is not captured by such a theoretical approach. We introduce a simple physical model to explain the formation of such a power-law density profile. This model shows that the behavior n(r) ~ 1/r^4 is the typical density profile that is obtained when the initial conditions are cold enough that mass and energy ejection occurs. In addition, we clarify the origin of the critical value of the initial virial ratio b_0^c.
We present a detailed analysis of a highly ionized, multiphased and collimated outflowing gas detected through O V, O VI, Ne VIII and Mg X absorption associated with the QSO HE 0238 - 1904 (z_em ~ 0.629). Based on the similarities in the absorption line profiles and estimated covering fractions, we find that the O VI and Ne VIII absorption trace the same phase of the absorbing gas. Simple photoionization models can reproduce the observed N(Ne VIII), N(O VI) and N(Mg X) from a single phase whereas the low ionization species (e.g. N III, N IV, O IV) originate from a different phase. The measured N(Ne VIII)/N(O VI) ratio is found to be remarkably similar (within a factor of ~ 2) in several individual absorption components kinematically spread over ~ 1800 km/s. Under photoionization this requires a fine tuning between hydrogen density (nH) and the distance of the absorbing gas from the QSO. Alternatively this can also be explained by collisional ionization in hot gas with T > 10^{5.7} K. Long-term stability favors the absorbing gas being located outside the broad line region (BLR). We speculate that the collimated flow of such a hot gas could possibly be triggered by the radio jet interaction.
The fast outflow emerging from a region associated with massive star formation in the Orion Molecular Cloud 1 (OMC-1), located behind the Orion Nebula, appears to have been set in motion by an explosive event. Here we study the structure and dynamics of outflows in OMC-1. We combine radial velocity and proper motion data for near-IR emission of molecular hydrogen to obtain the first 3-dimensional (3D) structure of the OMC-1 outflow. Our work illustrates a new diagnostic tool for studies of star formation that will be exploited in the near future with the advent of high spatial resolution spectro-imaging in particular with data from the Atacama Large Millimeter Array (ALMA). We use published radial and proper motion velocities obtained from the shock-excited vibrational emission in the H2 v=1-0 S(1) line at 2.122 $\mu$m obtained with the GriF instrument on the Canada-France-Hawaii Telescope, the Apache Point Observatory, the Anglo-Australian Observatory and the Subaru Telescope. These data give the 3D velocity of ejecta yielding a 3D reconstruction of the outflows. This allows one to view the material from different vantage points in space giving considerable insight into the geometry. Our analysis indicates that the ejection occurred <720 years ago from a distorted ring-like structure of ~15" (6000 AU) in diameter centered on the proposed point of close encounter of the stars BN, source I and maybe also source n. We propose a simple model involving curvature of shock trajectories in magnetic fields through which the origin of the explosion and the centre defined by extrapolated proper motions of BN, I and n may be brought into spatial coincidence.
Deposition of a massive ($10^4$ to $10^5 \msun$) giant molecular cloud (GMC) into the inner parsec of the Galaxy is widely believed to explain the origin of over a hundred unusually massive young stars born there $\sim 6$ Myr ago. An unknown fraction of that gas could have been accreted by Sgr A*, the supermassive black hole (SMBH) of the Milky Way. It has been recently suggested that two observed $\gamma$-ray-emitting bubbles emanating from the very center of our Galaxy were inflated by this putative activity of Sgr A*. We run a suite of numerical simulations to test whether the observed morphology of the bubbles could be due to the collimation of a wide angle outflow from Sgr A* by the disc-like Central Molecular Zone (CMZ), a well known massive repository of molecular gas in the central $\sim 200$ pc. We find that an Eddington-limited outburst of Sgr A* lasting $\simeq 1$ Myr is required to reproduce the morphology of the {\it Fermi} bubbles, suggesting that the GMC mass was $\sim 10^5 \msun$ and it was mainly accreted by Sgr A* rather than used to make stars. We also find that the outflow from Sgr A* enforces strong angular momentum mixing in the CMZ disc, robustly sculpting it into a much narrower structure -- a ring -- perhaps synonymous with the recently reported "Herschel ring". In addition, we find that Sgr A* outflow is likely to have induced formation of massive star-forming GMCs in the CMZ. In this scenario, the Arches and Quintuplet clusters, the two observed young star clusters in the central tens of parsecs of the Galaxy, and also GMCs such as Sgr B2, owe their existence to the recent Sgr A* activity.
We investigate whether stellar-mass black holes have to receive natal kicks in order to explain the observed distribution of low-mass X-ray binaries containing black holes within our Galaxy. Such binaries are the product of binary evolution, where the massive primary has exploded forming a stellar-mass black hole, probably after a common envelope phase where the system contracted down to separations of order 10-30 Rsun. We perform population synthesis calculations of these binaries, applying both kicks due to supernova mass-loss and natal kicks to the newly-formed black hole. We then integrate the trajectories of the binary systems within the Galactic potential. We find that natal kicks are in fact necessary to reach the large distances above the Galactic plane achieved by some binaries. Further, we find that the distribution of natal kicks would seem to be similar to that of neutron stars, rather than one where the kick velocities are reduced by the ratio of black hole to neutron-star mass (i.e. where the kicks have the same momentum). This result is somewhat surprising; in many pictures of stellar-mass black-hole formation, one might have expected black holes to receive kicks having the same momentum (rather than the same speed) as those given to neutron stars.
We present 21 cm observations of a 10 $\times$ 2 degree region in the Virgo cluster, obtained as part of the Arecibo Galaxy Environment Survey. 289 sources are detected over the full redshift range (-2,000 $<$ $v$$_{hel}$ $<$ + 20,000 km/s) with 95 belonging to the cluster ($v$$_{hel}$ $<$ 3,000 km/s). We combine our observations with data from the optically selected Virgo Cluster Catalogue (VCC) and the Sloan Digital Sky Survey (SDSS). Most of our detections can be clearly associated with a unique optical counterpart, and 30% of the cluster detections are new objects fainter than the VCC optical completeness limit. 7 detections may have no optical counterpart and we discuss the possible origins of these objects. 7 detections appear associated with early-type galaxies. We perform HI stacking on the HI-undetected galaxies listed in the VCC in this region and show that they must have significantly less gas than those actually detected in HI. Galaxies undetected in HI in the cluster appear to be really devoid of gas, in contrast to a sample of field galaxies from ALFALFA.
This article presents a power-spectrum analysis of 2,350 measurements of the $^{90}$Sr/$^{90}$Y decay process acquired over the interval 4 August 2002 to 6 February 2009 at the Lomonosov Moscow State University (LMSU). As we have found for other long sequences of decay measurements, the power spectrum is dominated by a very strong annual oscillation. However, we also find a set of low-frequency peaks, ranging from 0.26 year$^{-1}$ to 3.98 year$^{-1}$, which are very similar to an array of peaks in a power spectrum formed from Mt Wilson solar diameter measurements. The Mt Wilson measurements have been interpreted in terms of r-mode oscillations in a region where the sidereal rotation frequency is 12.08 year$^{-1}$. We find that the LMSU measurements may also be attributed to the same type of r-mode oscillations in a solar region with the same sidereal rotation frequency. We propose that these oscillations occur in an inner tachocline that separates the radiative zone from a more slowly rotating solar core.
We extend our investigation of magnetic field evolution in three-dimensional flows driven by the stationary accretion shock instability (SASI) with a suite of higher-resolution idealized models of the post-bounce core-collapse supernova environment. Our magnetohydrodynamic simulations vary in initial magnetic field strength, rotation rate, and grid resolution. Vigorous SASI-driven turbulence inside the shock amplifies magnetic fields exponentially; but while the amplified fields reduce the kinetic energy of small-scale flows, they do not seem to affect the global shock dynamics. The growth rate and final magnitude of the magnetic energy are very sensitive to grid resolution, and both are underestimated by the simulations. Nevertheless our simulations suggest that neutron star magnetic fields exceeding $10^{14}$ G can result from dynamics driven by the SASI, \emph{even for non-rotating progenitors}.
(Abridged) Aims: We study the effects related to departures from non-local thermodynamic equilibrium (NLTE) and homogeneity in the atmospheres of red giant stars in Galactic globular cluster NGC 6752, to assess their influence on the formation of Ba II lines. Methods: One-dimensional (1D) local thermodynamic equilibrium (LTE) and 1D NLTE barium abundances were derived using classical 1D ATLAS stellar model atmospheres. The three-dimensional (3D) LTE abundances were obtained for 8 red giants on the lower RGB, by adjusting their 1D LTE abundances using 3D-1D abundance corrections, i.e., the differences between the abundances obtained from the same spectral line using the 3D hydrodynamical (CO5BOLD) and classical 1D (LHD) stellar model atmospheres. Results: The mean 1D barium-to-iron abundance ratios derived for 20 giants are <[Ba/Fe]>_{1D NLTE} = 0.05 \pm0.06 (stat.) \pm0.08 (sys.). The 3D-1D abundance correction obtained for 8 giants is small (~+0.05 dex), thus leads to only minor adjustment when applied to the mean 1D NLTE barium-to-iron abundance ratio for the 20 giants, <[Ba/Fe]>_{3D+NLTE} = 0.10 \pm0.06(stat.) \pm0.10(sys.). The intrinsic abundance spread between the individual cluster stars is small and can be explained in terms of uncertainties in the abundance determinations. Conclusions: Deviations from LTE play an important role in the formation of barium lines in the atmospheres of red giants studied here. The role of 3D hydrodynamical effects should not be dismissed either, even if the obtained 3D-1D abundance corrections are small. This result is a consequence of subtle fine-tuning of individual contributions from horizontal temperature fluctuations and differences between the average temperature profiles in the 3D and 1D model atmospheres: owing to the comparable size and opposite sign, their contributions nearly cancel each other.
Context: The Kepler space mission is reaching continuous observing times long enough to start studying the fine structure of the observed p-mode spectra. Aims: In this paper, we aim to study the signature of stellar evolution on the radial and p-dominated l=2 modes in an ensemble of red giants that show solar-type oscillations. Results: We find that the phase shift of the central radial mode (eps_c) is significantly different for red giants at a given large frequency separation (Dnu_c) but which burn only H in a shell (RGB) than those that have already ignited core He burning. Even though not directly probing the stellar core the pair of local seismic observables (Dnu_c, eps_c) can be used as an evolutionary stage discriminator that turned out to be as reliable as the period spacing of the mixed dipole modes. We find a tight correlation between eps_c and Dnu_c for RGB stars and no indication that eps_c depends on other properties of these stars. It appears that the difference in eps_c between the two populations becomes if we use an average of several radial orders, instead of a local, i.e. only around the central radial mode, Dnu to determine the phase shift. This indicates that the information on the evolutionary stage is encoded locally, in the shape of the radial mode sequence. This shape turns out to be approximately symmetric around the central radial mode for RGB stars but asymmetric for core He burning stars. We computed radial modes for a sequence of RG models and find them to qualitatively confirm our findings. We also find that, at least in our models, the local Dnu is an at least as good and mostly better proxy for both the asymptotic spacing and the large separation scaled from the model density than the average Dnu. Finally, we investigate the signature of the evolutionary stage on the small frequency separation and quantify the mass dependency of this seismic parameter.
Our analysis of a VLBA 12-hour synthesis observations of the OH masers in W49N has provided detailed high angular-resolution images of the maser sources, at 1612, 1665 and 1667 MHz. The images, of several dozens of spots, reveal anisotropic scatter broadening; with typical sizes of a few tens of milli-arc-seconds and axial ratios between 1.5 to 3. The image position angles oriented perpendicular to the galactic plane are interpreted in terms of elongation of electron-density irregularities parallel to the galactic plane, due to a similarly aligned local magnetic field. However, we find the apparent angular sizes on the average a factor of 2.5 less than those reported by Desai et al., indicating significantly less scattering than inferred earlier. The average position angle of the scattered broadened images is also seen to deviate significantly (by about 10 degrees) from that implied by the magnetic field in the Galactic plane. More intriguingly, for a few Zeeman pairs in our set, we find significant differences in the scatter broadened images for the two hands of polarization, even when apparent velocity separation is less than 0.1 km/s. Here we present the details of our observations and analysis, and discuss the interesting implications of our results for the intervening anisotropic magneto-ionic medium, as well as a comparison with the expectations based on earlier work.
We have done a new analysis of the available observations for the GJ581 exoplanetary system. Today this system is controversial due to choices that can be done in the orbital determination. The main ones are the ocurrence of aliases and the additional bodies - the planets f and g - announced in Vogt et al. 2010. Any dynamical study of exoplanets requires the good knowledge of the orbital elements and the investigations involving the planet g are particularly interesting, since this body would lie in the Habitable Zone (HZ) of the star GJ581. This region,for this system, is very attractive of the dynamical point of view due to several resonances of two and three bodies present there. In this work, we investigate the conditions under which the planet g may exist. We stress the fact that the planet g is intimately related with the orbital elements of the planet d; more precisely, we conclude that it is not possible to disconnect its existence from the determination of the eccentricity of the planet d. Concerning the planet f, we have found one solution with period $\approx 450$ days, but we are judicious about any affirmation concernig this body because its signal is in the threshold of detection and the high period is in a spectral region where the ocorruence of aliases is very common. Besides, we outline some dynamical features of the habitable zone with the dynamical map and point out the role played by some resonances laying there.
We analyze the emission properties of a new sample of 3,579 type 1 AGN, selected from the SDSS DR7 based on the detection of broad H-alpha emission. The sample extends over a broad H-alpha luminosity L_bHa of 10^40 - 10^44 erg s^-1 and a broad H-alpha FWHM of 1,000 - 25,000 km s^-1, which covers the range of black hole mass 10^6<M_BH/M_Sun<10^9.5 and luminosity in Eddington units 10^-3 < L/L_Edd < 1. We combine ROSAT, GALEX and 2MASS observations to form the SED from 2.2 mic to 2 keV. We find the following: 1. The distribution of the H-alpha FWHM values is independent of luminosity. 2. The observed mean optical-UV SED is well matched by a fixed shape SED of luminous quasars, which scales linearly with L_bHa, and a host galaxy contribution. 3. The host galaxy r-band (fibre) luminosity function follows well the luminosity function of inactive non-emission line galaxies (NEG), consistent with a fixed fraction of ~3% of NEG hosting an AGN, regardless of the host luminosity. 4. The hosts of lower luminosity AGN have a mean z band luminosity and u-z colour which are identical to NEG with the same redshift distribution. With increasing L_bHa the AGN hosts become bluer and less luminous than NEG. The implied increasing star formation rate with L_bHa is consistent with the relation for SDSS type 2 AGN of similar bolometric luminosity. 5. The optical-UV SED of the more luminous AGN shows a small dispersion, consistent with dust reddening of a blue SED, as expected for thermal thin accretion disc emission. 6. There is a rather tight relation of nuL_nu(2 keV) and L_bHa, which provides a useful probe for unobscured (true) type 2 AGN. 7. The primary parameter which drives the X-ray to UV emission ratio is the luminosity, rather than M_BH or L/L_Edd.
Almost all Galactic black hole binaries with low mass donor stars are transient X-ray sources; we expect most of the X-ray transients observed in external galaxies to be black hole binaries also. Obtaining period estimates for extra-galactic transients is challenging, but the resulting period distribution is an important tool for modeling the evolution history of the host galaxy. We have obtained periods, or upper limits, for 12 transients in M31, using an updated relation between the optical and X-ray luminosities. We have monitored the central region of M31 with Chandra for the last ~12 years, and followed up promising transients with HST; 4\sigma B magnitude limits for optical counterparts are ~26--29, depending on crowding. We obtain period estimates for each transient for both neutron star and black hole accretors. Periods range from <0.4 to 490+/-90 hours (<0.97 to <175 hrs if all are BH systems). These M31 transients appear to be somewhat skewed towards shorter periods than the Milky Way (MW) transients; indeed, comparing the M31 and MW transients with survival analysis techniques used to account for some data with only upper limits yield probabilities of ~0.02--0.08 that the two populations are drawn from the same distribution. We also checked for a correlation between orbital period and distance from the nucleus, finding a 12% probability of no correlation. Further observations of M31 transients will strengthen these results.
GYOTO, a general relativistic ray-tracing code, is presented. It aims at computing images of astronomical bodies in the vicinity of compact objects, as well as trajectories of massive bodies in relativistic environments. This code is capable of integrating the null and timelike geodesic equations not only in the Kerr metric, but also in any metric computed numerically within the 3+1 formalism of general relativity. Simulated images and spectra have been computed for a variety of astronomical targets, such as a moving star or a toroidal accretion structure. The underlying code is open source and freely available. It is user-friendly, quickly handled and very modular so that extensions are easy to integrate. Custom analytical metrics and astronomical targets can be implemented in C++ plug-in extensions independent from the main code.
A model for a homogeneous and isotropic spatially flat Universe, composed of baryons, radiation, neutrinos, dark matter and dark energy is analyzed. We infer that dark energy (considered to behave as a scalar field) interacts with dark matter (either by the Wetterich model, or by the Anderson and Carroll model) and with neutrinos by a model proposed by Brookfield et al.. The latter is understood to have a mass-varying behavior. We show that for a very-softly varying field, both interacting models for dark matter give the same results. The models reproduce the expected red-shift performances of the present behavior of the Universe.
Recent direct detection experiments of Dark Matter (DM), CoGeNT and DAMA implicate a light DM of a few GeV. Such a light DM would generate a large amount of anti-proton since suppression for anti-proton flux from DM annihilation is ineffective. We discuss whether a light dark matter with mass of 5-15 GeV, which is especially in favor of the recent experiments reported by CoGeNT, is compatible with the anti-proton no excess in the cosmic-ray. In view of the direct detection of DM and no anti-proton excess in the cosmic-ray both, we show that a Dirac DM is favored than a scalar one since there is no s-wave of the annihilation cross section for the Dirac DM. A large elastic cross section for direct detection can be obtained through the additional light Higgs exchange. We show an allowed region that simultaneously satisfies the DM relic density, the elastic cross section favored by CoGeNT and also the constraint of H_L Z Z coupling of the light Higgs boson by LEP.
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We describe the design and data sample from the DEEP2 Galaxy Redshift Survey, the densest and largest precision-redshift survey of galaxies at z ~ 1 completed to date. The survey has conducted a comprehensive census of massive galaxies, their properties, environments, and large-scale structure down to absolute magnitude M_B = -20 at z ~ 1 via ~90 nights of observation on the DEIMOS spectrograph at Keck Observatory. DEEP2 covers an area of 2.8 deg^2 divided into four separate fields, observed to a limiting apparent magnitude of R_AB=24.1. Objects with z < 0.7 are rejected based on BRI photometry in three of the four DEEP2 fields, allowing galaxies with z > 0.7 to be targeted ~2.5 times more efficiently than in a purely magnitude-limited sample. Approximately sixty percent of eligible targets are chosen for spectroscopy, yielding nearly 53,000 spectra and more than 38,000 reliable redshift measurements. Most of the targets which fail to yield secure redshifts are blue objects that lie beyond z ~ 1.45. The DEIMOS 1200-line/mm grating used for the survey delivers high spectral resolution (R~6000), accurate and secure redshifts, and unique internal kinematic information. Extensive ancillary data are available in the DEEP2 fields, particularly in the Extended Groth Strip, which has evolved into one of the richest multiwavelength regions on the sky. DEEP2 surpasses other deep precision-redshift surveys at z ~ 1 in terms of galaxy numbers, redshift accuracy, sample number density, and amount of spectral information. We also provide an overview of the scientific highlights of the DEEP2 survey thus far. This paper is intended as a handbook for users of the DEEP2 Data Release 4, which includes all DEEP2 spectra and redshifts, as well as for the publicly-available DEEP2 DEIMOS data reduction pipelines. [Abridged]
The variation of the dimensionless fundamental physical constant mu = m_p/m_e (the proton to electron mass ratio) can be constrained via observation of Lyman and Werner lines of molecular hydrogen in the spectra of damped Lyman alpha systems (DLAs) in the line of sight to distant QSOs. Drawing on VLT-UVES high resolution data sets of QSO 0347-383 and its DLA obtained in 2009 our analysis yields dmu/mu = (4.3 +/- 7.2) * 10^-6 at z_abs =3.025. We apply corrections for the observed offsets between discrete spectra and for the first time we find indications for inter-order distortions. Current analyses tend to underestimate the impact of systematic errors. Based on the scatter of the measured redshifts and the corresponding low significance of the redshift-sensitivity correlation we estimate the limit of accuracy of line position measurements to about 220 m/s, consisting of roughly 150 m/s due to the uncertainty of the absorption line fit and about 150 m/s allocated to systematics related to instrumentation and calibration.
Any theory invoked to explain cosmic acceleration predicts consistency relations between the expansion history, structure growth, and all related observables. Currently there exist high-quality measurements of the expansion history from Type Ia supernovae, the cosmic microwave background temperature and polarization spectra, and baryon acoustic oscillations. We can use constraints from these datasets to predict what future probes of structure growth should observe. We apply this method to predict what range of cosmic shear power spectra would be expected if we lived in a LambdaCDM universe, with or without spatial curvature, and what results would be inconsistent and therefore falsify the model. Though predictions are relaxed if one allows for an arbitrary quintessence equation of state $-1\le w(z)\le 1$, we find that any observation that rules out LambdaCDM due to excess lensing will also rule out all quintessence models, with or without early dark energy. We further explore how uncertainties in the nonlinear matter power spectrum, e.g. from approximate fitting formulas such as Halofit, warm dark matter, or baryons, impact these limits.
The ultrahigh-energy cosmic-ray anisotropies discovered by the Pierre Auger Observatory give the potential to finally address both the particles' origins and properties of the nearby extragalactic magnetic field (EGMF). We examine the implications of the excess of ~ 10^20 eV events around the nearby radio galaxy Centaurus A. We find that, if Cen A is the source of these cosmic rays, the angular distribution of events constrains the EGMF strength within several Mpc of the Milky Way to > 20 nG for a proton composition. Our conclusions suggest that either the observed excess is a statistical anomaly or the local EGMF is stronger then conventionally thought. We discuss the implications of this field, including UHECR scattering from more distant sources, time delays from transient sources, and the possibility of using magnetic lensing signatures to attain tighter constraints.
Dust-obscured galaxies (DOGs) are a subset of high-redshift (z \approx 2) optically-faint ultra-luminous infrared galaxies (ULIRGs, e.g. L_{IR} > 10^{12} Lsun). We present new far-infrared photometry, at 250, 350, and 500 um (observed-frame), from the Herschel Space Telescope for a large sample of 113 DOGs with spectroscopically measured redshifts. Approximately 60% of the sample are detected in the far-IR, confirming their high IR luminosities, which range from 10^{11.6} Lsun < L_{IR} (8-1000 um) <10^{13.6} Lsun. 90% of the Herschel detected DOGs in this sample are ULIRGs and 30% have L_{IR} > 10^{13} Lsun. The rest-frame near-IR (1 - 3 um) SEDs of the Herschel detected DOGs are predictors of their SEDs at longer wavelengths. DOGs with "power-law" SEDs in the rest-frame near-IR show observed-frame 250/24 um flux density ratios similar to the QSO-like local ULIRG, Mrk 231. DOGs with a stellar "bump" in their rest-frame near-IR show observed-frame 250/24 um flux density ratios similar to local star-bursting ULIRGs like NGC 6240. For the Herschel detected DOGs, accurate estimates (within \approx 25%) of total IR luminosity can be predicted from their rest-frame mid-IR data alone (e.g. from Spitzer observed-frame 24 um luminosities). Herschel detected DOGs tend to have a high ratio of infrared luminosity to rest-frame 8 um luminosity (the IR8= L_{IR}(8-1000 um)/v L_{v}(8 um) parameter of Elbaz et al. 2011). Instead of lying on the z=1-2 "infrared main-sequence" of star forming galaxies (like typical LIRGs and ULIRGs at those epochs) the DOGs, especially large fractions of the bump sources, tend to lie in the starburst sequence. While, Herschel detected DOGs are similar to scaled up versions of local ULIRGs in terms of 250/24 um flux density ratio, and IR8, they tend to have cooler far-IR dust temperatures (20-40 K for DOGs vs. 40-50 K for local ULIRGs). Abridged.
The Nearby Young Moving Groups (NYMGs) of stars are ideal for the study of evolution circumstellar disks in which planets may form because their ages range from a few Myr to about 100 Myr, about the same as the interval over which planets are thought to form. Their stars are distributed over large regions of the sky. Hence, the Wide Field Infrared Survey Explorer (WISE) which scanned the entire sky in four bands from 3.4 to 22.1 mu provides a database well-suited for the study of members of the NYMGs, particularly those identified after the eras of the IRAS and Spitzer observatories. We report our study of the stars in the epsilon and eta Cha, TW Hya, beta Pic, Tuc-Hor, and AB Dor NYMGs. The WISE Preliminary Release Source Catalog, which covers 57% of the sky, contains data for 64% of the stars in our search lists. WISE detected the 11.6 and 22.1 mu emission of all the previously known disks except for the coldest one, AU Mic. WISE detected no disks in the Tuc-Hor and AB Dor groups, the two oldest in our sample; the frequency of disks detected by WISE decreases rapidly with age of the group. WISE detected a circumstellar disk associated with 2M J0820-8003, a pre-main sequence star with episodic accretion in the ~ 6 Myr old eta Cha cluster. The inner radius of the disk extends close to the star, ~0.02 AU and its luminosity is about a tenth that of the star. The episodic accretion is probably powered by the circumstellar disk discussed here.
We measured polarized dust emission at 350um towards the high-mass star forming massive dense clump IRAS 20126+4104 using the SHARC II Polarimeter, SHARP, at the Caltech Submillimeter Observatory. Most of the observed magnetic field vectors agree well with magnetic field vectors obtained from a numerical simulation for the case when the global magnetic field lines are inclined with respect to the rotation axis of the dense clump. The results of the numerical simulation show that rotation plays an important role on the evolution of the massive dense clump and its magnetic field. The direction of the cold CO 1-0 bipolar outflow is parallel to the observed magnetic field within the dense clump as well as the global magnetic field, as inferred from optical polarimetry data, indicating that the magnetic field also plays a critical role in an early stage of massive star formation. The large-scale Keplerian disk of the massive (proto)star rotates in almost opposite sense to the clump's envelope. The observed magnetic field morphology and the counter-rotating feature of the massive dense clump system provide hints to constrain the role of magnetic fields in the process of high mass star formation.
We use type Ia supernovae (SN Ia) data in combination with recent baryonic acoustic oscillations (BAO) and cosmic microwave background (CMB) observations to constrain a kink-like parametrization of the deceleration parameter ($q$). This $q$-parametrization can be written in terms of the initial ($q_i$) and present ($q_0$) values of the deceleration parameter, the redshift of the cosmic transition from deceleration to acceleration ($z_t$) and the redshift width of such transition ($\tau$). By assuming a flat space geometry, $q_i=1/2$ and adopting a likelihood approach to deal with the SN Ia data we obtain, at the 68% confidence level (C.L.), that: $z_t=0.56^{+0.13}_{-0.10}$, $\tau=0.47^{+0.16}_{-0.20}$ and $q_0=-0.31^{+0.11}_{-0.11}$ when we combine BAO/CMB observations with SN Ia data processed with the MLCS2k2 light-curve fitter. When in this combination we use the SALT2 fitter we get instead, at the same C.L.: $z_t=0.64^{+0.13}_{-0.07}$, $\tau=0.36^{+0.11}_{-0.17}$ and $q_0=-0.53^{+0.17}_{-0.13}$. Our results indicate, with a quite general and model independent approach, that MLCS2k2 favors Dvali-Gabadadze-Porrati-like cosmological models, while SALT2 favors $\Lambda$CDM-like ones. Progress in determining the transition redshift and/or the present value of the deceleration parameter depends crucially on solving the issue of the difference obtained when using these two light-curve fitters.
The observational coverage with HESS of the Carina region in VHE gamma-rays benefits from deep exposure (40 h) of the neighboring open cluster Westerlund 2. The observations have revealed a new extended region of VHE gamma-ray emission. The new VHE source HESS J1018-589 shows a bright, point-like emission region positionally coincident with SNR G284.3-1.8 and 1FGL J1018.6 - 5856 and a diffuse extension towards the direction of PSR J1016-5857. A soft Gamma=2.7\pm0.5 photon index, with a differential flux at 1TeV of N0=(4.2\pm1.1)\dot 10-13 TeV-1 cm-2 s-1 is found for the point-like source, whereas the total emission region including the diffuse emission region is well fit by a power-law function with spectral index Gamma=2.9\pm0.4 and differential flux at 1TeV of N0=(6.8\pm1.6)\dot10-13 TeV-1 cm-2 s-1. This H.E.S.S. detection motivated follow-up X-ray observations with the XMM-Newton satellite to investigate the origin of the VHE emission. The analysis of the XMM-Newton data resulted in the discovery of a bright, non-thermal point-like source (XMMU J101855.4-58564) with a photon index of Gamma=1.65\pm0.08 in the center of SNRG284.3-1.8, and a thermal, extended emission region coincident with its bright northern filament. The characteristics of this thermal emission are used to estimate the plasma density in the region as n\approx0.5 cm-3(2.9kpc/d)2. The position of XMMUJ101855.4-58564 is compatible with the position reported by the Fermi-LAT collaboration for the binary system 1FGL J1018.6-5856 and the variable Swift XRT source identified with it. The new X-ray data are used alongside archival multi-wavelength data to investigate the relationship between the VHE gamma-ray emission from HESSJ1018-589 and the various potential counterparts in the Carina arm region.
We present a very large high-resolution cosmological N-body simulation, the Millennium-XXL or MXXL, which uses 303 billion particles to represent the formation of dark matter structures throughout a 4.1Gpc box in a LambdaCDM cosmology. We create sky maps and identify large samples of galaxy clusters using surrogates for four different observables: richness estimated from galaxy surveys, X-ray luminosity, integrated Sunyaev-Zeldovich signal, and lensing mass. The unprecedented combination of volume and resolution allows us to explore in detail how these observables scale with each other and with cluster mass. The scatter correlates between different mass-observable relations because of common sensitivities to the internal structure, orientation and environment of clusters, as well as to line-of-sight superposition of uncorrelated structure. We show that this can account for the apparent discrepancies uncovered recently between the mean thermal SZ signals measured for optically and X-ray selected clusters by stacking data from the Planck satellite. Related systematics can also affect inferences from extreme clusters detected at high redshift. Our results illustrate that cosmological conclusions from galaxy cluster surveys depend critically on proper modelling, not only of the relevant physics, but also of the full distribution of the observables and of the selection biases induced by cluster identification procedures.
In this work we present the results of a novel approach devoted to disentangle the role of the environmental processes affecting galaxies in clusters. This is based on the analysis of the NUV-r' distributions of a large sample of star-forming galaxies in clusters spanning more than four absolute magnitudes. The galaxies inhabit three distinct environmental regions: virial regions, cluster infall regions and field environment. We have applied rigorous statistical tests in order to analyze both, the complete NUV-r' distributions and their averages for three different bins of r'-band galaxy luminosity down to M_r' ~ -18, throughout the three environmental regions considered. We have identified the environmental processes that significantly affect the star-forming galaxies in a given luminosity bin by using criteria based on the characteristics of these processes: their typical time-scales, the regions where they operate and the galaxy luminosity range for which their effects are more intense. We have found that the high-luminosity (M_r'<=-20) star-forming galaxies do not show significant signs in their star formation activity neither of being affected by the environment in the last ~10^8 yr nor of a sudden quenching in the last 1.5 Gyr. The intermediate-luminosity (-20<M_r'<=-19) star-forming galaxies appear to be affected by starvation in the virial regions and by the harassment both, in the virial and infall regions. Low-luminosity (-19<M_r'<=-18.2) star-forming galaxies seem to be affected by the same environmental processes as intermediate-luminosity star-forming galaxies in a stronger way, as it would be expected for their lower luminosities.
We examine the global properties of the stellar and HI components of 229 low HI mass dwarf galaxies extracted from the ALFALFA survey, including a complete sample of 176 galaxies with HI masses < 10^{7.7} M_sun and HI line widths < 80 km s^{-1}. SDSS data are combined with photometric properties derived from GALEX to derive stellar masses (M_*) and star formation rates (SFRs) by fitting their UV-optical spectral energy distributions (SEDs). In optical images, many of the ALFALFA dwarfs are faint and of low surface brightness; only 56% of those within the SDSS footprint have a counterpart in the SDSS spectroscopic survey. A large fraction of the dwarfs have high specific star formation rates (SSFRs) and estimates of their SFRs and M_* obtained by SED fitting are systematically smaller than ones derived via standard formulae assuming a constant SFR. The increased dispersion of the SSFR distribution at M_* < 10^8 M_sun is driven by a set of dwarf galaxies that have low gas fractions and SSFRs; some of these are dE/dSphs in the Virgo cluster. The imposition of an upper HI mass limit yields the selection of a sample with lower gas fractions for their M_* than found for the overall ALFALFA population. Many of the ALFALFA dwarfs, particularly the Virgo members, have HI depletion timescales shorter than a Hubble time. An examination of the dwarf galaxies within the full ALFALFA population in the context of global star formation laws is consistent with the general assumptions that gas-rich galaxies have lower star formation efficiencies than do optically selected populations and that HI disks are more extended than stellar ones.
We report the detection of GeV gamma-ray emission from the molecular cloud complex that surrounds the supernova remnant (SNR) W44 using the Large Area Telescope (LAT) onboard Fermi. While the previously reported gamma-ray emission from SNR W44 is likely to arise from the dense radio-emitting filaments within the remnant, the gamma-ray emission that appears to come from the surrounding molecular cloud complex can be ascribed to the cosmic rays (CRs) that have escaped from W44. The non-detection of synchrotron radio emission associated with the molecular cloud complex suggests the decay of neutral pi mesons produced in hadronic collisions as the gamma-ray emission mechanism. The total kinetic energy channeled into the escaping CRs is estimated to be (0.3--3)x10^{50} erg, in broad agreement with the conjecture that SNRs are the main sources of Galactic CRs.
A type stars are expected to be X-ray dark, yet weak emission has been detected from several objects in this class. We present new Chandra/HRC-I observations of the A5 V star \beta{} Pictoris. It is clearly detected with a flux of 9+-2 10^{-4} counts/s. In comparison with previous data this constrains the emission mechanism and we find that the most likely explanation is an optically thin, collisionally dominated, thermal emission component with a temperature around 1.1 MK. We interpret this component as a very cool and dim corona, with \log L_X/L_{bol}=-8.2 (0.2-2.0 keV). Thus, it seems that \beta{} Pictoris shares more characteristics with cool stars than previously thought.
The propagation properties of coronal mass ejections (CMEs) are crucial to predict its geomagnetic effect. A newly developed three dimensional (3D) mask fitting reconstruction method using coronagraph images from three viewpoints has been described and applied to the CME ejected on August 7, 2010. The CME's 3D localisation, real shape and morphological evolution are presented. Due to its interaction with the ambient solar wind, the morphology of this CME changed significantly in the early phase of evolution. Two hours after its initiation, it was expanding almost self-similarly. CME's 3D localisation is quite helpful to link remote sensing observations to in situ measurements. The investigated CME was propagating to Venus with its flank just touching STEREO B. Its corresponding ICME in the interplanetary space shows a possible signature of a magnetic cloud with a preceding shock in VEX observations, while from STEREO B only a shock is observed. We have calculated three principle axes for the reconstructed 3D CME cloud. The orientation of the major axis is in general consistent with the orientation of a filament (polarity inversion line) observed by SDO/AIA and SDO/HMI. The flux rope axis derived by the MVA analysis from VEX indicates a radial-directed axis orientation. It might be that locally only the leg of the flux rope passed through VEX. The height and speed profiles from the Sun to Venus are obtained. We find that the CME speed possibly had been adjusted to the speed of the ambient solar wind flow after leaving COR2 field of view and before arriving Venus. A southward deflection of the CME from the source region is found from the trajectory of the CME geometric center. We attribute it to the influence of the coronal hole where the fast solar wind emanated from.
We address two selection effects that operate on samples of gravitationally lensed dusty galaxies identified in millimeter and submillimeter-wavelength surveys. First, we point out the existence of a "size bias" in such samples: due to finite source effects, sources with higher observed fluxes are increasingly biased towards more compact objects. Second, we examine the effect of differential lensing in individual lens systems by modelling each source as a compact core embedded in an extended diffuse halo. Considering the ratio of magnifications in these two components, we find that at high overall magnifications the compact component is amplified by a much larger factor than the diffuse component, but at intermediate magnifications (~10) the probability of a larger magnification for the extended region is higher. Lens models determined from resolved imaging data, rather than the typically unresolved discovery images, are crucial to correct for this effect.
We use a Quadratic Maximum Likelihood (QML) method to estimate the angular power spectrum of the cross-correlation between cosmic microwave background and large scale structure maps as well as their individual auto-spectra. We describe our implementation of this method and demonstrate its accuracy on simulated maps. We apply this optimal estimator to WMAP 7-year and NRAO VLA Sky Survey (NVSS) data and explore the robustness of the angular power spectrum estimates obtained by the QML method. With the correction of the declination systematics in NVSS, we can safely use most of the information contained in this survey. We then make use of the angular power spectrum estimates obtained by the QML method to derive constraints on the dark energy critical density in a flat $\Lambda$CDM model by different likelihood prescriptions. When using just the cross-correlation between WMAP 7 year and NVSS maps with 1.8$^\circ$ resolution, the best-fit model has a cosmological constant of approximatively 70% of the total energy density, disfavouring an Einstein-de Sitter Universe at more than 2 $\sigma$ CL (confidence level).
Planetary migration is the process by which a forming planet undergoes a drift of its semi-major axis caused by the tidal interaction with its parent protoplanetary disc. One of the key quantities to assess the migration of embedded planets is the tidal torque between the disc and planet, which has two components: the Lindblad torque and the corotation torque. We review the latest results on both torque components for planets on circular orbits, with a special emphasis on the various processes that give rise to additional, large components of the corotation torque, and those contributing to the saturation of this torque. These additional components of the corotation torque could help address the shortcomings that have recently been exposed by models of planet population syntheses. We also review recent results concerning the migration of giant planets that carve gaps in the disc (type II migration) and the migration of sub-giant planets that open partial gaps in massive discs (type III migration).
Carbon-enhanced metal-poor (CEMP) stars are believed to show the chemical imprints of more massive stars (M < 0.8 Msun) that are now extinct. In particular, it is expected that the observed abundance of Li should deviate in these stars from the standard Spite lithium plateau. We study here a sample of 11 metal-poor stars and a double-lined spectroscopic binary with -1.8 <[Fe/H]< -3.3 observed with VLT/UVES spectrograph. Among these 12 metal-poor stars, there are 8 CEMP stars for which we measure or constrain the Li abundance. In contrast to previous arguments, we demonstrate that an appropriate regime of dilution permits the existence of "Li-Spite plateau and C-rich" stars, whereas some of the "Li-depleted and C-rich" stars call for an unidentified additional depletion mechanism that cannot be explained by dilution alone. We find evidence that rotation is related to the Li depletion in some CEMP stars. Additionally, we report on a newly recognized double-lined spectroscopic binary star in our sample. For this star, we develop a new technique from which estimates of stellar parameters and luminosity ratios can be derived based on a high-resolution spectrum alone, without the need for input from evolutionary models.
We report on the serendipitous discovery of the first central star of a planetary nebula (PN) that mimics the helium- and nitrogen-rich WN sequence of massive Wolf-Rayet (WR) stars. The central star of IC 4663 (PN G346.2-08.2) is dominated by broad He II and N V emission lines which correspond to a [WN3] spectral type. Unlike previous [WN] candidates, the surrounding nebula is unambiguously a PN. At an assumed distance of 3.5 kpc, corresponding to a stellar luminosity of 4000 Lsun, the V=16.9 mag central star remains 4-6 mag fainter than the average luminosity of massive WN3 stars even out to an improbable d=8 kpc. The nebula is typical of PNe with an elliptical morphology, a newly discovered Asymptotic Giant Branch (AGB) halo, a relatively low expansion velocity (v_exp=30 km/s) and a highly ionised spectrum with an approximately Solar chemical abundance pattern. The [WN3] star is hot enough to show Ne VII emission (T_*=140+/-20 kK) and exhibits a fast wind (v_infty=1900 km/s), which at d=3.5 kpc would yield a clumped mass loss rate of Mdot = 1.8 x 10^-8 Msun/yr with a small stellar radius (R_*=0.11 Rsun). Its atmosphere consists of helium (95%), hydrogen (<2%), nitrogen (0.8%), neon (0.2%) and oxygen (0.05%) by mass. Such an unusual helium-dominated composition cannot be produced by any extant scenario used to explain the H-deficiency of post-AGB stars. The O(He) central stars share a similar composition and the discovery of IC 4663 provides the first evidence for a second He-rich/H-deficient post-AGB evolutionary sequence [WN]->O(He). This suggests there is an alternative mechanism responsible for producing the majority of H-deficient post-AGB stars that may possibly be expanded to include other He-rich/H-deficient stars such as R Coronae Borealis stars and AM Canum Venaticorum stars. The origin of the unusual composition of [WN] and O(He) central stars remains unexplained.
Solar energetic transients occurring in solar atmosphere are associated with catastrophic release of energy in the solar corona. These transients inject a part of their energy by various physical processes to the deeper, denser photospheric layer at which velocity and magnetic fields are measured using suitable spectral lines. Serious questions have been raised about the nature of the observed magnetic (and velocity) field changes associated with energetic transients as their measurements are expected to be affected by flare-induced line profile changes. In this paper, we shall discuss some recent progress on our understanding of the physical processes associated with such events.
The electric solar wind sail (E-sail) is a novel, efficient propellantless propulsion concept which utilises the natural solar wind for spacecraft propulsion with the help of long centrifugally stretched charged tethers. The E-sail requires auxiliary propulsion applied to the tips of the main tethers for creating the initial angular momentum and possibly for modifying the spinrate later during flight to counteract the orbital Coriolis effect and possibly for mission specific reasons. We introduce the possibility of implementing the required auxiliary propulsion by small photonic blades (small radiation pressure solar sails). The blades would be stretched centrifugally. We look into two concepts, one with and one without auxiliary tethers. The use of photonic blades has the benefit of providing sufficient spin modification capability for any E-sail mission while keeping the technology fully propellantless. We conclude that the photonic blades appear to be a feasible and attractive solution to E-sail spinrate control.
We derive the mass function of condensations (clumps) which were formed through a turbulent cascade over a range of spatial scales $L\le20$ pc during early, predominantly turbulent evolution of a molecular cloud. The approach rests upon the assumption of a statistical clump mass-density relationship $n\propto m^x$ with a scale dependence of the exponent $x$ obtained from equipartition relations between various forms of energy of clumps. The derived clump mass function (ClMF) could be represented by series of 2 or 3 power laws, depending on the chosen equipartition relation, the velocity scaling index and the type of turbulent forcing. The high-mass ClMF exhibits an average slope $\Gamma\simeq-1$, typical for fractal clouds, whereas its intermediate-mass part is shallower or flattened, in agreement with some observational studies.
According to the now strongly supported concordance $\Lambda$CDM model, galaxies may be grossly described as a luminous component embedded in a dark matter halo. The density profile of these mass dominating haloes may be determined by N - body simulations which mimic the evolution of the tiny initial density perturbations during the process leading to the structures we observe today. Unfortunately, when the effect of baryons is taken into account, the situation gets much more complicated due to the difficulties in simulating their physics. As a consequence, a definitive prediction of how dark matter haloes should presently look like is still missing. We revisit here this issue from an observational point of view devoting our attention to dwarf galaxies. Being likely dark matter dominated, these systems are ideal candidates to investigate the present day halo density profiles and check whether dark matter related quantities correlate with the stellar ones or the environment. By fitting a large sample of well measured rotation curves, we infer constraints on both halo structural parameters (such as the logarithmic slope of the density profile and its concentration) and derived quantities (e.g., the mass fraction and the Newtonian acceleration) which could then be used to constrain galaxy formation scenarios. Moreover, we investigate whether the halo properties correlates with the environment the galaxy lives in thus offering a new tool to deepen our understanding of galaxy formation.
We present 16 GHz (1.9 cm) deep radio continuum observations made with the Arcminute Microkelvin Imager (AMI) of a sample of low-mass young stars driving jets. We combine these new data with archival information from an extensive literature search to examine spectral energy distributions (SEDs) for each source and calculate both the radio and sub-mm spectral indices in two different scenarios: (1) fixing the dust temperature (Td) according to evolutionary class; (2) allowing Td to vary. We use the results of this analysis to place constraints on the physical mechanisms responsible for the radio emission. From AMI data alone, as well as from model fitting to the full SED in both scenarios, we find that 80 per cent of the objects in this sample have spectral indices consistent with free-free emission. We find an average spectral index in both Td scenarios consistent with free-free emission. We examine correlations of the radio luminosity with bolometric luminosity, envelope mass, and outflow force and find that these data are consistent with the strong correlation with envelope mass seen in lower luminosity samples. We examine the errors associated with determining the radio luminosity and find that the dominant source of error is the uncertainty on the opacity index, beta. We examine the SEDs for variability in these young objects, and find evidence for possible radio flare events in the histories of L1551 IRS 5 and Serpens SMM 1.
We describe the initial implementation of magnetohydrodynamics (MHD) in our astrophysical simulation code \genasis. Then, we present MHD simulations exploring the capacity of the stationary accretion shock instability (SASI) to generate magnetic fields by adding a weak magnetic field to an initially spherically symmetric fluid configuration that models a stalled shock in the post-bounce supernova environment. Upon perturbation and nonlinear SASI development, shear flows associated with the spiral SASI mode contributes to a widespread and turbulent field amplification mechanism. While the SASI may contribute to neutron star magnetization, these simulations do not show qualitatively new features in the global evolution of the shock as a result of SASI-induced magnetic field amplification.
The kinematics of the bipolar planetary nebulae Hb~5 and K 3-17 are investigated in detail by means of a comprehensive set of spatially resolved high spectral resolution, long-slit spectra. Both objects share particularly interesting characteristics, such as a complex filamentary, rosette-type nucleus, axial point-symmetry and very fast bipolar outflows. The kinematic information of Hb~5 is combined with {\it HST} imagery to construct a detailed 3D model of the nebula using the code SHAPE. The model shows that the large scale lobes are growing in a non-homologous way. The filamentary loops in the core are proven to actually be secondary lobes emerging from what appears to be a randomly punctured, dense, gaseous core and the material that forms the point symmetric structure flows within the lobes with a distinct kinematic pattern and its interaction with the lobes has had a shaping effect on them. Hb~5 and K~3-17 may represent a class of fast evolving planetary nebulae that will develop poly-polar characteristics once the nebular core evolves and expands.
A growing body of evidence indicates that the formation of filaments in interstellar clouds is a key component of the star formation process. In this paper, we present new Herschel PACS and SPIRE observations of the B59 and Stem regions in the Pipe Nebula complex, revealing a rich, organized network of filaments. The asymmetric column density profiles observed for several filaments, along with the bow-like edge of B59, indicates that the Pipe Nebula is being compressed from its western side, most likely by the winds from the nearby Sco OB2 association. We suggest that this compressive flow has contributed to the formation of some of the observed filamentary structures. In B59, the only region of the entire Pipe complex showing star formation activity, the same compressive flow has likely enhanced the initial column density of the clump, allowing it to become globally gravitationally unstable. Although more speculative, we propose that gravity has also been responsible for shaping the converging filamentary pattern observed in B59. While the question of the relative impact of large-scale compression and gravity remains open in B59, large-scale compression appears to be a plausible mechanism for the initial formation of filamentary structures in the rest of the complex
Cloud contraction and infall are the fundamental processes of star formation. While "blue-skewed" line profiles observed in high- mass star forming regions are commonly taken as evidence of infall by an ever increasing number of studies, their interpretation offers many pitfalls. Detecting infall via redshifted absorption in front of continuum sources is a much more direct and reliable method but so far mostly restricted toward absorption in the centimeter toward strong HII regions. Here we present a novel approach by probing absorption of rotational ammonia transitions in front of the strong dust emission of massive star-forming regions. A carefully selected sample of three regions with different stages of evolution is selected to study infall through the evolution of massive star-forming clumps. Redshifted absorption is detected toward all three sources and infall rates between 3-10x10-3 Msol yr-1 are derived.
We have mapped at small spatial scales the temperature and the velocity field in the protocluster associated with IRAS 05345+3157, which contains both intermediate-/high-mass protostellar candidates and starless condensations, and is thus an excellent location to investigate the role of massive protostars on protocluster evolution. We observed the ammonia (1,1) and (2,2) inversion transitions with the VLA. Ammonia is the best thermometer for dense and cold gas, and the observed transitions have critical densities able to trace the kinematics of the intracluster gaseous medium. The ammonia emission is extended and distributed in two filamentary structures. The starless condensations are colder than the star-forming cores, but the gas temperature across the whole protocluster is higher (by a factor of ~1.3-1.5) than that measured typically in both infrared dark clouds and low-mass protoclusters. The non-thermal contribution to the observed line broadening is at least a factor of 2 larger than the expected thermal broadening even in starless condensations, contrary to the close-to-thermal line widths measured in low-mass quiescent dense cores. The NH3-to-N2H+ abundance ratio is greatly enhanced (a factor of 10) in the pre--stellar core candidates, probably due to freeze-out of most molecular species heavier than He. The more massive and evolved objects likely play a dominant role in the physical properties and kinematics of the protocluster. The high level of turbulence and the fact that the measured core masses are larger than the expected thermal Jeans masses indicate that turbulence likely was an important factor in the initial fragmentation of the parental clump.
We focus here on one particular and poorly studied object, IRAS11472-0800. It is a highly evolved post-Asymptotic Giant Branch (post-AGB) star of spectral type F, with a large infrared excess produced by thermal emission of circumstellar dust. We deploy a multi-wavelength study which includes the analyses of optical and IR spectra as well as a variability study based on photometric and spectroscopic time-series. The spectral energy distribution (SED) properties as well as the highly processed silicate N-band emission show that the dust in IRAS11472-0800 is likely trapped in a stable disc. The energetics of the SED and the colour variability show that our viewing angle is close to edge-on and that the optical flux is dominated by scattered light. With photospheric abundances of [Fe/H] = -2.7 and [Sc/H]=-4.2, we discovered that IRAS11472-0800 is one of the most chemically-depleted objects known to date. Moreover, IRAS11472-0800 is a pulsating star with a period of 31.16 days and a peak-to-peak amplitude of 0.6 mag in V. The radial velocity variability is strongly influenced by the pulsations, but the significant cycle-to-cycle variability is systematic on a longer time scale, which we interpret as evidence for binary motion. We conclude that IRAS11472-0800 is a pulsating binary star surrounded by a circumbinary disc. The line-of-sight towards the object lies close the the orbital plane making that the optical light is dominated by scattered light. IRAS11472-0800 is one of the most chemically-depleted objects known so far and links the dusty RV\,Tauri stars to the non-pulsating class of strongly depleted objects.
We discuss the nature of the multi-component radio continuum and HI emission associated with the nearby galaxy group comprised of two dominant ellipticals, NGC 5898 and NGC 5903, and a dwarf lenticular ESO514-G003. Striking new details of radio emission are unveiled from the 2nd Data Release of the ongoing TIFR.GMRT.SKY.SURVEY (TGSS) which provides images with a resolution of ~ 24 arcsec x 18 arcsec and a typical rms noise of 5 mJy at 150 MHz. Previous radio observations of this compact triplet of galaxies include images at higher frequencies of the radio continuum as well as HI emission, the latter showing huge HI trails originating from the vicinity of NGC 5903 where HI is in a kinematically disturbed state. The TGSS 150 MHz image has revealed a large asymmetric radio halo around NGC 5903 and also established that the dwarf SO galaxy ESO514-G003 is the host to a previously known bright double radio source. The radio emission from NGC 5903 is found to have a very steep radio spectrum ({\alpha} ~ -1.5) and to envelope a network of radio continuum filaments bearing a spatial relationship to the HI trails. Another noteworthy aspect of this triplet of early-type galaxies highlighted by the present study is that both its radio loud members, namely NGC 5903 and ESO514-G003, are also the only galaxies that are seen to be connected to an HI filament. This correlation is consistent with the premise that cold gas accretion is of prime importance for triggering powerful jet activity in the nuclei of early-type galaxies.
Bipolar molecular outflows have been observed and studied extensively in the past, but some recent observations of periodic variations in maser intensity pose new challenges. Even quasi-periodic maser flares have been observed and reported in the literature. Motivated by these data, we have tried to study situations in binary systems with specific attention to the two observed features, i.e., the bipolar flows and the variabilities in the maser intensity. We have studied the evolution of spherically symmetric wind from one of the bodies in the binary system, in the plane of the binary. Our approach includes the analytical study of rotating flows with numerical computation of streamlines of fluid particles using PLUTO code. We present the results of our findings assuming simple configurations, and discuss the implications.
We analysed the Spitzer maps of Stephan's Quintet in order to investigate the nature of the dust emission associated with the X-ray emitting regions of the large scale intergalactic shock and of the group halo. This emission can in principle be powered by dust-gas particle collisions, thus providing efficient cooling of the hot gas. However the results of our analysis suggest that the dust emission from those regions is mostly powered by photons. Nonetheless dust collisional heating could be important in determining the cooling of the IGM gas and the large scale star formation morphology observed in SQ.
We investigated the star formation efficiency for all the dust emitting sources in Stephan's Quintet (SQ). We inferred star formation rates using Spitzer MIR/FIR and GALEX FUV data and combined them with gas column density measurements by various authors, in order to position each source in a Kennicutt-Schmidt diagram. Our results show that the bright IGM star formation regions in SQ present star formation efficiencies consistent with those observed within local galaxies. On the other hand, star formation in the intergalactic shock region seems to be rather inhibited.
We construct a set of binary evolutionary sequences for systems composed by a
normal, solar composition, donor star together with a neutron star. We consider
a variety of masses for each star as well as for the initial orbital period
corresponding to systems that evolve to ultra-compact or millisecond
pulsar-helium white dwarf pairs. Specifically, we select a set of donor star
masses of 0.50, 0.65, 0.80, 1.00, 1.25, 1.50, 1.75, 2.00, 2.25, 2.50, 3.00, and
3.50 solar masses, whereas for the accreting neutron star we consider initial
masses values of 0.8, 1.0, 1.2, and 1.4 solar masses. The considered initial
orbital period interval ranges from 0.5 to 12 days.
It is found that the evolution of systems, with fixed initial values for the
orbital period and the mass of the normal donor star, heavily depends upon the
mass of the neutron star. In some cases, varying the initial value of the
neutron star mass, we obtain evolved configurations ranging from ultra-compact
to widely separated objects.
We also analyse the dependence of the final orbital period with the mass of
the white dwarf. In agreement with previous expectations, our calculations show
that the final orbital period-white dwarf mass relation is fairly insensitive
to the initial neutron star mass value. A new period-mass relation based on our
own calculations is proposed, which is in good agreement with period-mass
relations available in the literature.
As consequence of considering a set of values for the initial neutron star
mass, these models allow finding different plausible initial configurations
(donor and neutron star masses and orbital period interval) for some of the
best observed binary systems of the kind we are interested in here. We apply
our calculations to analyse the case of PSR J0437-4715.
As we observe in the moon-earth system, tidal interactions in binaries can lead to angular momentum exchange. The presence of viscosity is generally regarded as the condition for such transfer to happen. In this paper, we how a dynamical mechanism can cause a persistent torque between the binary components, even for inviscid bodies. This preferentially occurs at the final stage of coalescence of compact binaries, when the orbit shrinks by gravitational waves on a timescale shorter than the viscous timescale. The total orbital energy transferred to the secondary is a few 10^(-3) of its binding energy. We further show that this persistent torque induces a differentially rotating quadrupolar perturbation. Specializing to the case of a neutron star, we find that the free energy associated with this non-equilibrium state can be at least ~ 5 \times 10^(46) erg just prior to coalescence. This energy is likely stored in internal fluid motions, with a sizable amount of differential rotation. Thus, a preexisting magnetic field could be substantially amplified, up to a few \times 10^(14) Gauss.
We argue that current observations of $M - \sigma$ relations for galaxies can be used to constrain theories of super-massive black holes (SMBH) feeding. In particular, assuming that SMBH mass is limited only by the feedback on the gas that feeds it, we show that SMBHs fed via a planar galaxy scale gas flow, such as a disc or a bar, should be much more massive than their counterparts fed by quasi-spherical inflows. This follows from the relative inefficiency of AGN feedback on a flattened inflow. We find that even under the most optimistic conditions for SMBH feedback on flattened inflows, the mass at which the SMBH expels the gas disc and terminates its own growth is a factor of several higher than the one established for quasi-spherical inflows. Any beaming of feedback away from the disc and any disc self-shadowing strengthens this result further. Contrary to this theoretical expectation, recent observations have shown that SMBH in pseudobulge galaxies (which are associated with barred galaxies) are typically under- rather than over-massive when compared with their classical bulge counterparts at a fixed value of $\sigma$. We conclude from this that SMBHs are not fed by large (100 pc to many kpc) scale gas discs or bars, most likely because such planar flows are turned into stars too efficiently to allow any SMBH growth. Based on this and other related observational evidence, we argue that most SMBHs grow by chaotic accretion of gas clouds with a small and nearly randomly distributed direction of angular momentum.
This document contains a summary of the workshop which took place on 22 - 24 February 2012 at the Kavli Institute of Cosmological Physics in the University of Chicago. The goal of the workshop was to discuss the physics reach of the JEM-EUSO mission and how best to implement a global ground based calibration system for the instrument to realize the physics goal of unveiling the origin of the highest energy cosmic rays.
We present deep observations of the 12CO(1-0) and (3-2) lines in 4C12.50, carried out with the 30m telescope of the Institut de Radioastronomie Millimetrique. Our observations revealed the cold molecular gas component of a warm molecular gas outflow that was previously known from Spitzer Space Telescope data. The 12CO(3-2) profile indicates the presence of absorption at -950 km/s from systemic velocity with a central optical depth of 0.22. Its profile is similar to that of the HI absorption that was seen in radio data of this source. A potential detection of the (0-1) absorption enabled us to place an upper limit of 0.03 on its central optical depth, and to constrain the excitation temperature of the outflowing CO gas to >=65K assuming that the gas is thermalized. If the molecular clouds are fully obscuring their background millimeter continuum that is emitted by the radio core, the H2 column density is >=1.8*10^22 /cm^2. The outflow is then carrying an estimated cold H2 mass of at least 4.2*10^3 M_sun along the nuclear line of sight. This mass will be even higher when integrated over several lines of sight, but if it were to exceed 3*10^9 M_sun, the outflow would most likely be seen in emission. Since the ambient cold gas reservoir of 4C12.50 is 1.0*10^10 M_sun, the outflowing-to-ambient mass ratio of the warm gas (37%) could be elevated with respect to that of the cold gas.
Using the NRGR effective field theory formalism we calculate the remaining source multipole moments necessary to obtain the spin contributions to the gravitational wave amplitude to 2.5 Post-Newtonian (PN) order. We also reproduce the tail contribution to the waveform linear in spin at 2.5PN arising from the nonlinear interaction between the current quadrupole and the mass monopole.
Once the temperature of a bosonic gas is smaller than the critical, density dependent, transition temperature, a Bose - Einstein Condensation process can take place during the cosmological evolution of the Universe. Bose - Einstein Condensates are very strong candidates for dark matter, since they can solve some major issues in observational astrophysics, like, for example, the galactic core/cusp problem. The presence of the dark matter condensates also drastically affects the cosmic history of the Universe. In the present paper we analyze the effects of the finite dark matter temperature on the cosmological evolution of the Bose-Einstein Condensate dark matter systems. We formulate the basic equations describing the finite temperature condensate, representing a generalized Gross-Pitaevskii equation that takes into account the presence of the thermal cloud in thermodynamic equilibrium with the condensate. The temperature dependent equations of state of the thermal cloud and of the condensate are explicitly obtained in an analytical form. By assuming a flat Friedmann-Robertson-Walker (FRW) geometry, the cosmological evolution of the finite temperature dark matter filled Universe is considered in detail in the framework of a two interacting fluid dark matter model, describing the transition from the initial thermal cloud to the low temperature condensate state. The dynamics of the cosmological parameters during the finite temperature dominated phase of the dark matter evolution are investigated in detail, and it is shown that the presence of the thermal excitations leads to an overall increase in the expansion rate of the Universe.
We study conformally-flat initial data for an arbitrary number of spinning black holes with exact analytic solutions to the momentum constraints constructed from a linear combination of the classical Bowen-York and conformal Kerr extrinsic curvatures. The solution leading to the largest intrinsic spin, relative to the ADM mass of the spacetime epsilon_S=S/M^2_{ADM}, is a superposition with relative weights of Lambda=0.783 for conformal Kerr and (1-Lambda)=0.217 for Bowen-York. In addition, we measure the spin relative to the initial horizon mass M_{H_0}, and find that the quantity chi=S/M_{H_0}^2 reaches a maximum of \chi^{max}=0.9856 for Lambda=0.753. After equilibration, the final black-hole spin should lie in the interval 0.9324<chi_{final}<0.9856. We perform full numerical evolutions to compute the energy radiated and the final horizon mass and spin. We find that the black hole settles to a final spin of chi_{final}^{max}=0.935 when Lambda=0.783. We also study the evolution of the apparent horizon structure of this "maximal" black hole in detail.
We present fifth order Runge-Kutta-Nystr\"om methods, where we allow the timestep coefficients to assume complex values. Among the methods with complex timesteps, we focus on the ones with the coefficients that have positive real parts. This property makes them suitable for problems where a negative coefficient is not acceptable. In addition, the leading order terms in the error expansion of these methods are purely imaginary, effectively increasing the order of the methods by one for real variables.
An excited state of $^{12}$C having excitation energy E$_x \sim$ 9.65 $\pm$ 0.02 MeV and width (FWHM) $\sim607\pm$ 55 keV, which decays to three $ \alpha $-particles via Hoyle state ($E_x \sim$ 7.65 MeV), has been directly identified for the first time in the exclusive inelastic scattering of 60 MeV $^{4}$He on $^{12}$C, measured in coincidence with the recoiling $^{12}$C$ ^* $ Hoyle state (decaying mostly as $^{12}$C$ ^* $ $\rightarrow \ ^{8} $Be + $ \alpha $ $\rightarrow \ \alpha + \alpha + \alpha$) by event-by-event kinematic reconstruction of the completely detected (4$ \alpha $) events. This state is likely to be a candidate for 2$_2^+$ first excited Hoyle state, the existence of which has recently been indirectly evidenced from the recent inclusive inelastic scattering studies.
The Weyl curvature hypothesis of Penrose attempts to explain the high
homogeneity and isotropy, and the very low entropy of the early universe, by
conjecturing the vanishing of the Weyl tensor at the Big Bang singularity.
In previous papers it has been proposed an equivalent form of Einstein's
equation, which extends it and remains valid at an important class of
singularities (including in particular the Schwarzschild, FLRW, and isotropic
singularities). Here it is shown that if the Big Bang singularity is from this
class, it also satisfies the Weyl curvature hypothesis.
We have investigated the six most tightly bound states of each of the atoms, helium and lithium, in intense magnetic fields. In this regard, we report new data for two new states of lithium that have not been studied thus far in the literature. The energy levels of these first few low-lying states are calculated in this study employing a pseudospectral method as the computational tool. The methodology involves computing the eigenvalues and eigenvectors of the generalized two-dimensional Hartree-Fock partial differential equations for these two- and three-electron systems in a self-consistent manner. The method described herein is applicable to calculations of atomic structure in magnetic fields of strength in the so-called intense-field regime, as it exploits the natural symmetries of the problem without assumptions of any basis functions for expressing the wave functions of the electrons or the commonly employed adiabatic approximation. It is seen that the results obtained herein are improvements upon single-configuration calculations as well as configuration-interaction methods. It is also seen that the pseudospectral method employed here is considerably more economical, from a computational point of view, than previously employed methods such as a finite-element based approach.
Recent LHC data suggest an excess in the Higgs decay channels into gamma gamma, W W and Z Z at roughly 125 GeV. The current excess in the diphoton channel is twice that expected from a Standard Model Higgs; whilst this may well change with more statistics, it is interesting to consider the implications should the result persist. Here, we assess whether the NMSSM with a neutralino dark matter candidate could explain this excess when astrophysical constraints (e.g. no overproduction of gamma rays and radio emission in the galaxy, no anomalous excess in the dark matter direct detection experiments and no dark matter overabundance) are imposed on the neutralino. This enables us to disregard unphysical regions of the parameter space even though the Higgs signal is compatible with the observed excess. The result of our analysis is that there are configurations of the parameter space which can explain the signal strength reported by the ATLAS and CMS collaborations for a Higgs mass within the required range. Should the observed signal strength finally be compatible with Standard Model expectations, it would be difficult to distinguish between the discovery of Standard Model Higgs and a SM-like Higgs from the NMSSM, unless one performs dedicated searches of very light Higgs bosons and possibly investigate peculiar signatures of supersymmetric particles. We also propose a new jets + missing E_T signal for the case where the LSP is a singlino-like neutralino.
We investigate the dynamics of single and multiple scalar fields with exponential potentials, leading to power-law and assisted inflation, in loop quantum cosmology. Unlike in the classical theory, dynamical trajectories in loop quantum cosmology are generically non-singular, with a big bounce replacing classical big bang in the Planck regime. Post bounce, after a phase of super-inflation, dynamical trajectories evolve towards the classical attractor in the inflationary scenarios. Depending on the initial conditions, bounce is shown to occur in kinetic as well as potential dominated regimes. We analyze the number of e-foldings resulting from the phase of super-inflation, and find the dependence of the maximum possible number of e-foldings on the equation of state at the bounce and on the steepness of the potential. We find that if the potential is not steep, this phase can lead to large number of e-foldings in power-law inflation. For the assisted inflation scenario, an increase in the number of fields can yield a significant increase in the number of e-foldings during super-inflation.
We argue that if the UV cutoff of the IR theory is of the order, or below, the scale of the stretched horizon in a black hole background, which in turn is significantly lower than the Planck scale, the black hole radiance is controlled by the UV completion of the field theory. In particular, if the UV completion of the theory involves degrees of freedom which cannot be efficiently emitted by the black hole, the naive radiance rate estimated by the counting of the IR degrees of freedom may be dramatically reduced. If we apply this argument to the RS2 brane world, it implies that the emission rates of the low energy CFT modes will be dramatically suppressed: its UV completion is given by the bulk gravity on $AdS_5 \times S^5$, and the only bulk modes that could be emitted by a black hole are the s-waves of bulk modes with small 4D masses. But their emission is suppressed by bulk warping. This lowers the radiation rate much below the IR estimate, by at least a factor of $N \simeq M_{Pl}^2 L^2$, and follows directly from low CFT cutoff $\mu \sim L^{-1} \ll M_{Pl}$, a large number of modes $N \gg 1$ and the fact that 4D gravity in RS2 is induced, $M_{Pl}^2 \simeq N \mu^2$.
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