We present spatially resolved 3 um spectra of Elias 1 obtained with an adaptive optics system. The central part of the disk is almost devoid of PAH emission at 3.3 um; it shows up only at 30 AU and beyond. The PAH emission extends up to 100 AU, at least to the outer boundary of our observation. The diamond emission, in contrast, is more centrally concentrated, with the column density peaked around 30 AU from the star. There are only three Herbig Ae/Be stars known to date that show diamond emission at 3.53 um. Two of them have low-mass companions likely responsible for the large X-ray flares observed toward the Herbig Ae/Be stars. We speculate on the origin of diamonds in circumstellar disks in terms of the graphitic material being transformed into diamond under the irradiation of highly energetic particles.
A primordial magnetic field (PMF) can affect the evolution of density field fluctuations in the early universe.In this paper we constrain the PMF amplitude $B_\lambda$ and power spectral index $n_\mathrm{B}$ by comparing calculated density field fluctuations with observational data, i.e. the number density fluctuation of galaxies.We show that the observational constraints on cosmological density fluctuations, as parameterized by $\sigma_8$, lead to strong constraints on the amplitude and spectral index of the PMF.
The cosmological background of ionizing radiation has been dominated by quasars once the Universe aged by ~2 billion years. At earlier times (redshifts z>3), the observed abundance of bright quasars declined sharply, implying that cosmic hydrogen was reionized by stars instead. Here, we explain the physical origin of the transition between the dominance of stars and quasars as a generic feature of structure formation in the concordance LCDM cosmology. At early times, the fraction of baryons in galaxies grows faster than the maximum (Eddington-limited) growth rate possible for quasars. As a result, quasars were not able to catch up with the rapid early growth of stellar mass in their host galaxies.
We present results from the first high-resolution hydrodynamical simulations of non-Gaussian cosmological models. We focus on the statistical properties of the transmitted Lyman-alpha flux in the high redshift intergalactic medium. Imprints of non-Gaussianity are present and are larger at high redshifts. Differences larger than 20 % at z>3 in the flux probability distribution function for high transmissivity regions (voids) are expected for values of the non linearity parameter f_NL=\pm 100 when compared to a standard LCDM cosmology with f_NL=0. We investigate also the one-dimensional flux bispectrum: at the largest scales (corresponding to tens of Mpc) we expect deviations in the flux bispectrum up to 20% at z~4 (for f_NL=\pm 100), significantly larger than deviations of ~ 3% in the flux power spectrum. We briefly discuss possible systematic errors that can contaminate the signal. Although challenging, a detection of non-Gaussianities in the interesting regime of scales and redshifts probed by the Lyman-alpha forest, could be possible with future data sets.
Early-type dwarf galaxies are the most common type of galaxies observed in the Universe. The origin of this kind of systems is still not well understood. The aim of this paper is to investigate whether the different locations of dwarf galaxies with respect to ellipticals in the face-on view of the fundamental plane could be due to the transformation of bright disc galaxies in low-mass systems by harassment. We have run high-resolution N-body numerical simulations to test the tidal stripping scenario of the dE galaxies. The present simulations modelled several individual tidal stripping events on initial disc-like galaxy models with different bulge-to-disc mass ratios. Tidal stripping is a very efficient mechanism for removing stars and dark matter particles from galaxies. The particles of the disc and halo components were easily stripped, while the bulge not. Thus, the scale length of the discs were 40-50% shorter than the initial ones. Prograde tidal interactions create tidal features like stable bars in the discs of the galaxies. After several tidal interactions the galaxy remnants looks like a dwarf spheroidal system. Simulated galaxies with initial large B/D ratios are closer to the face-on view of the fundamental plane defined by bright E and bulges of early-type galaxies. Nevertheless, galaxies with initial small B/D ratio are located, after four fast tidal encounters, at the position of dE galaxies in the face-on view of the fundamental plane. We conclude that fast galaxy-galaxy interactions are efficient mechanisms for transforming bright galaxies in dwarf ones. Indeed, the different location observed between Es and dEs in the face-on view of the fundamental plane can be explained by the formation of dwarf galaxies by harassment of late-type bright ones.
There has been much interest in possible violations of Lorentz invariance, particularly motivated by quantum gravity theories. It has been suggested that a small amount of Lorentz invariance violation (LIV) could turn off photomeson interactions of ultrahigh energy cosmic rays (UHECRs) with photons of the cosmic background radiation and thereby eliminate the resulting sharp steepening in the spectrum of the highest energy CRs predicted by Greisen Zatsepin and Kuzmin (GZK). Recent measurements of the UHECR spectrum reported by the HiRes and Auger collaborations, however, indicate the presence of the GZK effect. We present the results of a detailed calculation of the modification of the UHECR spectrum caused by LIV using the formalism of Coleman and Glashow. We then compare these results with the experimental UHECR data from Auger and HiRes. We find an upper limit on the amount of LIV of $5 \times 10^{-23}$. Within that limit we discuss how a small amount of LIV that is consistent with the experimental data can still lead to a recovery of the cosmic ray flux at higher energies than presently observed.
We present the CFHTLS-Archive-Research Survey (CARS). It is a virtual multi-colour survey based on public archive images from the CFHT-Legacy-Survey. Our main scientific interests in CARS are optical searches for galaxy clusters from low to high redshift and their subsequent study with photometric and weak-gravitational lensing techniques. As a first step of the project we present multi-colour catalogues from 37 sq. degrees of the CFHTLS-Wide component. Our aims are to create astrometrically and photometrically well calibrated co-added images. Second goal are five-band (u*, g', r', i', z') multi-band catalogues with an emphasis on reliable estimates for object colours. These are subsequently used for photometric redshift estimates. The article explains in detail data processing, multi-colour catalogue creation and photometric redshift estimation. Furthermore we apply a novel technique, based on studies of the angular galaxy cross-correlation function, to quantify the reliability of photo-z's. The accuracy of our high-confidence photo-z sample (10-15 galaxies per sq. arcmin) is estimated to $\sigma_{\Delta_z/(1+z)}\approx 0.04-0.05$ up to i'<24 with typically only 1-3% outliers. Interested users can obtain access to our data by request to the authors.
New, more detailed calculations of the emission spectra of the He-like K ALPHA complex of calcium, iron and nickel have been carried out using data from both distorted-wave and R-matrix calculations. The value of the GD ratio (an extended definition of the G ratio that accounts for the effect of resolved and unresolved satellite lines) is significantly enhanced at temperatures below the temperature of He-like maximum abundance. Furthermore it is shown that satellite lines are important contributors to the GD ratio such that GD/G>1 at temperatures well above the temperature of maximum abundance. These new calculations demonstrate, with an improved treatment of the KLn (n>=3) satellite lines, that K ALPHA satellite lines need to be included in models of He like spectra even at relatively high temperatures. The excellent agreement between spectra and line ratios calculated from R-matrix and distorted-wave data also confirms the validity of models based on distorted-wave data for highly charged systems, provided the effect of resonances are taken into account as independent processes.
We report on the results of a Markov Chain Monte Carlo (MCMC) analysis of an inverse power law (IPL) quintessence model using the Dark Energy Task Force (DETF) simulated data sets as a representation of future dark energy experiments. We generate simulated data sets for a Lambda-CDM background cosmology as well as a case where the dark energy is provided by a specific IPL fiducial model and present our results in the form of likelihood contours generated by these two background cosmologies. We find that the relative constraining power of the various DETF data sets on the IPL model parameters is broadly equivalent to the DETF results for the w_{0}-w_{a} parameterization of dark energy. Finally, we gauge the power of DETF "Stage 4" data by demonstrating a specific IPL model which, if realized in the universe, would allow Stage 4 data to exclude a cosmological constant at better than the 3-sigma level.
The time-scales of chemical enrichment are fundamental to understand the evolution of abundances and abundance ratios in galaxies. In particular, the time-scales for the enrichment by SNe II and SNe Ia are crucial in interpreting the evolution of abundance ratios such as [alpha/Fe]. In fact, the alpha-elements are produced mainly by SNe II on time-scales of the order of 3 to 30 Myr, whereas the Fe is mainly produced by SNe Ia on a larger range of time-scales, going from 30 Myr to a Hubble time. This produces differences in the [alpha/Fe] ratios at high and low redshift and it is known as "time-delay" model. In this talk we review the most common progenitor models for SNe Ia and the derived rates together with the effect of the star formation history on the [alpha/Fe] versus [Fe/H] diagram in the Galaxy. From these diagrams we can derive the timescale for the formation of the inner halo (roughly 2 Gyr), the timescale for the formation of the local disk (roughly 7-8 Gyr) as well the time-scales for the formation of the whole disk. These are functions of the galactocentric distance and vary from 2-3 Gyr in the inner disk up to a Hubble time in the outer disk (inside-out formation). Finally, the timescale for the formation of the bulge is found to be no longer than 0.3 Gyr, similar to the timescale for the formation of larger spheroids such as elliptical galaxies. We show the time-delay model applied to galaxies of different morphological type, identified by different star formation histories, and how it constrains differing galaxy formation models.
The sensitivity and astrometry upgrade ASTRA of the Keck Interferometer is introduced. After a brief overview of the underlying interferometric principles, the technology and concepts of the upgrade are presented. The interferometric dual-field technology of ASTRA will provide the KI with the means to observe two objects simultaneously, and measure the distance between them with a precision eventually better than 100 uas. This astrometric functionality of ASTRA will add a unique observing tool to fields of astrophysical research as diverse as exo-planetary kinematics, binary astrometry, and the investigation of stars accelerated by the massive black hole in the center of the Milky Way as discussed in this contribution.
Six hot topics in modern planetary astronomy are described: 1) lightcurves and densities of small bodies 2) colors of Kuiper belt objects and the distribution of the ultrared matter 3) spectroscopy and the crystallinity of ice in the outer Solar system 4) irregular satellites of the giant planets 5) the Main Belt Comets and 6) comets and meteor stream parents.
We discuss flaring variability of radio emission of microquasars, measured in monitoring programs with the RATAN-600 radio telescope. We carried out a multi-frequency (1-30 GHz) daily monitoring of the radio flux variability of the microquasars SS433, GRS1915+105, and Cyg X-3 during the recent sets in 2005-2007. A lot of bright short-time flares were detected from GRS 1915+105 and they could be associated with active X-ray events. In January 2006 we detected a drop down of the quiescent fluxes from Cyg X-3 (from 100 to $\sim$20 mJy), then the 1 Jy-flare was detected on 2 February 2006 after 18 days of quenched radio emission. The daily spectra of the flare in the maximum were flat from 2 to 110 GHz, using the quasi-simultaneous observations at 110 GHz with the RT45m telescope and the NMA millimeter array of NRO in Japan. Several bright radio flaring events (1-15 Jy) followed during the continuing state of very variable and intensive 1-12 keV X-ray emission ($\sim$0.5 Crab), which was monitored in the RXTE ASM program. Swift/BAT ASM hard X-ray fluxes correlated strongly with flaring radio data. The various spectral and temporal characteristics of the light curves from the microquasars could be determined from such comparison. We conclude that monitoring of the flaring radio emission is a good tracer of jet activity X-ray binaries.
Ways to give medium- and short-term predictions of solar flares are proposed according to the statistical analysis of events during solar cycle 23. On one hand, the time distribution of both C and M class flares shows two main periods of 13.2 and 26.4 months in this cycle by wavelet analysis. On the other hand, active regions of specific magnetic configurations and their evolutions give high productivity of C class flares but relatively low productivity of energetic (M and X class) flares. Furthermore, by considering the measurable kinetic features of active regions, i.e., the rotation of the sunspots, some active regions of specified types are observed to have high energetic flare productivity, above 66%. The periodicity of the activity revealed can be used for medium-term C and M class flare forecasting and the high productivity of active regions forms the basis for short-term prediction of individual energetic flares.
The third INTEGRAL/IBIS survey has revealed several new hard X-ray sources, which are still unclassified. To identify these sources, we need to find their counterparts at other wavelengths and then study their nature. The capability of XRT on board Swift to localize the sources with a positional accuracy of few arcseconds allows the search for optical/UV, infrared and radio counterparts to be more efficient and reliable. We analysed all XRT observations available for three unidentified INTEGRAL sources, IGR J18249-3243, IGR J19443+2117 and IGR J22292+6647, localized their soft X-ray counterparts and searched for associations with objects in the radio band. We also combined X-/gamma-ray data, as well as all the available radio, infrared and optical/UV information, in order to provide a broad-band spectral characterization of each source and investigate its nature. All three sources are found to be bright and repeatedly observed radio objects, although poorly studied. The X-/gamma-ray spectrum of each source is well described by power laws with photon indices typical of AGN; only IGR J19443+2117 may have absorption in excess of the Galactic value, while IGR J22292+6647 is certainly variable at X-ray energies. IGR J18249-3243 has a complex radio morphology and a steep radio spectrum; the other two sources show flatter radio spectra and a more compact morphology. Overall, their radio, optical/UV and infrared characteristics, as well as their X-/gamma-ray properties, point to an AGN classification for all three objects.
A number of important processes taking place around strong shocks in supernova remnants (SNRs) depend on the shock obliquity. The measured synchrotron flux is a function of the aspect angle between interstellar magnetic field (ISMF) and the line of sight. Thus a model of non-thermal emission from SNRs should account for the orientation of the ambient magnetic field. We develop a new method for the estimation of the aspect angle, based on the comparison between observed and synthesized radio maps of SNRs, making different assumptions about the dependence of electron injection efficiency on the shock obliquity. The method uses the azimuthal profile of radio surface brightness as a probe for orientation of ambient magnetic field because it is almost insensitive to the downstream distribution of magnetic field and emitting electrons. We apply our method to a new radio image of SN 1006 produced on the basis of archival VLA and Parkes data. The image recovers emission from all spatial structures with angular scales from few arcseconds to 15 arcmin. We explore different models of injection efficiency and find the following best-fitting values for the aspect angle of SN 1006: phi=70 +/- 4.2 deg if the injection is isotropic, phi=64 +/- 2.8 deg for quasi-perpendicular injection (SNR has an equatorial belt in both cases) and phi=11 +/- 0.8 deg for quasi-parallel injection (polar-cap model of SNR). In the last case, SN 1006 is expected to have a centrally-peaked morphology contrary to what is observed. Therefore, our analysis provides some indication against the quasi-parallel injection model.
We analyse two-dimensional near-IR K-band spectra from the inner 660x315 pc^2 of the Seyfert galaxy NGC7582 obtained with the Gemini GNIRS IFU. The nucleus harbors an unresolved source well reproduced by a blackbody of temperature T 1050 K, which we attribute to emission by circumnuclear dust located closer than 25 pc from the nucleus, with total mass of ~3x10^{-3}M_Sun. Surrounding the nucleus, we observe a ring of active star formation with radius of ~190 pc, an age of ~5 Myr. The radiation of the young stars in the ring accounts for at least 80 % of the ionization observed in the Brgamma emitting gas, the remaining being due to radiation emitted by the active nucleus. The stellar kinematics reveals: (1) a distorted rotation pattern in the radial velocity field with kinematic center apparently displaced from the nuclear source by a few tens of parsecs; (2) a high velocity dispersion in the bulge of sigma=170 km/s; (3) a partial ring of sigma=50 km/s interpreted as due to stars formed from cold gas in a previous burst of star formation. The kinematics of the ionized gas shows an additional blueshifted component with velocities > 100 km/s interpreted as due to an outflow along the ionization cone. The mass outflow rate in the ionized gas was estimated as ~0.05 M_Sun/yr, which is one order of magnitude larger than the accretion rate to the AGN. The flux distribution and kinematics of the hot molecular gas, traced by the H2l2.22um emission line, suggests that most of this gas is in the galactic plane. An excess blueshift along PA~-70 can be interpreted as an inflow towards the nucleus. An AGN-Starburst connection in the nucleus of NGC7582 is supported by the ratio between the mass accretion rate and the star formation rate in the circumnuclear region of ~0.26%, which is close to the Magorrian relation.
We present first results of a study of the halo kinematics for a sample of early type galaxies using planetary nebulae (PNe) as kinematical tracers. PNe allow to extend up to several effective radii (Re) the information from absorption line kinematics (confined to within 1 or 2 Re), providing valuable information and constraints for merger simulations and galaxy formation models. We find that the specific angular momentum per unit mass has a more complex radial dependence when the halo region is taken into account and that the halo velocity dispersion is related to the total galaxy luminosity, isophotal shape, and number of PNe per unit of luminosity
The Faulkes Telescope Project is an educational and research arm of the Las
Cumbres Observatory Global Telescope Network (LCOGTN). It has two 2-metre
robotic telescopes, located at Haleakala on Maui (FT North) and Siding Spring
in Australia (FT South). It is planned for these telescopes to be complemented
by a research network of eighteen 1-metre telescopes, along with an educational
network of twenty-eight 0.4-metre telescopes, providing 24 hour coverage of
both northern and southern hemispheres.
We have been conducting a monitoring project of 13 low-mass X-ray binaries
(LMXBs) using FT North since early 2006. The introduction of FT South has
allowed us to extend this to monitor a total of 30 LMXBs. New instrumentation
will allow us to expand this project to include both infrared wavelengths (z
and y band) and spectroscopy. Brighter targets (~ 16 - 18 mag.) are imaged
weekly in V, R and i' band (SNR ~ 50), while fainter ones (> 18 mag.) are
observed only in i' band (SNR ~ 20). We alter this cadence in response to our
own analysis or Astronomers Telegrams (ATels).
Starting from a few topical astrophysical questions which require the knowledge of the age of Pop I stars, we discuss the needed precision on the age in order to make progresses in these areas of research. Then we review the effects of various inputs of the stellar models on the age determination and try to identify those affecting the most the lifetimes of stars.
We present local numerical models of accretion disk turbulence driven by the magnetorotational instability with varying shear rate. The resulting turbulent stresses are compared with predictions of a closure model in which triple correlations are modelled in terms of quadratic correlations. This local model uses five nondimensional parameters to describe the properties of the flow. We attempt to determine these closure parameters for our simulations and find that the model does produce qualitatively correct behaviour. In addition, we present results concerning the shear rate dependency of the magnetic to kinetic energy ratio. We find both the turbulent stress ratio and the total stress to be strongly dependent on the shear rate.
Gaia is a satellite mission of the ESA, aiming at absolute astrometric measurements of about one billion stars (all stars down to 20th magnitude, with unprecedented accuracy. Additionally, magnitudes and colors will be obtained for all these stars, while radial-velocities and spectral properties will be determined only for bright objects (V<17.5). At 15th magnitude Gaia aims at an angular accuracy of 20 microarcseconds (muas). This goal can only be reached if the geometry of the telescopes, the detectors, and the pointing of Gaia at each moment ("attitude") can be inferred from the Gaia measurements itself with muas accuracy.
In 2005 February we observed Cygnus X-1 over a period of 10 days quasi-continuously with the Rossi X-ray Timing Explorer and the Ryle telescope. We present the results of the spectral and timing analysis on a timescale of 90 min and show that the behavior of Cyg X-1 is similar to that found during our years long monitoring campaign. As a highlight we present evidence for a full transition from the hard to the soft state that happened during less than three hours. The observation provided a more complete picture of a state transition than before, especially concerning the evolution of the time lags, due to unique transition coverage and analysis with high time resolution.
We study the evolution of the low-order moments of the galaxy overdensity distribution over the redshift interval 0.7<z<1.5. We find that the variance and the normalized skewness evolve over this redshift interval in a way that is remarkably consistent with predictions of first- and second-order perturbation theory. This finding confirms the standard gravitational instability paradigm over nearly 9 Gyrs of cosmic time and demonstrates the importance of accounting for the non-linear component of galaxy biasing to avoid disagreement between theory and observations.
The ARENA08 conference, held in Rome in June 2008, gave an almost complete overview on applications of the new techniques radio and acoustic detection of electromagnetic showers generated by high-energy cosmic particles in air or in dielectric media. There are vast activities all over the world, and the progress is remarkable. This was displayed by more than 30 contributions to the conference related to the radio detection technique, only. This paper gives a short summary on the status of 'radio detection of particles from the cosmos' as presented at the conference.
Observations are inconsistent with a homogeneous and isotropic universe with ordinary matter and gravity. The universe is far from exact homogeneity and isotropy at late times, and the effect of the non-linear structures has to be quantified before concluding that new physics is needed. We explain how structure formation can lead to accelerated expansion, and discuss a semi-realistic model where the timescale of the change in the expansion rate emerges from the physics of structure formation.
In the general matter composition where the multiple scalar fields and the multiple perfect fluids coexist, in the leading order of the gradient expansion, we construct all of the solutions of the nonlinear evolutions of the locally homogeneous universe. From the momentum constraint, we derive the constraints which the solution constants of the locally homogeneous universe must satisfy. We construct the gauge invariant perturbation variables in the arbitrarily higher order nonlinear cosmological perturbation theory around the spatially flat Friedmann-Robertson-Walker universe. We construct the nonlinear long wavelength limit formula representing the long wavelength limit of the evolution of the nonlinear gauge invariant perturbation variables in terms of perturbations of the evolutions of the locally homogeneous universe. By using the long wavelength limit formula, we investigate the evolution of nonlinear cosmological perturbations in the universe dominated by the multiple slow rolling scalar fields with an arbitrary potential. The tau function and the N potential introduced in this paper make it possible to write the evolution of the multiple slow rolling scalar fields with an arbitrary interaction potential and the arbitrarily higher order nonlinear Bardeen parameter at the end of the slow rolling phase analytically. It is shown that the nonlinear parameters such as fNL and gNL are suppressed by the slow rolling expansion parameters.
We model the cosmic medium as the mixture of a generalized Chaplygin gas and a pressureless matter component. Within a neo-Newtonian approach we compute the matter power spectrum. The 2dFGRS data are used to discriminate between unified models of the dark sector and different models, for which there is separate dark matter, in addition to that accounted for by the generalized Chaplygin gas. Leaving the corresponding density parameters free, we find that the unified models are strongly disfavored. On the other hand, using unified model priors, the observational data are also well described, in particular for small and large values of the generalized Chaplygin gas parameter $\alpha$.
Several Wide Field of view Adaptive Optics (WFAO) concepts like Multi-Conjugate AO (MCAO), Multi-Object AO (MOAO) or Ground-Layer AO (GLAO) are currently studied for the next generation of Extremely Large Telescopes (ELTs). All these concepts will use atmospheric tomography to reconstruct the turbulent phase volume. In this paper, we explore different reconstruction algorithms and their fundamental limitations. We conduct this analysis in the Fourier domain. This approach allows us to derive simple analytical formulations for the different configurations, and brings a comprehensive view of WFAO limitations. We then investigate model and statistical errors and their impact on the phase reconstruction. Finally, we show some examples of different WFAO systems and their expected performance on a 42m telescope case.
In this Paper we analyze the mid-infrared (mid-IR) emission of very small dust particles in a sample of 12 protoplanetary disks to see how they are connected to interstellar dust particles and to investigate the possibility that their emission can be used as a probe of the physical conditions and evolution of the disk. We define a basis made of three mid-IR template spectra PAH$^0$, PAH$^+$ and VSGs that were derived from the analysis of reflection nebulae, and an additional PAH$^x$ spectrum that was introduced by Joblin et al. (2008) for the analysis of the spectra of planetary nebulae. From the optimization of the fit of 12 star+disk spectra, using a linear combination of the 4 template spectra, we found that an additional small grain component with a broad feature at 8.3 $\mu$m is needed. We find that the fraction of VSG emission in disks decreases with increasing stellar temperature. VSGs appear to be destroyed by UV photons at the surface of disks, thus releasing free PAH molecules, which are eventually ionized as it is observed in photodissociation regions. On the opposite, we observe that the fraction of PAH$^x$ increases with increasing star temperature except in the case of B stars where they are absent. We argue that this is compatible with the identification of PAH$^x$ as large ionized PAHs, most likely emitting in regions of the disk that are close to the star. Finally, we provide a UV-dependant scheme to explain the evolution of PAHs and VSGs in protoplanetary disks. We show that A stars modify the size spectrum of PAHs and VSGs in favor of large PAHs while B stars destroy even the largest PAHs up to large radii in the disk. These results allow us to put new constrains on the properties of two sources: IRS 48 and "Gomez's Hamburger" which are poorly characterized.
The unified method for total electron-ion recombination is extended to study the dielectronic satellite (DES) lines. These lines, formed from radiative decay of autoionizing states, are highly sensitive temperature diagnostics of astrophysical and laboratory plasma sources. The computation of the unified recombination rates is based on the relativistic Breit-Pauli R-matrix method and close coupling approximation. Extending the theoretical formulation developed earlier we present recombination rate coefficients for the 22 satellite lines of KLL complexes of helium-like Fe XXV and Ni XXVII. The isolated resonance approximation, commonly used throughout plasma modeling, treats these resonances essentially as bound features except for dielectronic capture into, and autoionization out of, these levels. A line profile or cross section shape is often assumed. On the other hand, by including the coupling between the autoionizing and continuum channels, the unified method gives the intrinsic spectrum of DES lines which includes not only the energies and strengths, but also the natural line or cross section shapes. A formulation is presented to derive autoionization rates from unified resonance strengths and enable correspondence with the isolated resonance approximation. While the rates compare very well with existing rates for the strong lines to <20%, the differences for weaker DES lines are larger. We also illustrate the application of the present results to the analysis of K ALPHA complexes observed in high-temperature X-ray emission spectra of Fe XXV and Ni XXVII. There are considerable differences with previous results in the total KLL intensity for Fe XXV at temperatures below the temperature of maximum abundance in coronal equilibrium. (Abbreviated Abstract)
A Dyson Sphere is a hypothetical construct of a star purposely cloaked by a thick swarm of broken-up planetary material to better utilize all of the stellar energy. A clean Dyson Sphere identification would give a significant signature for intelligence at work. A search for Dyson Spheres has been carried out using the 250,000 source database of the IRAS infrared satellite which covered 96% of the sky. The search has used the Calgary data collection of the IRAS Low Resolution Spectrometer (LRS) to look for fits to blackbody spectra. Searches have been conducted for both pure (fully cloaked) and partial Dyson Spheres in the blackbody temperature region 100 < T < 600 deg K. Other stellar signatures that resemble a Dyson Sphere are reviewed. When these signatures are used to eliminate sources that mimic Dyson Spheres very few candidates remain and even these are ambiguous. Upper limits are presented for both pure and partial Dyson Spheres. The sensitivity of the LRS was enough to find solar-sized Dyson Spheres out to 300 pc, a reach that encompasses a million solar- type stars.
In this poster contribution we highlight the equivalence between an Imaging Air Cherenkov Telescope (IACT) array and an Intensity Interferometer for a range of technical requirements. We touch on the differences between a Michelson and an Intensity Interferometer and give a brief overview of the current IACT arrays, their upgrades and next generation concepts (CTA, AGIS, completion 2015). The latter are foreseen to include 30-90 telescopes that will provide 400-4000 different baselines that range in length between 50m and a kilometre. Intensity interferometry with such arrays of telescopes attains 50 micro-arcseconds resolution for a limiting V magnitude of ~8.5. This technique opens the possibility of a wide range of studies, amongst others, probing the stellar surface activity and the dynamic AU scale circumstellar environment of stars in various crucial evolutionary stages. Here we discuss possibilities for using IACT arrays as optical Intensity Interferometers.
The kinematic approach to cosmological tests provides a direct evidence to the present accelerating stage of the universe which does not depend on the validity of general relativity, as well as on the matter-energy content of the Universe. In this context, we consider here a linear two-parameter expansion for the decelerating parameter, $q(z)=q_0+q_1z$, where $q_0$ and $q_1$ are arbitrary constants to be constrained by the Union supernovae data. By assuming a flat Universe we find that the best fit to the pair of free parameters is ($q_0,q_1$) = ($-0.73,1.5)$ whereas the transition redshift is $z_t = 0.49^{+0.14}_{-0.07}$ ($1\sigma$) $^{+0.54}_{-0.12}$ ($2\sigma$). This kinematic result is in agreement with some independent analyzes and accommodates more easily many dynamical flat models (like $\Lambda$CDM).
In this talk we review existing cosmological and astrophysical bounds on light (with the mass in keV - MeV range) and super-weakly interacting dark matter candidates. A particular attention is paid to the sterile neutrino DM candidate.
The combination of two-dimensional kinematics and gravitational lens modelling permits detailed reconstruction of the phase-space structure of early-type galaxies and sets constraints on the dark-matter distribution in their inner regions. We describe a project which combines integral-field spectroscopy from an ESO Large Programme using VIMOS on the VLT with deep HST ACS and NICMOS images to study a sample of 17 early-type lens galaxies at redshifts between 0.1 and 0.3, drawn from the Sloan Lens ACS survey (SLACS).
We present a study of accurate stellar parameters and iron abundances for 39 giants and 16 dwarfs in the 13 open clusters IC2714, IC4651, IC4756, NGC2360, NGC2423, NGC2447 (M93), NGC2539, NGC2682 (M67), NGC3114, NGC3680, NGC4349, NGC5822, NGC6633. The analysis was done using a set of high-resolution and high-S/N spectra obtained with the UVES spectrograph (VLT). These clusters are currently being searched for planets using precise radial velocities. For all the clusters, the derived average metallicities are close to solar. Interestingly, the values derived seem to depend on the line-list used. This dependence and its implications for the study of chemical abundances in giants stars are discussed. We show that a careful choice of the lines may be crucial for the derivation of metallicities for giant stars on the same metallicity scale as those derived for dwarfs. Finally, we discuss the implications of the derived abundances for the metallicity- and mass-giant planet correlation. We conclude that a good knowledge of the two parameters is necessary to correctly disentangle their influence on the formation of giant planets.
We describe a Windows compatible version of the evolutionary synthesis code Starburst99. Starburst99 for Windows was developed from the public UNIX based version at STScI. We converted the original Fortran77 source code into a version for a Win32 environment with an Absoft Fortran Pro x86 compiler. Extensive testing showed no significant numerical differences in comparison with the previous UNIX version. The software application consists of the source code, executable, and a number of auxiliary files. The package installs on any PC running Windows 2000, XP, or Vista and can be obtained as freeware at this http URL We give an overview of the different running modes and provide instructions for getting started with the initial set-up.
Images obtained with the CTIO 4-m telescope and the MOSAIC-2 wide field
camera in [O III] 5007 and H\alpha on-band and off-band filters are analyzed to
search for emission lines objects in the galaxy NGC 6822. In particular we
search for PN candidates. In addition, data of a sub-sample of objects obtained
with ESO VLT-FORS2 are used to calibrate the MOSAIC imaging. A large number of
line emission regions were detected, for which we measured instrumental
magnitudes in all the filters. Based on some criteria to distinguish between
PNe and compact HII regions, we found 26 PN candidates, increasing the known
sample in 8 objects. Also we detected a number of compact HII regions and 20
stellar objects emitting in Halpha. For all the objects we present coordinates,
instrumental magnitudes and nebular [O III] and Halpha+[N II] fluxes. The
observed PNLF for the PN [O III] 5007 magnitudes and the cumulative PNLF were
calculated. We confirm that the PNLF presents a dip similar to the one detected
for the SMC at 2.5 mag down the maximum. The cumulative PNLF returns a value
M^\star_{5007}=-3.71^{+0.21}_{-0.42} for the peak absolute magnitude of the
PNLF which is faint compared to the value expected for galaxies with
metallicity similar to the one of NGC 6822 but similar within uncertainties.
From our best fit to the observed PNLF we obtained a rough distance modulus
m-M = 23.64 ^{+0.23}_{-0.43} mag, which agrees within uncertainties with recent
values reported in the literature. The number of PN in the brightest 0.5 mag
normalized to the galactic bolometric luminosity, alpha_{0.5} was estimated to
be (3.8^{+0.90}_{-0.71}) E-9, which is similar to the values derived for
galaxies with recent star formation and small galaxies (M_B fainter than - 18
mag).
This meeting is entitled "A Century of Cosmology." But most of the papers
being given here are based on work done very recently and there is really no
attempt being made to critically review what has taken place in the last 90 or
100 years. Instead, in general the participants accept without question that
cosmology equates to "hot big bang cosmology" with all of its bells and
whistles. All of the theory and the results obtained from observations are
interpreted on the assumption that this extremely popular model is the correct
one, and observers feel that they have to interpret its results in terms of
what this theory allows. No one is attempting to seriously test the model with
a view to accepting it or ruling it out. They are aware, as are the theorists,
that there are enough free parameters available to fix up almost any model of
the type.
The current scheme given in detail for example by Spergel et al (206, 2007)
demonstrates this. How we got to this stage is never discussed, and little or
no attention is paid to the observations obtained since the 1960s on activity
in the centers of galaxies and what they imply. We shall show that they are an
integral part of a realistic cosmological model. In this paper I shall take a
different approach, showing first how cosmological ideas have developed over
the last 90 years and where mistakes have been made. I shall conclude with a
realistic model in which all of the observational material is included, and
compare it with the popular model. Not surprisingly I shall show that there
remain many unsolved problems, and previously unexpected observations, most of
which are ignored or neglected by current observers and theorists, who believe
that the hot big bang model must be correct.
Signatures of warm absorbers are seen in soft X-ray spectra of about half of all Seyfert1 galaxies observed and in some quasars and blazars. We use the thermal equilibrium curve to study the influence of the shape of the ionizing continuum, density and the chemical composition of the absorbing gas on the existence and nature of the warm absorbers. We describe circumstances in which a stable warm absorber can exist as a multiphase medium or one with continuous variation in pressure. In particular we find the following results: i) the warm absorber exists only if the spectral index of the X-ray power-law ionizing continuum $\alpha > 0.2$ and has a multiphase nature if $\alpha \sim 0.8$, which interestingly is the spectral index for most of the observed Seyfert 1 galaxies; ii) thermal and ionization states of highly dense warm absorbers are sensitive to their density if the ionizing continuum is sufficiently soft, i.e. dominated by the ultraviolet iii) absorbing gas with super Solar metallicity is more likely to have a multiphase nature; iv) the nature of the warm absorber is significantly influenced by the absence of iron and associated elements which are produced in the later stages of star formation history in supernovae of type Ia.
The magnetic field pervading our Galaxy is a crucial constituent of the interstellar medium: it mediates the dynamics of interstellar clouds, the energy density of cosmic rays, and the formation of stars. The field associated with ionized interstellar gas has been determined through observations of pulsars in our Galaxy. Radio-frequency measurements of pulse dispersion and the rotation of the plane of linear polarization, i.e., Faraday rotation, yield an average value B ~ 3 microGauss. The possible detection of Faraday rotation of linearly polarized photons emitted by high-redshift quasars suggests similar magnetic fields are present in foreground galaxies with redshifts z > 1. As Faraday rotation alone, however, determines neither the magnitude nor the redshift of the magnetic field, the strength of galactic magnetic fields at redshifts z > 0 remains uncertain. Here we report a measurement of a magnetic field of B ~ 84 microGauss in a galaxy at z =0.692, using the same Zeeman-splitting technique that revealed an average value of B = 6 microGauss in the neutral interstellar gas of our Galaxy. This is unexpected, as the leading theory of magnetic field generation, the mean-field dynamo model, predicts large-scale magnetic fields to be weaker in the past rather than stronger.
I present a class of objects called gravitational strings (GS) for their similarity to the conventional cosmic strings: even though the former are just singularities in flat spacetime, both varieties are equally "realistic", they may play equally important cosmological r\^ole and their lensing properties are akin. I argue that the enigmatic object CSL-1 is an evidence in favor of the existence of GS.
Despite the recent advances in graphics hardware capabilities, a brute force approach is incapable of interactively displaying terabytes of data. We have implemented a system that uses hierarchical level-of-detailing for the results of cosmological simulations, in order to display visually accurate results without loading in the full dataset (containing over 10 billion points). The guiding principle of the program is that the user should not be able to distinguish what they are seeing from a full rendering of the original data. Furthermore, by using a tree-based system for levels of detail, the size of the underlying data is limited only by the capacity of the IO system containing it.
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Our goal is to study the existing star formation rate calibrations based on emission-line luminosities and to provide new ones. We use the SDSS data release DR4, which gives star formation rates and emission-line luminosities of more than 100000 star-forming galaxies. We confirm that the best results are obtained with the Halpha calibration. This calibration has an uncertainty of 0.17 dex. We show that one has to check carefully the method used to derive the dust attenuation and to use the adequate calibration: in some cases, the standard scaling law has to be replaced by a more general power law. When data is corrected for dust attenuation but the Halpha emission line not observed, the use of the Hbeta emission line, has to be preferred to the [OII]3727 emission line. In the case of uncorrected data, the correction for dust attenuation can be assumed as a constant value but we show that such method leads to poor results, in terms of dispersion and residual slope. Self-consistent corrections, based e.g. on the absolute magnitude, give better results in terms of dispersion but still suffer from systematic shifts, and/or residual slopes. The best results with data not corrected for dust attenuation are obtained when using the observed [OII]3727 and Hbeta emission lines together. This calibration has an uncertainty of 0.23 dex.
Standard solar models (SSM) are facing nowadays a new puzzle: the solar composition problem. New determinations of solar metal abundances lead SSM calculations to conflict with helioseismological measurements, showing discrepancies that extend from the convection zone to the solar core and can not be easily assigned to deficiencies in the modelling of the solar convection zone. We present updated solar neutrino fluxes and uncertainties for two SSM with high (old) and low (new) solar metallicity determinations. The uncertainties in iron and carbon abundances are the largest contribution to the uncertainties of the solar neutrino fluxes. The uncertainty on the ^14N+p -> ^15O+g rate is the largest of the non-composition uncertainties to the CNO neutrino fluxes. We propose an independent method to help identify which SSM is the correct one. Present neutrino data can not distinguish the solar neutrino predictions of both models but ongoing measurements can help to solve the puzzle.
The hierarchical growth of dark matter haloes, in which galaxies are hosted, has been studied and modeled using various approaches. In this paper we use a modified version the Sheth & Lemson algorithm for a $\mathrm{\Lambda CDM}$ power spectrum, and model the growth of a Milky-Way-size halo with microsolar mass resolution, corresponding to the Jeans mass for a dark matter Weakly Interacting Massive Particle with $m_{\rm DM}$=100GeV. We then compute the unevolved subhalo mass function and build-up a Milky-Way halo placing and evolving its satellites. This subhalo population is used to study the $\gamma$-ray emission from dark matter particles annihilation. In this case, the subhaloes which populate the host halo have been computed considering only progenitor haloes accreted by the main branch of the tree. Each subhalo will host at the present-time sub-subhaloes accreted when it was an isolated system. In order to compute the sub-subhalo population of a Milky-Way dwarf galaxy, like Draco, and to study its $\gamma$-ray emission, we first estimate the Draco virial mass at merging redshift $z_m$ and then we run the merger tree from $z_m$ following the halo down to the dark matter Jeans mass. We then study the effect on the Fermi-LAT (GLAST) detectability for both subhaloes in the Milky-Way and in Draco, and we show how subhaloes cannot be responsible for the boost factor needed for detection.
The extremely red colors of some transneptunian objects and Centaurs are not seen among the Jupiter family comets which supposedly derive from them. Could this mismatch result from sublimation loss of colorless ice? Radiative transfer models show that mixtures of volatile ice and nonvolatile organics could be extremely red, but become progressively darker and less red as the ice sublimates away.
A candidate < 3 Jupiter mass, extrasolar planet was recently imaged by Kalas et al. (2008) using HST/ACS at 12.7" (96 AU) separation from the nearby (d = 7.7 pc) young (~200 Myr) A2V star Fomalhaut. Here we report results from M-band (4.8 micron) imaging of Fomalhaut on 5 Dec 2006 using the Clio IR imager on the 6.5-m MMT with the adaptive secondary mirror. Our images are sensitive to giant planets at orbital radii comparable to the outer solar system (~5-40 AU). Comparing our 5-sigma M-band photometric limits to theoretical evolutionary tracks for substellar objects, our results rule out the existence of planets with masses greater than 2 Jupiter masses, from ~13-40 AU and objects greater than 13 Jupiter masses from ~8-40 AU.
We discuss the age of the stellar disks in the solar neighbourhood. After reviewing the various methods for age dating we discuss current estimates of the age of both the thin and the thick disk. We present preliminary results for kinematically-selected stars that belong to the thin as well as the thick disk. All of these dwarf and sub-giant stars have been studied spectroscopically and we have derived both elemental abundances as well as ages for them. A general conclusion is that in the solar neighbourhood, on average, the thick disk is older than the thin disk. However, we caution that the exclusion of stars with effective temperatures around 6500 K might result in a biased view on the full age distribution for the stars in the thick disk.
We review the most decisive currently available measurements of the surface effective temperatures, Teff, of white dwarf (WD) primaries in cataclysmic variables (CVs) during accretion quiescence, and use these as a diagnostic for their time averaged accretion rate, <Mdot>. Using time-dependent calculations of the WD envelope, we investigate the sensitivity of the quiescent Teff to long term variations in the accretion rate. We find that the quiescent Teff provides one of the best available tests of predictions for the angular momentum loss and resultant mass transfer rates which govern the evolution of CVs. While gravitational radiation is sufficient to explain the <Mdot> of strongly magnetic CVs at all Porb, faster angular momentum loss is required by the temperatures of dwarf nova primaries (non-magnetic systems). This provides evidence that a normal stellar magnetic field structure near the secondary is essential for the enhanced braking mechanism to work, supporting the well-known stellar wind braking hypothesis. The contrast in <Mdot> is most prominent for orbital periods Porb > 3 hours, above the period gap, but a modest enhancement is also present at shorter Porb. The averaging time which <Mdot> reflects is as much as 10^5 years for low-<Mdot> systems and as little as 10^3 years for high-<Mdot> systems. We discuss the security of conclusions drawn about the CV population in light of these time scales and our necessarily incomplete sample of systems. Measurements for non-magnetic systems above the period gap fall below predictions from traditional stellar wind braking prescriptions, but above more recent predictions with somewhat weaker angular momentum loss. We also discuss the apparently high Teff's found in the VY Scl stars. (abridged)
Nighttime sky transparency statistics on Mauna Kea are reported based on data from the Canada-France-Hawaii Telescope SkyProbe monitor. We focus on the period beginning with the start of MegaCam wide-field optical imager operations in 2003, and continuing for almost three years. Skies were clear enough to observe on 76% of those nights; attenuations were less than 0.2 magnitudes up to 60% of the time. An empirical model of cloud attenuation and duration is presented allowing us to further characterize the photometric conditions. This is a good fit tothe SkyProbe data, and indicates that Mauna Kea skies are truly photometric (without cloud) an average of 56% of the time, with moderate seasonal variation. Continuous monitoring of transparency during the night is necessary to overcome fluctuations in attenuation due to thin cloud.
We show that there exists a maximal possible accretion rate, beyond which global slim disk solutions cannot be constructed because in the vertical direction the gravitational force would be unable to balance the pressure force to gather the accreted matter. The principle for this restriction is the same as that for the Eddington luminosity and the corresponding critical accretion rate, which were derived for spherical accretion by considering the same force balance in the radial direction. If the assumption of hydrostatic equilibrium is waived and vertical motion is included, this restriction may become even more serious as the value of the maximal possible accretion rate becomes smaller. Previous understanding in the literature that global slim disk solutions could stand for any large accretion rates is due to the overestimation of the vertical gravitational force by using an approximate potential. For accretion flows with large accretion rates at large radii, outflows seem unavoidable in order for the accretion flow to reduce the accretion rate and follow a global solution till the central black hole.
The eigenfrequency problem of fundamental vibrational mode in a highly inhomogeneous star modeled by self-gravitating mass of viscous liquid with singular density at the center is considered in juxtaposition with that for Kelvin fundamental mode in the liquid star model with uniform density. Particular attention is given to the difference between spectral equations for the frequency and lifetime of f-mode in the singular and homogeneous star models. The newly obtained results are discussed in the context of theoretical asteroseismology of white dwarfs.
LS I +61 303 has been recently detected as a periodic $\gamma$-ray source by the Major Atmospheric Imaging Cerenkov (MAGIC) telescope. A distinctive orbital correlation of the $\gamma$-ray emission was found. This work shows that the range of uncertainties yet at hand in the orbital elements of the binary system \LSI as well as in the possible assumptions on the stellar wind of the optical companion play a non-negligible role in the computation of opacities to high energy processes leading to $\gamma$-ray predictions. The geometry influence on the propagation and escape of $\gamma$-ray photons is explored. With this study at hand, we analyse the results of a pulsar wind zone model for the production of $\gamma$-rays and compare it with recent MAGIC observations.
We present evidence that the accretion of warm gas onto the Galaxy today is at least as important as cold gas accretion. For more than a decade, the source of the bright H-alpha emission (up to 750 mR) along the Magellanic Stream has remained a mystery. We present a hydrodynamical model that explains the known properties of the H-alpha emission and provides new insights on the lifetime of the Stream clouds. The upstream clouds are gradually disrupted due to their interaction with the hot halo gas. The clouds that follow plough into gas ablated from the upstream clouds, leading to shock ionisation at the leading edges of the downstream clouds. Since the following clouds also experience ablation, and weaker H-alpha (100-200 mR) is quite extensive, a disruptive cascade must be operating along much of the Stream. In order to light up much of the Stream as observed, it must have a small angle of attack (~20 deg) to the halo, and this may already find support in new HI observations. Another prediction is that the Balmer ratio will be substantially enhanced due to the slow shock. We find that the clouds are evolving on timescales of 100-200 Myr, such that the Stream must be replenished by the Magellanic Clouds at a fairly constant rate (>0.1 Msun/yr). The ablated material falls onto the Galaxy as a warm drizzle; diffuse ionized gas at 10^4 K is an important constituent of galactic accretion. We consider the stability of HI clouds falling towards the Galactic disk and show that most of these must break down into smaller fragments that become partially ionized. The Galactic halo is expected to have huge numbers of smaller neutral and ionized fragments. When the ionized component is accounted for, the rate of gas accretion is ~0.4 Msun/yr, roughly twice the rate deduced from HI observations alone.
Observational facilities allow now the detection of optical and IR spectra of
young M- and L-dwarfs. This enables empirical comparisons with old M- and L-
dwarfs, and detailed studies in comparison with synthetic spectra. While
classical stellar atmosphere physics seems perfectly appropriate for old
M-dwarfs, more physical and chemical processes, cloud formation in particular,
needs to be modelled in the substellar regime to allow a detailed spectral
interpretation.
Not much is known so far about the details of the inset of cloud formation at
the spectral transition region between M and L dwarfs. Furthermore there is
observational evidence for diversity in the dust properties of objects having
the same spectral type. Do we understand these differences? The question is
also how young M- and L-dwarfs need to be classified, which stellar parameter
do they have and whether degenerations in the stellar parameter space due to
the changing atmosphere physics are present, like in the L-T transition region.
The Splinter was driven by these questions which we will use to encourage
interactions between observation and theory. Given the recent advances, both in
observations and spectral modelling, an intensive discussion between observers
and theoreticians will create new synergies in our field.
We present first results from a multi-object spectroscopy campaign in IC2602, the Hyades, the Pleiades, and the Coma cluster using VLT/FLAMES. We analysed the data for radial velocity, rotational velocity, and H-alpha activity. Here, we highlight three aspects of this study in the context of rotational braking and the rotation-activity relationship among low mass stars. Finally we discuss the cluster membership of sources in IC2602.
We present the first results of a large imaging survey to identify wide brown
dwarf companions to stars within 10 pc. We have performed a deep (H-band limit
~ 19.0 mag), wide field (up to 16x16 arcmin) astrometric imaging campaign in
two epochs around more than 230 nearby stars.
Preliminary results show that the wide low-mass companion fraction is far
lower than expected, indicating that interactions with the galactic disk may
have removed the weakly bound wide companions around old stars.
The dynamics of artificial asteroids on the Trojan-like orbits around Neptune is investigated in this paper. We describe the dependence of the orbital stability on the initial semimajor axis a and inclination i by constructing a dynamical map on the (a,i)-plane. Rich details are revealed in the dynamical map, especially a unstable gap at i=45 deg is determined and the mechanism triggering chaos in this region is figured out. Our investigation can be used to guide the observations.
We combine multifrequency observations from the millimeter to near infrared wavelengths that demonstrate the spatial distributions of H2, CO, and NH3 emission, which are all manifestations of various shocks driven by outflows of deeply embedded sources in NGC6334I. In addition to the well-known northeast-southwest outflow we detect at least one more outflow in the region by combining observations from APEX, ATCA, SMA, Spitzer and VLT/ISAAC. Potential driving sources will be discussed. NGC6334I exhibits several signs of active star formation and will be a major target for future observatories such as Herschel and ALMA.
The physical characterization of exoplanets will require to take spectra at several orbital positions. For that purpose, a direct imaging capability is necessary. Direct imaging requires an efficient stellar suppression mechanism, associated with an ultrasmooth telescope. We show that before future large space missions (interferometer, 4-8 m class coronograph, external occulter or Fresnel imager), direct imaging of giant planets and close-by super-Earth are at the cross-road of a high scientific interest and a reasonable feasibility. The scientific interest lies in the fact that super-Earths share common geophysical attributes with Earths. They already begin to be detected by radial velocity (RV) and, together with giant planets, they have a larger area than Earths, making them detectable with a 1.5-2 m class telescope in reflected light. We propose such a (space) telescope be a first step before large direct imaging missions.
Non-thermal X-ray emission in some supernova remnants originates from synchrotron radiation of ultra-relativistic particles in turbulent magnetic fields. We address the effect of a random magnetic field on synchrotron emission images and spectra. A random magnetic field is simulated to construct synchrotron emission maps of a source with a steady distribution of ultra-relativistic electrons. Non-steady localized structures (dots, clumps and filaments), in which the magnetic field reaches exceptionally high values, typically arise in the random field sample. These magnetic field concentrations dominate the synchrotron emission (integrated along the line of sight) from the highest energy electrons in the cut-off regime of the distribution, resulting in an evolving, intermittent, clumpy appearance. The simulated structures resemble those observed in X-ray images of some young supernova remnants. The lifetime of X-ray clumps can be short enough to be consistent with that observed even in the case of a steady particle distribution. The efficiency of synchrotron radiation from the cut-off regime in the electron spectrum is strongly enhanced in a turbulent field compared to emission from a uniform field of the same magnitude.
The discovery of the Spite plateau in the abundances of 7Li for metal-poor stars led to the determination of an observationally deduced primordial lithium abundance. However, after the success of the Wilkinson Microwave Anisotropy Probe (WMAP) in determining the baryon density, OmegaBh^2, there was a discrepancy between observationally determined and theoretically determined abundances in the case of 7Li. One of the most important uncertain factors in the calculation of the stellar 7Li abundance is the effective temperature, Teff. We use sixteen metal-poor halo dwarfs to calculate new Teff values using the excitation energy method. With this temperature scale we then calculate new Li abundances for this group of stars in an attempt to resolve the 7Li discrepancy. Using high signal-to-noise (S/N ~ 100) spectra of 16 metal-poor halo dwarfs, obtained with the UCLES spectrograph on the AAT, measurements of equivalent widths from a set of unblended FeI lines are made. These equivalent widths are then used to calculate new Teff values with the use of the single line radiative transfer program WIDTH6, where we have constrained the gravity using either theoretical isochrones or the Hipparcos parallax, rather than the ionization balance. The lithium abundances of the stars are calculated with these temperatures. The physical parameters are derived for the 16 programme stars, and two standards. These include Teff, log g, [Fe/H], microturbulence and 7Li abundances. A comparison between the temperature scale of this work and those adopted by others has been undertaken. We find good consistency with the temperatures derived from the Halpha line by Asplund et al. (2006), but not with the hotter scale of Melendez & Ramirez (2004).
Brown dwarfs are natural clocks, cooling and dimming over time due to insufficient core fusion. They are also numerous and present in nearly all Galactic environments, making them potentially useful chronometers for a variety of Galactic studies. For this potential to be realized, however, precise and accurate ages for individual sources are required, a prospect made difficult by the complex atmospheres and spectra of low-temperature brown dwarfs; degeneracy between mass, age and luminosity; and the lack of useful age trends in magnetic activity and rotation. In this contribution, I review five ways in which ages for brown dwarfs are uniquely determined, discuss their applicability and limitations, and give current empirical precisions.
The excellent radio frequency transparency of cold polar ice, combined with
the coherent Cherenkov emission produced by neutrino-induced showers when
viewed at wavelengths longer than a few centimeters, has spurred considerable
interest in a large-scale radio-wave neutrino detector array.
The AURA (Askaryan Under-ice Radio Array) experimental effort, within the
IceCube collaboration, seeks to take advantage of the opportunity presented by
IceCube drilling through 2010 to establish the radio frequency technology
needed to achieve 100-1000 km^3 effective volumes.
In the 2006-2007 Austral summer 3 deep in-ice radio frequency (RF) clusters
were deployed at depths of 1300m and 300m on top of the IceCube strings.
Additional 3 clusters will be deployed in the Austral summer of 2008-2009.
Verification and calibration results from the current deployed clusters are
presented, and the detector design and performances are discussed. Augmentation
of IceCube with large-scale 1000km^3sr radio and acoustic arrays would extend
the physics reach of IceCube into the EeV-ZeV regime and offer substantial
technological redundancy.
We present radio transient search algorithms, results, and statistics from the ongoing Arecibo Pulsar ALFA (PALFA) Survey of the Galactic plane. We have discovered seven objects by detecting isolated dispersed pulses and one of the new discoveries has a duty cycle of 0.01%, the smallest known. The impact of selection effects on the detectability and classification of intermittent sources is discussed, and the relative efficiencies of periodicity vs. single pulse searches are compared for various pulsar classes. We find that scintillation, off-axis detection and few rotation periods within an observation may misrepresent normal periodic pulsars as intermittent sources. Finally, we derive constraints on transient pulse rate and flux density from the PALFA survey parameters and results.
We present revised and improved mid-infrared Period-Luminosity (PL) relations for Large Magellanic Cloud (LMC) Cepheids based on double-epoch data of 70 Cepheids observed by Spitzer at 3.6, 4.5, 5.8 and 8.0um. The observed scatter at all wavelengths is found to decrease from +/-0.17 mag to +/-0.14 mag, which is fully consistent with the prediction that the total scatter is made up of roughly equal contributions from random sampling of the light curve and nearly-uniform samplings of stars across the instability strip. It is calculated that the Cepheids in this sample have a full amplitude of about 0.4 mag and that their fully-sampled, time-averaged magnitudes should eventually reveal mid-infrared PL relations that each have intrinsic scatter at most at the +/-0.12 mag level, and as low as +/-0.08 mag after correcting for the tilt of the LMC.
Finite-difference simulations of fluid dynamics and magnetohydrodynamics generally require an explicit diffusion operator, either to maintain stability by attenuating grid-scale structure, or to implement physical diffusivities such as viscosity or resistivity. If the goal is stability only, the diffusion must act at the grid scale, but should affect structure at larger scales as little as possible. For physical diffusivities the diffusion scale depends on the problem, and diffusion may act at larger scales as well. Diffusivity undesirably limits the computational timestep in both cases. We construct tuned finite-difference diffusion operators that minimally limit the timestep while acting as desired near the diffusion scale. Such operators reach peak values at the diffusion scale rather than at the grid scale, but behave as standard operators at larger scales. We focus on the specific applications of hyperdiffusivity for numerical stabilization, and high Schmidt and high Prandtl number simulations where the diffusion scale greatly exceeds the grid scale.
The rotation rate of the solar radiative zone is an important diagnostic for angular-momentum transport in the tachocline and below. In this paper we study the contribution of viscous and magnetic stresses to the global angular-momentum balance. By considering a simple linearized toy model, we discuss the effects of field geometry and applied boundary conditions on the predicted rotation profile and rotation rate of the radiative interior. We compare these analytical predictions with fully nonlinear simulations of the dynamics of the radiative interior, as well as with observations. We discuss the implications of these results as constraints on models of the solar interior.
Based on spectrophotometric observations from the Guillermo Haro Observatory (Cananea, Mexico), a study of the spectral properties of the complete sample of 24 blue straggler stars (BSs) in the old Galactic open cluster M67 (NGC 2682) is presented. All spectra, calibrated using spectral standards, were recalibrated by means of photometric magnitudes in the Beijing-Arizona-Taipei-Connecticut system, which includes fluxes in 11 bands covering ~3500-10000 A. The set of parameters was obtained using two complementary approaches that rely on a comparison of the spectra with (i) an empirical sample of stars with well-established spectral types and (ii) a theoretical grid of optical spectra computed at both low and high resolution. The overall results indicate that the BSs in M67 span a wide range in Teff(~ 5600 -12600 K) and surface gravities that are fully compatible with those expected for main-sequence objects (log g = 3.5 -5.0 dex).
In mean-field theory of magnetic fields or passive scalars, for example, turbulent transport is usually assumed to be proportional to the corresponding mean fields and their spatial derivatives. However, this is an approximation that is valid only if the mean fields vary slowly in time. Examples are presented where turbulent transport possesses memory, i.e. it depends crucially on the past history of the mean fields at earlier times. Such effects are captured by replacing turbulent transport coefficients with time integral kernels, resulting in transport coefficients that depend effectively on the frequency or the growth rate of the mean fields themselves. In this paper we perform numerical experiments to find the characteristic timescale of this effect as well as simple analytical models of the integral kernels in the case of passive scalar concentrations and kinetic dynamos. The integral kernels can then be used to find self-consistent growth or decay rates of the mean fields. In mean-field dynamos the growth rates and cycle periods based on steady state values of alpha effect and turbulent diffusivity can be quite different from the actual values.
Context. We have investigated the structure and kinematics of triaxial final models formed due to radial-orbit instability from a set of equilibrium anisotropic spherical systems of the Osipkov-Merritt type. Aims. We show that the instability is a natural way to build nonspherical systems and thus can be considered as a new technique for constructing equilibrium $N$-body models. Methods. The dynamical evolution of the models was followed numerically by means of the Dehnen's public code gyrfacON. Results. We found that the shape of the density profiles for various initial spherical models didn't change despite of the systems were drastically rearranged into triaxial configurations and had got the new scale lengths. The cusp was found to be an invariant feature of such a rearranging. Starting from a certain unstable spherical $\gamma$-model we obtain a triaxial system with the same cusp. The end-products are anisotropic at large radii and have anisotropy profiles of the Osipkov-Merrit type. The size of the isotropic core once rescaled corresponds to the value of marginally stable $\gamma$-progenitors and is almost independent of the unstable starting point. Conclusions. We conclude that the end-products reach a new steady state and have quite predictable properties. They can be used as equilibrium models to describe the elliptical galaxies and bulges. They also can be incorporated in $N$-body simulations deal with multicomponent systems.
We present a rigorous mathematical solution to the generalized photometric inversion problem. The challenge we address is to meaningfully constrain unknown properties of astronomical sources based on given observables, usually multicolor photometry, with the help of a training set that provides an empirical relation between the measurements and the desired quantities. Photometric redshift estimation is an example of such methods. We establish a formalism that blurs the boundary between the traditional empirical and template fitting algorithms, as both are just special cases that are discussed in detail to put them in context. The new approach enables the development of more sophisticated methods that go beyond the classic techniques to combine their advantages. The basic concepts are illustrated in a simple case that is analogous to the classic empirical methods. We look at the directions for further improvement as well as the technical aspects of practical implementations, and study the qualities of the calibrators with the design of future training sets in mind that will greatly enhance the reliability of the photometric properties in the new era of upcoming survey telescopes.
Direct imaging of exoplanetary systems is a powerful technique that can reveal Jupiter-like planets in wide orbits, can enable detailed characterization of planetary atmospheres, and is a key step towards imaging Earth-like planets. Imaging detections are challenging due to the combined effect of small angular separation and large luminosity contrast between a planet and its host star. High-contrast observations with the Keck and Gemini telescopes have revealed three planets orbiting the star HR 8799, with projected separations of 24, 38, and 68 astronomical units. Multi-epoch data show counter-clockwise orbital motion for all three imaged planets. The low luminosity of the companions and the estimated age of the system imply planetary masses between 5 and 13 times that of Jupiter. This system resembles a scaled-up version of the outer portion of our Solar System.
There is an ongoing debate in the literature concerning the effects of averaging out inhomogeneities (``backreaction'') in cosmology. In particular, some simple models of structure formation studied in the literature seem to indicate that the backreaction can play a significant role at late times, and it has also been suggested that the standard perturbed FLRW framework is no longer a good approximation during structure formation, when the density contrast becomes nonlinear. In this work we use Zalaletdinov's covariant averaging scheme (macroscopic gravity or MG) to show that as long as the metric of the Universe can be described by the perturbed FLRW form, the corrections due to averaging remain negligibly small. Further, using a fully relativistic and reasonably generic model of pressureless spherical collapse, we show that as long as matter velocities remain small (which is true in our model), the perturbed FLRW form of the metric can be explicitly recovered. Together, these results imply that the backreaction remains small even during nonlinear structure formation, and we confirm this within the toy model with a numerical calculation.
The Planck satellite is expected to improve the measurement of most cosmological parameters by several factors with respect to current WMAP results. The actual performance may depend upon various aspects of the data analysis. In this paper we analyse the impact of specifics of the data analysis on the actual final results. We also explore the synergies in combining Planck results with future galaxy surveys. We find that Planck will improve constraints on most cosmological parameters by a factor 3-4 and on the tensor-to-scalar ratio r by a factor 9. Also inflationary parameters, like r, n_s and n_run, are no longer degenerate. The tensor spectral index, however, is little constrained. A combination of the 70 to 143 GHz channels will contain ~90% of all possible information, with 143 GHz polarisation information carrying about half of the constraining power on r. Also, the error on r degrades by a factor 2 if no B modes are included in the analysis. High-l temperature information is essential for determination of n_s and \Omega_b, while improving noise properties increase the l-range where Planck would be cosmic variance limited in polarisation, with a significant improvement on the determination of r, \tau and A_s. However, a sub-percent difference in the FWHM used in the data analysis with respect to the one in the map will result in a bias for several parameters. Finally, Planck will greatly help future missions like LSST and CIP reach their potentials by providing tight constraints on parameters like n_s and n_run. Considering Planck together with these probes will help in breaking degeneracies between \Omega_K and \Omega_\Lambda or \Omega_dm and f_\nu, resulting in improvements of several factors in the error associated to these parameters.
There is still considerable debate over the progenitors of type Ia supernovae (SNe Ia). Likewise, it is not agreed how single white dwarfs with masses less than ~0.5 Msun can be formed in the field, even though they are known to exist. We consider whether single low-mass white dwarfs (LMWDs) could have been formed in binary systems where their companions have exploded as a SN Ia. In this model, the observed single LMWDs are the remnants of giant-branch donor stars whose envelopes have been stripped off by the supernova explosion. We investigate the likely remnants of SNe Ia, including the effects of the explosion on the envelope of the donor star. We also use evolutionary arguments to examine alternative formation channels for single LMWDs. In addition, we calculate the expected kinematics of the potential remnants of SNe Ia. SN Ia in systems with giant-branch donor stars can naturally explain the production of single LMWDs. It seems difficult for any other formation mechanism to account for the observations, especially for those single LMWDs with masses less than ~0.4 Msun. Independent of those results, we find that the kinematics of one potentially useful population containing single LMWDs is consistent with our model. Studying remnant white-dwarf kinematics seems to be a promising way to investigate SN Ia progenitors. The existence of single LMWDs appears to constitute evidence for the production of SNe Ia in binary systems with a red-giant donor star. Other single white dwarfs with higher space velocities support a second, probably dominant, population of SN Ia progenitors which contained main-sequence or subgiant donor stars at the time of explosion. The runaway stars LP400-22 and US 708 suggest the possibility of a third formation channnel for some SNe Ia in systems where the donor stars are hot subdwarfs.
The cluster baryon fraction is estimated from the CMB-scattering leptonic component of the intracluster medium (ICM); however, the observed cluster baryon fraction is less than the cosmic one. Understanding the origin of this discrepancy is necessary for correctly describing the structure of the ICM. We estimate the baryonic mass in the outskirts of galaxy clusters which is difficult to observe because of low electron temperature and density in these regions. The time scale for the electrons and protons to reach equipartition in the outskirts is longer than the cluster age. Since thermal equilibrium is not achieved, a significant fraction of the ICM baryons may be hidden in shells around galaxy clusters. We derive the necessary condition on the cluster mass for the concealment of missing baryons in an outer baryon shell and show that this condition is fulfilled because cluster masses are comparable to the estimated characteristic mass $M=e^4/(m^3_{p} G^2)=1.3x10^{15}$ solar masses. The existence of extreme-ultraviolet emission haloes around galaxy clusters is predicted.
Nonlinear growth of the bar-mode deformation is studied for a differentially rotating star with supercritical rotational energy. In particular, the growth mechanism of some azimuthal modes with odd wave numbers is examined by comparing a simplified mathematical model with a realistic simulation. Mode coupling to even modes, i.e., the bar mode and higher harmonics, significantly enhances the amplitudes of odd modes, unless they are exactly zero initially. Therefore, other modes which are not axially symmetric cannot be neglected at late times in the growth of the unstable bar-mode even when starting from an almost axially symmetric state.
In this work we analyze a sample of AGN spectra, selected from the 6th Data Release of the Sloan Digital Sky Survey, exploiting a generalized technique of line profile analysis, designed to take into account the whole profiles of their broad emission lines. We find that the line profile broadening functions result from a complex structure, but we may be able to infer some constraints about the role of the geometrical factor, thus improving our ability to estimate AGN properties and their relation with the host galaxy. Our results suggest that flattening and inclination within the structure of the Broad Line Region (BLR) must be taken into account. We detect low inclinations of the BLR motion plane with respect to our line of sight, typically i < 20 degrees, with a geometrical effect which generally decreases as the line profile becomes broader.
We present the first results of a high-resolution study of the distribution and kinematics of molecular gas in two nearby radio galaxies, 4C31.04 and 3C293, representative of two different stages of evolution in radio-loud active galactic nuclei (AGN). These observations, conducted with the IRAM Plateau de Bure Interferometer (PdBI), map with unprecedented spatial resolution (0.5"-1") and sensitivity the emission and absorption of key molecular species such as CO, HCN and HCO+. We report on the detection of a kinematically disturbed and massive (Mgas~10^10Msun) molecular/dusty disk of ~1.4kpc-size fueling the central engine of the compact symmetric object (CSO) 4C31.04. We also report on the detection of a massive (Mgas~10^10Msun) regularly rotating ~7kpc-size disk in the FRII radio galaxy 3C293. A complex system of molecular line absorptions is detected against the mm-continuum source of this galaxy (AGN and jet). We compare the properties of the molecular disks in the two sources and discuss them in the light of the different theories describing the evolution of radio galaxies.
After three years of no unusual activity, Anomalous X-ray Pulsar 1E 1048.1-5937 reactivated in 2007 March. We report on the detection of a large glitch (Delta(nu)/nu =1.63(2)X~10^{-5}) on 2007 March 26 (MJD 54185.9), contemporaneous with the onset of a pulsed-flux flare, the third flare observed from this source in 10 years of monitoring with the Rossi X-ray Timing Explorer. Additionally, we report on a detailed study of the evolution of the timing properties, the pulsed flux, and the pulse profile of this source as measured by RXTE from 1996 July to 2008 January. In our timing study, we attempted phase coherent timing of all available observations. We show that in 2001, a timing anomaly of uncertain nature occurred near the rise of the first pulsed flux flare; we show that a likely glitch (Delta(nu)/nu =2.91(9)X10^{-6}) occurred in 2002, near the rise of the second flare, and we present a detailed description of the variations in the spin-down. In our pulsed flux study, we compare the decays of the three flares and discuss changes in the hardness ratio. In our pulse profile study, we show that the profile exhibited large variations near the peak of the first two flares, and several small short-term profile variations during the most recent flare. Finally, we report on the discovery of a small burst 27 days after the peak of the last flare, the fourth burst discovered from this source. We discuss the relationships between the observed properties in the framework of the magnetar model.
The broad-band 1-300 keV Suzaku spectrum of IGR J17497-2821, the X-ray transient discovered by INTEGRAL in September 2006, is presented. Suzaku observed IGR J17497-2821 on September 25, eight days after its discovery, for a net exposure of about 53 ksec. During the Suzaku observation, IGR J17497-2821 is very bright, 2 x 10^37 erg/s at 8 kpc in the 1-300 keV range, and shows a hard spectrum, typical of black hole candidates in the low-hard state. Despite the multi-mission X-ray monitoring of the source, only with Suzaku is it possible to obtain a broad-band spectrum in the 1-300 keV range with a very high signal to noise ratio. A sum of a multi-color disc (DISKBB) and a thermal Comptonization component (COMPPS) with mild reflection is a good representation of our IGR J17497-2821 Suzaku spectrum. The spectral properties of the accretion disc as well as the cut-off energy in the spectrum at about 150 keV are clearly detected and constrained. We discuss the implications on the physical model used to interpret the data and the comparison with previous results.
We report on the first detection in space of fulminic acid, HCNO. This isomer of HNCO has been observed in three starless cores, B1, L1544 and L183, and in the low mass star forming region L1527 with a measured abundance ratio of HNCO/HCNO between 40-70. However, HCNO was not detected towards the direction of the cyanopolyyne peak of TMC-1 or towards the Orion Hot Core region. The derived HNCO/HCNO abundance ratio in these cases is greater than 350 and 1000 in TMC-1 and Orion, respectively. We find that CH_2 + NO \to HCNO + H is a key reaction for the formation of fulminic acid. A value of 5.5 10^{-12} cm^3 s^{-1} of the corresponding reaction rate coefficient, as given by Miller et al. (2003), allows to reproduce the observed abundances of fulminic acid in both the observed dark clouds and low mass star forming core, where the determined abundance of HNCO in these regions with respect to molecular hydrogen is 1-5 10^{-10}.
We present a new model for the Z-track phenomenon, based on analysis of the spectral evolution around the Z-track in several Z-track sources, in which radiation pressure plays a major role. Increasing mass accretion rate on the normal branch causes heating of the neutron star with the emissive flux from the surface increasing by an order of magnitude to become super-Eddington at the horizontal branch where radio detection shows the presence of jets. We propose that the radiation pressure disrupts the inner disk leading to the launching of the jets. Secondly, by timing analysis of the same data we find a correlation of the frequency of kHz QPO with the emissive flux and propose that the higher frequency QPO is an oscillation at the inner disk edge which progressively moves to larger radial positions as the disk is disrupted by radiation pressure.
This series of papers explores the evolution of late-type galaxies in the rich cluster Abell 85. Here, we revisit the complex dynamical state of A 85 by using independent methods. We analyze the redshift distribution towards the cluster out to 40,000 km/s, and determine the mean redshifts of the background clusters A 87 and A 89. We then search for substructures in A 85 by considering the 2-D galaxy distribution for its members and by applying the kinematical 3-D Delta-test to both projected positions and radial velocities. This clearly reveals several substructures that we describe. We also analyse the distribution of the brightest blue galaxies across a major fraction of the cluster volume, considering if they are gas-rich or poor. We report a very asymmetric distribution of the blue member galaxies, and connect it with substructures revealed in the optical and X-rays. By matching our sample of bright blue member galaxies with HI detections reported in the literature, we identify gas-rich and gas-poor ones. HI-rich blue galaxies also turn out to be asymmetrically distributed, with most of them projected on the eastern side of the cluster. No blue objects have been detected in HI up to a projected radius of 2 Mpc in this zone. We estimate the ram pressure stripping exerted by the intra-cluster medium as a function of the projected distance from A 85, and quantify how important this mechanism may be in sweeping the gas out of the infalling spirals.
Microlensing events are usually selected among single-peaked non-repeating light curves in order to avoid confusion with variable stars. However, a microlensing event may exhibit a second microlensing brightening episode when the source or/and the lens is a binary system. A careful analysis of these repeating events provides an independent way to study the statistics of wide binary stars and to detect extrasolar planets. Previous theoretical studies predicted that 0.5 - 2 % of events should repeat due to wide binary lenses. We present a systematic search for such events in about 4000 light curves of microlensing candidates detected by the Optical Gravitational Lensing Experiment (OGLE) towards the Galactic Bulge from 1992 to 2007. The search reveals a total of 19 repeating candidates, with 6 clearly due to a wide binary lens. As a by-product we find that 64 events (~2% of the total OGLE-III sample) have been miss-classified as microlensing; these miss-classified events are mostly nova or other types of eruptive stars. The number and importance of repeating events will increase considerably when the next-generation wide-field microlensing experiments become fully operational in the future.
We report on results of two years of INTEGRAL/SPI monitoring of the Galactic microquasar GRS 1915+105. From September 2004 to May 2006, the source has been observed twenty times with long (approx 100 ks) exposures. We present an analysis of the SPI data and focus on the description of the high-energy (> 20 keV) output of the source. We found that the 20 - 500 keV spectral emission of GRS 1915+105 was bound between two states. It seems that these high-energy states are not correlated with the temporal behavior of the source, suggesting that there is no direct link between the macroscopic characteristics of the coronal plasma and the the variability of the accretion flow. All spectra are well fitted by a thermal comptonization component plus an extra high-energy powerlaw. This confirms the presence of thermal and non-thermal electrons around the black hole.
We present resolved images of the dust continuum emission from the debris disk around the young (80-200 Myr) solar-type star HD 107146 with CARMA at $\lambda$1.3 mm and the CSO at $\lambda$350 $\mu$m. Both images show that the dust emission extends over an $\sim$10\arcsec diameter region. The high resolution (3\arcsec) CARMA image further reveals that the dust is distributed in a partial ring with significant decrease in flux inward of 97 AU. Two prominent emission peaks appear within the ring separated by $\sim$140 degrees in position angle. The morphology of the dust emission is suggestive of dust captured into a mean motion resonance, which would imply the presence of a planet at an orbital radius of $\sim$45-75 AU.
Abridged. Context. The metal content of dwarf galaxies and the metal
enrichment of the intergalactic medium both suggest that mass loss from
galaxies is a significant factor for the chemical evolution history of
galaxies, in particular of dwarf galaxies. However, no clear evidence of a
blow-away in local dwarf galaxies has been found so far.
Aims. We therefore performed a detailed kinematic analysis of the neutral and
ionised gas in the nearby star-forming irregular dwarf galaxy NGC 2366 in order
to make predictions about the fate of the gas and to get a more complete
picture of this galaxy.
Methods. A deep Halpha image and Fabry-Perot interferometric data of NGC 2366
were obtained. They were complemented by HI synthesis data from the THINGS
survey. We searched for line-splitting both in Halpha and HI by performing a
Gaussian decomposition. To get an idea whether the expansion velocities are
high enough for a gas blow-away, we used the pseudo-isothermal halo model,
which gives us realistic values for the escape velocities of NGC 2366. The good
data quality also allowed us to discuss some peculiarities of the morphology
and the dynamics in NGC 2366.
Results. A large red-shifted outflow north west of the giant extragalactic
HII region with an expansion velocity of up to 50 km/s is found in Halpha, but
not in HI. Additionally, a blue-shifted component north of the giant
extragalactic HII region was detected both in Halpha and HI with an expansion
velocity of up to 30 km/s. A comparison with the escape velocities of NGC 2366
reveals that the gas does not have enough kinetic energy to leave the
gravitational potential.
A novel map of the sky representing the degree of randomness in the Cosmic Microwave Background (CMB) temperature is obtained. The map based on the estimation of the Kolmogorov stochasticity parameter clearly distinguishes the contribution of the Galactic disk from the CMB and reveals regions of various degree of randomness which can reflect the properties of inhomogeneities in the Universe. For example, among the high randomness regions is the southern non-Gaussian anomaly, the Cold Spot, with a stratification expected for the voids. Existence of its counterpart, a Northern Cold Spot with almost identical randomness properties among other low temperature regions is revealed. By its informative power Kolmogorov's map can be complementary to the CMB temperature and polarization sky maps.
Collimated outflows (jets) are ubiquitous in the universe appearing around sources as diverse as protostars and extragalactic supermassive blackholes. Jets are thought to be magnetically collimated, and launched from a magnetized accretion disk surrounding a compact gravitating object. We have developed the first laboratory experiments to address time-dependent, episodic phenomena relevant to the poorly understood jet acceleration and collimation region. The experimental results show the periodic ejections of magnetic bubbles naturally evolving into a heterogeneous jet propagating inside a channel made of self-collimated magnetic cavities. The results provide a unique view of the possible transition from a relatively steady-state jet launching to the observed highly structured outflows.
Context: The atmosphere of the quiet Sun is controlled by photospheric flows
sweeping up concentrations of mixed polarity magnetic field. Along supergranule
boundaries and junctions, there is a strong correlation between magnetic flux
and bright chromospheric and transition region emission.
Aim: The aim is to investigate the relationship between photospheric flows
and small flare-like brightenings seen in Extreme Ultraviolet images.
Method: We describe observations of small eruptions seen in quiet Sun images
taken with the Extreme UltraViolet Imager (EUVI) on STEREO. The photospheric
flows during the eruption build-up phase are investigated by tracking granules
in high resolution MDI continuum images.
Results: Eruptions with characteristics of small coronal mass ejections
(CMEs) occur at the junctions of supergranular cells. The eruptions produce
brightening at the onset site, dark cloud or small filament ejections, and
faint waves moving with plane-of-sky speeds up to 150 km/s. In the two examples
studied, they appear to be activated by converging and rotating supergranular
flows, twisting small concentrations of opposite polarity magnetic field. An
estimate of the occurrence rate is about 1400 events per day over the whole
Sun. One third of these events seem to be associated with waves. Typically, the
waves last for about 30 min and travel a distance of 100 arcsec, so at any one
time they cover 1/30th of the lower corona.
The penumbra of a sunspot is a fascinating phenomenon featuring complex velocity and magnetic fields. It challenges both our understanding of radiative magneto-convection and our means to measure and derive the actual geometry of the magnetic and velocity fields. In this contribution we attempt to summarize the present state-of-the-art from an observational and a theoretical perspective.
We investigate the effect of primordial non-Gaussianity of the local type on the auto- and cross-power spectrum of dark matter haloes using a series of large N-body simulations of the LCDM cosmology. Theoretical models predict a scale-dependent bias correction \Delta b(k,f_NL) that depends on the linear halo bias b(M). We measure the power spectra for a range of halo mass and redshifts covering the relevant range of existing galaxy and quasar populations. We show that auto and cross-correlation analyses of bias are consistent with each other. We find that, on large scales (k < 0.01 h/Mpc), the theory and the simulations agree well for biased haloes with b(M)>1.5. At smaller scales, the effect in simulations is suppressed relative to theoretical predictions, in qualitative agreement with the expectations based on peak-background split. The suppression relative to the theory reaches a factor of three at k=0.1 h/Mpc. We give a fitting formula for it, which should be used when analysing observational data. The current limits on f_NL from Slosar et al. (2008) come mostly from very large scales and are only mildly affected. For the halo samples with b(M)<1.5 we find that the nonlinear bias from non-Gaussianity actually exceeds the theoretical predictions on very large scales, k <0.01 h/Mpc.
We have investigated the effects of uniform rotation and a specific model for differential rotation on the pulsation frequencies of 10 \Msun\ stellar models. Uniform rotation decreases the frequencies for all modes. Differential rotation does not appear to have a significant effect on the frequencies, except for the most extreme differentially rotating models. In all cases, the large and small separations show the effects of rotation at lower velocities than do the individual frequencies. Unfortunately, to a certain extent, differential rotation mimics the effects o f more rapid rotation, and only the presence of some specific observed frequencies with well identified modes will be able to uniquely constrain the internal rotation of pulsating stars.
Contributions of the IceCube Collaboration to the 3rd International Workshop on Acoustic and Radio EeV Neutrino detection Activities (ARENA 2008). The conference was held at Roma University "Sapienza," June 25-27, 2008, in Rome, Italy. This is an html index of the IceCube Collaboration contributions, with clickable links to the individual papers.
When an open system of classical point particles interacting by Newtonian gravity collapses and relaxes violently, an arbitrary amount of energy may in principle be carried away by particles which escape to infinity. We investigate here, using numerical simulations, how this released energy and other related quantities (notably the binding energy and size of the virialized structure) depends on the initial conditions, for the one parameter family of starting configurations given by randomly distributing N cold particles in a spherical volume. Previous studies have established that the minimal size reached by the system scales approximately as N^{1/3}, a behaviour which follows trivially when the growth of perturbations (which regularize the singular behaviour in limit of infinite N) are assumed to be unaffected by the boundaries. Our study shows that the energy ejected grows approximately in proportion to N^{1/3}, while the fraction of the initial mass ejected grows only very slowly with N, approximately logarithmically, in the range of N simulated. We examine in detail the mechanism of this mass and energy ejection, showing explicitly that it arises from the interplay of the growth of perturbations with the finite size of the system. A net lag of particles compared to their uniform spherical collapse trajectories develops first at the boundaries and then propagates into the volume during the collapse. Particles in the outer shells are then ejected as they scatter through the time dependent potential of an already re-expanding central core. Using modified initial configurations we explore the importance of fluctuations at different scales, and discreteness (i.e. non-Vlasov) effects in the dynamics.
We report on a successful, simultaneous observation and modeling of the sub-millimeter to near-infrared flare emission of the Sgr A* counterpart associated with the super-massive black hole at the Galactic center. Our modeling is based on simultaneous observations that have been carried out on 03 June, 2008 using the NACO adaptive optics (AO) instrument at the ESO VLT and the LABOCA bolometer at the APEX telescope. Inspection and modeling of the light curves show that the sub-mm follows the NIR emission with a delay of 1.5+/-0.5 hours. We explain the flare emission delay by an adiabatic expansion of the source components.
Among the many experimental techniques available, those providing directional information have the potential of yielding an unambiguous observation of WIMPs even in the presence of insidious backgrounds. A measurement of the distribution of arrival direction of WIMPs can also discriminate between Galactic Dark Matter halo models. In this article, I will discuss the motivation for directional detectors and review the experimental techniques used by the various experiments. I will then describe one of them, the DMTPC detector, in more detail.
The ROSAT Galactic wind observations confirm that our Galaxy launches supernova driven Galactic winds with wind speeds of about 150 km/s in the Galactic plane. Galactic winds of this strength are incompatible with current isotropic models for Cosmic Ray transport. In order to reproduce our local CRs in the presence of Galactic winds, charged CRs are required to be much more localized than in the standard isotropic GALPROP models. This requires that anisotropic diffusion is the dominant diffusion mode in the interstellar medium, particularly that the diffusion in the disk and in the halo are different. In addition small scale phenomena such as trapping by molecular cloud complexes and the structure of our local environment might influence the secondary CR production rate and our local CR density gradients. We introduce an anisotropic convection driven transport model (aCDM) which is consistent with the Galactic wind observations by ROSAT. This also explains the large bulge/disk ratio as observed by INTEGRAL. Furthermore such models predict an increase in the $e^+/(e^++e^-)$-fraction as observed by PAMELA and HEAT, if the synchrotron constraints in the 408 MHz and WMAP range are taken into account. No additional contribution from Dark Matter is required. The aCDM is able to explain the absence of a positron annihilation signal from molecular clouds as observed by INTEGRAL by virtue of a mechanism which confines and isotropizes CRs between MCs. We find that the EGRET excess of diffuse $\gamma$-rays currently cannot be explained by astrophysical effects in this type of model and that the interpretation of the EGRET excess as Dark Matter annihilation is perfectly consistent with all observational constraints from local CR fluxes and synchrotron radiation.
We describe a combined dynamic atmosphere and maser propagation model of SiO maser emission in Mira variables. This model rectifies many of the defects of an earlier model of this type, particularly in relation to the infra-red (IR) radiation field generated by dust and various wavelength-dependent, optically thick layers. Modelled masers form in rings with radii consistent with those found in VLBI observations and with earlier models. This agreement requires the adoption of a radio photosphere of radius approximately twice that of the stellar photosphere, in agreement with observations. A radio photosphere of this size renders invisible certain maser sites with high amplification at low radii, and conceals high-velocity shocks, which are absent in radio continuum observations. The SiO masers are brightest at an optical phase of 0.1 to 0.25, which is consistent with observed phase-lags. Dust can have both mild and profound effects on the maser emission. Maser rings, a shock and the optically thick layer in the SiO pumping band at 8.13\micron \,appear to be closely associated in three out of four phase samples.
The Tail region of the Small Magellanic Cloud (SMC) was imaged using the MIPS instrument on the Spitzer Space Telescope as part of the SAGE-SMC Spitzer Legacy. Diffuse infrared emission from dust was detected in all the MIPS bands. The Tail gas-to-dust ratio was measured to be 1200 +/- 350 using the MIPS observations combined with existing IRAS and HI observations. This gas-to-dust ratio is higher than the expected 500-800 from the known Tail metallicity indicating possible destruction of dust grains. Two cluster regions in the Tail were resolved into multiple sources in the MIPS observations and local gas-to-dust ratios were measured to be ~440 and ~250 suggests dust formation and/or significant amounts of ionized gas in these regions. These results support the interpretation that the SMC Tail is a tidal tail recently stripped from the SMC that includes gas, dust, and young stars.
We propose a comprehensive theory of dark matter that explains the recent proliferation of unexpected observations in high-energy astrophysics. Cosmic ray spectra from ATIC and PAMELA require a WIMP with mass M_chi ~ 500 - 800 GeV that annihilates into leptons at a level well above that expected from a thermal relic. Signals from WMAP and EGRET reinforce this interpretation. Taken together, we argue these facts imply the presence of a GeV-scale new force in the dark sector. The long range allows a Sommerfeld enhancement to boost the annihilation cross section as required, without altering the weak scale annihilation cross section during dark matter freezeout in the early universe. If the dark matter annihilates into the new force carrier, phi, its low mass can force it to decay dominantly into leptons. If the force carrier is a non-Abelian gauge boson, the dark matter is part of a multiplet of states, and splittings between these states are naturally generated with size alpha m_phi ~ MeV, leading to the eXciting dark matter (XDM) scenario previously proposed to explain the positron annihilation in the galactic center observed by the INTEGRAL satellite. Somewhat smaller splittings would also be expected, providing a natural source for the parameters of the inelastic dark matter (iDM) explanation for the DAMA annual modulation signal. Since the Sommerfeld enhancement is most significant at low velocities, early dark matter halos at redshift ~10 potentially produce observable effects on the ionization history of the universe, and substructure is more detectable than with a conventional WIMP. Moreover, the low velocity dispersion of dwarf galaxies and Milky Way subhalos can greatly increase the substructure annihilation signal.
We consider the nuclear scattering cross section for the eXciting Dark Matter (XDM) model. In XDM, the Weakly Interacting Massive Particles (WIMPs) couple to the Standard Model only via an intermediate light scalar which mixes with the Higgs: this leads to a suppression in the nuclear scattering cross section relative to models in which the WIMPs couple to the Higgs directly. We estimate this suppression factor to be of order 10^(-5). The elastic nuclear scattering cross section for XDM can also be computed directly: we perform this computation for XDM coupled to the Higgs sector of the Standard Model and find a spin-independent cross section in the order of 4 x 10^(-13) pb in the decoupling limit, which is not within the range of any near-term direct detection experiments. However, if the XDM dark sector is instead coupled to a two-Higgs-doublet model, the spin-independent nuclear scattering cross section can be enhanced by up to four orders of magnitude for large tan(beta), which should be observable in the upcoming SuperCDMS and ton-scale xenon experiments.
We show that models of inflection point inflation exhibit a phase transition from a region in parameter space where they are of large field type to a region where they are of small field type. The phase transition is between a universal behavior, with respect to the initial condition, at the large field region and non-universal behavior at the small field region. The order parameter is the number of e-foldings. We find integer critical exponents at the transition between the two phases.
In this paper we investigate the phenomenological implications of boundary localized terms (BLTs) in the model of Universal Extra Dimensions (UED). In particular, we study the electroweak Kaluza-Klein mass spectrum resulting from BLTs and their effect on electroweak symmetry breaking via the five dimensional Higgs mechanism. We find that the addition of BLTs to massive five dimensional fields induces a non-trivial extra dimensional profile for the zero and non-zero Kaluza-Klein (KK) modes. Hence BLTs generically lead to a modification of Standard Model parameters and are therefore experimentally constrained, even at tree level. We study Standard Model constraints on three representative non-minimal UED models in detail and find that the constraints on BLTs are weak. On the contrary, non-zero BLTs have a major impact on the spectrum and couplings of non-zero KK modes. For example, there are regions of parameter space where the Lightest Kaluza-Klein particle (LKP) is either the Kaluza-Klein Higgs boson or the first KK mode of the W^3.
If you fall into a real astronomical black hole (choosing a supermassive black hole, to make sure that the tidal forces don't get you first), then you will probably meet your fate not at a central singularity, but rather in the exponentially growing, relativistic counter-streaming instability at the inner horizon first pointed out by Poisson & Israel (1990), who called it mass inflation. The purpose of this paper is to present a clear exposition of the physical cause and consequence of inflation in spherical, charged black holes. Inflation acts like a particle accelerator in that it accelerates cold ingoing and outgoing streams through each other to prodigiously high energies. Inflation feeds on itself: the acceleration is powered by the gravity produced by the streaming energy.
Variational principles for magnetohydrodynamics were introduced by previous authors both in Lagrangian and Eulerian form. In a previous work Yahalom & Lynden-Bell introduced a simpler Eulerian variational principles from which all the relevant equations of magnetohydrodynamics can be derived. The variational principle was given in terms of six independent functions for non-stationary flows and three independent functions for stationary flows. This is less then the seven variables which appear in the standard equations of magnetohydrodynamics which are the magnetic field $\vec B$ the velocity field $\vec v$ and the density $\rho$. In this work I will improve on the previous results showing that non-stationary magnetohydrodynamics should be described by four functions .
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There is a long-standing discrepancy between galaxy cluster masses determined from X-ray and gravitational lensing observations of which Abell 1689 is a well-studied example. In this work we take advantage of 180 ks of Chandra X-ray observations and a new weak gravitational study based on a Hubble Space Telescope mosaic covering the central 1.8 Mpc x 1.4 Mpc to eliminate the mass discrepancy. In contrast to earlier X-ray analyses where the very circular surface brightness has been inferred as Abell 1689 being spherically symmetric and in hydrostatic equilibrium, a hardness ratio map analysis reveals a regular and symmetric appearing main clump with a cool core plus some substructure in the North Eastern part of the cluster. The gravitational lensing mass model supports the interpretation of Abell 1689 being composed of a main clump, which is possibly a virialized cluster, plus some substructure. In order to avoid complications and mis-interpretations due to X-ray emission from the substructure, we exclude it from the mass reconstruction. Comparing X-ray and lensing mass profiles of the regular main part only, shows no significant discrepancy between the two methods and the obtained mass profiles are consistent over the full range where the mass can be reconstructed from X-rays (out to approx. 1 Mpc). The obtained cluster mass within approx. 875 kpc derived from X-rays alone is 6.4 plus/minus 2.1 x 10^14 solar masses compared to a weak lensing mass of 8.6 plus/minus 3.0 x 10^14 solar masses within the same radius.
Recent results have shown that a substantial fraction of high-redshift Lyman alpha galaxies contain considerable amounts of dust. This implies that Lyman alpha galaxies are not primordial, as has been thought in the past. However, this dust has not been directly detected in emission; rather it has been inferred based on extinction estimates from rest-frame ultraviolet (UV) and optical observations. This can be tricky, as both dust and old stars redden galactic spectra at the wavelengths used to infer dust. Measuring dust emission directly from these galaxies is thus a more accurate way to estimate the total dust mass, giving us real physical information on the stellar populations and interstellar medium (ISM) enrichment. New generation instruments such as the Atacama Large Millimeter Array (ALMA) and Sub-Millimeter Array (SMA), should be able to detect dust emission from some of these galaxies in the sub-mm. Using measurements of the UV spectral slopes, we derive far-infrared flux predictions for of a sample of 23 z > 4 Lyman alpha galaxies. We find that in only a few hours, we can detect dust emission from 39 +/- 22% of our Lyman alpha galaxies. Comparing these results to those found from a sample of 21 Lyman break galaxies (LBGs), we find that LBGs are on average 60% more likely to be detected than Lyman alpha galaxies, implying that they are more dusty, and thus indicating an evolutionary difference between these objects. These observations will provide better constraints on dust in these galaxies than those derived from their UV and optical fluxes alone. Undeniable proof of dust in these galaxies could explain the larger than expected Lyman alpha equivalent widths seen in many Lyman alpha galaxies today.
We examine the stability of a standing shock wave within a spherical accretion flow onto a gravitating star, in the context of core-collapse supernova explosions. Our focus is on the effect of nuclear dissociation below the shock on the linear growth, and non-linear saturation, of non-radial oscillations of the shocked fluid. We combine two-dimensional, time-dependent hydrodynamic simulations using FLASH2.5 with a solution to the linear eigenvalue problem, and demonstrate the consistency of the two approaches. Previous studies of this `Standing Accretion Shock Instability' (SASI) have focused either on zero-energy accretion flows without nuclear dissociation, or made use of a detailed finite-temperature nuclear equation of state and included strong neutrino heating. Our main goal in this and subsequent papers is to introduce equations of state of increasing complexity, in order to isolate the various competing effects. In this work we employ an ideal gas equation of state with a constant rate of nuclear dissociation below the shock, and do not include neutrino heating. We find that a negative Bernoulli parameter below the shock significantly lowers the real frequency, growth rate, and saturation amplitude of the SASI. A decrease in the adiabatic index has similar effects. The non-linear development of the instability is characterized by an expansion of the shock driven by turbulent kinetic energy at nearly constant internal energy. Our results also provide further insight into the instability mechanism: the rate of growth of a particular mode is fastest when the radial advection time from the shock to the accretor overlaps with the period of a standing lateral sound wave. The identity of the fastest-growing mode can therefore be modified by nuclear dissociation.
We demonstrate that two approximations to the chi^2 statistic as popularly employed by observational astronomers for fitting Poisson-distributed data can give rise to intrinsically biased model parameter estimates, even in the high counts regime, unless care is taken over the parameterization of the problem. For a small number of problems, previous studies have shown that the fractional bias introduced by these approximations is often small when the counts are high. However, we show that for a broad class of problem, unless the number of data bins is far smaller than \sqrt{N_c}, where N_c is the total number of counts in the dataset, the bias will still likely be comparable to, or even exceed, the statistical error. Conversely, we find that fits using Cash's C-statistic give comparatively unbiased parameter estimates when the counts are high. Taking into account their well-known problems in the low count regime, we conclude that these approximate chi^2 methods should not routinely be used for fitting an arbitrary, parameterized model to Poisson-distributed data, irrespective of the number of counts per bin, and instead the C-statistic should be adopted. We discuss several practical aspects of using the C-statistic in modelling real data. We illustrate the bias for two specific problems, measuring the count-rate from a lightcurve and obtaining the temperature of a thermal plasma from its X-ray spectrum measured with the Chandra X-ray observatory. In the context of X-ray astronomy, we argue the bias could give rise to systematically mis-calibrated satellites and a ~5-10% shift in galaxy cluster scaling relations.
We examine the class of barotropic fluid models of dark energy, in which the pressure is an explicit function of the density, p = f(\rho). Through general physical considerations we constrain the asymptotic past and future behaviors and show that this class is equivalent to the sum of a cosmological constant and a decelerating perfect fluid, or "aether", with w_{AE}\ge0. Barotropic models give disjoint predictions from quintessence, except in the limit of \LambdaCDM. They are also interesting in that they simultaneously can ameliorate the coincidence problem and yet "predict" a value of w\approx-1.
It has recently been pointed out by Kowalski et. al. (arxiv:0804.4142) that there is `an unexpected brightness of the SnIa data at z>1'. We quantify this statement by constructing a new statistic which is applicable directly on the Type Ia Supernova (SnIa) distance moduli. This statistic is designed to pick up systematic brightness trends of SnIa datapoints with respect to a best fit cosmological model at high redshifts. It is based on binning the normalized differences between the SnIa distance moduli and the corresponding best fit values in the context of a specific cosmological model (eg LCDM). We then focus on the highest redshift bin and extend its size towards lower redshifts until the Binned Normalized Difference (BND) changes sign (crosses 0) at a redshift z_c (bin size N_c). The bin size N_c of this crossing (the statistical variable) is then compared with the corresponding crossing bin size N_{mc} for Monte Carlo data realizations based on the best fit model. We find that the crossing bin size N_c obtained from the Union08 and Gold06 data with respect to the best fit LCDM model is anomalously large compared to N_{mc} of the corresponding Monte Carlo datasets obtained from the best fit LCDM in each case. In particular, only 2.2% of the Monte Carlo LCDM datasets are consistent with the Gold06 value of N_c while the corresponding probability for the Union08 value of N_c is 5.3%. Thus, according to this statistic, the probability that the high redshift brightness bias of the Union08 and Gold06 datasets is realized in the context of a (w_0,w_1)=(-1,0) model (LCDM cosmology) is less than 6%. The corresponding realization probability in the context of a (w_0,w_1)=(-1.4,2) model is more than 30% for both the Union08 and the Gold06 datasets.
We estimate the absolute magnitude distribution of galaxies which lie within about a Mpc of Mg II absorption systems. The absorption systems themselves lie along 1880 lines of sight to QSOs from the Sloan Digital Sky Survey Data Release 3, have rest equivalent widths greater than 0.88 Angstroms, and redshifts between 0.37 < z < 0.82. Our measurement is based on all galaxies which lie within a projected distance of about 900 kpc/h of each QSO demonstrating absorption. The redshifts of these projected neighbors are not available, so we use a background subtraction technique to estimate the absolute magnitude distribution of true neighbors. (Our method exploits the fact that, although we do not know the redshifts of the neighbors, we do know the redshift of the absorbers.) The absolute magnitude distribution we find is well described by a bell-shaped curve peaking at about rest-frame M_B = -20, corresponding to L/L* = 1.4. A comparison of this observed distribution to ones in the literature suggests that it is unlikely to be drawn from a population dominated by late-type galaxies. However, the strong equivalent width systems may be associated with later galaxy types. Finally we use the absolute magnitude distribution, along with the observed covering fraction of about 8 percent, to estimate the extent of the MgII absorbing gas around a galaxy. For an L* galaxy, this scale is about 70 kpc/h. We provide an analytic description of our method, which is generally applicable to any dataset in which redshifts are only available for a small sub-sample. Hence, we expect it to aid in the analysis of galaxy scaling relations from photometric redshift datasets.
In this study, we investigate the shapes of starless and protostellar cores using hydrodynamic, self-gravitating adaptive mesh refinement simulations of turbulent molecular clouds. We simulate observations of these cores in dust emission, including realistic noise and telescope resolution, and compare to the observed core shapes measured in Orion by Nutter & Ward-Thompson (2007). The simulations and the observations have generally high statistical similarity, with particularly good agreement between simulations and Orion B. Although protostellar cores tend to have semi-major axis to semi-minor axis ratios closer to one, the distribution of axis ratios for starless and protostellar cores are not significantly different for either the actual observations of Orion or the simulated observations. Because of the high level of agreement between the non-magnetic hydrodynamic simulations and observation, contrary to a number of previous authors, one cannot infer the presence of magnetic fields from core shape distributions.
We show that the algorithm proposed by Gauss to compute the secular evolution of gravitationally interacting Keplerian rings extends naturally to softened gravitational interactions. The resulting tool is ideal for the study of the secular dynamical evolution of nearly Keplerian systems such as stellar clusters surrounding black holes in galactic nuclei, cometary clouds, or planetesimal discs. We illustrate its accuracy, efficiency and versatility on a variety of configurations.
The large range of time and length scales involved in type Ia supernovae (SN Ia) requires the use of flame models. As a prelude to exploring various options for flame models, we consider, in this paper, high-resolution three-dimensional simulations of the small-scale dynamics of nuclear flames in the supernova environment in which the details of the flame structure are fully resolved. The range of densities examined, 1 to $8 \times 10^7$ g cm$^{-3}$, spans the transition from the laminar flamelet regime to the distributed burning regime where small scale turbulence disrupts the flame. The use of a low Mach number algorithm facilitates the accurate resolution of the thermal structure of the flame and the inviscid turbulent kinetic energy cascade, while implicitly incorporating kinetic energy dissipation at the grid-scale cutoff. For an assumed background of isotropic Kolmogorov turbulence with an energy characteristic of SN Ia, we find a transition density between 1 and $3 \times 10^7$ g cm$^{-3}$ where the nature of the burning changes qualitatively. By $1 \times 10^7$ g cm$^{-3}$, energy diffusion by conduction and radiation is exceeded, on the flame scale, by turbulent advection. As a result, the effective Lewis Number approaches unity. That is, the flame resembles a laminar flame, but is turbulently broadened with an effective diffusion coefficient, $D_T \sim u' l$, where $u'$ is the turbulent intensity and $l$ is the integral scale. For the larger integral scales characteristic of a real supernova, the flame structure is predicted to become complex and unsteady. Implications for a possible transition to detonation are discussed.
In this thesis we focus on studying the physics of cosmological recombination and how the details of recombination affect the Cosmic Microwave Background (CMB) anisotropies. We present a detailed calculation of the spectral line distortions on the CMB spectrum arising from the Lyman-alpha and the lowest two-photon transitions in the recombination of hydrogen (H), and the corresponding lines from helium (He). The peak of these distortions mainly comes from the Lyman-alpha transition and occurs at about 170 microns, which is the Wien part of the CMB. The major theoretical limitation for extracting cosmological parameters from the CMB sky lies in the precision with which we can calculate the cosmological recombination process. With this motivation, we perform a multi-level calculation of the recombination of H and He with the addition of the spin-forbidden transition for neutral helium (He I), plus the higher order two-photon transitions for H and among singlet states of He I. We find that the inclusion of the spin-forbidden transition results in more than a percent change in the ionization fraction, while the other transitions give much smaller effects. Last we modify RECFAST by introducing one more parameter to reproduce recent numerical results for the speed-up of helium recombination. Together with the existing hydrogen `fudge factor', we vary these two parameters to account for the remaining dominant uncertainties in cosmological recombination. By using a Markov Chain Monte Carlo method with Planck forecast data, we find that we need to determine the parameters to better than 10% for He I and 1% for H, in order to obtain negligible effects on the cosmological parameters.
We describe a new technique to measure stellar kinematics and line-strengths at large radii in nearby galaxies. Using the integral-field spectrograph SAURON as a 'photon-collector', we obtain spectra out to four effective radii (Re) in the early-type galaxy NGC 3379. By fitting orbit-based models to the extracted stellar velocity profile, we find that ~40% of the total mass within 5 Re is dark. The measured absorption line-strengths reveal a radial gradient with constant slope out to 4 Re.
The high Galactic longitude end of the Aquila Rift comprises the large Aquila molecular cloud complex, however, few young stars are known to be located in the area, and only one is directly associated with the Rift. In contrast, the Serpens star-forming region at the low Galactic longitude end of the Rift contains hundreds of young stars. We review studies of the raw molecular material and describe searches for young objects in the Aquila clouds. The characteristics of the known young stars and associated jets and outflows are also provided. Finally, we suggest some possible explanations for the dearth of star formation in this gas-rich region and propose some future observations to examine this mystery further.
Knowledge of the binary population in stellar groupings provides important information about the outcome of the star forming process in different environments (see, e.g., Blaauw 1991, and references therein). Binarity is also a key ingredient in stellar population studies, and is a prerequisite to calibrate the binary evolution channels. In this paper we present an overview of several commonly used methods to pair individual stars into binary systems, which we refer to as pairing functions. These pairing functions are frequently used by observers and computational astronomers, either for their mathematical convenience, or because they roughly describe the expected outcome of the star forming process. We discuss the consequences of each pairing function for the interpretation of observations and numerical simulations. The binary fraction and mass ratio distribution generally depend strongly on the selection of the range in primary spectral type in a sample. The mass ratio distribution and binary fraction derived from a binarity survey among a mass-limited sample of targets is thus not representative for the population as a whole. Neither theory nor observations indicate that random pairing of binary components from the mass distribution, the simplest pairing function, is realistic. It is more likely that companion stars are formed in a disk around a star, or that a pre-binary core fragments into two binary components. The results of our analysis are important for (i) the interpretation of the observed mass ratio distribution and binary fraction for a sample of stars, (ii) a range of possible initial condition algorithms for star cluster simulations, and (iii) how to discriminate between the different star formation scenarios.
We investigate the three-dimensional structure of the pulsar magnetosphere through time-dependent numerical simulations of a magnetic dipole that is set in rotation. We developed our own Eulerian finite difference time domain numerical solver of force-free electrodynamics and implemented the technique of non-reflecting and absorbing outer boundaries. This allows us to run our simulations for many stellar rotations, and thus claim with confidence that we have reached a steady state. A quasi-stationary corotating pattern is established, in agreement with previous numerical solutions. We discuss the prospects of our code for future high-resolution investigations of dissipation, particle acceleration, and temporal variability.
We have developed an imaging Fourier transform spectrometer (FTS) for space-based far-infrared astronomical observations. The FTS employs a newly developed photoconductive detector arrays with a capacitive trans-impedance amplifier, which makes the FTS a completely unique instrument. The FTS was installed as a function of the far-infrared instrument (FIS: Far-Infrared Surveyor) on the Japanese astronomical satellite, AKARI, which was launched on February 21, 2006 (UT) from the Uchinoura Space Center. The FIS-FTS had been operated for more than one year before liquid helium ran out on August 26, 2007. The FIS-FTS was operated nearly six hundreds times, which corresponds to more than one hundred hours of astronomical observations and almost the same amount of time for calibrations. As expected from laboratory measurements, the FIS-FTS performed well and has produced a large set of astronomical data for valuable objects. Meanwhile, it becomes clear that the detector transient effect is a considerable factor for FTSs with photoconductive detectors. In this paper, the instrumentation of the FIS-FTS and interesting phenomena related to FTS using photoconductive detectors are described, and future applications of this kind of FTS system are discussed.
We describe some results obtained with N-MODY, a code for N-body simulations of collisionless stellar systems in modified Newtonian dynamics (MOND). We found that a few fundamental dynamical processes are profoundly different in MOND and in Newtonian gravity with dark matter. In particular, violent relaxation, phase mixing and galaxy merging take significantly longer in MOND than in Newtonian gravity, while dynamical friction is more effective in a MOND system than in an equivalent Newtonian system with dark matter.
Scalar wavelets have been used extensively in the analysis of Cosmic Microwave Background (CMB) temperature maps. Spin needlets are a new form of (spin) wavelets which were introduced in the mathematical literature by Geller and Marinucci (2008) as a tool for the analysis of spin random fields. Here we adopt the spin needlet approach for the analysis of CMB polarization measurements. The outcome of experiments measuring the polarization of the CMB are maps of the Stokes Q and U parameters which are spin 2 quantities. Here we discuss how to transform these spin 2 maps into spin 2 needlet coefficients and outline briefly how these coefficients can be used in the analysis of CMB polarization data. We review the most important properties of spin needlets, such as localization in pixel and harmonic space and asymptotic uncorrelation. We discuss several statistical applications, including the relation of C_l^EE,C_l^BB and C_l^TE to the needlet coefficients, testing for non-Gaussianity on polarization data, and reconstruction of the E and B scalar maps.
Episodic ejection of plasma blobs have been observed in many black hole systems. While steady, continuous jets are believed to be associated with large-scale open magnetic fields, what causes the episodic ejection of blobs remains unclear. Here by analogy with the coronal mass ejection on the Sun, we propose a magnetohydrodynamical model for episodic ejections from black holes associated with the closed magnetic fields in an accretion flow. Shears and turbulence of the accretion flow deform the field and result in the formation of a flux rope in the disk corona. Energy and helicity are accumulated and stored until a threshold is reached. The system then loses its equilibrium and the flux rope is thrust outward by the magnetic compression force in a catastrophic way.
We have undertaken a long-term project, Planets in Stellar Clusters Extensive Search (PISCES), to search for transiting planets in open clusters. In this paper we present the results for NGC 188, an old, rather populous cluster. We have monitored the cluster for more than 87 hours, spread over 45 nights. We have not detected any good transiting planet candidates. We have discovered 18 new variable stars in the cluster, bringing the total number of identified variables to 46, and present for them high precision light curves, spanning 15 months.
Combining the results of targeted observations, H.E.S.S. has accumulated a large amount of extra-galactic exposure at TeV energies. Due to its large field of view a considerable part of the sky (0.6 sr) has been observed with high sensitivity outside the targeted observation positions. Since this exposure region contains little inherent bias, it is well suited for studies of extra-galactic source populations. Given the correlation between ultra-high energy cosmic rays and nearby extra-galactic objects recently claimed by the Auger collaboration, this unbiased sky sample by H.E.S.S. is of interest since it includes (besides the targeted sources) 63 AGN within 100 Mpc, for which very-high energy gamma-ray flux limits are derived.
We use the Spitzer IRAC catalogue of the Galactic Center (GC) point sources
(Ramirez et al. 2008) and combine it with new isochrones (Marigo et al. 2008)
to derive extinctions based on photometry of red giants and asymptotic giant
branch (AGB) stars. This new extinction map extends to much higher values of Av
than previoulsy available. Our new extinction map of the GC region covers 2.0 x
1.4 degree (280 x 200 pc at a distance of 8 kpc). We apply it to deredden the
LPVs found by Glass et al. (2001) near the GC. We make period-magnitude
diagrams and compare them to those from other regions of different metallicity.
The Glass-LPVs follow well-defined period-luminosity relations (PL) in the
IRAC filter bands at 3.6, 4.5, 5.8, and 8.0 micron. The period-luminosity
relations are similar to those in the Large Magellanic Cloud, suggesting that
the PL relation in the IRAC bands is universal. We use ISOGAL data to derive
mass-loss rates and find for the Glass-LPV sample some correlation between
mass-loss and pulsation period, as expected theoretically.The GC has an excess
of high luminosity and long period LPVs compared to the Bulge, which supports
previous suggestions that it contains a younger stellar population.
Spiral arm spurs are prominent features that have been observed in extinction and 8$\mu$m emission in nearby galaxies. In order to understand their molecular gas properties, we used the Owens Valley Radio Observatory to map the CO(J=1--0) emission in three spurs emanating from the inner northwestern spiral arm of M51. We report CO detections from all three spurs. The molecular gas mass and surface density are M$_{H2} \sim3\times10^6$ M$_{\sun}$ and $\Sigma_{H2} \sim$50 M$_{\sun}$ pc$^{-2}$. Thus, relative to the spiral arms, the spurs are extremely weak features. However, since the spurs are extended perpendicular to the spiral arms for $\sim$500 pc and contain adequate fuel for star formation, they may be the birthplace for observed inter-arm HII regions. This reduces the requirement for the significant time delay that would be otherwise needed if the inter-arm star formation was initiated in the spiral arms. Larger maps of galaxies at similar depth are required to further understand the formation and evolution of these spurs and their role in star formation - such data should be forthcoming with the new CARMA and future ALMA telescopes and can be compared to several recent numerical simulations that have been examining the evolution of spiral arm spurs.
Aims. Exoplanet-host stars (EHS) are known to present superficial chemical abundances different from those of stars without any detected planet (NEHS). EHS are, on the average, overmetallic compared to the Sun. The observations also show that, for cool stars, lithium is more depleted in EHS than in NEHS. The aim of this paper is to obtain constraints on possible models able to explain this difference, in the framework of overmetallic models compared to models with solar abundances. Methods. We have computed main sequence stellar models with various masses and metallicities. The results show different behaviour for the lithium destruction according to those parameters. We compare these results to the spectroscopic observations of lithium. Results. Our models show that the observed lithium differences between EHS and NEHS are not directly due to the overmetallicity of the EHS: some extra mixing is needed below the convective zones. We discuss possible explanations for the needed extra mixing, in particular an increase of the mixing efficiency associated with the development of shear instabilities below the convective zone, triggered by angular momentum transfer due to the planetary migration.
Asteroseismology provides powerful means to probe stellar interiors. The oscillations frequencies are closely related to stellar interior properties via the density and sound speed profiles. Since these are tightly linked with the mass and evolutionary state, we can expect to determine the age and mass of a star from the comparison of its oscillation spectrum with predictions of stellar models. Such a comparison suffers both from the problems we face when modeling a particular star (as the uncertainties on global parameters and chemical composition) and from our misunderstanding of processes at work in stellar interiors (as the transport processes that may lead to core mixing and affect the model ages). For stars where observations have provided precise and numerous oscillation frequencies together with accurate global parameters and additional information (as the radius or the mass if the star is in a binary system, the interferometric radius or the mean density if the star is an exoplanet host), we can also expect to better constrain the physical description of the stellar structure and to get a more reliable age estimation. After a survey of stellar pulsations, we present some seismic diagnostics that can be used to infer the age of a star as well as their limitations. We then illustrate the ability of asteroseismology to scrutinize stellar interiors on the basis of a few exemples. In the years to come, extended very precise asteroseismic observations are expected, in photometry or in spectroscopy, from ground-based (HARPS, CORALIE, ELODIE, UVES, UCLES, SIAMOIS, SONG) or spatial devices (MOST, CoRoT, WIRE, Kepler, PLATO). This will considerably enlarge the sample of stars eligible to asteroseismic age determination and should allow to estimate the age of individual stars with a 10-20% accuracy.
Synchrotron emission from jets produced by X-ray binaries can be detected at optical and infrared (IR) frequencies. I show that optical/IR colour-magnitude diagrams of the outbursts of nine X-ray binaries successfully separate thermal disc emission from non-thermal jet emission, in both black hole and neutron star sources. A heated single-temperature blackbody is able to reproduce the observed relations between colour and magnitude, except when excursions are made to a redder colour than expected, which is due to jet emission. The general picture that is developed is then incorporated into the unified picture of disc-jet behaviour in black hole X-ray binaries. At a given position of a source in the X-ray hardness-intensity diagram, the radio, IR and optical properties can be inferred. Similarly, it is possible to predict the X-ray and radio luminosities and spectral states from optical/IR monitoring.
Directional detection of Dark Matter allows for unambiguous direct detection of WIMPs as well as discrimination between various Dark Matter models in our galaxy. The DMTPC detector is a low-pressure TPC with optical readout designed for directional direct detection of WIMPs. By using CF4 gas as the active material, the detector also has excellent sensitivity to spin-dependent interactions of Dark Matter on protons.
Near infrared spectra of 133 red giant stars from ten Galactic open clusters and two Galactic globular clusters spanning 2.2 dex in metallicity and 11 Gyr in age are presented. We combine this sample with ten clusters from Cole and collaborators to investigate the Ca II triplet line strengths and their relation to cluster metallicity and position along the red giant branch. We show that characterizing the stellar surface gravity using Ks band photometry (relative to the horizontal branch) taken from the Two Micron All-Sky Survey allows for metallicity measurements at least as precise as those derived using V or I band data. This has the great advantage that uniform photometry and reliable astrometry is available for a large number of clusters. Using Ks band photometry also reduces the effect of differential reddening within a given cluster. We find no significant evidence for age or metallicity effects to the linear Ca II triplet - metallicity relationship over the small range in magnitudes studied when homogeneous reference metallicities are used. We derive the first spectroscopic metallicity and new radial velocity estimates for five open clusters: Berkeley 81, Berkeley 99, IC 1311, King 2, and NGC 7044. King 2 has an anomalous radial velocity compared with the local disk population. We discuss the possibility that it is part of the Monoceros tidal stream.
The upper envelope of the amplitude of the VLBI visibility function usually represents the most compact structural pattern of extragalactic radio sources, in particular, the "core-jet" morphologies. By fitting the envelope to a circular Gaussian model in ~3000 parsec-scale core-jet structures, we find that the apparent angular size shows significant power-law dependence on the observing frequency (power index n = -0.95 pm 0.37). The dependence is likely to result from synchrotron self-absorption in the inhomogeneous jet and not the free-free absorption (n = -2.5), nor the simple scatter broadening (n leq -2).
We measure and analyse the sizes of 82 massive (M >= 10^11 M_Sun) galaxies at 1.7<z<3 utilizing deep HST NICMOS data taken in the GOODS North and South fields. Our sample provides the first statistical study of massive galaxy sizes at z>2. We split our sample into disk-like (Sersic index n<=2) and spheroid-like (Sersic index n>2) galaxies, and find that at a given stellar mass, disk-like galaxies at z~2.3 are a factor of 2.6+/-0.3 smaller than present day equal mass systems, and spheroid-like galaxies at the same redshift are 4.3+/-0.7 times smaller than comparatively massive elliptical galaxies today. We furthermore show that the stellar mass densities of very massive galaxies at z~2.5 are similar to present-day globular clusters with values ~2x10^10 M_Sun kpc^-3
DAOSPEC is a Fortran code for measuring equivalent widths of absorption lines in stellar spectra with minimal human involvement. It works with standard FITS format files and it is designed for use with high resolution (R>15000) and high signal-to-noise-ratio (S/N>30) spectra that have been binned on a linear wavelength scale. First, we review the analysis procedures that are usually employed in the literature. Next, we discuss the principles underlying DAOSPEC and point out similarities and differences with respect to conventional measurement techniques. Then experiments with artificial and real spectra are discussed to illustrate the capabilities and limitations of DAOSPEC, with special attention given to the issues of continuum placement; radial velocities; and the effects of strong lines and line crowding. Finally, quantitative comparisons with other codes and with results from the literature are also presented.
SAX J1818.6-1703 is a flaring transient X-ray source serendipitously
discovered by BeppoSAX in 1998 during an observation of the Galactic centre.
The source was identified as a High-Mass X-ray Binary with an OB SuperGiant
companion. Displaying short and bright flares and an unusually very-low
quiescent level implying intensity dynamical range as large as 1e3-4, the
source was classified as a Supergiant Fast X-ray Transient. The mechanism
triggering the different temporal behaviour observed between the classical
SGXBs and the recently discovered class of SFXTs is still debated. The
discovery of long orbits (>15 d) should help to discriminate between emission
models and bring constraints.
We analysed archival INTEGRAL data on SAX J1818.6-1703. We built short- and
long-term light curves and performed timing analysis in order to study the
temporal behaviour of SAX J1818.6-1703 on different time scales. INTEGRAL
revealed an unusually long orbital period of 30.0+/-0.2 d and an elapsed
accretion phase of ~6 d in the transient SGXB SAX J1818.6-1703. This implies an
elliptical orbit and constraints the possible supergiant spectral type between
B0.5-1I with eccentricities e~0.3-0.4 (for average fundamental parameters of
supergiant stars). During the accretion phase, the source behaved like
classical SGXBs. The huge variations of the observed X-ray flux can be
explained through accretion of macro-clumps formed within the stellar wind. Our
analysis strengthens the model which predicts that SFXTs behave as SGXBs but
with different orbital parameters, thus different temporal behaviour.
The luminous Galactic Cepheid RS Puppis is unique in being surrounded by a dust nebula illuminated by the variable light of the Cepheid. In a recent paper in this journal, Kervella et al. (2008) report a very precise geometric distance to RS Pup, based on measured phase lags of the light variations of individual knots in the reflection nebula. In this commentary, we examine the validity of the distance measurement, as well as the reality of the spatial structure of the nebula determined by Feast (2008) based upon the phase lags of the knots. {Kervella et al. assumed that the illuminated dust knots lie, on average, in the plane of the sky (otherwise it is not possible to derive a geometric distance from direct imaging of light echoes). We consider the biasing introduced by the high efficiency of forward scattering. We conclude that most of the knots are in fact likely to lie in front of the plane of the sky, thus invalidating the Kervella et al. result. We also show that the flat equatorial disk structure determined by Feast is unlikely; instead, the morphology of the nebula is more probably bipolar, with a significant tilt of its axis with respect to the plane of the sky. Although the Kervella et al. distance result is invalidated, we show that high-resolution polarimetric imaging has the potential to yield a valid geometric distance to this important Cepheid.
We expand our pervious numerical study of the properties of the stellar velocity distribution within the disk of a two-armed spiral galaxy by considering spiral stellar density waves with different global Fourier amplitudes, C_2. We confirm our previous conclusion that the ratio \sigma_1:\sigma_2 of smallest versus largest principal axes of the stellar velocity ellipsoid becomes abnormally small near the outer edges of the stellar spiral arms. The extent to which the stellar velocity ellipsoid is elongated (as compared to the unperturbed value typical for the axisymmetric disk) increases with the strength of the spiral density wave. In particular, the C_2=0.06 spiral can decrease the unperturbed value of \sigma_1:\sigma_2 by 20%, while the C_2=0.13 spiral can decrease the unperturbed \sigma_1:\sigma_2 by a factor of 3. The abnormally small values of the \sigma_1:\sigma_2 ratio can potentially be used to track the position of {\it stellar} spiral density waves. The \sigma_{\phi\phi}:\sigma_{rr} ratio is characterized by a more complex behaviour and exhibits less definite minima near the outer edges of the spiral arms. We find that the epicycle approximation is violated near the spiral arms and cannot be used in spiral galaxies with C_2 >= 0.05-0.06 or in galaxies with the amplitude of the spiral stellar density wave (relative to the unperturbed background) of order 0.1 or greater.
Horizontal branch (HB) stars play a particularly important role in the "age debate," since they are at the very center of the long-standing "second parameter" problem. In this review, I discuss some recent progress in our understanding of the nature and origin of HB stars.
We investigate the presence of silicon atoms adsorbed on the surface of interstellar polycyclic aromatic hydrocarbons (PAHs) to form SiPAH pi-complexes. We use quantum chemistry calculations to obtain structural, thermodynamic and mid-IR properties of neutral and cationic SiPAH complexes. The binding energy was found to be at least 1.5 eV for [SiPAH]+ complexes whereas it is roughly 0.5 eV for their neutral counterparts. From the spectral analysis of the calculated IR spectra, we found that the coordination of silicon to PAH+ does not strongly affect the intensities of the PAH+ spectra, but systematically introduces blueshifts of the C-C in-plane and the C-H out-of-plane bands. The thermodynamic data calculated for [SiPAH]+ complexes show that these species are stable and can be easily formed by radiative association of Si+ and PAH species that are known to be abundant in photodissociation regions. Their mid-IR fingerprints show features induced by the coordination of silicon that could account for (i) the blueshifted position of the 6.2 micron AIB and (ii) the presence of satellite bands observed on the blue side of the 6.2 and 11.2 micron AIBs. From such an assignment, we can deduce that typically 1% of the cosmic silicon appears to be attached to PAHs.
The prompt GRB emission is thought to arise from electrons accelerated in internal shocks propagating within a highly relativistic outflow. The launch of Fermi offers the prospect of observations with unprecedented sensitivity in high-energy (>100 MeV) gamma-rays. The aim is to explore the predictions for HE emission from internal shocks, taking into account both dynamical and radiative aspects, and to deduce how HE observations constrain the properties of the relativistic outflow. The emission is modeled by combining a time-dependent radiative code with a dynamical code giving the evolution of the physical conditions in the shocked regions.Synthetic lightcurves and spectra are compared to observations. The HE emission deviates significantly from analytical estimates, which tend to overpredict the IC component, when the time dependence and full cross-sections are included. The exploration of the parameter space favors the case where the dominant process in the BATSE range is synchrotron emission. The HE component becomes stronger for weaker magnetic fields. The HE lightcurve can display a prolonged pulse duration due to IC emission, or even a delayed peak compared to the BATSE range.Alternatively, having dominant IC emission in the BATSE range requires most electrons to be accelerated into a steep power-law distribution and implies strong 2nd order IC scattering. In this case, the BATSE and HE lightcurves are very similar. The combined dynamical and radiative approach allows a firm appraisal of GRB HE prompt emission. A diagnostic procedure is presented to identify from observations the dominant emission process and derive constrains on the bulk Lorentz factor, particle density and magnetic field of the outflow.
We report preliminary results of mid-infrared (MIR) and X-ray observations of
GRS 1915+105 that we carried out between 2004 October 2 and 2006 June 5. Our
main goals were to study its variability, to detect the presence of dust, and
to investigate the possible links between MIR and X-ray emissions.
We performed photometric and spectroscopic observations of GRS 1915+105,
using the IRAC photometer and the IRS spectrometer mounted on the Spitzer Space
Telescope. We completed our set of MIR data with quasi-simultaneous high-energy
data obtained with RXTE and INTEGRAL.
In the hard state, we detect PAH emission features in the MIR spectrum of GRS
1915+105, which prove the presence of dust in the system. The dust is confirmed
by the detection in the hard state of a warm MIR excess in the broadband
spectral energy distribution of GRS 1915 105. This excess cannot be explained
by the MIR synchrotron emission from the compact jets as GRS 1915+105 was not
detected at 15 GHz with the Ryle telescope. We also show that the MIR emission
of GRS 1915+105 is strongly variable; it is likely correlated to the soft X-ray
emission as it increases in the soft state. We suggest that, beside the dust
emission, part of the MIR excess in the soft state is non-thermal, and could be
due either to free-free emission from an X-ray driven wind or X-ray
reprocessing in the outer part of the accretion disc.
The study of the broad-band emission of GHz-Peaked-Spectrum (GPS) radio galaxies is a powerful tool to investigate the physical processes taking place in the central, kpc-sized region of their active hosts, where the jets propagate and the lobes expand, interacting with the surrounding interstellar medium (ISM). We recently developed a new dynamical-radiative model to describe the evolution of the GPS phenomenon (Stawarz et al. 2008): as the relativistic jets propagate through the ISM, gradually engulfing narrow-line emitting gas clouds along their way, the electron population of the expanding lobes evolves, emitting synchrotron light, as well as inverse-Compton radiation via up-scattering of the photon fields from the host galaxy and its active nucleus. The model, which successfully reproduces the key features of the GPS radio sources as a class, provides a description of the evolution of their spectral energy distribution (SED) with the lobes' expansion, predicting significant and complex X-ray to gamma-ray emission. We apply here the model to the broad-band SED's of a sample of known, X-ray emitting GPS galaxies, and show that: (i) the free-free absorption mechanism enables us to reproduce the radio continuum at frequencies below the turnover; (ii) the lobes' non-thermal, inverse-Compton emission can account for the observed X-ray spectra, providing a viable alternative to the thermal, accretion-dominated scenario. We also show that, in our sample, the relationship between the X-ray and radio hydrogen column densitities, N_H and N_HI, is suggestive of a positive correlation, which, if confirmed, would support the scenario of high-energy emitting lobes.
We study the post-main sequence evolution of products of collisions between main sequence stars (blue stragglers), with particular interest paid to the horizontal branch and asymptotic giant branch phases. We found that the blue straggler progeny populate the colour-magnitude diagram slightly blueward of the red giant branch and between 0.2 and 1 magnitudes brighter than the horizontal branch. We also found that the lifetimes of collision products on the horizontal branch is consistent with the numbers of so-called "evolved blue straggler stars" (E-BSS) identified by various authors in a number of globular clusters, and is almost independent of mass or initial composition profile. The observed ratio of the number of E-BSS to blue stragglers points to a main sequence lifetime for blue stragglers of approximately 1-2 Gyr on average.
We report the discovery of planetary companions around HD191760 with orbital periods of 8.64+/-0.02 and 86.83+/-0.50 days, semimajor axes of 0.09 and 0.42 AU and masses of 0.29+/-0.05 and 7.20+/-0.44 MJ respectively. The star has a spectral type of G3IV/V and a metallicity of 0.29 dex. HD191760 adds to the list of metal-rich multiple planet systems. The periods indicate the planets are located at the 10:1 mean motion resonance points. The outer planet exerts a large reflex velocity of 322.17+/-18.98 m/s on HD191760, whereas the inner planet's amplitude is found to be 24.22+/-2.86 m/s. The best fit to the Doppler data suggest a low eccentricity of 0.04+/-0.12 for the inner planet and a somewhat larger eccentricity of 0.49+/-0.07 for the outer planet. Dynamical simulations show the system to be stable, at least for the next 100,000 years. However, the eccentricity of the inner planet is found to oscillate with a frequency of around 140 years which may be measurable with more epochs of high quality radial-velocity data. In addition we also refine the orbits found for HD48265b, HD143361b and HD154672b. These systems have been announced by the Magellan Planet Search.
We calculate the spectra of two-component accretion flows around black holes of various masses, from quasars to nano-quasars. Specifically, we fit the observational data of M87 very satisfactorily using our model and find that the spectrum may be well fitted by a sub-Keplerian component alone, and there is little need of any Keplerian component. The non-thermal distribution of electrons produced by their acceleration across the standing shock in the sub-Keplerian component is enough to produce the observed flat spectrum through the synchrotron radiation.
I present a brief review on the determination of the primordial helium abundance by unit mass, Yp. I discuss the importance of the primordial helium abundance in: (a) cosmology, (b) testing the standard big bang nucleosynthesis, (c) studying the physical conditions in H II regions, (d) providing the initial conditions for stellar evolution models, and (e) testing the galactic chemical evolution models.
Star formation in the Local spiral arm in the direction of the Galactic longitudes 132--158 deg is reviewed. Recent star-forming activity in this Milky Way direction is evidenced by the presence here of the Cam OB1 association and dense dust and molecular clouds containing H$\alpha$ emission stars, young irregular variables and infrared stellar objects. The clouds of the Local arm concentrate in two layers at 150-300 pc and at about 900 pc from the Sun. The Perseus arm objects in this direction are at a distance of about 2 kpc.
We present a noncommutative extension of Quantum Cosmology and study the Kantowski-Sachs (KS) cosmological model requiring that the two scale factors of the KS metric, the coordinates of the system, and their conjugate canonical momenta do not commute. Through the ADM formalism, we obtain the Wheeler-DeWitt (WDW) equation for the noncommutative system. The Seiberg-Witten map is used to transform the noncommutative equation into a commutative one, i.e. into an equation with commutative variables, which depend on the noncommutative parameters, $\theta$ and $\eta$. Numerical solutions are found both for the classical and the quantum formulations of the system. These solutions are used to characterize the dynamics and the state of the universe. From the classical solutions we obtain the behavior of quantities such as the volume expansion, the shear and the characteristic volume. However the analysis of these quantities does not lead to any restriction on the value of the noncommutative parameters, $\theta$ and $\eta$. On the other hand, for the quantum system, one can obtain, via the numerical solution of the WDW equation, the wave function of the universe both for commutative as well as for the noncommutative models. Interestingly, we find that the existence of suitable solutions of the WDW equation imposes bounds on the values of the noncommutative parameters. Moreover, the noncommutativity in the momenta leads to damping of the wave function implying that this noncommutativity can be of relevance for the selection of possible initial states of the early universe.
We show that simple chaotic inflation with quadratic potential occurs naturally in theories where a pseudoscalar axion-like field dynamically mixes with a 4-form. Such an axion is massive, with the effective mass term arising from the mixing being protected by the axion shift symmetry. The 4-form backgrounds break this symmetry spontaneously and comprise a mini-landscape, parameterized by the 4-form background flux, which can change from place to place by emission of membranes. Wherever the mixing mass is smaller than the Planck scale, inflation can begin when the 4-form dominates energy density. After this energy is reduced by membrane emission, the axion starts to roll slowly towards its low energy minimum, set by the value of the 4-form flux after the membrane nucleation ceases. Thus the last stages of inflation will look exactly as the simplest version of chaotic inflation. When the mass of the inflation is ~ 10^13 GeV, its quantum fluctuations will yield nearly scale invariant density contrast ~ 10^(-5), as required for postinflationary structure formation.
We formulate a statistical model for description of nuclear composition and equation of state of stellar matter at subnuclear densities and temperature up to 20 MeV, which are expected during the collapse and explosion of massive stars. The model includes nuclear, electromagnetic and weak interactions between all kinds of particles, under condition of statistical equilibrium. We emphasize importance of realistic description of the nuclear composition for understanding stellar dynamics and nucleosynthesis. It is demonstrated that the experience accumulated in studies of nuclear multifragmentation reactions can be used for better modelling properties of stellar medium.
The breathing-mode isoscalar giant monopole resonance (GMR) is investigated using the generator coordinate method within the relativistic mean-field (RMF) theory. Employing the Lagrangian models of the nonlinear-$\sigma$ model (NL$\sigma$), the scalar-vector interaction model (SVI) and the $\sigma$-$\omega$ coupling model (SIGO), we show that each Lagrangian model exhibits a distinctly different GMR response. Consequently, Lagrangian models yield a different value of the GMR energy for a given value of the nuclear matter incompressibility $K_\infty$. It is shown that this effect arises largely from a different value of the surface incompressibility $K_{surf}$ inherent to each Lagrangian model, thus giving rise to the ratio $K_{surf}/K_\infty$ which depends upon the Lagrangian model used. This is attributed to a difference in the density dependence of the meson masses and hence to the density dependence of the nuclear interaction amongst various Lagrangian models. The sensitivity of the GMR energy to the Lagrangian model used and thus emergence of a multitude of GMR energies for a given value of $K_\infty$ renders the method of extracting $K_\infty$ on the basis of interpolation amongst forces as inappropriate. As a remedy, the need to 'calibrate' the density dependence of the nuclear interaction in the RMF theory is proposed.
The puzzle of the thermodynamic arrow of time reduces to the question of how the universe could have had lower entropy in the past. I show that no special entropy lowering mechanism (or fluctuation) is necessary. As a consequence of expansion, at a particular epoch in the history of the universe a state that was near maximum entropy under the dominant short range forces becomes extremely unlikely, due to a switchover to newly dominant long range forces. This happened at about the time of decoupling, prior to which I make no statement about arrows. The role of cosmology in thermodynamics was first suggested by T. Gold.
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We calculate the high energy (sub-GeV to TeV) prompt and afterglow emission of GRB 080319B that was distinguished by a naked-eye optical flash and by an unusual strong early X-ray afterglow. There are three possible sources for high energy emission: the prompt optical and $\gamma$-ray photons IC scattered by the internal shock electrons, the prompt photons IC scattered by the early external reverse-forward shock electrons, and the higher band of the synchrotron and the synchrotron self-Compton emission of the external shock. There should have been in total $\sim 500$ high energy photons detectable for the Large Area Telescope (LAT) onboard the Fermi satellite, and $> 30$ photons of those with energy $> 10$ GeV. The $> 10$ GeV emission had a duration about twice that of the soft $\gamma$-rays. AGILE could have observed these energetic signals if it was not occulted by the Earth at that moment. The physical origins of the high energy emission detected in GRB 080514B, GRB 080916C and GRB 081024B are also discussed. These observations can be reasonably interpreted by available high energy emission models based on our current understanding of GRBs and afterglows.
We show that the scalar field that drives inflation can have a dynamical origin, being a strongly coupled right handed neutrino condensate. The resulting model is phenomenologically tightly constrained, and can be experimentally (dis)probed in the near future. The mass of the right handed neutrino obtained this way (a crucial ingredient to obtain the right light neutrino spectrum within the see-saw mechanism in a complete three generation framework) is related to that of the inflaton and both completely determine the inflation features that can be tested by current and planned experiments.
The signal-to-noise ratio (SNR) for black hole quasinormal mode sources of low-frequency gravitational waves is estimated using a Monte Carlo approach that replaces the all-sky average approximation. We consider an eleven dimensional parameter space that includes both source and detector parameters. We find that in the black-hole mass range $M\sim 4$-$10\times 10^6M_{\odot}$ the SNR is significantly higher than the SNR for the all-sky average case, as a result of the variation of the spin parameter of the sources. This increased SNR may translate to a higher event rate for the Laser Interferometer Space Antenna (LISA). We also study the directional dependence of the SNR, and show at which directions in the sky LISA will have greater response.
We re-analyze the Chandra ACIS spectrum of the kpc-scale jet in PKS 0637-752 to investigate the possible low energy cutoff in the relativistic electron spectrum producing the non-thermal radiation in the scenario of inverse Compton emission off the cosmic microwave background. This was among the first objects targeted by the Chandra Observatory and gives a unique opportunity to study the low energy X-ray emission free of detector contamination. As previously reported in the literature, the spectrum can be fit by a power law, with the slope predicted by the radio spectrum, modified by low energy absorption through the Galaxy as determined from the spectrum of the quasar core and by HI 21 cm observations. We obtain a marginally better fit with an model of inverse Compton emission produced by an electron population that exhibits a cutoff at (gamma_min delta_10) between about 50 and 80 (assuming Gamma = delta). This range for gamma_min is higher than has previously been assumed in broad-band spectral fits to the jet emission. The observed optical flux can be used to place a lower limit on gamma_min; the constraint is not very strong, but does suggest that gamma_min must be higher than 1 to avoid overproducing the optical emission. We investigate the effect of uncertainties in the column density for galactic absorption as well as the calibration of Chandra for these early observations. Finally, we discuss the implication of these limits on the jet luminosity in this source.
Powering the 10E62 erg AGN outburst in the MS0735.6+7421 cluster's central galaxy by accretion implies that its putative supermassive black hole (SMBH) grew by ~6E8 solar masses or nearly 1/3 of its mass over the past 100 Myr. Guided by data at several wavelengths, we place restrictive upper limits on the amount of cold gas and star formation near the nucleus of <10E9 solar masses and <2 solar masses per year, respectively. These limits imply that much of the preexisting gas in the inner several kpc must have been consumed by its SMBH during the past 100 Myr at the rate of ~3-5 solar masses per year, or roughly 1/10 of the Eddington rate, while leaving no trace of star formation. These properties are inconsistent with an accretion-powered AGN. We suggest instead that MS0735's AGN is powered by a rapidly-spinning black hole. The rotational energy and power are consistent with the cavity and shock energetics and their ages inferred from X-ray observations. The host galaxy's unusually large, 3.8 kpc stellar core may have been scoured-out in part during the inspiral of one or more SMBH's, thus endowing the merged remnant with its enormous size and spin. A maximally-spinning, 1E9 solar mass SMBH contains enough rotational energy, ~10E62 erg, to quench a cooling flow over its lifetime and to contribute significantly to the excess entropy found in the hot atmospheres of groups and clusters. We suggest two modes of AGN feedback are quenching star formation in elliptical galaxies centered in cooling halos at late times. An accretion mode that operates in gas-rich systems, and a spin mode that operates at modest accretion rates. The central galaxy's large core and demanding AGN power suggest it harbors a >10E10 solar mass ultramassive black hole.
We present evidence for the existence of significant substructure in the cold front cluster Abell 3667 based on multi-object spectroscopy taken with the 3.9m Anglo Australian Telescope. This paper is the second in a series analyzing the relationship between cold fronts observed in Chandra X-ray images and merger activity observed at optical wavelengths. We have obtained 910 galaxy redshifts in the field of Abell 3667 out to 3.5 Mpc, of which 550 are confirmed cluster members, more than doubling the number of spectroscopically confirmed members previously available and probing some 3 mag down the luminosity function. From this sample, we derive a cluster redshift of z=0.0553 +/-0.0002 and velocity dispersion of 1056 +/- 38 km/s and use a number of statistical tests to search for substructure. We find significant evidence for substructure in the spatial distribution of member galaxies and also in the localized velocity distributions and, in spite of this evidence, find the global velocity distribution does not deviate significantly from a Gaussian. Using combined spatial and velocity information, we find the cluster can be separated into two major structures, with roughly equal velocity dispersions, but offset in peculiar velocity from each other by ~500 km/s, and a number of minor substructures. We propose two scenarios which explain the radio and X-ray observations. Our data show the cold front is directly related to cluster merger activity, and also highlights the extent of optical data required to unambiguously detect the presence of substructure.
We review recent advances in modeling global-scale convection and dynamo processes with the Anelastic Spherical Harmonic (ASH) code. In particular, we have recently achieved the first global-scale solar convection simulations that exhibit turbulent pumping of magnetic flux into a simulated tachocline and the subsequent organization and amplification of toroidal field structures by rotational shear. The presence of a tachocline not only promotes the generation of mean toroidal flux, but it also enhances and stabilizes the mean poloidal field throughout the convection zone, promoting dipolar structure with less frequent polarity reversals. The magnetic field generated by a convective dynamo with a tachocline and overshoot region is also more helical overall, with a sign reversal in the northern and southern hemispheres. Toroidal tachocline fields exhibit little indication of magnetic buoyancy instabilities but may be undergoing magneto-shear instabilities.
We measure the evolution of the [O II] lambda 3727 luminosity function at 0.75 < z < 1.45 using high-resolution spectroscopy of ~ 14,000 galaxies observed by the DEEP2 galaxy redshift survey. We find that brighter than L([O II])=10^{42} erg s^{-1} the luminosity function is well-represented by a power law dN/dL \propto L^{\alpha} with slope \alpha ~ -3. The number density of [O II]-emitting galaxies above this luminosity declines by a factor of \gtrsim 2.5 between z ~ 1.35 and z ~ 0.84. In the limit of no density evolution, the characteristic [O II] luminosity, defined as the luminosity where the space density equals 10^{-3.5} dex^{-1} Mpc^{-3}, declines by a factor of ~ 1.7 over the same redshift interval. These results imply a ~ 25% per Gyr decrease in the amount of star formation in galaxies during this epoch. Integrating the observed [O II] luminosity function assuming a faint-end power-law slope of -1.3 +/- 0.2, we derive the integrated star formation rate density in four redshift bins centered around z ~ 1, and find that the evolution is consistent with previous measurements based on independent star formation rate indicators.
We present high-resolution 4.6micron CO spectra of the circumstellar environments of two RSGs that are potential SN progenitors: Betelgeuse and VY CMa. Around Betelgeuse, 12CO emission within 3arcsec follows a mildly clumpy but otherwise spherical shell, smaller than its 55arcsec shell in KI lambda7699. In stark contrast, 4.6micron CO emission around VY CMa is coincident with bright KI in its clumpy asymmetric reflection nebula, within 5arcsec of the star. Our CO data reveal redshifted features not seen in KI spectra of VY CMa, indicating a more isotropic distribution of gas punctuated by randomly distributed asymmetric clumps. The relative CO and KI distribution in Betelgeuse arises from ionization effects within a steady wind, whereas in VY CMa, KI is emitted from skins of CO cloudlets resulting from episodic mass ejections 500--1000 yr ago. In both cases, CO and KI trace potential pre-SN circumstellar matter: we conclude that an extreme RSG like VY CMa might produce a Type IIn event like SN1988Z if it were to explode in its current state, but Betelgeuse will not. VY CMa demonstrates that LBVs are not necessarily the only progenitors of SNe IIn, but it underscores the requirement that SNe IIn suffer enhanced episodic mass loss shortly before exploding.
By combining test-particle and self-consistent techniques, we have developed a method to rapidly explore the parameter space of galactic encounters. Our method, implemented in an interactive graphics program, can be used to find the parameters required to reproduce the observed morphology and kinematics of interacting disk galaxies. We test this system on an artificial data-set of 36 equal-mass merging encounters, and show that it is usually possible to reproduce the morphology and kinematics of these encounters and that a good match strongly constrains the encounter parameters.
Berkeley conducts 7 SETI programs at IR, visible and radio wavelengths. Here
we review two of the newest efforts, Astropulse and Fly's Eye.
A variety of possible sources of microsecond to millisecond radio pulses have
been suggested in the last several decades, among them such exotic events as
evaporating primordial black holes, hyper-flares from neutron stars, emissions
from cosmic strings or perhaps extraterrestrial civilizations, but to-date few
searches have been conducted capable of detecting them.
We are carrying out two searches in hopes of finding and characterizing these
uS to mS time scale dispersed radio pulses. These two observing programs are
orthogonal in search space; the Allen Telescope Array's (ATA) "Fly's Eye"
experiment observes a 100 square degree field by pointing each 6m ATA antenna
in a different direction; by contrast, the Astropulse sky survey at Arecibo is
extremely sensitive but has 1/3,000 of the instantaneous sky coverage.
Astropulse's multibeam data is transferred via the internet to the computers of
millions of volunteers. These computers perform a coherent de-dispersion
analysis faster than the fastest available supercomputers and allow us to
resolve pulses as short as 400 nS. Overall, the Astropulse survey will be 30
times more sensitive than the best previous searches. Analysis of results from
Astropulse is at a very early stage.
The Fly's Eye was successfully installed at the ATA in December of 2007, and
to-date approximately 450 hours of observation has been performed. We have
detected three pulsars and six giant pulses from the Crab pulsar in our
diagnostic pointing data. We have not yet detected any other convincing bursts
of astronomical origin in our survey data. (Abridged)
A distribution of the meter-wave luminous objects, which are bright at frequency 74 MHz (a wavelength of 4 m) but not detectable at 1.4 GHz (21 cm) in the VLA surveys, shows a notable concentration in a scale of a few degrees toward Monoceros [(l, b)=(225, 4)]. We argue that it is a part of giant radio relics associated with a nearby cluster of galaxies with cz~2400$ km s^{-1} centered on the spiral galaxy NGC 2377. The angular separation of these objects from the clustering center is consistent with the separation of distant relics to the cluster center if scaled by distance. This fact implies that the concentrations of meter-wave luminous objects can be used as a tracer of the structure of the Local Supercluster and it's vicinity.
Knowledge of the binary population in stellar groupings provides important information about the outcome of the star forming process in different environments. Binarity is also a key ingredient in stellar population studies and is a prerequisite to calibrate the binary evolution channels. In these proceedings we present an overview of several commonly used methods to pair individual stars into binary systems, which we refer to as the pairing function. Many pairing functions are frequently used by observers and computational astronomers, either for the mathematical convenience, or because they roughly describe the expected outcome of the star forming process. We discuss the consequences of each pairing function for the interpretation of observations and numerical simulations. The binary fraction and mass ratio distribution generally depend strongly on the selection of the range in primary spectral type in a sample. These quantities, when derived from a binary survey with a mass-limited sample of target stars, are thus not representative for the population as a whole.
The analysis of the multicolour photometric observations of MW Lyr, a large modulation amplitude Blazhko variable, shows for the first time how the mean global physical parameters vary during the Blazhko cycle. About 1-2 percent changes in the mean radius, luminosity and surface effective temperature are detected. The mean radius and temperature changes are in good accordance with pulsation model results, which show that these parameters do indeed vary within this order of magnitude if the amplitude of the pulsation changes significantly. We interpret the phase modulation of the pulsation to be a consequence of period changes. Its magnitude corresponds exactly what one expects from the detected changes of the mean radius assuming that the pulsation constant remains the same during the modulation. Our results indicate that during the modulation the pulsation remains purely radial, and the underlying mechanism is most probably a periodic perturbation of the stellar luminosity with the modulation period.
We present a new method for determining physical parameters of RRab variables exclusively from multicolour light curves. Our method is an Inverse Photometric Baade-Wesselink analysis which, using a nonlinear least squares algorithm, searches for the effective temperature (T_eff) and pulsational velocity (V_p) curves and other physical parameters that best fit the observed light curves, utilising synthetic colours and bolometric corrections from static atmosphere models. The T_eff and V_p curves are initially derived from empirical relations then they are varied by the fitting algorithm. The method yields the variations and the absolute values of the radius, the effective temperature, the visual brightness, and the luminosity of individual objects. Distance and mass are also determined. The method is tested on 9 RRab stars subjected to Baade-Wesselink analyses earlier by several authors. The physical parameters derived by our method using only the light curve data of these stars are well within their possible ranges defined by direct Baade-Wesselink and other techniques. A new empirical relation between the I_C magnitude and the pulsational velocity is also presented, which allows to construct the V_p curve of an RRab star purely from photometric observations to an accuracy of about 3.5 km/s.
We investigate the causes of the different shape of the $K$-band number counts when compared to other bands, analyzing in detail the presence of a change in the slope around $K\sim17.5$. We present a near-infrared imaging survey, conducted at the 3.5m telescope of the Calar Alto Spanish-German Astronomical Center (CAHA), covering two separated fields centered on the HFDN and the Groth field, with a total combined area of $\sim0.27$deg$^{2}$ to a depth of $K\sim19$ ($3\sigma$,Vega). We derive luminosity functions from the observed $K$-band in the redshift range [0.25-1.25], that are combined with data from the references in multiple bands and redshifts, to build up the $K$-band number count distribution. We find that the overall shape of the number counts can be grouped into three regimes: the classic Euclidean slope regime ($d\log N/dm\sim0.6$) at bright magnitudes; a transition regime at intermediate magnitudes, dominated by $M^{\ast}$ galaxies at the redshift that maximizes the product $\phi^{\ast}\frac{dV_{c}}{d\Omega}$; and an $\alpha$ dominated regime at faint magnitudes, where the slope asymptotically approaches -0.4($\alpha$+1) controlled by post-$M^{\ast}$ galaxies. The slope of the $K$-band number counts presents an averaged decrement of $\sim50%$ in the range $15.5<K<18.5$ ($d\log N/dm\sim0.6-0.30$). The rate of change in the slope is highly sensitive to cosmic variance effects. The decreasing trend is the consequence of a prominent decrease of the characteristic density $\phi^{\ast}_{K,obs}$ ($\sim60%$ from $z=0.5$ to $z=1.5$) and an almost flat evolution of $M^{\ast}_{K,obs}$ (1$\sigma$ compatible with $M^{\ast}_{K,obs}=-22.89\pm0.25$ in the same redshift range).
A new scenario is suggested to explain a large diversity of the AGN radio properties and their dependence on the galaxy morphology. The scenario is based on the assumption that the growth of supermassive BHs is dominated by the accretion only during the quasar (high accretion rate) phase, otherwise - by mergers with less massive black holes. Following that, BHs are expected to spin much faster in giant ellipticals than in disk galaxies. Within the frame of the spin paradigm this explains the observed relation of the radio-dichotomy with the galaxy morphology. Various theoretical and observational aspects of such a dichotomy are discussed. In particular, the issue of the intermittency and suppression of a jet production at high accretion rates is addressed and a scenario for production of powerful, extended radio sources is drafted.
The crossing of the Galactic disk by a Globular Cluster could produce star formation due to gravitational focussing or compression of disk material. We report on simulations of the effect on disk material which reveal that the crossing can sometimes cause local gravitational focussing of disk material. We also present the salient points of a little-known paper by Levy (2000), that shows that strong compression can result from the shock wave generated by GC disk crossing. The main thrust of our paper is a search for remnants of disk crossings by Globular Clusters. Using the gravitational potential of the Galaxy to locate the position of the most recent crossings of a subset of fifty-four Globular Clusters reveals that systematic errors and uncertainties in initial conditions limit the scope for unequivocal identification. From the subset of fifty-four, six possible search sites with the best constraints are retained for further scrutiny. Three of the six potentially promising search areas in the disk are from Globular Clusters NGC 3201, 6397 and NGC 6838, for which we cannot rule out some observed star associations observed nearby as being remnants. The three other of the six areas are too large to provide meaningful identification of remnants. Also, a possible remnant (open cluster NGC6231) is shown not to be due to Globular Cluster impact, contrary to a previous report. In a more wide-ranging screening of one hundred and fifty-five Globular Clusters we identify which Globular Clusters are compatible with being responsible for the formation of any of the Galaxy's five most prominent Star Super Clusters.
We report two new XMM-Newton observations of PG1211+143 in December 2007, finding further evidence of the fast outflow of highly ionised gas, first detected in 2001. Stacking the new spectra with those from two earlier XMM-Newton observations reveals a broad PCygni profile in the Fe K band, showing the fast outflow to have a large covering factor, and confirming its significance as a powerful feed of mechanical energy into the host galaxy.
We show that collisions with stellar--mass black holes can partially explain the absence of bright giant stars in the Galactic Centre, first noted by Genzel et al, 1996. We show that the missing objects are low--mass giants and AGB stars in the range 1-3 M$_{\odot}$. Using detailed stellar evolution calculations, we find that to prevent these objects from evolving to become visible in the depleted K bands, we require that they suffer collisions on the red giant branch, and we calculate the fractional envelope mass losses required. Using a combination of Smoothed Particle Hydrodynamic calculations, restricted three--body analysis and Monte Carlo simulations, we compute the expected collision rates between giants and black holes, and between giants and main--sequence stars in the Galactic Centre. We show that collisions can plausibly explain the missing giants in the $10.5<K<12$ band. However, depleting the brighter ($K<10.5$) objects out to the required radius would require a large population of black hole impactors which would in turn deplete the $10.5<K<12$ giants in a region much larger than is observed. We conclude that collisions with stellar--mass black holes cannot account for the depletion of the very brightest giants, and we use our results to place limits on the population of stellar--mass black holes in the Galactic Centre.
We study magnetic field evolution in flows with fluctuating in time governing parameters in electrically conducting fluid. We use a standard mean-field approach to derive equations for large-scale magnetic field for the fluctuating Arnold-Beltrami-Childress (ABC) flow as well as for the fluctuating Roberts flow. The derived mean-field dynamo equations have growing solutions with growth rate of the large-scale magnetic field which is not controlled by molecular magnetic diffusivity. Our study confirms the Zeldovich idea that the nonstationarity of the fluid flow may remove the obstacle in large-scale dynamo action of classic stationary flows and provide fast dynamos.
Within the last 10 years, long-baseline optical interferometry (LBOI) has benefited significantly from increased sensitivity, spatial resolution, and spectral resolution, e.g., measuring the diameters and asymmetries of single stars, imaging/fitting the orbits of multiple stars, modeling Be star disks, and modeling AGN nuclei. Similarly, polarimetry has also yielded excellent astrophysical results, e.g., characterizing the atmospheres and shells of red giants/supergiants, modeling the envelopes of AGB stars, studying the morphology of Be stars, and monitoring the short- and long- term behavior of AGNs. The next logical evolutionary step in instrumentation is to combine LBOI with polarimetry, which is called optical interferometric polarimetry (OIP). In other words, measurements of spatial coherence are performed simultaneously with measurements of coherence between orthogonal polarization states.
Observations of galaxies suggest a one-to-one analytic relation between the inferred gravity of dark matter at any radius and the enclosed baryonic mass, a relation summarized by Milgrom's law of modified Newtonian dynamics (MOND). However, present-day covariant versions of MOND usually require some additional fields contributing to the geometry, as well as an additional hot dark matter component to explain cluster dynamics and cosmology. Here, we envisage a slightly more mundane explanation, suggesting that dark matter does exist but is the source of MOND-like phenomenology in galaxies. We assume a canonical action for dark matter, but also add an interaction term between baryonic matter, gravity, and dark matter, such that standard matter effectively obeys the MOND field equation in galaxies. We show that even the simplest realization of the framework leads to a model which reproduces some phenomenological predictions of cold dark matter (CDM) and MOND at those scales where these are most successful. We also devise a more general form of the interaction term, introducing the medium density as a new order parameter. This allows for new physical effects which should be amenable to observational tests in the near future. Hence, this very general framework, which can be furthermore related to a generalized scalar-tensor theory, opens the way to a possible unification of the successes of CDM and MOND at different scales.
[Abridged] We investigate the effect of energy feedback from galaxies on the intracluster medium (ICM) using a novel approach that couples a non-radiative cosmological hydrodynamical N-body simulation to a semi-analytic model (SAM) of galaxy formation. The SAM we employ is the Munich L-Galaxies model presented by De Lucia & Blaizot (2007). For each model galaxy, we calculate the energy returned to the ICM by Type II supernovae (SNe) and active galactic nuclei (AGN) and inject it into the gas component of the simulation at the appropriate location and time. To assess the impact of this feedback on the ICM, we focus on two key observables of galaxy groups and clusters: the X-ray luminosity-temperature (L-T) relation and the halo gas fraction. Using a suite of test simulations, we demonstrate that the level of stellar and AGN feedback predicted by L-Galaxies is insufficient to explain the observational data. This is because the energy liberated by quiescent 'radio' mode accretion onto the central black hole only reduces the rate at which gas can cool out of the halo in L-Galaxies, rather than heating intracluster gas. We address this problem by incorporating a model of AGN feedback into our hybrid approach that allows for explicit heat input into the ICM. The model we adopt is that used in the version of the Durham SAM GALFORM recently developed by Bower et al. (2008). With this AGN feedback scheme, we obtain an L-T relation that is in excellent agreement with observational data over a wide range of mass scales. The stellar and gas fractions of our simulated objects are also consistent with observations. Simultaneously reproducing these observed properties of groups and clusters is notoriously difficult in direct hydrodynamical simulations. These encouraging results demonstrate the potential power of our method.
We report on two epochs of VLBI observations of the Type Ib/c supernova SN 2008D, which was associated with the X-ray outburst XRF 080109, At our first epoch, at t=30 days after the explosion, we observed at 22 and 8.4 GHz, and at our second, at t=133 days, at 8.4 and 5.0 GHz. The VLBI observations allow us to accurately measure the source's size and position at each epoch, and thus constrain its expansion velocity and proper motion. We find the source at best marginally resolved at both epochs, allowing us to place a 3sigma upper limit of ~0.75c on the expansion velocity of a circular source. For an elongated source, our measurements are compatible with mildly relativistic expansion. However, our 3sigma upper limit on the proper motion is 4 micro-arcsec/day, corresponding to an apparent velocity of <0.6c, and is consistent with a stationary flux centroid. This limit rules out a relativistic jet such as an gamma-ray burst jet away from the line of sight, which would be expected to show apparent proper motion of >c. Taken together, our measurements argue against the presence of any long-lived relativistic outflow in SN 2008D. On the other hand, our measurements are consistent with the non-relativistic expansion velocities of <30,000 km/s and small proper motions (<500 km/s) seen in typical supernovae.
The Galactic Centre (GC) has experienced a high degree of recent star-forming activity, as evidenced by the large number of massive stars currently residing there. The relative abundances of chemical elements in the GC may provide insights into the origins of this activity. Here, we present high-resolution $H$-band spectra of two Red Supergiants in the GC (IRS~7 and VR~5-7), and in combination with spectral synthesis we derive abundances for Fe and C, as well as other $\alpha$-elements Ca, Si, Mg Ti and O. We find that the C-depletion in VR~5-7 is consistent with the predictions of evolutionary models of RSGs, while the heavy depletion of C and O in IRS~7's atmosphere is indicative of deep mixing, possibly due to fast initial rotation and/or enhanced mass-loss. Our results indicate that the {\it current} surface Fe/H content of each star is slightly above Solar. However, comparisons to evolutionary models indicate that the {\it initial} Fe/H ratio was likely closer to Solar, and has been driven higher by H-depletion at the stars' surface. Overall, we find $\alpha$/Fe ratios for both stars which are consistent with the thin Galactic disk. These results are consistent with other chemical studies of the GC, given the precision to which abundances can currently be determined. We argue that the GC abundances are consistent with a scenario in which the recent star-forming activity in the GC was fuelled by either material travelling down the Bar from the inner disk, or from the winds of stars in the inner Bulge -- with no need to invoke top-heavy stellar Initial Mass Functions to explain anomalous abundance ratios.
We present the results of a Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) study of dwarf galaxies in the core of the rich nearby Perseus Cluster, down to M_V=-12. We identify 29 dwarfs as cluster members, 17 of which are previously unstudied. All the dwarfs we examine are remarkably smooth in appearance, and lack internal features. Based on these observations, and the sizes of these dwarfs, we argue that some of the dwarfs in our sample must have a large dark matter content to prevent disruption by the cluster potential. We derive a new method, independent of kinematics, for measuring the dark matter content of dEs, based on the radius of the dwarf, the projected distance of the dwarf from the cluster centre, and the total mass of the cluster interior to it. We find that the mass-to-light ratios of these dwarfs are comparable to those of the Local Group dSphs, ranging between 1 and 120.
We investigate the global photometric scaling relations traced by early-type galaxies in different environments, ranging from dwarf spheroidals, over dwarf elliptical galaxies, up to giant ellipticals (-8 mag > M_V > -24 mag). These results are based in part on our new HST/ACS F555W and F814W imagery of dwarf spheroidal galaxies in the Perseus Cluster. These scaling relations are almost independent of environment, with Local Group and cluster galaxies coinciding in the various diagrams. We show that at M_V ~ -14 mag, the slopes of the photometric scaling relations involving the Sersic parameters change significantly. We argue that these changes in slope reflect the different physical processes that dominate the evolution of early-type galaxies in different mass regimes. As such, these scaling relations contain a wealth of information that can be used to test models for the formation of early-type galaxies.
The main methods grown Cadmium Zinc Telluride (CZT) crystals with high yield and excellent homogeneity are Modified Horizontal Bridgman (MHB) and High Pressure Bridgman (HPB) processes, respectively. In this contribution, the readout system based on two 32-channel NCI-ASICs for pixellated CZT detector arrays has been developed and tested. The CZT detectors supplied by Orbotech (MHB) and eV products (HPB) are tested by NCI-ASIC readout system. The CZT detectors have an array of 8x8 or 11x11 pixel anodes fabricated on the anode surface with the area up to 2 cm x2 cm and the thickness of CZT detectors ranges from 0.5 cm to 1 cm. Energy spectra resolution and electron mobility-lifetime products of 8x8 pixels CZT detector with different thicknesses have been investigated.
The lowest order constrained variational method is applied to calculate the polarized symmetrical nuclear matter properties with the modern $AV_{18}$ potential performing microscopic calculations. Results based on the consideration of magnetic properties show no sign of phase transition to a ferromagnetic phase.
In this paper, we calculate some of the polarized neutron matter properties, using the lowest order constrained variational method with the $AV_{18}$ potential and employing a microscopic point of view. A comparison is also made between our results and those of other many-body techniques.
In this paper, we calculate properties of the spin polarized asymmetrical nuclear matter and neutron star matter, using the lowest order constrained variational (LOCV) method with the $AV_{18}$, $Reid93$, $UV_{14}$ and $AV_{14}$ potentials. According to our results, the spontaneous phase transition to a ferromagnetic state in the asymmetrical nuclear matter as well as neutron star matter do not occur.
Some properties of the polarized neutron matter at finite temperature has been studied using the lowest order constrained variational (LOCV) method with the $AV_{18}$ potential. Our results indicate that spontaneous transition to the ferromagnetic phase does not occur. Effective mass, free energy, magnetic susceptibility, entropy and the equation of state of the polarized neutron matter at finite temperature are also calculated. A comparison is also made between our results and those of other many-body techniques.
We have investigated some of the thermodynamic properties of spin polarized liquid $^3\mathrm{He}$ at finite temperature using the lowest order constrained variational method. For this system, the free energy, entropy and pressure are calculated for different values of the density, temperature and polarization. We have also presented the dependence of specific heat, saturation density and incompressibility on the temperature and polarization.
Higher dimensional non-renormalizable operators may modify the Standard Model Higgs potential in many interesting ways. Here, we consider the appearance of a second vacuum which may play an important role in cosmology. For the certain range of parameters, the usual second order electroweak phase transition is followed by a first order phase transition that may drive the late time accelerated expansion of the universe. Such a potential contains kink-like solutions which in turn can play a crucial role in reconstructing the global shape of the potential in colliders, as we explicitly demonstrate.
We consider the third order Lovelock equations without the cosmological constant term of an empty $n(\geq 8)$-dimensional Kaluza-Klein spacetime $\mathcal{M}^{4}\times \mathcal{K}^{n-4}$, where $\mathcal{K}^{n-4}$ is a constant curvature space, and show that the emptiness of the higher-dimensional spacetime imposes a constraint on the metric function(s). We, first consider the effects of this constraint equation in the context of black hole physics, and present an asymptotically (A)dS charged black hole solution in 4 dimensions in the absence of electromagnetic field and the cosmological constant. This 4-dimensional solution has Riessner-Nordstrom-(A)dS behavior at large $r$ and it satisfies the Kaluza-Klein idea of being empty in higher dimensions. In the context of cosmology, we show that one may have an accelerated expanding universe without a cosmological constant term or the concept of dark energy in 4 dimensions. These two solutions show that one may have dark energy and matter, with non-traceless energy-momentum tensor, in 4 dimensions out of pure curvature of the empty higher-dimensional Kaluza-Klein spacetime.
Many cosmological observations call for the existence of dark matter. The most direct evidence for dark matter is inferred from the measured flatness of galactic rotation curves. The latter is based on Newtonian gravity. Alternative approaches to the rotation curve problem by means of general relativity have recently been put forward. The class of models of interest is a subset of the axially symmetric and stationary solutions of Einstein's equations with rotating dust. As a step toward the understanding of general relativistic galaxy models, we analyse rigidly as well as non-rigidly rotating (Post-)Newtonian spacetimes. We find that the Newtonian limit of the considered general relativistic galaxy model leads to Post-Newtonian terms in the metric.
In recent years, a rapidly growing literature has focussed on the construction of wavelet systems to analyze functions defined on the sphere. Our purpose in this paper is to generalize these constructions to situations where sections of line bundles, rather than ordinary scalar-valued functions, are considered. In particular, we propose {\em needlet-type spin wavelets} as an extension of the needlet approach recently introduced by Narcowich, Petrushev and Ward, and then considered for more general manifolds by Geller and Mayeli. We discuss localization properties in the real and harmonic domains, and investigate stochastic properties for the analysis of spin random fields. Our results are strongly motivated by cosmological applications, in particular in connection to the analysis of Cosmic Microwave Background polarization data.
We study gravitino dark matter and slow gravitino decays within the framework of R-violating supersymmetry, with particular emphasis on the flavour dependence of the branching ratios. The dominant decay modes and final state products turn out to be very sensitive to the R-violating hierarchies. Mixing effects can be crucial in correctly deriving the relative magnitude of the various contributions, particularly for heavy flavours with phase space suppression. The study of the strength of different decay rates for the gravitino is also correlated to collider signatures expected from decays of the Next-to-Lightest Supersymmetric Particle (NLSP) and to single superparticle production.
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We present new planetary nebulae (PNe) positions, radial velocities, and magnitudes for 6 early-type galaxies obtained with the Planetary Nebulae Spectrograph, their two-dimensional velocity and velocity dispersion fields. We extend this study to include an additional 10 early-type galaxies with PNe radial velocity measurements available from the literature, to obtain a broader description of the outer-halo kinematics in early-type galaxies. These data extend the information derived from stellar kinematics to typically up to ~8 Re. The combination of photometry, stellar and PNe kinematics shows: i) good agreement between the PNe number density and the stellar surface brightness in the region where the two data sets overlap; ii) good agreement between PNe and stellar kinematics; iii) that the mean rms velocity profiles fall into two groups: with of the galaxies characterized by slowly decreasing profiles and the remainder having steeply falling profiles; iv) a larger variety of velocity dispersion profiles; v) that twists and misalignments in the velocity fields are more frequent at large radii, including some fast rotators; vi) that outer haloes are characterised by more complex radial profiles of the specific angular momentum-related lambda_R parameter than observed within 1Re; vii) that many objects are more rotationally dominated at large radii than in their central parts; and viii) that the halo kinematics are correlated with other galaxy properties, such as total luminosity, isophotal shape, total stellar mass, V/sigma, and alpha parameter, with a clear separation between fast and slow rotators.
We use the photoionisation code Cloudy to determine both the location and the kinematics of the optical forbidden, high ionisation line (hereafter, FHIL) emitting gas in the narrow line Seyfert 1 galaxy Ark 564. The results of our models are compared with the observed properties of these emission lines to produce a physical model that is used to explain both the kinematics and the source of this gas. The main features of this model are that the FHIL emitting gas is launched from the putative dusty torus and is quickly accelerated to its terminal velocity of a few hundred km/s. Iron-carrying grains are destroyed during this initial acceleration. This velocity is maintained by a balance between radiative forces and gravity in this super-Eddington source. Eventually the outflow is slowed at large radii by the gravitational forces of and interactions with the host galaxy. In this model, FHIL emission traces the transition between the AGN and bulge zones of influence.
A summary of JENAM 2008 Symposium 9 "Star Formation from Spitzer (Lyman) to Spitzer (Space Telescope) and Beyond", held in Vienna, 10-12 September 2008.
Aims: To detect line effects using spectropolarimetry in order to find evidence of rotating disks and their respective symmetry axes in T Tauri stars. Methods: We used the IAGPOL imaging polarimeter along with the Eucalyptus-IFU to obtain spectropolarimetric measurements of the T Tauri stars RY Tau (two epochs) and PX Vul (one epoch). Evidence of line effects showing a loop on the Q-U diagram favors a compact rather than an extended source for the line photons in a rotating disk. In addition, the polarization position angle (PA) obtained using the line effect can constrain the symmetry axis of the disk. Results: RY Tau shown a variable Halpha double peak on 2004-2005 data. Polarization line effect is evident on the Q-U diagram for both epochs confirming a clockwise rotating disk. A single loop is evident on 2004 changing to a linear excursion plus a loop on 2005. Interestingly, the intrinsic PA calculated using the line effect is consistent between our two epochs (~167deg). An alternative intrinsic PA computed from the interstellar polarization corrected continuum and averaged between 2001-2005 yielded a PA 137deg. This last value is closer to be perpendicular to the observed disk direction (~25deg) as expected by single scattering in an optically thin disk. For PX Vul, we detected spectral variability in Halpha along with non-variable continuum polarization when compared with previous data. The Q-U diagram shows a well-defined loop in Halpha associated to a counter-clockwise rotating disk. The symmetry axis inferred by the line effect has a PA~91deg (with an ambiguity of 90deg). Our results confirm previous evidence that the emission line in T Tauri stars has its origin in a compact source scattered off a rotating accretion disk.
We want to derive bias free, accurate photometric redshifts for those fields of the CFHTLS-Wide data which are covered in the u*, g', r', i' and z' filters and are public on January 2008. These are 37 square degrees in the W1, W3 and W4 fields with photometric data for a total of 2.597.239 galaxies. We use the photometric redshift code PHOTO-z of Bender et al. (2001). We compare our redshifts for the W1, W3 and W4 fields to about 7500 spectroscopic redshifts from the VVDS therein. For galaxies with 17.5 <= i' AB <= 22.5 the accuracies and outlier rates become sigma=0.033, eta~2 % for W1, sigma=0.037, eta~2% for W3 and sigma=0.035, eta~2.5 % outliers for W4 fields. For the total galaxy sample with about 9000 spectroscopic redshifts from VVDS, DEEP2 or SDSS we obtain a sigma=0.04 and eta~5.7% for the PHOTO-z redshifts. We consider the photometric redshifts of Erben et al. (2008) which were obtained with exactly the same photometric catalog using the BPZ-redshift code and compare them with our computed redshifts. We also merge the subsample with good photometric redshifts from PHOTO-z with that one from BPZ to obtain a sample which then contains 'secure' redshifts according to both the PHOTO-z and the BPZ codes. This sample contains about 6100 spectra and the photometric redshift qualities become sigma=0.037 and eta~1.0% for our PHOTO-z redshifts. We conclude that this work provides a bias free, low dispersion photometric redshift catalog, that we have criteria at hand to select a 'robust' subsample with fewer outliers. Such a subsample is very useful to study the redshift dependent growth of the dark matter fluctuations with weak lensing cosmic shear analyses or to investigate the redshift dependent weak lensing signal behind clusters of galaxies in the framework of dark energy equation of state constraints.
Aims. We investigate the validity of mass segregation indicators commonly used in the analysis of young stellar clusters. Methods. We simulate observations by constructing synthetic seeing limited images of a 1000 massive clusters (10^4 Msun) with a standard IMF and a King density distribution function. Results. We find that commonly used indicators are highly sensitive to sample incompleteness in observational data, and that radial completeness determinations do not provide satisfactory corrections, rendering the studies of radial properties highly uncertain. On the other hand, we find that under certain conditions, the global completeness can be estimated accurately, allowing for the correction of the global luminosity and mass functions of the cluster. Conclusions. We argue that there is currently no observational evidence for mass segregation in young compact clusters since there is not a robust way to differentiate between true mass segregation and sample incompleteness effects. Caution should then be exercised when interpreting results from observations as evidence for mass segregation.
In this paper we study the angular momentum properties of simulated dark matter halos at high redshift that likely host the first stars in the Universe. Calculating the spin distributions of these $10^6 - 10^7 \Msun$ halos in redshift slices from $z = 15 - 6$, we find that they are well fit by a log-normal distribution as is found for lower redshift and more massive halos in earlier work. We find that both the mean value of the spin and dispersion are largely unchanged with redshift for all halos. Our key result is that subsamples of low and high spin $10^6 \Msun$ and $10^7 \Msun$ halos show difference in clustering strength. In both mass bins, higher spin halos are more strongly clustered in concordance with a tidal torquing picture for the growth of angular momentum in dark matter halos in the CDM paradigm.
We provide limits on the alignment of galaxy orientations with the direction to the void center for galaxies lying near the edges of voids. We locate spherical voids in volume limited samples of galaxies from the Sloan Digital Sky Survey using the HB inspired void finder and investigate the orientation of (color selected) spiral galaxies that are nearly edge-on or face-on. In contrast with previous literature, we find no statistical evidence for departure from random orientations. Expressed in terms of the parameter c, introduced by Lee & Pen to describe the strength of such an alignment, we find that c<0.11(0.13) at 95% (99.7%) confidence limit within a context of a toy model that assumes a perfectly spherical voids with sharp boundaries.
With the advent of deep photometric surveys the use of photometric redshifts,
obtained with a variety of techniques, has become more and more widespread.
Giving access to galaxies with a wide range of luminosities out to high
redshifts, these surveys include many faint galaxies with significantly
sub-solar metallicities.
We use our chemically consistent galaxy evolutionary synthesis code GALEV to
produce a large grid of template Spectral Energy Distributions (SEDs) for
galaxies of spectral types E and Sa through Sd - one accounting in a chemically
consistent way for the increasing initial metallicities of successive stellar
generations, the other one for exclusively solar metallicities - for
comparison.
We use our new photometric redshift code GAZELLE based on the comparison of
observed and model SEDs. Comparing the photometric redshifts obtained using
solar metallicity templates when working on a catalogue of artificially created
chemically consistent SEDs, typical for low-metallicity local late-type
galaxies and for intrinsically low-luminosity, and hence low-metallicity,
galaxies in the high-redshift universe, we find a significant bias resulting
from this metallicity mismatch. This bias consists in a systematic
underestimate of the photometric redshift by typically Delta z ~ 0.1 ... 0.2
until z ~ 1.2, depending on galaxy type, of distant, faint and low-metallicity
galaxies if analysed with solar-metallicity templates.
Data from 11 years of continuous spectroscopic observations of the active RS CVn-type binary star EI Eridani - gained at NSO/McMath-Pierce, KPNO/Coude Feed and during the MUSICOS 98 campaign - were used to obtain 34 Doppler maps in three spectroscopic lines for 32 epochs, 28 of which are independent of each other. Various parameters are extracted from our Doppler maps: average temperature, fractional spottedness, and longitudinal and latitudinal spot-occurrence functions. We find that none of these parameters show a distinct variation nor a correlation with the proposed activity cycle as seen from photometric long-term observations. This suggests that the photometric brightness cycle may not necessarily be due to just a cool spot cycle. The general morphology of the spot pattern remains persistent over the whole period of 11 years. A large cap-like polar spot was recovered from all our images. A high degree of variable activity was noticed near latitudes of approx. 60-70 degrees where the appendages of the polar spot emerged and dissolved.
While often the point sources in X-ray surveys are dominated by AGN, with the high sensitivity of modern X-ray telescopes such as Chandra and XMM-Newton normal/starburst galaxies are also being detected in large numbers. We have made use of Bayesian statistics for both the selection of galaxies from deep X-ray surveys and in the analysis of the luminosity functions for galaxies. These techniques can be used to similarly select galaxies from wide-area X-ray surveys and to analyze their luminosity function. The prospects for detecting galaxies and AGN from a proposed ``wide-deep'' XMM-Newton survey and from future wide-area X-ray survey missions (such as WFXT and eRosita) are also discussed.
We perform the first kinematic analysis of a CME observed by both imaging and in situ instruments on board STEREO, namely the SECCHI, PLASTIC, and IMPACT experiments. Launched on 2008 February 4, the CME is tracked continuously from initiation to 1 AU using the SECCHI imagers on both STEREO spacecraft, and is then detected by the PLASTIC and IMPACT particle and field detectors on board STEREO-B. The CME is also detected in situ by ACE and SOHO/CELIAS at Earth's L1 Lagrangian point. The CME hits STEREO-B, ACE, and SOHO on 2008 February 7, but misses STEREO-A entirely. This event provides a good example of just how different the same event can look when viewed from different perspectives. We also demonstrate many ways in which the comprehensive and continuous coverage of this CME by STEREO improves confidence in our assessment of its kinematic behavior, with potential ramifications for space weather forecasting. The observations provide several lines of evidence in favor of the observable part of the CME being narrow in angular extent, a determination crucial for deciding how best to convert observed CME elongation angles from Sun-center to actual Sun-center distances.
Attenuation of high--energy gamma rays by pair--production with UV, optical and IR background photons provides a link between the history of galaxy formation and high--energy astrophysics. We present results from our latest semi-analytic models (SAMs), based upon a $\Lambda$CDM hierarchical structural formation scenario and employing all ingredients thought to be important to galaxy formation and evolution, as well as reprocessing of starlight by dust to mid- and far-IR wavelengths. Our models also use results from recent hydrodynamic galaxy merger simulations. These latest SAMs are successful in reproducing a large variety of observational constraints such as number counts, luminosity and mass functions, and color bimodality. We have created 2 models that bracket the likely ranges of galaxy emissivities, and for each of these we show how the optical depth from pair--production is affected by redshift and gamma-ray energy. We conclude with a discussion of the implications of our work, and how the burgeoning science of gamma-ray astronomy will continue to help constrain cosmology.
(Abridged) The gravitational term for clouds and cores entering in the virial theorem is usually assumed to be equal to the gravitational energy, since the contribution to the gravitational force from the mass distribution outside the volume of integration is assumed to be negligible. Such approximation may not be valid in the presence of an important external net potential. In the present work we analyze the effect of an external gravitational field on the gravitational budget of a density structure. Our cases under analysis are (a) a giant molecular cloud (GMC) with different aspect ratios embedded within a galactic net potential, and (b) a molecular cloud core embedded within the gravitational potential of its parent molecular cloud. We find that for roundish GMCs, the tidal tearing due to the shear in the plane of the galaxy is compensated by the tidal compression in the z direction. The influence of the external effective potential on the total gravitational budget of these clouds is relatively small, although not necessarily negligible. However, for more filamentary GMCs, the external effective potential can be dominant and can even overwhelm self-gravity, regardless of whether its main effect on the cloud is to disrupt it or compress it. This may explain the presence of some GMCs with few or no signs of massive star formation, such as the Taurus or the Maddalena's clouds. In the case of dense cores embedded in their parent molecular cloud, we found that the gravitational content due to the external field may be more important than the gravitational energy of the cores themselves. This effect works in the same direction as the gravitational energy, i.e., favoring the collapse of cores. We speculate on the implications of these results for star formation models.
The exact profile of a gamma-ray burst (GRB) afterglow image on the plane of the sky can provide important constraints on the underlying physics. In particular, it can test whether the magnetic field in the emitting shocked external medium decreases significantly with the distance behind the shock front, or remains roughly constant. Moreover, it enables more accurate measurements of the afterglow image size and the expected scintillation properties. In this work analytic expressions are derived for the afterglow image in power law segments (PLSs) of the afterglow synchrotron spectrum in which the emission originates from a very thin layer just behind the shock, while simple semi-analytic expressions are derived for the remaining PLSs in which the emission arises from the bulk of the shocked fluid. In all cases the expressions are for a general power law external density profile, and are convenient to use in afterglow studies.
The distributions of L(oiii 5007), black hole (BH) mass and L/L(Edd) in two large samples of type-I and type-II active galactic nuclei (AGNs) are compared in order to test the suggestion that radiation pressure force is affecting the gas velocity in the broad line region and hence the BH mass determination. The samples are drawn from the SDSS archive and are modified to represent the same parent AGN population at 0.1 < z < 0.2. BH masses in type-I sources are calculated in two different ways, one using a simple virial mass assumption and the other by taking into account the effect of radiation pressure force on the gas. The simple virial mass estimate results in good agreement with sigma*-based BH mass and L/L(Edd) in type-II sources. In contrast, there is a clear disagreement in the two distributions when radiation pressure-based estimates are used. This indicates that radiation pressure force is not important in 0.1 < z < 0.2 AGNs with L(5100)=10^{42.8-44.8} erg/s. This has important implications to the physics of the gas producing the broad emission lines in AGNs, in particular the need for extremely large (about 10^{24} cm^(-2)) column density clouds.
We examine the accretion properties in a sample of 42 hard (3-60keV) X-ray selected nearby broad-line AGNs. The energy range in the sample is harder than that usually used in the similar previous studies. These AGNs are mainly complied from the RXTE All Sky Survey (XSS), and complemented by the released INTEGRAL AGN catalog. The black hole masses, bolometric luminosities of AGN, and Eddington ratios are derived from their optical spectra in terms of the broad H$\beta$ emission line. The tight correlation between the hard X-ray (3-20keV) and bolometric/line luminosity is well identified in our sample. Also identified is a strong inverse Baldwin relationship of the H$\beta$ emission line. In addition, all these hard X-ray AGNs are biased toward luminous objects with high Eddington ratio (mostly between 0.01 to 0.1) and low column density ($<10^{22} \mathrm{cm^{-2}}$), which is most likely due to the selection effect of the surveys. The hard X-ray luminosity is consequently found to be strongly correlated with the black hole mass. We believe the sample completeness will be improved in the next few years by the ongoing Swift and INTEGRAL missions, and by the next advanced missions, such as NuSTAR, Simbol-X, and NeXT. Finally, the correlation between RFe (=optical FeII/H$\beta$) and disk temperature as assessed by $T\propto (L/L_{\mathrm{Edd}})M_{\mathrm{BH}}^{-1}$ leads us to suggest that the strength of the FeII emission is mainly determined by the shape of the ionizing spectrum.
In the outer envelope of the Sun and in other stars, differential rotation and meridional circulation are maintained via the redistribution of momentum and energy by convective motions. In order to properly capture such processes in a numerical model, the correct spherical geometry is essential. In this paper I review recent insights into the maintenance of mean flows in the solar interior obtained from high-resolution simulations of solar convection in rotating spherical shells. The Coriolis force induces a Reynolds stress which transports angular momentum equatorward and also yields latitudinal variations in the convective heat flux. Meridional circulations induced by baroclinicity and rotational shear further redistribute angular momentum and alter the mean stratification. This gives rise to a complex nonlinear interplay between turbulent convection, differential rotation, meridional circulation, and the mean specific entropy profile. I will describe how this drama plays out in our simulations as well as in solar and stellar convection zones.
The whole sky differential star counts (DSC) with 1 degree resolution are retrieved from 2MASS online data service. Galaxy with double exponential thin and thick disks and a single power law luminosity function (LF) is used to interpret the 2MASS data. The slope of the DSC appears roughly isotropic over the whole sky, the average value is ~0.32, which corresponds to a power law index ~1.8 of the LF. We find that the scale-length and scale-height the thin disk are ~3.0 kpc and ~245 pc, and those of the thick disk are ~3.0 kpc and ~780 pc. The ratio of the thick disk to the thin disk is ~7%. The location of Sun above the disk is ~15 pc. A comparison of the data and model and their discrepancy are also provided.
I present an homogeneous determination of the physical properties of 14 transiting extrasolar planetary systems for which good data are available. The input quantities for each system are the results of the light curve analyses (Paper 1), and published measurements of the stellar velocity amplitude, Teff and [Fe/H]. The physical properties are determined by interpolating within tabulated predictions from stellar theory. Statistical uncertainties are found using a perturbation algorithm, which gives a detailed error budget for every output quantity. Systematic uncertainties are assessed for each quantity by comparing the values found using different stellar models. As a theory-free alternative, physical properties are also calculated using an empirical mass-radius relation constructed using low-mass eclipsing binary stars. The properties of the planets depend mostly on parameters measured from the light and velocity curves, and have only a minor sensitivity to theoretical predictions. In contrast, the orbital semimajor axes and stellar masses have a strong dependence on theoretical predictions, and their systematic uncertainties can be substantially larger than the statistical ones. Using the empirical mass--radius relation instead, their values are smaller by up to 15%. Thus our understanding of extrasolar planets is currently limited by our lack of understanding of low-mass stars. Using all known transiting planets, I find that correlations between their orbital periods, masses and surface gravities are significant at the 2-3 sigma level. However, the separation of the known planets into two classes according to their Safronov number is weaker than previously found, and may not be statistically significant (abridged).
Recent observations on structural properties of the Large Magellanic Cloud (LMC) based on the Deep Near-Infrared Southern Sky Survey (DENIS) and Two Micron All-Sky Survey (2MASS) have revealed that the LMC has an off-center bar even in the older stellar populations. Previous dynamical models including tidal interaction between the LMC, the Small Magellanic Cloud (SMC), and the Galaxy, however, did not reproduce so well the older off-center bar. We here show that the off-center bar can be formed if the LMC with an already existing bar can collide with a low-mass Galactic subhalo as massive as 5 * 10^8 M_sun (corresponding roughly to a few % of the LMC mass). The simulated stellar distribution after the collision appears to show an ``off-center bar'', not because the center of the bar significantly deviates from the dynamical center of the LMC, but because the underlying stellar distribution of the disk is significantly asymmetric with respect to the center of the bar. We discuss whether off-center bars observed in Magellanic-type dwarf galaxies can be formed as a result of tidal interaction with low-mass halos with no or little visible matters.
Rotation periods and projected equatorial velocities of pre-main-sequence (PMS) stars in star forming regions can be combined to give projected stellar radii. Assuming random axial orientation, a Monte-Carlo model is used to illustrate that distributions of projected stellar radii are very sensitive to ages and age dispersions between 1 and 10 Myr which, unlike age estimates from conventional Hertzsprung-Russell diagrams, are relatively immune to uncertainties due to extinction, variability, distance etc. Application of the technique to the Orion Nebula cluster reveals radius spreads of a factor of 2--3 (FWHM) at a given effective temperature. Modelling this dispersion as an age spread suggests that PMS stars in the ONC have an age range larger than the mean cluster age, that could be reasonably described by the age distribution deduced from the Hertzsprung-Russell diagram. These radius/age spreads are certainly large enough to invalidate the assumption of coevality when considering the evolution of PMS properties (rotation, disks etc.) from one young cluster to another.
Context : Dynamical studies of prestellar cores search for small velocity differences between different tracers. The highest radiation frequency precision is therefore required for each of these species. Aims : We want to adjust the frequency of the first three rotational transitions of N2H+ and N2D+ and extrapolate to the next three transitions. Methods : N2H+ and N2D+ are compared to NH3 the frequency of which is more accurately known and which has the advantage to be spatially coexistent with N2H+ and N2D+ in dark cloud cores. With lines among the narrowests, and N2H+ and NH3 emitting region among the largests, L183 is a good candidate to compare these species. Results : A correction of ~10 kHz for the N2H+ (J:1-0) transition has been found (~0.03 km/s) and similar corrections, from a few m/s up to ~0.05 km/s are reported for the other transitions (N2H+ J:3-2 and N2D+ J:1-0, J:2-1, and J:3-2) compared to previous astronomical determinations. Einstein spontaneous decay coefficients (Aul) are included.
In 1996, Sakurai's object (V4334 Sgr) suddenly brightened in the centre of a faint Planetary Nebula (PN). This very rare event was interpreted as the reignition of a hot white dwarf that caused a rapid evolution back to the cool giant phase. From 1998 on, a copious amount of dust has formed continuously, screening out the star which has remained embedded in this expanding high optical depth envelope. The new observations, reported here, are used to study the morphology of the circumstellar dust in order to investigate the hypothesis that Sakurai's Object is surrounded by a thick spherical envelope of dust. We have obtained unprecedented, high-angular resolution spectro-interferometric observations, taken with the mid-IR interferometer MIDI/VLTI, which resolve the dust envelope of Sakurai's object. We report the discovery of a unexpectedly compact (30 x 40 milliarcsec, 105 x 140 AU assuming a distance of 3.5 kpc), highly inclined, dust disk. We used Monte Carlo radiative-transfer simulations of a stratified disk to constrain its geometric and physical parameters, although such a model is only a rough approximation of the rapidly evolving dust structure. Even though the fits are not fully satisfactory, some useful and robust constraints can be inferred. The disk inclination is estimated to be 75+/-3 degree with a large scale height of 47+/-7 AU. The dust mass of the disk is estimated to be 6 10^{-5} solar mass. The major axis of the disk (132+/-3 degree) is aligned with an asymmetry seen in the old PN that was re-investigated as part of this study. This implies that the mechanism responsible for shaping the dust envelope surrounding Sakurai's object was already at work when the old PN formed.
Aims: Taking advantage of the forthcoming Catalog of the HETE-2 mission, the aim of this paper is to evaluate the main properties of HETE-2 GRBs - the E_peak, the T_90 and the E_iso - in their source frames and to derive their unbiased distribution. Methods: We first construct a complete sample containing all the bursts localized by the WXM on-board HETE-2, which are selected with a uniform criterion and whose observed parameters can be constrained. We then derive the intrinsic E_peak, T_90 and E_iso distributions using their redshift when it is available, or their pseudo-redshift otherwise. We finally compute the number of GRB (N_Vmax) within the visibility volume (V_max) of each GRB, in order to derive a weight for each detected burst accounting both for the detection significance and the star formation history of the universe. Results: The unbiased distributions obtained clearly show the predominence of X-ray flashes (XRFs) in the global GRB population. We also derive the rate of local GRBs: R0^H2 > 11 Gpc-3 yr-1, which is intermediate between the local rate obtained by considering only the high-luminosity bursts (~1 Gpc-3 yr-1) and that obtained by including the low-luminosity bursts (>200 Gpc-3 yr-1).
We present an internal shocks model to investigate particle acceleration and radiation production in microquasar jets. The jet is modelled with discrete ejecta at various time intervals. These ejecta (or 'shells') may have different properties including the bulk velocity. Faster shells can catch up and collide with the slower ones, thus giving rise to shocks. The particles are accelerated inside the shocked plasma. Each collision results in a new shell, which may take part in any subsequent collisions as well as radiate due to synchrotron radiation. Almost continuous energy dissipation along the jet can be obtained with a large number of shell collisions. We investigate the spectral energy distribution of such jets as well as the physical significance of various parameters (e.g. the time interval between ejections and the shell size).
The correlation between the pointing direction of ultra high energy cosmic rays and AGN observed by the Pierre Auger Collaboration is explained in the framework of acceleration process in AGN. This acceleration process is produced by a rotating accretion disk around a black hole that is frozen-in magnetic field. In a result the accretion disk is acting as a induction accelerator of cosmic rays. We estimate the resulting magnetic field in the framework of the magnetic coupling process. The results of our calculations allow to make the conclusion that the Flat Spectrum Radio Quasars appear the effective cosmic accelerators. We estimate also the attenuation of highest-energy cosmic rays in a result of their interaction with ambient radiation field.
We compute photometric redshifts based on the template-fitting method in the fourth public release of the Canada-France-Hawaii Telescope Legacy Survey. This unique multi-colour catalogue comprises u*,g',r',i',z' photometry in four deep fields of 1 deg2 each and 35 deg2 distributed over three Wide fields. Our photometric redshifts are calibrated with and compared to 16,983 high-quality spectroscopic redshifts from several surveys. We find a dispersion of 0.028 and an outlier rate of 3.5% in the Deep field at i'AB < 24 and a dispersion of 0.036 and an outlier rate of 2.8% in the Wide field at i'AB < 22.5. Beyond i'AB = 22.5 in the Wide field the number of outliers rises from 5% to 10% at i'AB<23 and i'AB<24 respectively. For the Wide sample, we find the systematic redshift bias keeps below 1% to i'AB < 22.5, whereas we find no significant bias in the Deep field. We investigated the effect of tile-to-tile photometric variations and demonstrate that the accuracy of our photometric redshifts is reduced by at most 21%. We separate stars from galaxies using both the size and colour information, reducing the contamination by stars in our catalogues from 50% to 8% at i'AB < 22.5 in fields with the highest stellar density while keeping a complete galaxy sample. Our CFHTLS T0004 photometric redshifts are distributed to the community. Our release include 592,891 (i'AB < 22.5) and 244,701 (i'AB < 24) reliable galaxy photometric redshifts in the Wide and Deep fields, respectively.
In this article some of the hydrodynamical (HD) aspects of steady shocks as described by the steady-state shock model are reviewed and discussed. It is found that, at least in some of the contexts in which the steady-state model is used, the steady-state assumption cannot be satisfied. Moreover, the main result of the present work is that even if the assumptions on steadiness and on the geometry are fully satisfied, serious limitations in the application of the model are found: (i) in the absence of down-stream boundary conditions the model is not related to the physical process(es) that originate the shock, (ii) matter shocked during the presumed phase of steadiness of the shock is not hydrodynamically interacting with previously shocked matter, and (iii) the steady-state model assumes that the flow is stable against perturbations. Furthermore, even if boundary conditions were assumed, the link between the steady model and the astrophysical context would not be strictly speaking the correct HD link. Time-dependent HD computations in different astrophysical contexts (e.g. SNRs and molecular shocks) show that the steady-state approximation is inadequate to describe these post-shock structures. Based on the HD limitations of the steady-state model, it is advised that the model be used to describe post-shock structures only in those astrophysical contexts where full time-dependent HD models have already positively tested the steadiness of the flow. Alternatively, it is suggested to replace the steady-state model either with time-dependent HD models, or with less problematic approximations.
Aims. Investigating stochastically driven pulsation puts strong requirements
on the quality of (observed) pulsation frequency spectra, such as the accuracy
of frequencies, amplitudes, and mode life times and -- important when fitting
these parameters with models -- a realistic error estimate which can be quite
different to the formal error. As has been shown by other authors, the method
of fitting Lorentzian profiles to the power spectrum of time-resolved
photometric or spectroscopic data via the Maximum Likelihood Estimation (MLE)
procedure delivers good approximations for these quantities. We, however,
intend to demonstrate that a conservative Bayesian approach allows to treat
this problem in a more consistent way.
Methods. We derive a conservative Bayesian treatment for the probability of
Lorentzian profiles being present in a power spectrum and describe its
implementation via evaluating the probability density distribution of
parameters by using the Markov-Chain Monte Carlo (MCMC) technique. In addition,
we compare the results obtained by Appourchaux et al. (2008), who used the MLE
technique, on the CoRoT data of HD 49933 to our Bayesian approach.
Results. Rather than using a "best-fit" procedure like MLE, which can only
deliver formal uncertainties, our procedure automatically leads to
statistically correct probability distributions for all parameters involved
without resorting to simulations. Moreover, it helps avoiding shortcomings that
make the MLE treatment susceptible to the complexity of a model that is fitted
to the data. This is especially relevant when analysing solar-type pulsation in
other stars than the Sun where the observations usually have lower quality and
we illustrate this claim in a reassessment of the pulsation of HD 49933.
We investigate the morphology and kinematics of the interstellar medium in the environs of the open cluster Mrk50, which includes the Wolf-Rayet star WR157 and a number of early B-type stars. The analysis was performed using radio continuum images at 408 and 1420 MHz, and HI 21cm line data taken from the Canadian Galactic Plane Survey, molecular observations of the 12CO (J=1-0) line at 115 GHz from the Five College Radio Astronomy Observatory and available mid and far IR observations obtained with the MSX and IRAS satellites, respectively. This study allowed identification of the radio continuum and molecular counterpart of the ring nebula SG13, while no neutral atomic structure was found to be associated. The nebula is also detected in images in the mid and far infrared, showing the existence of dust well mixed with the ionized gas. We estimate the main physical parameters of the material linked to the nebula. The interstellar gas distribution in the environs of Mrk50 is compatible with a stellar wind bubble created by the mass loss from WR157. The distribution of young stellar object (YSO) candidates in the region shows that stellar formation activity may be present in the molecular shell that encircles the ring nebula.
We show that the PAMELA anomaly in the positron fraction as well as the ATIC/PPB-BETS excesses in the e^- + e^+ flux are simultaneously explained in our scenario that a hidden U(1)H gauge boson constitutes dark matter of the Universe and decays into the standard-model particles through a kinetic mixing with an U(1)B-L gauge boson. Interestingly, the B-L charge assignment suppresses an antiproton flux in consistent with the PAMELA and BESS experiments, while the hierarchy between the B-L symmetry breaking scale and the weak scale naturally leads to the right lifetime of O(10^26) seconds.
Recent results from the Advanced Thin Ionization Calorimeter (ATIC) balloon experiment have identified the presence of a spectral feature between approximately 300 and 800 GeV in the cosmic ray electron spectrum. This spectral feature appears to imply the existence of a local (within about 1 kpc) source of high energy electrons. Emission from a local pulsar and dark matter annihilations have each been put forth as possible origins of this signal. In this letter, we consider the sensitivity of ground based atmospheric Cherenkov telescopes to electrons and show that observatories such as HESS and VERITAS should be able to resolve this feature with sufficient precision to discriminate between the dark matter and pulsar hypotheses with considerably greater than 5 sigma significance, even for conservative assumptions regarding their performance. In addition, this feature provides an opportunity to perform an absolute calibration of the energy scale of ground based, gamma ray telescopes.
Three-millimeter-wavelength spectra of a number of nearby galaxies have been obtained at the Five College Radio Astronomy Observatory (FCRAO) using a new, very broadband receiver. This instrument, which we call the Redshift Search Receiver, has an instantaneous bandwidth of 36 GHz and operates from 74 to 110.5 GHz. The receiver has been built at UMass/FCRAO to be part of the initial instrumentation for the Large Millimeter Telescope (LMT) and is intended primarily for determination of the redshift of distant, dust-obscured galaxies. It is being tested on the FCRAO 14m by measuring the 3mm spectra of a number of nearby galaxies. There are interesting differences in the chemistry of these galaxies.
We present simultaneous dual-frequency radio observations of Cygnus X-3 during a phase of low-level activity. We constrain the minimum variability timescale to be 20 minutes at 43 GHz and 30 minutes at 15 GHz, implying source sizes of 2 to 4 AU. We detect polarized emission at a level of a few per cent at 43 GHz which varies with the total intensity. The delay of approximately 10 minutes between the peaks of the flares at the two frequencies is seen to decrease with time, and we find that synchrotron self-absorption and free-free absorption by entrained thermal material play a larger role in determining the opacity than absorption in the stellar wind of the companion. A shock-in-jet model gives a good fit to the lightcurves at all frequencies, demonstrating that this mechanism, which has previously been used to explain the brighter, longer-lived giant outbursts in this source, is also applicable to these low-level flaring events. Assembling the data from outbursts spanning over two orders of magnitude in flux density shows evidence for a strong correlation between the peak brightness of an event, and the timescale and frequency at which this is attained. Brighter flares evolve on longer timescales and peak at lower frequencies. Analysis of the fitted model parameters suggests that brighter outbursts are due to shocks forming further downstream in the jet, with an increased electron normalisation and magnetic field strength both playing a role in setting the strength of the outburst.
The microquasar 1E 1740.7-2942 is observed with Integral since Spring 2003.
Here, we report on the source high energy behaviour by using the first three
years of data collected with SPI and IBIS telescopes, taking advantage of the
instruments complementarity. Light curves analysis showed two main states for
1E 1740.7-2942: the canonical low/hard state of black-hole candidates and a
``dim'' state, characterised by a ~ 20 times fainter emission, detected only
below 50 keV and when summing more than 1Ms of data. For the first time the
continuum of the low/hard state has been measured up to ~ 600 keV with a
spectrum that is well represented by a thermal Comptonization plus an
additional component necessary to fit the data above 200 keV. This high energy
component could be related to non-thermal processes as already observed in
other black-hole candidates. Alternatively, we show that a model composed by
two thermal Comptonizations provides an equally representative description of
the data: the temperature of the first population of electrons results as
(kTe)_1 ~ 30 keV while the second, (kTe)_2, is fixed at 100 keV.
Finally, searching for 511 keV line showed no feature, either narrow or
broad, transient or persistent.
We begin an exploration of the capacity of the stationary accretion shock instability (SASI) to generate magnetic fields by adding a weak, stationary, and radial (but bipolar) magnetic field to a spherically symmetric fluid configuration that models a stalled shock in the post-bounce supernova environment. Upon perturbation the SASI develops, and its lateral flows alternately advect the initially radial magnetic field towards and away from the polar regions. Lateral flows into the polar regions result in partially radial outflows along the symmetry axis, and over several SASI cycles the magnetic field parallel to the axis grows--{\em even in the absence of rotation}--to dynamical significance ($\gtrsim 10^{15}$ G), finally saturating upon local equipartition in the polar regions. While the resulting field configuration creates low-density `funnels' and enables energy transport along the field through MHD waves, it does not induce qualitatively new features in the global evolution of the shock.
We report a correlation based on a spectral simulation study of the prompt emission spectra of gamma-ray bursts (GRBs) detected by the Swift Burst Alert Telescope (BAT). The correlation is between the Epeak energy, which is the peak energy in the \nu F_\nu spectrum, and the photon index (\Gamma) derived from a simple power-law model. The Epeak - \Gamma relation, assuming the typical smoothly broken power-law spectrum of GRBs, is \log Epeak = 3.258 - 0.829\Gamma (1.3 < \Gamma < 2.3). We take into account not only a range of Epeak energies and fluences, but also distributions for both the low-energy photon index and the high-energy photon index in the smoothly broken power-law model. The distribution of burst durations in the BAT GRB sample is also included in the simulation. Our correlation is consistent with the index observed by BAT and Epeak measured by the BAT, and by other GRB instruments. Since about 85% of GRBs observed by the BAT are acceptably fit with the simple power-law model because of the relatively narrow energy range of the BAT, this relationship can be used to estimate Epeak when it is located within the BAT energy range.
We present 1.35 mm SMA observations around the low-mass Class 0 source IRAS 19156+1906, at the the center of the L723 dark cloud. We detected emission from dust as well as emission from H2CO, DCN and CN, which arise from two cores, SMA 1 and SMA 2, separated by 2.9" (880 AU). SMA 2 is associated with VLA 2. SiO 5-4 emission is detected, possibly tracing a region of interaction between the dense envelope and the outflow. We modeled the dust and the H2CO emission from the two cores: they have similar physical properties but SMA 2 has a larger p-H2CO abundance than SMA 1. The p-H2CO abundances found are compatible with the value of the outer part of the circumstellar envelopes associated with Class 0 sources. SMA 2 is likely more evolved than SMA 1. The kinematics of the two sources show marginal evidence of infall and rotation motions. The mass detected by the SMA observation, which trace scales of ~1000 AU, is only a small fraction of the mass contained in the large scale molecular envelope, which suggests that L723 is still in a very early phase of star formation. Despite the apparent quiescent nature of the L723, fragmentation is occurring at the center of the cloud at different scales. Thus, at 1000 AU the cloud has fragmented in two cores, SMA 1 and SMA 2. At the same time, at least one of these cores, SMA 2, has undergone additional fragmentation at scales of 150 AU, forming a multiple stellar system.
Using axisymmetric MHD simulations we investigate how the overall jet formation is affected by a variation in the disk magnetic flux profile and/or the existence of a central stellar magnetosphere. Our simulations evolve from an initial, hydrostatic equilibrium state in a force-free magnetic field configuration. We find a unique relation between the collimation degree and the disk wind magnetization power law exponent. The collimation degree decreases for steeper disk magnetic field profiles. Highly collimated outflows resulting from a flat profile tend to be unsteady. We further consider a magnetic field superposed of a stellar dipole and a disk field in parallel or anti-parallel alignment. Both stellar and disk wind may evolve in a pair of outflows, however, a reasonably strong disk wind component is essential for jet collimation. Strong flares may lead to a sudden change in mass flux by a factor two. We hypothesize that such flares may eventually trigger jet knots.
The first fully integrated explicit exact solution of the Einstein field equations corresponding to the superposition of a counterrotating dust disk with a central black hole is presented. The obtained solution represents an infinite annular thin disk (a disk with an inner edge) around the Schwarszchild black hole. The mass of the disk is finite and the energy-momentum tensor agrees with all the energy conditions. Furthermore, the total mass of the disk when the black hole is present is less than the total mass of the disk alone. The solution can also be interpreted as describing a thin disk made of two counterrotanting dust fluids that are also in agreement with all the energy conditions. Additionally, as we will show shortly in a subsequent paper, the above solution is the first one of an infinite family of solutions.
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