We report the first attempt to observe the secondary eclipse of a transiting extra-solar planet at radio wavelengths. We observed HD 189733 b with the Robert C. Byrd Green Bank Telescope of the NRAO over about 5.5 hours before, during and after secondary eclipse, at frequencies of 307 - 347 MHz. In this frequency range, we determine the 3-sigma upper limit to the flux density to be 81 mJy. The data are consistent with no eclipse or a marginal reduction in flux at the time of secondary eclipse in all subsets of our bandwidth; the strongest signal is an apparent eclipse at the 2-sigma level in the 335.2 - 339.3 MHz region. Our observed upper limit is close to theoretical predictions of the flux density of cyclotron-maser radiation from the planet.
Blue stragglers in globular clusters are abnormally massive stars that should have evolved off the stellar main sequence long ago. There are two known processes that can create these objects: direct stellar collisions and binary evolution. However, the relative importance of these processes has remained unclear. In particular, the total number of blue stragglers found in a given cluster does not seem to correlate with the predicted collision rate, providing indirect support for the binary-evolution model. Yet the radial distributions of blue stragglers in many clusters are bimodal, with a dominant central peak: this has been interpreted as an indication that collisions do dominate blue straggler production, at least in the high-density cluster cores. Here we report that there is a clear, but sublinear, correlation between the number of blue stragglers found in a cluster core and the total stellar mass contained within it. From this we conclude that most blue stragglers, even those found in cluster cores, come from binary systems. The parent binaries, however, may themselves have been affected by dynamical encounters. This may be the key to reconciling all of the seemingly conflicting results found to date.
(Abridge) Bars are very common in the centre of the disc galaxies, and they drive the evolution of their structure. A volume-limited sample of 2106 disc galaxies extracted from the Sloan Digital Sky Survey Data Release 5 was studied to derive the bar fraction, length, and strength as a function of the morphology, size, local galaxy density, light concentration, and colour of the host galaxy. The bars were detected using the ellipse fitting method and Fourier analysis method. The ellipse fitting method was found to be more efficient in detecting bars in spiral galaxies. The fraction of barred galaxies turned out to be 45%. A bar was found in 29% of the lenticular galaxies, in 55% and 54% of the early- and late-type spirals, respectively. The bar length (normalised by the galaxy size) of late-type spirals is shorter than in early-type or lenticular ones. A correlation between the bar length and galaxy size was found with longer bars hosted by larger galaxies. The bars of the lenticular galaxies are weaker than those in spirals. Moreover, the unimodal distribution of the bar strength found for all the galaxy types argues against a quick transition between the barred and unbarred statues. There is no difference between the local galaxy density of barred and unbarred galaxies. Besides, neither the length nor strength of the bars are correlated with the local density of the galaxy neighbourhoods. In contrast, a statistical significant difference between the central light concentration and colour of barred and unbarred galaxies was found. Bars are mostly located in less concentrated and bluer galaxies. These results indicate that the properties of bars are strongly related to those of their host galaxies, but do not depend on the local environment.
The COSMOS survey is a multiwavelength survey aimed to study the evolution of galaxies, AGN and the large scale structure. The XMM-COSMOS is a deep X-ray survey over the full 2 deg2 of the COSMOS area. It consists of 55 XMM-Newton pointings for a total exposure of ~1.5 Ms with an average vignetting corrected depth of 40 ks across the field of view and a sky coverage of 2.13 deg2. We present the catalogue of point-like X-ray sources detected with the EPIC CCD cameras, the logN-logS relations and the X-ray colour-colour diagrams. The analysis was performed in the 0.5-2 keV, 2-10 keV and 5-10 keV energy bands. The completeness of the catalogue as well as logN-logS have been calibrated using Monte Carlo simulations. The catalogs contains a total of 1887 unique sources detected in at least one band. The survey, that shows unprecedented homogeneity, has a flux limit of ~1.7x10-15 erg cm-2 s-1, ~9.3x10-15 erg cm-2 s-1 and ~1.3x10-14 erg cm-2 s-1 over 90% of the area (1.92 deg2) in the 0.5-2 keV, 2-10 keV and 5-10 keV energy band, respectively. Thanks to the rather homogeneous exposure over a large area, the derived logN-logS relations are very well determined over the flux range sampled by XMM-COSMOS. These relations have been compared with XRB synthesis models, which reproduce the observations with an agreement of ~10% in the 5-10 keV and 2-10 keV band, while in the 0.5-2 keV band the agreement is of the order of ~20%. The hard X-ray colors confirmed that the majority of the extragalactic sources, in a bright subsample, are actually Type I or Type II AGN. About 20% of the sources have X-ray luminosity typical of AGN (L_X >1042 erg/s) although they do not show any clear signature of nuclear activity in the optical spectrum.
We explore the connection between different classes of active galactic nuclei (AGNs) and the evolution of their host galaxies, by deriving host galaxy properties, clustering, and Eddington ratios of AGNs selected in the radio, X-ray, and infrared (IR) wavebands from the wide-field (9 deg^2) Bootes survey. We study a sample of 598 AGNs at 0.25 < z < 0.8 using redshifts from the AGN and Galaxy Evolution Survey (AGES). We find that radio and X-ray AGNs reside in relatively large dark matter halos (M_halo ~ 3x10^13 and 10^13 h^-1 M_sun, respectively) and are found in galaxies with red and "green" colors. In contrast, IR AGNs are in less luminous galaxies, have higher Eddington ratios, and reside in halos with M_halo < 10^12 M_sun. We interpret these results in terms of a general picture for AGNs and galaxy evolution, in which quasar activity is triggered when M_halo ~ 10^12 - 10^13 M_sun, after which star formation ceases and AGN accretion shifts to optically-faint, X-ray and radio-bright modes.
The duration of a starburst is a fundamental parameter affecting the evolution of galaxies yet, to date, observational constraints on the durations of starbursts are not well established. Here we study the recent star formation histories (SFHs) of three nearby dwarf galaxies to rigorously quantify the duration of their starburst events using a uniform and consistent approach. We find that the bursts range from ~200 - ~400 Myr in duration resolving the tension between the shorter timescales often derived observationally with the longer timescales derived from dynamical arguments. If these three starbursts are typical of starbursts in dwarf galaxies, then the short timescales (3 - 10 Myr) associated with starbursts in previous studies are best understood as "flickering" events which are simply small components of the larger starburst. In this sample of three nearby dwarfs, the bursts are not localized events. All three systems show bursting levels of star formation in regions of both high and low stellar density. The enhanced star formation moves around the galaxy during the bursts and covers a large fraction of the area of the galaxy. These massive, long duration bursts can significantly affect the structure, dynamics, and chemical evolution of the host galaxy and can be the progenitors of "superwinds" that drive much of the recently chemically enriched material from the galaxy into the intergalactic medium.
We perform direct numerical simulations of the compressible magnetohydrodynamical equations in a spherical shell domain with random helical forcing which has negative (positive) helicity in the northern (southern) hemisphere. We find a large-scale magnetic field, which is uniform in the azimuthal direction and shows equatorward migration. Furthermore, the large-scale magnetic field in each hemisphere oscillates on nearly dynamical time scales with reversals of polarity. We calculate the gauge-independent magnetic helicity in each hemisphere and find that they also show oscillations with the same frequency. This indicates the possible role of the exchange of helicity in these oscillations. As far as we are aware, these dynamical features of large-scale magnetic field have not been observed earlier in simulations of full magnetohydrodynamical equations.
We perform a new analysis of the extant ROSAT and XMM-Newton X-ray surveys of the southern open cluster Blanco 1, utilizing new BVIc photometric and proper motion data sets. In our study, we match optical counterparts to 47 X-ray sources associated with Blanco 1 cluster members, 6 of which were listed in previous X-ray studies as cluster nonmembers. Our new catalog of optical counterparts to X-ray sources clearly traces out the Blanco 1 main sequence in a CMD, extending from early G to mid-M spectral types. Additionally, we derive new Lx as well as Lx/Lbol ratios for confirmed cluster members. We compare these X-ray properties to other young open clusters, including the coeval Pleiades cluster, to investigate the relationship between age and X-ray activity. We find that stars in Blanco 1 generally exhibit X-ray properties similar to those of other open clusters, namely increasing Lx/Lbol with reducing mass for earlier-type stars, and a saturation limit of Lx/Lbol at a magnitude of 10^-3 for stars with V-Ic > 1.25. More generally, the X-ray detected stars in Blanco 1 have X-ray emission magnitudes that agree with the overall trends seen in the other young clusters. In a direct comparison of Blanco 1 to the Pleiades open cluster, members of both clusters have similar X-ray characteristics; however, there does appear to be some discrepancies in the distribution of Lx/Lbol as a function of color that may be related to scatter seen in the Pleiades CMD. Moreover, previous comparisons of this nature for Blanco 1 were not possible due to the reliance on photographic photometry. This is where the power of precise, homogeneous, and standardized CCD photometry allows for a high fidelity, detailed study of the X-ray properties of stars in Blanco 1. [abridged]
Using H I absorption spectra taken from the recent surveys of 21-cm line and continuum emission in the Galactic plane, the distribution of cool atomic clouds in the outer disk of the Milky Way is revealed. The warp of the midplane is clearly seen in absorption, as it is in emission, and the cool, neutral medium also shows flaring or increase in scale height with radius similar to that of the warm atomic hydrogen. The mixture of phases, as measured by the fraction of H I in the cool clouds relative to the total atomic hydrogen, stays nearly constant from the solar circle out to about 25 kpc radius. Assuming cool phase temperature ~50 K this indicates a mixing ratio of 15% to 20% cool H I, with the rest warm.
The papers in this volume represent a broad spectrum of observational, theoretical, and computational astrophysics, sharing as a unifying core the Disk-Halo Interaction in the Milky Way and other spiral galaxies. This topic covers a wide range of Galactic and extra-galactic research, built on a foundation of numerous and diverse physical processes. This summary groups the papers according to six themes, with some historical background and finally a look to the future. The final message is that the astrophysical techniques discussed and reviewed at this conference will grow over the next decade to answer even more fundamental questions about galaxy evolution and the history of the universe.
Using the atmospheric neutrinos to probe the density profile of the Earth depends on knowing the angular distribution of the neutrinos at production and the neutrino cross section. This paper reviews the essential features of the angular distribution with emphasis on the relative contributions of pions, kaons and charm.
Previous theoretical work has speculated about the existence of double-diffusive magnetic buoyancy instabilities of a dynamically evolving horizontal magnetic layer generated by the interaction of forced vertically sheared velocity and a background vertical magnetic field. Here we confirm numerically that if the ratio of the magnetic to thermal diffusivities is sufficiently low then such instabilities can indeed exist, even for high Richardson number shear flows. Magnetic buoyancy may therefore occur via this mechanism for parameters that are likely to be relevant to the solar tachocline, where regular magnetic buoyancy instabilities are unlikely.
Over the last few years certain class of dark energy models decaying inversely proportional to the square of the horizon distance emerged on the bases either of Heisenberg uncertainty relations or of uncertainty relation between the four volume and the cosmological constant. The very nature of these dark energies is understood to be the same, namely it is the energy of background space/metric fluctuations. Putting together these uncertainty relations one can gain new insights into the problem.
Amplitudes of bolometric light curves produced by 2D and 3D simulations are used to determine the corresponding visual amplitudes. They turn out to be about 10 times lower than typical amplitudes of superhumps. This means a major failure of the tidal model of superhumps.
We present some of the High Dynamic Range Imaging activities developed around the coronagraphic test-bench of the Laboratoire A. H. Fizeau (Nice). They concern research and development of an Apodized Lyot Coronagraph (ALC) for the VLT-SPHERE instrument and experimental results from our testbed working in the visible domain. We determined by numerical simulations the specifications of the apodizing filter and searched the best technological process to manufacture it. We present the results of the experimental tests on the first apodizer prototype in the visible and the resulting ALC nulling performances. The tests concern particularly the apodizer characterization (average transmission radial profile, global reflectivity and transmittivity in the visible), ALC nulling performances compared with expectations, sensitivity of the ALC performances to misalignments of its components.
We present mid-IR observations of the Galactic Luminous Blue Variable (LBV) HR Car and its associated nebula carried out with the Spitzer Space Telescope using both IRAC and IRS, as part of a GTO program aimed to study stellar ejecta from evolved stars. Our observations reveal a rich mid-IR spectrum of the inner nebula showing both solid state and atomic gas signatures. Strong low-excitation atomic fine structure lines such as $ 26.0 \mu$m [\ion{Fe}{2}] and $ 34.8 \mu$m [\ion{Si}{2}], indicate, for the first time, the presence of a PDR in this object class. While the physics and chemistry of the low-excitation gas appears to be dominated by photodissociation, a possible contribution due to shocks can be inferred from the evidence of gas phase Fe abundance enhancement. The presence of amorphous silicates, inferred from the observed characteristic broad feature at $10 \mu$m located in the inner nebula, suggests that dust has formed during the LBV outburst. This is in contrast with the detection of crystalline dust in other probably more evolved Galactic LBVs, which is similar to the crystalline dust observed in red supergiants. This has been considered to be evidence of dust production during evolutionary phases prior to the outburst.
We present a simple theoretical framework for massive galaxies at high redshift, where most of the assembly and star formation occurred. The evolution is governed by the interplay between fueling by smooth and clumpy streams and stabilization by a spheroid, leading to a bimodality in galaxy type by z~3. Disks of giant clumps and high star formation rate (SFR) form when the streams are smoother than average. The streams maintain a dense disk that undergoes gravitational fragmentation into several giant clumps, each a few percent of the disk mass. The disk may reach a disk-to-total mass ratio d~0.5 due to the dark-matter halo before it settles into a steady state with a slowly growing bulge, d=0.5-0.25. The clump interactions self-regulate an unstable disk with a dispersion-to-rotation ratio sigma_r/V=0.3-0.15. Encounters and dynamical friction induce inward clump migration in 10 dynamical times, ~0.5Gyr, while the disk expands in response. The inflowing smooth streams replenish the draining disk and prolong the clumpy phase to several Gyrs. The clumps form stars at the accretion rate, ~100 Msun/yr, each clump converting into stars in 6-10 dynamical times. The migrating clumps coalesce dissipatively into a compact bulge. Passive spheroid-dominated galaxies form when the incoming streams contain more than average dense clumps. These clumps stir up turbulence in the disk and grow a dominant bulge; together they stabilize the disk and suppress in-situ clump and star formation. The spheroid is surrounded by a smooth gas disk, as in simulated wet-merger remnants. This scenario explains the bimodality observed at z~2, of giant-clump star-forming extended disks alongside with compact spheroids of suppressed SFR. We present first maps from cosmological simulations that reveal clumpy disks consistent with our analysis.
We develop a Monte-Carlo technique based on L.B. Lucy's indivisible photon packets method to calculate X-ray continuum spectra of comptonized thermal plasma in arbitrary geometry and apply it to describe the broadband X-ray continuum of the galactic superaccreting microquasar SS433 observed by INTEGRAL. A physical model of the X-ray emitting region is proposed that includes thermal emission from the accretion disk, jets and hot corona where the photons of different origin are comptonized. From comparison with INTEGRAL observations, we estimate physical parameters of the complex X-ray emitting region in SS433 and present model spectra for different viewing angles of the object.
We propose a methodology to perform a self-consistent analysis of the physical properties of the emitting gas of HII galaxies adequate to the data that can be obtained with the XXI century technology. This methodology requires the production and calibration of empirical relations between the different line temperatures that should superseed currently used ones based on very simple, and poorly tested, photo-ionization model sequences. Then, these observations are analysed applying a methodology designed to obtain accurate elemental abundances of oxygen, sulphur, nitrogen, neon, argon and iron in the ionsied gas. Four electron temperatures and one electron density are derived from the observed forbidden line ratios using the five-level atom approximation. For our best objects errors of 1% in T([OIII]), 3% in T([OII]) and 5% in T([SIII]) are achieved with a resulting accuracy between 5 and 9% in total oxygen abundances, O/H. These accuracies are expected to improve as better calibrations based on more precise measurements, both on electron temperatures and densities, are produced.
Using a time-dependent multifluid, magnetohydrodynamic code, we calculated the structure of steady perpendicular and oblique C-type shocks in dusty plasmas. We included relevant processes to describe mass transfer between the different fluids, radiative cooling by emission lines and grain charging and studied the effect of single-sized and multiple sized grains on the shock structure. Our models are the first of oblique fast-mode molecular shocks in which such a rigorous treatment of the dust grain dynamics has been combined with a self-consistent calculation of the thermal and ionisation structures including appropriate microphysics. At low densities the grains do not play any significant role in the shock dynamics. At high densities, the ionisation fraction is sufficiently low that dust grains are important charge and current carriers and, thus, determine the shock structure. We find that the magnetic field in the shock front has a significant rotation out of the initial upstream plane. This is most pronounced for single-sized grains and small angles of the shock normal with the magnetic field. Our results are similar to previous studies of steady C-type shocks showing that our method is efficient, rigorous and robust. Unlike the method employed in the previous most detailed treatment of dust in steady oblique fast-mode shocks, ours allows a reliable calculation even when chemical or other conditions deviate from local statistical equilibrium. We are also able to model transient phenomena.
We examine the possibility of evolution with redshift in the mean rest-frame ultraviolet (UV; <4500A) spectrum of Type Ia Supernovae (SNe Ia) sampling the redshift range 0<z<1.3. We find new evidence for a decrease with redshift in the strength of intermediate-mass element (IME) features, particularly Si II and to a lesser extent Ca II "H&K" and Mg II blends, indicating lower IME abundances in the higher redshift SNe. A larger fraction of luminous, wider light-curve width (higher "stretch") SNe Ia are expected at higher redshift than locally, so we compare our observed spectral evolution with that predicted by a redshift-evolving stretch distribution (Howell et al. 2007) coupled with a stretch-dependent SN Ia spectrum. We show that the sense of the spectral evolution can be reproduced by this simple model, though the highest redshift events seem additionally deficient in Si and Ca. We also examine the mean SN Ia UV-optical colors as a function of redshift, thought to be sensitive to variations in progenitor composition. We find that the expected stretch variations are sufficient to explain the differences, although improved data at z~0 will enable more precise tests. Thus, to the extent possible with the available datasets, our results support the continued use of SNe Ia as standardized candles.
We performed astrometric observations with the VLBA of WB89-437, an H2O maser source in the Outer spiral arm of the Galaxy. We measure an annual parallax of 0.167 +/- 0.006 mas, corresponding to a heliocentric distance of 6.0 +/- 0.2 kpc or a Galactocentric distance of 13.4 +/- 0.2 kpc. This value for the heliocentric distance is considerably smaller than the kinematic distance of 8.6 kpc. This confirms the presence of a faint Outer arm toward l = 135 degrees. We also measured the full space motion of the object and find a large peculiar motion of ~20 km/s toward the Galactic center. This peculiar motion explains the large error in the kinematic distance estimate. We also find that WB89-437 has the same rotation speed as the LSR, providing more evidence for a flat rotation curve and thus the presence of dark matter in the outer Galaxy.
Astronomic line mapping with single-pixel instruments is usually performed in
an on-the-fly (OTF) or a raster-mapping mode depending on the capabilities of
the telescope and the instrument. The observing efficiency can be increased by
combining several source-point integrations with a common reference
measurement. This is implemented at many telescopes, but a thorough
investigation of the optimum calibration of the modes and the best way of
performing these observations is still lacking.
We use knowledge of the instrumental stability obtained by an Allan variance
measurement to derive a mathematical formalism for optimizing the setup of
mapping observations. Special attention has to be paid to minimizing of the
impact of correlated noise introduced by the common OFF integrations and to the
correction of instrumental drifts. Both aspects can be covered using a
calibration scheme that interpolates between two OFF measurements and an
appropriate OFF integration time.
The total uncertainty of the calibrated data consisting of radiometric noise
and drift noise can be minimized by adjusting the source integration time and
the number of data points observed between two OFF measurements. It turns out
that OTF observations are very robust. They provide a low relative noise, even
if their setup deviates considerably from the optimum. Fast data readouts are
often essential to minimize the drift contributions. In particular, continuum
measurements may be easily spoiled by instrumental drifts. The main drawback of
the described mapping modes is the limited use of the measured data at
different spatial or spectroscopic resolutions obtained by additional
rebinning.
A cosmological model dominated at the beginning by a dark radiation followed by a period of inflation is presented. This model is based on a Randall-Sundrum II type brane-world. Current observational data are used to fix the parameters associated to the dark radiation.
A microlensing event may exhibit a second brightening when the source and/or the lens is a binary star. Previous study revealed 19 such repeating event candidates among 4120 investigated microlensing light curves of the Optical Gravitational Lensing Experiment (OGLE). The same study gave the probability ~ 0.0027 for a repeating event caused by a binary lens. We present the simulations of binary source lensing events and calculate the probability of observing a second brightening in the light curve. Applying to simulated light curves the same algorithm as was used in the analysis of real OGLE data, we find the probability ~ 0.0018 of observing a second brightening in a binary source lensing curve. The expected and measured numbers of repeating events are in agreement only if one postulates that all lenses and all sources are binary. Since the fraction of binaries is believed to be <= 50%, there seems to be a discrepancy.
We report on the identification of the X/soft gamma-ray source AX J183039-1002 detected with ASCA and INTEGRAL/IBIS. The source, which has an observed 20-100 keV flux of about 8.6 x 10^-11 erg/cm^2/s, is inside a diffuse radio supernova remnant (SNR) and is spatially coincident with a compact radio source. We analyzed archival Chandra and XMM-Newton observations in order to identify the ASCA/INTEGRAL source. A point-like Chandra X-ray object was found to be positionally coincident with the compact radio source and within the error circle of the ASCA and INTEGRAL sources. Although the association of a compact radio/X-ray source with a radio supernova remnant could be indicative of a pulsar wind nebula (PWN), the XMM-Newton X-ray spectrum is compatible with an absorbed, Seyfert-2 like AGN, since it provides evidence for an iron emission line of about 1 keV equivalent width; furthermore the X-ray source spectrum is similar to that of other Compton thick AGN where the <2 keV data are associated to a warm reflector and the >10 keV one to a cold reflector.
An intensive spectroscopic study was performed for three representative solar twins (HIP 56948, HIP 79672, and HIP 100963) as well as for the Sun (Moon; reference standard), with an intention of (1) quantitatively discussing the relative-to-Sun similarities based on the precisely established differential parameters and (2) investigating the reason causing the Li abundance differences despite their similarities. It was concluded that HIP 56948 most resembles the Sun in every respect including the Li abundance (though not perfectly similar) among the three and deserves the name of "closest-ever solar twin", while HIP 79672 and HIP 100963 have somewhat higher effective temperature and appreciably higher surface Li composition. While there is an indication of Li being rotation-dependent because the projected rotation in HIP 56948 (and the Sun) is slightly lower than the other two, the rotational difference alone does not seem to be so large as to efficiently produce the marked change in Li. Rather, this may be more likely to be attributed (at least partly) to the slight difference in T_eff via some T_eff-sensitive Li-controlling mechanism. Since the abundance of beryllium was found to be essentially solar for all stars irrespective of Li, any physical process causing the Li diversity should work only on Li without affecting Be.
We discuss the optical properties, X-ray detections, and Active Galactic Nucleus (AGN) populations of four clusters at z ~ 1 in the Subaru-XMM Deep Field (SXDF). The velocity distribution and plausible extended X-ray detections are examined, as well as the number of X-ray point sources and radio sources associated with the clusters. We find that the two clusters that appear virialised and have an extended X-ray detection contain few, if any, AGN, whereas the two pre-virialised clusters have a large AGN population. This constitutes evidence that the AGN fraction in clusters is linked to the clusters' evolutionary stage. The number of X-ray AGN in the pre-virialised clusters is consistent with an overdensity of factor ~ 200; the radio AGN appear to be clustered with a factor of three to six higher. The median K-band luminosities of L_K = 1.7 +/- 0.7 L* for the X-ray sources and L_K = 2.3 +/- 0.1 L* for the radio sources support the theory that these AGN are triggered by galaxy interaction and merging events in sub-groups with low internal velocity distributions, which make up the cluster environment in a pre-virialisation evolutionary stage.
Data Models are an essential part of automatic data processing, but even more so when trying to tie together data coming from many different data sources, as is the case for the International Virtual Observatory. In this talk we will review the different data models used in the IVOA, which parts of that Data Modelling work are still incomplete, specially in radio wavelengths, and the work the AMIGA group has done within the IVOA Data Modelling Working Group to overcome those shortcomings both in missing data models and support for Radio Astronomy.
The Pierre Auger Observatory has a unique potential to search for ultra-high energy photons (above ~1 EeV). First experimental limits on photons were obtained during construction of the southern part of the Observatory. Remarkably, already these limits have proven useful to falsify proposals about the origin of cosmic rays, and to perform fundamental physics by constraining Lorentz violation. A final discovery of photons at the upper end of the electromagnetic spectrum is likely to impact various branches of physics and astronomy.
We revisit the mass ratio R between molecular hydrogen (H2) and atomic hydrogen (HI) in different galaxies from a phenomenological and theoretical viewpoint. First, the local H2-mass function (MF) is estimated from the local CO-luminosity function (LF) of the FCRAO Extragalactic CO-Survey, adopting a variable CO-to-H2 conversion fitted to nearby observations. This implies an average H2-density Omega_H2=(6.9+-2.7) 10^5/h and Omega_H2/Omega_HI=0.26+-0.11 in the local Universe. Second, we investigate the correlations between R and global galaxy properties in a sample of 245 local galaxies. Based on these correlations we introduce four phenomenological models for R, which we apply to estimate H2-masses for each HI-galaxy in the HIPASS catalogue. The resulting H2-MFs (one for each model for R) are compared to the reference H2-MF derived from the CO-LF, thus allowing us to determine the Bayesian evidence of each model and to identify a clear best model, in which, for spiral galaxies, R negatively correlates with both galaxy Hubble type and total gas mass. Third, we derive a theoretical model for R for regular galaxies based on an expression for their axially symmetric pressure profile dictating the degree of molecularization. This model is quantitatively similar to the best phenomenological one at redshift z=0, and hence represents a consistent generalization while providing a physical explanation for the dependence of R on global galaxy properties. Applying the best phenomenological model for R to the HIPASS sample, we derive the first integral cold gas-MF (HI+H2+helium) of the local Universe.
The principal paradigm for gamma-ray bursts (GRBs) suggests that the prompt transient gamma-ray signal arises from multiple shocks internal to the relativistic expansion. This paper explores how GRB prompt emission spectra can constrain electron (or ion) acceleration properties at the relativistic shocks that pertain to GRB models. The array of possible high-energy power-law indices in accelerated populations is highlighted, focusing on how spectra above 1 MeV can probe the field obliquity in GRB internal shocks, and the character of hydromagnetic turbulence in their environs. When encompassing the MeV-band spectral break, fits to BATSE/EGRET burst data indicate that the preponderance of electrons responsible for the prompt emission reside in an intrinsically non-thermal population. This differs markedly from typical populations generated in acceleration simulations; potential resolutions of this conflict such as the action of self-absorption are mentioned. Spectral modeling also suggests that the synchrotron mechanism is favored over synchrotron self-Compton scenarios due to the latter's typically broad curvature near the peak. Such diagnostics will be enhanced by the broadband spectral coverage of bursts by the Fermi Gamma-Ray Space Telescope; the GBM will provide key information on the lower energy portions of the non-thermal particle population, while the LAT will constrain the power-law regime of particle acceleration.
Observations of high redshift galaxies have revealed a multitude of large clumpy rapidly star-forming galaxies. Their formation scenario and their link to present day spirals is still unknown. In this Letter we perform AMR simulations of disk formation in a cosmological context that are unrivaled in terms of mass and spatial resolution. We find that the so called "chain-galaxies" and "clump-clusters" are a natural outcome of early epochs of enhanced gas accretion from cold dense streams as well as tidally and ram-pressured stripped material from minor mergers and satellites. Through interaction with the hot halo gas, this freshly accreted cold gas settles into a large disk-like system, not necessarily aligned to an older stellar component, that undergoes fragmentation and subsequent star formation, forming large clumps in the mass range 10^7-10^9 M_sun. Galaxy formation is a complex process at this important epoch when most of the central baryons are being acquired through a range of different mechanisms - we highlight that a rapid mass loading epoch is required to fuel the fragmentation taking place in the massive arms in the outskirts of extended disks, an accretion mode that occurs naturally in the hierarchical assembly process at early epochs.
While the high-entropy wind (HEW) of Type II supernovae remains one of the more promising sites for the rapid neutron-capture (r-) process, hydrodynamic simulations have yet to reproduce the astrophysical conditions under which the latter occurs. We have performed large-scale network calculations within an extended parameter range of the HEW, seeking to identify or to constrain the necessary conditions for a full reproduction of all r-process residuals N_{r,\odot}=N_{\odot}-N_{s,\odot} by comparing the results with recent astronomical observations. A superposition of weighted entropy trajectories results in an excellent reproduction of the overall N_{r,\odot}-pattern beyond Sn. For the lighter elements, from the Fe-group via Sr-Y-Zr to Ag, our HEW calculations indicate a transition from the need for clearly different sources (conditions/sites) to a possible co-production with r-process elements, provided that a range of entropies are contributing. This explains recent halo-star observations of a clear non-correlation of Zn and Ge and a weak correlation of Sr - Zr with heavier r-process elements. Moreover, new observational data on Ru and Pd seem to confirm also a partial correlation with Sr as well as the main r-process elements (e.g. Eu).
Macroscopic plasma polarization, which is created by gravitation and other mass-acting (inertial) forces in massive astrophysical objects (MAO) is under discussion. Non-ideality effect due to strong Coulomb interaction of charged particles is introduced into consideration as a new source of such polarization. Simplified situation of totally equilibrium isothermal star without relativistic effects and influence of magnetic field is considered. The study is based on density functional approach combined with local density approximation. It leads to conditions of constancy for generalized (electro) chemical potentials and/or conditions of equilibrium for the forces acting on each charged specie. New non-ideality force appears in this consideration. Hypothetical sequences of gravitational, inertial and non-ideality polarization on thermo- and hydrodynamics of MAO are under discussion.
The constraint on the total energy in a given spatial region is given from holography by the mass of a black hole which just fits in that region, which leads to an UV/IR relation: the maximal energy density in that region is proportional to $M_p^2/L^2$, where $M_p$ is the Planck mass and $L$ is the spatial scale of that region under consideration. Assuming the maximal black hole in the universe is formed through gravitational collapse of perturbations in the universe, then the "Jeans" scale of the perturbations gives a causal connection scale $R_{\rm CC}$. For gravitational perturbations, $R^{-2}_{\rm CC}={\rm Max}(\dot H+2H^2, -\dot H)$ for a flat universe. We study the cosmological dynamics of the corresponding vacuum energy density by choosing the causal connection scale as the IR cutoff in the UV/IR relation, in the cases of the vacuum energy density as an independently conserved energy component and an effective dynamical cosmological constant, respectively. It turns out that only the case with the choice $R_{\rm CC}^{-2}= \dot H +2H^2$, could be consistent with the current cosmological observations when the vacuum density appears as an independently conserved energy component. In this case, the model is called holographic Ricci scalar dark energy model in the literature.
Possible mechanisms of baryogenesis are reviewed. Special attention is payed to those which allow for creation of astronomically significant domains or objects consisting of antimatter. Observational manifestations of cosmological antimatter are discussed.
We investigate new physics effects in the production and detection of high energy neutrinos at neutrino telescopes. Analysing the flavor ratios \phi_\mu/\phi_\tau and \phi_\mu/(\phi_\tau+\phi_e), we find that the Standard Model predictions for them can be sensibly altered by new physics effects.
We show that, if decaying gravitino dark matter is responsible for the PAMELA and ATIC/PPB-BETS anomalies in the cosmic-ray electron and positron fluxes, both a reheating temperature and a gluino mass are constrained from above. In particular, the gluino mass is likely within the reach of LHC, if the observed baryon asymmetry is explained by thermal leptogenesis scenario.
In this paper we compare the existing observational data on type Ia Supernovae with the theoretical evolutions of the universe predicted by a one-parameter family of tachyon models which we have introduced recently in paper [6]. Among the set of the trajectories of the model which are compatible with the data there is a consistent subset for which the fate of the universe ends up in a new type of soft cosmological singularity dubbed Big Brake. This opens up yet another scenario for the future history of the universe besides the one predicted by the standard $\Lambda$CDM model.
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The Virtual Observatory is useful. I summarise some of my works where I extensively use the Aladin sky atlas. Topics cover from the search and common proper motion confirmation of very low-mass stars and brown dwarfs in wide (rho > 1000 AU) binaries and multiple systems, to the identification and characterisation of stellar and substellar populations in young open clusters and OB associations at heliocentric distances of up to 1000 pc. I present three practical examples of what one can do with Aladin in one morning: a fruitful proper-motion search of objects with available ugrizJHKs photometry, an analysis of the 21 cm radio sources towards the young sigma Orionis cluster, and a novel study of X-ray young stars surrounding Alnilam in the Orion Belt.
We report on the detection of a population of weak metal-line absorbers in the halo or nearby intergalactic environment of the Milky Way. Using high-resolution ultraviolet absorption-line spectra of bright QSOs obtained with the Space Telescope Imaging Spectrograph (STIS), along six sight lines we have observed unsaturated, narrow absorption in OI and SiII together with mildly saturated CII absorption at high radial velocities (|v_LSR|=100-320 km/s). The measured OI column densities are small, implying that these structures represent Lyman-Limit Systems and sub-Lyman-Limit System with HI column densities < 3x10^18 cm^-2, thus below the detection limits of current 21cm all-sky surveys of high-velocity clouds (HVCs). The absorbers apparently are not directly associated with any of the large high-column density HVC complexes, but rather represent isolated, partly neutral gas clumps embedded in a more tenuous, ionized gaseous medium situated in the halo or nearby intergalactic environment of the Galaxy. We speculate that this absorber population represents the local analog of weak MgII systems that are commonly observed in the circumgalactic environment of low- and high-redshift galaxies.
The sterile neutrino is an excellent dark matter candidate, which can be searched for in a wide range of astrophysical sites. It has previously been shown that the optimal search strategy is to consider dwarf galaxies in our Milky Way. We use recently published Chandra X-ray observations of the dwarf galaxy Draco to search for a signature of decaying dark matter particles. We do not find any emission line from decaying dark matter, which leads us to improve the conservative constraints in the parameter space of mass and mixing angle of the sterile neutrino by up to an order of magnitude in the mixing angle.
We apply a new model for the spherically averaged correlation function at large pair separations to the measurement of the clustering of luminous red galaxies (LRGs) made from the SDSS by Cabre & Gaztanaga (2008). Our model takes into account the form of the BAO peak and the large scale shape of the correlation function. We perform a Monte Carlo Markov chain analysis for different combinations of datasets and for different parameter sets. The correlation function measurements by themselves can constrain the dark energy equation of state parameter to w_DE=-1.02+-0.13, independently of CMB or supernovae data. When used in combination with a compilation of the latest CMB measurements, the LRG clustering and the latest supernovae results give constraints on cosmological parameters which are comparable and in remarkably good agreement, resolving the tension reported in some studies. The best fitting model in the context of a flat, Lambda-CDM cosmology is specified by Omega_m=0.261+-0.011, Omega_b=0.044+-0.001, n_s=0.96+-0.01, H_0=71.5+-1.1 km/s/Mpc and sigma_8=0.80+-0.02. If we allow the time-independent dark energy equation of state parameter to vary, we find results consistent with a cosmological constant at the 5% level using all data sets: w_DE=-0.97+-0.05. We do not find convincing evidence for an evolving equation of state. We provide a set of ``extended distance priors'' that contain the most relevant information from the CMB power spectrum and the shape of the LRG correlation function which can be used to constrain dark energy models and spatial curvature. Our model should provide an accurate description of the clustering even in much larger, forthcoming surveys, such as those planned with NASA's JDEM or ESA's Euclid mission.
We have applied the optimal estimator for f_{NL}^{local} to the 5 year WMAP data. Marginalizing over the amplitude of foreground templates we get -4 < f_{NL}^{local} < 80 at 95% CL. Error bars of previous (sub-optimal) analyses are roughly 40% larger than these. The probability that a Gaussian simulation, analyzed using our estimator, gives a result larger in magnitude than the one we find is 7%. Our pipeline gives consistent results when applied to the three and five year WMAP data releases and agrees well with the results from our own sub-optimal pipeline. We find no evidence of any residual foreground contamination.
The Lomb-Scargle periodogram is a common tool in the frequency analysis of unequally spaced data equivalent to least-squares fitting of sine waves. We give an analytic solution for the generalisation to a full sine wave fit, including an offset and weights ($\chi^{2}$ fitting). Compared to the Lomb-Scargle periodogram, the generalisation is superior as it provides more accurate frequencies, is less susceptible to aliasing, and gives a much better determination of the spectral intensity. Only a few modifications are required for the computation and the computational effort is similar. Our approach brings together several related methods that can be found in the literature, viz. the date-compensated discrete Fourier transform, the floating-mean periodogram, and the "spectral significance" estimator used in the SigSpec program, for which we point out some equivalences. Furthermore, we present an algorithm that implements this generalisation for the evaluation of the Keplerian periodogram that searches for the period of the best-fitting Keplerian orbit to radial velocity data. The systematic and non-random algorithm is capable of detecting eccentric orbits, which is demonstrated by two examples and can be a useful tool in searches for the orbital periods of exoplanets.
We present a filtering technique that can be applied to individual baselines of wide-bandwidth, wide-field interferometric data to geometrically select regions on the celestial sphere that contain primary calibration sources. The technique relies on the Fourier transformation of wide-band frequency spectra from a given baseline to obtain one-dimensional "delay images", and then the transformation of a time-series of delay images to obtain two-dimensional "delay/delay-rate images." Source selection is possible in these images given appropriate combinations of baseline, bandwidth, integration time and source location. Strong and persistent radio frequency interference (RFI) limits the effectiveness of this source selection owing to the removal of data by RFI excision algorithms. A one-dimensional, complex CLEAN algorithm has been developed to compensate for RFI-excision effects. This approach allows CLEANed, source-isolated data to be used to isolate bandpass and primary beam gain functions. These techniques are applied to data from the Precision Array for Probing the Epoch of Reionization (PAPER) as a demonstration of their value in calibrating a new generation of low-frequency radio interferometers with wide relative bandwidths and large fields-of-view.
I review the observational constraints on the star formation histories in the spheroids of M33 and M31, the other two spiral galaxies in the Local Group. M33 does not possess a traditional bulge; instead, it has a small nuclear region hosting stars with a wide range of ages. The star formation history of the M33 halo is poorly constrained, but composite spectra of its halo globular clusters imply a wide age spread of 5 - 7 years, while the presence of RR Lyrae stars in the halo implies at least some of the population is ancient. Although it is possible to obtain the detailed star formation history of the M33 halo via deep photometry, this has not been done to date. M31 hosts a traditional bulge that is apparently dominated by stars older than 10 Gyr. Deep photometry of the M31 halo demonstrates that it hosts both a population of ancient metal-poor stars and a significant population extending to younger ages and high metallicity, apparently due to its active merger history.
We investigate shock structure and particle acceleration in relativistic magnetized collisionless pair shocks by means of 2.5D and 3D particle-in-cell simulations. We explore a range of inclination angles between the pre-shock magnetic field and the shock normal. We find that only magnetic inclinations corresponding to "subluminal" shocks, where relativistic particles following the magnetic field can escape ahead of the shock, lead to particle acceleration. The downstream spectrum in such shocks consists of a relativistic Maxwellian and a high-energy power-law tail with exponential cutoff. For increasing magnetic inclination in the subluminal range, the high-energy tail accounts for an increasing fraction of particles (from ~1% to ~2%) and energy (from ~4% to ~12%). The spectral index of the power law increases with angle from -2.8+-0.1 to -2.3+-0.1. Particle energization is driven by the Diffusive Shock Acceleration process for nearly parallel shocks, and switches to Shock-Drift Acceleration for larger subluminal inclinations. For "superluminal" shocks, the downstream particle spectrum does not show any significant suprathermal tail. As seen from the upstream frame, efficient acceleration in relativistic (Lorentz factor gamma0 > 5) magnetized (sigma > 0.03) flows exists only for a very small range of magnetic inclination angles (< 34/gamma0 degrees), so relativistic astrophysical pair shocks have to be either nearly parallel or weakly magnetized to generate nonthermal particles. These findings place constraints on the models of AGN jets, Pulsar Wind Nebulae and Gamma Ray Bursts that invoke particle acceleration in relativistic magnetized shocks. (Abridged)
After quasars ionize intergalactic HeII at z~3, a large radiation field builds up above the HeII ionization edge. Unlike the background responsible for HI ionizations, this field should be highly variable, thanks to the scarcity of bright quasars and the relatively short attenuation lengths (~50 Mpc) of these high-energy photons. Recent observations of the HeII and HI Lyman-alpha forests show that this background does indeed vary strongly, with substantial fluctuations on scales as small as ~2 Mpc. Here we show that such spatial fluctuation scales are naturally expected in any model in which the sources are as rare as bright quasars, so long as the attenuation length is relatively small. The correlation length itself is comparable to the attenuation length (~10 Mpc) for the most plausible physical scenarios, but we find order-of-magnitude fluctuations on all scales smaller than ~6 Mpc. Moreover, aliasing along the one-dimensional skewers probed by the HeII and HI Lyman-alpha forests exaggerates these variations, so that order-of-magnitude fluctuations should be observed on all scales smaller than ~20 Mpc. Complex radiative transfer is therefore not required to explain the observed fluctuations, at least at the level of current data.
The WiggleZ Dark Energy Survey is a large-scale structure survey of intermediate-redshift UV-selected emission-line galaxies scheduled to cover 1000 sq deg, spanning a broad redshift range 0.2 < z < 1.0. The main scientific goal of the survey is the measurement of baryon acoustic oscillations (BAO) in the galaxy clustering pattern at a significantly higher redshift than previous studies. The BAO may be applied as a standard cosmological ruler to constrain dark energy models. Based on the first 20% of the dataset, we present initial results concerning the small-scale clustering of the WiggleZ targets, together with survey forecasts. The WiggleZ galaxy population possesses a clustering length r_0 = 5.23 +/- 0.15 Mpc/h, which is significantly larger than z=0 UV-selected samples, with a slope gamma = 1.82 +/- 0.07. This clustering length is comparable to z=3 Lyman Break Galaxies with similar UV luminosities. The full survey, scheduled for completion in 2010, will map an effective volume V_eff ~ 1 Gpc^3 (evaluated at a scale k = 0.15 h/Mpc) and will measure the angular-diameter distance and Hubble expansion rates in three redshift bins with accuracies ~ 5%. We will determine the value of a constant dark energy equation-of-state parameter, w, with a higher precision than existing supernovae observations using an entirely independent technique. The WiggleZ and supernovae measurements lie in highly complementary directions in the plane of w and the matter density Omega_m. The forecast using the full combination of WiggleZ, supernovae and CMB datasets is a marginalized error sigma(w) = 0.07, providing a robust and precise measurement of the properties of dark energy including cross-checking of systematic errors.
We use published optical spectral and IR excess data from nine young clusters and associations to study the stellar mass dependent dispersal of circumstellar disks. All clusters older than ~3 Myr show a decrease in disk fraction with increasing stellar mass for Solar to higher mass stars. This result is significant at about the 1 $\sigma$ level in each cluster. For the complete set of clusters we reject the null hypothesis--that Solar and intermediate-mass stars lose their disks at the same rate--with 95-99.9% confidence. To interpret this behaviour, we investigate the impact of grain growth, binary companions, and photoevaporation on the evolution of disk signatures. Changes in grain growth timescales at fixed disk temperature may explain why early-type stars with IR excesses appear to evolve faster than their later-type counterparts. Little evidence that binary companions affect disk evolution suggests that photoevaporation is the more likely mechanism for disk dispersal. A simple photoevaporation model provides a good fit to the observed disk fractions for Solar and intermediate-mass stars. Although the current mass-dependent disk dispersal signal is not strong, larger and more complete samples of clusters with ages of 3-5 Myr can improve the significance and provide better tests of theoretical models. In addition, the orbits of extra-Solar planets can constrain models of disk dispersal and migration. We suggest that the signature of stellar mass dependent disk dispersal due to photoevaporation may be present in the orbits of observed extra Solar planets. Planets orbiting hosts more massive than ~1.6 Msun may have larger orbits because the disks in which they formed were dispersed before they could migrate.
We present a theoretical model that explains the high energy phenomenology of the neighborhood of SNR IC 443, as observed with the Major Atmospheric Gamma Imaging Cherenkov (MAGIC) telescope and the Energetic Gamma-Ray Experiment Telescope (EGRET). We also discuss how the model can be tested with observations by the Fermi Gamma-ray Large Area Space Telescope. We interpret MAGIC J0616+225 as delayed TeV emission of cosmic-rays diffusing from IC 443 and interacting with a known cloud located at a distance of about 20 pc in the foreground of the remnant. This scenario naturally explains the displacement between EGRET and MAGIC sources, their fluxes, and their spectra. Finally, we predict how this context can be observed by Fermi.
AM CVn systems are interacting binaries similar to cataclysmic variables (CVs), but more compact with orbital periods of less than 80 minutes. The primary is a white dwarf, whereas the nature of the secondary is not completely clear, yet. Abundances and composition of the outer layer of the secondary can be found by analysis of the accretion disk (presented by Nagel et al. these proceedings). Spectra from high-state AM CVn systems do not only show typical signatures of accretion disks, but also P Cygni line profiles, a sign of outflow being present in the system. Here we present the first quantitative spectral analysis of an accretion-disk wind in AM CVn systems. Emergent wind spectra are modeled with our 3-D Monte Carlo radiative transfer code WOMPAT. We show that P Cygni profiles can be reproduced with our wind models.
We present self-consistent global, steady-state MHD models and synthetic optically thin synchrotron emission maps for the jet of M87. The model consist of two distinct zones: an inner relativistic outflow, which we identify with the observed jet, and an outer cold disk-wind. While the former does not self-collimate efficiently due to its high effective inertia, the latter fulfills all the conditions for efficient collimation by the magneto-centrifugal mechanism. Given the right balance between the effective inertia of the inner flow and the collimation efficiency of the outer disk wind, the relativistic flow is magnetically confined into a well collimated beam and matches the measurements of the opening angle of M87 over several orders of magnitude in spatial extent. The synthetic synchrotron maps reproduce the morphological structure of the jet of M87, i.e. center-bright profiles near the core and limb-bright profiles away from the core. At the same time, they also show a local increase of brightness at some distance along the axis associated to a recollimation shock in the MHD model. Its location coincides with the position of the optical knot HST-1. In addition our best fitting model is consistent with a number of observational constraints such as the magnetic field in the knot HST-1, and the jet-to-counterjet brightness ratio.
I will discuss the motivations for Neutrino Astronomy and its prospects given the current experimental scenario, which is the main focus of this paper. I will also go through the first results of the IceCube detector deep in the ice and of the ANTARES undersea telescope underlying complementary aspects, common and different challenges. It is an exciting time for this science since the first completed undersea detector is successfully taking data and the first cubic kilometer detector is going to be shortly more than half-way from its completion in Antarctica.
The South Pole is an optimal location for hosting astrophysical observatories. The status of the construction of the IceCube Observatory and some selected physics results will be discussed. Moreover prospects for detection of Ultra-High Energy cosmogenic neutrinos and techniques that can address this energy region will be considered.
By definition, brown dwarfs never reach the main-sequence, cooling and dimming over their entire lifetime, thus making substellar models challenging to test because of the strong dependence on age. Currently, most brown dwarfs with independently determined ages are companions to nearby stars, so stellar ages are at the heart of the effort to test substellar models. However, these models are only fully constrained if both the mass and age are known. We have used the Keck adaptive optics system to monitor the orbit of HD 130948BC, a brown dwarf binary that is a companion to the young solar analog HD 130948A. The total dynamical mass of 0.109+/-0.003 Msun shows that both components are substellar, and the ensemble of available age indicators from the primary star suggests an age comparable to the Hyades, with the most precise age being 0.79 Gyr based on gyrochronology. Therefore, HD 130948BC is unique among field L and T dwarfs as it possesses a well-determined mass, luminosity, and age. Our results indicate that substellar evolutionary models may underpredict the luminosity of brown dwarfs by as much as a factor of ~2-3x. The implications of such a systematic error in evolutionary models would be far-reaching, for example, affecting determinations of the initial mass function and predictions of the radii of extrasolar gas-giant planets. This result is largely based on the reliability of stellar age estimates, and the case study of HD 130948A highlights the difficulties in determining the age of an arbitrary field star, even with the most up-to-date chromospheric activity and gyrochronology relations. In order to better assess the potential systematic errors present in substellar models, more refined age estimates for HD 130948A and other stars with binary brown dwarf companions (e.g., eps Ind Bab) are critically needed.
The complete census of globular clusters formerly belonging to the Sgr dSph and now deposited into the Galactic halo is an important contribution to our comprehension of the evolution and disruption of this dwarf galaxy. We investigate in this study the possibility that the poorly known "old" globular AM 4 might be associated with the Sagittarius dwarf galaxy, and at the same time provide more solid estimate of its basic parameters. New high quality BVI photometry is presented, from which an improved Color Ma gnitude Diagram is constructed, and estimates of age and distance are then derived. The distance and Galactic position are finally investigated in details. AM~4 is found to be a low luminosity (M$_V$=-1.82) cluster undergoing strong tidal stress by the Milky Way and on the verge to be dissolved. Besides, and at odds with previous suggestions, we provide evidences that AM 4 is indeed young, with an age around 9 Gyrs (as Terzan~7), but somewhat more metal poor ([Fe/H=-0.97]). AM~4 is located at 33$_{-4}^{+3}$ kpc from the Sun, in a direction and at distance not totally incompatible with the Sgr dSph stream. Although we significantly improved our knowledge of AM 4, further studies are encouraged to obtain radial velocity and metallicity to d emonstrate more firmly (or deny) the association to Sgr
We propose a nonlinear self-consistent model of the turbulent non-resonant particle acceleration in solar flares. We simulate temporal evolution of the spectra of charged particles accelerated by strong long-wavelength MHD turbulence taking into account back reaction of the accelerated particles on the turbulence. The main finding is that the nonlinear coupling of accelerated particles and MHD turbulence result in prominent evolution of the spectra of accelerated particles, which can be either soft-hard-soft or soft-hard-harder depending on the particle injection efficiency. Such evolution patterns are widely observed in hard X-ray and gamma-ray emission from solar flares.
In this paper, a consistent model of the multifrequency emission of the starburst galaxy M82, from radio to gamma-rays, and neutrinos, is presented and discussed. Predictions for Fermi, MAGIC II/VERITAS and CTA telescopes are made. The model is used to self-consistenty compute the emission of neutrinos resulting from this starburst galaxy, what can be used in considerations of the diffuse contributions of such objects.
In this paper we describe in detail the implementation and main properties of a new inversion code for the polarized radiative transfer equation (VFISV: Very Fast inversion of the Stokes vector). VFISV will routinely analyze pipeline data from the Helioseismic and Magnetic Imager (HMI) on-board of the Solar Dynamics Observatory (SDO). It will provide full-disk maps (4096$\times$4096 pixels) of the magnetic field vector on the Solar Photosphere every 10 minutes. For this reason VFISV is optimized to achieve an inversion speed that will allow it to invert 16 million pixels every 10 minutes with a modest number (approx. 50) of CPUs. Here we focus on describing a number of important details, simplifications and tweaks that have allowed us to significantly speed up the inversion process. We also give details on tests performed with data from the spectropolarimeter on-board of the Hinode spacecraft.
The DAMA/NaI and DAMA/LIBRA annual modulation data, which may be interpreted as a signal for the existence of weakly interacting dark matter (WIMPs) in our galactic halo, are re-examined in light of new measurements of the local velocity relative to the galactic halo. In the vicinity of the Sun, the velocity of the Galactic disk has been estimated to be 250 km/s rather than 220 km/s. Our analysis is performed both with and without the channeling effect included. The best fit regions to the DAMA data are shown to move to slightly lower WIMP masses. Compatibility of DAMA data with null results from other experiments (CDMS, XENON10, and CRESST I) is investigated given these new velocities. A small region of spin-independent (elastic) scattering for 7-8 GeV WIMP masses remains at 3$\sigma$. Spin-dependent scattering off of protons is viable for 5-15 GeV WIMP masses for direct detection experiments (but has been argued by others to be further constrained by Super-Kamiokande due to annihilation in the Sun).
The years 1998 to 2008 were very exciting years for cosmology. It was a pleasure to accept this invitation to describe my contributions to the development of our knowledge and understanding of the universe over the course of the past decade. Here, I begin by describing some of my work on radio galaxies as a modified standard yardstick and go on to describe model-independent studies of the accelerating universe and the properties of the dark energy. During the course of these studies, I came upon interesting ways to study the spin and other properties of supermassive black holes, some of which are briefly mentioned.
Based on millimeter-wavelength continuum observations we suggest that the recent 'spectacle' of comet 17P/Holmes can be explained by a thick, air-tight dust cover and the effects of H2O sublimation, which started when the comet arrived at the heliocentric distance <= 2.5 AU. The porous structure inside the nucleus provided enough surface for additional sublimation, which eventually led to the break up of the dust cover and to the observed outburst. The magnitude of the particle burst can be explained by the energy provided by insolation, stored in the dust cover and the nucleus within the months before the outburst: the subliming surface within the nucleus is more than one order of magnitude larger than the geometric surface of the nucleus -- possibly an indication of the latter's porous structure. Another surprise is that the abundance ratios of several molecular species with respect to H2O are variable. During this apparition, comet Holmes lost about 3% of its mass, corresponding to a 'dirty ice' layer of 20m.
The amplitude and phase of the cosmic ray anisotropy are well established experimentally between 10^{11} eV and 10^{14} eV. The study of their evolution into the energy region 10^{14}-10^{16} eV can provide a significant tool for the understanding of the steepening ("knee") of the primary spectrum. In this letter we extend the EAS-TOP measurement performed at E_0 around 10^{14} eV, to higher energies by using the full data set (8 years of data taking). Results derived at about 10^{14} and 4x10^{14} eV are compared and discussed. Hints of increasing amplitude and change of phase above 10^{14} eV are reported. The significance of the observation for the understanding of cosmic ray propagation is discussed.
We report the discovery of a trend of increasing barium abundance with decreasing age for a large sample of Galactic open clusters. The observed pattern of [Ba/Fe] vs. age can be reproduced with a Galactic chemical evolution model only assuming a higher Ba yield from the $s$-process in low-mass stars than the average one suggested by parametrized models of neutron-capture nucleosynthesis. We show that this is possible in a scenario where the efficiency of the extra-mixing processes producing the neutron source $^{13}$C is anti-correlated with the initial mass, with a larger efficiency for lower masses. This is similar to the known trend of extended mixing episodes acting in H-rich layers and might suggest a common physical mechanism.
Ram pressure stripping of the multiphase ISM is studied in the perturbed Virgo cluster spiral galaxy NGC 4438. This galaxy underwent a tidal interaction ~100 Myr ago and is now strongly affected by ram pressure stripping. Deep VLA radio continuum observations at 6 and 20 cm are presented. We detect prominent extraplanar emission to the west of the galactic center, which extends twice as far as the other tracers of extraplanar material. The spectral index of the extraplanar emission does not steepen with increasing distance from the galaxy. This implies in situ re-acceleration of relativistic electrons. The comparison with multiwavelength observations shows that the magnetic field and the warm ionized interstellar medium traced by Halpha emission are closely linked. The kinematics of the northern extraplanar Halpha emission, which is ascribed to star formation, follow those of the extraplanar CO emission. In the western and southern extraplanar regions, the Halpha measured velocities are greater than those of the CO lines. We suggest that the ionized gas of this region is excited by ram pressure. The spatial and velocity offsets are consistent with a scenario where the diffuse ionized gas is more efficiently pushed by ram pressure stripping than the neutral gas. We suggest that the recently found radio-deficient regions compared to 24 mum emission are due to this difference in stripping efficiency.
We used the revised New Luyten Two-Tenths (rNLTT) catalog to select high proper motion white dwarf candidates. We studied the spectra of 70 hydrogen-rich (DA) white dwarfs, which were obtained at the Cerro Tololo Inter-American Observatory (CTIO) and extracted from the Sloan Digital Sky Survey (SDSS). We determined their effective temperature and surface gravity by fitting their Balmer line profiles to model white dwarf spectra. Using evolutionary mass-radius relations we determined their mass and cooling age. We also conducted a kinematical study of the white dwarf sample and found that most belong to the thin disk population. We have identified three magnetic white dwarfs and estimated their surface magnetic field. Finally, we have identified 6 white dwarfs that lie within 20 pc from the Sun.
Comet NEAT C/2001 Q4 was observed for linear polarization using the optical polarimeter mounted at the 1.2m telescope at Mt. Abu Observatory, during the months of May and June 2004. Observations were conducted through the International Halley Watch narrow band (continuum) and B,V,R broad band filters. During the observing run the phase angle ranged from 85.6 deg in May to 55 deg in June. As expected, polarization increases with wavelength in this phase angle range. Polarization colour in the narrow bands changes at different epochs, perhaps related to cometary activity or molecular emission contamination. The polarization was also measured in the cometary coma at different locations along a line, in the direction of the tail. As expected, we notice minor decrease in the polarization as photocenter (nucleus) is traversed while brightness decreases sharply away from it. Based on these polarization observations we infer that the comet NEAT C/2001 Q4 has high polarization and a typical grain composition- mixture of silicates and organics.
Independent of established data centers, and partly for my own research, since 1989 I have been collecting the tabular data from over 2600 articles concerned with radio sources and extragalactic objects in general. Optical character recognition (OCR) was used to recover tables from 740 papers. Tables from only 41 percent of the 2600 articles are available in the CDS or CATS catalog collections, and only slightly better coverage is estimated for the NED database. This fraction is not better for articles published electronically since 2001. Both object databases (NED, SIMBAD, LEDA) as well as catalog browsers (VizieR, CATS) need to be consulted to obtain the most complete information on astronomical objects. More human resources at the data centers and better collaboration between authors, referees, editors, publishers, and data centers are required to improve data coverage and accessibility. The current efforts within the Virtual Observatory (VO) project, to provide retrieval and analysis tools for different types of published and archival data stored at various sites, should be balanced by an equal effort to recover and include large amounts of published data not currently available in this way.
We present an analysis of the X-ray point source populations in 182 Chandra
images of galaxy clusters at z>0.1 with exposure time >10 ksec, as well as 44
non-cluster fields. Analysis of the number and flux of these sources, using a
detailed pipeline to predict the distribution of non-cluster sources in each
field, reveals an excess of X-ray point sources associated with the galaxy
clusters. A sample of 148 galaxy clusters at 0.1<z<0.9, with no other nearby
clusters, show an excess of 230 cluster sources in total, an average of ~1.5
sources per cluster. The lack of optical data for these clusters limits the
physical interpretation of this result, as we cannot calculate the fraction of
cluster galaxies hosting X-ray sources. However, the fluxes of the excess
sources indicate that over half of them are very likely to be AGN, and the
radial distribution shows that they are quite evenly distributed over the
central 1 Mpc of the cluster, with almost no sources found beyond this radius.
We also use this pipeline to successfully reproduce the results of previous
studies, particularly the higher density of sources in the central 0.5 Mpc of a
few cluster fields, but show that these conclusions are not generally valid for
this larger sample of clusters. We conclude that some of these differences may
be due to the sample properties, such as the size and redshift of the clusters
studied, or a lack of publications for cluster fields with no excess sources.
This paper also presents the basic X-ray properties of the galaxy clusters, and
in subsequent papers in this series the dependence of the AGN population on
these cluster properties will be evaluated.
In addition the properties of over 9500 X-ray point sources in the fields of
galaxy clusters are tabulated in a separate catalogue available online.
We explore joint observations of the South-East limb made by Hinode, TRACE and SOHO/SUMER on April 12, 2008 as part of the Whole Heliosphere Interval (WHI) Quiet Sun Characterization targeted observing program. During the sequence a large, 10Mm long, macro-spicule was sent upward and crossed the line-of-sight of the SUMER slit, an event that affords us an opportunity to study the coupling of cooler chromospheric material to transition region emission formed as hot as 600,000K. This short article provides preliminary results of the data analysis.
We continue the investigation of a CME-driven coronal dimming from December 14 2006 using unique high resolution imaging of the chromosphere and corona from the Hinode spacecraft. Over the course of the dimming event we observe the dynamic increase of non-thermal line broadening of multiple emission lines as the CME is released and the corona opens; reaching levels seen in coronal holes. As the corona begins to close, refill and brighten, we see a reduction of the non-thermal broadening towards the pre-eruption level. The dynamic evolution of non-thermal broadening is consistent with the expected change of Alfven wave amplitudes in the magnetically open rarefied dimming region, compared to the dense closed corona prior to the CME. The presented data reinforce the belief that coronal dimmings must be temporary sources of the fast solar wind. It is unclear if such a rapid transition in the thermodynamics of the corona to a solar wind state has an effect on the CME itself.
We report spatially-resolved variations in the 3.4micron hydrocarbon absorption feature and the 3.3micron polycyclic aromatic hydrocarbon (PAH) emission band in the Circinus galaxy over the central few arcsec. The absorption is measured towards warm emitting dust associated with Coronal line regions to the east and west of the nucleus. There is an absorption optical depth tau(3.4um) ~0.1 in the core which decreases to the west and increases to the east. This is consistent with increased extinction out to ~40 pc east of the core, supported by the Coronal emission line intensities which are significantly lower to the east than the west. PAH emission is measured to be symmetrically distributed out to +/- 4 arcsec, outside the differential extinction region. The asymmetry in the 3.4micron absorption band reflects that seen in the 9.7micron silicate absorption band reported by Roche et al. (2006) and the ratio of the two absorption depths remains approximately constant across the central regions, with tau(3.4um) / tau(9.7um) ~ 0.06 +/-0.01. This indicates well-mixed hydrocarbon and silicate dust populations, with no evidence for significant changes near the nucleus.
The GMRT has been used to make deep, wide-field surveys of several fields at 610 MHz, with a resolution of about 5 arcsec. These include the Spitzer Extragalactic First Look Survey field, where 4 square degrees were observed with a r.m.s. sensitivity of about 30 microJy/beam, and several SWIRE fields (namely the Lockman Hole, ELAIS-N1 and N2 fields) covering more than 20 square degrees with a sensitivity of about 80 microJy beam or better. The analysis of these observations, and some of the science results are described.
The classification of time series from photometric large scale surveys into variability types and the description of their properties is difficult for various reasons including but not limited to the irregular sampling, the usually few available photometric bands, and the diversity of variable objects. Furthermore, it can be seen that different physical processes may sometimes produce similar behavior which may end up to be represented as same models. In this article we will also be presenting our approach for processing the data resulting from the Gaia space mission. The approach may be classified into following three broader categories: supervised classification, unsupervised classifications, and "so-called" extractor methods i.e. algorithms that are specialized for particular type of sources. The whole process of classification- from classification attribute extraction to actual classification- is done in an automated manner.
The evidence presented earlier by several authors for the substantial disk eccentricity in dwarf novae during their superoutbursts is shown to result either from errors or from arbitrary, incorrect assumptions. In particular, the evidence resulting from hot spot eclipses was based on the assumption that the spot distances are identical with disk radii which is not always correct.
The ESA gamma-ray telescope, INTEGRAL, is detecting relatively more intrinsically rare cataclysmic variables (CVs) than were found by surveys at lower energies. Specifically, a large fraction of the CVs that are INTEGRAL sources consists of asynchronous polars and intermediate polars (IPs). IP classifications have been proposed for the majority of CVs discovered by INTEGRAL, but, in many cases, there is very little known about these systems. In order to address this, I present time-resolved optical data of five CVs discovered through INTEGRAL observations. The white dwarf spin modulation is detected in high-speed photometry of three of the new CVs (IGR J15094-6649, IGR J16500-3307, and IGR J17195-4100), but two others (XSS J12270-4859 and IGR J16167-4957) show no evidence of magnetism, and should be considered unclassified systems. Spectroscopic orbital period (P_orb) measurements are also given for IGR J15094-6649, IGR J16167-4957, IGR J16500-3307, and IGR J17195-4100.
The interacting binary white dwarf (AM CVn) systems HM Cnc and V407 have orbital periods of 5.4 min and 9.5 min, respectively. The two systems are characterized by an "on/off" behaviour in the X-ray light curve, and optical light curves that are nearly sinusoidal and which lead the X-ray light curves in phase by about 0.2 in both systems. Of the models that have been proposed to explain the observations, the one that seems to require the least fine tuning is the direct impact model of Marsh & Steeghs (2002). In this model, the white dwarf primary is large enough relative to the semi-major axis that the accretion stream impacts the surface of the primary white dwarf directly without forming an accretion disc. Marsh & Steeghs proposed that in this situation there could be a flow set up around the equator with a decreasing surface temperature the further one measured from the impact point. In this study, we estimate the light curves that might result from such a temperature distribution, and find them to be reasonable approximations to the observations. One unexpected result is that two distinct X-ray spots must exist to match the shape of the X-ray light curves.
We continue our earlier studies of quasi-periodic oscillations (QPOs) in the power spectra of accreting, rapidly-rotating black holes that originate from the geometric "light echoes" of X-ray flares occurring within the black hole ergosphere. Our present work extends our previous treatment to three-dimensional photon emission and orbits to allow for arbitrary latitudes in the positions of the distant observers and the X-ray sources in place of the mainly equatorial positions and photon orbits of the earlier consideration. Following the trajectories of a large number of photons we calculate the response functions of a given geometry and use them to produce model light curves which we subsequently analyze to compute their power spectra and autocorrelation functions. In the case of an optically-thin environment, relevant to advection-dominated accretion flows, we consistently find QPOs at frequencies of order of ~kHz for stellar-mass black hole candidates while order of ~mHz for typical active galactic nuclei (~10^7 Msun) for a wide range of viewing angles (30 to 80deg) from X-ray sources predominantly concentrated toward the equator within the ergosphere. As in our previous treatment, here too, the QPO signal is produced by the frame-dragging of the photons by the rapidly-rotating black hole, which results in photon "bunches" separated by constant time-lags, the result of multiple photon orbits around the hole. Our model predicts for various source/observer configurations the robust presence of a new class of QPOs, which is inevitably generic to curved spacetime structure in rotating black hole systems.
In a programme of observations of local luminous blue compact galaxies (BCGs), we are investigating kinematics by using tracers of both stars and ionized gas. Here we summarise our program and present new data on the local Lyman break galaxy analogue Haro 11. From spatially-resolved spectroscopy around the near-infrared Ca II triplet, we find that its stars and ionized gas have similar velocity fields. Our programme so far indicates however that emission line velocities can differ locally by a few tens of km/s from the Ca II values. Comparing our data to simple stellar population models, we assess which stellar population the Ca II triplet traces and its potential beyond the local universe.
The study of PopI and PopII indicators in galaxies has a profound impact on our understanding of galaxy evolution. Their present (z=0) ratio suggests that the star formation history of galaxies was primarily dictated by their global mass. Since 1989 Luis Carrasco and I spent most of our sleepless nights gathering H_alpha and near infrared surface photometry of galaxies in the local Universe and focused most of our scientific career on these two indicators trying to convince the community that the mass was the key parameter to their evolution. We were unsuccessful, until in 2004 the Sloan team rediscovered this phenomenon and named it "downsizing"
Mutual sticking of dust aggregates is the first step toward planetesimal formation in protoplanetary disks. In spite that the electric charging of dust particles is well recognized in some contexts, it has been largely ignored in the current modeling of dust coagulation. In this study, we present a general analysis of the dust charge state in protoplanetary disks, and then demonstrate how the electric charging could dramatically change the currently accepted scenario of dust coagulation. First, we describe a new semianalytical method to calculate the dust charge state and gas ionization state self-consistently. This method is far more efficient than previous numerical methods, and provides a general and clear description of the charge state of a gas-dust mixture. Second, we apply this analysis to compute the collisional cross section of growing aggregates taking their charging into account. As an illustrative example, we focus on early evolutionary stages where the dust has been thought to experience ballistic cluster-cluster aggregation (BCCA). We find that, for a wide range of model parameters, the BCCA growth is strongly inhibited by the electric repulsion between colliding aggregates and eventually "freezes out". Strong disk turbulence would help the aggregates to overcome this growth barrier, but it would cause the collisional fragmentation in later growth stages. These facts suggest that the combination of electric repulsion and collisional fragmentation would impose a serious limitation on dust growth in protoplanetary disks. We propose a possible scenario of dust evolution after the freeze-out. Finally, we point out that the fractal growth of dust aggregates tends to maintain a low ionization degree and, as a result, a large magnetorotationally stable region in the disk.
Aims: The aim of this work is to collect a complete, mass--selected sample of galaxies with very low specific star formation rate, for a comparison with the prediction of recent theoretical models. Method: We use the 24/K flux ratio, complemented by the SED fitting to the full 0.35-8.0 mum spectral distribution, to select quiescent galaxies from z~0.4 to z~4 in the GOODS--MUSIC sample. Our observational selection can be translated into thresholds on the specific star formation rate SFR/M_*, that can be used to compare with the theoretical predictions. Results: We find that, in the framework of the well known global decline of the quiescent fraction with redshift, a non-negligible fraction ~15-20% of massive galaxies with very low specific star formation rate exists up to z~4, including a tail of "Red&Dead" galaxies with SFR/M_*<10^{-11}/yr. Recent theoretical models vary to a large extent in the prediction of the fraction of galaxies with very low specific star formation rates, and are unable to provide a global match to our data.
We present mid-infrared Period-Luminosity relations for Cepheids in the Local Group galaxy IC1613. Using archival IRAC imaging data from Spitzer we were able to measure single-epoch magnitudes for five, 7 to 50-day, Cepheids at 3.6 and 4.5 microns. When fit to the calibrating relations, measured for the Large Magellanic Cloud Cepheids, the data give apparent distance moduli of 24.29 +/- 0.07 and 24.28 +/- 0.07 at 3.6 and 4.5 microns, respectively. A multi-wavelength fit to previously published BVRIJHK apparent moduli and the two IRAC moduli gives a true distance modulus of 24.27 +/- 0.02 mag with E(B-V) = 0.08 mag, and a corresponding metric distance of 715 kpc. Given that these results are based on single-phase observations derived from exposures having total integration times of only 1,000 sec/pixel we suggest that Cepheids out to about 2 Mpc are accessible to Spitzer with modest integration times during its warm mission. We identify the main limiting factor to this method to be crowding/contamination induced by the ubiquitous population of infrared-bright AGB stars.
We survey four nearby irregular galaxies for radio supernova remnants (SNRs) using deep (1 sigma ~ 20 microJy), high resolution (~20 pc) VLA continuum data at 20, 6, and 3.6 cm. We identify discrete sources in these galaxies and use radio spectral indices and H alpha images to categorize them as SNRs, H II regions, or background radio galaxies. Our classifications are generally in good agreement agreement with the literature. We identify a total of 43 SNR candidates: 23 in NGC 1569, 7 in NGC 4214, 5 in NGC 2366, and 8 in NGC 4449. Only one SNR--the well-studied object J1228+441 in NGC 4449--is more luminous at 20 cm than Cas A. By comparing the total thermal flux density in each galaxy to that localized in H II regions, we conclude that a significant fraction must be in a diffuse component or in low-luminosity H II regions.
We study the flux and the angular power spectrum of gamma-rays produced by Dark Matter (DM) annihilations in the Milky Way (MW) and in extra-galactic halos. The annihilation signal receives contributions from: a) the smooth MW halo, b) resolved and unresolved substructures in the MW, c) external DM halos at all redshifts, including d) their substructures. Adopting a self-consistent description of local and extra-galactic substructures, we show that the annihilation flux from substructures in the MW dominates over all the other components for angles larger than O(1) degrees from the Galactic Center, unless an extreme prescription is adopted for the substructures concentration. We also compute the angular power spectrum of gamma-ray anisotropies and find that, for an optimistic choice of the particle physics parameters, an interesting signature of DM annihilations could soon be discovered by the Fermi LAT satellite at low multipoles, l<100, where the dominant contribution comes from MW substructures with mass M>10^4 solar masses. For the substructures models we have adopted, we find that the contribution of extra-galactic annihilations is instead negligible at all scales.
We examine if a generally covariant modification to the dynamics of the empty space-time is capable of describing the flat rotational velocity curves of the `spiral' galaxies. We present a modification to the Einstein-Hilbert action with the cost of introducing a new parameter beside the Newtonian gravitational constant (G) that resolves both the missing mass problem and dark energy. We discuss that this modification can naturally reproduce all the effects assigned to the presence of dark matter and dark energy.
We numerically examine the influence of the viscosity on the relaxation process of localized clouds in thermally-unstable two-phase media, which are locally heated by cosmic ray and cooled by radiation. Stationary pulse-like exact solutions of the media are numerically obtained by a shooting method. In one-dimensional direct numerical simulations, localized clouds are formed during the two-phase separation and sustained extraordinarily. Such long-lived clouds have been recently observed in interstellar media. We demonstrate that the balance of the viscosity with a pressure gradient remarkably suppresses the evaporation of the clouds and controls the relaxation process. This balance fixes the peak pressure of localized structures and then the structure is attracted and trapped to one of the pulse-like exact solutions. While the viscosity has been neglected in most of previous studies, our study suggests the precise treatment of the viscosity is necessary to discuss the evaporation of the clouds.
Environmental research aimed at monitoring and predicting O2 depletion is still lacking or in need of improvement, in spite of many attempts to find a relation between atmospheric gas content and climate variability. The aim of the present project is to determine accurate historical sequences of the atmospheric O2 depletion by using the telluric lines present in stellar spectra. A better understanding of the role of oxygen in atmospheric thermal equilibrium may become possible if high-resolution spectroscopic observations are carried out for different airmasses, in different seasons, for different places, and if variations are monitored year by year. The astronomical spectroscopic technique involves mainly the investigation of the absorption features in high-resolution stellar spectra, but we are also considering whether accurate measures of the atmospheric O2 abundances can be obtained from medium and low resolution stellar spectra.
We introduce two new fermionic variational wavefunctions, which sustain superfluidity. Applications include quark matter, nuclei, neutron stars and the high temperature superconductors. Spin up and down fermions are, in principle, inequivalent, and a normal fluid component coexists with the superfluid one. A wider class of Hamiltonians than sheer Bardeen-Cooper-Schrieffer (BCS) type, comprising hybridization and interaction between different fermion species, can be treated exactly, as in the well known manner of BCS theory. A simple model of interacting electrons in a lattice yields a ratio of the maximum superconducting gap to the transition temperature in the range 3 to 6, as compared to the typical isotropic s-wave BCS value of 1.76. However, the BCS solutions are dominant for this simple model.
We investigate the signatures of antimatter in cosmic rays that would result from annihilations of the scalar dark matter candidate of the Inert Doublet Model. We consider three benchmark candidates, all consistent with the WMAP cosmic abundance and existing direct detection experiments, and confront the predictions of the model with the recent PAMELA, ATIC and HESS data. For a light IDM WIMP candidate, M_{DM} = 10 GeV, we argue that the positron and antiproton fluxes are large, but consistent with expected backgrounds, unless there is an enhancement in the local density of dark matter. For an IDM WIMP candidate with M_{DM} = 70 GeV, the contribution is lower than the expected backgrounds unless there is a large boost factor. However, the candidate is enable to explain the excesses observed by the recent experiments. Finally, for an IDM WIMP candidate with M_{DM}=10 TeV, it is possible to fit the PAMELA excess, while satisfying the anti-protons data, but, unfortunately, not the ATIC one.
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Submillimeter-emitting galaxies (SMGs) are z~2 bolometrically luminous systems hosting energetic starburst and AGN activity. SMGs may represent a rapid growth phase that every massive galaxy undergoes before lying on the well-established black-hole-spheroid mass relationship in the local Universe. Here we briefly discuss our recent results from Alexander et al. (2008) where we estimated the masses of the black holes in SMGs using the black-hole virial mass estimator, finding M_BH~6x10^7 M_solar for typical SMGs. We show that the black-hole-spheroid mass ratio for SMGs at z~2 was suggestively below that found for massive galaxies in the local Universe and more than an order of magnitude below the black-hole-spheroid mass ratio estimated for z~2 quasars and radio galaxies. We demonstrate that SMGs and their progeny cannot lie on the elevated z~2 black-hole-spheroid mass relationship of quasars-radio galaxies without overproducing the space density of the most massive black holes (M_BH~10^9 M_solar), unless the galaxy spheroid of SMGs is an order of magnitude lower than that typically assumed (M_SPH~10^10 M_solar). We also show that the relative black-hole-spheroid growth rates of typical SMGs appear to be insufficient to significantly increase the black-hole-spheroid mass ratio, without requiring long duty cycles (~10^9 years), and argue that a more AGN-dominated phase (e.g., an optically bright quasar) is required to significantly move SMGs (and their progeny) up the black-hole-spheroid mass plane.
Being able to quickly select among gamma-ray bursts (GRBs) seen by the Swift satellite those which are high-z candidates would give ground-based observers a better chance to determine a redshift for such distant GRBs. Information about these high-z GRBs is important in helping to resolve questions about the early universe such as the formation rate of high-z GRBs, the re-ionization period of the universe, the metallicity of the early universe, and the Hubble expansion. Initially using a sample of 51 GRBs with previously measured redshifts, we have developed high-z screening criteria employing the GRB spectral as well as temporal characteristics of the prompt emission from the Burst Alert Telescope (BAT) on Swift. Now that the sample has increased to 81 GRBs, we have revisited the screening criteria and our methodology. Our updated high-z screening criteria are presented in this paper.
We report the discovery of the most-distant double-peaked emitter, CXOECDFS J033115.0-275518, at z=1.369. A Keck/DEIMOS spectrum shows a clearly double-peaked broad Mg II $\lambda2799$ emission line, with FWHM 11000 km/s for the line complex. The line profile can be well fit by an elliptical relativistic Keplerian disk model. This is one of a handful of double-peaked emitters known to be a luminous quasar, with excellent multiwavelength coverage and a high-quality X-ray spectrum. CXOECDFS J033115.0-275518 is a radio-loud quasar with two radio lobes (FR II morphology) and a radio loudness of f_{5 GHz}/f_{4400 \AA}~429. The X-ray spectrum can be modeled by a power law with photon index 1.72 and no intrinsic absorption; the rest-frame 0.5-8.0 keV luminosity is $5.0\times10^{44}$ erg/s. The spectral energy distribution (SED) of CXOECDFS J033115.0-275518 has a shape typical for radio-loud quasars and double-peaked emitters at lower redshift. The local viscous energy released from the line-emitting region of the accretion disk is probably insufficient to power the observed line flux, and external illumination of the disk appears to be required. The presence of a big blue bump in the SED along with the unexceptional X-ray spectrum suggest that the illumination cannot arise from a radiatively inefficient accretion flow.
We present the results of a spectroscopic survey of the kinematic structure of star-forming galaxies at redshift z ~ 2 - 3 using Keck/OSIRIS integral field spectroscopy. Our sample is comprised of 12 galaxies between redshifts z ~ 2.0 - 2.5 and one galaxy at z ~ 3.3 which are well detected in either HAlpha or [O III] emission. These observations were obtained in conjunction with the Keck laser guide star adaptive optics system, with a typical angular resolution after spatial smoothing ~ 0.15" (approximately 1 kpc at the redshift of the target sample). At most five of these 13 galaxies have spatially resolved velocity gradients consistent with rotation while the remaining galaxies have relatively featureless or irregular velocity fields. All of our galaxies show local velocity dispersions ~ 60 - 100 km/s (for a kinematic ratio v/sigma < 1), suggesting that even for those galaxies with clear velocity gradients rotation about a preferred axis may not be the dominant mechanism of physical support. While some galaxies show evidence for major mergers such evidence is unrelated to the kinematics of individual components (one of our strongest merger candidates also exhibits unambiguous rotational structure), refuting a simple bimodal disk/merger classification scheme. We discuss these data in light of complementary surveys and extant UV-IR spectroscopy and photometry, concluding that the dynamical importance of cold gas may be the primary factor governing the observed kinematics of z ~ 2 galaxies. We conclude by speculating on the importance of mechanisms for accreting low angular-momentum gas and the early formation of quasi-spheroidal systems in the young universe.
Some models for quantum gravity (QG) violate Lorentz invariance and predict an energy dependence of the speed of light, leading to a dispersion of high-energy gamma-ray signals that travel over cosmological distances. Limits on the dispersion from short-duration substructures observed in gamma-rays emitted by gamma-ray bursts (GRBs) at cosmological distances have provided interesting bounds on Lorentz invariance violation (LIV). Recent observations of unprecedentedly fast flares in the very-high energy gamma-ray emission of the active galactic nuclei (AGNs) Mkn 501 in 2005 and PKS 2155-304 in 2006 resulted in the most constraining limits on LIV from light-travel observations, approaching the Planck mass scale, at which QG effects are assumed to become important. I review the current status of LIV searches using GRBs and AGN flare events, and discuss limitations of light-travel time analyses and prospects for future instruments in the gamma-ray domain.
At low Eddington ratio (mdot), two effects make it harder to detect AGN given some selection criteria. First, they may transition to a radiatively inefficient state, changing SED shape and dramatically decreasing in optical/IR luminosity. Second, even with fixed accretion physics, AGN are diluted/less luminous relative to their hosts; the magnitude of this depends on host properties and so on luminosity and redshift. These effects lead to differences in observed AGN samples, even at fixed bolometric luminosity and after correction for obscuration. The true Eddington ratio distribution may depend strongly on luminosity, but this will be seen only in surveys robust to dilution and radiative inefficiency (X-ray or narrow-line samples); selection effects imply that AGN in optical samples will have uniformly high mdot. This also implies that different selection methods yield systems with different hosts: the clustering of faint optical/IR sources will be weaker than that of X-ray sources, and optical/IR Seyferts will reside in more disk-dominated galaxies while X-ray selected Seyferts will preferentially occupy early-type systems. If observed mdot distributions are correct, a large fraction of low-luminosity AGN currently classified as 'obscured' are in fact radiatively inefficient and/or diluted, not obscured by gas or dust. This is equally true if X-ray hardness is used as a proxy for obscuration, since radiatively inefficient SEDs near mdot~0.01 are X-ray hard. These effects can explain most of the claimed luminosity/redshift dependence in the 'obscured' AGN population, with the true obscured fraction as low as 20%.
Predicting the local flux of dark matter particles is vital for dark matter direct detection experiments. To date, such predictions have been based on simulations that model the dark matter alone. Here we include the influence of the baryonic matter for the first time. We use two different approaches. Firstly, we use dark matter only simulations to estimate the expected merger history for a Milky Way mass galaxy, and then add a thin stellar disc to measure its effect. Secondly, we use three cosmological hydrodynamic simulations of Milky Way mass galaxies. In both cases, we find that a stellar/gas disc at high redshift (z~1) causes merging satellites to be preferentially dragged towards the disc plane. This results in an accreted dark matter disc that contributes ~0.25 - 1 times the non-rotating halo density at the solar position. An associated thick stellar disc forms with the dark disc and shares a similar velocity distribution. If these accreted stars can be separated from those that formed in situ, future astronomical surveys will be able to infer the properties of the dark disc from these stars. The dark disc, unlike dark matter streams, is an equilibrium structure that must exist in disc galaxies that form in a hierarchical cosmology. Its low rotation lag with respect to the Earth significantly boosts WIMP capture in the Earth and Sun, increases the likelihood of direct detection at low recoil energy, boosts the annual modulation signal, and leads to distinct variations in the flux as a function of recoil energy that allow the WIMP mass to be determined (see contribution from T. Bruch this volume).
We explore the physics of crystallization in the deep interiors of white dwarf stars using the color-magnitude diagram and luminosity function constructed from proper motion cleaned Hubble Space Telescope photometry of the globular cluster NGC 6397. We demonstrate that the data are consistent with the theory of crystallization of the ions in the interior of white dwarf stars and provide the first empirical evidence that the phase transition is first order: latent heat is released in the process of crystallization as predicted by van Horn (1968). We outline how this data can be used to observationally constrain the value of Gamma = E_{Coulomb}/E_{thermal} near the onset of crystallization, the central carbon/oxygen abundance, and the importance of phase separation.
One of the five key science projects for the Square Kilometre Array (SKA) is "The Origin and Evolution of Cosmic Magnetism", in which radio polarimetry will be used to reveal what cosmic magnets look like and what role they have played in the evolving Universe. Many of the SKA prototypes now being built are also targeting magnetic fields and polarimetry as key science areas. Here I review the prospects for innovative new polarimetry and Faraday rotation experiments with forthcoming facilities such as ASKAP, LOFAR, the ATA, the EVLA, and ultimately the SKA. Sensitive wide-field polarisation surveys with these telescopes will provide a dramatic new view of magnetic fields in the Milky Way, in nearby galaxies and clusters, and in the high-redshift Universe.
Gamma-ray emission from cocoons of young radio galaxies is predicted. Considering the process of adiabatic injection of the shock dissipation energy and mass of the relativistic jet into the cocoon, we find that the thermal electron temperature of the cocoon is typically predicted to be of the order of $\sim$ MeV, and is determined only by the bulk Lorentz factor of the jet. Together with the time-dependent dynamics of the cocoon expansion, we find that young cocoons can yield thermal Bremsstrahlung emissions at energies $\sim$MeV. Hotter cocoons (i.e., GeV) for younger sources are also discussed.
Using a cross-correlation method, we study the X-ray halo of Cyg X-3. Two components of dust distributions are needed to explain the time lags derived by the cross-correlation method. Assuming the distance as 1.7 kpc for Cygnus OB2 association (a richest OB association in the local Galaxy) and another uniform dust distribution, we get a distance of $7.2^{+0.3}_{-0.5}$ kpc (68$%$ confidence level) for Cyg X-3. When using the distance estimation of Cygnus OB2 as 1.38 kpc or 1.82 kpc, the inferred distance for Cyg X-3 is $3.4^{+0.2}_{-0.2}$ kpc or $9.3^{+0.6}_{-0.4}$ kpc respectively. The distance estimation uncertainty of Cyg X-3 is mainly related to the distance of the Cygnus OB2, which may be improved in the future with high precision astrometric measurements. The advantage of this method is that the result depends weakly on the photon energy, dust grain radius, scattering cross-section and so on.
We propose a model of magnetic connection (MC) of a black hole with its surrounding accretion disc based on large-scale magnetic field. The MC gives rise to transport of energy and angular momentum between the black hole and the disc, and the closed field lines pipe the hot matter evaporated from the disc, and shape it in the corona above the disc to form a magnetically induced disc-corona system, in which the corona has the same configuration as the large-scale magnetic field. We numerically solve the dynamic equations in the context of the Kerr metric, in which the large-scale magnetic field is determined by dynamo process and equipartition between magnetic pressure and gas pressure. Thus we can obtain a global solution rather than assuming the distribution of large-scale magnetic field beforehand. The main MC effects lie in three aspects. (1) The rotational energy of a fast-spinning black hole can be extracted, enhancing the dissipation in the accretion disc, (2) the closed field lines provide a natural channel for corona matter escaping from disc and finally falling into black hole, and (3) the scope of the corona can be bounded by the conservation of magnetic flux. We simulate the high-energy spectra of this system by using Monte-Carlo method, and find that the relative hardness of the spectra decreases as accretion rate or black hole spin $a_*$ increases. We fit the typical X-ray spectra of three black-hole binaries (GRO J1655-40, XTE 1118+480 and GX 339-4) in the low/hard or very high state.
Observational evidences point to a common explosion mechanism of Type Ia supernovae based on a delayed detonation of a white dwarf. Although several scenarios have been proposed and explored by means of one, two, and three-dimensional simulations, the key point still is the understanding of the conditions under which a stable detonation can form in a destabilized white dwarf. One of the possibilities that have been invoked is that an inefficient deflagration leads to the pulsation of a Chandrasekhar-mass white dwarf, followed by formation of an accretion shock around a carbon-oxygen rich core. The accretion shock confines the core and transforms kinetic energy from the collapsing halo into thermal energy of the core, until an inward moving detonation is formed. This chain of events has been termed Pulsating Reverse Detonation (PRD). In this work we explore the robustness of the detonation ignition for different PRD models characterized by the amount of mass burned during the deflagration phase, M_defl. The evolution of the white dwarf up to the formation of the accretion shock has been followed with a three-dimensional hydrodynamical code with nuclear reactions turned off. We found that detonation conditions are achieved for a wide range of M_defl. However, if the nuclear energy released during the deflagration phase is close to the white dwarf binding energy (~ 0.46 foes -> M_defl ~ 0.30 M_sun) the accretion shock cannot heat and confine efficiently the core and detonation conditions are not robustly achieved.
Observational evidences point to a common explosion mechanism of Type Ia supernovae based on a delayed detonation of a white dwarf. However, all attempts to find a convincing ignition mechanism based on a delayed detonation in a destabilized, expanding, white dwarf have been elusive so far. One of the possibilities that has been invoked is that an inefficient deflagration leads to pulsation of a Chandrasekhar-mass white dwarf, followed by formation of an accretion shock that confines a carbon-oxygen rich core, while transforming the kinetic energy of the collapsing halo into thermal energy of the core, until an inward moving detonation is formed. This chain of events has been termed Pulsating Reverse Detonation (PRD). In this work we present three dimensional numerical simulations of PRD models from the time of detonation initiation up to homologous expansion. Different models characterized by the amount of mass burned during the deflagration phase, M_defl, give explosions spanning a range of kinetic energies, K ~ (1.0-1.2) foes, and 56Ni masses, M(56Ni) ~ 0.6-0.8 M_sun, which are compatible with what is expected for typical Type Ia supernovae. Spectra and light curves of angle-averaged spherically symmetric versions of the PRD models are discussed. Type Ia supernova spectra pose the most stringent requirements on PRD models.
Stochastic backgrounds or relic gravitons, if ever detected, will constitute a prima facie evidence of physical processes taking place during the earliest stages of the evolution of the plasma. The essentials of the stochastic backgrounds of relic gravitons are hereby introduced and reviewed. The pivotal observables customarily employed to infer the properties of the relic gravitons are discussed both in the framework of the $\Lambda$CDM paradigm as well as in neighboring contexts. The complementarity between experiments measuring the polarization of the Cosmic Microwave Background (such as, for instance, WMAP, Capmap, Quad, Cbi, just to mention a few) and wide band interferometers (e.g. Virgo, Ligo, Geo, Tama) is emphasized. While the analysis of the microwave sky strongly constrains the low-frequency tail of the relic graviton spectrum, wide-band detectors are sensitive to much higher frequencies where the spectral energy density depends chiefly upon the (poorly known) rate of post-inflationary expansion.
Methods: We analyse an XMM-Newton observation of 1RXS J115928.5-524717, an ultracool dwarf with spectral type M9 and compare its X-ray properties to those of other similar very late-type stars. Results: We clearly detected 1RXS J115928.5-524717 at soft X-ray energies in all EPIC detectors. Only minor variability was present during the observation and we attribute the X-ray emission to quasi-quiescent activity. The coronal plasma is described well by a two-temperature model at solar metallicity with temperatures of 2 MK and 6 MK and an X-ray luminosity of about L_x = 1.0 x 10^26 erg/s in the 0.2-2.0 keV band. The corresponding activity level of log L_x/L_bol = -4.1 points to a moderately active star. Altogether, X-ray activity from very low-mass stars shows similar trends to more massive stars, despite their different interior structure. 1RXSJ115928.5-524717 is, after LHS 2065, the second ultracool M9 dwarf that emits X-rays at detectable levels in quasi-quiescence. While faint in absolute numbers,both stars are rather X-ray active, implying the existence of an efficient dynamo mechanisms that is capable of creating magnetic activity and coronal X-ray emission.
Asymptotic Giant Branch variables are found to obey period-luminosity relations in the mid-IR similar to those seen at K_S (2.14 microns), even at 24 microns where emission from circumstellar dust is expected to be dominant. Their loci in the M, logP diagrams are essentially the same for the LMC and for NGC6522 in spite of different ages and metallicities. There is no systematic trend of slope with wavelength. The offsets of the apparent magnitude vs. logP relations imply a difference between the two fields of 3.8 in distance modulus. The colours of the variables confirm that a principal period with log P > 1.75 is a necessary condition for detectable mass-loss. At the longest observed wavelength, 24 microns, many semi-regular variables have dust shells comparable in luminosity to those around Miras. There is a clear bifurcation in LMC colour-magnitude diagrams involving 24 micron magnitudes.
We present a new implementation of the infrared flux method (IRFM) using the 2MASS catalogue. We compute the theoretical quantities in the 2MASS JHKs filters by integrating theoretical fluxes computed from ATLAS models, and compare them directly with the observed 2MASS JHKs magnitudes. This is the main difference between our implementation of the IRFM and that of Ramirez & Melendez, since to introduce new stars at the lowest metallicities they transform the 2MASS JHKs magnitudes into the TCS photometric system. We merge in our sample the dwarfs stars from Alonso and collaborators with the stars in the sample of Ramirez & Melendez, Casagrande et al., Christlieb et al. and Bonifacio et al. The final number of stars in our sample is 555 dwarf and subgiant field stars, and 264 giant field stars. We derive a new bolometric flux calibration using the available Johnson-Cousins UBVRI and the 2MASS JHKs photometry. We also compute new Teff versus colour empirical calibrations using our extended sample of stars. We derive effectives temperatures for almost all the stars in the Alonso et al. sample and find that our scales of temperature are hotter by ~64K(dT=104K,N=332 dwarfs) and ~54K(dT=131K,N=202 giants). The same comparison with the sample of Ramirez & Melendez for stars with [Fe/H]<-2.5 provides a difference of ~-87K(dT=194K,N=12 dwarfs) and ~61K(dT=62K,N=18 giants). Our temperature scale is slightly hotter than that of Alonso et al. and Ramirez & Melendez for metal-rich dwarf stars but cooler than that of Ramirez & Melendez for metal-poor dwarfs. We have performed a fully self-consistent IRFM in the 2MASS photometric system. For those who wish to use 2MASS photometry and colour-temperature calibrations to derive effective temperatures, especially for metal-poor stars, we recommend our calibrations.
We address the problem of discretizing continuous cosmological signals such as a galaxy distribution for further processing with Fast Fourier techniques. Discretizing, in particular representing continuous signals by discrete sets of sample points, introduces an enormous loss of information, which has to be understood in detail if one wants to make inference from the discretely sampled signal towards actual natural physical quantities. We therefore review the mathematics of discretizing signals and the application of Fast Fourier Transforms to demonstrate how the interpretation of the processed data can be affected by these procedures. It is also a well known fact that any practical sampling method introduces sampling artifacts and false information in the form of aliasing. These sampling artifacts, especially aliasing, make further processing of the sampled signal difficult. For this reason we introduce a fast and efficient supersampling method, frequently applied in 3D computer graphics, to cosmological applications such as matter power spectrum estimation. This method consists of two filtering steps which allow for a much better approximation of the ideal sampling procedure, while at the same time being computationally very efficient.Thus, it provides discretely sampled signals which are greately cleaned from aliasing contributions.
High quality, high resolution X-ray spectra were obtained of Sco X-1 with the Reflection Grating Spectrometer (RGS) on board the XMM-Newton satellite. The spectrum around the Oxygen K-edge is searched for signatures indicative for EXAFS. Analysis shows a clear indication for the existence of EXAFS with photo-electron scattering distances in the absorbing medium in a range which applies to many solids. When scattering of the photo-electron on Oxygen atoms is assumed, the Oxygen to Oxygen atom distances found are 2.75 Angstrom. This fits with distances as found in amorphous water-ice, although water ice is thought to be an unlikely constituent of the diffuse interstellar clouds which form the absorbing medium towards Sco X-1
The measurement of proper motions in CSOs is a powerful tool to determine the dynamical evolution of the newly born extragalactic radio sources. We observed 3 CSOs with the VLBA in 2004 and in 2006 to monitor changes in their structure and measure the separation velocity of the hot spots. It is important to increase the size of the samples of CSOs with measured expansion velocity to test the existance of frustrated objects, and put stringent constraints on the current models. We found for all the three objects observed a transverse motion of the hotspots, and we suggest as the more likey explanation a precession in the jet axis. This behaviour likely inhibits or at least slows down the radio source growth because the head of the hotspot continuously hits new regions of the ISM. Therefore these radio sources may represent an old population of GPS/CSOs.
We present a sample of sources with convex radio spectra peaking at frequencies above a few GHz, known as "High Frequency Peakers" (HFPs). A "bright" sample with a flux density limit of 300 mJy at 5 GHz has been presented by Dallacasa et al. (2000). Here we present the "faint" sample with flux density between 50 and 300 mJy at 5GHz, restricted to the area around the North Galactic Cap, where the FIRST catalogue is available. The candidates have been observed with the VLA at several frequencies ranging from 1.4 to 22 GHz, in order to derive a simultaneous radio spectrum. The final list of confirmed HFP sources consists of 61 objects.
We explore some properties of twin kilohertz quasiperiodic oscillations (QPOs) in a simple toy-model consisting of two oscillation modes coupled by a general nonlinear force. We examine resonant effects by slowly varying the values of the tunable, and nearly commensurable, eigenfrequencies. The behavior of the actual oscillation frequencies and amplitudes during a slow transition through the 3:2 resonance is examined in detail and it is shown that both are significantly affected by the nonlinearities in the governing equations. In particular, the amplitudes of oscillations reflect a resonant exchange of energy between the modes, as a result the initially weaker mode may become dominant after the transition. We note that a qualitatively similar behavior has been recently reported in several neutron star sources by Torok (2008, arXiv:0812.4751), who found that the difference of amplitudes in neutron star twin peak QPOs changes sign as the observed frequency ratio of the QPOs passes through the value 3:2.
Each transiting planet discovered is characterized by 7 measurable quantities, that may or may not be linked together (planet mass, radius, orbital period, and star mass, radius, effective temperature, and metallicity). Correlations between planet mass and period, surface gravity and period, planet radius and star temperature have been previously observed among the known transiting giant planets. Two classes of planets have been previously identified based on their Safronov number. We use the CoRoTlux code to compare simulated events to the sample of discovered planets and test the statistical significance of these correlations. We first generate a stellar field with planetary companions based on radial velocity discoveries and a planetary evolution model, then apply a detection criterion that includes both statistical and red noise sources. We compare the yield of our simulated survey with the ensemble of 31 well-characterized giant transiting planets, using a multivariate logistic analysis to assess whether the simulated distribution matches the known transiting planets. Our multivariate analysis shows that our simulated sample and observations are consistent to 76%. The mass vs. period correlation for giant planets first observed with radial velocity holds with transiting planets. Our model naturally explains the correlation between planet surface gravity and period and the one between planet radius and stellar effective temperature. Finally, we are also able to reproduce the previously observed apparent bimodal distribution of Safronov numbers in 10% of our simulated cases, although our model predicts a continuous distribution. This shows that the evidence for the existence of two groups of planets with different intrinsic properties is not statistically significant.
Forthcoming photometric redshift surveys should provide an accurate probe of
the acoustic peak in the two-point galaxy correlation function, in the form of
angular clustering of galaxies within a given shell in redshift space. We
investigate the form of the anticipated signal, quantifying the distortions
that arise due to projection effects, and in particular explore the validity of
applying the Limber approximation. A single-integral prescription is presented,
which provides an alternative to Limber's equation, and produces a
significantly improved prediction in the regime of interest.
The position of the acoustic peak within the angular correlation function
relates to the angular diameter distance to the far side of the redshift bin.
Thicker redshift bins therefore shift comoving features towards smaller angular
scales. As a result, the value of the photometric redshift error acquires a
greater significance, particularly at lower redshifts. In order to recover the
dark energy equation of state to a level of 1%, we find the total redshift
dispersion must be determined to within \Delta \sigma_z ~ 10^-3, which may
prove challenging to achieve in practice.
We report the discovery of an eclipsing polar, 2XMMi J225036.9+573154, using XMM-Newton. It was discovered by searching the light curves in the 2XMMi catalogue for objects showing X-ray variability. Its X-ray light curve shows a total eclipse of the white dwarf by the secondary star every 174 mins. An extended pre-eclipse absorption dip is observed in soft X-rays at phi=0.8-0.9, with evidence for a further dip in the soft X-ray light curve at phi~0.4. Further, X-rays are seen from all orbital phases (apart from the eclipse) which makes it unusual amongst eclipsing polars. We have identified the optical counterpart, which is faint (r=21), and shows a deep eclipse (>3.5 mag in white light). Its X-ray spectrum does not show a distinct soft X-ray component which is seen in many, but not all, polars. Its optical spectrum shows Halpha in emission for a fraction of the orbital period.
We report VRI CCD observations of nine Cepheids in the South Polar (Sculptor) Group spiral galaxy NGC 0247. Periods of these Cepheids range from 20 to 70 days. Over the past 20 years the very brightest Cepheid in our sample, NGC 0247:[MF09] C1, has decreased its period by 6%, faded by 0.8 mag in the V band, and become bluer by 0.23 mag in (V-I). A multi-wavelength analysis of the Cepheid data yields a true distance modulus of mod = 27.81 +/- 0.10 mag (3.36 +/- 0.16 Mpc) with a total line-of-sight reddening of E(V-I) = 0.07 +/-0.04 mag, after adopting an LMC true distance modulus of 18.5 mag and reddening of E(B-V) = 0.10 mag. These results are in excellent agreement with other very recently published (Cepheid and TRGB) distances to NGC 0247. Combining both Cepheid datasets gives mod_o = 27.85 +/-0.09 mag (3.72 +/- 0.15 Mpc) with E(V-I) = 0.11 +/- 0.03 mag.
Methods. We analyse two observations taken with the Low Energy Transmission Grating Spectrometer of Chandra. We investigated the spectral response to a sudden flux decrease by a factor of 5, which occurred during the second observation. Results. We detect a highly ionised absorption component with an outflow velocity of -4670 km/s, one of the highest outflow velocity components observed in a Seyfert 1 galaxy. The spectra contain a relativistic O VIII Ly alpha line, and four absorption components spanning a range in ionisation parameter xi between 0.07 and 3.19. An emission component producing radiative recombination continua of C VI and C V appears during the low state. The black body temperature decreases with the drop in flux observed in the second observation. Conclusions. For all absorber components we exclude that the ionisation parameter linearly responded to the decrease in flux by a factor of 5. The variability of the absorber suggest that at least three out of four detected components are located in the range 0.02-1 pc. ABRIDGED
In previous work [L. Blanchet and A. Le Tiec, Phys. Rev. D 78, 024031 (2008)], a model of dark matter and dark energy based on the concept of gravitational polarization was investigated. This model was shown to recover the concordance cosmological scenario (Lambda-CDM) at cosmological scales, and the phenomenology of the modified Newtonian dynamics (MOND) at galactic scales. In this Letter we prove that the model can be formulated with a simple and physically meaningful matter action in general relativity. We also provide alternative derivations of the main results of the model.
The monitoring of quiescent emission from neutron star transients with accretion outbursts long enough to significantly heat the neutron star crust has opened a new vista onto the physics of dense matter. In this paper we construct models of the thermal relaxation of the neutron star crust following the end of a protracted accretion outburst. We confirm the finding of Shternin et al., that the thermal conductivity of the neutron star crust is high, consistent with a low impurity parameter. We describe the basic physics that sets the broken power-law form of the cooling lightcurve. The initial power law decay gives a direct measure of the temperature profile, and hence the thermal flux during outburst, in the outer crust. The time of the break, at hundreds of days post-outburst, corresponds to the thermal time where the solid transitions from a classical to quantum crystal, close to neutron drip. We calculate in detail the constraints on the crust parameters of both KS 1731-260 and MXB 1659-29 from fitting their cooling lightcurves. Our fits to the lightcurves require that the neutrons do not contribute significantly to the heat capacity in the inner crust, and provides evidence in favor of the existence of a neutron superfluid throughout the inner crust. Our fits to both sources indicate an impurity parameter of order unity in the inner crust.
We describe the current status of CATS (astrophysical CATalogs Support system), a publicly accessible tool maintained at Special Astrophysical Observatory of the Russian Academy of Sciences (SAO RAS) (this http URL) allowing one to search hundreds of catalogs of astronomical objects discovered all along the electromagnetic spectrum. Our emphasis is mainly on catalogs of radio continuum sources observed from 10 MHz to 245 GHz, and secondly on catalogs of objects such as radio and active stars, X-ray binaries, planetary nebulae, HII regions, supernova remnants, pulsars, nearby and radio galaxies, AGN and quasars. CATS also includes the catalogs from the largest extragalactic surveys with non-radio waves. In 2008 CATS comprised a total of about 10e9 records from over 400 catalogs in the radio, IR, optical and X-ray windows, including most source catalogs deriving from observations with the Russian radio telescope RATAN-600. CATS offers several search tools through different ways of access, e.g. via web interface and e-mail. Since its creation in 1997 CATS has managed about 10,000 requests. Currently CATS is used by external users about 1500 times per day and since its opening to the public in 1997 has received about 4000 requests for its selection and matching tasks.
The X-Ray Telescope (XRT) on the Japanese/USA/UK {\it Hinode (Solar-B)} spacecraft has detected emission from a quiescent active region core that is consistent with nanoflare heating. The fluxes from 10 broadband X-ray filters and filter combinations were used to constructed Differential Emission Measure (DEM) curves. In addition to the expected active region peak at Log T = 6.3-6.5, we find a high-temperature component with significant emission measure at Log T $>$ 7.0. This emission measure is weak compared to the main peak -- the DEM is down by almost three orders of magnitude -- which accounts of the fact that it has not been observed with earlier instruments. It is also consistent with spectra of quiescent active regions: no Fe XIX lines are observed in a CHIANTI synthetic spectrum generated using the XRT DEM distribution. The DEM result is successfully reproduced with a simple two-component nanoflare model.
We explore the properties of 24 field early-type galaxies at 0.20<z<0.75 down to M_B<=-19.30 in a sample extracted from the FORS Deep Field and the William Herschel Deep Field. High S/N intermediate-resolution VLT spectroscopy was complemented by deep high-resolution HST/ACS imaging and additional ground-based multi-band photometry. To clarify the low level of star formation (SF) detected in some galaxies, we identify the amount of AGN activity in our sample using archive data of Chandra and XMM-Newton X-ray surveys. The B and K-band Faber-Jackson relations and the Fundamental Plane display a moderate evolution for the field early-type galaxies. Lenticular (S0) galaxies feature on average a stronger luminosity evolution and bluer rest-frame colours which can be explained that they comprise more diverse stellar populations compared to elliptical galaxies. The evolution of the FP can be interpreted as an average change in the dynamical mass-to-light ratio of our galaxies as <\Delta \log{(M/L_B)}/z>=-0.74\pm0.08. The M/L evolution of these field galaxies suggests a continuous mass assembly of field early-type galaxies during the last 5 Gyr, that gets support by recent studies of field galaxies up to z~1. Independent evidence for recent SF activity is provided by spectroscopic (OII em., Hdelta) and photometric (rest-frame colors) diagnostics. Based on the Hdelta absorption feature we detect a weak residual SF for galaxies that accounts for 5%-10% in the total stellar mass of these galaxies. The co-evolution in the luminosity and mass of our galaxies favours a downsizing formation process. We find some evidence that our galaxies experienced a period of SF quenching, possible triggered by AGN activity that is in good agreement with recent results on both observational and theoretical side. (abridged)
It is well known that stable weak scale particles are viable dark matter candidates since the annihilation cross section is naturally about the right magnitude to leave the correct thermal residual abundance. Many dark matter searches have focused on relatively light dark matter consistent with weak couplings to the Standard Model. However, in a strongly coupled theory, or even if the coupling is just a few times bigger than the Standard Model couplings, dark matter can have TeV-scale mass with the correct thermal relic abundance. Here we consider neutral TeV-mass scalar dark matter, its necessary interactions, and potential signals. We consider signals both with and without higher-dimension operators generated by strong coupling at the TeV scale, as might happen for example in an RS scenario. We find some potential for detection in high energy photons that depends on the dark matter distribution. Detection in positrons at lower energies, such as those PAMELA probes, would be difficult though a higher energy positron signal could in principle be detectable over background. However, a light dark matter particle with higher-dimensional interactions consistent with a TeV cutoff can in principle match PAMELA data.
Explicit time-dependent solutions of the 10d vacuum Einstein equations are found for which spacetime is compactified on a six-dimensional warped space. We explicitly work out an example where the internal space is a six-dimensional generalized conifold having positive, negative or zero scalar curvature, whose base is a five-dimensional Einstein space $X_5=(S^2\times S^2)\ltimes S^1$ or $S^5$. We also present solutions for which the three non-compact dimensions grow in size much faster than the internal dimensions. Inflationary de Sitter solutions are found just by solving the 10d vacuum Einstein equations. Our results show that the limitation with warped models studied to date arise from an oversimplification of the 10d metric ansatz; we give an explicit example of a non-singular warped compactification on de Sitter space dS$_4$ with a finite four-dimensional Newton's constant.
Using accurate and fully general-relativistic simulations we assess the effect that magnetic fields have on the gravitational-wave emission produced during the inspiral and merger of magnetized neutron stars. In particular, we show that magnetic fields have an impact after the merger, because amplified by a Kelvin-Helmholtz instability, but also during the inspiral, because the magnetic tension reduces the stellar tidal deformation for extremely large initial magnetic fields, B_0>10^{17}G. We quantify the influence of magnetic fields by computing the overlap, O, between the waveforms produced during the inspiral by magnetized and unmagnetized binaries. We find that for B_0~10^{17}G, O<0.76 for stars with mass M~1.4Msun, dropping to O<0.67 for M~1.6Msun; in both cases O decreases further after the merger. These results shed light on the recent debate on whether the presence of magnetic fields can be detected during the inspiral and highlight that the use of higher-order methods is essential to draw robust conclusions on this complex process.
A unified treatment of all known types of singularities for flat, isotropic and homogeneous spacetimes in the framework of loop quantum cosmology (LQC) is presented. These include bangs, crunches and all future singularities. Using effective spacetime description we perform a model independent general analysis of the properties of curvature, behavior of geodesics and strength of singularities. For illustration purposes a phenomenological model based analysis is also performed. We show that all values of the scale factor at which a strong singularity may occur are excluded from the effective loop quantum spacetime. Further, if the evolution leads to either a vanishing or divergent scale factor then the loop quantum universe is asymptotically deSitter in that regime. We also show that there exist a class of sudden extremal events, which includes a recently discussed possibility, for which the curvature or its derivatives will always diverge. Such events however turn out to be harmless weak curvature singularities beyond which geodesics can be extended. Our results point towards a generic resolution of physical singularities in LQC.
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We discuss the angular resolution obtained for events registered with the surface detector alone and for hybrid events, i.e., those observed simultaneously by both the surface and fluorescence detectors. The angular accuracy of the surface detector is directly extracted from the data itself and on an event by event basis, and is given as a function of the number of stations triggered by the event and of the zenith angle of the shower. We compare the angular resolution of the surface detector obtained from hybrid events with the one obtained from the surface detector alone.
Violent relaxation -- the protocluster dynamical response to the expulsion of its leftover star forming gas -- is a short albeit crucial episode in the evolution of star clusters and star cluster systems. In this contribution, I survey how it influences the cluster age distribution, the cluster mass function and the ratio between the cluster mass and the stellar mass. I highlight the promising potential that the study of this phase holds in terms of deciphering star cluster formation and galaxy evolution, and (some of) the issues which are to be dealt with before achieving this goal.
During the September-October 2008 outburst of the accreting millisecond pulsar SAX J1808.4-3658, the source was observed by both Suzaku and XMM-Newton approximately 1 day apart. Spectral analysis reveals a broad relativistic Fe K-alpha emission line which is present in both data-sets, as has recently been reported for other neutron star low-mass X-ray binaries. The properties of the Fe K line observed during each observation are very similar. From modeling the Fe line, we determine the inner accretion disk radius to be 13.2 +/- 2.5 GM/c^2. The inner disk radius measured from the Fe K line suggests that the accretion disk is not very receded in the island state. If the inner disk (as measured by the Fe line) is truncated at the magnetospheric radius this implies a magnetic field strength of ~3E8 G at the magnetic poles, consistent with other independent estimates.
Astronomy and cosmology have embraced the internet. We routinely and successfully use the internet as a repository for sharing code, publications and information, and as a computational resource. However the interactive nature of the web, for use as an alternative to downloading code has been largely overlooked. In this article we will outline a simple framework in which a cosmological code can be turned into an interactive web interface. This is presented as a result of creating this http URL which is a front-end for the open-source software iCosmo. We explain how an HTML page can be created and how a cosmological code can be incorporated into a web environment using CGI scripts. We outline how plots and downloadable text can be made, and describe how help and documentation can be created. By using simple HTML and CGI scripts a basic web interface for any cosmological code can be created easily. We provide a worked example of the methods outlined, which can be used as a simple template by any researcher who wants to share their work online.
We present a combined analysis of previously published high-precision radial velocities and astrometry for the GJ876 planetary system using a self-consistent model that accounts for the planet-planet interactions. Assuming the three planets so far identified in the system are coplanar, we find that including the astrometry in the analysis does not result in a best-fit inclination significantly different than that found by Rivera and collaborators from analyzing the radial velocities alone. In this unique case, the planet-planet interactions are of such significance that the radial velocity data set is more sensitive to the inclination of the system through the dependence of the interactions on the true masses of the two gas giant planets in the system (planets b and c). The astrometry does allow determination of the absolute orbital inclination (i.e. distinguishing between i and 180-i) and longitude of the ascending node for planet b, which allows us to quantify the mutual inclination angle between its orbit and planet c's orbit when combined with the dynamical considerations. We find that the planets have a mutual inclination of 5.0 +3.9 -2.3 degrees. This result constitutes the first determination of the degree of coplanarity in an exoplanetary system around a normal star. That we find the two planets' orbits are nearly coplanar, like the orbits of the Solar System planets, indicates that the planets likely formed in a circumstellar disk, and that their subsequent dynamical evolution into a 2:1 mean motion resonance only led to excitation of a small mutual inclination. This investigation demonstrates how the degree of coplanarity for other exoplanetary systems could also be established using data obtained from existing facilities.
A new scheme for incorporating radiative cooling in hydrodynamical codes is presented, centered around exact integration of the governing semi-discrete cooling equation. Using benchmark calculations based on the cooling downstream of a radiative shock, I demonstrate that the new scheme outperforms traditional explicit and implicit approaches in terms of accuracy, while remaining competitive in terms of execution speed.
We present predictions for galactic halo baryon fractions from cosmological hydrodynamic simulations with a well-constrained model for galactic outflows. Without outflows, halos contain roughly the cosmic fraction of baryons, slightly lowered at high masses owing to pressure support from hot gas. The star formation efficiency is large and increases monotonically to low masses, in disagreement with data. With outflows, the baryon fraction is increasingly suppressed in halos to lower masses. A Milky Way-sized halo at z=0 has about 60% of the cosmic fraction of baryons, so "missing" halo baryons have largely been evacuated, rather than existing in some hidden form. Large halos (>10^13 Mo) contain 85% of their cosmic share of baryons, which explains the mild missing baryon problem seen in clusters. By comparing results at z=3 and z=0, we show that most of the baryon removal occurs at early epochs in larger halos, while smaller halos lose baryons more recently. Star formation efficiency is maximized in halos of ~10^13 Mo, dropping significantly to lower masses, which helps reconcile the sub-L* slope of the observed stellar and halo mass functions. These trends are predominantly driven by differential wind recycling, namely, that wind material takes longer to return to low-mass galaxies than high-mass galaxies. The hot gas content of halos is mostly unaffected by outflows, showing that outflows tend to blow holes and escape rather than deposit their energy into halo gas.
We use the full bispectrum of spherical needlets applied to the WMAP data of the cosmic microwave background as an estimator for the primordial non-Gaussianity parameter f_NL. We use needlet scales up to l_max=1000 and the KQ75 galactic cut and find f_NL=84 +/- 40 corrected for point source bias. We also introduce a set of consistency tests to validate our results against the possible influence of foreground residuals or systematic errors. In particular, fluctuations in the value of f_NL obtained from different frequency channels, different masks and different multipoles are tested against simulated maps. All variations in f_NL estimates are found statistically consistent with simulations.
Massive stars produce so much light that the radiation pressure they exert on the gas and dust around them is stronger than their gravitational attraction, a condition that has long been expected to prevent them from growing by accretion. We present three-dimensional radiation-hydrodynamic simulations of the collapse of a massive prestellar core and find that radiation pressure does not halt accretion. Instead, gravitational and Rayleigh-Taylor instabilities channel gas onto the star system through non-axisymmetric disks and filaments that self-shield against radiation, while allowing radiation to escape through optically-thin bubbles. Gravitational instabilities cause the disk to fragment and form a massive companion to the primary star. Radiation pressure does not limit stellar masses, but the instabilities that allow accretion to continue lead to small multiple systems.
The region in the HR-diagram where the main sequence intersects the classical instability strip hosts A- and F-type stars exhibiting a rich variety of physical phenomena, such as pulsations on various time scales and chemical peculiarities. We aim to investigate the occurrence of these phenomena among suspected binary systems in this region of the HR-diagram and their mutual interactions.
Continued study of the BATSE catalog verifies previously-identified correlations between pulse lag and pulse duration and corresponding anti-correlations between both properties and pulse peak flux for a large sample of Long GRB pulses; the study also finds correlations between pulse peak lags, pulse asymmetry, and pulse hardness. These correlations apparently can be used to delineate Long GRBs from Short ones. Correlated pulse properties represent constraints that can be used to guide theoretical modeling, whereas bulk prompt emission properties appear to be constructed by combining and smearing out pulse characteristics in ways that potentially lose valuable information.
One of the longstanding debates in the history of paleontology focuses on the issue of whether or not there have been long term cycles (operating over tens of millions of years) in biodiversity and extinction. Here we consider the history of this debate by connecting the skein from Grabau up to 2008. We focus on the evidence for periodicity that has emerged thus far, and conclude that there is indeed some evidence that periodicity may be real, though of course more work is needed. We also comment on possible causal mechanisms, focusing especially on the motion of our solar system in the Galaxy. Moreover, we consider the reasons why some scientists have opposed periodicity over the years. Finally, we consider the significance of this for our understanding of evolution and the history of life.
Correlations among pulse properties in the prompt emission of long GRBs can potentially be used as cosmological distance indicators to estimate redshifts of GRBs to which these pulses belong. We demonstrate application of this technique to a sample of GRBs for which redshifts are not known. We also study the scatter of predicted redshifts of pulses found within individual bursts. We explore the characteristics of this scatter in hopes of identifying systematic corrections and/or pulse subsets that can be used to increase the technique's reliability.
Coordinates, magnitudes and spectra are presented for 39 cataclysmic variables found in Sloan Digital Sky Survey spectra that were primarily obtained in 2006. Of these, 12 were CVs identified prior to the SDSS spectra (GY Cnc, GO Com, ST LMi, NY Ser, MR Ser, QW Ser, EU UMa, IY UMa, HS1340+1524, RXJ1610.1+0352, Boo 1, Leo 5). Follow-up spectroscopic observations of seven systems (including one from year 2005 and another from year 2004) were obtained, resulting in estimates of the orbital periods for 3 objects. The new CVs include two candidates for high inclination, eclipsing systems, 4 new Polars and three systems whose spectra clearly reveal atmospheric absorption lines from the underlying white dwarf.
We have combined recent Hubble Space Telescope WFPC2 images in the [O III] 5007 and [N II] 6583 lines with similar images made 9.557 years earlier to determine the motion of the Ring Nebula within the plane of the sky. Scaled ratio images argue for homologous expansion, that is, larger velocities scale with increasing distance from the central star. The rather noisy pattern of motion of individual features argues for the same conclusion and that the silhouetted knots move at the same rate as the surrounding gas. These tangential velocities are combined with information from a recent high resolution radial velocity study to determine a dynamic distance, which is in basic agreement with the distance determined from the parallax of the central star. We have also obtained very high signal to noise ratio moderate resolution spectra (9.4 Angstrom) along the major and minor axes of the nebula and from this determined the electron temperatures and density in the multiple ionization zones present. These results confirm the status of the Ring Nebula as one of the older planetary nebulae, with a central star transitioning to the white dwarf cooling curve. (Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA Contract No. NAS 5-26555 and the San Pedro Martir Observatory operated by the Universidad Nacional Autonoma de Mexico.)
Gamma ray bursts (GRBs) have recently attracted much attention as a possible way to extend the Hubble diagram to very high redshift. To this aim, the luminosity (or isotropic emitted energy) of a GRB at redshift z must be evaluated from a correlation with a distance independent quantity so that one can then solve for the luminosity distance D_L(z) and hence the distance modulus mu(z). Averaging over five different two parameters correlations and using a fiducial cosmological model to calibrate them, Schaefer (2007) has compiled a sample of 69 GRBs with measured mu(z) which has since then been widely used to constrain cosmological parameters. We update here that sample by many aspects. First, we add a recently found correlation for the X - ray afterglow and use a Bayesian inspired fitting method to calibrate the different GRBs correlations known insofar assuming a fiducial LCDM model in agreement with the recent WMAP5 data. Averaging over six correlations, we end with a new GRBs Hubble diagram comprising 83 objects. We also extensively explore the impact of varying the fiducial cosmological model considering how the estimated mu(z) change as a function of the $(\Omega_M, w_0, w_a)$ parameters of the Chevallier - Polarski - Linder phenomenological dark energy equation of state. In order to avoid the need of assuming an {\it a priori} cosmological model, we present a new calibration procedure based on a model independent local regression estimate of mu(z) using the Union SNeIa sample to calibrate the GRBs correlations. This finally gives us a GRBs Hubble diagram made out of 69 GRBs whose estimated distance modulus mu(z) is almost independent on the underlying cosmological model.
We study the dynamics of the FLRW flat cosmological models in which the vacuum energy density varies with time, $\Lambda(t)$. Using different versions of the $\Lambda(t)$ model, namely modified vacuum, mild vacuum and general vacuum, we find that the main cosmological functions such as the scale factor of the universe and the Hubble flow are defined analytically. Comparing the various $\Lambda(t)$ models with the traditional $\Lambda$ cosmology we prove that the latter model is a particular solution of the time varying vacuum models. Finally, within the framework of either the modified or general vacuum the corresponding vacuum term in the radiation era varies as $\Lambda(a) \sim a^{-4}$ while in the matter era we have $\Lambda(a) \sim a^{-3}$ up to $z\simeq 3$ and $\Lambda(a)\simeq \Lambda$ for $z\le 3$. The confirmation of such a behavior would be of paramount importance because it could provide a solution to the cosmic coincidence problem as well as to the fine tuning problem, despite the fact that the $\Lambda(t)$ models share almost the same Hubble expansion with that of the concordance $\Lambda$-cosmology. In particular, we find that the ratio of the vacuum energy at the Planck epoch to its present value is $\Lambda(t_{pl})/\Lambda(t_{0})\sim 10^{124}$. The case of the mild vacuum does not solve the cosmic coincidence problem, in which during the radiation period we have $\Lambda(a) \sim a^{-2}$, in the matter era the vacuum term evolves as $\Lambda(a) \sim a^{-3/2}$ for $z\ge 11$ and it reduces to a cosmological constant look-alikes. Note, that for the mild vacuum model we find $\Lambda(t_{pl})/\Lambda(t_{0})\sim 10^{62}$.
Recent developments on the study of mixed morphology supernova remnants (MMSNRs) have revealed the presence of metal rich X-ray emitting plasma inside a fraction of these remnant, a feature not properly addressed by traditional models for these objects. Radial profiles of thermodynamical and chemical parameters are needed for a fruitful comparison of data and model of MMSNRs, but these are available only in a few cases. We analyze XMM-Newton data of two MMSNRs, namely IC443 and G166.0+4.3, previously known to have solar metal abundances, and we perform spatially resolved spectral analysis of the X-ray emission. We detected enhanced abundances of Ne, Mg and Si in the hard X-ray bright peak in the north of IC443, and of S in the outer regions of G166.0+4.3. The metal abundances are not distributed uniformly in both remnants. The evaporating clouds model and the radiative SNR model fail to reproduce consistently all the observational results. We suggest that further deep X-ray observations of MMSNRs may reveal more metal rich objects. More detailed models which include ISM-ejecta mixing are needed to explain the nature of this growing subclass of MMSNRs.
The far-IR spectral window plays host to a wide range of both spectroscopic and photometric diagnostics with which to open the protoplanetary disks and exoplanet research to wavelengths completely blocked by the Earth's atmosphere. These include some of the key atomic (e.g., oxygen) and molecular (e.g., water) cooling lines, the dust thermal emission, the water ice features as well as many other key chemical tracers. Most of these features can not be observed from ground-based telescopes but play a critical diagnostic in a number of key areas including the early stages of planet formation and potentially exoplanets. The proposed Japanese-led IR space telescope SPICA, with its 3.5m cooled mirror will be the next step in sensitivity after Herschel. SPICA has been recently selected to go to the next stage of the ESA's Cosmic Vision 2015-2025 process. This contribution summarizes the design concept behind SAFARI: an imaging far-IR spectrometer covering the ~30-210um waveband that is one of a suite of instruments for SPICA; it also highlights some of the science questions that it will be possible to address in the field of exoplanets and planet formation.
As outflow activity in low mass protostars is strongly connected to ac- cretion it is reasonable to expect accreting brown dwarfs to also be driving out- flows. In the last three years we have searched for brown dwarf outflows using high quality optical spectra obtained with UVES on the VLT and the technique of spectro-astrometry. To date five brown dwarf outflows have been discovered. Here the method is discussed and the results to date outlined.
The polarization properties of RX J1856.5-3754 are investigated, based on the plasma emission model presented in previous works. It is shown that if the emission of this source is generated by the synchrotron mechanism, the X-ray and the optical emission are linearly polarized and the corresponding degrees of linear polarization are calculated. The measurement of the polarization patterns of this source appears to be most reliable way, to make clear its real emission nature.
We present the survey strategy and the data characteristics of the North Ecliptic Pole (NEP) Wide Survey of AKARI. The survey was carried out for about one year starting from May 2006 with 9 passbands from 2.5 to 24 micron and the areal coverage of about 5.8 sq. degrees centered on NEP. The survey depth reaches to 21.8 AB magnitude near infrared (NIR) bands, and ~ 18.6 AB maggnitude at the mid infrared (MIR) bands such as 15 and 18 micron. The total number of sources detected in this survey is about 104,000, with more sources in NIR than in the MIR. We have cross matched infrared sources with optically identified sources in CFHT imaging survey which covered about 2 sq. degrees within NEP-Wide survey region in order to characterize the nature of infrared sources. The majority of the mid infrared sources at 15 and 18 micron band are found to be star forming disk galaxies, with smaller fraction of early type galaxies and AGNs. We found that a large fraction (60~80 %) of bright sources in 9 and 11 micron stars while stellar fraction decreases toward fainter sources. We present the histograms of the sources at mid infrared bands at 9, 11, 15 and 18 micron. The number of sources per magnitude thus varies as m^0.6 for longer wavelength sources while shorter wavelength sources show steeper variation with m, where m is the AB magnitude.
We study the validity of the approximation of a Gaussian cosmic shear likelihood. We estimate the true likelihood for a fiducial cosmological model from a large set of ray-tracing simulations and investigate the impact of non-Gaussianity on cosmological parameter estimation. We investigate how odd the recently reported very low value of $\sigma_8$ as derived from the \textit{Chandra} Deep Field South (CDFS) using cosmic shear really is by taking into account the non-Gaussianity of the likelihood as well as the possibility of biases coming from the way the CDFS was selected. A brute force approach to estimate the likelihood from simulations must fail due to the high dimensionality of the problem. We therefore use Independent Component Analysis to transform the cosmic shear correlation functions to a new basis, in which the likelihood approximately factorises into a product of one-dimensional distributions. We find that the cosmic shear likelihood is significantly non-Gaussian. This leads to both a shift of the maximum of the posterior distribution and a significantly smaller credible region compared to the Gaussian case. We re-analyse the CDFS cosmic shear data using the non-Gaussian likelihood and find $\sigma_8=0.68_{-0.16}^{+0.09}$ for fixed $\Omega_{\mathrm{m}}=0.25$. In a WMAP5-like cosmology, a value as low as this or lower would be expected in $\approx 5%$ of the times if the CDFS were a random pointing. We estimate that this probability might rise to $\approx 15$-20% if the field selection biases are taken into account, and that the $\sigma_8$ estimate from the CDFS might be biased low by $\approx 15%$.
Recently, Valiviita et al. (2008) have reported a large-scale early-time instability in coupled dark energy and dark matter models. We take the same form of energy-momentum exchange and specialise to the case when the interaction rate is proportional to Hubble's parameter and the dark energy density only. Provided the coupling is made small enough for a given equation of state parameter, we show that the instability can be avoided. Expressions are derived for non-adiabatic modes on super-horizon scales in both the radiation and matter dominated regimes. We also examine the growth of dark matter perturbations in the sub-horizon limit. There we find that the coupling has almost no effect upon the growth of structure before dark energy begins to dominate. Once the universe begins to accelerate, the relative dark matter density fluctuations not only cease to grow as in uncoupled models, but actually decay as the universe continues to expand.
3C 279 is one of the best studied flat spectrum radio quasars located at a comparatively large redshift of z = 0.536. Observations in the very high energy band of such distant sources were impossible until recently due to the expected steep energy spectrum and the strong gamma-ray attenuation by the extragalactic background light photon field, which conspire to make the source visible only with a low energy threshold. Here the detection of a significant gamma-ray signal from 3C 279 at very high energies (E > 75 GeV) during a flare in early 2006 is reported. Implications of its energy spectrum on the current understanding of the extragalactic background light and very high energy gamma-ray emission mechanism models are discussed.
A maximum likelihood (ML) technique for detecting compact sources in images of the x-ray sky is examined. Such images, in the relatively low exposure regime accessible to present x-ray observatories, exhibit Poissonian noise at background flux levels. A variety of source detection methods are compared via Monte Carlo, and the ML detection method is shown to compare favourably with the optimized-linear-filter (OLF) method when applied to a single image. Where detection proceeds in parallel on several images made in different energy bands, the ML method is shown to have some practical advantages which make it superior to the OLF method. Some criticisms of ML are discussed. Finally, a practical method of estimating the sensitivity of ML detection is presented, and is shown to be also applicable to sliding-box source detection.
By analogy with a mechanism proposed by Gold and Soter to explain the retrograde rotation of Venus, Arras and Socrates suggest that thermal tides may excite hot jovian exoplanets into nonsynchronous rotation, and perhaps also noncircular orbits. It is shown here that because of the absence of a solid surface above the convective core of a jovian planet, the coupling of the gravitational and thermal tides vanishes to zeroth order in the ratio of the atmospheric scale height to the planetary radius. At the next order, the effect probably has the sign opposite to that claimed by the latter authors, hence reinforcing synchronous and circular orbits.
Surprisingly few solar coronal loops have been observed simultaneously with TRACE and SOHO/CDS, and even fewer analyses of these loops have been conducted and published. The SOHO Joint Observing Program 146 was designed in part to provide the simultaneous observations required for in-depth temperature analysis of active region loops and determine whether these loops are isothermal or multithermal. The data analyzed in this paper were taken on 2003 January 17 of AR 10250. We used TRACE filter ratios, emission measure loci, and two methods of differential emission measure analysis to examine the temperature structure of three different loops. TRACE and CDS observations agree that Loop 1 is isothermal with Log T $=$ 5.85, both along the line of sight as well as along the length of the loop leg that is visible in the CDS field of view. Loop 2 is hotter than Loop 1. It is multithermal along the line of sight, with significant emission between 6.2 $<$ Log T $<$ 6.4, but the loop apex region is out of the CDS field of view so it is not possible to determine the temperature distribution as a function of loop height. Loop 3 also appears to be multithermal, but a blended loop that is just barely resolved with CDS may be adding cool emission to the Loop 3 intensities and complicating our results. So, are coronal loops isothermal or multithermal? The answer appears to be yes!
We present the results of mapping the HgMn star AR Aur using the Doppler Imaging technique for several elements and discuss the obtained distributions in the framework of a magnetic field topology.
From a study of BAL + IR + Fe II QSOs (using deep Gemini GMOS-IFU
spectroscopy) new results are presented: for IRAS 04505-2958. From this study
the following main results were obtained: (i) In general the GMOS data show
strong emission lines, in almost all the observed GMOS field. Furthermore,
multiple emission line systems were detected, in the regions of the shells.
(ii) For the two more internal blobs (at r $\sim$ 1 and 2 kpc) the GMOS data
show that these structures are symmetric shells in expansion. (iii) A strong
blue continuum component was observed in all the observed GMOS field (including
the 3 shells). (iv) For the external hyper giant shell at r = 2.0" (11 kpc) the
kinematics GMOS maps of the ionized gas ([O II], [Ne III], [O III], Hbeta) show
very similar features to those of the prototype of exploding external hyper
shell: in NGC 5514. Furthermore, in the knots of the shells S3 the stellar
population and the ELR show all typical feature of of starburst, poststarburst
plus OF/shocks.
The nature of the extreme OF process in IRAS 04505-2958, with very large
scale super/hyper shells (from 1 to 100 kpc) is discussed. The new GMOS data
show a good agreement with an extreme + explosive OF scenario: where part of
the ISM of the host galaxy was ejected in the form of multiple shells. Finally,
the presence of UHE cosmic rays and neutrino/ dark-matter in BAL + IR + Fe II
QSO (associated with HyN) is discussed.
The presence of magnetic fields in O-type stars has been suspected for a long time. The discovery of such fields would explain a wide range of well documented enigmatic phenomena in massive stars, in particular cyclical wind variability, Halpha emission variations, chemical peculiarity, narrow X-ray emission lines and non-thermal radio/X-ray emission. Here we present the results of our studies of magnetic fields in O-type stars, carried out over the last years.
Aims. We analyse SUMER spectral scans of a large sunspot within active region NOAA 10923, obtained on 14-15 November 2006, to determine the morphology and dynamics of the sunspot atmosphere at different heights/temperatures. Methods: The data analysed here consist of spectroheliograms in the continuum around 142.0 nm and in the Si iv 140.2 nm, O iii 70.3 nm, N iv 76.5 nm, and O iv 79.0 nm spectral lines. Gaussian-fitting of the observed profiles provides line-of-sight velocity and Doppler-width maps. Results: The data show an asymmetric downflow pattern compatible with the presence of the inverse Evershed flow in a region within roughly twice the penumbral radius at transition-region temperatures up to 0.18 MK. The motions, highly inhomogeneous on small scales, seem to occur in a collar of radially directed filamentary structures, with an average width less than the 1 Mm spatial resolution of SUMER and characterised by different plasma speeds. Assuming that the flows are directed along the field lines, we deduce that such field lines are inclined by 10 deg to 25 deg with respect to the solar surface.
We present the results of the continuation of our magnetic survey with FORS1 at the VLT of a sample of B-type stars consisting of confirmed or candidate beta Cephei stars and Slowly Pulsating B stars. Roughly one third of the studied beta Cephei stars have detected magnetic fields. The fraction of magnetic Slowly Pulsating B and candidate Slowly Pulsating B stars is found to be higher, up to 50%. We find that the domains of magnetic and non-magnetic pulsating stars in the H-R diagram largely overlap, and no clear picture emerges as to the possible evolution of the magnetic field across the main sequence.
We present the results of a new magnetic field survey of Herbig Ae/Be and A debris disk stars. They are used to determine whether magnetic field properties in these stars are correlated with the mass-accretion rate, disk inclinations, companion(s), Silicates, PAHs, or show a more general correlation with age and X-ray emission as expected for the decay of a remnant dynamo.
Deep ACS slitless grism observations and identification of stellar sources are presented within the Great Observatories Origins Deep Survey (GOODS) North and South fields which were obtained in the Probing Evolution And Reionization Spectroscopically (PEARS) program. It is demonstrated that even low resolution spectra can be a very powerful means to identify stars in the field, especially low mass stars with stellar types M0 and later. The PEARS fields lay within the larger GOODS fields, and we used new, deeper images to further refine the selection of stars in the PEARS field, down to a magnitude of mz = 25 using a newly developed stellarity parameter. The total number of stars with reliable spectroscopic and morphological identification was 95 and 108 in the north and south fields respectively. The sample of spectroscopically identified stars allows constraints to be set on the thickness of the Galactic thin disk as well as contributions from a thick disk and a halo component. We derive a thin disk scale height, as traced by the population of M4 to M9 dwarfs along two independent lines of sight, of h_thin = 370 +60/-65 pc. When including the more massive M0 to M4 dwarf population, we derive h_thin = 300 +/- 70pc. In both cases, we observe that we must include a combination of thick and halo components in our models in order to account for the observed numbers of faint dwarfs. The required thick disk scale height is typically h_thick=1000 pc and the acceptable relative stellar densities of the thin disk to thick disk and the thin disk to halo components are in the range of 0.00025<f_halo<0.0005 and 0.05<f_thick<0.08 and are somewhat dependent on whether the more massive M0 to M4 dwarfs are included in our sample.
We report the results of our study of magnetic fields in a sample of Be stars using spectropolarimetric data obtained at the European Southern Observatory with the multi-mode instrument FORS1 installed at the 8m Kueyen telescope. The detected magnetic fields are rather weak, not stronger than ~150G. A few classical Be stars display cyclic variability of the magnetic field with periods of tens of minutes.
The discovery of events in time series can have important implications, such as identifying microlensing events in astronomical surveys, or changes in a patient's electrocardiogram. Current methods for identifying events require a sliding window of a fixed size, which is not ideal for all applications and could overlook important events. In this work, we develop probability models for calculating the significance of an arbitrary-sized sliding window and use these probabilities to find areas of significance. Because a brute force search of all sliding windows and all window sizes would be computationally intractable, we introduce a method for quickly approximating the results. We apply our method to over 100,000 astronomical time series from the MACHO survey, in which 56 different sections of the sky are considered, each with one or more known events. Our method was able to recover 100% of these events in the top 1% of the results, essentially pruning 99% of the data. Interestingly, our method was able to identify events that do not pass traditional event discovery procedures.
We constrain the space density and properties of massive galaxy candidates at redshifts of z\geq3.5 in the GOODS-N field. By selecting sources in the Spitzer+IRAC bands, a highly stellar mass-complete sample is assembled,including massive galaxies which are very faint in the optical/near-IR bands that would be missed by samples selected at shorter wavelengths. The z\geq3.5 sample was selected down to 23 mag at 4.5 micron using photometric redshifts that have been obtained by fitting the galaxies SEDs at optical, near-IR and IRAC bands. We also require that the brightest band in which candidates are detected is the IRAC 8 micron band in order to ensure that the near-IR 1.6 micron (rest-frame) peak is falling in or beyond this band. We found 53 z\geq3.5 candidates, with masses in the range of M~10^10-10^11M_sun. At least ~81% of these galaxies are missed by traditional Lyman Break selection methods based on UV light. Spitzer+MIPS emission is detected for 60% of the sample of z\geq3.5 galaxy candidates. Although in some cases this might suggest a residual contamination from lower redshift star-forming galaxies or AGN, 37% of these objects are also detected in the sub-mm/mm bands in recent SCUBA,AzTEC and MAMBO surveys, and have properties fully consistent with vigorous starburst galaxies at z\geq3.5. The comoving number density of galaxies with stellar masses \geq 5x10^10M_sun(a reasonable stellar mass completeness limit for our sample) is 2.6x10^-5Mpc^-3 (using the volume within 3.5<z<5), and the corresponding stellar mass density is ~2.9x10^6M_sunMpc^-3, or~3% of the local density above the same stellar mass limit.For the sub-sample of MIPS-undetected galaxies,we find a number density of ~0.97x10^-5Mpc^-3 and a stellar mass density of ~1.15x10^6M_sun Mpc^-3.
We summarise recent progress in the understanding of the rotational evolution of low-mass stars (here defined as solar mass down to the hydrogen burning limit) both in terms of observations and modelling. Wide-field imaging surveys on moderate-size telescopes can now efficiently derive rotation periods for hundreds to thousands of open cluster members, providing unprecedented sample sizes which are ripe for exploration. We summarise the available measurements, and provide simple phenomenological and model-based interpretations of the presently-available data, while highlighting regions of parameter space where more observations are required, particularly at the lowest masses and ages >~ 500 Myr.
We revisit in more detail a model for element abundance fractionation in the solar chromosphere, that gives rise to the "FIP Effect" in the solar corona and wind. Elements with first ionization potential below about 10 eV, i.e. those that are predominantly ionized in the chromosphere, are enriched in the corona by a factor 3-4. We model the propagation of Alfven waves through the chromosphere using a non-WKB treatment, and evaluate the ponderomotive force associated with these waves. Under solar conditions, this is generally pointed upwards in the chromosphere, and enhances the abundance of chromospheric ions in the corona. Our new approach captures the essentials of the solar coronal abundance anomalies, including the depletion of He relative to H, and also the putative depletion of Ne, recently discussed in the literature. We also argue that the FIP effect provides the strongest evidence to date for energy fluxes of Alfven waves sufficient to heat the corona. However it appears that these waves must also be generated in the corona, in order to preserve the rather regular fractionation pattern without strong variations from loop to loop observed in the solar corona and slow speed solar wind.
The gravitino is a promising supersymmetric dark matter candidate which does not require exact R-parity conservation. In fact, even with some small R-parity breaking, gravitinos are sufficiently long-lived to constitute the dark matter of the Universe, while yielding a cosmological scenario consistent with primordial nucleosynthesis and the high reheating temperature required for thermal leptogenesis. In this paper, we compute the neutrino flux from direct gravitino decay and gauge boson fragmentation in a simple scenario with bilinear R-parity breaking. Our choice of parameters is motivated by a proposed interpretation of anomalies in the extragalactic gamma-ray spectrum and the positron fraction in terms of gravitino dark matter decay. We find that the generated neutrino flux is compatible with present measurements. We also discuss the possibility of detecting these neutrinos in present and future experiments and conclude that it is a challenging task. However, if detected, this distinctive signal might bring significant support to the scenario of gravitinos as decaying dark matter.
Electrodynamics of charged scalar bosons and spin 1/2 fermions is studied at non-zero temperature, chemical potentials, and possible Bose condensate of the charged scalars. Debye screening length, plasma frequency, and the photon dispersion relation are calculated. It is found that in presence of the condensate the time-time component of the photon polarization operator in the first order in electric charge squared acquires infrared singular parts proportional to inverse powers of the spatial photon momentum k.
Corrections to the relativistic orbits are studied considering higher order approximations induced by gravitomagnetic effects. We discuss in details how such corrections come out taking into account magnetic components in the weak field limit of gravitational field and then the theory of orbits is developed starting from the Newtonian one, the lowest order in the approximation. Finally, the orbital structure and the stability conditions are discussed giving numerical examples. Beside the standard periastron corrections of General Relativity, a new nutation effect is due to the c^{-3} corrections. The transition to a chaotic behavior strictly depends on the initial conditions. The orbital phase space portrait is discussed.
We show that any analytic $f(R)$-gravity model, in the metric approach, presents a weak field limit where the standard Newtonian potential is corrected by a Yukawa-like term. This general result has never been pointed out but often derived for some particular theories. This means that only $f(R)=R$ allows to recover the standard Newton potential while this is not the case for other relativistic theories of gravity. Some considerations on the physical consequences of such a general solution are addressed.
We construct a Dark Matter (DM) annihilation module that can encompass the predictions from a wide array of models built to explain the recently reported PAMELA and ATIC/PPB-BETS excesses. We present a detailed analysis of the injection spectrums for DM annihilation and quantitatively demonstrate effects that have previously not been included from the particle physics perspective. With this module we demonstrate the parameter space that can account for the aforementioned excesses and be compatible with existing high energy gamma ray and neutrino experiments. However, we find that it is relatively generic to have some tension between the results of the HESS experiment and the ATIC/PPB-BETS experiments within the context of annihilating DM. We discuss ways to alleviate this tension and how upcoming experiments will be able to differentiate amongst the various possible explanations of the purported excesses.
A leading interpretation of the electron/positron excesses seen by PAMELA and ATIC is dark matter annihilation in the galactic halo. Depending on the annihilation channel, the electron/positron signal could be accompanied by a galactic gamma ray or neutrino flux, and the non-detection of such fluxes constrains the couplings and halo properties of dark matter. In this paper, we study the interplay of electron data with gamma ray and neutrino constraints in the context of cascade annihilation models, where dark matter annihilates into light degrees of freedom which in turn decay into leptons in one or more steps. Electron and muon cascades give a reasonable fit to the PAMELA and ATIC data. Compared to direct annihilation, cascade annihilations can soften gamma ray constraints from final state radiation by an order of magnitude. However, if dark matter annihilates primarily into muons, the neutrino constraints are robust regardless of the number of cascade decay steps. We also examine the electron data and gamma ray/neutrino constraints on the recently proposed "axion portal" scenario.
Dark Matter annihilation (DMA) may yield an excess of gamma rays and antimatter particles, like antiprotons and positrons, above the background from cosmic ray interactions. The excess of diffuse Galactic Gamma Rays from EGRET shows all the features expected from DMA. The new precise measurements of the antiproton and positron fractions from PAMELA are compared with the EGRET excess. It is shown that the charged particles are strongly dependent on the propagation model used. The usual propagation models with isotropic propagation models are incompatible with the recently observed convection in our Galaxy. Convection leads to an order of magnitude uncertainty in the yield of charged particles from DMA, since even a rather small convection will let drift the charged particles in the halo to outer space. It is shown that such anisotropic propagation models including convection prefer a contribution from DMA for the antiprotons, but the rise in the positron fraction, as observed by PAMELA, is incompatible with DMA, if compared with the EGRET excess. A rise in the positron/electron ratio is expected, if the observed rise in the proton/electron ratio is carefully fitted in a propagation model, although the rise is slightly larger than expected, so additional local sources may contribute as well within the limited accuracy of the data.
Increasing the sensitivity of a gravitational-wave (GW) detector improves our ability to measure the characteristics of detected sources. It also increases the number of weak signals that contribute to the data. Because GW detectors have nearly all-sky sensitivity, they can be subject to a confusion limit: Many sources which cannot be distinguished may be measured simultaneously, defining a stochastic noise floor to the sensitivity. For GW detectors operating at present and for their planned upgrades, the projected event rate is sufficiently low that we are far from the confusion-limited regime. However, some detectors currently under discussion may have large enough reach to binary inspiral that they enter the confusion-limited regime. In this paper, we examine the binary inspiral confusion limit for terrestrial detectors. We consider a broad range of inspiral rates in the literature, several planned advanced gravitational-wave detectors, and the highly advanced "Einstein Telescope" design. Though most advanced detectors will not be impacted by this limit, the Einstein Telescope with a very low frequency "seismic wall" may be subject to confusion noise. At a minimum, careful data analysis will be require to separate signals which will appear confused. This result should be borne in mind when designing highly advanced future instruments.
What the outer regions of a typical spiral disk galaxy would look like if the MOdified Newtonian Dynamics(MOND) framework was valid? This is the question we try to preliminarily address by numerically integrating the accordingly modified equations of motion of a test particle orbiting at some tens kpc from a localized central body with approximately the same mass of the electromagnetically-detected part of a typical galaxy (M\approx 6.5\times 10^10 M_\odot): we use initial conditions corresponding to circular Keplerian orbits. The result is a characteristic pattern which can be compared to the observed configurations of the farthest regions of the galaxies. Moving to the periphery of our Solar System, thousands AU far from the Sun, where the MONDian scheme would be valid, it turns out that MOND strongly circularizes trajectories which, otherwise, would be very elliptic Keplerian orbits. As a consequence, the Oort cloud, extending for about 10-100 kAU far from the Sun, should be different from what believed so far and, perhaps, we should have seen less comets in the Solar System than we effectively did.
Analytical and numerical calculations show that a putative temporal variation of the speed of light c, with the meaning of space-time structure constant c_ST, assumed to be linear over timescales of about one century, would induce a secular precession of the longitude of the pericenter \varpi of a test particle orbiting a spherically symmetric body. By comparing such a predicted effect to the corrections \Delta\dot\varpi to the usual Newtonian/Einsteinian perihelion precessions of the inner planets of the Solar System, recently estimated by E.V. Pitjeva by fitting about one century of modern astronomical observations with the standard dynamical force models of the EPM epehemerides, we obtained \dot c/c =(0.5 +/- 2)\times 10^-7 yr^-1. Moreover, the possibility that \dot c/c\neq 0 over the last century is ruled out at 3-12\sigma level by taking the ratios of the perihelia for different pairs of planets. Our results are independent of any measurement of the variations of other fundamental constants which may be explained by a variation of $c$ itself (with the meaning of electromagnetic constant c_EM). It will be important to repeat such tests if and when other teams of astronomers will estimate their own corrections to the standard Newtonian/Einsteinian planetary perihelion precessions.
We investigate the cosmological properties of an "induced gravity" brane scenario in the absence of mirror symmetry with respect to the brane. We find that brane evolution can proceed along one of four distinct branches. By contrast, when mirror symmetry is imposed, only two branches exist, one of which represents the self-accelerating brane, while the other is the so-called normal branch. This model incorporates many of the well-known possibilities of brane cosmology including phantom acceleration (w < -1), self-acceleration, transient acceleration, quiescent singularities, and cosmic mimicry. Significantly, the absence of mirror symmetry also provides an interesting way of inducing a sufficiently small cosmological constant on the brane. A small (positive) Lambda-term in this case is induced by a small asymmetry in the values of bulk fundamental constants on the two sides of the brane.
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All the observations available in the Chandra and XMM-Newton archives have been used to investigate the X-ray spectral properties of 3C 33. In this paper is presented a complete X-ray analysis of the nuclear emission of this narrow line radio galaxy. The broad band spectrum of 3C 33 is complex. The hard part resembles that of Seyfert 2 galaxies, with a heavily obscured nuclear continuum (N_H~10^23 cm^-2) and a prominent Fe Kalpha line. This represents the nuclear radiation directly observed in transmission through a cold circumnuclear gas. On the other hand an unabsorbed continuum plus emission lines seem to fit well the soft part of the spectrum (0.5-2 keV) suggesting that the jet does not significantly contribute to the X-ray emission. We discuss the possible collisional or photoionized origin of the gas that emits the soft X-ray lines. Our results, strengthened by optical spectroscopy favor the photoionization scenario.
We study the stellar mass assembly of the Spiderweb Galaxy (MRC 1138-262), a massive z = 2.2 radio galaxy in a protocluster and the probable progenitor of a brightest cluster galaxy. Nearby protocluster galaxies are identified and their properties are determined by fitting stellar population models to their rest-frame ultraviolet to optical spectral energy distributions. We find that within 150 kpc of the radio galaxy the stellar mass is centrally concentrated in the radio galaxy, yet most of the dust-uncorrected, instantaneous star formation occurs in the surrounding low-mass satellite galaxies. We predict that most of the galaxies within 150 kpc of the radio galaxy will merge with the central radio galaxy by z = 0, increasing its stellar mass by up to a factor of ~ 2. However, it will take several hundred Myr for the first mergers to occur, by which time the large star formation rates are likely to have exhausted the gas reservoirs in the satellite galaxies. The tidal radii of the satellite galaxies are small, suggesting that stars and gas are being stripped and deposited at distances of tens of kpc from the central radio galaxy. These stripped stars may become intracluster stars or form an extended stellar halo around the radio galaxy, such as those observed around cD galaxies in cluster cores.
The question of determining the spatial geometry of the Universe is of greater relevance than ever, as precision cosmology promises to verify inflationary predictions about the curvature of the Universe. We revisit the question of what can be learnt about the spatial geometry of the Universe from the perspective of a three-way Bayesian model comparison. We show that, given current data, the probability that the Universe is spatially infinite lies between 67% and 98%, depending on the choice of priors. For the strongest prior choice, we find odds of order 50:1 (200:1) in favour of a flat Universe when compared with a closed (open) model. We also report a robust, prior-independent lower limit to the number of Hubble spheres in the Universe, N_U > 5 (at 99% confidence). We forecast the accuracy with which future CMB and BAO observations will be able to constrain curvature, finding that a cosmic variance limited CMB experiment together with an SKA-like BAO observation will constrain curvature with a precision of about sigma ~ 4.5x10^{-4}. We demonstrate that the risk of 'model confusion' (i.e., wrongly favouring a flat Universe in the presence of curvature) is much larger than might be assumed from parameter errors forecasts for future probes. We argue that a 5-sigma detection threshold guarantees a confusion- and ambiguity-free model selection. Together with inflationary arguments, this implies that the geometry of the Universe is not knowable if the value of the curvature parameter is below |Omega_curvature| ~ 10^{-4}, a bound one order of magnitude larger than the size of curvature perturbations, ~ 10^{-5}. [abridged]
Tidal disruption events are possible sources of temporary nuclear activity in galactic nuclei and can be considered as good indicators of the existence of super massive black holes in the centers of galaxies. A new X-ray source has been serendipitously detected with ROSAT in a PSPC pointed observation of the galaxy cluster A3571. Given the strong flux decay of the object in subsequent detections, the tidal disruption scenario is investigated as possible explanationof the event. We followed up the evolution of the X-ray transient with ROSAT, XMM-Newton and Chandra for a total period of ~13 years. We also obtained 7-band optical/NIR photometry with GROND at the ESO/MPI 2.2m telescope. We report a very large decay of the X-ray flux of ROSAT source identified with the galaxy LEDA 095953 a member of the cluster Abell 3571. We measured a maximum 0.3-2.4 keV luminosity Log(L_X)=42.8 erg s^-1. The high state of the source lasted at least 150 ks, afterwards L_X declined as ~t^-2. The spectrum of the brightest epoch is consistent with a black body with temperature kT ~0.12 keV. The total energy released by this event in 10 yr was estimated to be Delta_E>2x10^50 erg. We interpret this event as a tidal disruption of a solar type star by the central supermassive black hole (i.e. ~10^7 M_sun) of the galaxy.
A number of experiments are set to measure the 21-cm signal of neutral hydrogen from the Epoch of Reionization (EoR). The common denominator of these experiments are the large data sets produced, contaminated by various instrumental effects, ionospheric distortions, RFI and strong Galactic and extragalactic foregrounds. In this paper, the first in a series, we present the Data Model that will be the basis of the signal analysis for the LOFAR (Low Frequency Array) EoR Key Science Project (LOFAR EoR KSP). Using this data model we simulate realistic visibility data sets over a wide frequency band, taking properly into account all currently known instrumental corruptions (e.g. direction-dependent gains, complex gains, polarization effects, noise, etc). We then apply primary calibration errors to the data in a statistical sense, assuming that the calibration errors are random Gaussian variates at a level consistent with our current knowledge based on observations with the LOFAR Core Station 1. Our aim is to demonstrate how the systematics of an interferometric measurement affect the quality of the calibrated data, how errors correlate and propagate, and in the long run how this can lead to new calibration strategies. We present results of these simulations and the inversion process and extraction procedure. We also discuss some general properties of the coherency matrix and Jones formalism that might prove useful in solving the calibration problem of aperture synthesis arrays. We conclude that even in the presence of realistic noise and instrumental errors, the statistical signature of the EoR signal can be detected by LOFAR with relatively small errors. A detailed study of the statistical properties of our data model and more complex instrumental models will be considered in the future.
In agreement with previous work, we show that the presence of the short-lived radionuclide Al-26 in the early Solar System was unlikely (<2% a priori probability) to be the result of direct introduction of supernova ejecta into the gaseous disk during the Class II stage of protosolar evolution. We also show that any Bondi-Hoyle accretion of contaminated residual gas from the natal star cluster made a negligible contribution to the primordial Al-26 inventory of the Solar System. These results are consistent with the absence of the oxygen isotopic signature expected with any late introduction of supernova ejecta into the protoplanetary disk. Instead, the presence of Al-26 in the oldest Solar System solids (calcium-aluminum-rich inclusions or CAIs) and its apparent uniform distribution with the inferred canonical Al-26/Al-27 ratio of (4.5-5)E-5 support the inheritance of Al-26 from the parent giant molecular cloud. We propose that this radionuclide originated in a prior generation of massive stars that formed in the same host molecular cloud as the Sun and contaminated that cloud by Wolf-Rayet winds. We calculated the Galactic distribution of Al-26/Al-27 ratios that arise from such contamination using the established embedded cluster mass and stellar initial mass functions, published nucleosynthetic yields from the winds of massive stars, and by assuming rapid and uniform mixing into the cloud. Although our model predicts that the majority of stellar systems contain no Al-26 from massive stars, and that the a priori probability that the Al-26/Al-27 ratio will reach or exceed the canonical Solar System value is only ~6%, the maximum in the distribution of non-zero values is close to the canonical ratio.
We explore the cosmic evolution of radio AGN with low radio powers (L_1.4GHz < 5\times10^25 W/Hz) out to z=1.3 using to-date the largest sample of ~600 low luminosity radio AGN at intermediate redshift drawn from the VLA-COSMOS survey. We derive the radio luminosity function for these AGN, and its evolution with cosmic time assuming two extreme cases: i) pure luminosity and ii) pure density evolution. The former and latter yield L_*\propto(1+z)^(0.8+/-0.1), and Phi*\propto (1+z)^(1.1+/-0.1), respectively, both implying a fairly modest change in properties of low radio-power AGN since z=1.3. We show that this is in stark contrast with the evolution of powerful (L_1.4GHz > 5\times10^25 W/Hz) radio AGN over the same cosmic time interval, constrained using the 3CRR, 6CE, and 7CRS radio surveys by Willott et al. (2001). We demonstrate that this can be explained through differences in black hole fueling and triggering mechanisms, and a dichotomy in host galaxy properties of weak and powerful AGN. Our findings suggest that high and low radio-power AGN activity is triggered in different stages during the formation of massive red galaxies. We show that weak radio AGN occur in the most massive galaxies already at z~1, and they may significantly contribute to the heating of their surrounding medium and thus inhibit gas accretion onto their host galaxies, as recently suggested for the `radio mode' in cosmological models.
We present near-infrared spectra of ten luminous, intermediate redshift quasars observed with SofI at the NTT of ESO/La Silla. With these rest-frame optical spectra we probe the Hb -[OIII] emission line region. Using the standard scaling relation involving the width of the Hb line and the continuum luminosity, we measure black hole masses in the range of ~2x10^9 to 10^10 Msol. We also used SDSS spectra to probe MgII2798 and CIV1549 emission lines and used these for black hole mass measurements as well. The massive black holes we observe could not have grown by simple radiatively efficient accretion at the observed accretion rate starting from seeds of up to thousand solar masses. About 10% of the observed black hole mass must have been accumulated by earlier merger events and radiatively inefficient accretion. Radiatively efficient accretion would further grow these BHs to masses of several 10^9 Msol in 2 to 3 e-folding times i.e. in several 10^8yrs. The Hb-based Eddington luminosity ratios are in the range of ~0.2 to ~0.7, with an average of <Lbol/Ledd> = 0.39+-0.05. We find that for luminous quasars the Eddington luminosity ratio anti-correlates with black hole mass. The Lbol/Ledd ratio distribution follows a log-normal distribution which is consistent with prior studies of quasars with comparable luminosity. The Lbol/Ledd ratio distribution of less luminous quasars tend to be shifted to lower Eddington ratios. We also find that the gas metallicity of the broad-line region is ~3Z/Zsol, using NIII]/OIII] and NV/CIV emission line ratios. We find no correlation of the gas metallicity with the optical FeII emission line strength.
We report the discovery of a high proper motion L subdwarf ($\mu$ =0.617arcsec/yr) in the Sloan Digital Sky Survey spectral database. The optical spectrum from the star SDSS J125637-022452 has mixed spectral features of both late-M spectral subtype (strong TiO and CaH at 7000A) and mid-L spectral subtype (strong wings of KI at 7700A, CrH and FeH), which is interpreted as the signature of a very low-mass, metal-poor star (ultra-cool subdwarf) of spectral type sdL. The near infrared (NIR) (J-Ks) colors from 2MASS shows the object to be significantly bluer compared to normal L dwarfs, which is probably due a strong collision induced absorption (CIA) due to H2 molecule. This is consistent with the idea that CIA from H2 is more pronounced at low metallicities. Proper motion and radial velocity measurements also indicate that the star is kinematically "hot" and probably associated with the Galactic halo population.
We present a search for CO(3-2) emission in SDF-26821, a BzK-selected star-forming galaxy (sBzK) at z = 2.044, using the 45-m telescope of the Nobeyama Radio Observatory and the Nobeyama Millimeter Array. We do not detect significant emission and derive 2 \sigma limits: the CO luminosity of L'CO < 3.1 x 10^10 K km s^{-1} pc^{-2}, the ratio of far-infrared luminosity to CO luminosity of L_FIR/L'CO > 57 Lsun (K km s^{-1} pc^{-2})^{-1}, and the molecular gas mass of M_H2 < 2.5 x 10^10 Msun, assuming a velocity width of 200 km s^{-1} and a CO-to-H2 conversion factor of alpha_CO=0.8 Msun (K km s^{-1} pc^{-2})^{-1}. The ratio of L_FIR/L'CO, a measure of star formation efficiency (SFE), is comparable to or higher than the two z ~ 1.5 sBzKs detected in CO(2-1) previously, suggesting that sBzKs can have a wide range of SFEs. Comparisons of far-infrared luminosity, gas mass, and stellar mass among the sBzKs suggest that SDF-26821 is at an earlier stage of forming stars with a similar SFE and/or more efficiently forming stars than the two z ~ 1.5 sBzKs. The higher SFEs and specific star formation rates of the sBzKs compared to local spirals are indicative of the difference in star formation modes between these systems, suggesting that sBzKs are not just scaled-up versions of local spirals.
The determination of the mass composition of the highest energy cosmic rays is one of the greatest challenges in cosmic ray experiments. The highest energy cosmic rays are only detected indirectly because of their very low flux. Using the atmosphere as a large target, Air Fluorescence Detectors are capable of tracing the evolution of the size of the Extensive Air Shower through the atmosphere (the shower longitudinal profile). The analysis of the characteristics of the detected longitudinal profiles is currently the most reliable way for extracting some information about the primary cosmic ray mass composition. In this proceeding, I will describe in some detail the Pierre Auger elongation rate studies, and I will show the potential for mass composition studies using the surface and the fluorescence detectors information as part of a single analysis. The interpretation of the current data with regard to mass composition, relies heavily on high energy hadron interaction models. Using standard hadron interaction models, the data suggest that the composition becomes lighter up to about 2 $\times$ 10$^{18}$ $eV$ and above that it becomes heavier again. This apparent change in the mass composition at 2 $\times$ 10$^{18}$ $eV$ seems to be correlated with a spectrum index change in the observed energy spectrum.
The connection of cluster mergers with the presence of extended, diffuse radio sources in galaxy clusters is still being debated. In this paper we aim to obtain new insights into the internal dynamics of Abell 959, showing evidence of a diffuse radio source, analyzing velocities and positions of member galaxies. Our analysis is based on redshift data for 107 galaxies in the cluster field acquired at the Telescopio Nazionale Galileo. We also use photometric data from the Sloan Digital Sky Survey (Data Release 6). We combine galaxy velocities and positions to select 81 galaxies recognized as cluster members and determine global dynamical properties. We analyze the cluster searching for substructures by using several statistical methods. We also study the 2D galaxy distribution in the field of the cluster. We compare our results with those from X-ray and gravitational lensing analyses. We estimate a cluster redshift of z=0.2883 +/- 0.0004. We detect an NE high velocity group at 5' from the cluster center with a relative line--of--sight (LOS) velocity of ~ +1900 km/s with respect to the main system. We also detect a central, dense structure elongated along the SE--NW direction likely connected with the two dominant galaxies and their surrounding cores. This elongated central structure is probably the trace of an old cluster merger. The LOS velocity dispersion of galaxies is very high (1025 (-75/+104) km/s). The virial mass is M(<R=1.48 Mpc)= 1.15 (-0.19/+0.25) Msun. Our results suggest that this cluster is forming along two main directions of mass accretion and show the typical characteristics of radio clusters; i.e., it is very massive and shows a young dynamical state. However, deeper radio observations are needed to clarify the nature of the diffuse radio emission in Abell 959.
The diffuse morphology and transient nature of coronal mass ejections (CMEs)
make them difficult to identify and track using traditional image processing
techniques. We apply multiscale methods to enhance the visibility of the faint
CME front. This enables an ellipse characterisation to objectively study the
changing morphology and kinematics of a sample of events imaged by the Large
Angle Spectrometric Coronagraph (LASCO) onboard the Solar and Heliospheric
Observatory (SOHO) and the Sun Earth Connection Coronal and Heliospheric
Investigation (SECCHI) onboard the Solar Terrestrial Relations Observatory
(STEREO). The accuracy of these methods allows us to test the CMEs for
non-constant acceleration and expansion.
We exploit the multiscale nature of CMEs to extract structure with a
multiscale decomposition, akin to a Canny edge detector. Spatio-temporal
filtering highlights the CME front as it propagates in time. We apply an
ellipse parameterisation of the front to extract the kinematics (height,
velocity, acceleration) and changing morphology (width, orientation).
The kinematic evolution of the CMEs discussed in this paper have been shown
to differ from existing catalogues. These catalogues are based upon
running-difference techniques that can lead to over-estimating CME heights. Our
resulting kinematic curves are not well-fitted with the constant acceleration
model. It is shown that some events have high acceleration below $\sim$5
R$_{\sun}$. Furthermore, we find that the CME angular widths measured by these
catalogues are over-estimated, and indeed for some events our analysis shows
non-constant CME expansion across the plane-of-sky.
We perform a linear analysis to investigate the dynamical response of a non-synchronized hot Jupiter to stellar irradiation. In this work, we consider the diurnal Fourier harmonic of the stellar irradiation acting at the top of a radiative layer of a hot Jupiter with no clouds and winds. In the absence of the Coriolis force, the diurnal thermal forcing can excite internal waves propagating into the planet's interior when the thermal forcing period is longer than the sound crossing time of the planet's surface. When the Coriolis effect is taken into consideration, the latitude-dependent stellar heating can excite weak internal waves (g modes) and/or strong baroclinic Rossby waves (buoyant r modes) depending on the asynchrony of the planet. When the planet spins faster than its orbital motion (i.e. retrograde thermal forcing), these waves carry negative angular momentum and are damped by radiative loss as they propagate downwards from the upper layer of the radiative zone. As a result, angular momentum is transferred from the lower layer of the radiative zone to the upper layer and generates a vertical shear. We estimate the resulting internal torques for different rotation periods based on the parameters of HD 209458b.
The Large Area Telescope on the recently launched Fermi Gamma-ray Space Telescope (formerly GLAST), with its large field of view and effective area, combined with its excellent timing capabilities, is poised to revolutionize the field of gamma-ray astrophysics. The large improvement in sensitivity over EGRET is expected to result in the discovery of many new gamma-ray pulsars, which in turn should lead to fundamental advances in our understanding of pulsar physics and the role of neutron stars in the Galaxy. Almost immediately after launch, Fermi clearly detected all previously known gamma-ray pulsars and is producing high precision results on these. An extensive radio and X-ray timing campaign of known (primarily radio) pulsars is being carried out in order to facilitate the discovery of new gamma-ray pulsars. In addition, a highly efficient time-differencing technique is being used to conduct blind searches for radio-quiet pulsars, which has already resulted in new discoveries. I present some recent results from searches for pulsars carried out on Fermi data, both blind searches, and using contemporaneous timing of known radio pulsars.
We present the first direct detection of cold atomic gas in the Magellanic Stream, through 21 cm line absorption toward a background radio source, J0119 - 6809, using the Australia Telescope Compact Array. Two absorption components were identified at heliocentric velocities 218.6 km/s and 227.0 km/s, with optical depths of tau ~ 0.02. The corresponding H I emission region has a column density in excess of 2 x 10^20 cm^{-2}. The inferred spin temperature of the emitting gas is ~70 K. We failed to find cool gas in observations of three other radio continuum sources. Although we have definitively detected cool gas in the Stream, its spin temperature is higher than similar components in the LMC, SMC and Bridge, and its contribution to the total H I density is probably lower. No corresponding 12CO(J = 1 -> 0) or dust appears to be associated with the cool gas, suggesting that the cloud is not forming stars.
We present a detailed study of the X-ray and optical spectra of the luminous Seyfert galaxy Mrk 1393, which revealed variable partial obscuration of the active nucleus. The X-ray spectra obtained by XMM-Newton and Swift show moderate absorption with a column density around 3x10^21 cm^-2, consistent with a dust-reddening interpretation of the steep Balmer decrement seen in recent optical spectra. The X-ray flux in the 0.5 to 2 keV band during the XMM-Newton observation in 2005 and Swift observation in 2006 was a factor 6 brighter than that of the ROSAT All Sky Survey in 1991. In the past 4 years, the broad H\alpha line brightened by a factor of 4 accompanied by a decrease in the Balmer decrement. A comparison with literature spectra reveals variations in the dust extinction on time scales of several years, suggesting that the obscuring material is very close to the active nucleus. These observations indicate that a dust-to-gas ratio as high as the Galactic value can be present in moderately thick gas in the vicinity of the central engine within a few parsecs. We suggest that the obscuring material may be debris disrupted from the dusty torus.
We observed the northern rim of the Cygnus Loop with the \textit{Suzaku}
observatory in 5 pointings (P21-P25). From the spatially resolved analysis, all
the spectra are well fitted by the single component of the non-equilibrium
ionization plasma model. From the best-fit parameters, we found that the
abundances of the heavy elements are significantly lower than the solar values
except those at the outermost edge in P21 and P22. The origin of the depleted
metal abundances is still unclear while such deficiencies have been reported
from many other rim observations of the Loop. To explain these depletion at the
rim regions, we considered the several possibilities. The effects of the
resonance-line-scattering and the grain condensation lower the values of the
abundances. However, these are not sufficient to account for the abundance
depletion observed.
We found that the abundances at the outermost edge in P21 and P22 are higher
than those at the other regions. From the morphological point of view, it is
reasonable to consider that this abundance inhomogeneity is derived from the
breakout or the thinness of the cavity wall of the Loop.
We analyzed the metal distribution of the Cygnus Loop using 14 and 7 pointings observation data obtained by the \textit{Suzaku} and the \textit{XMM-Newton} observatories. The spectral analysis shows that all the spectra are well fitted by the two-$kT_e$ non-equilibrium ionization plasma model as shown by the earlier observations. From the best-fit parameters of the high-$kT_e$ component, we calculated the emission measures about various elements and showed the metal distribution of the ejecta component. We found that the distributions of Si and Fe are centered at the southwest of the geometric center toward the blow-out region. From the best-fit parameters, we also estimated the progenitor mass of the Cygnus Loop from our field of view and the metal rich region with a radius of 25 arcmin from the metal center. The result from the metal circle is similar to that from our entire FOV, which suggests the mixing of the metal. From the results, we estimated the mass of the progenitor star at 12-15\MO.
Accurate measurement of the cluster mass function is a crucial element in efforts to constrain structure formation models, the normalisation of the matter power spectrum and the cosmological matter density, and the nature and evolution of dark energy. Large weak lensing surveys of ~20,000 galaxy clusters and groups will be key tools in the observational pursuit of that goal. These weak lensing studies often proceed by stacking the lensing signals of many clusters and groups binned by mass-correlated observables such as richness and luminosity; typically such analyses ignore the triaxial structure of dark matter halos on the assumption that the averaging of many shear signals within each mass bin makes its effects (as large as factors of two in mass model parameter estimates from individual clusters) negligible. We test this assumption and find that triaxiality can bias 3D virial mass estimates compared to those for a spherical population by a few percent if suboptimal mass estimators are used. This bias affects not only direct lensing constraints on the mass function but can also affect the scatter and normalization of the mass-observable relations derived from lensing that are so crucial to constraining the cluster mass function with large samples. However, we demonstrate that a careful choice of mass estimator can remove the bias very effectively if the lensing signals from a sufficient number of triaxial halos are averaged together, and further quantify that sufficient number for adequate shape averaging. We thus show that by choosing observable bins to contain an adequate number of halos and by utilizing a carefully chosen 3D mass estimator stacked weak-lensing analyses can give unbiased constraints on the triaxial mass function.
The compact radio source Sagittarius A (Sgr A) at the centre of our Galaxy harbours a supermassive black hole, whose mass has been measured from stellar orbital motions. Sgr A is therefore the nearest laboratory where super-massive black hole astrophysics can be tested, and the environment of black holes can be investigated. Since it is not an active galactic nucleus, it also offers the possibility of observing the capture of small objects that may orbit the central black hole. We study the effects of the strong gravitational field of the black hole on small objects, such as a comet or an asteroid. We also explore the idea that the flares detected in Sgr A might be produced by the final accretion of single, dense objects with mass of the order of 10^20 g, and that their timing is not a characteristic of the sources, but rather of the space-time of the central galactic black hole in which they are moving. We find that tidal effects are strong enough to melt the solid object, and present calculations of the temporal evolution of the light curve of infalling objects as a function of various parameters. Our modelling of tidal disruption suggests that during tidal squeezing, the conditions for synchrotron radiation can be met. We show that the light curve of a flare can be deduced from dynamical properties of geodesic orbits around black holes and that it depends only weakly on the physical properties of the source.
We present the first Suzaku observation of the new Soft Gamma Repeater SGR 0501+4516, performed on 2008 August 26, four days after the onset of bursting activity of this new member of the magnetar family. The soft X-ray persistent emission was detected with the X-ray Imaging Spectrometer (XIS) at a 0.5-10 keV flux of 3.8E-11 erg/s/cm2, with a spectrum well fitted by an absorbed blackbody plus power-law model. The source pulsation was confirmed at a period of 5.762072+/-0.000002 s, and 32 X-ray bursts were detected by the XIS, four of which were also detected at higher energies by the Hard X-ray Detector (HXD). The strongest burst, which occurred at 03:16:16.9 (UTC), was so bright that it caused instrumental saturation, but its precursor phase, lasting for about 200 ms, was detected successfully over the 0.5-200 keV range, with a fluence of ~2.1E-7 erg/cm2 and a peak intensity of about 89 Crab. The entire burst fluence is estimated to be ~50 times higher. The precursor spectrum was very hard, and well modeled by a combination of two blackbodies. We discuss the bursting activity and X/gamma-ray properties of this newly discovered Soft Gamma Repeater in comparison with other members of the class.
With the invention of new far-infrared (FIR) and radio mm and sub-mm instruments (DESIR on SMESE satellite, ESO-ALMA), there is a growing interest in observations and analysis of solar flares in this so far unexplored wavelength region. Two principal radiation mechanisms play a role: the synchrotron emission due to accelerated particle beams moving in the magnetic field and the thermal emission due to the energy deposit in the lower atmospheric layers. In this contribution we explore the time-dependent effects of beams on thermal FIR and radio continua. We show how and where these continua are formed in the presence of time dependent beam heating and non-thermal excitation/ionisation of the chromospheric hydrogen plasma.
There is growing evidence that the properties of the molecular gas in the nuclei of starburst galaxies and in AGN may be very different from those seen in Galactic star forming regions and that a high kinetic temperature in the molecular gas may lead to a non-standard initial mass function in the next generation of stars. Unfortunately, among the fundamental parameters derived from molecular line observations, the kinetic temperature of the molecular gas in external galaxies is often not well determined due to a lack of suitable tracer molecules. We discuss the diagnostic power of selected transition lines of formaldehyde (H_2CO), which can be used as a molecular thermometer as well as an excellent tracer of the molecular gas density. As a proof of concept, we present the results of our multi-transition line study of the H_2CO emission from the prototypical starburst galaxy M82. Using our large velocity gradient model, we tightly constrain the physical properties of the dense gas in the prominent molecular lobes, completely independent of the standard "cloud thermometer" ammonia (NH_3) or other molecular tracers. Our results agree well with the properties of the high-excitation molecular gas component found in the most comprehensive CO studies. Our observations also indicate that there may be an asymmetry between the two molecular lobes.
Interpretation of the recently observed VHE pulsed emission from the Crab pulsar is presented. Taking into account the fact that Crab pulsar's radiation from the optical band up to very high energies peak at the same phases we argue that the source of this broad band radiation is spatially localized and the only mechanism providing the results of the MAGIC Cherenkov telescope, should be the synchrotron emission. It is shown that in the magnetospheric electron-positron plasma, due to the cyclotron instability, the pitch angle becomes non-vanishing, which leads to the efficient synchrotron radiation which intensifying on the light cylinder lengthscales.
The Groth field is one of the sky regions that will be targeted by the OTELO (OSIRIS Tunable Filter Emission Line Object) survey in the optical 820 nm and 920 nm atmospheric windows. This field has been observed by AEGIS (All-wavelength Extended Groth strip International Survey) covering the full spectral range, from X-rays to radio waves. Chandra X-ray data with total exposure time of 200ksec are analyzed and combined with optical broadband data of the Groth field in order to study a set of structural parameters of the X-ray emitters and its relation with X-ray properties. We processed the raw, public X-ray data using the Chandra Interactive Analysis of Observations and determined and analyzed different structural parameters in order to produce a morphological classification of X-ray sources. Finally, we analyzed the angular clustering of these sources using 2-point correlation functions. We present a catalog of 340 X-ray emitters with optical counterpart. We obtained the number counts and compared them with AEGIS data. Objects have been classified by nuclear type using a diagnostic diagram relating X-ray-to-optical ratio (X/O) to hardness ratio (HR). Also, we combined structural parameters with other X-ray and optical properties, and found for the first time an anticorrelation between the X/O ratio and the Abraham concentration index which might suggest that early type galaxies have lower Eddington rates than those of late type galaxies. A significant positive angular clustering was obtained from a preliminary analysis of 4 subsamples of the X-ray sources catalog. The clustering signal of the opticaly extended counterparts is similar to that of strongly clustered populations like red and very red galaxies, suggesting that the environment plays an important role in AGN phenomena.
Recently, Dufour et al. (2007) reported the unexpected discovery that a few white dwarfs found in the Sloan Digital Sky Survey had an atmosphere dominated by carbon with little or no trace of hydrogen and helium. Here we present a progress report on these new objects based on new high signal-to-noise follow-up spectroscopic observations obtained at the 6.5m MMT telescope on Mount Hopkins, Arizona.
We present some of the results of a survey aimed at exploring the asteroseismological potential of the newly-discovered carbon-atmosphere white dwarfs. We show that, in certains regions of parameter space, carbon-atmosphere white dwarfs may drive low-order gravity modes. We demonstrate that our theoretical results are consistent with the recent exciting discovery of luminosity variations in SDSS J1426+5752 and some null results obtained by a team of scientists at McDonald Observatory. We also present follow-up photometric observations carried out by ourselves at the Mount Bigelow 1.6-m telescope using the new Mont4K camera. The results of follow-up spectroscopic observations at the MMT are also briefly reported, including the surprising discovery that SDSS J1426+5752 is not only a pulsating star but that it is also a magnetic white dwarf with a surface field near 1.2 MG. The discovery of $g$-mode pulsations in SDSS J1426+5752 is quite significant in itself as it opens a fourth asteroseismological "window", after the GW Vir, V777 Her, and ZZ Ceti families, through which one may study white dwarfs.
Type Ia supernovae (SNe Ia) play an important role in astrophysics, especially in the study of cosmic evolution. There are several progenitor models for SNe Ia proposed in the past years. In this paper, we have carried out a detailed study of the He star donor channel, in which a carbon-oxygen white dwarf (CO WD) accretes material from a He main sequence star or a He subgiant to increase its mass to the Chandrasekhar mass. Employing Eggleton's stellar evolution code with an optically thick wind assumption, and adopting the prescription of Kato & Hachisu (2004) for the mass accumulation efficiency of the He-shell flashes onto the WDs, we performed binary evolution calculations for about 2600 close WD binary systems. According to these calculations, we mapped out the initial parameters for SNe Ia in the orbital period--secondary mass ($\log P^{\rm i}-M^{\rm i}_2$) plane for various WD masses from this channel. The study shows that the He star donor channel is noteworthy for producing SNe Ia (i.e. $\sim 1.2\times10^{-3} {\rm yr}^{-1}$ in the Galaxy), and that the progenitors from this channel may appear as supersoft X-ray sources. Importantly, this channel can explain SNe Ia with short delay times ($\la 10^{8}$ yr), which is consistent with recent observational implications of young populations of SN Ia progenitors.
Politano and Pouquet's law, a generalization of Kolmogorov's four-fifths law to incompressible MHD, makes it possible to measure the energy cascade rate in incompressible MHD turbulence by means of third-order moments. In hydrodynamics, accurate measurement of third-order moments requires large amounts of data because the probability distributions of velocity-differences are nearly symmetric and the third-order moments are relatively small. Measurements of the energy cascade rate in solar wind turbulence have recently been performed for the first time, but without careful consideration of the accuracy or statistical uncertainty of the required third-order moments. This paper investigates the statistical convergence of third-order moments as a function of the sample size N. It is shown that the accuracy of the third-moment depends on the number of correlation lengths spanned by the data set and a method of estimating the statistical uncertainty of the third-moment is developed. The technique is illustrated using both wind tunnel data and solar wind data.
We describe the structure and composition of six major stellar streams in a population of 20 574 local stars in the New Hipparcos Reduction with known radial velocities. We find that, once fast moving stars are excluded, almost all stars belong to one of these streams. The results of our investigation have lead us to re-examine the hydrogen maps of the Milky Way, from which we identify the possibility of a symmetric two-armed spiral with half the conventionally accepted pitch angle. We describe a model of spiral arm motions which matches the observed velocities and composition of the six major streams, as well as the observed velocities of the Hyades and Praesepe clusters at the extreme of the Hyades stream. Stellar orbits are perturbed ellipses aligned at a focus in coordinates rotating at the rate of precession of pericentre. Stars join a spiral arm just before apocentre, follow the arm for more than half an orbit, and leave the arm soon after pericentre. Spiral pattern speed equals the mean rate of precession of pericentre. Spiral arms are shown to be stable configurations of stellar orbits, up to the formation of a bar and/or ring. Pitch angle is directly related to the distribution of orbital eccentricities in a given spiral galaxy. We show how spiral galaxies can evolve to form bars and rings. We show that orbits of gas clouds are stable only in bisymmetric spirals. We conclude that the evolution of spiral galaxies is toward grand design two-armed spirals. We infer from the velocity distributions that the Milky Way evolved into this form about 9 Gyrs ago.
The variable star V1735 Cyg (= Elias 1-12) lies in the IC 5146 dark cloud and is a member of the class of FU Orionis objects whose dramatic optical brightenings are thought to be linked to episodic accretion. We report the first X-ray detections of V1735 Cyg and a deeply-embedded class I protostar lying 24 arcsecs to its northeast. X-ray spectra obtained with EPIC on XMM-Newton reveal very high-temperature plasma (kT > 5 keV) in both objects, but no large flares. Such hard X-ray emission is not anticipated from accretion shocks and is a signature of magnetic processes. We place these new results into the context of what is presently known about the X-ray properties of FU Orionis stars and other accreting young stellar objects.
Context. The origin, evolution, and ultimate fate of magnetic cataclysmic variables are poorly understood. It is largely the nature of the magnetic fields in these systems that leads to this poor understanding. Fundamental properties, such as the field strength and the axis alignment, are unknown in a majority of these systems. Aims. We undertake to put all the previous circular polarization measurements into context and systematically survey intermediate polars for signs of circular polarization, hence to get an indication of their true magnetic field strengths and try to understand the evolution of magnetic cataclysmic variables. Methods. We used the TurPol instrument at the Nordic Optical Telescope to obtain simultaneous UBVRI photo-polarimetric observations of a set of intermediate polars, during the epoch 2006 July 31 - August 2. Results. Of this set of eight systems two (1RXS J213344.1+510725 and 1RXS J173021.5-055933) were found to show significant levels of circular polarization, varying with spin phase. Five others (V2306 Cyg, AO Psc, DQ Her, FO Aqr, and V1223 Sgr) show some evidence for circular polarization and variation of this with spin phase, whilst AE Aqr shows little evidence for polarized emission. We also report the first simultaneous UBVRI photometry of the newly identified intermediate polar 1RXS J173021.5-055933. Conclusions. Circular polarization may be ubiquitous in intermediate polars, albeit at a low level of one or two percent or less. It is stronger at longer wavelengths in the visible spectrum. Our results lend further support to the possible link between the presence of soft X-ray components and the detectability of circular polarization in intermediate polars.
Integral field spectroscopy (IFS) represents a powerful technique for the detection and characterization of extrasolar planets through high contrast imaging, since it allows to obtain simultaneously a large number of monochromatic images. These can be used to calibrate and then to reduce the impact of speckles, once their chromatic dependence is taken into account. The main concern in designing integral field spectrographs for high contrast imaging is the impact of the diffraction effects and the non-common path aberrations together with an efficient use of the detector pixels. We focus our attention on integral field spectrographs based on lenslet-arrays, discussing the main features of these designs: the conditions of appropriate spatial and spectral sampling of the resulting spectrograph's slit functions and their related cross-talk terms when the system works at the diffraction limit. We present a new scheme for the integral field unit (IFU) based on a dual-lenslet device (BIGRE), that solves some of the problems related to the classical TIGER design when used for such applications. We show that BIGRE provides much lower cross-talk signals than TIGER, allowing a more efficient use of the detector pixels and a considerable saving of the overall cost of a lenslet-based integral field spectrograph.
Cosmic rays have valuable information about universe surroundings us. Finding energy, mass and arrival direction of primary cosmic ray particle are the most important aspects of extensive air shower studies. In order to determine these parameters, arrival direction and core position of extensive air showers should be determined at first. In this article, a new method has been introduced that utilizes arrival time information of secondary particles of extensive air showers for finding their core location and correcting plane wave front approximation so that calculate the arrival direction of extensive air showers. This method does not need number sensitive detectors-detectors which are sensitive to the number of crossing particles- and consequently there is no need for lateral distribution models. This model has been developed by analysis of simulated events generated by CORSIKA package.
We discuss the uncertainties and the systematic effects that exist in the estimates of the stellar masses of high redshift galaxies, using broad band photometry, and how they affect the deduced galaxy stellar mass function. We use at this purpose the latest version of the GOODS-MUSIC catalog. In particular, we discuss the impact of different synthetic models, of the assumed initial mass function and of the selection band. Using Charlot & Bruzual 2007 and Maraston 2005 models we find masses lower than those obtained from Bruzual & Charlot 2003 models. In addition, we find a slight trend as a function of the mass itself comparing these two mass determinations with that from Bruzual & Charlot 2003 models. As consequence, the derived galaxy stellar mass functions show diverse shapes, and their slope depends on the assumed models. Despite these differences, the overall results and scenario remains unchanged. The masses obtained with the assumption of the Chabrier initial mass function are in average 0.24 dex lower than those from the Salpeter assumption, at all redshifts, causing a shift of galaxy stellar mass function of the same amount. Finally, using a 4.5 um-selected sample instead of a Ks-selected one, we add a new population of highly absorbed, dusty galaxies at z\simeq 2-3 of relatively low masses, yielding stronger constraints on the slope of the galaxy stellar mass function at lower masses.
We explore the possibility that weakly interacting dark matter can form bound states - WIMPonium. Such states are expected in a wide class of models of particle dark matter, including some limits of the Minimal Supersymmetric Standard Model. We examine the conditions under which we expect bound states to occur, and use analogues of NRQCD applied to heavy quarkonia to provide estimates for their properties, including couplings to the Standard Model. We further find that it may be possible to produce WIMPonium at the LHC, and explore the properties of the WIMP that can be inferred from measurements of the WIMPonium states.
We study the field profile of a scalar field $\phi$ that couples to a matter fluid (dubbed a chameleon field) in the relativistic gravitational background of a spherically symmetric spacetime. Employing a linear expansion in terms of the gravitational potential $\Phi_c$ at the surface of a compact object with a constant density, we derive the thin-shell field profile both inside and outside the object, as well as the resulting effective coupling with matter, analytically. We also carry out numerical simulations for the class of inverse power-law potentials $V(\phi)=M^{4+n} \phi^{-n}$ by employing the information provided by our analytical solutions to set the boundary conditions around the centre of the object and show that thin-shell solutions in fact exist if the gravitational potential $\Phi_c$ is smaller than 0.3. Thus the chameleon mechanism is present in the relativistic gravitational backgrounds, capable of reducing the effective coupling. For still stronger gravitational backgrounds with $\Phi_c > 0.3$, however, we find that the chameleon field typically approaches the singularity at $\phi=0$ due to the existence of the strong relativistic pressure unless its boundary condition around the centre of the body is chosen to be far from the maximum of the effective potential.
We report the results of a first study that uses numerical simulations to
estimate the accuracy with which one can use gravitational wave observations of
double neutron star inspiral to measure parameters of the neutron-star equation
of state. The simulations use the evolution and initial-data codes of Shibata
and Uryu to compute the last several orbits and the merger of neutron stars,
with matter described by a parametrized equation of state. Previous work
suggested the use of an effective cutoff frequency to place constraints on the
equation of state. We find, however, that greater accuracy is obtained by
measuring departures from the point-particle limit of the gravitational
waveform produced during the late inspiral.
As the stars approach their final plunge and merger, the gravitational wave
phase accumulates more rapidly for smaller values of the neutron star
compactness (the ratio of the mass of the neutron star to its radius). We
estimate that realistic equations of state will lead to gravitational waveforms
that are distinguishable from point particle inspirals at an effective distance
(the distance to an optimally oriented and located system that would produce an
equivalent waveform amplitude) of 100 Mpc or less. As Lattimer and Prakash
observed, neutron-star radius is closely tied to the pressure at density not
far above nuclear. Our results suggest that broadband gravitational wave
observations at frequencies between 500 and 1000 Hz will constrain this
pressure, and we estimate the accuracy with which it can be measured. Related
first estimates of radius measurability show that the radius can be determined
to an accuracy of ~1 km at 100 Mpc.
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