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We explore conditions and structure of accretion disks in the short-period Cataclysmic Variables, which have evolved beyond the period minimum. We show that the accretion disk in a system with extreme mass ratio grows in the size reaching 2:1 resonance radius and are relatively cool. They also become largely optically thin in the continuum, contributing to the total flux less than the stellar components of the system. In contrast, the viscosity and the temperature in spiral arms formed at the outer edge of the disk are higher and their contribution in continuum plays an increasingly important role. We model such disks and generate light curves which successfully simulate the observed double-humped light curves in the quiescence.
Magnetoconvection in a horizontal layer of incompressible fluid is simulated numerically. The initial magnetic field is assumed to be uniform and horizontal. The interaction of quasi-ordered cellular convection with the magnetic field is shown to be able to produce bipolar (and also diverse more complex) configurations of a substantially amplified magnetic field. The operation of this mechanism, which can be regarded as a modification of the mechanism suggested by Tverskoi (1966), is controlled by the very topology of the cellular flow, should be manifest on various spatial scales, and does not require strong initial fields. Magnetic configurations develop both in the central parts of convection cells, where circulatory fluid motion “winds” magnetic field lines, and in the network formed by their peripheral regions due to the “sweeping” of magnetic field lines.
Thermal emission during X-ray bursts is a powerful tool to determine neutron star masses and radii, if the Eddington flux and the apparent radius in the cooling tail can be measured accurately, and distances to the sources are known. We propose here an improved method of determining the basic stellar parameters using the data from the cooling phase of long, photospheric radius expansion bursts covering a large range of luminosities. For this purpose, we computed a large set of atmosphere models for burst luminosities varying by two orders of magnitude and for various chemical compositions and surface gravities. We show that the variation of the inverse square root of the apparent blackbody radius with the flux, observed during the photospheric radius expansion bursts from a number of sources at low accretion rate is entirely consistent with the theoretical expectations of the color-correction factor evolution. However, for bursts happening at higher accretion rates the observed evolution is inconsistent with theory, implying that accretion strongly disturbs the neutron star atmosphere. These findings have profound implications for the recent claims on determination of the neutron star radii and masses from such bursts. Our method allows us to determine both the Eddington flux and the ratio of the stellar apparent radius to the distance much more reliably. For 4U 1724-307, we find a lower limit on the neutron star radius of 13 km, independently of the chemical composition. These results suggest that the matter inside neutron stars is characterized by a stiff equation of state.
We present GALEX ultraviolet (UV) emission results of star-formation in a small sample of nearby, gas-rich early-type galaxies. The first observational evidence of star-formation in this sample was presented by Leeuw et al.2008, using 350 μm continuum data. The measured far-infrared (far-IR) excess of these galaxies showed that the most likely and dominant heating source of the observed 350 μm continuum emission from dust is star-formation, that could have been triggered by an accretion or merger event. Consistent with starbursts that are less than 1 Gyr (e.g., Kaviraj 2010), the GALEX near-UV (NUV) minus SDSS r-band emission of the galaxies is < 5.5. The UV results corroborate those of mid-IR to radio data for the sample.
We present a study of the observational properties of Millisecond Pulsars (MSPs) by way of their magnetic fields, spin periods and masses. These measurements are derived through the scenario of Accretion Induced Collapse (AIC) of white dwarfs (WDs) in stellar binary systems, in order to provide a greater understanding of the characteristics of MSP populations. In addition, we demonstrate a strong evolutionary connection between neutron stars and WDs with binary companions from a stellar binary evolution perspective via the AIC process.
A visualization of 3D structures and cosmic flows is presented using information from the Extragalactic Distance Database V8k redshift catalog and peculiar velocities from the Cosmicflows-1 survey. Structures within a volume bounded at 8000 km s−1 on the cardinal Supergalactic axes are explored in terms of both displaying the positions of the 30,124 galaxies of the catalog and its reconstructed luminosity density field, corrected to account for growing incompleteness with increasing distance. Cosmography of the local Universe is discussed with the intent to identify the most prominent structures, including voids, galaxy clusters, filaments, and walls. The mapping also benefits from precise distance measures provided through the Cosmicflows-1 observational program. Three-dimensional visualizations of the coherent flows of galaxies in the nearby Universe are presented, using recent results based on reconstruction of cosmic flows with the Wiener filter approach. The three major components of the Milky Way's motion, namely expulsion from the Local Void, infall toward the Virgo Cluster, and the bulk flow of the historic Local Supercluster toward the Great Attractor are illustrated using different visualization techniques and analyzed in light of the cosmography derived from the V8k redshift and Cosmicflows-1 distance catalogs.
Possibility of disintegration of proto-comet nucleus of sungraser comets in three zones of Solar System predicted by one of authors is considered. Testing of parameters of 118 split comets confirms the basic idea. Results of the statistical analysis of comet outbursts gave us additional argument in favor of this assumption. Almost twenty years have passed since, as a result of the search for host phases of isotopically unusual noble gases, the first discovery in 1987 of surviving pre-solar minerals (diamond and silicon carbide) in primitive meteorites. These were followed by others (graphite, refractory oxides, silicon nitride, and finally silicates) in the years since. Pre-solar grains occur in even higher abundance than in meteorites in interplanetary dust particles (IDPs). The result is a kind of ‘new astronomy’ based on the study of pre-solar condensates with all the methods available in modern analytical laboratories.
Several recent surveys (HERACLES, NGLS, KINGFISH, VNGS) have provided us with sensitive high-resolution observations of the molecular gas and dust content in spiral galaxies within 25 Mpc. I review recent results on the molecular gas content and its relation to star formation, as well as on the gas to dust ratio and the dust heating in spiral galaxies. I also present new results on the effect of environment on the molecular gas content of spiral galaxies.
We report on the parsec program, which observed 140 L and T dwarfs on a regular basis from 2007 to 2011, using the WIFI camera on the ESO/2.2 m telescope. Trigonometric parallaxes at 5 mas precision are derived for 49 objects, and mas yr−1-level proper motions are derived for approximately 200,000 objects in the same fields. We discuss image cleaning, object centroiding, and astrometric methods, in particular three different approaches for trigonometric parallax determination.
Structure within a galaxy is not random, instead emerging as a direct function of its evolutionary path. It is thought that secular evolutionary processes leave behind distinct structural tracers in the form of bars, pseudo-bulges and rings. We have developed a robust automated structural analysis pipeline (Kelvin et al., 2012) able to accurately map structure across a range of ground and space-based datasets. Using reprocessed SDSS and UKIDSS data from the GAMA survey: an imaging and spectroscopic survey with over 300,000 redshifts across 300 square degrees (Driver et al., 2009); we measure the relative abundance and stellar mass locked up within these structures in the local (z<0.06) Universe. Future robust calculations of the stellar mass budget within bulges, bars, disks and pseudo-bulges should allow us to measure the relative importance of secular evolution against other mechanisms across cosmic time.
We investigate the resolved star formation properties of a sample of 45 massive galaxies (M* > 1011 M⊙) within a redshift range of 1.5 ⩽ z ⩽ 3 detected in the GOODS NICMOS Survey (Conselice et al. 2011), a HST H160-band imaging program. We derive the star formation rate as a function of radius using rest frame UV data from deep z850 ACS imaging. The star formation present at high redshift is then extrapolated to z = 0, and we examine the stellar mass produced in individual regions within each galaxy. We also construct new stellar mass profiles of the in situ stellar mass at high redshift from Sérsic fits to rest-frame optical, H160-band, data. We combine the two stellar mass profiles to produce an evolved stellar mass profile. We then fit a new Sérsic profile to the evolved profile, from which we examine what effect the resulting stellar mass distribution added via star formation has on the structure and size of each individual galaxy.
Low-resolution spectroscopy (R ≈ 1000) is used to efficiently characterize faint stars suspected to host planets. Stellar parameters, i.e. effective temperature, surface gravity, and metallicity can be assessed from these spectra by methods of quantitative classification. For this purpose, more than 130 template stars have been observed with the faint object spectrograph at the Tautenburg 2m telescope, Germany. A large number of lines are measured and the dependence of line depths on stellar parameters is studied.
We identified 132,684 clusters in the redshift range of 0.05 < z < 0.8 from SDSS DR8. The spectroscopic redshifts of 52,683 clusters have been included in the catalog using SDSS DR9 data. We found that BCGs are more luminous in richer clusters and at higher redshifts.
During the quiescent phases, the spectra of cataclysmic variables are studied. We model the fluxes by means of the photoionization code CLOUDY, and in the model it is assumed that the geometry of disks is cylindrical. Using this method, we input a series of reasonable parameters and get a spectral library.
We present the results of the distribution of CO-dark H2 gas in a sample of 2223 interstellar clouds in the inner Galaxy (l=−90° to +57°) detected in the velocity resolved [CII] spectra observed in the GOT C+ survey using the Herschel HIFI. We analyze the [CII] intensities along with the ancillary HI, 12CO and 13CO data for each cloud to determine their evolutionary state and to derive the H2 column densities in the C+ and C+/CO transition layers in the cloud. We discuss the overall Galactic distribution of the [CII] clouds and their properties as a function Galactic radius. GOT C+ results on the global distribution of [CII] clouds and CO-dark H2 gas traces the FUV intensity and star formation rate in the Galactic disk.
The last version of the planet part of EPM's ephemerides of IAA RAS (EPM2011) is described briefly. At present EPM ephemerides are the basis for the Russian Astronomical and Nautical Astronomical Yearbooks and are used for scientific research.
VERA is a Very Long Baseline Interferometry (VLBI) array for astrometry, composed of four 20 m radio telescopes. They are located over a range of around 2300 km in Japan. VERA consists of a two-beam system equipped with 2, 6.7, 8, 22, and 43 GHz receivers. The two-beam system is used for phase referencing of the VLBI observations, to compensate for atmospheric-turbulence effects between two nearby objects. It has achieved measurements of annual parallaxes within 5 kpc with 10% accuracy. Observed sources are water, SiO, and methanol masers, which are found in molecular gas around star-forming regions and evolved stars. We have carried out a large program of astrometry to reveal the Galaxy's structure and velocity field. VERA has already measured trigonometric parallaxes of more than 30 sources and observed around a hundred sources using the two-beam astrometry technique. Maser sources are associated with high-mass star-forming regions, which are thought to trace the arm structure of the Galaxy. Using annual parallax and proper-motion measurements, their structure will be shown without kinematic distance assumptions. Some sources exhibit large differences between trigonometric-parallax measurements and kinematic distances. We present the status of the VERA project as well as recent results.
The first attempt at a census of all molecular clouds (MoC) in the Milky Way observed to date is presented. The catalog of MoC includes all observed and estimated physical parameters. The data will be used to compute a model of the MoC system in the Galaxy.
Infrared water line emission from protoplanetary disks, recently observed by the Spitzer and Herschel space telescopes, is thought to trace the surface layer of the inner to outer regions of the disks. We have modelled the water abundance profile and line emission, especially focusing on the effects of dust size growth and turbulent mixing. Comparison between model calculations and observations suggests a small grain model with turbulent mixing is preferred.
We present the results from our cosmological simulations of the first stages of galaxy formation. We use Gadget-2 (Springel 2005), modified to include detailed cooling, chemistry, and radiative transfer of primordial gas to study the impact of the first stars on galaxy formation. In contrast to previous work, we apply a realistic treatment of stellar feedback by using updated stellar models for the first stars. In this proceeding, we briefly summarize how stellar feedback from the first stars affects the primordial IGM inside the first galaxies.