- ID:
- ivo://CDS.VizieR/J/AJ/138/606
- Title:
- Hot subdwarf stars in rejected PG catalog
- Short Name:
- J/AJ/138/606
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The hot subdwarf (sd) stars in the Palomar Green (PG) catalog of ultraviolet excess (UVX) objects play a key role in investigations of the frequency and types of binary companions and the distribution of orbital periods. These are important for establishing whether and by which channels the sd stars arise from interactions in close binary systems. It has been suggested that the list of PG sd stars is biased by the exclusion of many stars in binaries, whose spectra show the CaII K line in absorption. A total of 1125 objects that were photometrically selected as candidates were ultimately rejected from the final PG catalog using this K-line criterion. We study 88 of these "PG-Rejects" (PGRs), to assess whether there are significant numbers of unrecognized sd stars in binaries among the PGR objects.
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- ID:
- ivo://CDS.VizieR/J/ApJS/256/28
- Title:
- Hot subdwarf stars with Gaia DR2 and LAMOST DR7 data
- Short Name:
- J/ApJS/256/28
- Date:
- 28 Feb 2022 15:07:37
- Publisher:
- CDS
- Description:
- Based on the Gaia DR2 catalog of hot subdwarf star candidates, we identified 1587 hot subdwarf stars with spectra in LAMOST DR7. We present atmospheric parameters for these stars by fitting the LAMOST spectra with TLUSTY/SYNSPEC non-LTE synthetic spectra. Combining LAMOST radial velocities and Gaia Early Data Release 3 (EDR3) parallaxes and proper motions, we also present the Galactic space positions, velocity vectors, orbital parameters and the Galactic population memberships of the stars. With our He classification scheme, we identify four groups of He rich hot subdwarf stars in the T_eff_-logg and T_eff_-log(nHe/nH) diagrams. We find two extreme He-rich groups (eHe-1 and eHe-2) for stars with log(nHe/nH)>=0 and two intermediate He-rich groups (iHe-1 and iHe-2) for stars with -1<=log(nHe/nH)<0. We also find that over half of the stars in Group eHe-1 are thick-disk stars, while over half of the stars in Group eHe-2 correspond to thin-disk stars. The disk population fractions of Group iHe-1 are between those of Group eHe-1 and eHe-2. Almost all of the stars in Group iHe-2 belong to the thin disk. These differences indicate that the four groups probably have very different origins. Comparisons between hot subdwarf stars in the halo and in the Galactic globular cluster {omega} Cen show that only He-deficient stars with -2.2<=log(nHe/nH){<}-1 have similar fractions. Hot subdwarfs with log(nHe/nH)>=0 in {omega} Cen have no counterparts in the thick-disk and halo populations, but they appear in the thin disk.
- ID:
- ivo://CDS.VizieR/J/AJ/135/1350
- Title:
- Hot variable stars in NGC 330
- Short Name:
- J/AJ/135/1350
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In a sample of 150 hot stars in NGC 330, a SMC cluster containing a high fraction of Be stars, we searched for photometric variables using OGLE II data. At least one third of all stars are variable, with 38 being periodic. We found 27 pulsators ({lambda} Eri variables), six eclipsing systems, two bursting sources, and several stars with unusual photometric behavior. Pulsations are present in ~30% of known Be stars, and they are long lived, lasting more than a decade. The strongest pulsators are associated with stars evolved from the main sequence.
- ID:
- ivo://CDS.VizieR/J/MNRAS/411/2770
- Title:
- Hot white dwarfs in GALEX-DR5
- Short Name:
- J/MNRAS/411/2770
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present comprehensive catalogues of hot star candidates in the Milky Way (MW), selected from Galaxy Evolution Explorer (GALEX) far-UV (FUV; 1344-1786{AA}) and near-UV (NUV; 1771-2831{AA}) imaging. The FUV and NUV photometry allows us to extract the hottest stellar objects, in particular hot white dwarfs (WD), which are elusive at other wavelengths because of their high temperatures and faint optical luminosities. We generated catalogues of UV sources from two GALEX's surveys: All-Sky Imaging Survey (AIS; depth AB magnitude ~19.9/20.8 in FUV/NUV) and Medium-depth Imaging Survey (MIS; depth ~22.6/22.7mag). The two catalogues (from GALEX fifth data release) contain 65.3/12.6 million (AIS/MIS) unique UV sources with errorNUV<= 0.5 mag, over 21 435/1579deg^2^. We also constructed subcatalogues of the UV sources with matched optical photometry from Sloan Digital Sky Survey (SDSS; seventh data release): these contain 0.6/0.9 million (AIS/MIS) sources with errors <=0.3mag in both FUV and NUV, excluding sources with multiple optical counterparts, over an area of 7325/1103 deg2. All catalogues are available online. We then selected 28 319 (AIS)/9028 (MIS) matched sources with FUV-NUV<-0.13; this colour cut corresponds to stellar Teff hotter than ~18 000K (the exact value varying with gravity). An additional colour cut of NUV-r>0.1 isolates binaries with largely differing Teffs, and some intruding quasi-stellar objects (QSOs; more numerous at faint magnitudes). Available spectroscopy for a subsample indicates that hot-star candidates with NUV-r<0.1 (mostly 'single' hot stars) have negligible contamination by non-stellar objects. We discuss the distribution of sources in the catalogues, and the effects of error and colour cuts on the samples. The density of hot-star candidates increases from high to low Galactic latitudes, but drops on the MW plane due to dust extinction. Our hot-star counts at all latitudes are better matched by MW models computed with an initial-final mass relation (IFMR) that favours lower final masses. The model analysis indicates that the brightest sample is likely composed of WDs located in the thin disc, at typical distances between 0.15 and 1kpc, while the fainter sample comprises also a fraction of thick disc and halo stars. Proper motion distributions, available only for the bright sample (NUV<18mag), are consistent with the kinematics of a thin-disc population.
- ID:
- ivo://CDS.VizieR/J/ApJ/871/63
- Title:
- How to constrain your M dwarf. II. Nearby binaries
- Short Name:
- J/ApJ/871/63
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The mass-luminosity relation for late-type stars has long been a critical tool for estimating stellar masses. However, there is growing need for both a higher-precision relation and a better understanding of systematic effects (e.g., metallicity). Here we present an empirical relationship between M_Ks_ and M_*_ spanning 0.075M_{sun}_<M_*_<0.70M_{sun}_. The relation is derived from 62 nearby binaries, whose orbits we determine using a combination of near infra-red (Keck/NIRC2) imaging, archival adaptive optics data, and literature astrometry. From their orbital parameters, we determine the total mass of each system, with a precision better than 1% in the best cases. We use these total masses, in combination with resolved Ks magnitudes and system parallaxes, to calibrate the M_Ks_-M_*_ relation. The resulting posteriors can be used to determine masses of single stars with a precision of 2%-3%, which we confirm by testing the relation on stars with individual dynamical masses from the literature. The precision is limited by scatter around the best-fit relation beyond measured M_*_ uncertainties, perhaps driven by intrinsic variation in the M_Ks_-M_*_ relation or underestimated uncertainties in the input parallaxes. We find that the effect of [Fe/H] on the M_Ks_-M_*_ relation is likely negligible for metallicities in the solar neighborhood (0.0%{+/-}2.2% change in mass per dex change in [Fe/H]). This weak effect is consistent with predictions from the Dartmouth Stellar Evolution Database, but inconsistent with those from modules for experiments in stellar astrophysics (MESA) Isochrones and Stellar Tracks (MIST) (at 5{sigma}). A sample of binaries with a wider range of abundances will be required to discern the importance of metallicity in extreme populations (e.g., in the Galactic halo or thick disk).
- ID:
- ivo://nasa.heasarc/hperseicxo
- Title:
- H Persei Chandra X-Ray Point Source Catalog
- Short Name:
- HPERSEICXO
- Date:
- 27 Sep 2024
- Publisher:
- NASA/GSFC HEASARC
- Description:
- This table contains some of the results from a Chandra/ACIS-I observations of the massive ~ 13-14 Myr-old cluster, h Persei, part of the famous Double Cluster (h and Chi Persei) in Perseus. Combining the list of 330 Chandra-detected sources with new optical/IR photometry and optical spectroscopy reveals ~ 165 X-ray bright stars with V <~ 23. Roughly 142 have optical magnitudes and colors consistent with cluster membership. The observed distribution of X-ray luminosity L<sub>x</sub> peaks at L<sub>x</sub> ~ 10<sup>30.3</sup> erg s<sup>-1</sup> and likely traces the bright edge of a far larger population of ~ 0.4-2 M<sub>sun</sub> X-ray active stars. From a short list of X-ray active stars with IRAC 8-micron excess from warm, terrestrial zone dust, the authors derive a maximum X-ray flux incident on forming terrestrial planets. Although there is no correlation between X-ray activity and IRAC excess, the fractional X-ray luminosity correlates with optical colors and spectral type. By comparing the distribution of L<sub>x</sub>/L<sub>star</sub> versus spectral type and (V-I) in h Per with results for other 1-100 Myr-old clusters, the authors show that stars slightly more massive than the Sun (>~ 1.5 M<sub>sun</sub>) fall out of X-ray saturation by ~ 10-15 Myr. Changes in stellar structure for >~ 1.5 M<sub>sun</sub> stars likely play an important role in this decline of X-ray emission. Chandra observations of h Persei were taken with a 41.1 ks exposure on 2004 December 2, (Obs. ID 5407; Sequence Number 200341) with the ACIS detector (chips 0, 1, 2, 3, 6, and 7). The data were obtained in dithered, timed mode, with a frametime of 3.2 s. On-board event rejection and event telemetry was in the VFAINT mode. The field was centered on RA(2000) = 2h19m00s, Dec(2000) = 57d07'12", close to the center of h Persei from Bragg & Kenyon (2005, AJ, 130, 134) (RA(2000) = 2h18m56.4s, Dec(2000) = 57d08'25") and observed at a roll angle of 229 degrees. The data were not registered to an astrometric reference frame (e.g., Two Micron All Sky Survey, 2MASS). The ACIS-I field covers a 17' x 17' area. This table was created by the HEASARC in March 2009 based on the electronic versions of Tables 1 and 2 from the paper which were obtained from the Astronomical Journal web site. This is a service provided by NASA HEASARC .
- ID:
- ivo://CDS.VizieR/J/A+A/626/A54
- Title:
- HR4796A dust ring Stokes images
- Short Name:
- J/A+A/626/A54
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The scattering properties of the dust originating from debris discs are still poorly known. The analysis of scattered light is however a powerful remote-sensing tool to understand the physical properties of dust particles orbiting other stars. Scattered light is indeed widely used to characterise the properties of cometary dust in the solar system. We aim to measure the morphology and scattering properties of the dust from the debris ring around HR4796A in polarised optical light. We obtained high-contrast polarimetric images of HR4796A in the wavelength range 600-900nm with the SPHERE/ZIMPOL instrument on the Very Large Telescope. We measured for the first time the polarised phase function of the dust in a debris system over a wide range of scattering angles in the optical. We confirm that it is incompatible with dust particles being compact spheres under the assumption of the Mie theory, and propose alternative scenarios compatible with the observations, such as particles with irregular surface roughness or aggregate particles.
- ID:
- ivo://CDS.VizieR/J/A+A/630/A142
- Title:
- HR4796 debris disk Qphi and Uphi images
- Short Name:
- J/A+A/630/A142
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Debris disks are the natural by-products of the planet formation process. Scatte red or polarized light observations are mostly sensitive to small dust grains that are released from the grinding down of bigger planetesimals. High angular resolution observations at optical wavelengths can provide key constraints on the radial and azimuthal distribution of the small dust grains. These constraints can help us better understand where most of the dust grains are released upon collisions. We present SPHERE/ZIMPOL observations of the debris disk around HR 4796A, and model the radial profiles along several azimuthal angles of the disk with a code that accounts for the effect of stellar radiation pressure. This enables us to derive an appropriate description for the radial and azimuthal distribution of the small dust grains. Even though we only model the radial profiles along (or close to) the semi-major axis of the disk, our best-fit model is not only in good agreement with our observations but also with previously published datasets (from near-IR to sub-mm wavelengths). We find that the reference radius is located at 76.4+/-0.4au, and the disk has an eccentricity of 0.076_-0.010_^+0.016^, with the pericenter located on the front side of the disk (north of the star). We find that small dust grains must be preferentially released near the pericenter to explain the observed brightness asymmetry. Even though parent bodies spend more time near the apocenter, the brightness asymmetry implies that collisions happen more frequently near the pericenter of the disk. Our model can successfully reproduce the shape of the outer edge of the disk, without having to invoke an outer planet shepherding the debris disk. With a simple treatment of the effect of the radiation pressure, we conclude that the parent planetesimals are located in a narrow ring of about 3.6au in width.
- ID:
- ivo://CDS.VizieR/J/ApJ/754/62
- Title:
- HRDS III. HII region kinematic distances
- Short Name:
- J/ApJ/754/62
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using the H I emission/absorption method, we resolve the kinematic distance ambiguity and derive distances for 149 of 182 (82%) H II regions discovered by the Green Bank Telescope H II Region Discovery Survey (GBT HRDS). The HRDS is an X-band (9 GHz, 3 cm) GBT survey of 448 previously unknown H II regions in radio recombination line and radio continuum emission. Here, we focus on HRDS sources from 67{deg}>={ell}>=18{deg}, where kinematic distances are more reliable. The 25 HRDS sources in this zone that have negative recombination line velocities are unambiguously beyond the orbit of the Sun, up to 20kpc distant. They are the most distant H II regions yet discovered. We find that 61% of HRDS sources are located at the far distance, 31% at the tangent-point distance, and only 7% at the near distance. "Bubble" H II regions are not preferentially located at the near distance (as was assumed previously) but average 10 kpc from the Sun. The HRDS nebulae, when combined with a large sample of H II regions with previously known distances, show evidence of spiral structure in two circular arc segments of mean Galactocentric radii of 4.25 and 6.0kpc. We perform a thorough uncertainty analysis to analyze the effect of using different rotation curves, streaming motions, and a change to the solar circular rotation speed. The median distance uncertainty for our sample of H II regions is only 0.5 kpc, or 5%. This is significantly less than the median difference between the near and far kinematic distances, 6 kpc. The basic Galactic structure results are unchanged after considering these sources of uncertainty.
- ID:
- ivo://CDS.VizieR/J/ApJ/764/34
- Title:
- HRDS IV. H, He and C radio recombination lines
- Short Name:
- J/ApJ/764/34
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Green Bank Telescope H II Region Discovery Survey (GBT HRDS) found hundreds of previously unknown Galactic regions of massive star formation by detecting hydrogen radio recombination line (RRL) emission from candidate H II region targets. Since the HRDS nebulae lie at large distances from the Sun, they are located in previously unprobed zones of the Galactic disk. Here, we derive the properties of helium and carbon RRL emission from HRDS nebulae. Our target sample is the subset of the HRDS that has visible helium or carbon RRLs. This criterion gives a total of 84 velocity components (14% of the HRDS) with helium emission and 52 (9%) with carbon emission. For our highest quality sources, the average ^4^He^+^/H^+^ abundance ratio by number, <y^+^>, is 0.068+/-0.023(1{sigma}). This is the same ratio as that measured for the sample of previously known Galactic H II regions. Nebulae without detected helium emission give robust y^+^ upper limits. There are 5 RRL emission components with y^+^ less than 0.04 and another 12 with upper limits below this value. These H II regions must have either a very low ^4^He abundance or contain a significant amount of neutral helium. The HRDS has 20 nebulae with carbon RRL emission but no helium emission at its sensitivity level. There is no correlation between the carbon RRL parameters and the 8um mid-infrared morphology of these nebulae.