- ID:
- ivo://CDS.VizieR/J/ApJS/256/41
- Title:
- Grid of synthetic spectra for subdwarfs
- Short Name:
- J/ApJS/256/41
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- A new grid of detailed atmosphere model spectra for hot and moderately cool subdwarf stars is presented. High-resolution spectra and synthetic photometry are calculated in the range from 1000{AA} to 10,000{AA} using Non-LTE fully line- blanketed atmosphere structures. Our grid covers eight temperatures within 10000<Teff[K]<65000, three surface gravities in the range 4.5<logg[cgs]<6.5, two helium abundances matching two extreme helium-rich and helium-poor scenarios, and two limiting metallicity boundaries regarding both solar ([Fe/H]=0) and Galactic halo ([Fe/H]=-1.5 and [alpha/Fe]=+0.4). Besides its application in the determination of fundamental parameters of subdwarfs in isolation and in binaries, the resulting database is also of interest for population synthesis procedures in a wide variety of stellar systems.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/AJ/159/30
- Title:
- High proper-motion M-type stars spectroscopic obs.
- Short Name:
- J/AJ/159/30
- Date:
- 11 Mar 2022
- Publisher:
- CDS
- Description:
- Large numbers of low-to-medium-resolution spectra of M-type dwarf stars from both the local Galactic disk and halo are available from various surveys. In order to fully exploit these data, we develop a template-fit method using a set of empirically assembled M dwarf/subdwarf classification templates, based on the measurements of the TiO and CaH molecular bands near 7000{AA}, which are used to classify M dwarfs/subdwarfs by spectral type and metallicity class. We further present a pipeline to automatically determine the effective temperature Teff, metallicity [M/H], {alpha}-element to iron abundance ratio [{alpha}/Fe], and surface gravity logg of M dwarfs/subdwarfs using the latest version of BT-Settl model atmospheres. We apply these methods to a set of low-to-medium-resolution spectra of 1544 high proper-motion ({mu}>=0.4"/yr) M dwarfs/subdwarfs, collected at the MDM observatory, Lick Observatory, Kitt-Peak National Observatory, and Cerro-Tololo Interamerican Observatory.
- ID:
- ivo://CDS.VizieR/J/MNRAS/318/1206
- Title:
- High proper motion stars in SA 94
- Short Name:
- J/MNRAS/318/1206
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have applied the astrometric techniques devised by Murray (1986MNRAS.223..649M) for analysis of 48-inch Schmidt photographic data to SuperCOSMOS scans of UK Schmidt plates centred on Kapteyn's Selected Area 94 (RA=2h53m, DE=0{deg}). In this preliminary study, we combine astrometric data from four short-exposure V-band plates, taken in 1987 August (2 plates) and 1993 August (2 plates), with BVRI photometry from sky-limited plate material, to identify stars with proper motions exceeding 0.1"/yr. This paper discusses the completeness of the resulting sample and presents spectroscopy of 30 stars with {mu}>0.2"/yr. Based on the latter observations and the distribution in the [H_V_, (V-I)] reduced proper-motion diagram, we have classified stars in the complete sample as candidate white dwarfs, main-sequence dwarfs and halo subdwarfs, and derived estimates of the disc and halo luminosity functions.
- ID:
- ivo://CDS.VizieR/J/A+A/576/A44
- Title:
- Hot subdwarf binaries from MUCHFUSS
- Short Name:
- J/A+A/576/A44
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The project Massive Unseen Companions to Hot Faint Underluminous Stars from SDSS (MUCHFUSS) aims at finding hot subdwarf stars with massive compact companions like massive white dwarfs (M>1.0M_{sun}_), neutron stars, or stellar-mass black holes. The existence of such systems is predicted by binary evolution theory, and recent discoveries indicate that they exist in our Galaxy. We present orbital and atmospheric parameters and put constraints on the nature of the companions of 12 close hot subdwarf B star (sdB) binaries found in the course of the MUCHFUSS project. The systems show periods between 0.14 and 7.4days. In nine cases the nature of the companions cannot be constrained unambiguously whereas three systems most likely have white dwarf companions. We find that the companion to SDSSJ083006.17+475150.3 is likely to be a rare example of a low-mass helium-core white dwarf. SDSSJ095101.28+034757.0 shows an excess in the infrared that probably originates from a third companion in a wide orbit, which makes this system the second candidate hierarchical triple system containing an sdB star. SDSSJ113241.58-063652.8 is the first helium deficient sdO star with a confirmed close companion. This study brings to 142 the number of sdB binaries with orbital periods of less than 30 days and with measured mass functions. We present an analysis of the minimum companion mass distribution and show that it is bimodal. One peak around 0.1M_{sun}_ corresponds to the low-mass main sequence (dM) and substellar companions. The other peak around 0.4M_{sun}_ corresponds to the white dwarf companions. The derived masses for the white dwarf companions are significantly lower than the average mass for single carbon-oxygen white dwarfs. In a T_eff_-logg diagram of sdB+dM companions, we find signs that the sdB components are more massive than the rest of the sample. The full sample was compared to the known population of extremely low-mass white dwarf binaries as well as short-period white dwarfs with main sequence companions. Both samples show a significantly different companion mass distribution indicating either different selection effects or different evolutionary paths. We identified 16 systems where the dM companion will fill its Roche Lobe within a Hubble time and will evolve into a cataclysmic variable; two of them will have a brown dwarf as donor star. Twelve systems with confirmed white dwarf companions will merge within a Hubble time, two of them having a mass ratio to evolve into a stable AMCVn-type binary and another two which are potential supernova Ia progenitor systems. The remaining eight systems will most likely merge and form RCrB stars or massive C/O white dwarfs depending on the structure of the white dwarf companion.
- ID:
- ivo://CDS.VizieR/J/A+A/317/689
- Title:
- Hot subdwarfs proper motions
- Short Name:
- J/A+A/317/689
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on first results from an ongoing program to measure and analyze proper motions for hot subdwarf and white dwarf stars, with the aim of determining to which stellar population sdB stars (in the V magnitude range 10.5 to 14.5) belong. Ours is the largest sample of hot subdwarf proper motions measured to date. Our kinematic analysis suggests that the parent population of these hydrogen-rich sdB stars is as old or older than the old disk. We measure the absolute magnitude of the sdB in the field as M_V_=4.5, providing independent confirmation of absolute V magnitude estimates for these stars from clusters and spectroscopic analyses. Provided it can be shown that the sdO stars evolve from the sdB, then the sdO absolute V magnitude distribution is about 1 magnitude brighter than for the sdB, and 1 magnitude wider.
- ID:
- ivo://CDS.VizieR/J/A+A/642/A180
- Title:
- Hot subdwarf stars binarity
- Short Name:
- J/A+A/642/A180
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Hot subdwarfs are core-helium burning stars that show lower masses and higher temperatures than canonical horizontal branch stars. They are believed to be formed when a red giant suffers an extreme mass-loss episode. Binary interaction is suggested to be the main formation channel, but the high fraction of apparently single hot subdwarfs (up to 30%) has prompted single star formation scenarios to be proposed. We investigate the possibility that hot subdwarfs could form without interaction by studying wide binary systems. If single formation scenarios were possible, there should be hot subdwarfs in wide binaries that have undergone no interaction. Angular momentum accretion during interaction is predicted to cause the hot subdwarf companion to spin up to the critical velocity. The effect of this should still be observable given the timescales of the hot subdwarf phase. To study the rotation rates of companions, we have analysed light curves from the Transiting Exoplanet Survey Satellite for all known hot subdwarfs showing composite spectral energy distributions indicating the presence of a main sequence wide binary companion. If formation without interaction were possible, that would also imply the existence of hot subdwarfs in very wide binaries that are not predicted to interact. To identify such systems, we have searched for common proper motion companions with projected orbital distances of up to 0.1pc to all known spectroscopically confirmed hot subdwarfs using Gaia DR2 astrometry. We find that the companions in composite hot subdwarfs show short rotation periods when compared to field main sequence stars. They display a triangular-shaped distribution with a peak around 2.5 days, similar to what is observed for young open clusters. We also report a shortage of hot subdwarfs with candidate common proper motion companions. We identify only 16 candidates after probing 2938 hot subdwarfs with good astrometry. Out of those, at least six seem to be hierarchical triple systems, in which the hot subdwarf is part of an inner binary. The observed distribution of rotation rates for the companions in known wide hot subdwarf binaries provides evidence of previous interaction causing spin-up. Additionally, there is a shortage of hot subdwarfs in common proper motion pairs, considering the frequency of such systems among progenitors. These results suggest that binary interaction is always required for the formation of hot subdwarfs.
- ID:
- ivo://CDS.VizieR/J/ApJ/868/70
- Title:
- Hot subdwarf stars from Gaia DR2 and LAMOST DR5
- Short Name:
- J/ApJ/868/70
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We selected 4593 hot subdwarf candidates from the Gaia DR2 Hertzsprung-Russell (HR) diagram. By combining the sample with Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST) DR5, we identified 294 hot subdwarf stars, including 169 sdB, 63 sdOB, 31 He-sdOB, 22 sdO, 7 He-sdO, and 2 He-sdB stars. The atmospheric parameters (e.g., Teff, logg, log(nHe/nH)) are obtained by fitting the hydrogen (H) and helium (He) line profiles with synthetic spectra. Two distinct He sequences of hot subdwarf stars are clearly presented in the Teff-logg diagram. We found that the He-rich sequence consists of the bulk of sdB and sdOB stars, as well as all of the He-sdB, He-sdO, and He-sdOB stars in our samples, while all the stars in the He-weak sequence belong to the sdO spectral type, combined with a few sdB and sdOB stars. We demonstrated that the combination of Gaia DR2 and LAMOST DR5 allows one to uncover a huge number of new hot subdwarf stars in our Galaxy.
- ID:
- ivo://CDS.VizieR/J/ApJ/881/135
- Title:
- Hot subdwarf stars from Gaia DR2 and LAMOST DR5. II.
- Short Name:
- J/ApJ/881/135
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Three hundred and eighty eight hot subdwarf stars have been identified by using the Hertzsprung-Russell (HR) diagram built from the second data release of the Gaia mission. By analyzing their observed Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST) spectra, we characterized 186 sdB, 73 He-sdOB, 65 sdOB, 45 sdO, 12 He-sdO, and 7 He-sdB stars. The atmospheric parameters of these stars (e.g., Teff, logg, log(nHe/nH)) are obtained by fitting the hydrogen (H) and helium (He) line profiles with synthetic spectra calculated from non-local thermodynamic equilibrium model atmospheres. Among these stars, we have 135 new identified hot subdwarfs which have not been cataloged before. Although 253 stars appear in the catalog by Geier+ (2017, J/A+A/600/A50), only 91 of them have atmospheric parameters. Together with the 294 hot subdwarf stars found by Lei+ (Paper I, 2018, J/ApJ/868/70), we identified 682 hot subdwarf stars in total by using the Gaia HR-diagram and LAMOST spectra. These results demonstrate the efficiency of our method to combine large surveys to search for hot subdwarf stars. We found a distinct gap in our He-sdOB stars based on their He abundance, which is also presented in extreme horizontal branch (EHB) stars of the globular cluster {omega} Cen. The number fraction of the sample size for the two subgroups is very different between the two counterparts. However, the distinct gap between the H-sdB stars and He-sdOB stars in {omega} Cen is not visible in our sample. More interestingly, the He-sdB population with the highest He abundance in our sample is completely missing in {omega} Cen. The discrepancy between our field hot subdwarf stars and the EHB stars in {omega} Cen indicate different origins for the two counterparts.
- ID:
- ivo://CDS.VizieR/J/ApJ/889/117
- Title:
- Hot subdwarf stars from Gaia DR2 & LAMOST DR6+7. I.
- Short Name:
- J/ApJ/889/117
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- 182 single-lined hot subdwarf stars are identified by using spectra from the sixth and seventh data releases (DR6 and DR7) of the Large Sky Area Multi-Object Fibre Spectroscopic Telescope survey. We classified all the hot subdwarf stars using a canonical classification scheme, and got 89 sdB, 37 sdOB, 26 sdO, 24 He-sdOB, 3 He-sdO, and 3 He-sdB stars, respectively. Among these stars, 108 hot subdwarfs are newly discovered, while 74 stars were reported by previous catalogs. The atmospheric parameters of these stars were obtained by fitting the hydrogen (H) and helium (He) lines with non-local thermodynamic equilibrium model atmospheres. The atmospheric parameters confirm the two He sequences and the two subgroups of He-sdOB stars in our samples, which were found by previous studies in the T_eff_-log(nHe/nH) diagram. Our results demonstrate different origins of field hot subdwarf stars and extreme horizontal branch stars in globular clusters, and provide strict observational limits on the formation and evolution models of the different sub-types of these evolved objects. Based on the results, we evaluated the completeness of the Geier+ (2017, J/A+A/600/A50) catalog. We found the fraction of hot subwarf stars is between 10% and 60%, depending on the brightness of the sample. A more accurate estimation for the hot subdwarf fraction can be obtained when similar results from composite spectra will become available.
- ID:
- ivo://CDS.VizieR/J/ApJ/818/202
- Title:
- Hot subdwarf stars in LAMOST DR1
- Short Name:
- J/ApJ/818/202
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a catalog of 166 spectroscopically identified hot subdwarf stars from LAMOST DR1, 44 of which show the characteristics of cool companions in their optical spectra. Atmospheric parameters of 122 subdwarf stars with non-composite spectra were measured by fitting the profiles of hydrogen (H) and helium (He) lines with synthetic spectra from non-LTE model atmospheres. A unique property of our sample is that it covers a large range in apparent magnitude and galactic latitude, therefore it contains a mix of stars from different populations and galactic environments.
