- ID:
- ivo://CDS.VizieR/J/A+A/547/A96
- Title:
- Low-mass He-core white dwarfs seismic properties
- Short Name:
- J/A+A/547/A96
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present detailed tabulations of stellar models and pulsational properties for low-mass He-core white dwarf stars, for different stellar masses and effective temperatures. Pulsation periods were computed for g- and p-modes with harmonic degree l=1. The stellar mass ranges from 0.17M_{sun} to 0.45M_{sun}, while the effective temperature ranges from 13000 to 8000K. The pulsation periods are listed in files named ava_m.mmm_g.tgz and ava_m.mmm_p.tgz, for g- and p-modes, respectively, were m.mmm denotes the stellar mass in solar mass units. These files contain a sequence of tables (avannn_m.mmm_g.out and avannn_m.mmm_p.out) corresponding to models with decreasing effective temperature, where nnn correspond to the number of file, starting with nnn=001. In each avannn_m.mmm_g.out and avannn_m.mmm_p.out files, the following quantities are listed: harmonic degree (l), radial order (k), Period, period spacing (DP), kinetic energy (log(Ek)) and first order rotation splitting coefficient (C_kl). The stellar parameters characterizing each model are listed at the top of the table as a header: stellar mass in solar units (M_*/M_{sun}), luminosity in solar units (L_*/L_{sun}), effective temperature in Kelvin (Teff[K]), hydrogen mass in units of the stellar mass (log(M_H/M_*)), age in millions of years (Time [10^6^yr]), and asymptotic period spacing in seconds (DPa [s], for g-modes only). The chemical profiles and critical frequencies are listed in the files par_m.mmm.tgz, which contain a sequence of tables corresponding to models with decreasing effective temperature (parnnn_m.mmm.out). Stellar parameters of each model are listed as a header: stellar mass in solar units (M_*/M_{sun}), effective temperature in Kelvin (Teff[K]), luminosity in solar units (L_*/L_{sun}) and hydrogen mass in units of stellar mass (log(M_H/M_*)). Below the header, the following quantities are listed: normalized radial coordinate (r/R_*), the outer mass fraction coordinate (-log q, with q=1-M_r/M_*), the squared Brunt-Vaisala (N^2^) and Lamb (L^2^) frequencies, the Ledoux term (B Ledoux), and the abundances by mass of hydrogen (H1), helium (He4), carbon (C12) and oxygen (O16).
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/595/A35
- Title:
- Low-mass helium white dwarfs evolutionary models
- Short Name:
- J/A+A/595/A35
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A large number of extremely low-mass helium white dwarfs (ELM WDs) have been discovered in recent years. The majority of them are found in close binary systems suggesting they are formed either through a common-envelope phase or via stable mass transfer in a low-mass X-ray binary (LMXB) or a cataclysmic variable (CV) system. Here, we investigate the formation of these objects through the LMXB channel with emphasis on the proto-WD evolution in environments with different metallicities. We study for the first time the combined ects of rotational mixing and element diffusion (e.g. gravitational settling, thermal and chemical diffusion) on the evolution of proto-WDs and on the cooling properties of the resulting WDs. We present state-of-the-art binary stellar evolution models computed with MESA for metallicities of Z=0.02, 0.01, 0.001 and 0.0002, producing WDs with masses between ~0.16-0.45M_{sun}_. Our results confirm that element diffusion plays a significant role in the evolution of proto-WDs that experience hydrogen shell flashes. The occurrence of these flashes produces a clear dichotomy in the cooling timescales of ELM WDs, which has important consequences e.g. for the age determination of binary millisecond pulsars. In addition, we confirm that the threshold mass at which this dichotomy occurs depends on metallicity. Rotational mixing is found to counteract the effect of gravitational settling in the surface layers of young, bloated ELM proto-WDs and therefore plays a key role in determining their surface chemical abundances, i.e. the observed presence of metals in their atmospheres. We predict that these proto-WDs have helium-rich envelopes through a significant part of their lifetime. This is of great importance as helium is a crucial ingredient in the driving of the {kappa}-mechanism suggested for the newly observed ELM proto-WD pulsators. However, we find that the number of hydrogen shell flashes and, as a result, the hydrogen envelope mass at the beginning of the cooling track, are not influenced significantly by rotational mixing. In addition to being dependent on proto-WD mass and metallicity, the hydrogen envelope mass of the newly formed proto-WDs depends on whether or not the donor star experiences a temporary contraction when the H-burning shell crosses the hydrogen discontinuity left behind by the convective envelope. The hydrogen envelope at detachment, although small compared to the total mass of the WD, contains enough angular momentum such that the spin frequency of the resulting WD on the cooling track is well above the orbital frequency.
- ID:
- ivo://CDS.VizieR/J/MNRAS/471/4218
- Title:
- 4 low-mass white-dwarf candidates velocities
- Short Name:
- J/MNRAS/471/4218
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results from a Gemini snapshot radial-velocity survey of 44 low-mass white-dwarf candidates selected from the Sloan Digital Sky Survey (SDSS) spectroscopy. To find sub-hour orbital period binary systems, our time-series spectroscopy had cadences of 2-8min over a period of 20-30min. Through follow-up observations at Gemini and the MMT, we identify four double-degenerate binary systems with periods ranging from 53min to 7h. The shortest period system, SDSS J123549.88+154319.3, was recently identified as a sub-hour period detached binary by Breedt and collaborators. Here, we refine the orbital and physical parameters of this system. High-speed and time-domain survey photometry observations do not reveal eclipses or other photometric effects in any of our targets. We compare the period distribution of these four systems with the orbital period distribution of known double white dwarfs; the median period decreases from 0.64 to 0.24d for M=0.3-0.5M_{sun}_ to M<0.3M_{sun}_ white dwarfs. However, we do not find a statistically significant correlation between the orbital period and white-dwarf mass.
- ID:
- ivo://CDS.VizieR/III/70
- Title:
- Luyten's White Dwarf Catalogues
- Short Name:
- III/70
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The catalogue includes all probable white dwarf and degenerate stars found in the Proper Motion and Faint Blue Star Surveys conducted by W.J. Luyten. The catalogue was originally published in two booklets, one in 1970 (3035 entries), and the part II in 1977 (3511 entries). As a guideline for the inclusion of stars into this catalogue, the author has used stars which present minimal values of the combined proper motions - magnitude quantity H defined by H = m + 5 + 5 log {mu} ({mu} is the proper motion in arcsec/yr) which show the minimal H values according to the color class: b 13.5 f 15.5 g-k 17.7 a 14.4 g 17.0 k 18.3 with the following exceptions: a) evidence from photoelectric colors or spectra indicate the object is a degenerate star (e.g. LB 3303) or b) the object is close to the antapex (which is the case for many stars at alpha=21h and delta =+42{deg}, plate 234). The bluest stars (color classes b or a) will probably prove to be genuine white dwarfs; probably no more than 40% of the yellower objects (color class k) will prove to be genuine degenerates.
- ID:
- ivo://CDS.VizieR/J/A+A/506/1341
- Title:
- Magnetic fields in white dwarfs
- Short Name:
- J/A+A/506/1341
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A large number of magnetic white dwarfs discovered in the SDSS have so far only been analyzed by visual comparison of the observations with relatively simple models of the radiation transport in a magnetised stellar atmosphere. We model the structure of the surface magnetic fields of the hydrogen-rich white dwarfs in the SDSS.
- ID:
- ivo://CDS.VizieR/J/AJ/130/734
- Title:
- Magnetic white dwarfs from SDSS DR2 and DR3
- Short Name:
- J/AJ/130/734
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Fifty-two magnetic white dwarfs have been identified in spectroscopic observations from the Sloan Digital Sky Survey (SDSS) obtained between mid-2002 and the end of 2004, including Data Releases 2 and 3. Although not as numerous or diverse as the discoveries from the first data release, the collection exhibits polar field strengths ranging from 1.5 to ~1000MG and includes two new unusual atomic DQA examples, a molecular DQ, and five stars that show hydrogen in fields above 500MG. The highest field example, SDSS J2346+3853, may be the most strongly magnetic white dwarf yet discovered. Analysis of the photometric data indicates that the magnetic sample spans the same temperature range as for non-magnetic white dwarfs from the SDSS, and support is found for previous claims that magnetic white dwarfs tend to have larger masses than their non-magnetic counterparts. A glaring exception to this trend is the apparently low-gravity object SDSS J0933+1022, which may have a history involving a close binary companion.
- ID:
- ivo://CDS.VizieR/J/A+A/626/A128
- Title:
- Main-sequence and subgiant Barium stars
- Short Name:
- J/A+A/626/A128
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Barium (Ba) dwarfs and CH subgiants are the less evolved analogues of Ba and CH giants. They are F- to G-type main-sequence stars polluted with heavy elements by their binary companions when the companion was on the asymptotic giant branch (AGB). This companion is now a white dwarf that in most cases cannot be directly detected. We present a large systematic study of 60 objects classified as Ba dwarfs or CH subgiants. Combining radial-velocity measurements from HERMES and SALT high-resolution spectra with radial-velocity data from CORAVEL and CORALIE, we determine the orbital parameters of 27 systems. We also derive their masses by comparing their location in the Hertzsprung-Russell diagram with evolutionary models. We confirm that Ba dwarfs and CH subgiants are not at different evolutionary stages, and that they have similar metallicities, despite their different names. Additionally, Ba giants appear significantly more massive than their main-sequence analogues. This is likely due to observational biases against the detection of hotter main- sequence post-mass-transfer objects. Combining our spectroscopic orbits with the Hipparcos astrometric data, we derive the orbital inclination and the mass of the WD companion for four systems. Since this cannot be done for all systems in our sample yet (but should be possible with upcoming Gaia data releases), we also analyse the mass-function distribution of our binaries. We can model this distribution with very narrow mass distributions for the two components and random orbital orientations on the sky. Finally, based on BINSTAR evolutionary models, we suggest that the orbital evolution of low-mass Ba systems can be affected by a second phase of interactions along the red giant branch of the Ba star, which impact the eccentricities and periods of the giants.
- ID:
- ivo://CDS.VizieR/J/A+A/557/A19
- Title:
- Mass and age of extreme low-mass white dwarfs
- Short Name:
- J/A+A/557/A19
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The number of detected extremely low mass (ELM) white dwarf stars has increased drastically in recent year thanks to the results of many surveys. In addition, some of these stars have been found to exhibit pulsations, making them potential targets for asteroseismology. We provide a fine and homogeneous grid of evolutionary sequences for helium (He) core white dwarfs for the whole range of their expected masses (0.15<~M_*_/M_{sun}_<~0.45), including the mass range for ELM white dwarfs (M_*_/M_{sun}_<~0.20). The grid is appropriate for mass and age determination of these stars, as well as to study their adiatabic pulsational properties. White dwarf sequences have been computed by performing full evolutionary calculations that consider the main energy sources and processes of chemical abundance changes during white dwarf evolution.
- ID:
- ivo://CDS.VizieR/J/A+A/419/L5
- Title:
- Masses and radii of DA white dwarfs in SDSS DR1
- Short Name:
- J/A+A/419/L5
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate the sample of 1175 new nonmagnetic DA white dwarfs with the effective temperatures T_eff_>=12000K, which were extracted from the Data Release 1 of the Sloan Digital Sky Survey. We determined masses, radii, and bolometric luminosities of stars in the sample. The above parameters were derived from the effective temperatures T_eff_ and surface gravities logg published in the DR1, and the new theoretical M-R relations for carbon-core and oxygen-core white dwarfs. Mass distribution of white dwarfs in this sample exhibits the peak at M=0.562M_{sun}_ (carbon-core stars), and the tail towards higher masses. Both the shape of the mass distribution function and the empirical mass-radius relation are practically identical for white dwarfs with either pure carbon or pure oxygen cores.
- ID:
- ivo://CDS.VizieR/J/AJ/129/2428
- Title:
- M dwarf-white dwarf binary systems
- Short Name:
- J/AJ/129/2428
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate the relationship between age and chromospheric activity for 139 M dwarf stars in wide binary systems with white dwarf companions. We present the measured radial velocities and complete space motions for 161 white dwarf stars in wide binaries.
