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24631. White dwarfs from the Kiso survey
ID:
ivo://CDS.VizieR/J/ApJ/714/1037
Title:
White dwarfs from the Kiso survey
Short Name:
J/ApJ/714/1037
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a spectroscopic analysis of white dwarfs found in the Kiso survey. Spectroscopic observations at high signal-to-noise ratio have been obtained for all DA and DB stars in the Kiso Schmidt ultraviolet excess survey (KUV stars). These observations led to the reclassification of several KUV objects, including the discovery of three unresolved DA+DB double-degenerate binaries. The atmospheric parameters (T_eff_ and logg) are obtained from detailed model atmosphere fits to optical spectroscopic data. The mass distribution of our sample is characterized by a mean value of 0.606M_{sun}_ and a dispersion of 0.135M_{sun}_ for DA stars, and 0.758M_{sun}_ and a dispersion of 0.192M_{sun}_ for DB stars. Absolute visual magnitudes obtained from our spectroscopic fits allow us to derive an improved luminosity function for the DA and DB stars identified in the Kiso survey. Our luminosity function is found to be significantly different from earlier estimates based on empirical photometric calibrations of M_V_ for the same sample. The results for the DA stars now appear entirely consistent with those obtained for the PG survey using the same spectroscopic approach. The space density for DA stars with M_V_<=12.75 is 2.80x10^-4^pc^-3^ in the Kiso survey, which is 9.6% smaller than the value found in the PG survey.
24632. White dwarfs in Galactic plane
ID:
ivo://CDS.VizieR/J/MNRAS/457/1988
Title:
White dwarfs in Galactic plane
Short Name:
J/MNRAS/457/1988
Date:
21 Oct 2021
Publisher:
CDS
Description:
We investigated the prospects for systematic searches of white dwarfs at low Galactic latitudes, using the VLT Survey Telescope H{alpha} Photometric Survey of the Galactic plane and Bulge (VPHAS+). We targeted 17 white dwarf candidates along sightlines of known open clusters, aiming to identify potential cluster members. We confirmed all the 17 white dwarf candidates from blue/optical spectroscopy, and we suggest five of them to be likely cluster members. We estimated progenitor ages and masses for the candidate cluster members, and compare our findings to those for other cluster white dwarfs. A white dwarf in NGC 3532 is the most massive known cluster member (1.13M_{sun}_), likely with an oxygen-neon core, for which we estimate an M_{sun}_ progenitor, close to the mass-divide between white dwarf and neutron star progenitors. A cluster member in Ruprecht 131 is a magnetic white dwarf, whose progenitor mass exceeded 2-3M_{sun}_. We stress that wider searches, and improved cluster distances and ages derived from data of the ESA Gaia mission, will advance the understanding of the mass-loss processes for low- to intermediate-mass stars.
24633. White dwarfs in SDSS Stripe 82
ID:
ivo://CDS.VizieR/J/MNRAS/473/3241
Title:
White dwarfs in SDSS Stripe 82
Short Name:
J/MNRAS/473/3241
Date:
21 Oct 2021
Publisher:
CDS
Description:
Binary evolution theory predicts that accreting white dwarfs with substellar companions dominate the Galactic population of cataclysmic variables (CVs). In order to test these predictions, it is necessary to identify these systems, which may be difficult if the signatures of accretion become too weak to be detected. The only chance to identify such 'dead' CVs is by exploiting their close binary nature. We have therefore searched the Sloan Digital Sky Survey (SDSS) Stripe 82 area for apparently isolated white dwarfs that undergo eclipses by a dark companion. We found no such eclipses in either the SDSS or Palomar Transient Factory data sets among our sample of 2264 photometrically selected white dwarf candidates within Stripe 82. This null result allows us to set a firm upper limit on the space density, {rho}0, of dead CVs. In order to determine this limit, we have used Monte Carlo simulations to fold our selection criteria through a simple model of the Galactic CV distribution. Assuming a T_WD_=7500K, the resulting 2{sigma} limit on the space density of dead CVs is {rho}0<~2x10^-5^pc^-3^, where TWD is the typical effective temperature of the white dwarf in such systems.
24634. White Dwarfs in the SDSS
ID:
ivo://CDS.VizieR/J/AJ/126/1023
Title:
White Dwarfs in the SDSS
Short Name:
J/AJ/126/1023
Date:
21 Oct 2021
Publisher:
CDS
Description:
An initial assessment is made of white dwarf and hot subdwarf stars observed in the Sloan Digital Sky Survey. In a small area of sky (190 square degrees), observed much like the full survey will be, 269 white dwarfs (WDs) and 56 hot subdwarfs are identified spectroscopically where only 44 white dwarfs and five hot subdwarfs were known previously. Most are ordinary DA (hydrogen atmosphere) and DB (helium) types. In addition, in the full survey to date, a number of WDs have been found with uncommon spectral types. Among these are blue DQ stars displaying lines of atomic carbon; red DQ stars showing molecular bands of C2 with a wide variety of strengths; DZ stars where Ca and occasionally Mg, Na, and/or Fe lines are detected; and magnetic WDs with a wide range of magnetic field strengths in DA, DB, DQ, and (probably) DZ spectral types. Photometry alone allows identification of stars hotter than 12000K, and the density of these stars for magnitude g 15<g<20 is found to be ~2.2deg^-2^ at Galactic latitudes of 29{deg}-62{deg}. Spectra are obtained for roughly half of these hot stars. The spectra show that for 15<g<17, 40% of hot stars are WDs, and the fraction of WDs rises to ~90% at g=20. The remainder are hot sdB and sdO stars.
24635. White dwarfs in 47 Tuc (NGC 104) with HST
ID:
ivo://CDS.VizieR/J/AJ/143/50
Title:
White dwarfs in 47 Tuc (NGC 104) with HST
Short Name:
J/AJ/143/50
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a new distance determination to the Galactic globular cluster 47 Tucanae (47 Tuc, NGC 104) by fitting the spectral energy distributions of its white dwarfs (WDs) to pure hydrogen atmosphere WD models. Our photometric data set is obtained from a 121-orbit Hubble Space Telescope program using the Wide Field Camera 3 UVIS/IR channels, capturing F390W, F606W, F110W, and F160W images. These images cover more than 60 arcmin^2^ and extend over a radial range of 5-13.7arcmin (6.5-17.9pc) within the globular cluster. Using a likelihood analysis, we obtain a best-fitting unreddened distance modulus of (m-M)_o_=13.36+/-0.02+/-0.06 corresponding to a distance of 4.69+/-0.04+/-0.13kpc, where the first error is random and the second is systematic. We also search the WD photometry for infrared excess in the F160W filter, indicative of low-mass companions, and find no convincing cases within our sample.
24636. White dwarfs with cool companions
ID:
ivo://CDS.VizieR/J/ApJ/586/1356
Title:
White dwarfs with cool companions
Short Name:
J/ApJ/586/1356
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present near-infrared (IR) magnitudes for all white dwarfs (selected from the catalog of McCook & Sion, 1999, See Cat. <III/235>) contained in the Two Micron All-Sky Survey second incremental data release (2MASS 2IDR, Cat. <II/241>). We show that the near-IR color-color diagram is an effective means of identifying candidate binary stars containing a WD and a low-mass, main-sequence star. The loci of single WDs and WD+red dwarf binaries occupy distinct regions of the near-IR color-color diagram. We recovered all known unresolved WD+red dwarf binaries located in the 2IDR sky coverage and also identified as many new candidate binaries (47 new candidates out of 95 total). Using observational near-IR data for WDs and M-L dwarfs, we have compared a sample of simulated WD+red dwarf binaries with our 2MASS data. The colors of the simulated binaries are dominated by the low-mass companion through the late M to early L spectral types. As the spectral type of the companion becomes progressively later, however, the colors of unresolved binaries become progressively bluer. Binaries containing the lowest mass companions will be difficult to distinguish from single WDs solely on the basis of their near-IR colors.
24637. White dwarfs within 25pc of the Sun
ID:
ivo://CDS.VizieR/J/AJ/147/129
Title:
White dwarfs within 25pc of the Sun
Short Name:
J/AJ/147/129
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the fractional distribution of spectroscopic subtypes, range and distribution of surface temperatures, and kinematical properties of the white dwarfs (WDs) within 25pc of the Sun. There is no convincing evidence of halo WDs in the total 25pc sample of 224 WDs. There is also little to suggest the presence of genuine thick disk subcomponent members within 25pc. It appears that the entire 25pc sample likely belongs to the thin disk. We also find no significant kinematic differences with respect to spectroscopic subtypes. The total DA to non-DA ratio of the 25pc sample is 1.8, a manifestation of deepening envelope convection, which transforms DA stars with sufficiently thin H surface layers into non-DAs. We compare this ratio with the results of other studies. We find that at least 11% of the WDs within 25pc of the Sun (the DAZ and DZ stars) have photospheric metals that likely originate from accretion of circumstellar material (debris disks) around them. If this interpretation is correct, then it suggests the possibility that a similar percentage have planets, asteroid-like bodies, or debris disks orbiting them. Our volume-limited sample reveals a pileup of DC WDs at the well-known cutoff in DQ WDs at T_eff_~6000K. Mindful of small number statistics, we speculate on its possible evolutionary significance. We find that the incidence of magnetic WDs in the 25pc sample is at least 8% in our volume-limited sample, dominated by cool WDs. We derive approximate formation rates of DB and DQ degenerates and present a preliminary test of the evolutionary scenario that all cooling DB stars become DQ WDs via helium convective dredge-up with the diffusion tail of carbon extending upward from their cores.
24638. White-light flares models
ID:
ivo://CDS.VizieR/J/A+AS/110/99
Title:
White-light flares models
Short Name:
J/A+AS/110/99
Date:
21 Oct 2021
Publisher:
CDS
Description:
Based on detailed analyses of the solar white-light flares (WLFs) of 1974 September 10, 1979 September 19 and 1991 October 24, the characteristics of two types of WLFs have been distinguished.
24639. White-light flares on close binaries from Kepler
ID:
ivo://CDS.VizieR/J/ApJS/224/37
Title:
White-light flares on close binaries from Kepler
Short Name:
J/ApJS/224/37
Date:
21 Oct 2021
Publisher:
CDS
Description:
Based on Kepler data, we present the results of a search for white light flares on 1049 close binaries. We identify 234 flare binaries, of which 6818 flares are detected. We compare the flare-binary fraction in different binary morphologies ("detachedness"). The result shows that the fractions in over-contact and ellipsoidal binaries are approximately 10%-20% lower than those in detached and semi-detached systems. We calculate the binary flare activity level (AL) of all the flare binaries, and discuss its variations along the orbital period (P_orb_) and rotation period (P_rot_, calculated for only detached binaries). We find that the AL increases with decreasing P_orb_ or P_rot_, up to the critical values at P_orb_~3 days or P_rot_~1.5 days, and thereafter the AL starts decreasing no matter how fast the stars rotate. We examine the flaring rate as a function of orbital phase in two eclipsing binaries on which a large number of flares are detected. It appears that there is no correlation between flaring rate and orbital phase in these two binaries. In contrast, when we examine the function with 203 flares on 20 non-eclipse ellipsoidal binaries, bimodal distribution of amplitude-weighted flare numbers shows up at orbital phases 0.25 and 0.75. Such variation could be larger than what is expected from the cross section modification.
24640. White-light flares on cool stars from Kepler
ID:
ivo://CDS.VizieR/J/AJ/141/50
Title:
White-light flares on cool stars from Kepler
Short Name:
J/AJ/141/50
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the results of a search for white-light flares on ~23000 cool dwarfs in the Kepler Quarter 1 long cadence data. We have identified 373 flaring stars, some of which flare multiple times during the observation period. We calculate relative flare energies, flare rates, and durations and compare these with the quiescent photometric variability of our sample.

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