- ID:
- ivo://CDS.VizieR/J/AJ/125/2239
- Title:
- Hard X-ray emission from white dwarfs
- Short Name:
- J/AJ/125/2239
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Inspired by the hard X-ray emission from WD 2226-210, the central star of the Helix Nebula, we have made a systematic search for similar sources by correlating the white dwarf catalog of McCook & Sion (1999, See Cat. <III/235>) and the ROSAT Position Senstive Proportional Counter (PSPC) point-source catalog of White et al. (2000, Cat. <IX/31>). We find 76 white dwarfs coincident with X-ray sources at a high level of confidence. Among these sources, 17 show significant hard X-ray emission at energies greater than 0.5keV. Twelve of these white dwarfs with hard X-ray emission are in known binary systems, in two of which the accretion of the close companion's material onto the white dwarf produces hard X-ray emission, and in the other 10 the late-type companions' coronal activity emits hard X-rays. One apparently single white dwarf is projected near an active galactic nucleus that is responsible for the hard X-ray emission. The remaining four white dwarfs and two additional white dwarfs with hard X-ray emission appear single.
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Search Results
- ID:
- ivo://CDS.VizieR/J/AJ/127/477
- Title:
- Hard X-ray emissions of white dwarfs
- Short Name:
- J/AJ/127/477
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have previously conducted a search for X-ray sources coincident with white dwarfs using the white dwarf catalog compiled by McCook & Sion (1999, Cat. <III/210>, <III/235>) and the ROSAT sources in the WGA (<IX/31>) Catalog (Paper I, O'Dwyer et al., 2003AJ....125.2239O). To include the white dwarfs discovered since 1999 and to include the X-ray sources detected in ROSAT Position Sensitive Proportional Counter (PSPC, <IX/30>) observations made with a boron filter, we have carried out another search using an updated list of white dwarfs and the final catalogs of the ROSAT PSPC observations with and without a boron filter. Forty-seven new X-ray sources convincingly coincident with white dwarfs are found and reported in this paper.
- ID:
- ivo://CDS.VizieR/J/ApJ/892/L35
- Title:
- He+He white dwarf SDSSJ232230.20+050942.0 RVels
- Short Name:
- J/ApJ/892/L35
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the discovery of a 1201s orbital period binary, the third shortest-period detached binary known. Sloan Digital Sky Survey J232230.20+050942.06 contains two He-core white dwarfs orbiting with a 27{deg} inclination. Located 0.76kpc from the Sun, the binary has an estimated Laser Interferometer Space Antenna (LISA) 4yr signal-to-noise ratio of 40. J2322+0509 is the first He+He white dwarf LISA verification binary, a source class that is predicted to account for one-third of resolved LISA ultra-compact binary detections.
- ID:
- ivo://CDS.VizieR/J/ApJ/885/74
- Title:
- 1340 Helium rich white dwarfs in the Gaia era
- Short Name:
- J/ApJ/885/74
- Date:
- 09 Mar 2022 22:00:00
- Publisher:
- CDS
- Description:
- We present an analysis of 1023 DBZ/DZ(A) and 319 DQ white dwarf stars taken from the Montreal White Dwarf Database. This represents a significant increase over the previous comprehensive studies on these types of objects. We use new trigonometric parallax measurements from the Gaia second data release, together with photometry from the Sloan Digital Sky Survey, Pan-STARRS, Gaia, or BVRI from the literature, which allow the determination of the mass for the majority of the objects in our sample. We use the photometric and spectroscopic techniques with our recently improved model atmospheres code, which include high-density effects, to accurately determine the effective temperature, surface gravity, and heavy-element abundances for each object. We study the abundance of hydrogen in DBZ/DZ white dwarfs and the properties of the accreted planetesimals. We explore the nature of the second sequence of DQ stars using proper motions from Gaia and highlight evidence of crystallization in massive DQ stars. We also present mass distributions for both spectral types. Finally, we discuss the implications of our findings in the context of the spectral evolution of white dwarfs and provide the atmospheric parameters for each star.
- ID:
- ivo://CDS.VizieR/J/MNRAS/429/2143
- Title:
- Hidden population of AM CVns in the SDSS
- Short Name:
- J/MNRAS/429/2143
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the latest results from a spectroscopic survey designed to uncover the hidden population of AM Canum Venaticorum (AM CVn) binaries in the photometric database of the Sloan Digital Sky Survey (SDSS). We selected ~2000 candidates based on their photometric colours, a relatively small sample which is expected to contain the majority of all AM CVn binaries in the SDSS (expected to be ~50). We present two new candidate AM CVn binaries discovered using this strategy: SDSS J104325.08+563258.1 and SDSS J173047.59+554518.5. We also present spectra of 29 new cataclysmic variables, 23 DQ white dwarfs and 21 DZ white dwarfs discovered in this survey. The survey is now approximately 70 per cent complete, and the discovery of seven new AM CVn binaries indicates a lower space density than previously predicted. From the essentially complete g~19 sample, we derive an observed space density of (5+/-3)*10^-7^pc^-3^; this is lower than previous estimates by a factor of 3. The sample has been cross-matched with the GALEX All-Sky Imaging Survey database, and with Data Release 9 of the UKIRT (United Kingdom Infrared Telescope) Infrared Deep Sky Survey (UKIDSS). The addition of UV photometry allows new colour cuts to be applied, reducing the size of our sample to ~1100 objects. Optimising our followup should allow us to uncover the remaining AM CVn binaries present in the SDSS, providing the larger homogeneous sample required to more reliably estimate their space density.
- ID:
- ivo://CDS.VizieR/J/ApJ/886/100
- Title:
- High-mass white dwarfs in Gaia DR2
- Short Name:
- J/ApJ/886/100
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Revealed by Gaia DR2, the Q branch is a narrow and prominent branch of white dwarf overdensity on the H-R diagram. We find that there are significantly more fast-moving white dwarfs on the Q branch, which have very old true ages but young photometric ages. This age discrepancy suggests a cooling anomaly in some white dwarfs on the Q branch, posing a challenge to current white dwarf cooling models. We tabulate the information of nearby high-mass white dwarfs (d<250, 1.08<m_WD<1.23), which is used to investigate the Q branch and its physical origin in Cheng et al. (2019). This table contains the WD name, photometry and astrometry from Gaia DR2, H-R diagram coordinates and transverse velocity that we derive, and spectral information from Montreal White Dwarf Database (MWDD).
- ID:
- ivo://CDS.VizieR/J/MNRAS/425/1394
- Title:
- High proper-motion white dwarfs
- Short Name:
- J/MNRAS/425/1394
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We conducted a spectropolarimetric survey of 58 high proper-motion white dwarfs which achieved uncertainties of >~2kG in the H{alpha} line and >~5kG in the upper Balmer line series. The survey aimed at detecting low magnetic fields (<~100kG) and helped identify the new magnetic white dwarfs NLTT2219, with a longitudinal field B_l_=-97kG, and NLTT10480 (B_l_=-212kG). Furthermore, we report the possible identification of a very low-field white dwarf with B_l_=-4.6kG. The observations show that ~~5 per cent of white dwarfs harbour low fields (~10 to ~10^2^kG) and that increased survey sensitivity may help uncover several new magnetic white dwarfs with fields below ~1kG. A series of observations of the high-field white dwarf NLTT12758 revealed changes in polarity occurring within an hour possibly associated with an inclined, fast rotating dipole. Also, the relative strength of the {pi} and {sigma} components in NLTT12758 possibly revealed the effect of a field concentration ('spot'), or, most likely, the presence of a non-magnetic white dwarf companion. Similar observations of NLTT13015 also showed possible polarity variations, but without a clear indication of the time-scale. The survey data also proved useful in constraining the chemical composition, age and kinematics of a sample of cool white dwarfs as well as in constraining the incidence of double degenerates.
- ID:
- ivo://CDS.VizieR/J/ApJ/818/L7
- Title:
- High-speed photometry obs. of WD 1145+017 syst.
- Short Name:
- J/ApJ/818/L7
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We obtained high-speed photometry of the disintegrating planetesimals orbiting the white dwarf WD 1145+017, spanning a period of four weeks. The light curves show a dramatic evolution of the system since the first observations obtained about seven months ago. Multiple transit events are detected in every light curve, which have varying durations (~=3-12 minutes) and depths (~=10%-60%). The time-averaged extinction is ~=11%, much higher than at the time of the Kepler observations. The shortest-duration transits require that the occulting cloud of debris has a few times the size of the white dwarf, longer events are often resolved into the superposition of several individual transits. The transits evolve on timescales of days, both in shape and in depth, with most of them gradually appearing and disappearing over the course of the observing campaign. Several transits can be tracked across multiple nights, all of them recur on periods of ~=4.49hr, indicating multiple planetary debris fragments on nearly identical orbits. Identifying the specific origin of these bodies within this planetary system, and the evolution leading to their current orbits remains a challenging problem.
- ID:
- ivo://CDS.VizieR/J/ApJS/231/1
- Title:
- Hot DA white dwarfs grid of synthetic spectra
- Short Name:
- J/ApJS/231/1
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this work we present a grid of LTE and non-LTE synthetic spectra of hot DA white dwarfs (WDs). In addition to its usefulness for the determination of fundamental stellar parameters of isolated WDs and in binaries, this grid will be of interest for the construction of theoretical libraries for stellar studies from integrated light. The spectral grid covers both a wide temperature and gravity range, with 17000K<=Teff<=100000K and 7.0<=log(g)<=9.5. The stellar models are built for pure hydrogen and the spectra cover a wavelength range from 900{AA} to 2.5um. Additionally, we derive synthetic HST/ACS, HST/WFC3, Bessel UBVRI, and SDSS magnitudes. The grid was also used to model integrated spectral energy distributions of simple stellar populations and our modeling suggests that DAs might be detectable in ultraviolet bands for populations older than ~8Gyr.
- ID:
- ivo://CDS.VizieR/J/AJ/162/188
- Title:
- Hot degenerates in the MCT survey. III.
- Short Name:
- J/AJ/162/188
- Date:
- 21 Mar 2022 00:13:43
- Publisher:
- CDS
- Description:
- We present optical spectra of 144 white dwarfs detected in the Montreal-Cambridge-Tololo colorimetric survey, including 120 DA, 12 DB, 4 DO, 1 DQ, and 7 DC stars. We also perform a model atmosphere analysis of all objects in our sample using the so-called spectroscopic technique, or the photometric technique in the case of DC white dwarfs. The main objective of this paper is to contribute to the ongoing effort of confirming spectroscopically all white dwarf candidates in the Gaia survey, in particular in the southern hemisphere. All our spectra are made available in the Montreal White Dwarf Database.
