68 research outputs found
The sdA problem - II. Photometric and Spectroscopic Follow-up
Subdwarf A star (sdA) is a spectral classification given to objects showing
H-rich spectra and sub-main sequence surface gravities, but effective
temperature lower than the zero-age horizontal branch. Their evolutionary
origin is an enigma. In this work, we discuss the results of follow-up
observations of selected sdAs. We obtained time resolved spectroscopy for 24
objects, and time-series photometry for another 19 objects. For two targets, we
report both spectroscopy and photometry observations. We confirm seven objects
to be new extremely-low mass white dwarfs (ELMs), one of which is a known
eclipsing star. We also find the eighth member of the pulsating ELM class.Comment: Accepted for publication in MNRAS. 19 pages, 30 figures, 6 table
The sdA problem - III. New extremely low-mass white dwarfs and their precursors from Gaia astrometry
The physical nature of the sdA stars---cool hydrogen-rich objects with
spectroscopic surface gravities intermediate between main sequence and
canonical mass white dwarfs---has been elusive since they were found in Sloan
Digital Sky Survey Data Release 12 spectra. The population is likely dominated
by metal-poor A/F stars in the halo with overestimated surface gravities, with
a small contribution of extremely low-mass white dwarfs and their precursors,
i.e., ELMs and pre-ELMs. In this work, we seek to identify (pre-)ELMs with
radii smaller than is possible for main sequence stars, allowing even for very
low metallicity. We analyse 3891 sdAs previously identified in the Sloan
Digital Sky Survey using Gaia DR2 data. Our Monte Carlo analysis supports that
90 of these are inconsistent with the main sequence. 37 lie close to or within
the canonical white dwarf cooling sequence, while the remaining 53 lie between
the canonical white dwarfs and main sequence, which we interpret as likely
(pre-)ELMs given their spectral class. Of these, 30 pass more conservative
criteria that allow for higher systematic uncertainties on the parallax, as
well as an approximate treatment of extinction. Our identifications increase
the number of known (pre-)ELMs by up to 50 per cent, demonstrating how Gaia
astrometry can reveal members of the compact (pre-)ELM subpopulation of the sdA
spectral class.Comment: 13 pages, 19 figures, 1 table. Accepted for publication in MNRA
The sdA problem : III. New extremely low-mass white dwarfs and their precursors from Gaia astrometry
The physical nature of the sdA stars – cool hydrogen-rich objects with spectroscopic surface gravities intermediate between main-sequence and canonical-mass white dwarfs – has been elusive since they were found in Sloan Digital Sky Survey Data Release 12 spectra. The population is likely dominated by metal-poor A/F stars in the halo with overestimated surface gravities, with a small contribution of extremely low-mass white dwarfs and their precursors, i.e. ELMs and pre-ELMs. In this work, we seek to identify (pre-)ELMs with radii smaller than what is possible for main-sequence stars, allowing even for very low metallicity. We analyse 3891 sdAs previously identified in the Sloan Digital Sky Survey using Gaia DR2 data. Our Monte Carlo analysis supports that 90 of these are inconsistent with the main sequence. 37 lie close to or within the canonical white dwarf cooling sequence, while the remaining 53 lie between the canonical white dwarfs and main sequence, which we interpret as likely (pre-)ELMs given their spectral class. Of these, 30 pass more conservative criteria that allow for higher systematic uncertainties on the parallax, as well as an approximate treatment of extinction. Our identifications increase the number of known (pre-)ELMs by up to 50 per cent, demonstrating how Gaia astrometry can reveal members of the compact (pre-)ELM subpopulation of the sdA spectral class
White dwarf and subdwarf stars in the Sloan Digital Sky Survey Data Release 14
White dwarfs carry information on the structure and evolution of the Galaxy,
especially through their luminosity function and initial-to-final mass
relation. Very cool white dwarfs provide insight into the early ages of each
population. Examining the spectra of all stars with proper motion in
the Sloan Digital Sky Survey Data Release 14, we report the classification for
20 088 spectroscopically confirmed white dwarfs, plus 415 hot subdwarfs, and
311 cataclysmic variables. We obtain Teff, log g and mass for hydrogen
atmosphere white dwarf stars (DAs), warm helium atmosphere white dwarfs (DBs),
hot subdwarfs (sdBs and sdOs), and estimate photometric Teff for white dwarf
stars with continuum spectra (DCs). We find 15793 sdAs and 447 dCs between the
white dwarf cooling sequence and the main sequence, especially below Teff=
10000 K; most are likely low-mass metal-poor main sequence stars, but some
could be the result of interacting binary evolution.Comment: 18 pages, 13 figure
White dwarf and subdwarf stars in the Sloan Digital Sky Survey Data Release 16
White dwarfs are the end state of the evolution of more than 97 per cent of all stars, and therefore carry information on the structure and evolution of the Galaxy through their luminosity function and initial-to-final mass relation. Examining the new spectra of all white or blue stars in the Sloan Digital Sky Survey Data Release 16, we report the spectral classification of 2410 stars, down to our identification cut-off of signal-to-noise ratio equal to three. We newly identify 1404 DAs, 189 DZs, 103 DCs, 12 DBs, and nine CVs. The remaining objects are a mix of carbon or L stars (dC/L), narrow-lined hydrogen-dominated stars (sdA), dwarf F stars, and P Cyg objects. As white dwarf stars were not targeted by SDSS DR16, the number of new discoveries is much smaller than in previous releases. We also report atmospheric parameters and masses for a subset consisting of 555 new DAs, 10 new DBs, and 85 DZs for spectra with signal-to-noise ratio larger than 10
White dwarf and subdwarf stars in the Sloan Digital Sky Survey Data Release 16
White dwarfs are the end state of the evolution of more than 97 per cent of all stars, and therefore carry information on the structure and evolution of the Galaxy through their luminosity function and initial-to-final mass relation. Examining the new spectra of all white or blue stars in the Sloan Digital Sky Survey Data Release 16, we report the spectral classification of 2410 stars, down to our identification cut-off of signal-to-noise ratio equal to three. We newly identify 1404 DAs, 189 DZs, 103 DCs, 12 DBs, and nine CVs. The remaining objects are a mix of carbon or L stars (dC/L), narrow-lined hydrogen-dominated stars (sdA), dwarf F stars, and P Cyg objects. As white dwarf stars were not targeted by SDSS DR16, the number of new discoveries is much smaller than in previous releases. We also report atmospheric parameters and masses for a subset consisting of 555 new DAs, 10 new DBs, and 85 DZs for spectra with signal-to-noise ratio larger than 10
- …