The spectral evolution of hot white dwarfs

2019 ◽  
Vol 15 (S357) ◽  
pp. 162-165
Author(s):  
Antoine Bédard ◽  
Pierre Bergeron ◽  
Gilles Fontaine
Keyword(s):  
White Dwarfs ◽  
Spectroscopic Analysis ◽  
State Of The Art ◽  
Sloan Digital Sky Survey ◽  
Atmospheric Composition ◽  
Spectral Evolution ◽  
Sky Survey

AbstractAs they evolve, white dwarfs undergo major changes in their atmospheric composition, a phenomenon known as spectral evolution. In particular, most hot He-rich (DO) stars transform into H-rich (DA) stars as they cool off, most likely as a result of the float-up of residual H. We investigate this DO-to-DA transition by taking advantage of the extensive spectroscopic dataset provided by the Sloan Digital Sky Survey (SDSS). Using our new state-of-the-art non-LTE model atmospheres, we perform a spectroscopic analysis of 1882 hot (Teff >30,000 K) white dwarfs identified in the SDSS. We find that at least 15% of all white dwarfs are born with a He-dominated atmosphere. Among these, ∼2/3 turn into H-rich stars before they reach Teff ∼40,000 K, while the remaining ∼1/3 maintain their He-rich surface throughout their entire evolution. We speculate on the origin of these two groups of objects.

scholarly journals Carbon-rich (DQ) white dwarfs in the Sloan Digital Sky Survey

2019 ◽  
Vol 628 ◽  
pp. A102 ◽  
Author(s):  
D. Koester ◽  
S. O. Kepler
Keyword(s):  
White Dwarfs ◽  
Sloan Digital Sky Survey ◽  
Significant Fraction ◽  
Atmospheric Parameters ◽  
Spectral Evolution ◽  
Large Sample ◽  
Synthetic Spectra ◽  
Sky Survey ◽  
Data Release

Context. Among the spectroscopically identified white dwarfs, a fraction smaller than 2% have spectra dominated by carbon lines, mainly molecular C2, but also a smaller group dominated by C I and C II lines. These are together called DQ white dwarfs. Aims. We want to derive atmospheric parameters Teff, log g, and carbon abundances for a large sample of these stars and discuss implications for their spectral evolution. Methods. Sloan Digital Sky Survey spectra and ugriz photometry were used, together with Gaia Data Release 2 parallaxes and G band photometry. These were fitted to synthetic spectra and theoretical photometry derived from model atmospheres. Results. We found that the DQ hotter than Teff ~ 10 000 K have masses ~ 0.4 M⊙ larger than the classical DQ, which have masses typical for the majority of white dwarfs (~ 0.6 M⊙). We found some evidence that the peculiar DQ below 10 000 K also have significantly larger masses and may thus be the descendants of the hot and warm DQ above 10 000 K. A significant fraction of the hotter objects with Teff > 14 500 K have atmospheres dominated by carbon.

scholarly journals Computational tools for the spectroscopic analysis of white dwarfs

2020 ◽  
Vol 497 (3) ◽  
pp. 2688-2698 ◽  
Author(s):  
Vedant Chandra ◽  
Hsiang-Chih Hwang ◽  
Nadia L Zakamska ◽  
Tamás Budavári
Keyword(s):  
White Dwarf ◽  
White Dwarfs ◽  
Spectroscopic Analysis ◽  
Theoretical Models ◽  
Sloan Digital Sky Survey ◽  
Random Forest Regression ◽  
Computational Tools ◽  
Sky Survey ◽  
Stellar Photosphere ◽  
Temperature Surface

ABSTRACT The spectroscopic features of white dwarfs are formed in the thin upper layer of their stellar photosphere. These features carry information about the white dwarf’s surface temperature, surface gravity, and chemical composition (hereafter ‘labels’). Existing methods to determine these labels rely on complex ab-initio theoretical models, which are not always publicly available. Here, we present two techniques to determine atmospheric labels from white dwarf spectra: a generative fitting pipeline that interpolates theoretical spectra with artificial neural networks and a random forest regression model using parameters derived from absorption line features. We test and compare our methods using a large catalogue of white dwarfs from the Sloan Digital Sky Survey (SDSS), achieving the same accuracy and negligible bias as compared to previous studies. We package our techniques into an open-source python module ‘wdtools’ that provides a computationally inexpensive way to determine stellar labels from white dwarf spectra observed from any facility. We will actively develop and update our tool as more theoretical models become publicly available. We discuss applications of our tool in its present form to identify interesting outlier white dwarf systems including those with magnetic fields, helium-rich atmospheres, and double-degenerate binaries.

scholarly journals White Dwarf Stars

2017 ◽  
Vol 45 ◽  
pp. 1760023
Author(s):  
S. O. Kepler ◽  
Alejandra Daniela Romero ◽  
Ingrid Pelisoli ◽  
Gustavo Ourique
Keyword(s):  
White Dwarf ◽  
Final Stage ◽  
White Dwarfs ◽  
Sloan Digital Sky Survey ◽  
Dwarf Stars ◽  
Multiple Systems ◽  
White Dwarf Stars ◽  
Sky Survey ◽  
Data Release ◽  
Low Mass

White dwarf stars are the final stage of most stars, born single or in multiple systems. We discuss the identification, magnetic fields, and mass distribution for white dwarfs detected from spectra obtained by the Sloan Digital Sky Survey up to Data Release 13 in 2016, which lead to the increase in the number of spectroscopically identified white dwarf stars from 5[Formula: see text]000 to 39[Formula: see text]000. This number includes only white dwarf stars with [Formula: see text], i.e., excluding the Extremely Low Mass white dwarfs, which are necessarily the byproduct of stellar interaction.

scholarly journals The frequency of gaseous debris discs around white dwarfs

2020 ◽  
Vol 493 (2) ◽  
pp. 2127-2139 ◽  
Author(s):  
Christopher J Manser ◽  
Boris T Gänsicke ◽  
Nicola Pietro Gentile Fusillo ◽  
Richard Ashley ◽  
Elmé Breedt ◽  
...  
Keyword(s):  
White Dwarf ◽  
White Dwarfs ◽  
Signal To Noise Ratio ◽  
Infrared Emission ◽  
Sloan Digital Sky Survey ◽  
Emission Lines ◽  
Occurrence Rate ◽  
Limited Sample ◽  
Sky Survey ◽  
Gaseous Disc

ABSTRACT A total of 1–3 per cent of white dwarfs are orbited by planetary dusty debris detectable as infrared emission in excess above the white dwarf flux. In a rare subset of these systems, a gaseous disc component is also detected via emission lines of the Ca ii 8600 Å triplet, broadened by the Keplerian velocity of the disc. We present the first statistical study of the fraction of debris discs containing detectable amounts of gas in emission at white dwarfs within a magnitude and signal-to-noise ratio limited sample. We select 7705 single white dwarfs spectroscopically observed by the Sloan Digital Sky Survey (SDSS) and Gaia with magnitudes g ≤ 19. We identify five gaseous disc hosts, all of which have been previously discovered. We calculate the occurrence rate of a white dwarf hosting a debris disc detectable via Ca ii emission lines as $0.067\, \pm \, ^{0.042}_{0.025}$ per cent. This corresponds to an occurrence rate for a dusty debris disc to have an observable gaseous component in emission as 4 ± $_{2}^{4}$ per cent. Given that variability is a common feature of the emission profiles of gaseous debris discs, and the recent detection of a planetesimal orbiting within the disc of SDSS J122859.93+104032.9, we propose that gaseous components are tracers for the presence of planetesimals embedded in the discs and outline a qualitative model. We also present spectroscopy of the Ca ii triplet 8600 Å region for 20 white dwarfs hosting dusty debris discs in an attempt to identify gaseous emission. We do not detect any gaseous components in these 20 systems, consistent with the occurrence rate that we calculated.

scholarly journals barry and the BAO model comparison

2020 ◽  
Vol 493 (3) ◽  
pp. 4078-4093 ◽  
Author(s):  
Samuel R Hinton ◽  
Cullan Howlett ◽  
Tamara M Davis
Keyword(s):  
Model Comparison ◽  
State Of The Art ◽  
Model Fitting ◽  
Power Spectra ◽  
Acoustic Oscillation ◽  
Effective Field ◽  
Sloan Digital Sky Survey ◽  
Data Sets ◽  
New Public ◽  
Sky Survey

ABSTRACT We compare the performance of four state-of-the-art models for extracting isotropic measurements of the baryon acoustic oscillation (BAO) scale. To do this, we created a new, public, modular code barry, which contains data sets, model fitting tools, and model implementations incorporating different descriptions of non-linear physics and algorithms for isolating the BAO feature. These are then evaluated for bias, correlation, and fitting strength using mock power spectra and correlation functions developed for the Sloan Digital Sky Survey Data Release 12. Our main findings are as follows: (1) all of the models can recover unbiased constraints when fit to the pre- and post-reconstruction simulations. (2) Models that provide physical descriptions of the damping of the BAO feature (using e.g. standard perturbation or effective-field theory arguments) report smaller errors on average, although the distribution of mock χ2 values indicates these are underestimated. (3) Allowing the BAO damping scale to vary can provide tighter constraints for some mocks, but is an artificial improvement that only arises when noise randomly sharpens the BAO peak. (4) Unlike recent claims in the literature when utilizing a BAO Extractor technique, we find no improvement in the accuracy of the recovered BAO scale. (5) We implement a procedure for combining all models into a single consensus result that improves over the standard method without obviously underestimating the uncertainties. Overall, barry provides a framework for performing the cosmological analyses for upcoming surveys, and for rapidly testing and validating new models.

scholarly journals Pulsating white dwarfs in cataclysmic variables: The marriage of ZZ Cet and dwarf nova

2004 ◽  
Vol 193 ◽  
pp. 382-386 ◽  
Author(s):  
Brian Warner ◽  
Patrick A. Woudt
Keyword(s):  
White Dwarf ◽  
Large Amplitude ◽  
White Dwarfs ◽  
Cataclysmic Variables ◽  
Sloan Digital Sky Survey ◽  
Dwarf Novae ◽  
Dwarf Nova ◽  
Sky Survey

AbstractThere are now four dwarf novae known with white dwarf primaries that show large amplitude non-radial oscillations of the kind seen in ZZ Cet stars. We compare the properties of these stars and point out that by the end of the Sloan Digital Sky Survey more than 30 should be known.

scholarly journals A spectroscopic analysis of a sample of narrow-line Seyfert 1 galaxies selected from the Sloan Digital Sky Survey

2016 ◽  
Vol 462 (2) ◽  
pp. 1256-1280 ◽  
Author(s):  
V. Cracco ◽  
S. Ciroi ◽  
M. Berton ◽  
F. Di Mille ◽  
L. Foschini ◽  
...  
Keyword(s):  
Spectroscopic Analysis ◽  
Sloan Digital Sky Survey ◽  
Narrow Line ◽  
Sky Survey
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