Found: The Missing Blue Opacity in Atmosphere Models of Cool Hydrogen White Dwarfs

By Piotr M. Kowalski, D. Saumon. 2006

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We investigate the importance of the far red wing of the Lyα line of hydrogen in the atmospheres of cool white dwarfs of pure hydrogen composition. We find that this absorption process dominates all important sources of opacity in the blue part of the optical spectrum of these stars. Our successful fits to the spectra of cool DA/DC white dwarfs indicate that the far red wing of the Lyα line is the source of opacity that had been missing in the models. The observed sequence of cool white dwarfs in color-color diagrams is very well reproduced by our new pure hydrogen atmosphere models, suggesting that the atmospheric composition of the coolest DC white dwarfs must be revisited.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/d90da17565e295248033b862713cd1b31f79f007

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Citations in the corpus

Three Hypervelocity White Dwarfs in Gaia DR2: Evidence for Dynamically Driven Double-degenerate Double-detonation Type Ia Supernovae (2018, methodology): “Using publicly available DB WD cooling tables1 (Holberg & Bergeron 2006; Kowalski & Saumon 2006; Tremblay et al. 2011; Bergeron et al. 2011), we find that a 0.6 (1.0)M WD that has cooled for 1 Gyr since its birth has an absolute visual magnitude of 12.9 (12.8).”
KNOW YOUR NEIGHBORHOOD: A DETAILED MODEL ATMOSPHERE ANALYSIS OF NEARBY WHITE DWARFS (2012, methodology): “…described below relies heavily on the flux at the B bandpass, we now include in our models the opacity from the red wing of Lyα calculated by Kowalski & Saumon (2006) and kindly provided to us by P. Kowalski, which is known to affect the flux in the ultraviolet region of the energy…”
NEW COOLING SEQUENCES FOR OLD WHITE DWARFS (2010, methodology): “For the purpose of the present work, the model atmospheres explicitly included the Lyα quasi-molecular opacity according to the approximation used by Kowalski & Saumon (2006).”
SPECTROSCOPIC ANALYSIS OF DA WHITE DWARFS: STARK BROADENING OF HYDROGEN LINES INCLUDING NONIDEAL EFFECTS (2009, background): “Furthermore, at very low effective temperatures, H–H2 collisions become the main source of broadening for Lα (Kowalski & Saumon 2006).”
Spectroscopic analysis of DA white dwarfs with 3D model atmospheres (2013, background): “Other aspects that were recently improved include the H-H2, H-H, and H-H+ broadening of the lower Lyman lines (Allard et al. 2004; Kowalski & Saumon 2006).”
AGaiaData Release 2 catalogue of white dwarfs and a comparison with SDSS (2018, methodology): “We employ standard H-atmosphere spectral models (Tremblay et al. 2011) including the Lα red wing absorption of Kowalski & Saumon (2006) and covering the range 1500 < Teff (K) < 140 000 and 6.5 < log g < 9.5.”
The Sirius System and Its Astrophysical Puzzles: Hubble Space Telescope and Ground-based Astrometry (2017, methodology): “These tables are based on evolutionary sequences and model atmospheres calculated by Holberg & Bergeron (2006), Kowalski & Saumon (2006), Tremblay et al. (2011), and Bergeron et al. (2011). measure 89.60± 0.75 km s−1.”
Prospects for detection of detached double white dwarf binaries with Gaia, LSST and LISA (2017, methodology): “The absolute magnitudes for WDs are deduced from the WD cooling curves of pure hydrogen atmosphere models (Holberg & Bergeron 2006; Kowalski & Saumon 2006; Tremblay, Bergeron & Gianninas 2011, and references therein1).”