Astronomy and Astrophysics – Astronomy
Scientific paper
Jul 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009aj....138..102k&link_type=abstract
The Astronomical Journal, Volume 138, Issue 1, pp. 102-109 (2009).
Astronomy and Astrophysics
Astronomy
7
Stars: Atmospheres, Stars: Evolution, White Dwarfs
Scientific paper
We present near-infrared photometric observations of 15 and spectroscopic observations of 38 cool white dwarfs (WDs). This is the largest near-infrared spectroscopic survey of cool WDs to date. Combining the Sloan Digital Sky Survey photometry and our near-infrared data, we perform a detailed model atmosphere analysis. The spectral energy distributions of our objects are explained fairly well by model atmospheres with temperatures ranging from 6300 K down to 4200 K. Two WDs show significant absorption in the infrared, and are best explained with mixed H/He atmosphere models. Based on the up-to-date model atmosphere calculations by Kowalski & Saumon, we find that the majority of the stars in our sample have hydrogen-rich atmospheres. We do not find any pure helium atmosphere WDs below 5000 K, and we find a trend of increasing hydrogen to helium ratio with decreasing temperature. These findings present an important challenge to understanding the spectral evolution of WDs.
Based on observations obtained with the Infrared Telescope Facility (IRTF) and the Hobby-Eberly Telescope (HET). The IRTF is operated by the University of Hawaii under Cooperative Agreement NCC 5-538 with the National Aeronautics and Space Administration, Office of Space Science, Planetary Astronomy Program. The HET is a joint project of the University of Texas at Austin, the Pennsylvania State University, Stanford University, Ludwig-Maximilians-Universität München, and Georg-August-Universität Göttingen.
Hippel Ted von
Kilic Mukremin
Kowalski Piotr M.
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