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.
The Astronomical Journal
Institute of Physics Publishing, Inc.
Scholarly Commons Citation
Kilic, M., Kowalski, P. M., & von Hippel, T. (2009). A Near-Infrared Spectroscopic Survey of Cool White Dwarfs in the Sloan Digital Sky Survey. The Astronomical Journal, 138(n/a). https://doi.org/10.1088/0004-6256/138/1/102