A DETAILED MODEL ATMOSPHERE ANALYSIS OF COOL WHITE DWARFS IN THE SLOAN DIGITAL SKY SURVEY
- Smithsonian Astrophysical Observatory, 60 Garden Street, Cambridge, MA 02138 (United States)
- Gemini Observatory, 670 N. A'ohoku Place, Hilo, HI 96720 (United States)
- Departement de Physique, Universite de Montreal, C.P. 6128, Succursale Centre-Ville, Montreal, Quebec H3C 3J7 (Canada)
- Physics Department, Siena College, 515 Loudon Road, Loudonville, NY 12211 (United States)
- U.S. Naval Observatory, Flagstaff Station, 10391 W. Naval Observatory Road, Flagstaff, AZ 86001 (United States)
- Department of Astronomy, 1 University Station C1400, Austin, TX 78712 (United States)
- Kavli Institute for Cosmological Physics and Department of Astronomy and Astrophysics, The University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637 (United States)
- Department of Physics and Astronomy, University of Leicester, Leicester LE1 7RH (United Kingdom)
We present optical spectroscopy and near-infrared photometry of 126 cool white dwarfs (WDs) in the Sloan Digital Sky Survey (SDSS). Our sample includes high proper motion targets selected using the SDSS and USNO-B astrometry and a dozen previously known ultracool WD candidates. Our optical spectroscopic observations demonstrate that a clean selection of large samples of cool WDs in the SDSS (and the SkyMapper, Pan-STARRS, and the Large Synoptic Survey Telescope data sets) is possible using a reduced proper motion diagram and a tangential velocity cut-off (depending on the proper motion accuracy) of 30 km s{sup -1}. Our near-infrared observations reveal eight new stars with significant absorption. We use the optical and near-infrared photometry to perform a detailed model atmosphere analysis. More than 80% of the stars in our sample are consistent with either pure hydrogen or pure helium atmospheres. However, the eight stars with significant infrared absorption and the majority of the previously known ultracool WD candidates are best explained with mixed hydrogen and helium atmosphere models. The age distribution of our sample is consistent with a Galactic disk age of 8 Gyr. A few ultracool WDs may be as old as 12-13 Gyr, but our models have problems matching the spectral energy distributions of these objects. There are only two halo WD candidates in our sample. However, trigonometric parallax observations are required for accurate mass and age determinations and to confirm their membership in the halo.
- OSTI ID:
- 21454953
- Journal Information:
- Astrophysical Journal, Supplement Series, Vol. 190, Issue 1; Other Information: DOI: 10.1088/0067-0049/190/1/77; ISSN 0067-0049
- Country of Publication:
- United States
- Language:
- English
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