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Register a new userThe Solar Neighborhood. XX. Discovery and Characterization of 21 New Nearby White Dwarf Systems
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Added by
John Subasavage Jr.
Publication date
2008
fields
Physics
and research's language is
English
Authors
John P. Subasavage
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We present medium resolution spectroscopy and multi-epoch VRI photometry for 21 new nearby (< 50 pc) white dwarf systems brighter than V ~ 17. Of the new systems, ten are DA (including a wide double degenerate system with two DA components), eight are DC, two are DZ, and one is DB. In addition, we include multi-epoch VRI photometry for eleven known white dwarf systems that do not have trigonometric parallax determinations. Using model atmospheres relevant for various types of white dwarfs (depending on spectral signatures), we perform spectral energy distribution modeling by combining the optical photometry with the near-infrared JHK from the Two Micron All-Sky Survey to derive physical parameters (i.e., effective temperature and distance estimates). We find that twelve new and six known white dwarf systems are estimated to be within the NStars and Catalog of Nearby Stars horizons of 25 pc. Coupled with identical analyses of the 56 white dwarf systems presented in Paper XIX of this series, a total of 20 new white dwarf systems and 18 known white dwarf systems are estimated to be within 25 pc. These 38 systems of the 88 total studied represent a potential 34% increase in the 25 pc white dwarf population (currently known to consist of 110 systems with trigonometric parallaxes of varying qualities). We continue an ongoing effort via CTIOPI to measure trigonometric parallaxes for the systems estimated to be within 25 pc to confirm proximity and further fill the incompleteness gap in the local white dwarf population. Another 38 systems (both new and known) are estimated to be between 25 and 50 pc and are viable candidates for ground-based parallax efforts wishing to broaden the horizon of interest.
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The study of the stellar formation history in the solar neighborhood is a powerful technique to recover information about the early stages and evolution of the Milky Way. We present a new method which consists of directly probing the formation history from the nearby stellar remnants. We rely on the volume complete sample of white dwarfs within 20 pc, where accurate cooling ages and masses have been determined. The well characterized initial-final mass relation is employed in order to recover the initial masses (1 < M/Msun < 8) and total ages for the local degenerate sample. We correct for moderate biases that are necessary to transform our results to a global stellar formation rate, which can be compared to similar studies based on the properties of main-sequence stars in the solar neighborhood. Our method provides precise formation rates for all ages except in very recent times, and the results suggest an enhanced formation rate for the solar neighborhood in the last 5 Gyr compared to the range 5 < Age (Gyr) < 10. Furthermore, the observed total age of ~10 Gyr for the oldest white dwarfs in the local sample is consistent with the early seminal studies that have determined the age of the Galactic disk from stellar remnants. The main shortcoming of our study is the small size of the local white dwarf sample. However, the presented technique can be applied to larger samples in the future.
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