Planetary Systems around Close Binary Stars: The Case of the Very Dusty, Sun-like, Spectroscopic Binary BD+20 307


First Author:
B. Zuckerman
Email: ben AT astro.ucla.edu
UCLA
Physics & Astronomy Dept.

Coauthors:
Weinberger, A., Carnegie Inst. of Washington
Fekel, F., Tennessee State Univ.
Hnery, G., Tennessee State Univ.
Williamson, M., Tennessee State Univ.
Muno, M., Lincoln Laboratory
Marois, C., HIA
Melis, C., UCLA
Becklin, E., UCLA
Song, I., Univ. Georgia

Abstract

Field star BD+20 307 is the dustiest known main sequence star, based on the fraction of its bolometric luminosity, ~4\%, that is emitted at infrared wavelengths (Song et al 2005; Rhee et al 2008). The particles that carry this large IR luminosity are unusually warm, comparable to the temperature of the zodiacal dust in our solar system, and their existence is likely to be a consequence of a fairly recent collision of large objects such as planets or planetary embryos. BD+20 307 is now known to be a ~3.4 day spectroscopic binary composed of two nearly equal solar-mass stars (Weinberger 2008; Zuckerman et al 2008). We have obtained and analyzed data from all three Spitzer instruments (Weinberger et al 2008). The spectral energy distribution indicates that the dust is confined to a rather narrow region in semi-major axis; there is no evidence for hot dust near the stars, nor for cold dust in a region analogous to the Sun's Kuiper Belt. The Spitzer IRS data enable a great improvement in modeling the composition of the dust particles beyond what was possible based on only ground-based spectra (Song et al 2005). Initially BD+20 307 was thought to be a youthful star (hundreds of Myr old, Song et al 2005), in the final stages of planet formation. However discovery of its binarity and concomitant consideration of a variety of age indicators, lead to a very different conclusion -- the star is likely to be at least one Gyr old (Weinberger 2008; Zuckerman et al 2008). Probably the dust around this close binary star has nothing at all to do with planet formation and everything to do with some major catastrophic event that recently took place near 1 AU in a mature planetary system.
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