AAS 206th Meeting, 29 May - 2 June 2005
Session 9 Brown Dwarfs and Extrasolar Planets
Poster, Monday, 9:20am-6:30pm, Tuesday, 10:00am-7:00pm, May 30, 2005, Ballroom A

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[9.04] Barnard's Star as a Proxy for Old Disk dM Stars: Magnetic Activity, Light Variations, XUV Irradiances, and Planetary Habitable Zones

A.R. Riedel, E.F. Guinan, L.E. DeWarf, S.G. Engle, G.P. McCook (Villanova University)

Barnard's Star (GJ 699) is a nearby, high velocity (UVW = -148,+0,+16 km/s), Thick Disk / Intermediate-age Pop II dM4 star. Although old (7-12 Gyr), Barnard's Star appears to be magnetically active, having coronal X-ray emission as well as moderately strong chromospheric UV emissions. Barnard's star holds the speed record for having the largest proper motion of any star yet known (10.4"/yr). At a distance of only 1.82 pc (5.9 lt yrs), it is the nearest star to us after the \alpha Cen system. Recent measures of Barnard's Star results in a luminosity of L = 3.46 ± 0.17 \times 10-3 L\odot, R = 0.20 ± 0.008 R\odot, and Teff = 3134 ± 102 K (Dawson & De Robertis 2004, AJ, 127, 2909). Because of its proximity and age, we have selected Barnard's Star for more intensive study, and to serve as a proxy for the numerous old-population dM stars in our Galaxy. These stars may be targets of future planet search missions such as SIM, Kepler, and TPF/Darwin in the next several years. For exobiology, dM stars make interesting targets because the habitable zones (HZ) around dM stars are close to the host star (HZ ~ 0.05-0.40 AU), making the hypothetical HZ planet more strongly influenced by stellar flares, winds, and plasma ejection events that are frequent in dM stars.

We are conducting intensive photoelectric UBVRI and TiO (719nm) photometry of Barnard's Star using the Four College Automatic Photoelectric Telescope in Arizona. This photometry is being conducted to determine starspot coverage and the rotation period. We have also determined X-ray to UV irradiances that will characterize dM stars of similar ages. These measures will be useful in the future if large numbers of older dM stars are found to harbor planets. We will discuss the results of this study, which is a component of a larger program aimed at improving (and testing) our understanding of magnetic-related phenomena in dM stars. This research is supported by NASA and NSF/RUI grants.

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