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Paper: Red Dwarf Stars: Ages, Rotation, Magnetic Dynamo Activity and the Habitability of Hosted Planets
Volume: 451, 9th Pacific Rim Conference on Stellar Astrophysics
Page: 285
Authors: Engle, S. G.; Guinan, E. F.
Abstract: We report on our continued efforts to understand and delineate the magnetic dynamo-induced behavior/variability of red dwarf (K5 V – M6 V) stars over their long lifetimes. These properties include: rotation, light variations (from star spots), coronal–chromospheric XUV activity and flares. This study is being carried out as part of the NSF-sponsored Living with a Red Dwarf program. The Living with a Red Dwarf program's database of dM stars with photometrically determined rotation rates (from starspot modulations) continues to expand, as does the inventory of archival XUV observations. Recently, the photometric properties of several hundred dM stars from the Kepler database are being analyzed to determine the rotation rates, starspot areal coverage/distributions and stellar flare rates. When all data setsare combined with ages from cluster/population memberships and kinematics, the determination of Age-Rotation-Activity relationships is possible. Such relationships have broad impacts not only on the studies of magnetic dynamo theory and angular momentum loss of low-mass stars with deep convective zones, but also on the suitability of planets hosted by red dwarfs to support life. With intrinsically low luminosities (L< 0.02L), the liquid water habitable zones (HZs) for hosted planets are very close to their host stars – typically at ∼0.1 AU < HZ < 0.4 AU. Planets located close to their host stars risk damage and atmospheric loss from coronal & chromospheric XUV radiation, flares and plasma blasts via strong winds and coronal mass ejections. In addition, our relationships permit the stellar ages to be determined through measures of either the stars' rotation periods (best way) or XUV activity levels. This also permits a determination of the ages of their hosted planets. We illustrate this with examples of age determinations of the exoplanet systems: GJ 581 and HD 85512 (both with large Earth-size planets within the host star's HZ), GJ 1214 (hot, close-in transiting super-Earth planet) and HD 189733 (short period, hot-Jupiter planet interacting with its host star – age from its dM4 star companion).
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