Scott G. Engle, Edward F. Guinan
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. When all data sets are
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 & 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_sun), the liquid water habitable
zones (HZs) for hosted planets are very close to their host stars - typically
at ~0.1-0.4 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).
View original:
http://arxiv.org/abs/1111.2872
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