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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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