The Ages of Stars Hosting Substellar Companions


Eric Mamajek


University of Rochester


Accurate stellar ages are a critical parameter in characterizing substellar companions and in planning imaging surveys to find new benchmark systems. I’ll review recent results on the estimation of the ages of stars hosting substellar companions, with particular emphasis on HR 8799, Fomalhaut, and GJ 758. One new result is that Fomalhaut is likely to be older than previously claimed. A modern isochronal analysis for Fomalhaut yields an age of 320 Myr. From revised Hipparcos astrometry and published radial velocities, it appears that Fomalhaut and TW PsA have a 3D separation of only 58000+-3000 AU and have statistically consistent 3D velocities differing by only 0.6+-0.5 km/s. Hence, Fomalhaut and TW PsA appear to constitute a wide physical binary, and I adopt the gyrochronology age for TW PsA (410 Myr) as another independent age estimate for Fomalhaut. Combining these new estimates yields a consensus age for Fomalhaut of 360+-50 Myr, which is nearly a factor of two older than previous estimates (200+-100 Myr). The preponderance of age-related evidence seems to suggest that HR 8799 is young ( 0.1 Gyr), and that GJ 758 is old ( 7 Gyr) and the mass of its companion is well above the D-burning limit ( 35 Jupiter masses). I’ll also discuss results from an upcoming study on ages derived from chromospheric activity for solar-type dwarf exoplanet hosts (Slipski & Mamajek, submitted to ApJ) which support the use of activity-derived ages even for stars older than 1 Gyr (albeit with sizeable uncertainties).

Attached documents

Lyot2010proc s6 talk MamajekE.pdf
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