John Asher Johnson, Timothy D. Morton, Jason T. Wright
Doppler surveys have shown that the occurrence rate of Jupiter-mass planets appears to increase as a function of stellar mass. However, this result depends on the ability to accurately measure the masses of evolved stars. Recently, Lloyd (2011) called into question the masses of subgiant stars targeted by Doppler surveys. He argues that very few observable subgiants have masses greater than 1.5 Msun, and that most of them have masses in the range 1.0-1.2 Msun. To investigate this claim, we use Galactic stellar population models to generate an all-sky distribution of stars. We incorporate the effects that make massive subgiants less numerous, such as the initial mass function and differences in stellar evolution timescales. We find that these effects lead to neglibily small systematic errors in stellar mass estimates, in contrast to the 50% errors predicted by Lloyd. Additionally, our simulated target sample does in fact include a significant fraction of stars in excess of 1.5 Msun. The inclusion of an apparent magnitude limit results in a Malmquist-like bias toward more massive stars, in contrast to the volume-limited simulated sample of Lloyd. The magnitude limit shifts the mean of our simulated distribution toward higher masses and results in a relatively smaller number of evolved stars with masses in the range 1.0-1.2 Msun. Thus, many of the subgiants targeted by Doppler surveys are likely the evolved counterparts of massive main-sequence stars.
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http://arxiv.org/abs/1208.4377
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