Title:

Planet Hunting in New Stellar Domains



John Johnson
IfA



Abstract:

Very little is known about the occurrence rate and orbital
properties of planets around A type stars, corresponding to
stellar masses ranging from 1.5 Msun to 2.5 Msun. This
apparent lack of planets around massive stars is due to a
strong selection bias against early-type, main-sequence
stars in Doppler-based planet searches.  A and F stars have
relatively few narrow spectral lines due to their high
surface temperatures and large rotational velocities. These
features make the Doppler-detection of planets around these
stars exceedingly difficult. One method to circumvent the
difficulties inherent to massive dwarfs is to instead
observe these stars after they have evolved off of the main
sequence. I'll show how the cooler atmospheres and slower
rotation velocities of subgiants make them ideal proxies for
A and F stars in Doppler-based planet searches. I present
the early results from my planet search, including 7 new
exoplanets, and 3 additional strong candidates, orbiting
stars with masses greater than 1.5 Msun. My preliminary
results reveal a paucity of planets orbiting within 0.8 AU
of their host stars, which is significantly different than
the semimajor axis distribution of planets around Sun-like
stars. I also present evidence of a steeply rising trend in
giant planet occurrence with stellar mass, indicating that A
stars are about 4 times more likely than M dwarfs to harbor
Jovian planets.