EVIDENCE FOR THE TIDAL DESTRUCTION OF HOT JUPITERS BY SUBGIANT STARS

Abstract

Tidal transfer of angular momentum is expected to cause hot Jupiters to\nspiral into their host stars. Although the timescale for orbital decay is very\nuncertain, it should be faster for systems with larger and more evolved stars.\nIndeed, it is well established that hot Jupiters are found less frequently\naround subgiant stars than around main-sequence stars. However, the\ninterpretation of this finding has been ambiguous, because the subgiants are\nalso thought to be more massive than the F- and G-type stars that dominate the\nmain-sequence sample. Consequently it has been unclear whether the absence of\nhot Jupiters is due to tidal destruction, or inhibited formation of those\nplanets around massive stars. Here we show that the Galactic space motions of\nthe planet-hosting subgiant stars demand that on average they be similar in\nmass to the planet-hosting main-sequence F- and G-type stars. Therefore the two\nsamples are likely to differ only in age, and provide a glimpse of the same\nexoplanet population both before and after tidal evolution. As a result, the\nlack of hot Jupiters orbiting subgiants is clear evidence for their tidal\ndestruction. Questions remain, though, about the interpretation of other\nreported differences between the planet populations around subgiants and\nmain-sequence stars, such as their period and eccentricity distributions and\noverall occurrence rates.\n