An assessment of the rotation rates of the host stars of extrasolar planets

Abstract

The rotation periods of the host stars of extrasolar planets have been assessed against those of the Mt. Wilson stars, open cluster stars, and evolutionary stellar models that include rotation. They appear to be normal, modulo certain inconsistencies in various necessary inputs. Selection of candidate planet hosts for radial velocity surveys by low rotation or activity has resulted in a planet host sample skewed towards older stars. Thus, cross-comparisons must be age dependent. However, self-consistent ages are difficult to obtain, and activity ages show signs of systematic errors. There are indications that activity ages ought to be increased for lower-than-solar-mass stars and decreased for higher-than-solar-mass stars. Age uncertainties and a scarcity of measured rotation periods for planet host stars inflate the dispersion in older stars relative to those in open clusters. The presently available rotational models display inadequacies, most notably in producing fast-enough early-type stars. The fact that only one planet host star, $τBoo$, strongly suggests tidal spin-up, while of order ten systems suggest orbital circularization is explicable in terms of the differing timescales for these two phenomena. The rotational normalcy of the planet host stars and other considerations suggest that they are not especially different from other main sequence stars and that circumstellar matter and/or planets are probably ubiquitous, at least among sufficiently metal-rich solar-type stars.