The Abundance Distribution in the Extrasolar-Planet Host Star HD 19994

Abstract

Abundances of 22 elements have been determined from a high-resolution, high signal-to-noise spectrum of HD 19994, a star recently announced as harboring an extrasolar planet. A detailed spectroscopic analysis of this star finds it to have a mass of 1.2 ± 0.1 M⊙. HD 19994 is found to be slightly enriched in "metals" relative to the Sun ([Fe/H] = +0.09 ± 0.05 and an average of all elements of [m/H] = +0.13), as are most stars known with extrasolar planets. In an investigative search for possible signatures of accretion of metal-rich gas onto the parent stars in such systems (using HD 19994 and published abundances for other stars), it is found that a small subset of stars with planets exhibits a trend of increasing [X/H] with increasing condensation temperature for a given element X. This trend may point to the accretion of chemically fractionated solid material into the outer (thin) convection zones of these solar-type stars. It is also found that this small group of stars exhibiting an accretion signature all have large planets orbiting much closer than is found, in general, for stars with planets not showing this peculiar abundance trend, suggesting a physical link between accretion and orbital separation. In addition, the stars showing evidence of fractionated accretion are, on average, of larger mass (1.2 M⊙) than stars not showing measurable evidence of this accretion (1.0 M⊙).