Rocky Planetesimals as the Origin of Metals in DZ Stars

TL;DR

This study shows that metals in DZ stars originate from rocky planetary debris rather than interstellar medium, implying many stars form terrestrial planets and that these stars are polluted by water-rich planetesimals.

Contribution

It provides evidence that metals in DZ stars come from rocky planetary remnants, not interstellar medium, and predicts the prevalence of terrestrial planets and water-rich planetesimals.

Findings

Calcium and hydrogen abundances indicate planetary debris origin.

Metal masses are comparable to large asteroids.

At least 3.5% of A- and F-type stars form terrestrial planets.

Abstract

{Abridged}. An analysis of the calcium and hydrogen abundances, Galactic positions and kinematics of 146 DZ stars from the Sloan Digital Sky Survey demonstrates that interaction with the interstellar medium cannot account for their externally polluted atmospheres. The calcium-to-hydrogen ratios for the 37 DZA stars are dominated by super-solar values, as are the lower limits for the remaining 109 DZ stars. All together their metal-contaminated convective envelopes contain 10^{20+-2} g of calcium, commensurate with the masses of calcium inferred for large asteroids. It is probable that these stars are contaminated by circumstellar matter; the rocky remains of terrestrial planetary systems. In this picture, two predictions emerge: 1) at least 3.5% of all main sequence A- and F-type stars build terrestrial planets; and 2) the DZA stars are externally polluted by both metals and hydrogen, and hence constrain the frequency and mass of water-rich, extrasolar planetesimals.