HST/FGS Parallaxes of AM CVn Stars and Astrophysical Consequences

TL;DR

This study measures precise distances to five AM CVn stars using Hubble Space Telescope data, refining their space density, donor star masses, and gravitational-wave signals, with implications for future space-based gravitational wave detection.

Contribution

First precise parallax measurements for five AM CVn stars, leading to revised space density estimates and improved understanding of their masses and gravitational-wave emissions.

Findings

Distances to five AM CVn stars were accurately measured.

Previous space density estimates were too high by about an order of magnitude.

Most systems are promising candidates for detection by LISA.

Abstract

We present absolute parallaxes and relative proper motions for five AM CVn stars, which we obtained using the Fine Guidance Sensors on board the Hubble Space Telescope. Our parallax measurements translate into distances d(AM CVn)=606+135-93 pc, d(HP Lib)=197+14-12 pc, d(CR Boo)=337+44-35 pc, d(V803 Cen)=347+32-27 pc, and d(GP Com)=75+2-2 pc. From these distances we estimate the space density of AM CVn stars and suggest that previous estimates have been too high by about an order of magnitude. We also infer the mass accretion rates which allows us to constrain the masses of the donor stars, and we show that relatively massive, semi-degenerate donor stars are favored in all systems except GP Com. Finally, we give updated estimates for their gravitational-wave signals, relevant for future space missions such as the proposed Laser Interferometer Space Antenna (LISA), based on their distances and the inferred masses of the binary components. We show that all systems but GP Com are excellent candidates for detection with LISA.