A New Sirius-like System at Only 21 Parsecs: An Elusive White Dwarf Companion to the Nearby K-dwarf HD 38230

Abstract

White dwarfs are among the rarest and faintest stars found in the solar neighbourhood and are therefore persistently challenging to detect. Whereas the \textit{Gaia} mission has vastly expanded our knowledge of isolated white dwarfs, limited contrast sensitivity means that white dwarfs companions to much brighter solar-type stars are easily missed, leaving a subset of white dwarfs in "Sirius-like systems" that can only be discovered via high-contrast imaging. Here we report the discovery of a white dwarf companion to the nearby K0V star HD 38230 (HIP 27207). The companion, HD 38230 B, was originally detected with Keck/NIRC2 observations taken as part of the TRENDS high-contrast imaging survey, was detected by \textit{Gaia} without an astrometric solution, and was independently observed using Lick/ShaneAO and Palomar/PHARO in the literature. Combining these multiple imaging detections spanning 6 years, we demonstrate that HD 38230 B is a gravitationally bound companion and has photometry consistent only with a white dwarf. Our analysis of the binary orbit, combining relative astrometry with over 25 years of precise radial velocity observations and \textit{Hipparcos-Gaia} astrometry, results in strong constraints on the $P$ = $1390_{-200}^{+310}$ year orbit despite the short observational span, and provides a precise dynamical mass of $M_B$ = $0.71_{-0.05}^{+0.06}$ $M_{\odot }$ for the white dwarf. At 21 pc, this is the 11th-nearest Sirius-like system known to date, highlighting residual incompleteness in the local white dwarf census.

18 pages, 6 figures, 4 tables. Submitted to AAS Journals. Comments welcome!