Companions to APOGEE Stars I: A Milky Way-Spanning Catalog of Stellar and Substellar Companion Candidates and their Diverse Hosts

TL;DR

This paper presents a catalog of 382 stellar and substellar companion candidates detected by APOGEE, revealing a truncated brown dwarf desert at close separations and widespread companions across the Galaxy, challenging existing formation models.

Contribution

The study introduces a novel orbit-fitting pipeline with quality metrics and provides the first large-scale catalog of companion candidates from APOGEE data, including many new detections.

Findings

Evidence for a truncated brown dwarf desert at <0.2 AU.

Detection of companions around metal-poor stars, challenging core accretion.

Ubiquity of companions throughout the Galactic disk.

Abstract

In its three years of operation, the Sloan Digital Sky Survey (SDSS-III) Apache Point Observatory Galactic Evolution Experiment (APOGEE-1) observed $>$14,000 stars with enough epochs over a sufficient temporal baseline for the fitting of Keplerian orbits. We present the custom orbit-fitting pipeline used to create this catalog, which includes novel quality metrics that account for the phase and velocity coverage of a fitted Keplerian orbit. With a typical RV precision of $\sim100-200$ m s$^{-1}$, APOGEE can probe systems with small separation companions down to a few Jupiter masses. Here we present initial results from a catalog of 382 of the most compelling stellar and substellar companion candidates detected by APOGEE, which orbit a variety of host stars in diverse Galactic environments. Of these, 376 have no previously known small separation companion. The distribution of companion candidates in this catalog shows evidence for an extremely truncated brown dwarf (BD) desert with a paucity of BD companions only for systems with $a < 0.1-0.2$ AU, with no indication of a desert at larger orbital separation. We propose a few potential explanations of this result, some which invoke this catalog's many small separation companion candidates found orbiting evolved stars. Furthermore, 16 BD and planet candidates have been identified around metal-poor ([Fe/H] $< -0.5$) stars in this catalog, which may challenge the core accretion model for companions $>10 M_{Jup}$. Finally, we find all types of companions are ubiquitous throughout the Galactic disk with candidate planetary-mass and BD companions to distances of $\sim6$ and $\sim16$ kpc, respectively.