A Dearth of Close-In Stellar Companions to M-dwarf TESS Objects of Interest

TL;DR

This study used high-resolution imaging to search for close-in stellar companions to M-dwarf TESS Objects of Interest, finding a scarcity of such companions and suggesting a shift towards longer orbital periods compared to field M dwarfs.

Contribution

The paper provides the first extensive high-resolution imaging survey of M-dwarf TOIs, revealing a dearth of close-in companions and analyzing their orbital period distribution.

Findings

Only two close-in stellar companions detected among 58 M-dwarf TOIs.

Additional 15 widely-separated companions identified through catalog cross-matching.

Orbital period distribution of companions is shifted to longer periods than in field M dwarfs.

Abstract

TESS has proven to be a powerful resource for finding planets, including those that orbit the most prevalent stars in our galaxy: the M dwarfs. Identification of stellar companions (both bound and unbound) has become a standard component of the transiting planet confirmation process in order to assess the level of light curve dilution and the possibility of the target being a false positive. Studies of stellar companions have also enabled investigations into stellar multiplicity in planet-hosting systems, which has wide-ranging implications for both exoplanet detection and characterization, as well as for the formation and evolution of planetary systems. Speckle and AO imaging are some of the most efficient and effective tools for revealing close-in stellar companions; we therefore present observations of 58 M-dwarf TOIs obtained using a suite of speckle imagers at the 3.5-m WIYN telescope, the 4.3-m Lowell Discovery Telescope, and the 8.1-m Gemini North and South telescopes. These observations, as well as near-infrared adaptive optics images obtained for a subset (14) of these TOIs, revealed only two close-in stellar companions. Upon surveying the literature, and cross-matching our sample with Gaia, SUPERWIDE, and the catalog from El-Badry et al. (2021), we reveal an additional 15 widely-separated common proper motion companions. We also evaluate the potential for undetected close-in companions. Taking into consideration the sensitivity of the observations, our findings suggest that the orbital period distribution of stellar companions to planet-hosting M dwarfs is shifted to longer periods compared to the expected distribution for field M dwarfs.