A Method for Selecting M dwarfs with an Increased Likelihood of Unresolved Ultra-cool Companionship

TL;DR

This paper introduces a refined method to identify M dwarfs with a higher likelihood of having unresolved ultra-cool companions, aiding studies of low-mass star formation and sub-stellar objects.

Contribution

The authors develop an optimized selection technique using multi-band photometry and proper motion data to find candidate M dwarf + ultra-cool dwarf systems.

Findings

Identified 1,082 candidate systems for follow-up.

Estimated the occurrence rate of unresolved ultra-cool companions to be at least four times higher than average.

Discussed contamination, bias, and predicted candidate yields based on simulations.

Abstract

Locating ultra-cool companions to M dwarfs is important for constraining low-mass formation models, the measurement of sub-stellar dynamical masses and radii, and for testing ultra-cool evolutionary models. We present an optimised method for identifying M dwarfs which may have unresolved ultra-cool companions. We construct a catalogue of 440,694 candidates, from WISE, 2MASS and SDSS, based on optical and near-infrared colours and reduced proper motion. With strict reddening, photometric and quality constraints we isolate a sub-sample of 36,898 M dwarfs and search for possible mid-infrared M dwarf + ultra-cool dwarf candidates by comparing M dwarfs which have similar optical/near-infrared colours (chosen for their sensitivity to effective temperature and metallicity). We present 1,082 M dwarf + ultra-cool dwarf candidates for follow-up. Using simulated ultra-cool dwarf companions to M dwarfs, we estimate that the occurrence of unresolved ultra-cool companions amongst our M dwarf + ultra-cool dwarf candidates should be at least four times the average for our full M dwarf catalogue. We discuss possible contamination and bias and predict yields of candidates based on our simulations.