Poster Abstracts

Name/Affiliation:  Kimberly Ward-Duong (Arizona State University)

Title:  Cool and Cooler: A Volume-Limited Companion Survey of Local M-dwarfs

M-dwarfs constitute the major fraction of stars within both the solar neighborhood and nearby star-forming regions, and their binary properties present observational tests of the star formation process. Key M-dwarf companion characteristics -- including multiplicity fraction, mass ratios, and separation distributions -- hold important implications for the universality of star formation, dynamical interactions, and the origin of the Galactic field stars. We present results of a large-scale, comprehensive M-dwarf companion study covering separations from ~1 to 10,000 AU, based on a volume-limited survey of 250 M-dwarfs within 15 pc. Diffraction-limited infrared archival data were analyzed from the Very Large Telescope, Canada-France-Hawaii Telescope, and MMT Observatory to detect nearby companions to M-dwarfs from ~1 to 100 AU. To supplement the high-resolution data, digitized wide-field archival plates were searched for companions with separations of 100 to 10,000 AU. The survey is fully sensitive to companions at the bottom of the main sequence over an unprecedented survey separation range of ~2 to 10,000 AU, and the deepest images also reveal a number of substellar candidates. With multiple AO and wide-field epochs, follow-up observations have allowed us to confirm or reject companion candidates detected during our analysis. This provides confirmation of common proper motions, minimizes background contamination, and enables comprehensive statistics for M-dwarf binaries. We find a stellar multiplicity fraction of approximately 30%, the shape of the companion separations fit by a log-normal distribution with mean of 18 AU, and a mass ratio distribution exhibiting a very shallow rise toward systems with components of similar mass. Characterizations of the binary and multiple star frequency for M-dwarfs provide crucial insights into the low-mass star formation environment, and hold additional implications for the frequency and evolutionary histories of their associated disks and planets.