Much like people, stars arrange themselves in various configurations -- singles, doubles, multiples, clusters, and great aggregations known as galaxies. Each of these collections is different, depending on the proximity of the members and the shared history and composition of the stars involved. Stellar multiplicity provides fundamental clues about the nature of star formation, the distribution of baryonic mass in the Universe, and the evolution of stellar systems over time. How stars are parceled into singles, doubles, and higher order multiples also provides clues about the angular momentum distribution in stellar systems and constraints on whether or not planets may be found (Raghavan et al. 2010). Of all the populations in the Galaxy, the nearest stars provide the fundamental framework upon which stellar astrophysics is based because they contain the most easily studied representatives of their kinds. Because red dwarfs dominate the nearby stellar population, accounting for more than 70% of all stars (Henry et al. 2006), they are arguably the best sample that can be studied for understanding stellar multiplicity.
We are currently systematically surveying ~1200 red dwarfs that have trigonometric parallaxes placing them within 25 pc of the Sun for stellar companions at separations of 1" to 600". By obtaining I-band images using the CTIO 0.9m and 1.0m in the south and the Lowell 42in in the north, we are probing the environs of these systems for companions at separations of 1" to 180". A complementary reconnaissance of wider companions out to 600" is also being done via blinking of SuperCOSMOS BRI images. Because the systems all have accurate parallaxes, biases inherent to photometrically-selected samples are eliminated. This is the largest, most comprehensive study ever done of the multiplicity of the most common stars in the Galaxy.
The results will allow statistical analyses of the nearby M dwarf population, refinement of the solar neighborhood membership roster, and improvement of the mass and luminosity functions for these objects at the end of the main sequence. Ultimately, we will reveal the kinds of stellar families that reside nearby and will be able to make informed predictions about where exoplanets may be likely to exist.
Henry, T.J., Jao, W.-C., Subasavage, J.P., et al. 2006, aj, 132, 2360
Raghavan, D., McAlister, H.A., Henry, T.J., et al. 2010, apjs, 190, 1