UCAC4 Nearby Star Survey: A Search for Our Stellar Neighbors

We use data from the U.S. Naval Observatory fourth CCD Astrograph Catalog (UCAC4) in combination with photometry from the AAVSO Photometric All-Sky Survey (APASS) and Two Micron All-Sky Survey (2MASS) to identify stars within 25 pc of the Sun. A sample of nearby stars with accurate trigonometric parallaxes from the Research Consortium On Nearby Stars (RECONS) is used to generate a set of 16 new photometric color-$M_{K{_s}}$ relations that provide distance estimates with uncertainties of 15\%. This work expands the available suites of well-calibrated photometric distance relations that can be used to identify nearby stellar systems. The distance relations are used with quality cuts to extract an initial sample of stars from the UCAC4 estimated to be within 25 pc. Color, proper motion and existing literature sources are then used to obtain a clean sample of red dwarfs, while limiting the amount of contamination from background giants, resulting in a sample of 1761 candidate nearby stars within 25 pc. Of these, 339 are new discoveries with no previously known published parallax or distance estimate, primarily with proper motions less than 0.2 arcsec/year. Five stars are estimated to be within 10 pc, with the nearest, TYC 3980 1081 1 with V$=$ 10.50, estimated to be at 5.93 pc. That several hundred new stars have been revealed so close to the Sun illustrates once again that there is considerable work yet to be done to map the solar neighborhood, and that additional nearby stars are likely still to be discovered.