Meeting the Cool Neighbors. I. Nearby Stars in the NLTT Catalogue: Defining the Sample

We are currently undertaking a program aimed at identifying previously unrecognized late-type dwarfs within 20 pc of the Sun. As a first step, we have cross-referenced Luyten's NLTT proper-motion catalog against the second incremental release of the Two Micron All Sky Survey (2MASS) Point Source Catalog and use optical/infrared colors, derived by combining Luyten's m_r estimates with 2MASS data, to identify candidate nearby stars. This paper describes the definition of a reference sample of 1245 stars and presents a compilation of literature data for more than one-third of the sample. Only 274 stars have trigonometric parallax measurements, but we have used data for nearby stars with well-determined trigonometric parallaxes to compute color-magnitude relations in the (M_V, V-K), (M_V, V-I), and (M_I, I-J) planes and use those relations to determine photometric parallaxes for NLTT stars with optical photometry. Based on the 2MASS JHK_s data alone, we have identified a further 42 ultracool dwarfs (J-K_s>0.99) and use J-K_s colors to estimate photometric parallaxes. Combining these various techniques, we identify 308 stars with formal distances of less than 20 pc, while a further 46 have distance estimates within 1 σ of our survey limit. Of these 354 stars, 75, including 39 of the ultracool dwarfs, are new to nearby-star catalogs. Two stars with both optical and near-infrared photometry are potential additions to the immediate solar neighborhood, with formal distance estimates of less than 10 pc.