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Description
We are currently undertaking a program aimed at identifying previously unrecognized late-type dwarfs within 20pc of the Sun. As a first step, we have cross-referenced Luyten's NLTT proper-motion catalog (Cat. <I/98>) against the second incremental release of the Two Micron All Sky Survey (2MASS) Point Source Catalog (Cat. <B/2mass>) 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 JHKs data alone, we have identified a further 42 ultracool dwarfs (J-Ks>0.99) and use J-Ks 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{sigma} of 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.
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