Thomas D. Beaulieu

THE SOLAR NEIGHBORHOOD. XVII. PARALLAX RESULTS FROM THE CTIOPI 0.9 m PROGRAM: 20 NEW MEMBERS OF THE RECONS 10 PARSEC SAMPLE

Astrometric measurements for 25 red dwarf systems are presented, including the first definitive trigonometric parallaxes for 20 systems within 10 pc of the Sun, the horizon of the RECONS sample. The three nearest systems that had no previous trigonometric parallaxes (other than perhaps rough preliminary efforts) are SO 0253+1652 (3.84 ± 0.04 pc, the 23rd nearest system), SCR 1845-6357 AB (3.85 ± 0.02 pc, 24th nearest), and LHS 1723 (5.32 ± 0.04 pc, 56th nearest). In total, seven of the systems reported here rank among the nearest 100 stellar systems. Supporting photometric and spectroscopic observations have been made to provide full characterization of the systems, including complete VRIJHKs photometry and spectral types. A study of the variability of 27 targets reveals six obvious variable stars, including GJ 1207, for which we observed a flare event in the V band that caused it to brighten by 1.7 mag. Improved parallaxes for GJ 54 AB and GJ 1061, both important members of the 10 pc sample, are also reported. Definitive parallaxes for GJ 1001 A, GJ 633, and GJ 2130 ABC, all of which have been reported to be within 10 pc, indicate that they are beyond 10 pc. From the analysis of systems with (previously) high trigonometric parallax errors, we conclude that parallaxes with errors in excess of 10 mas are insufficiently reliable for inclusion in the RECONS sample. The cumulative total of new additions to the 10 pc sample since 2000 is now 34 systems: 28 by the RECONS team and six by other groups. This total represents a net increase of 16% in the number of stellar systems reliably known to be nearer than 10 pc.

The Solar Neighborhood. X. New Nearby Stars in the Southern Sky and Accurate Photometric Distance Estimates for Red Dwarfs

Photometric (VJRCIC) and spectroscopic (6000–9500 A) observations of high–proper-motion stars discovered during the first phase of the SuperCOSMOS RECONS (SCR) search are used to estimate accurate distances to eight new nearby red dwarfs, including probable 10 pc sample members SCR 1845-6357 (M8.5 V at 4.6 pc), the binary SCR 0630-7643AB (M6.0 V J at 7.0 pc), and SCR 1138-7721 (M5.0 V at 9.4 pc). Distance estimates are determined using a suite of new photometric color-M relations defined using a robust set of nearby stars with accurate VRIJHKs photometry and trigonometric parallaxes. These relations are used with optical and infrared photometry to estimate distances on a uniform system (generally good to 15%) for two additional samples of red nearby star candidates: several recently discovered members of the solar neighborhood and known faint stars with proper motions in excess of 10 yr-1 south of decl. = -575. Of those without accurate trigonometric parallax measurements, there are five stars in the first sample and three in the second that are likely to be within 10 pc. The two nearest are SO 0253+1652 (M7.0 V at 3.7 pc) and DENIS 1048-3956 (M8.5 V at 4.5 pc). When combined with SCR 1845-6357, these three stars together represent the largest increase in the 5 pc sample in several decades. Red spectra are presented for the red dwarfs, and types are given on the RECONS standard spectral system. Red spectra are also given for two new nearby white dwarfs for which we estimate distances from the photometry of less than 20 pc: WD 0141-675 (LHS 145; 9.3 pc) and SCR 2012-5956 (17.4 pc). WD 0141-675 brings the total number of systems nearer than 10 pc discussed in this paper to 12.