The Astronomical Journal, 155:265 (23pp), 2018 June https://doi.org/10.3847/1538-3881/aac262 © 2018. The American Astronomical Society. All rights reserved. The Solar Neighborhood XLIV: RECONS Discoveries within 10 parsecs Todd J. Henry1,8, Wei-Chun Jao2,8 , Jennifer G. Winters3,8 , Sergio B. Dieterich4,8, Charlie T. Finch5,8, Philip A. Ianna1,8, Adric R. Riedel6,8 , Michele L. Silverstein2,8 , John P. Subasavage7,8 , and Eliot Halley Vrijmoet2 1 RECONS Institute, Chambersburg, PA 17201, USA; [email protected], [email protected] 2 Department of Physics and Astronomy, Georgia State University, Atlanta, GA 30302, USA; [email protected], [email protected], [email protected] 3 Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138, USA; [email protected] 4 Department of Terrestrial Magnetism, Carnegie Institution for Science, Washington, DC 20015, USA; [email protected] 5 Astrometry Department, U.S. Naval Observatory, Washington, DC 20392, USA; charlie.fi[email protected] 6 Space Telescope Science Institute, Baltimore, MD 21218, USA; [email protected] 7 United States Naval Observatory, Flagstaff, AZ 86001, USA; [email protected] Received 2018 April 12; revised 2018 April 27; accepted 2018 May 1; published 2018 June 4 Abstract We describe the 44 systems discovered to be within 10 pc of the Sun by the RECONS team, primarily via the long- term astrometry program at the CTIO/SMARTS 0.9 m that began in 1999. The systems—including 41 with red dwarf primaries, 2 white dwarfs, and 1 brown dwarf—have trigonometric parallaxes greater than 100 mas, with errors of 0.4–2.4 mas in all but one case. We provide updated astrometric, photometric (VRIJHK magnitudes), spectral type, and multiplicity information here. Among these are 14 systems that are new entries to the 10 pc sample, including the first parallaxes for 9 systems and new values for 5 systems that had previous parallaxes with errors greater than 10 mas or values placing them beyond 10 pc. We also provide new data for 22 systems known to lie within 10 pc and 9 systems reported to be closer than that horizon but for which new parallaxes place them further away, bringing the total to 75 systems. The 44 systems added by RECONS comprise one of every 7 systems known within 10 pc. We illustrate the evolution of the 10 pc sample from the 191 systems known when the final Yale Parallax Catalog was published in 1995 to the 317 systems known today. Even so close to the Sun, additional discoveries of white, red, and brown dwarfs are possible, both as primaries and secondaries, although we estimate that at least 90% of the stellar systems closer than 10 pc have now been identified. Key words: astrometry – solar neighborhood – stars: distances – stars: low-mass – stars: statistics – surveys Supporting material: machine-readable tables 1. Introduction systems discovered by RECONS to be within 10 pc. We also outline the growth of the 10 pc sample since the 1995 The solar neighborhood holds a special place in the human publication of the largest ground-based compendium, The psyche, because by our very nature, humans explore the nearest ( fi General Catalogue of Trigonometric Stellar Parallaxes van locales rst. Space is no exception. The nearest stars provide Altena et al. 1995), also known as the “Yale Parallax Catalog” the framework upon which stellar astrophysics is based because (hereafter YPC). We include the contributions by the space- the nearby star population contains the most easily studied based Hipparcos effort (ESA 1997; Perryman et al. 1997), with representatives of their kinds. So, it is essential that we make a initial results published in 1997, and utilize the updated careful reconnaissance of the nearest stars to understand our parallaxes from the van Leeuwen (2007) reduction done a Sun and Solar System in context. decade later; for stars within 10 pc, there are no significant The REsearch Consortium On Nearby Stars (RECONS, differences that change the sample membership. The new www.recons.org) was established in 1994 to discover “miss- results and overview presented here set the stage for the full ing” members of the solar neighborhood and to characterize the analysis of the 10 pc sample to be evaluated after parallaxes are complete sample of nearby star systems and their environs. available from Gaia in Data Release 2. Over the past two decades, we have published RECONS results We outline the observing program and target sample in in papers in this series, The Solar Neighborhood,inThe Section 2, followed by a description of the observations in Astronomical Journal. This paper focuses on the 10 pc sample, Section 3. Astrometric, photometric, and spectroscopic results in which a system composed of stars, brown dwarfs, and/or for all 75 systems in this study, including the 44 added by planets is included if a trigonometric parallax, πtrig, of at least RECONS to the 10 pc sample, are given in Section 4. Systems 100 mas has been determined, and the parallax has a formal worthy of note are described in Section 5. Finally, the evolution error, σπ, of 10 mas or less. Here we report trigonometric of the 10 pc sample since 1995 and the contributions made by parallaxes measured at the Cerro Tololo Inter-American RECONS and others are placed in context in Section 6. Observatory (CTIO)/Small and Moderate Aperture Research Telescope System (SMARTS) 0.9 m for 14 systems that are 2. Observing Program and Sample new additions to the 10 pc sample,9 as well as for 30 other A primary goal of the RECONS effort has been to discover and characterize white, red, and brown dwarfs in the southern 8 Visiting Astronomer, Cerro Tololo Inter-American Observatory. CTIO is operated by AURA, Inc., under contract to the National Science Foundation. sky within 25 pc. To this end, the RECONS team began a 9 We also provide parallaxes from URAT confirming that seven of the new parallax program at CTIO in 1999 under the auspices of the systems are within 10 pc. NOAO Surveys Program, using both the 0.9 m and 1.5 m 1 The Astronomical Journal, 155:265 (23pp), 2018 June Henry et al. CTIO/SMARTS telescopes. Optical photometry was also As this is the 20th paper to report parallaxes from the obtained at both telescopes, and spectra were obtained at the 0.9 m,11 we provide only brief information on the observing 1.5 m and CTIO 4.0 m. Parallaxes for a total of 58 systems with techniques and data reduction here; additional details can be VRI=11–23 were measured at the 1.5 m and published in found in previous papers in this series, particularly in Jao et al. Costa et al. (2005, 2006). The 0.9 m effort has continued to the (2005) and Henry et al. (2006). Data are reduced via IRAF with present as an expanded astrometry/photometry program via the typical bias subtraction and dome flat-fielding, using calibration SMARTS Consortium, which was formed in 2003. More than frames taken at the beginning of each night. The frames are 800 systems with VRI=9–18 have been observed for parallax then analyzed using our astrometric pipeline, utilizing images at the 0.9 m, with new results presented here in Section 4. taken within 120 minutes of transit to produce parallaxes, The objects targeted in the RECONS program at CTIO fall proper motions, and time-series photometry in the parallax into two general categories: those that have high proper filter (see Section 4.2). Target positions are measured relative to motions or crude trigonometric parallaxes indicating they 5–19 reference stars within a few arcminutes of the targets, might be nearby, and those with optical/infrared photometry or resulting in relative trigonometric parallaxes and proper spectroscopy hinting that they might be closer than 25 pc. motions. Parallaxes are corrected from relative to absolute Systems with declinations south of +30° have been observed values using the mean of the photometric distances to the astrometrically, photometrically, and spectroscopically to reference stars. For a few targets, the distant reference stars pinpoint their distances, proper motions, absolute magnitudes, appear reddened and result in corrections of 3 mas or more. In colors, and spectral types. By providing this full suite of data, these cases we adopt our typical correction of 1.50 ± 0.50 mas well-characterized new members can be added to the 25 pc for 0.9 m observations. This value is in the midst of the range sample. In this paper we collect and update results for the full of corrections for other stars in this sample (0.28–2.76 mas) and set of 44 new systems found within 10 pc via this effort, provides for a generous uncertainty (only three systems have provide new results for 22 previously identified 10 pc systems, larger correction uncertainties), which is appropriate given that and add results for 9 additional systems that were previously we have estimated the correction. reported to be within 10 pc for which our parallaxes place them We also report parallaxes from the United States Naval beyond that horizon. In total, we present information for 75 Observatory Robotic Astrometric Telescope (URAT) in the systems composed of primarily red dwarfs, with a few white notes for seven systems (Section 5) that support our RECONS and brown dwarfs as well. measurements placing these systems within 10 pc. URAT observations were taken at CTIO over a 2-year period that 3. Observations overlapped with the long-term work described for the RECONS effort, and details of the southern portion of the 3.1.