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Discoveries from a Near-Infrared Proper Motion Survey Using Multi-Epoch Two Micron All-Sky Survey Data∗

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Discoveries from a Near-Infrared Proper Motion Survey Using Multi-Epoch Two Micron All-Sky Survey Data∗ The Astrophysical Journal Supplement Series, 190:100–146, 2010 September doi:10.1088/0067-0049/190/1/100 C 2010. The American Astronomical Society. All rights reserved. Printed in the U.S.A. DISCOVERIES FROM A NEAR-INFRARED PROPER MOTION SURVEY USING MULTI-EPOCH TWO MICRON ALL-SKY SURVEY DATA∗ J. Davy Kirkpatrick1, Dagny L. Looper2, Adam J. Burgasser3, Steven D. Schurr4, Roc M. Cutri1, Michael C. Cushing5, Kelle L. Cruz6, Anne C. Sweet7, Gillian R. Knapp8, Travis S. Barman9, John J. Bochanski10, Thomas L. Roellig11, Ian S. McLean12, Mark R. McGovern13, and Emily L. Rice14 1 Infrared Processing and Analysis Center, MS 100-22, California Institute of Technology, Pasadena, CA 91125, USA; [email protected] 2 Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822, USA 3 Center for Astrophysics and Space Science, University of California, San Diego, CA 92093, USA 4 Planck Science Center, MS 220-6, California Institute of Technology, Pasadena, CA 91125, USA 5 Jet Propulsion Laboratory, Pasadena, CA 91109, USA 6 Department of Physics and Astronomy, Hunter College, New York, NY 10065, USA 7 British Consulate, San Francisco, CA 94104, USA 8 Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544, USA 9 Lowell Observatory, 1400 West Mars Hill Road, Flagstaff, AZ 86001, USA 10 Massachusetts Institute of Technology, 77 Massachusetts Avenue, Building 37, Cambridge, MA 02139, USA 11 NASA Ames Research Center, MS 245-6, Moffett Field, CA 94035-1000, USA 12 Department of Physics and Astronomy, UCLA, Los Angeles, CA 90095-1562, USA 13 Antelope Valley College, Lancaster, CA 93536, USA 14 American Museum of Natural History, New York, NY 10024, USA Received 2009 December 26; accepted 2010 July 12; published 2010 August 27 ABSTRACT We have conducted a 4030 deg2 near-infrared proper motion survey using multi-epoch data from the Two Micron All-Sky Survey (2MASS). We find 2778 proper motion candidates, 647 of which are not listed in SIMBAD. After comparison to Digitized Sky Survey images, we find that 107 of our proper motion candidates lack counterparts at B, R, and I bands and are thus 2MASS-only detections. We present results of spectroscopic follow-up of 188 targets that include the infrared-only sources along with selected optical-counterpart sources with faint reduced proper motions or interesting colors. We also establish a set of near-infrared spectroscopic standards with which to anchor near-infrared classifications for our objects. Among the discoveries are six young field brown dwarfs, five “red L” dwarfs, three L-type subdwarfs, twelve M-type subdwarfs, eight “blue L” dwarfs, and several T dwarfs. We further refine the definitions of these exotic classes to aid future identification of similar objects. We examine their kinematics and find that both the “blue L” and “red L” dwarfs appear to be drawn from a relatively old population. This survey provides a glimpse of the kinds of research that will be possible through time-domain infrared projects such as the UKIDSS Large Area Survey, various VISTA surveys, and WISE, and also through z-ory-band enabled, multi-epoch surveys such as Pan-STARRS and LSST. Key words: brown dwarfs – infrared: stars – proper motions – solar neighborhood – stars: late-type Online-only material: color figures, machine-readable table 1. INTRODUCTION AB by Innes (1915). Barnard (1916) discovered the second closest system—most commonly known as Barnard’s star—via During the first quarter of the 20th century, cataloging the its proper motion, which is still the highest known for any star stellar constituents of the Solar Neighborhood became a major (10.37 yr−1; Benedict et al. 1999). Wolf (1919) used proper focus of astronomical research. Although the closest of the motion to uncover the third closest system, known as Wolf bright stars were identifiable through dedicated trigonometric 359, and Ross (1926) did the same to reveal the seventh, parallax programs, such programs were not feasible for the eighth, and eleventh nearest systems, known as Ross 154, Ross wealth of dimmer objects. As a result the search for the faintest 248, and Ross 128, respectively. Taking this work to even fainter of the nearby stars came to rely heavily on the fact that tangential limits, van Biesbroeck (1944, 1961) performed a photographic motion of the closest objects would be measurable against the search for companions to nearby stars and revealed two late-M sea of non-moving background objects. As a result, these proper dwarfs, known as van Biesbroeck 8 (vB 8) and van Biesbroeck motion measurements using multi-epoch photographic plates 10 (vB 10). Deeper, larger scale proper motion surveys by became the primary means of discovery. Giclas et al. (1971, 1978) and by Luyten (1979a, 1979b, 1980a, The closest star to the Sun, Proxima Centauri, was discovered 1980b) were performed in the mid-20th century. These Luyten as a distant, common proper motion companion of α Centauri references tabulate the results of all previous motion surveys done through the 1970s. These surveys accounted for a total of −1 ∗ over 58,000 motion stars with μ>0.18 yr down to the Some of the spectroscopic data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the B-band plate limit of the Palomar Observatory Sky Survey California Institute of Technology, the University of California, and the (POSS) and to brighter limits for stars south of the POSS itself. National Aeronautics and Space Administration. The Observatory was made A major limitation of these previous surveys was their re- possible by the generous financial support of the W. M. Keck Foundation. Other spectroscopic data were collected at the Subaru Telescope, which is liance on optical data, primarily at B and R bands; a lack operated by the National Astronomical Observatory of Japan. of deep, dual-epoch material in the far southern sky; and an 100 No. 1, 2010 DISCOVERIES FROM AN NIR PROPER MOTION SURVEY 101 inability to probe close to the Galactic plane. Recent large- an unusually blue L dwarf. Even more recently, Deacon et al. area surveys have attempted to remove some of these bi- (2009) have matched up data from the United Kingdom Infrared ases while still using photographic plate material. Luyten’s Deep Sky Survey (UKIDSS; Lawrence et al. 2007) Data Release surveys, which generally required that objects be detectable 4 with 2MASS to identify 267 low-mass stars and brown dwarfs on both the B- and R-band plates and be located at rela- via their proper motions; of these, ten known L dwarfs and one tively high galactic latitude, have now been supplemented known T dwarf were recovered and nine new L dwarf candidates with the LSPM/LSR proper motion survey of Lepine´ et al. were identified. (2002, 2003) and Lepine´ (2005, 2008), which uses two-epoch We present here a large-area (∼4030 deg2,or∼10% of the R-band data only (when two epochs are available) to push to sky) proper motion survey where both epochs of coverage lie intrinsically redder and fainter objects. Similar investigations, longward of 1 μm. By performing a color-free proper motion many concentrating more heavily on the less-complete southern search we can achieve several goals. (1) We can determine sky, have been performed by the Wroblewski & Torres sur- the location of unusual objects in color space to enable future vey (WT; Wroblewski & Costa 2001 and references therein), photometric searches for these objects. (2) The kinematic bias the Calan European Southern Observatory survey (Calan-ESO; present in a proper motion survey will enable us to find very Ruiz et al. 2001), the Automated Plate Measuring Proper Motion old brown dwarfs, and such newfound discoveries will help survey (APMPM; Scholz et al. 2000), the SuperCOSMOS Sky to expand the list of observed low-metallicity, low-temperature Survey Proper Motion survey (SSSPM; Scholz & Meusinger atmospheres and provide invaluable tests of atmospheric theory. 2002), the Liverpool-Edinburgh High Proper Motion survey (3) We can begin to explore the mass function of substellar halo (LEHPM; Pokorny et al. 2004), and the SuperCOSMOS- objects, allowing us for the first time to probe the efficiency of RECONS survey (SCR; Finch et al. 2007 and references brown dwarf formation in low-metallicity environments. therein). CCD-based surveys have also begun to have an impact. The 2. SURVEY METHODOLOGY SkyMorph database from the Near Earth Asteroid Tracking program uncovered a previously unrecognized late-M dwarf 2.1. The 1X-6X Survey (List 1) −1 moving at 5.05 yr that now ranks as one of the closest stars For the first part of our survey we used data from the to the Sun (Teegarden et al. 2003). This discovery highlights 2MASS All-Sky Point Source Catalog (PSC) as epoch 1 and the fact that deeper visible-light surveys with shorter epoch from the 2MASS 6X Point Source Working Database/Catalog differences will be able to detect nearby stars with motions too as epoch 2. The latter catalog comprises a set of special large to have been detected with prior searches. Surveys by observations made at the end of 2MASS operations and taken the Panoramic Survey Telescope and Rapid Response System with exposures six times longer than the main survey. The (Pan-STARRS; Kaiser 2004) in the northern hemisphere and area covered by the 6X observations and hence the total area Large Synoptic Survey Telescope (LSST; Ivezic et al. 2008) overlapped by both data sets is ∼580 deg2. The epoch difference and SkyMapper Telescope (Southern Sky Survey, aka S3; Keller is 1–3 years. See Figure 1 for a graphical representation of the et al.
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