Looper, Dagny L. and Kirkpatrick, J. Davy and Cutri, Roc M. and Barman, Travis and Burgasser, Adam J. and Cushing, Michael C. and Roellig, Thomas and McGovern, Mark R. and McLean, Ian S. and Rice, Emily and Swift, Brandon J. and Schurr, Steven D. (2008) Discovery of two nearby peculiar L dwarfs from the 2MASS proper-motion survey: young or metal-rich? Astrophysical Journal, 686 (1). pp. 528-541. ISSN 0004-637X http://resolver.caltech.edu/CaltechAUTHORS:20090506-112250290
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We present the discovery of two nearby L dwarfs from our 2MASS proper-motion search, which uses multiepoch 2MASS observations covering ~4700 deg^2 of sky. 2MASS J18212815+1414010 and 2MASS J21481628+4003593 were overlooked by earlier surveys due to their faint optical magnitudes and their proximity to the Galactic plane (10° ≤ | b | ≤ 15°). Assuming that both dwarfs are single, we derive spectrophotometric distances of ~10 pc, thus increasing the number of known L dwarfs within 10 pc to 10. In the near-infrared, 2MASS J21481628+4003593 shows a triangular H-band spectrum, strong CO absorption, and a markedly red J − K_s color (2.38 ± 0.06) for its L6 optical spectral type. 2MASS J18212815+1414010 also shows a triangular H-band spectrum and a slightly red J − K_s color (1.78 ± 0.05) for its L4.5 optical spectral type. Both objects show strong silicate absorption at 9-11 μm. Cumulatively, these features imply an unusually dusty photosphere for both of these objects. We examine several scenarios to explain the underlying cause for their enhanced dust content and find that a metal-rich atmosphere or a low surface gravity are consistent with these results. 2MASS J18212815+1414010 may be young (and therefore have a low surface gravity) based on its low tangential velocity of 10 km s^−1. On the other hand, 2MASS J21481628+4003593 has a high tangential velocity of 62 km s^−1 and is therefore likely old. Hence, high metallicity and low surface gravity may lead to similar effects.
|Additional Information:||© 2008 The American Astronomical Society. Received 2008 May 5; accepted 2008 June 4. We thank our referee, Nigel Hambly, for a timely and helpful report. We would like to thank our Keck observing assistants Steven Magee and Julie Rivera and our IRTF observing assistants Paul Sears and Dave Griep for providing expert operation of the telescopes during our runs. We thank our instrument scientists Jim Lyke and Grant Hill at Keck and Bobby Bus and John Rayner at IRTF for their expertise in running the spectrographs, imagers, and reduction software packages. We thank Takashi Hattori for providing instrument support at Subaru. We would like to thank John Stauffer and Maria Morales-Calderon for giving us some telescope time in exchange for instrument expertise on 2005 December 9 (UT) at Keck II. D. L. L. thanks John Rayner for advising her on part of this project and Dave Sanders for financial support. We are grateful to Lee Rottler for assistance with setting up the REDSPEC package at IPAC. This paper uses data from the Brown Dwarf Spectroscopic Survey Archive (http://www.astro.ucla.edu/~mclean/BDSSarchive), the IRTF Spectral Library (http://irtfweb.ifa.hawaii.edu /~spex / spexlibrary/IRTFlibrary.html), the SpeX Prism Library (http:// web.mit.edu/ajb/www/browndwarfs/spexprism /index.html), and http://DwarfArchives.org. D. L. L. would like to thank the Northrop Grumman Corporation for a small grant to IPAC, which paid for partial salary support during the search phase of this project. This publication also makes use of data products from the Two Micron All Sky Survey (2MASS), which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation. D. L. L. is a guest user of the Canadian Astronomy Data Centre, which is operated by the Herzberg Institute of Astrophysics, National Research Council of Canada. This research has also made use of the NASA/IPAC Infrared Science Archive (IRSA), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. The 2006 August 4 UT NIRSPEC data were obtained at the W. M. Keck Observatory from telescope time allocated to the National Aeronautics and Space Administration through the agency’s scientific partnership with the California Institute of Technology and the University of California. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. As all spectroscopic and imaging follow-up data were obtained from the summit of Mauna Kea, the authors wish to recognize and acknowledge the very significant cultural role and reverence that this mountaintop has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations there.|
|Subject Keywords:||stars: individual (2MASS J18212815+1414010, 2MASS J21481628+4003593); stars: low-mass, brown dwarfs; techniques: spectroscopic|
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|Deposited By:||Tony Diaz|
|Deposited On:||11 May 2009 18:12|
|Last Modified:||26 Dec 2012 10:59|
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