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Title:
Ophiuchus 1622-2405: Not a Planetary-Mass Binary
Authors:
Luhman, K. L.; Allers, K. N.; Jaffe, D. T.; Cushing, M. C.; Williams, K. A.; Slesnick, C. L.; Vacca, W. D.
Affiliation:
AA(Department of Astronomy and Astrophysics, The Pennsylvania State University, University Park, PA 16802 ), AB(Institute for Astronomy, University of Hawaii at Manoa, Honolulu, HI 96822; Visiting Astronomer at the Infrared Telescope Facility, which is operated by the University of Hawaii under Cooperative Agreement NCC 5-538 with the National Aeronautics and Space Administration, Office of Space Science, Planetary Astronomy Program.), AC(Department of Astronomy, The University of Texas, Austin, TX 78712.), AD(Visiting Astronomer at the Infrared Telescope Facility, which is operated by the University of Hawaii under Cooperative Agreement NCC 5-538 with the National Aeronautics and Space Administration, Office of Space Science, Planetary Astronomy Program; Steward Observatory, The University of Arizona, Tucson, AZ 85721; Spitzer Fellow.), AE(Steward Observatory, The University of Arizona, Tucson, AZ 85721; Department of Astronomy, University of Texas, Austin, TX 78712.), AF(Department of Astronomy, MS105-24, California Institute of Technology, Pasadena, CA 91125.), AG(SOFIA-USRA, NASA Ames Research Center, MS N211-3, Moffett Field, CA 94035.)
Publication:
The Astrophysical Journal, Volume 659, Issue 2, pp. 1629-1636. (ApJ Homepage)
Publication Date:
04/2007
Origin:
UCP
Astronomy Keywords:
Stars: Binaries: Visual, Infrared: Stars, Stars: Evolution, Stars: Formation, Stars: Low-Mass, Brown Dwarfs, Stars: Pre-Main-Sequence
DOI:
10.1086/512539
Bibliographic Code:
2007ApJ...659.1629L

Abstract

We present an analysis of the mass and age of the young low-mass binary Oph 1622-2405. Using resolved optical spectroscopy of the binary, we measure spectral types of M7.25+/-0.25 and M8.75+/-0.25 for the A and B components, respectively. We show that our spectra are inconsistent with the spectral types of M9 and M9.5-L0 from Jayawardhana & Ivanov and M9+/-0.5 and M9.5+/-0.5 from Close and coworkers. Based on our spectral types and the theoretical evolutionary models of Chabrier and Baraffe, we estimate masses of ~0.055 and ~0.019 Msolar for Oph 1622-2405A and B, which are significantly higher than the values of 0.013 and 0.007 Msolar derived by Jayawardhana & Ivanov and above the range of masses observed for extrasolar planets (M<~0.015 Msolar). Planet-like mass estimates are further contradicted by our demonstration that Oph 1622-2405A is only slightly later (by 0.5 subclass) than the composite of the young eclipsing binary brown dwarf 2M 0535-0546, whose components have dynamical masses of 0.034 and 0.054 Msolar. To constrain the age of Oph 1622-2405, we compare the strengths of gravity-sensitive absorption lines in optical and near-infrared spectra of the primary to lines in field dwarfs (tau>1 Gyr) and members of Taurus (tau~1 Myr) and Upper Scorpius (tau~5 Myr). The line strengths for Oph 1622-2405A are inconsistent with membership in Ophiuchus (tau<1 Myr) and instead indicate an age similar to that of Upper Sco, which is in agreement with a similar analysis performed by Close and coworkers. We conclude that Oph 1622-2405 is part of an older population in Sco-Cen, perhaps Upper Sco itself.

This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory Chile.


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