S Orionis 70: Just a Foreground Field Brown Dwarf?

April 2004 • 2004ApJ...604..827B

Authors • Burgasser, Adam J. • Kirkpatrick, J. Davy • McGovern, Mark R. • McLean, Ian S. • Prato, L. • Reid, I. Neill

Abstract • We examine recent claims that the T-type brown dwarf S Ori 053810.1-203626 (S Ori 70) is a spectroscopically verified low-mass (3⁺⁵_-1 M_Jup) member of the 1-8 Myr σ Orionis cluster. Comparative arguments by Martín & Zapatero Osorio asserting that S Ori 70 exhibits low surface gravity spectral features indicative of youth and low mass are invalidated by the fact that their comparison object was not the field T dwarf 2MASS 0559-1404, but rather a nearby background star. Instead, we find that the 1-2.5 μm spectra of S Ori 70 are well matched to older (age~few Gyr) field T6-T7 dwarfs. Moreover, we find that spectral model fits to late-type field T dwarf spectra tend to yield low surface gravities (logg=3.0-3.5), and thus young ages (<~5 Myr) and low masses (<~3 M_Jup), inconsistent with expected and/or empirical values. Finally, we show that the identification of one T dwarf in the field imaged by Zapatero Osorio et al. is statistically consistent with the expected foreground contamination. Based on the reexamined evidence, we conclude that S Ori 70 may simply be an old, massive (30-60 M_Jup) field brown dwarf lying in the foreground of the σ Orionis cluster. This interpretation should be considered before presuming the existence of so-called ``cluster planets.''

Links

• SIMBAD http://simbad.u-strasbg.fr/simbo.pl?bibcode=2004ApJ...604..827B
• PDF https://stacks.iop.org/0004-637X/604/827/pdf
• PREPRINT http://arxiv.org/abs/astro-ph/0312285
• SPIRES http://inspirehep.net/search?p=find+j+ASJOA,604,827
• ELECTR https://doi.org/10.1086%2F382129
• SPIRES http://inspirehep.net/search?p=find+eprint+astro-ph/0312285