HIGH-RESOLUTION SPECTROSCOPY DURING ECLIPSE OF THE YOUNG SUBSTELLAR ECLIPSING BINARY 2MASS 0535-0546. I. PRIMARY SPECTRUM: COOL SPOTS VERSUS OPACITY UNCERTAINTIES
- Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States)
- Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 37235 (United States)
We present high-resolution Keck optical spectra of the very young substellar eclipsing binary 2MASS J05352184-0546085, obtained during eclipse of the lower-mass (secondary) brown dwarf. The observations yield the spectrum of the higher-mass (primary) brown dwarf alone, with negligible ({approx}1.6%) contamination by the secondary. We perform a simultaneous fine analysis of the TiO-{epsilon} band and the red lobe of the K I doublet, using state-of-the-art PHOENIX DUSTY and COND synthetic spectra. Comparing the effective temperature and surface gravity derived from these fits to the empirically determined surface gravity of the primary (log g = 3.5) then allows us to test the model spectra as well as probe the prevailing photospheric conditions. We find that: (1) fits to TiO-{epsilon} alone imply T{sub eff} = 2500 {+-} 50 K; (2) at this T{sub eff}, fits to K I imply log g = 3.0, 0.5 dex lower than the true value; and (3) at the true log g, K I fits yield T{sub eff} = 2650 {+-} 50 K, {approx}150 K higher than from TiO-{epsilon} alone. On the one hand, these are the trends expected in the presence of cool spots covering a large fraction of the primary's surface (as theorized previously to explain the observed T{sub eff} reversal between the primary and secondary). Specifically, our results can be reproduced by an unspotted stellar photosphere with T{sub eff} = 2700 K and (empirical) log g = 3.5, coupled with axisymmetric cool spots that are 15% cooler (2300 K), have an effective log g = 3.0 (0.5 dex lower than photospheric), and cover 70% of the surface. On the other hand, the trends in our analysis can also be reproduced by model opacity errors: there are lacks in the synthetic TiO-{epsilon} opacities, at least for higher-gravity field dwarfs. Stringently discriminating between the two possibilities requires combining the present results with an equivalent analysis of the secondary (predicted to be relatively unspotted compared to the primary).
- OSTI ID:
- 21464640
- Journal Information:
- Astrophysical Journal, Vol. 722, Issue 2; Other Information: DOI: 10.1088/0004-637X/722/2/1138; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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