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Characterization of low-mass, wide-separation substellar companions to stars in upper Scorpius : near-infrared photometry and spectroscopy

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Date
20/03/2015
Author
Lachapelle, F.-R.
Lafrenière, D.
Gagné, J.
Jayawardhana, R.
Janson, M.
Helling, C.
Witte, S.
Keywords
Brown dwarfs
Infrared: planetary systems
Stars: atmospheres
Stars: imaging
Stars: low-mass
Stars: pre-main sequence
QB Astronomy
QC Physics
NDAS
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Abstract
We present new 0.9–2.45 μm spectroscopy (R ∼ 1000), and Y, J, H, Ks,L photometry, obtained at Gemini North, of three low-mass brown dwarf companions on wide orbits around young stars of the Upper Scorpius OB association: HIP 78530 B, [PGZ 2001] J161031.9-191305 B, and GSC 06214-00210 B. We use these data to assess the companions' spectral type, temperature, surface gravity, and mass, as well as the ability of the BT-SETTL and Drift-Phoenix atmosphere models to reproduce the spectral features of young substellar objects. For completeness, we also analyze the archival spectroscopy and photometry of the Upper Scorpius planetary mass companion 1RXS J160929.1-210524 b. Based on a comparison with model spectra we find that the companions, in the above order, have effective temperatures of 2700 ± 100, 2500 ± 200, 2300 ± 100, and 1700 ± 100 K. These temperatures are consistent with our inferred spectral types, respectively M7 β, M9 γ, M9 γ, and L4 γ, obtained from spectral indices and comparisons with templates. From bolometric luminosities estimated from atmosphere model spectra adjusted to our photometry, and using evolution models at 5–10 Myr, we estimate masses of 21–25, 28–70, 14–17, and 7–12 MJup, respectively. [PGZ 2001] J161031.9-191305 B appears significantly overluminous for its inferred temperature, which explains its higher mass estimate. Synthetic spectra based on the BT-Settl and Drift-Phoenix atmosphere models generally offer a good fit to our observed spectra, although our analysis has highlighted a few problems. For example, the best fits in the individual near-infrared bands occur at different model temperatures. Also, temperature estimates based on a comparison of the broadband magnitudes and colors of the companions to synthetic magnitudes from the models are systematically lower than the temperature estimates based on a comparison with synthetic spectra.
Citation
Lachapelle , F-R , Lafrenière , D , Gagné , J , Jayawardhana , R , Janson , M , Helling , C & Witte , S 2015 , ' Characterization of low-mass, wide-separation substellar companions to stars in upper Scorpius : near-infrared photometry and spectroscopy ' , Astrophysical Journal , vol. 802 , no. 1 . https://doi.org/10.1088/0004-637X/802/1/61
Publication
Astrophysical Journal
Status
Peer reviewed
DOI
https://doi.org/10.1088/0004-637X/802/1/61
ISSN
0004-637X
Type
Journal article
Rights
© 2015. The American Astronomical Society. All rights reserved. Originally published in The Astrophysical Journal, http://dx.doi.org/10.1088/0004-637X/802/1/61
Description
F.-R.L. is supported by a Research Fellowship from the Fonds de Recherche du Québec—Nature et Technologies. D.L. is supported in part through grants from the Natural Sciences and Engineering Research Council, Canada (NSERC), and from the Université de Montréal. Additional support for this work came from NSERC grants to R.J. Ch.H. acknowledges an ERC starting grant under the FP7 program of the European Union.
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  • University of St Andrews Research
URI
http://hdl.handle.net/10023/6472

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