Astrophys. J., 656, 505-514 (2007/February-2)
First high-contrast science with an integral field spectrograph: the substellar companion to GQ Lupi.
McELWAIN M.W., METCHEV S.A., LARKIN J.E., BARCZYS M., ISERLOHE C., KRABBE A., QUIRRENBACH A., WEISS J. and WRIGHT S.A.
Abstract (from CDS):
We present commissioning data from the OSIRIS integral field spectrograph (IFS) on the Keck II 10 m telescope that demonstrate the utility of adaptive optics IFS spectroscopy in studying faint close-in substellar companions in the halos of bright stars. Our R~2000 J- and H-band spectra of the substellar companion to the 1-10 Myr old GQ Lup complement existing K-band spectra and photometry and improve on the original estimate of its spectral type. We find that GQ Lup B is somewhat hotter (M6-L0) than reported in the discovery paper by Neuhäuser and collaborators (M9-L4), mainly due to the surface gravity sensitivity of the K-band spectral classification indices used by the discoverers. Spectroscopic features characteristic of low surface gravity objects, such as lack of alkali absorption and a triangular H-band continuum, are indeed prominent in our spectrum of GQ Lup B. The peculiar shape of the H-band continuum and the difference between the two spectral type estimates is well explained in the context of the diminishing strength of H2collision-induced absorption with decreasing surface gravity, as recently proposed for young ultracool dwarfs by Kirkpatrick and collaborators. Using our updated spectroscopic classification of GQ Lup B and a reevaluation of the age and heliocentric distance of the primary, we perform a comparative analysis of the available substellar evolutionary models to estimate the mass of the companion. We find that the mass of GQ Lup B is 0.010-0.040 M☉. Hence, it is unlikely to be a wide-orbit counterpart to the known radial velocity extrasolar planets, whose masses are ≲0.015 M☉. Instead, GQ Lup A/B is probably a member of a growing family of very low mass ratio widely separated binaries discovered through high-contrast imaging.
Stars: Binaries: General - Instrumentation: Adaptive Optics - Stars: Individual: Constellation Name: GQ Lupi - Stars: Low-Mass, Brown Dwarfs
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