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Near-Infrared Observations of GQ Lup b Using the Gemini Integral Field Spectrograph NIFS
We present new JHK spectroscopy (R ~ 5000) of GQ Lup b, acquired withthe Near-Infrared Integral Field Spectrograph and the adaptive opticssystem ALTAIR at the Gemini North telescope. Angular differentialimaging was used in the J and H bands to suppress the speckle noise fromGQ Lup A; we show that this approach can provide improvements insignal-to-noise ratio (S/N) by a factor of 2-6 for companions located atsubarcsecond separations. Based on high-quality observations and GlobalAstrometric lnterferometer for Astrophysics synthetic spectra, weestimate the companion effective temperature to T eff = 2400± 100 K, its gravity to log g = 4.0 ± 0.5, and itsluminosity to log(L/L sun) = -2.47 ± 0.28.Comparisons with the predictions of the DUSTY evolutionary tracks allowus to constrain the mass of GQ Lup b to 8-60 M Jup, mostlikely in the brown dwarf regime. Compared with the spectra published bySeifahrt and collaborators, our spectra of GQ Lup b are significantlyredder (by 15%-50%) and do not show important Pa? emission. Ourspectra are in excellent agreement with the lower S/N spectra previouslypublished by McElwain and collaborators.
| First High-Contrast Science with an Integral Field Spectrograph: The Substellar Companion to GQ Lupi
We present commissioning data from the OSIRIS integral fieldspectrograph (IFS) on the Keck II 10 m telescope that demonstrate theutility of adaptive optics IFS spectroscopy in studying faint close-insubstellar companions in the halos of bright stars. Our R~2000 J- andH-band spectra of the substellar companion to the 1-10 Myr old GQ Lupcomplement existing K-band spectra and photometry and improve on theoriginal estimate of its spectral type. We find that GQ Lup B issomewhat hotter (M6-L0) than reported in the discovery paper byNeuhäuser and collaborators (M9-L4), mainly due to the surfacegravity sensitivity of the K-band spectral classification indices usedby the discoverers. Spectroscopic features characteristic of low surfacegravity objects, such as lack of alkali absorption and a triangularH-band continuum, are indeed prominent in our spectrum of GQ Lup B. Thepeculiar shape of the H-band continuum and the difference between thetwo spectral type estimates is well explained in the context of thediminishing strength of H2 collision-induced absorption withdecreasing surface gravity, as recently proposed for young ultracooldwarfs by Kirkpatrick and collaborators. Using our updated spectroscopicclassification of GQ Lup B and a reevaluation of the age andheliocentric distance of the primary, we perform a comparative analysisof the available substellar evolutionary models to estimate the mass ofthe companion. We find that the mass of GQ Lup B is 0.010-0.040Msolar. Hence, it is unlikely to be a wide-orbit counterpartto the known radial velocity extrasolar planets, whose masses are<~0.015 Msolar. Instead, GQ Lup A/B is probably a memberof a growing family of very low mass ratio widely separated binariesdiscovered through high-contrast imaging.
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