Near Infrared Observations of GQ Lup b Using the Gemini Integral Field Spectrograph NIFS

📝 Abstract

We present new JHK spectroscopy (R ~ 5000) of GQ Lup b, acquired with the near-infrared integral field spectrograph NIFS and the adaptive optics system ALTAIR at the Gemini North telescope. Angular differential imaging was used in the J and H bands to suppress the speckle noise from GQ Lup A; we show that this approach can provide improvements in signal-to-noise ratio (S/N) by a factor of 2 - 6 for companions located at subarcsecond separations. Based on high quality observations and GAIA synthetic spectra, we estimate the companion effective temperature to Teff = 2400 +/- 100 K, its gravity to log g = 4.0 +/- 0.5, and its luminosity to log(L/L_s) = -2.47 +/- 0.28. Comparisons with the predictions of the DUSTY evolutionary tracks allow us to constrain the mass of GQ Lup b to 8 - 60 MJup, most likely in the brown dwarf regime. Compared with the spectra published by Seifahrt and collaborators, our spectra of GQ Lup b are significantly redder (by 15 - 50%) and do not show important Pa\beta emission. Our spectra are in excellent agreement with the lower S/N spectra previously published by McElwain and collaborators.

💡 Analysis

We present new JHK spectroscopy (R ~ 5000) of GQ Lup b, acquired with the near-infrared integral field spectrograph NIFS and the adaptive optics system ALTAIR at the Gemini North telescope. Angular differential imaging was used in the J and H bands to suppress the speckle noise from GQ Lup A; we show that this approach can provide improvements in signal-to-noise ratio (S/N) by a factor of 2 - 6 for companions located at subarcsecond separations. Based on high quality observations and GAIA synthetic spectra, we estimate the companion effective temperature to Teff = 2400 +/- 100 K, its gravity to log g = 4.0 +/- 0.5, and its luminosity to log(L/L_s) = -2.47 +/- 0.28. Comparisons with the predictions of the DUSTY evolutionary tracks allow us to constrain the mass of GQ Lup b to 8 - 60 MJup, most likely in the brown dwarf regime. Compared with the spectra published by Seifahrt and collaborators, our spectra of GQ Lup b are significantly redder (by 15 - 50%) and do not show important Pa\beta emission. Our spectra are in excellent agreement with the lower S/N spectra previously published by McElwain and collaborators.

📄 Content

arXiv:0908.3723v1 [astro-ph.EP] 26 Aug 2009 Near Infrared Observations of GQ Lup b Using the Gemini Integral Field Spectrograph NIFS Jean-Fran¸cois Lavigne1,2,3 and Ren´e Doyon D´epartement de physique and Observatoire du Mont M´egantic, Universit´e de Montr´eal, C.P. 6128, succ. Centre-Ville, Montr´eal, QC, Canada lavigne@astro.umontreal.ca David Lafreniere Department of Astronomy and Astrophysics, University of Toronto, 50 St. George Street, Toronto, ON, M5S 3H4, Canada Christian Marois NRC Herzberg Institute of Astrophysics, 5071 West Saanich Rd, Victoria, BC, V9E 2E7, Canada and Travis Barman Lowell Observatory, 1400 West Mars Hill Road, Flagstaff, AZ 86001, USA Received ; accepted 1Visiting worker at the Herzberg Institute of Astrophysics 2Student fellow at the Institut national d’optique 3Present address: Institut national d’optique, Parc technologique du Qu´ebec m´etropolitain, 2740 rue Einstein, Qu´ebec, QC, Canada – 2 – ABSTRACT We present new JHK spectroscopy (R ∼5000) of GQ Lup b, acquired with the near-infrared integral field spectrograph NIFS and the adaptive optics system ALTAIR at the Gemini North telescope. Angular differential imaging was used in the J and H bands to suppress the speckle noise from GQ Lup A; we show that this approach can provide improvements in signal-to-noise ratio (S/N) by a factor of 2 −6 for companions located at subarcsecond separations. Based on high- quality observations and GAIA synthetic spectra, we estimate the companion effective temperature to Teff= 2400 ± 100 K, its gravity to log g = 4.0 ± 0.5, and its luminosity to log(L/L⊙) = −2.47 ± 0.28. Comparisons with the predictions of the DUSTY evolutionary tracks allow us to constrain the mass of GQ Lup b to 8 −60 MJup, most likely in the brown dwarf regime. Compared with the spectra published by Seifahrt and collaborators, our spectra of GQ Lup b are significantly redder (by 15 −50%) and do not show important Paβ emission. Our spectra are in excellent agreement with the lower S/N spectra previously published by McElwain and collaborators. Subject headings: planetary systems - stars: low mass, brown dwarfs - stars: pre-main sequence - stars: individual (GQ Lup) - techniques: spectroscopic - techniques: high angular resolution – 3 – 1. Introduction An important goal of exoplanet imaging is understanding how planetary systems form and this requires observing planets when they are very young, i.e. at ages less than a few million years. Ten years after the first discovery of an extra-solar giant planet (EGP), the imaging era of exoplanet science has finally started. The year 2008 has been particularly prolific in that matter with the discovery of the first planetary system around the ∼60 Myr old HR 8799 (Marois et al. 2008), of the exoplanet candidates in orbit around the 100 −300 Myr old Fomalhaut (Kalas et al. 2008), in orbit around the ∼12 Myr old β Pictoris (Lagrange et al. 2008), the potential companion to the ∼5 Myr old 1RXS J160929-210524 (Lafreniere et al. 2008) and the planetary mass object (PMO) candidate evolving round the 0.9 to 3 Myr old T-Tauri star CT CHA (Schmidt et al. 2008). These new discoveries add to a few previous detections of planet candidates such as the PMO in orbit around the young (∼10 Myrs) 25 MJup brown dwarf (BD) 2M1207 (Chauvin et al. 2004) and the companion in orbit around the ∼1 −10 Myr old T Tauri star GQ Lup (Neuh¨auser et al. 2005). GQ Lup b is particularly interesting; the co-moving companion is relatively bright (K=13) and lies at 0.7 arcsec (100 ± 50 AU) from the 7th magnitude K7eV primary. Despite several studies, the mass of GQ Lup b is still poorly constrained. Neuh¨auser et al. (2005) identified prominent CO and H2O bands typical of cool M9−L4 dwarfs but could not constrain accurately the mass of the companion (1 −42 MJup) because the effective temperature (Teff; 1600 −2500 K), the gravity and the distance of the object were not well determined. Marois et al. (2007) have analyzed archived HST WFPC2 and NICMOS data and Subaru CH4, H, Ks and L′ band images of GQ Lup b and provided estimates of its bolometric luminosity (log(L/L⊙) = −2.42 ± 0.07 at 140 pc), its radius (0.38 ± 0.05 R⊙) and its effective temperature (2335 ± 100 K). Assuming a log g = 3 and based on the evolutionary models of Baraffe et al. (2003), they inferred a mass ranging from – 4 – 10 to 20 MJup. McElwain et al. (2007) secured J- and H-band spectra and found the companion to be somewhat hotter than previously reported with a spectral type between M6 and L0 corresponding to effective temperatures between 2400 and 2900 K assuming the effective temperature - spectral type relationship from Golimowski et al. (2004). Using the evolutionary models from Burrows et al. (1997) and Chabrier et al. (2000) and their derived bolometric luminosity of log(L/L⊙) = −2.46 ± 0.14 they inferred a mass of 10 −40 MJup. A mass estimate has also been reported by Seifahrt et al. (2007) who acquired J-, H- and K-band spectra and compared them to th

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