High signal-to-noise spectral characterization of the planetary-mass object HD 106906 b

Abstract

We spectroscopically characterize the atmosphere of HD 106906b, a young low-mass companion near the deuterium burning limit. The wide separation from its host star of 7.1" makes it an ideal candidate for high S/N and high-resolution spectroscopy. We aim to derive new constraints on the spectral type, effective temperature, and luminosity of HD106906b and also to provide a high S/N template spectrum for future characterization of extrasolar planets. We obtained 1.1-2.5 $\mu$m integral field spectroscopy with the VLT/SINFONI instrument with a spectral resolution of R~2000-4000. New estimates of the parameters of HD 106906b are derived by analyzing spectral features, comparing the extracted spectra to spectral catalogs of other low-mass objects, and fitting with theoretical isochrones. We identify several spectral absorption lines that are consistent with a low mass for HD 106906b. We derive a new spectral type of L1.5$\pm$1.0, one subclass earlier than previous estimates. Through comparison with other young low-mass objects, this translates to a luminosity of log($L/L_{\odot }$)=$-3.65\pm 0.08$ and an effective temperature of Teff=$1820\pm 240$ K. Our new mass estimates range between $M=11.9_{-0.8}^{+1.7}{M}_{\mathrm{Jup}}$ (hot start) and $M=14.0_{-0.5}^{+0.2}{M}_{\mathrm{Jup}}$ (cold start). These limits take into account a possibly finite formation time, i.e., HD 106906b is allowed to be 0--3 Myr younger than its host star. We exclude accretion onto HD 106906b at rates $\dot{M}>4.8\times 10^{-10}{M}_{\mathrm{Jup}}$yr${}^{-1}$ based on the fact that we observe no hydrogen (Paschen-$\beta$, Brackett-$\gamma$) emission. This is indicative of little or no circumplanetary gas. With our new observations, HD 106906b is the planetary-mass object with one of the highest S/N spectra yet. We make the spectrum available for future comparison with data from existing and next-generation (e.g., ELT and JWST) spectrographs.

11 pages, 5 figures. Accepted for publication in Astronomy & Astrophysics. Fully reduced spectra will be made available for download on CDS

References in corpus (8)

• Gaia Data Release 1. Summary of the astrometric, photometric, and survey properties
• New evolutionary models for pre-main sequence and main sequence low-mass stars down to the hydrogen-burning limit
• Characterizing Young Brown Dwarfs using Low Resolution Near-IR Spectra
• Discovery of a warm, dusty giant planet around HIP65426
• Instrumentation for the detection and characterization of exoplanets
• Characterization of exoplanets from their formation III: The statistics of planetary luminosities
• Deuterium burning in objects forming via the core accretion scenario - Brown dwarfs or planets?
• HD 106906: A Case Study for External Perturbations of a Debris Disk

Cited by in corpus (8)

• A survey of the linear polarization of directly imaged exoplanets and brown dwarf companions with SPHERE-IRDIS. First polarimetric detections revealing disks around DH Tau B and GSC 6214-210 B
• A medium-resolution spectrum of the exoplanet HIP 65426 b
• Simulated performance of the molecular mapping for young giant exoplanets with the Medium Resolution Spectrometer of JWST/MIRI
• The case of HD 106906 debris disc: A binary's revenge
• A Deep Polarimetric Study of the Asymmetrical Debris Disk HD 106906
• CROCODILE \\ Incorporating medium-resolution spectroscopy of close-in directly imaged exoplanets into atmospheric retrievals via cross-correlation
• Millimeter Dust Emission and Planetary Dynamics in the HD 106906 System
• Obliquity Constraints on the Planetary-mass Companion HD 106906 b