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- Viswanath, Gayathri, 1992-, et al.
(författare)
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Exoplanet Accretion Monitoring Spectroscopic Survey (ENTROPY).I — Evidence for magnetospheric accretion in the young isolated planetary-mass object 2MASS J11151597+1937266
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Accretion among planetary mass companions is a poorly understood phenomenon, mainly due to the lack of observational studies that shed light on the process. Detection of emission lines from accreting gas giants facilitate detailed investigations into their formation mechanisms. This work adds another young, sub-stellar candidate to the sample of few planetary-mass objects with observed emission lines − an isolated L2ϒ dwarf 2MASS J11151597+1937266 with a mass between 7 and 21 MJup and an age of 5−45 Myr, located at 45.49±2.14 pc. We obtained the first high-resolution (R~50,000) spectrum of the target with VLT/UVES, an echelle spectrograph operating in the near-UV to visible wavelengths (3200−6800 Å). We report on several resolved H I (H3−H7) and He I emission lines (λ5875.6 Å ) in the spectrum. Based on the asymmetric line profiles of Hα and Hβ, the 10% width of Hα emission (198±5 km s-1), tentative He I emission at 6678 Å and indications of a disk from MIR excess, we confirm ongoing accretion at this object. We revise the physical parameters of the target based on the more accurate Gaia parallax-based distance measurement and derive a mass accretion rate of MJup yr-1 for 2MASS J11151597+1937266 based on the HI line luminosities using planetary scaling relations for Lline‾Lacc. Analysis of the observed H I profiles within the framework of planet-surface shock model implies a pre-shock gas velocity of v0= km s-1 and a pre-shock density of n0=1013 cm-3. The line-emitting area of the planet predicted from planet-surface shock model is very small (~0.09%), and points to a shock at the base of a magnetospherically induced funnel. The Hα profile exhibits a much stronger flux than predicted by the best-fitting model to the rest of the H I profiles, indicating that another mechanism than shock emission contributes to, or even dominates, the Hα emission. On comparison of line fluxes and mass accretion rate from this UVES epoch with those from archival low-resolution SDSS DR9 and DR12 spectra, we cannot exclude variability in accretion at 2MASS J11151597+1937266.
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