Accretion Properties of PDS 70b with MUSE*

Abstract

We report a new evaluation of the accretion properties of PDS 70b obtained with the Very Large Telescope/Multi Unit Spectroscopic Explorer. The main difference from the previous studies of Haffert et al. and Aoyama & Ikoma is in the mass accretion rate. Simultaneous multiple line observations, such as H α and H β , can better constrain the physical properties of an accreting planet. While we clearly detected H α emissions from PDS 70b, no H β emissions were detected. We estimate the line flux of H β with a 3 σ upper limit to be 2.3 × 10 −16  erg s −1  cm −2 . The flux ratio F H β / F H α for PDS 70b is <0.28. Numerical investigations by Aoyama et al. suggest that F H β / F H α should be close to unity if the extinction is negligible. We attribute the reduction of the flux ratio to the extinction, and estimate the extinction of H α ( A H α ) for PDS 70b to be >2.0 mag using the interstellar extinction value. By combining with the H α linewidth and the dereddening line luminosity of H α , we derive the PDS 70b mass accretion rate to be ≳5 × 10 −7   M Jup yr −1 . The PDS 70b mass accretion rate is an order of magnitude larger than that of PDS 70. We found that the filling factor f f  (the fractional area of the planetary surface emitting H α ) is ≳0.01, which is similar to the typical stellar value. The small value of f f indicates that the H α emitting areas are localized at the surface of PDS 70b.