Resolving Accretion onto the Giant Exoplanet DH Tau b

As giant planets form, it is expected they become surrounded by circumplanetary disks
embedded within a circumstellar disk. Forming planets are expected to gain additional mass
and angular momentum by accreting material from these circumplanetary disks. However, key
questions remain such as: What is the geometry of the accretion flows onto forming giant
planets? and, How rapidly do they accrete material from their disks? For example, accretion
could occur through an equatorial boundary layer or through a magnetically controlled funnel
flow similar to how young stars accrete material from their circumstellar disks. High resolution
spectrosccopy of emission line profiles can constrain the geometry of the accretion flow, and the
line flux can be used to estimate the accretion rate. Here, we use the HIRES on Keck I to, for
the first time, both spatially and spectrally resolve the H\alpha line profile from DH Tau b, an 11
M_{Jup} giant planet accreting material within the disk of DH Tau. Preliminary results show the
measured line profile is single peaked with a FWHM of ~140 km/s, and its shape is generally
consistent with expectations from magnetically controlled accretion models. The measured line
luminosity gives a preliminary accretion rate of about 10^{-7} to 10^{-6} M_{Jup} yr^{-1},
depending on whether stellar or planetary mass accretion rate calibrations are used. We present
these results and discuss their implications.