Title: Constraining accretion signatures of exoplanets in the TW Hya transitional disk,
Abstract: We present a near-infrared direct imaging search for accretion signatures of
possible protoplanets around the young stellar object (YSO) TW Hya, a
multi-ring disk exhibiting evidence of planet formation. The Pa$\beta$ line
(1.282 $\mu$m) is an indication of accretion onto a protoplanet, and its
intensity is much higher than that of blackbody radiation from the protoplanet.
We focused on the Pa$\beta$ line and performed Keck/OSIRIS spectroscopic
observations. Although spectral differential imaging (SDI) reduction detected
no accretion signatures, the results of the present study allowed us to set
5$\sigma$ detection limits for Pa$\beta$ emission of $5.8\times10^{-18}$ and
$1.5\times10^{-18}$ erg/s/cm$^2$ at 0\farcs4 and 1\farcs6, respectively. We
considered the mass of potential planets using theoretical simulations of
circumplanetary disks and hydrogen emission. The resulting masses were $1.45\pm
0.04$ M$_{\rm J}$ and $2.29 ^{+0.03}_{-0.04}$ M$_{\rm J}$ at 25 and 95 AU,
respectively, which agree with the detection limits obtained from previous
broadband imaging. The detection limits should allow the identification of
protoplanets as small as $\sim$1 M$_{\rm J}$, which may assist in direct
imaging searches around faint YSOs for which extreme adaptive optics
instruments are unavailable.