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 \times 10 ^ { -18 } and 1.5 \times 10 ^ { -18 } erg/s/cm ^ { 2 } at 0 \farcs 4 and 1 \farcs 6 , 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 _ { J } and 2.29 ^ { +0.03 } _ { -0.04 } M _ { 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 _ { J } , which may assist in direct imaging searches around faint YSOs for which extreme adaptive optics instruments are unavailable .