Detection of Galactic Center source G2 at 3.8 $\mu$m during periapse
  passage
  We report new observations of the Galactic Center source G2 from the W. M.
Keck Observatory. G2 is a dusty red object associated with gas that shows tidal
interactions as it nears closest approach with the Galaxy's central black hole.
Our observations, conducted as G2 passed through periapse, were designed to
test the proposal that G2 is a 3 earth mass gas cloud. Such a cloud should be
tidally disrupted during periapse passage. The data were obtained using the
Keck II laser guide star adaptive optics system (LGSAO) and the facility
near-infrared camera (NIRC2) through the K' [2.1 $\mu$m] and L' [3.8 $\mu$m]
broadband filters. Several results emerge from these observations: 1) G2 has
survived its closest approach to the black hole as a compact, unresolved source
at L'; 2) G2's L' brightness measurements are consistent with those over the
last decade; 3) G2's motion continues to be consistent with a Keplerian model.
These results rule out G2 as a pure gas cloud and imply that G2 has a central
star. This star has a luminosity of $\sim$30 $L_{\odot} $ and is surrounded by
a large ($\sim$2.6 AU) optically thick dust shell. The differences between the
L' and Br-$\gamma$ observations can be understood with a model in which L' and
Br-$\gamma$ emission arises primarily from internal and external heating,
respectively. We suggest that G2 is a binary star merger product and will
ultimately appear similar to the B-stars that are tightly clustered around the
black hole (the so-called S-star cluster).
