The Post-Periapse Evolution of Galactic Center Source G1: The second
  case of a resolved tidal interaction with a supermassive black hole
  We present new Adaptive Optics (AO) imaging and spectroscopic measurements of
Galactic Center source G1 from W. M. Keck Observatory. Our goal is to
understand its nature and relationship to G2, which is the first example of a
spatially-resolved object interacting with the supermassive black hole (SMBH).
Both objects have been monitored with AO for the past decade (2003 - 2014) and
are comparatively close to the black hole ($a_{\rm{min}} \sim$200-300 AU) on
very eccentric orbits ($e_{\rm{G1}}\sim$0.99; $e_{\rm{G2}}\sim$0.96). While G2
has been tracked before and during periapse passage ($T_{0} \sim$ 2014.2), G1
has been followed since soon after emerging from periapse ($T_{0} \sim$
2001.3). Our observations of G1 double the previously reported observational
time baseline, which improves its orbital parameter determinations. G1's
orbital trajectory appears to be in the same plane as that of G2, but with a
significantly different argument of periapse ($\Delta\omega$ = 21$\pm$4
degrees). This suggests that G1 is an independent object and not part of a gas
stream containing G2 as has been proposed. Furthermore, we show for the first
time that: (1) G1 is extended in the epochs closest to periapse along the
direction of orbital motion and (2) G1 becomes significantly smaller over time,
(450 AU in 2004 to less than 170 AU in 2009). Based on these observations, G1
appears to be the second example of an object tidally interacting with a SMBH.
G1's existence 14 years after periapse, along with its compactness in epochs
further from the time of periapse, suggest that this source is stellar in
nature.
