Hunting for Planetary Nebulae toward the Galactic Center
  We present near-infrared (IR) spectra of two planetary nebula (PN) candidates
in close lines of sight toward the Galactic center (GC) using the Gemini
Near-Infrared Spectrograph (GNIRS) at Gemini North. High-resolution images from
radio continuum and narrow-band IR observations reveal ringlike or
barrel-shaped morphologies of these objects, and their mid-IR spectra from the
Spitzer Space Telescope exhibit rich emission lines from highly-excited species
such as [S IV], [Ne III], [Ne V], and [O IV]. We also derive elemental
abundances using the Cloudy synthetic models, and find an excess amount of the
$s$-process element Krypton in both targets, which supports their nature as PN.
We estimate foreground extinction toward each object using near-IR hydrogen
recombination lines, and find significant visual extinctions ($A_V > 20$). The
distances inferred from the size versus surface brightness relation of other
PNe are $9.0\pm1.6$ kpc and $7.6\pm1.6$ kpc for SSTGC 580183 and SSTGC 588220,
respectively. These observed properties along with abundance patterns and their
close proximity to Sgr A$^*$ (projected distances $<20$ pc) make it highly
probable that these objects are the first confirmed PN objects in the nuclear
stellar disk. The apparent scarcity of such objects resembles the extremely low
rate of PN formation in old stellar systems, but is in line with the current
rate of the sustained star formation activity in the Central Molecular Zone.
