Evolved Massive Stars at Low-metallicity I. A Source Catalog for the
  Small Magellanic Cloud
  We present a clean, magnitude-limited (IRAC1 or WISE1 $\leq$ 15.0 mag)
multiwavelength source catalog for the SMC with 45,466 targets in total, with
the purpose of building an anchor for future studies, especially for the
massive star populations at low-metallicity. The catalog contains data in 50
different bands including 21 optical and 29 infrared bands, ranging from the
ultraviolet to the far-infrared. Additionally, radial velocities and spectral
classifications were collected from the literature, as well as infrared and
optical variability statistics were retrieved from different projects. The
catalog was essentially built upon a $1''$ crossmatching and a $3''$ deblending
between the SEIP source list and Gaia DR2 photometric data. Further constraints
on the proper motions and parallaxes from Gaia DR2 allowed us to remove the
foreground contamination. We estimated that about 99.5\% of the targets in our
catalog were most likely genuine members of the SMC. By using the evolutionary
tracks and synthetic photometry from MIST and the theoretical $\rm J-K_S$ color
cuts, we identified 1,405 RSG, 217 YSG and 1,369 BSG candidates in the SMC in
five different CMDs, where attention should also be paid to the incompleteness
of our sample. We ranked the candidates based on the intersection of different
CMDs. A comparison between the models and observational data shows that the
lower limit of initial mass for the RSGs population may be as low as 7 or even
6 $M_{\odot}$ and the RSG is well separated from the AGB population even at
faint magnitude, making RSGs a unique population connecting the evolved massive
and intermediate stars, since stars with initial mass around 6 to 8 $M_{\odot}$
are thought to go through a second dredge-up to become AGBs. We encourage the
interested reader to further exploit the potential of our catalog.
