Red supergiant stars in the Large Magellanic Cloud. II. Infrared
  properties and mid-infrared variability
  The characteristics of IR properties and MIR variability of RSGs in the LMC
are analyzed based on 12 bands of NIR to MIR co-added data from 2MASS, Spitzer
and WISE, and $\sim$6.6 years of MIR time-series data collected by the ALLWISE
and NEOWISE-R projects. 773 RSGs candidates were compiled from the literature
and verified by using the CMD, SED and MIR variability. About 15\% of valid
targets in the $IRAC1-IRAC2$/$IRAC2-IRAC3$ diagram may show PAH emission. We
show that arbitrary dereddening Q parameters related to the IRAC4, S9W, WISE3,
WISE4, and MIPS24 bands could be constructed based on a precise measurement of
MIR interstellar extinction law. Several peculiar outliers in our sample are
discussed, in which one outlier might be a RSG right before the explosion or an
x-AGB star in the very late evolutionary stage based on the MIR spectrum and
photometry. There are 744 identified RSGs in the final sample having both the
WISE1- and WISE2-band time-series data. The results show that the MIR
variability is increasing along with the increasing of brightness. There is a
relatively tight correlation between the MIR variability, MLR, and the warm
dust or continuum, where the MIR variability is evident for the targets with
$K_S-WISE3>1.0~mag$ and $WISE4<6.5~mag$, while the rest of the targets show
much smaller MIR variability. The MIR variability is also correlated with the
MLR for which targets with larger variability also show larger MLR with an
approximate upper limit of $-6.1~M_\odot/yr^{-1}$. Both the variability and the
luminosity may be important for the MLR since the WISE4-band flux is increasing
exponentially along with the degeneracy of luminosity and variability. The
identified RSG sample has been compared with the theoretical evolutionary
models and shown that the discrepancy between observation and evolutionary
models can be mitigated by considering both variability and extinction.
