Distances to the Supernova Remnants in the Inner Disk
  Distance measurements of supernova remnants (SNRs) are essential and
important. Accurate estimates of physical size, dust masses, and some other
properties of SNRs depend critically on accurate distance measurements.
However, the determination of SNR distances is still a tough task. Red clump
stars (RCs) have a long history been used as standard candles. In this work, we
take RCs as tracers to determine the distances to a large group of SNRs in the
inner disk. We first select RC stars based on the near-infrared (IR)
color-magnitude diagram (CMD). Then, the distance to and extinction of RC stars
are calculated. To extend the measurable range of distance, we combine near-IR
photometric data from the 2MASS survey with the deeper UKIDSS and VVV surveys.
With the help of the Gaia parallaxes, we also remove contaminants including
dwarfs and giants. Because an SN explosion compresses the surrounding
interstellar medium, the SNR region would become denser and exhibit higher
extinction than the surroundings. The distance of a SNR is then recognized by
the position where the extinction and its gradient is higher than that of the
ambient medium. A total of 63 SNRs' distances in the Galactic inner disk are
determined and divided into three Levels A, B, and C with decreasing
reliability. The distances to 43 SNRs are well determined with reliability A or
B. The diameters and dust masses of SNRs are estimated with the obtained
distance and extinction.
