Discovery of optical emission associated with the supernova remnant G107.5-1.5

We present the first results from an imaging and a spectroscopic survey of the optical emission associated with supernova remnant (SNR) G107.5-1.5. We discovered optical diffuse and filamentary emission from G107.5-1.5 using the 1.5- and 1-m telescopes. The optical emissions from the North-East (NE) and North-West (NW) regions show the diffuse structure, while the South-East (SE) and East (E) regions show filamentary structure. From long-slit spectra, we found [S II]/H α > 0.5 for the SE and E regions, which supports the origin of the emission being from shock-heated gas. The average [S II]/H α ratio is found to be ~0.4 and ~0.3 for the NW and NE regions, respectively, indicating that the optical emission is coming from ionized gas in an H II region. From the ratios of [S II]λλ 6716/6731, we estimate an average electron density of ~2400 cm^-3 for the NW region, which can be attributed to the dense ionized gas. The average [S II]λλ 6716/6731 ratios are ~1.25 and ~1.15 for the SE and E regions, respectively, which are indicative of low-electron density.