The article says they attributed it to HB9, which I was able to find in a catalog of supernova remnants (warning, PDF: http://www.mrao.cam.ac.uk/surveys/snrs/ta

The article says they attributed it to HB9, which I was able to find in a catalog of supernova remnants (warning, PDF: http://www.mrao.cam.ac.uk/surveys/snrs/table-IV-l.pdf http://www.mrao.cam.ac.uk/surveys/snrs/table-IV-l.pdf). On page 63, it gives the coordinates for the remnant to be 5h01m, +46°40', which would put it right around the brightest star in Auriga in this sky chart: https://en.wikipedia.org/wiki/File:Perseus_IAU.svg https://en.wikipedia.org/wiki/File:Perseus_IAU.svg. The catalog gives the size as 140x120 arcmin (2.3x2.0°), which is huge and probably means its very faint by now, which explains why it wouldn't be included in the sky chart by S&T. Curious if any astrophotographers have managed to capture it, I searched astrobin.com and found one photo: https://www.astrobin.com/229090/B/ https://www.astrobin.com/229090/B/ (edit: and a second: https://www.astrobin.com/73794/B/ https://www.astrobin.com/73794/B/). Edit: Looks like another designation for HB9 is Sh2-221, which turns up much more results in a search engine.