Deep South in Canis Major
NGC 2467, the t CMa cluster, Sharpless 301, and Sharpless 308
March 2007
NGC 2467, the t CMa Cluster and Sharpless 301 and 308 are four very interesting Deep Sky objects of the winter sky, which are quite unpopular with observers of Northern latitudes as they are very far south in the Canis Major/Puppis region and for which there are only few observing reports. Except for the the two Sharpless objects, they are relatively bright and conspicuous objects. But even Sharpless 301 and 308 are not at all extreme challenges and are accessible with much detail also in medium sized telescopes.
Sharpless 301 Sh2-301 (07h10, -18°30') is not that different from NGC 2467 and responds as well to both UHC and OIII filtering. With my 14-Inch Dob and OIII filter, the HII region appeared richly structured. Superimposed stars and a dark lane crossing the nebula diagonally were quite distinct. A narrow band image of Sharpless 301 by Dean Salman is here. By the way, Dean Salman has an excellent collection of images of the Sharpless catalog, which is very helpful in determining good observing targets. |
Sharpless 308 Sh2-308 (06h54, -23°55') is by far the weakest of the four objects, but also one of the most interesting ones. Sh 308 is the blown away outer atmosphere of the Wolf-Rayet star EZ CMa (that little star in the center of the image), similar to the Crescent Nebula, Thor's Helmet, or the WR137 shell (which is a complete list of the brighter WR nebula. The DSS image measures 1° and is a composite of red and blue plates of the southern SERC survey. The WR shell highly excited by EZ CMa and distinctly blue. Hence it responds extremely well to the OIII filter. The brightest parts are the western filaments, that curve from bright o1 CMa (in the lower part of the image) to the North and form a huge crescent shaped shell around EZ CMa. These filaments resemble both in shape and brightness those of IC443, the SNR in Gemini. Under very good conditions and low magnification, the shell can be seen as a complete bubble, including the eastern part bending back to o1 CMa. With 7mm exit pupil, a very dim OIII glow can be seen to fill the interior of the entire shell. Despite of being a spectacular WR shell, there are only few observing reports of Sharpless 308. I could find only three reports by Andreas Domenico, Ronald Stoyan and Steve Gottlieb. A spectacular image of Sharpless 308 was taken by Don Goldman and is shown here. Directly south of o1 CMa is the loose Open Cluster Collinder 121. |
Image composites of the SERC Survey on http://archive.stsci.edu/cgi-bin/dss_plate_finder (DSS copyright), Data from www.seds.org,