Mark McCarthy
December 30th, 2016, 08:11 PM
A couple months ago I was looking at the Interstellarum Deep Sky Atlas' index and noticed they had plotted three "Snow" galaxy clusters, numbers 6, 9, and 20. I had not heard of these before, and could not find anything written about them on the internet except for the April 1970 Astronomical Journal by T.P. Snow where he lists 34 objects (file attached below). These are southern galaxy clusters found on the plates from the Yale-Columbia southern proper-motion program—the same which Klemola used for his relatively better-known list of objects. Somehow they meet the criteria the Interstellarum editors used to select objects for the atlas. I was interested to try for them; the night of December 28-29 was my first opportunity. I used IRSA to generate field charts based on the J2000 coordinates I found on the SIMBAD database.
The site was private property in San Benito County in central California, elevation 2160 feet. I used my 20-inch f/5.25 reflector and 8mm Ethos for 333x 0.3° TFOV, and a 5mm Nagler for 553x 0.2° TFOV. Seeing while observing Snow 6 and Snow 9 was Pickering 6 and SQML pointed to the target was 21.2. Seeing improved to Pickering 7-8 while observing Snow 20, and SQML was 21.4. Transparency 4/5 and temperatures in the upper 30s F.
My star hop starting point was NGC 247, an impressive, large, but low surface brightness galaxy in Cetus. I nudged my scope a few minutes NNE to see Burbidge’s Chain (VV 518), a line of four small MCG galaxies. I could see three components – a, b, and c. MCG-4-3-10 = a was easy, small, yet the largest and brightest of the group, with an evenly bright core slightly elongated NE-SW, 14.4 mag. MCG-4-3-13 = b was on the other end of the chain; it is smaller than a, round, 14.6 mag., and also picked up easily. MCG-4-3-11 = c was nearby to b, seen averted vision only held about 70% of the time once noticed; 15.7 mag. MCG-4-3-12 = d was not seen; it is closer to a in the chain, and very small and too faint for me, 17.0 mag. Being able to see Burbidge’s Chain gave me some hope I might see something of the Snow galaxies, but more importantly gave me something to gauge galaxy size and brightness by, since the brightest members of the Snow galaxies are 15-16th magnitude – so I should expect marginal observations at best. I star-hopped to Snow 6 first, because is was further west and I needed to catch it before it got much lower.
Snow 6 (centered at J2000 00 17 37.0 -24 17 36): I with averted vision picked up one small, very faint round glow, which I later found to be MGC-04-01-29 (15.81B, 0.933’x0.747) – which is 7.8” north of where the cluster is centered (the darkest splotch to the upper center of the image below). Since Snow’s paper gives the magnitude range of 16-19B, it is not likely this is a cluster member. There were some very faint small stars in the field, but not galaxies. I tried 333x and 553x, but still only had the one galaxy. Aladin shows a string of three very small and faint galaxies to the east of the cluster center and to the east of the MGC I saw, but these are well beyond my scope.
2407
Snow 9 (centered at J2000 00 30 22.0 -22 58 12): I searched the area earnestly with averted vision but can only say I suspected two excessively faint very small glows – which unfortunately I can’t correspond my sketch to my finder chart image. This was a “no show”
2408
Snow 20 (centered at J2000 05 19 48.0 -25 17 00, near M79): I waited until Lepus culminated before attempting this one. It turned out to be the most engaging, as it is framed to the north by IC 408 and to the southeast by IC 411, both of which were very plain at 333x 0.3° TFOV. In the below image IC 408 is cut in half at the upper center, and IC 411 is to the center left. I centered my view near the bright star (HD 34895 – which appears as an optical double) at the center of the image, and strained my eyes with averted vision. I had the strong impression of a glow between this star and IC 411, and another glow to the west of the star. 553x strengthened the impression but did not resolve any galaxies. A friend who was with me, a far more experienced observer than me, had the same “feeling” and called it a “maybe.” Aladin shows galaxies in these areas but they are 16-17th magnitude.
2409
Clearly to see these clusters requires more aperture, better / southern skies, and more experienced eyes than my own. I hope others on the forum might take these up and find out if there's anything to be seen with these.
The site was private property in San Benito County in central California, elevation 2160 feet. I used my 20-inch f/5.25 reflector and 8mm Ethos for 333x 0.3° TFOV, and a 5mm Nagler for 553x 0.2° TFOV. Seeing while observing Snow 6 and Snow 9 was Pickering 6 and SQML pointed to the target was 21.2. Seeing improved to Pickering 7-8 while observing Snow 20, and SQML was 21.4. Transparency 4/5 and temperatures in the upper 30s F.
My star hop starting point was NGC 247, an impressive, large, but low surface brightness galaxy in Cetus. I nudged my scope a few minutes NNE to see Burbidge’s Chain (VV 518), a line of four small MCG galaxies. I could see three components – a, b, and c. MCG-4-3-10 = a was easy, small, yet the largest and brightest of the group, with an evenly bright core slightly elongated NE-SW, 14.4 mag. MCG-4-3-13 = b was on the other end of the chain; it is smaller than a, round, 14.6 mag., and also picked up easily. MCG-4-3-11 = c was nearby to b, seen averted vision only held about 70% of the time once noticed; 15.7 mag. MCG-4-3-12 = d was not seen; it is closer to a in the chain, and very small and too faint for me, 17.0 mag. Being able to see Burbidge’s Chain gave me some hope I might see something of the Snow galaxies, but more importantly gave me something to gauge galaxy size and brightness by, since the brightest members of the Snow galaxies are 15-16th magnitude – so I should expect marginal observations at best. I star-hopped to Snow 6 first, because is was further west and I needed to catch it before it got much lower.
Snow 6 (centered at J2000 00 17 37.0 -24 17 36): I with averted vision picked up one small, very faint round glow, which I later found to be MGC-04-01-29 (15.81B, 0.933’x0.747) – which is 7.8” north of where the cluster is centered (the darkest splotch to the upper center of the image below). Since Snow’s paper gives the magnitude range of 16-19B, it is not likely this is a cluster member. There were some very faint small stars in the field, but not galaxies. I tried 333x and 553x, but still only had the one galaxy. Aladin shows a string of three very small and faint galaxies to the east of the cluster center and to the east of the MGC I saw, but these are well beyond my scope.
2407
Snow 9 (centered at J2000 00 30 22.0 -22 58 12): I searched the area earnestly with averted vision but can only say I suspected two excessively faint very small glows – which unfortunately I can’t correspond my sketch to my finder chart image. This was a “no show”
2408
Snow 20 (centered at J2000 05 19 48.0 -25 17 00, near M79): I waited until Lepus culminated before attempting this one. It turned out to be the most engaging, as it is framed to the north by IC 408 and to the southeast by IC 411, both of which were very plain at 333x 0.3° TFOV. In the below image IC 408 is cut in half at the upper center, and IC 411 is to the center left. I centered my view near the bright star (HD 34895 – which appears as an optical double) at the center of the image, and strained my eyes with averted vision. I had the strong impression of a glow between this star and IC 411, and another glow to the west of the star. 553x strengthened the impression but did not resolve any galaxies. A friend who was with me, a far more experienced observer than me, had the same “feeling” and called it a “maybe.” Aladin shows galaxies in these areas but they are 16-17th magnitude.
2409
Clearly to see these clusters requires more aperture, better / southern skies, and more experienced eyes than my own. I hope others on the forum might take these up and find out if there's anything to be seen with these.