GSSP

Steve Gottlieb

Stretching across 35 degrees of western Hercules is an immense river of distant galaxies (redshift z = .034 translates into roughly 450 million light years) that connects the Hercules Supercluster (Abell Galaxy Clusters (AGC) 2151, 2152 and 2147) with another rich supercluster containing AGC 2197 and 2199. These galaxies are roughly twice the distance as the Perseus-Pisces Supercluster and more challenging to view, so I usually attempt to chase down members with my 18" Starmaster on nights of excellent transparency.

Although we still had the affect of some smoke from the wild fires on Friday night at GSSP, conditions were certainly good enough to dive into the southern end of the extended Hercules supercluster where it dips into Serpens and ends near the rich cluster AGC 2052. This Abell cluster contains no NGC members, so was missed by the Herschels and other 19th century visual observers with larger scopes. UGC 9799 (15 16.7 +07 01), a giant cD galaxy, sits in the center of the cluster and has likely cannibalized a few neighboring galaxies that have wandered too close. At 280x, UGC 9799 appeared fairly faint, moderately large, elongated 3:2 SW-NE, ~0.9'x0.6', broadly concentrated. A number of faint galaxies are huddled nearby including CGCG 49-89 1.1' S, PGC 54521 0.8' W, CGCG 49-91 2' N, CGCG 49-92 5.5' SSE, PGC 54554 8' SE and many more. It was a lot of fun tracking these down and 15 members were logged within 30' down to mag 16.4(B).

The best night at GSSP was still to come, though. Although it looked nearly certain we were going be skunked by clouds on Saturday night, conditions miraculously improved at the last minute and this turned out to be a perfect opportunity to chase after even fainter nasties. AGC 2256 is located in Ursa Minor, 1.7 degrees northeast of NGC 6217, the brightest galaxy in the constellation NGC 6217. At a redshift of z = .058 this cluster resides a whopping 800 million light years away. The barred spiral NGC 6217 was the perfect place to begin the hunt as it was showing off quite a bit of spiral structure (recorded earlier) --

NGC 6217 (16 32.7 +78 12). Fairly bright, fairly large, elongated 2:1 NW-SE, ~2.5'x1.5', small bright core. Contains a bright stellar nucleus or a star is superimposed at the center of the core. At the NW end a faint spiral arm is attached to the main body, winding north and then trailing back nearly halfway along the NE flank. With concentration a dark gap is visible between the arm and the main body (bar) of the galaxy. A very short extension is strongly suggested at the SE end, bending towards the west.

I moved over to AGC 2256 (17 03.7 +78 43) and Mark Wagner and I started to pick apart the cluster. Unfortunately, as Mark mentioned in an earlier report, my printed Megastar chart was not going deep enough and we started noticing ghostly patches that were popping out of the black background with averted vision. Mark fired up his laptop, turned on the dimmer galaxies in Megastar and we went to work again. The brightest 3 members of the clusters are NGC 6331, UGC 10726 and MCG +13-12-017 with many of the members arranged in a chain. I started sketching the members and then comparing the sketch with Megastar, but we couldn't quite make sense of the chart on the screen although the general flow of the galaxies appeared correct. So, we tried rotating the image one way and then the other without success. Finally, we realized Megastar was set to flip the charts east-west and by resetting the chart everything was now right with the universe!

Mark was curious how deep we were going. Well, we picked up three 17th magnitude (blue magnitude) members with the faintest member 2MASX J17035650+7837357 coming in at 17.4. (for comparison, I had originally printed my chart down to 16.0).

Here are some of my other favorite targets from GSSP -- Abell 43 (17 53.5 +10 37) was visible at 175x and NPB filer as a moderately large, round disc, ~70" diameter with an even surface brightness. Viewing the planetary unfiltered three stars were superimposed with the mag 14.7 central star the brightest of the trio. Fainter stars were visible at the south and east edge of the rim.

Abell 53 (19 06.8 +06 24) was picked up at 115x using an OIII filter as a very faint, fairly small, round disc, at least 25" diameter. With concentration and averted vision, the planetary was barely held continuously with averted vision.

Abell 55 (19 10.5 -02 21) appeared fairly faint at 175x and NPB filter, fairly small, elongated 4:3 SW-NE, even surface brightness, crisp-edged. Visible continuously in a rich star field, though there was no indication of annularity or structure. A few very faint stars are at the edges. Just visible unfiltered, though the outline was not as well defined.

Abell 57 (19 17.1 +25 37) appeared faint at 225x and NPB filter, fairly small, elongated WNW-ESE, ~30"x20". Located just 1' WNW of a mag 10.5 star. A string of three mag 12.5 stars oriented NW-SE lies ~2' south.

Abell 61 (19 19.2 +46 15) was picked up fairly easily at 73x using the OIII filter as a very faint, large, round disc, 2.5'-3' in diameter. The outline of the rim was fairly well defined and the disc was just visible continuously with averted vision and concentration. A few stars are just within or at the edge of the rim including one at the N edge and one just off the W edge. A group of stars is close to the SW.

Hoag's Ring (15 17.2 +21 35) -- to me this is one of the iconic HST images (see http://antwrp.gsfc.nasa.gov/apod/ap020909.html). The outer ring has too low of a surface brightness to be seen with my 18- inch but I was happy just to pick up this dim galaxy (B = 16.0). At 280x this ring galaxy appeared extremely faint, very small, round, 20" diameter, low even surface brightness. Visible roughly 1/4 to 1/3 of the time with averted vision and could hold only a few seconds at a time. Situated just east of the midpoint of a 8' line connecting two mag 10 and 11 stars oriented SE to NW.

2MASX J20433169+1507332 (20 43.5 +15 08) is hiding in the glare of mag 4.4 Delta Delphini (on the main stars in the Dolphin's outline), just 3' NNE of the bright star! At 280x it was visible as a very faint, 15" glow of even surface brightness just visible continuously with averted and concentration. The trick was to keep Delta just outside the field and with tracking this was easy to accomplish. Although very close to Delta, it still helped to use a photographic finder chart to identify several nearby mag 14 stars including one close SE and a N-S string of 3 stars just north of Delta and west of the galaxy.

Hickson 85 (18 50.4 +73 21) -- I had picked up the two brightest members HCG 85A (CGCG 341-010) and HCG 85B a couple of times previously (only 40" between centers), but this time Mark and I were clearly picking up an even fainter 3rd member intermittently. But every so often, the object seemed to pop out in a slightly different position. Jeff Gortatowsky came over and verified there were actually 4 galaxies in the field. The fainter two members come in at a total blue magnitude of 17.4 and 17.5!

Hickson 84 916 44.4 +77 50) resides just 42' SE of NGC 6217 in Ursa Minor -- even closer than AGC 2256. I was able to pick up HCG 84A, B and C (marginal)... HCG 84A 16 44.4 +77 50 -- at 280x, the brightest member of HCG 84 appeared faint, small, elongated 5:3 N-S, ~25"x15", very weak concentration. Located 1.6' NE of a mag 11.7 star and 2.1' SW of a mag 11.4 star. Also nearby is a mag 14.5 star 40" WSW and a mag 15 star 40" SSE (HCG 84C is attached to this star). I also asked Paul Alsing if we would take a look in his 25" and HCG 84C was easy to confirm and HCG 84D was glimpsed (17.3B).

One last thanks to all those who put together a great star party,

Steve