Abell 7 from Lake Sonoma 1/21/04

by Steve Gottlieb

Conditions were quite pleasant at Lake Sonoma last night. I called ahead and arranged for the Park Ranger to leave the gate at Grey Pine open which was fortunate as I ended up arriving after dark (about 6:20) after slogging through afternoon commute traffic up 101 past Santa Rosa. No one observers showed up and there was very little road traffic -- so it was a very quiet evening! By 7:00 I had set up my 18-inch Starmaster and was ready to go.

There was a little breeze at times but nothing that disturbed viewing and the transparency was very good (~6.5), despite the lack of low fog in Sonoma county. Seeing started off fine, but deteriorated and was fairly poor (5 stars were about it in the Trapezium) after 9:00. Still galaxies were easy pickings at 150x-200x and I ended up poking around for 3 hours almost exclusively between -30 degrees dec and -36 degrees dec in Fornax (including a careful tour of the Fornax galaxy cluster) and finishing up just over the border into Eridanus. By 10:30, I was packed up for the 90 minute drive back to the east bay and a few hours sleep before work today.

I spent most of my time poking around the Fornax galaxy cluster, but I also took a look at a challenging ancient planetary, Abell 7 in Lepus and the surrounding area. With listed dimensions of 871"x670", this is one of the largest of the Abell planetaries, a result of being situated relatively nearby and an advanced age. As expected, the surface brightness is quite low, so this is not an easy target unless conditions are excellent. Here's what I recorded in this area on Wednesday night with my 18-inch Starmaster:

Abell 7 = PK 215-30.1 = PN G215.5-30.8	05 03 08.0 -15 36 13	Size 871"x670"
18": at 73x and OIII filter, this ancient planetary appears as an extremely large, ghostly glow, perhaps 6' in diameter. Although the surface brightness is very low, it was visible as an irregularly-shaped, hazy patch involved with 5 or 6 stars on the south side. The edge of the planetary is better defined on the southern periphery and appears to fade out on the N side, so I was probably viewing only a portion of the object. Once identified, though, it was not difficult with averted vision.

Coincidentally, there's a very faint galaxy, MCG -03-13-058, just outside the edge of the halo, 10' NW of center! This required some hunting, though, as it's also a difficult object. And of course, the OIII filter had to go.

MCG -03-13-058	05 02 29.2 -15 32 43	V = 14.1; Size 1.5x0.7; SB = 14.0; PA = 75d
18": extremely faint, fairly small, round, very low even surface brightness, 0.7' diameter, elongation not noticed (probably just viewed the core). Located ~10' NW of the center of the giant planetary Abell 7 and 5' SW mag 9.9 SAO 150096.

As a bonus, there's a Hickson Compact Group (HCG 32) with brightest member MCG -03-13-053 just 12' NW of this galaxy! A quick look only netted one member, but a steadier night might bring out some of the fainter companions.

HCG 32a = MCG -03-13-053	05 01 45.2 -15 26 56	V = 13.4; Size 0.3x0.3
18": extremely faint, round, 15" diameter. Located close following a mag 13.5 star. Visible only half the time with averted vision.

If anyone is interested in going after these toughies, the field of Abell 7 is just 70' SE of Hind's Crimson Star (R Leporis), a great place to start your visit.

Posted on sf-bay-tac Sat Jan 24 16:09:04 2004 PT
Converted by report.pm 1.0 Sun Jan 25 08:44:56 2004 PT