Lake Sonoma Tuesday night (3/4/08)

Steve Gottlieb

I'm skipping ahead one observing report as I also had a successful Sunday night at Lake Sonoma observing with Carter Scholz. Greg Laflamme and I had talked about running up to Lake Sonoma midweek when the weather turned a bit sour last Saturday. We tentatively decided on Tuesday, but Greg e-mailed me in the morning that CSC was predicting miserable conditions for both cloud cover and transparency (all white!). I couldn't figure out what was going on with CSC as the NWS forecast was clear for Tuesday night with the next system not arriving until later in the week. I suggested to Greg we ignore CSC and take our chances. Fortunately, that turned out to be a good decision as conditions were excellent -- except for a few clouds drifting while packing up at the end, it was totally clear and quite transparent the entire evening with Greg recording SQM readings of 21.28-21.37 (early on) up to 21.48 (after 10:00 PM). The high end was the best readings I've seen at Lake Sonoma, though the lack of the Milky Way overhead in the spring skies may have nudged up the numbers. In any case, it was great night for viewing any type of deep sky object -- so I ran through a mix of splashy winter open clusters and HII regions as well as faint galaxy clusters.

Just over a half-degree southwest of mag 3.6 Theta Gemini is nice string of 5 NGC's galaxies (2288, 2289, 2290, 2291 and 2294). About 45' west of this group is another pair, NGC 2274 and 2275. Here's the rundown on the collection in my 18-inch Starmaster at 225x.

NGC 2274
Moderately bright and large, slightly elongated N-S, 0.9'x0.8', contains a sharply concentrated, bright 25" core and a much fainter halo. Forms a close pair with N2265 1.9' N.

NGC 2275
Fairly faint, fairly small, elongated N-S, 0.9'x0.6', contains a small bright core ~15" in diameter and a much fainter halo. Slightly fainter of a close pair with N2275

NGC 2288
Very faint, extremely small, round, no more than 10" diameter. Located just 1' SSW of N2289 and faintest of 5 in the group.

NGC 2289
Fairly faint, small, slightly elongated E-W, ~25"x20". A mag 13.5 star is close off the N side. One of the brightest two galaxies in a compact galaxy group (all within 6') of 5 NGCs including N2290 2.5' SSE and N2288 1' S.

NGC 2290
Brightest and furthest south in a compact group of 5 NGC's along with N2289. Appears moderately bright and large, elongated 2:1 SW-NE, ~45"x22", the halo is weakly concentrated with a sharply concentrated 10" core. N2289 and N2288 lie 2' N. The cluster is 0.6° SW of mag 3.6 Theta Gem.

NGC 2291
Faint, fairly small, round, 30" diameter, weak concentration to a very small slightly brighter core. Collinear with a mag 10 star 2.7' NNW and a mag 12 star 0.9' NNW.

NGC 2294
Fairly faint, fairly small, elongated 5:3 ~N-S, 0.6'x0.35', weak concentration. Furthest NE in a group of 5 NGCs. A wide double of mag 10.5-11 stars lies 2' SE.

Near the Cancer/Leo border is a faint cluster with brightest members NGC 2804 and 2809. John Herschel was the first one to look at this group and only picked up these two galaxies. Observing with a 48" f/9.4 Reflector (that's right) in the 1860's from Malta, Albert Marth picked up three fainter members (NGC 2801, 2812, 2813) but with a good finder chart I was also able to pick up several galaxies missed by these observers.

NGC 2801
Very faint, fairly small, round, 25" diameter, ver low surface brightness glow with little or no concentration. Located 4' SW of a mag 9.9 star in the N2804/2809 group.

NGC 2804
Moderately bright and large, elongated 4:3 WSW-ENE, 1.2'x0.9', weak concentration with a very small brighter core. This galaxy and N2809 are the brightest in a group of 6 NGC galaxies and several fainter members.

NGC 2807
Faint, small, slightly elongated NNW-SSE, 24"x20", weak concentration. Located 2.4' SW of N2809 in a group. Forms a close pair with N2807A = MCG +03-24-030 just 50" WSW.

NGC 2807A = MCG +03-24-030
Very faint, very small, round, 15". Located 50" WSW of N2807 and about a half-magnitude fainter.

CGCG 091-053
Very faint, very small, slightly elongated N-S, 18'x12". A mag 12.5 star is situated 40" SSE. Located 2' NNE of a mag 10.7 star.

NGC 2809
Moderately bright and large, slightly elongated ~N-S, 0.9'x0.7', gradually increases to a small bright core and faint stellar nucleus. Brightest in a group containing N2801, N2804, N2807, N2812, N2813 and a few fainter galaxies. The nearest two are N2807 2.4' SW and CGCG 91-055 5' N.

CGCG 091-055
Very faint, very small, round, 12" diameter. Located 1.4' SW of a mag 11 star in the NGC 2804/2809 group.

CGCG 091-058
Extremely faint and small, round, just 6" diameter. Only visible occasionally with concentration as a barely non-stellar spot. Located 2.4' SW of a mag 9.2 star in the N2804/2809 group. The catalogued blue magnitude for this galaxy is only 16.0

NGC 2812
Extremely faint, very small, slightly elongated, 0.3'x0.2'. This difficult galaxy is located just 1.3' NW of N2813 in the N2804/2809 group.

NGC 2813
Faint, fairly small, round, 25" diameter, weak concentration, very small brighter core, faint stellar nucleus with direct vision. Located 2' NE mag 9.2 star that detracts from viewing. Close pair with fainter N2812.

Earlier in the evening Greg and I took a look at several open clusters in Monoceros. Here are a few that I logged...

NGC 2251
At 175x, this is a fairly striking cluster that includes a fairly rich 6' string oriented N-S. The string contains ~20 stars including a mag 10.5/11.5 double at 5" (Barton 2120). The brightest star in near the geometric center and is part of second group of ~20 stars with several in a 2' loop. The bright star is a mag 9.5/11.5 pair at 9". Finally, on the N side is a small string of a half-dozen stars oriented E-W.

NGC 2254
Small, dense group of ~25 stars in 3' at 225x and 300x. About a dozen of the stars are arranged in a semi-circular chain or "C" that is open on the east side. Several mag 14+ stars are near this loop, segregated into small clumps.

NGC 2259
At 175x, appears as a 4' rich group of faint stars over haze. At 300x, about two dozen stars in total are resolved, mostly in a 2' circular clump. About 1' N of this dense patch of stars is the brightest mag 11.5 star which has a 13th magnitude companion. This cluster is located 5' E of mag 8.8 HD 47271.

NGC 2311
At 225x, ~40 stars are resolved in a fairly rich 5'x3' group, elongated NW-SE. The cluster includes a few pairs with a nice equal mag pair on the south side. A weak stream of stars trails off to the east from the SE end of the cluster towards a mag 9.8/10.4/13 triple at 3" and 9" (ADS 5636).

I had to cut the evening a bit short as I had a class to teach the next morning at 7:30, but on this night taking a chance with the weather paid off big time.

Steve