Lake Sonoma Saturday 12/8/07

Steve Gottlieb

Bill Cone, Pete Krottje and I enjoyed a surprisingly good evening at Lake Sonoma last night. Conditions were clear, generally calm, dry and the low temps were not an issue after I bundled up in winter gear. Transparency was good -- likely in the 21.3 or slightly darker SQM range with the zodiacal light forming a huge cone in the early evening, though seeing was only fair and more rough at times, particularly low in the south. Still, for most of the night I had no problem observing at 225-300x higher in the sky. As we were tearing down around 1:30 AM, a cool breeze from the south kicked in, chilling the air and disrupting the seeing, but by that time we had been logging objects for well over 6 hours.

I spent most of the evening on M31 and M33, specifically the numerous clusters and HII regions that pepper these galaxies. Bill had prepared labeled finder charts for the globulars and clusters in M31 and a very detailed chart of and HII regions and large star clouds in M33. Although I've gone over many of these objects previously, it was a lot of fun identifying and confirming over 30 different objects in these galaxies with our 18-inch Plettstone and Starmaster scopes. After working on several globulars and star clouds in M31 (I'll post these later), we turned to M33 --

Starting at the gigantic HII region, NGC 604, the most prominent object at the SE end of M33 we carefully worked around the galaxy in a counterclockwise direction (heading south on the east side of the galaxy) picking off numerous HII regions and star clouds (associations). To identify these objects a detailed finder charts is required and I used a hand labeled DSS image that identified several dozen knots in M33. Here's a rundown on the objects we identified in M33 at 225x.

Association #85: small, low surface brightness patch just 2' SE of NGC 604
Association #87: marginal spot with averted vision another 2' S of #85, perhaps 10" diameter.
Anon. HII region: found another 2' S of #87! This one was a bit more evident than #87, ~12" diameter. (identified as BCLMP 740W in SIMBAD) IC 135: faint, but moderately large patch, elongated N-S, ~0.8'x0.5', close E of the core of M33.
IC 136: faint, large, low surface brightness patch 3'-4' S of IC 135, roughly circular, 2' diameter, brighter star to south.
IC 139/140: a pair of similar, moderately bright, 45" diameter HII regions just 1' apart along the spiral arms winding towards the west on the south side of M33
IC 137: very large, ill-defined brightening in the same spiral arm on the south side of the core but further west, ~2.5' diameter.
Association #48: fairly faint, small glow, ~10" diameter, just south of the central core, collinear with three stars.
Association #14: faint, fairly small, 20"-25" diameter, round, low even surface brightness, ~3' SW of #48
Association #112: fairly large, irregular low surface brightness haze just south of the mag 8 star to the south of M33, ~1.5' diameter.
Association #116: faint, moderately large, 0.8' diameter, well- defined edge, a very faint stellar object appears to be superimposed. Association #127: very faint, moderately large hazy patch surrounding a mag 13 star, ~1' diameter.
Association #128: fairly faint, round, 35" diameter. Located 2' WNW of #127. These last two objects are in the spiral arm that heads north on the west side.
Association #21: very faint, low surface brightness haze, ~2' diameter. Forms an equilateral triangle with NGC 592 and 598 further north.
NGC 588: moderately bright and large, slightly elongated, ~45"x35". This well-defined patch is at the end of the spiral arm on the west side of the galaxy.
NGC 592: similar HII region as NGC 588, ~40" diameter. Appears to have a faint star superimposed or a stellar core. Located due west of the core.
NGC 595: another moderately bright patch, ~45"x35" elongated north- south, well defined, closer in the core of M33 than the previous two NGCs.
IC 131: very faint, quasi-stellar knot to the southeast of a wide N-S pair of mag 11/12 stars.
IC 132: faint, small, round, 20" diameter. Situated just 1' N of a 10" pair of mag 13 stars to the west of a mag 9 star.
IC 133: faint, fairly large patch , elongated 2:1 NNW-SSE, ~1.2'x0.6', off the NW side of M133. IC 132 lies 3.5' north.

At this point we had run out of steam and M33 was sinking in the west, though we missed visiting a few objects along the north side of the galaxy (Association #34, #66, #71, IC 142 and IC 143). These will have to wait to next time (Monday night?)


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