2/4/08 from Lake Sonoma

Steve Gottlieb

Despite some concerns about possible gusty winds, dewing issues and a muddy observing area I met Bob Douglas on Monday night at Lake Sonoma (Lone Rock) and found excellent transparency and generally calm and dry conditions. The drive up 101 went quickly for a workday and only slowed through Santa Rosa where road work has been going on for ages. After passing Cloverdale in a crystal blue sky I enjoyed the last portion of the ride past the Sonoma county vineyards.

As the sky darkened, a booming zodiacal cone emerged in the western sky, extending nearly to Taurus and I knew the transparency would be good. It felt exhilarating with all the recent clouds and rain to be observing under the dark canopy of winter constellations in good conditions. I had to quickly bundle up, though, as the temperature dropped rapidly after sunset. As far as observing, I did a quick tour of many of the winter highlights -- who knows when it will be clear again -- and followed up on some objects I wanted to return to this winter. Herer are a few highlights.

IC 2003 is a tiny planetary in Perseus (located in an outer arm of the galaxy beyond the Perseus Arm) which showed tantalizing detail in my 18-inch Starmaster at high power... easily swept up unfiltered at 115x as a vey small, blue-grey disc forming a close "double" with a mag 13.5 star just 18" SW. Increasing the magnification to 325x, the appearance is definitely asymmetric with a fainter NW quadrant and an intermittent stellaring (superimposed star, knot, or the central star) to the SE of the geometric center. At 450x, the dimmer quadrant on the NW side appears to bulge out slightly and the brighter region, centered to the SE, extends in an arc from the NE to the SW. An occasional stellar sparkle was clearly visible, though it was difficult to pinpoint the location. A faint galaxy, UGC 2902, was picked up 20' NE.

One of my favorite Abell planetaries is Abell 12 in Orion. It's not that faint, but the location is remarkable -- virtually attached to a 4th magnituide star... picked up at 175x using a NPB filter and easily visible at 225x as a round 30" "knot", just partly inside and partly outside the glare of 4th magnitude Mu Orionis on the NW side. Best view at 325x using the NPB filter by placing the bright star barely outside the field and then the sharply-defined glow of the planetary was cleanly separated from the distracting glare of the star and any scattered light.

Kohoutek 2-1 (K 2-1) has been classified as both an unusual planetary and a compact HII region. It was easily picked up unfiltered at 175x as a very large, irregular glow ~2' in diameter, nestled within a group of stars. Excellent view using an NPB filter with an irregular outline and interior structure. Appears elongated SW-NE, 2'x1.5', and brighter and better defined along the edge from the NW to the NE. Several stars are nearby or involved including a mag 12.5 on the N side. A mag 11 star is off the NE side and two mag 13 stars are barely off the S and SW sides. Located less than 5' NW of a mag 8.2 star.

Abell Galaxy Cluster 548 is a faint, sprawling cluster in Lepus (~5h 47m -25° 40') that extends roughly SW to NE for about one degree starting at ESO 488-007 and ending at ESO 488-033. The rich cluster includes several close pairs that look like barbells on the DSS and are challenging to resolve. None of these galaxies were discovered visually, so most carry ESO designations from the southern ESO-Schmidt survey. I was able to track down a dozen members, though most appeared as just small 20" knots.

The highlight of the evening was a tour of Sharpless 2-308, a giant Wolf-Rayet shell. I spent a half hour tracing the 35' outline using an OIII filter at 73x. The shell is striking along the 25' western border as it gently arcs from N to S with a sharp contrast against the sky immediately west. This region also has some weak filamentary structure and brightness variations (like the Veil in a small scope). At the south end of this long arc, the rim curves more sharply east, passing directly through a triangle of mag 7.5/8/9 stars and passing just south of 3.9-magnitude 16 CMa. To the east of 16 CMa, the SE portion of the shell is the only difficult part to follow but could be picked up again along the eastern edge. From this point the rim continues due north where material appears to pool up on the north end in a 10' brighter, circular patch. Superimposed on this patch is a number of mag 10-12 stars. The rim dims again for a short stretch at the NW end before reaching the bright western rim again. At the geometric center of the shell is the massive Wolf-Rayet star EZ CMa (mag 6.7-6.9) -- a supernova candidate -- and the interior is filled with very low surface brightness, patchy nebulosity.

It was surprising to get in such a good night, considering what we've been offered recently. Let's hope for more this weekend.

Steve