August 15, 2009: Lake Sonoma

Matthew Marcus

Though the bulk of TACos went to Coe, the obvious choice for me was Lake Sonoma. Aside from the smoke and the fact that LSo is almost always darker than Coe, the Clear Sky Charts showed much better prospects for LSo. I arrived at about 7 only to find to my surprise that I wasn't the first there. Peter K. from Richmond got there first with his 10" Dob. We spent the night trading views.

It was warm the whole night, with little wind and no dew. The CSCs were predicting humidity up to 95%, so that had been a concern. The transparency was rather good, and the seeing good at times. Epsilon Lyrae showed Airy rings around the 4 separate stars ~1/3 of the time.

Peter and I, without having consulted each other, started with the Sagittarius glob list in Sue French's article in the September S&T. This article didn't attempt a complete survey, nor did it just hit the eye-candy, but did a mix of both. The bright&easy ones were 6522, 6528 (sharing a low-power view), M22 and 6638 (dittto). The seeing was good enough to make globs a treat. The more difficult ones were the Djorgovski objects Djorg 1 and 2 (Djorg 1 = 6540). These look like faint open clusters but apparently are globs. 6540 is curious in that it's very non-spherical, appearing as a bent bar of aspect ratio ~3:1. I wonder how it is that a cluster as old as a glob must be could maintain such a shape. Is it spinning? Was it tidally disrupted? (Hang on a sec while I hit Google....) Hmm. One paper refers to it as Djorgovski 3, not Djorgovski 1. I was able to get the paper for free http://adsabs.harvard.edu/cgi-bin/bib_query?1994A%26A...283...67B. It shows that the cluster actually consists of a concentrated nucleus flanked in the E-W direction by two blobs of stars. No explanation is given for this morphology, except that they rule out a superimposed OC, and suggest a possible merger of clusters. They mention that the distribution of star types is consistent with a "post-core-collapse" history. Most of the other Google hits are ORs (many from TAC!) and papers about other, similar GCs.

A last note about 6540 - NSOG lists it as an OC with a magnitude of 14.6, which is why I'd never gone for it. Now I think that there was a typo and the magnitude listed was for its brightest stars, with the overall magnitude listing having gone into the bit bucket.

Peter pointed out that the dark nebula B90 was nearby, and since I'd never logged it, I sketched it.

Next was Djorgovski 2, which is something like a fainter version of 6540. The article mentioned Dana Patchick's observation in a 16" when he didn't know it was there but happened upon it, and in an 8". This object is plotted in Uranometria as ESO 456-SC 38, as mentioned in the French article. It was easily found by starhopping from 6540, passing on the way E by the Ink Spot (B86), on the border of which lies bright, spangly OC 6520. The GC is quite large and not hard to spot once you know where to look.

The other two non-eye-candy GCs on the list were Palomar 9 (6717) and Palomar 8. Pal 9 was pretty easy, with a bright star both showing the way and "attempting" to drown it out with its glare. It's a small fuzzy, but contains a couple of bright patches. It may be the easiest Palomar cluster.

Pal 8 wasn't that much harder. It completes a rectangle with three field stars and shows as a pretty uniform blob with not much central brightening.

The same issue of S&T had an article (Ken Hewitt-White's Going Deep column) about spotting a detached fragment of the Cat's Eye nebula. The article included lots of pretty pictures including one of actual cat's-eyes, belonging to Neptune, the author's Himalayan-cross cat. His eyes were the blue of the nebula, seen in unfiltered view. The detached nebula bit (IC4677) is beautifully shown in an image which also shows a "bright" galaxy (6552) in the opposite direction from the nebula.

I went for IC4677 and couldn't spot it. Mark, with his 16" did get it and showed me. After seeing it in the 16", I didn't feel so bad about not spotting it in 8" - it was fairly faint. The factor of 4 light grasp between our scopes should translate into 1.5 magnitudes at equal magnification. Then we both went for the galaxy. At first I couldn't find it, but Peter did in his 10" and corrected my errant navigation, after which I spotted it without too much difficulty. According to the database Mark was using, it's mag 13.7, which is beyond my limit in 8". I think it looked more like mag 12. It seemed easier than Stefan's Quintet.

As to the Cat's Eye itself, in Mark's scope it showed a nice pale blue color in an unfiltered view, with the central star shining steadily in a dark hole in the middle. There seemed to be "glare" all around it, as if from dirty optics. I'd believe that explanation in my scope, which needs a good clean-out, but I think what we were really seeing is the concentric outer shells visible in the famous Hubble image.

Later, Mark showed me Jupiter through his Hbeta filter, which, unlike mine, doesn't have an orange passband. The detail was extraordinary, looking just like the pictures. The seeing over those few minutes must have been phenomenal. The GRS was clear and obvious as a big blank "eye" in the belt. It was light, not dark, as one migh expect a "Red" spot to look in a green filter. I guess the GRS must be in its GWS (Great White Spot) phase. There were plenty of fine features in the belts. My scope didn't deliver half as nice a view (seeing changed? 8" vs. 16"? filter?) but it did show some festoons and the moons as little disks of unequal sizes and colors. I used Jupter to hop to Neptune which looked as it always does - a little blue-gray disk, with some color fringing due to atmospheric dispersion.

Peter and I stuck it out through moonrise and did some eye-candy stuff. We left at 3:00.