Monday night at Lake Sonoma 1/26/09

Steve Gottlieb

I was a little concerned about possible dew, wind and unsteady seeing but conditions turned out really nice. Conditions were dry, cold, calm with fair to good seeing. Best of all it was generally clear and and transparent. In early evening, though, there appeared to be some haze or low clouds in the western sky as Venus had a small, but noticeable halo around it. But when we scrutinized the western sky we realized Venus was smack in the zodiacal cone which was quite prominent, reaching nearly 90 degrees up to Taurus. There was most likely some low clouds in the west causing the scattered light around Venus, but does any know if bright zodiacal light could create the same effect? As far as transparency, early on I recorded SQM-L reading of 21.35-21.40 and 21.47 when we were packing up. Within an 80 min drive from Berkeley/Albany, I don't think I could find darker skies.

The first couple of hours were spent trawling the dregs of the NGC -- for me these are the poor, scattered star groups that I wouldn't glorify by calling "star clusters". Both the Herschels logged a number of these "Milky Way fields" that caught their attention for some reason, though that reason is often not apparent! Why bother?? Well, I'm trying to complete observing the entire 7840 entries in the NGC and I'm left with about 100 objects visible for the bay area latitude and many of these are scattered groups of stars tagged with NGC numbers (but really just asterisms).

For example here's NGC 2039 --
18" (1/26/09): large, scattered field with a number of mag 8 to 10 stars, though too dispersed to resemble a cluster. the most distinctive part is a nice 8' string of 6 collinear stars oriented E- W with mag 8 HD 38096 at the W end and mag 8.5 HD 38163 at the E end. A larger elongated group of stars extends to the SE out to the edge of the 35' field. This group probably contains unrelated field stars and there is no listing in SIMBAD.

and NGC 2234 --
18" (1/26/09): at 175x only a scattered group of ~75 stars in a non- descript 10' region. Includes a number of mag 12 stars forming the outline of two rough loops or a butterfly shape. This poor grouping is immediately SE of the listed position. The Milky Way is patchy here and the stars are set over unresolved haze. This grouping appears a very weak field enhancement at best and not a cluster.

I could go on, but you get the bleak picture. As this could be the last winter observing session of the year if we're shut out because of the weather next month, I spent the next couple of hours touring the winter showpieces in Orion, Canis Major, Puppis and Monoceros. In the middle of this tour, Greg called out that he thought he had the white dwarf companion to Sirius -- the Pup -- in his 12.5" scope.

Instead of taking a look in his scope, I pointed my 18" at Sirius and immediately noticed the faint star that Greg mentioned. But it seemed way too far away from Sirius -- perhaps 1.5' to 2. I knew Sirius B was closer to 10" separation (the current separation which I checked the next day is 8.5"). But nothing showed near Sirius at 285x, though the bright star (say goodbye to dark adaptation) was quite sharp and unwavering at this power. When I upped the mag to 450x Sirius was then surrounded by turbulent, scattered light but I kept scrutinizing for a faint speck nearby. Suddenly I picked up a sharp point close east at the edge of the scattered glow and when the seeing steadied is was not very difficult to repeatedly reacquire this star in the same position perhaps 25% of the time. A few times it was visible continuously for several seconds before disappearing. To rule out I was seeing some kind of reflection, I let Sirius drift through the field and noted the position of the Pup as east- southeast. When I checked and found the current position angle is 95 degrees (ESE), that clinched the observation. By the way, the period of the system is about 50 years and the companion will become slightly easier in the coming years as the separation is slowly widening to 11".

Steve Gottlieb