by Steve Gottlieb
Conditions were very pleasant last night at Lake Sonoma -- fairly warm with no breeze and some low clouds dampening the glow to the south with a fair number of bright Perseids visible throughout the evening. I brought along my daughter Andrea who had a blast with her 10-inch f/5.6 dob and decided to hunt down a few PNe along with the usual suspects (clusters and galaxies). Sky conditions were typical for this site -- close to mag 6.5, although dew was a problem before moonrise about 12:30. There was only one other observer (from the SVAS), who was doing astrophotography and left around 11:00).
The first object was a surprisingly easy bi-polar PN, Sanduleak 2-237, which is a good target for larger scopes. I discovered some interesting images and info on this object at http://www.ctio.noao.edu/REU/ctioreu_2001/rudy/PN.html. I haven't seen a mag estimate (discovered in 1975), but its probably a bit brighter than mag 14. The other three milky way PNe were all stellar or nearly so, and required a bit of care to identify the field. M 1-43 has a computed visual magnitude between 17.5-18, but this must be in error and shows you never can take these too seriously!
| Sa 2-237 = PK 11+7.1 | 17 44 42.1 -15 45 13 | |
|---|---|---|
| 17.5": this very unusual bi-polar planetary was picked up unfiltered at 220x as a faint, elongated glow, appearing more like a dim galaxy than a PN. At this power there was a modest contrast gain with a UHC filter. The best view as unfiltered at 280x-380x. This object appeared elongated ~7:2 SW-NE, ~25"x7" and seemed brighter toward the center. At moments a very star seemed involved. Based on the CCD image at http://www.ctio.noao.edu/REU/ctioreu_2001/rudy/PN.html, this may have been the central star or a superimposed star very close north of center. The extensions are reminiscent of the two bi-polar jets in M2-9. Discovered in 1975. | ||
| Minkowski 3-24 = PK 5-2.1 = E521-PN30 | 18 07 54.0 -25 24 03 | V = 14.3; Size 10"x10" |
| 17.5": identified location at 100x using a GSC finder chart. At 220x, a mag 13 star 1' following the PN was centered but M1-43 was not seen. Using a UHC filter, a faint stellar object was glimpsed and verified at the correct location with blinking. With the filter inserted the PN could be be held steadily with concentration. Similar view at 280x although the appearance seemed slightly "soft", perhaps 3" in diameter. Estimate mag 14.5-15. Located 4.4' SW of mag 8.1 SAO 186332. | ||
| Minkowski 1-43 = PK 11-0.1 = E590-PN5 | 18 11 48.9 -18 46 21 | V = 17.5; Size 7"x4" |
| 17.5": identified field at 100x using a GSC finder chart, though nothing seen at position indicated either with or without an OIII filter. At 220x, one or two very faint "stars" were just visible close SW of a mag 12.5 star near the plotted position. At 380x, these two faint stellar objects were better seen unfiltered. With a UHC filter, only M1-43 was still visible intermittently, ~30" SW of the mag 12.5 star. The image was "softer" than comparable stars and seemed a couple of arcseconds in size. Situated in a rich star field 3.4' ENE of a mag 10 star (SE of trio in a 1.5' string) and 4.6' SW of a mag 9.2 star. Marling's computed visual magnitude of 17.5 and Brazell's 18.2 appear to be too faint. | ||
| Minkowski 2-33 = PK 2-6.1 = E456-PN80 | 18 15 06.5 -30 15 33 | V = 13.7; Size 5"x4" |
| 17.5": the position was pinpointed within a string of stars by starhopping at 100x, but this compact PN was not seen at this power (viewed a couple of hours west of the meridian at 17 degrees elevation). At 220x, two mag 13.5-14 "stars" were visible close to the plotted position, less than 1' N and NW of a mag 10.5 star. With a UHC filter at 220x and 280x, M2-33 was easily identified as the stellar object 45" NW of the brighter star. Using the similar comparison star 30" NE, there was a 2-3 magnitude contrast gain. Estimate mag 13.5. The planetary is conveniently situated within a small 3' string NW-SE bracketed by the mag 10.5 star 30" SE and a close mag 11 pair 2.5' NW. The close pair has a couple of faint companions just NNE. Another mag 11.5 star is within the string 1.5' NW. | ||