A one-night break in the ongoing winter storms allowed for a quick mid-winter observing session. While it was a bit cold for this coastal resident (low 30’s, poor me ) I was able to spend an hour or so observing a few double stars. Based on some recommendations in this forum, these doubles are taken from four constellations - Eridanus, Orion, Canis Major and Cancer. There were a few standouts that came to light. But I’ll share the entire set of observations with both OTAs (optical tube assemblies) - the AT115EDT refractor and Celestron-11 SCT.
- 32 Eridani (Σ 470) - 4.8/5.9/10.5 magnitudes @ 6.9/165 arc-seconds
With both the refractor and SCT @ 73-160X the pair was orange and blue, though the SCT made for more saturated colors. Both could make out the three components A, B and C along with a 4th star of 11th magnitude. This is just a beautiful pair, nicely separated with attractive color contrast. The little refractor produced more beautiful star images, though the big SCT made the fainter components easier to see.
- 40 Eridani (Keid) - 4.4/9.3 magnitudes @ 84 arc-seconds (A to B-C), 9.5/11.2 magnitudes @ 8.3 arc-seconds (B-C)
The B-C pair consists of a white dwarf and a red dwarf, the former among the brightest of its breed in the sky. All three components are seen with both OTAs. But the C-component was only seen by the refractor using averted vision after it had been seen with the SCT. The refractor added a 4th component of 12th magnitude. The SCT showed that along with another companion of 13th magnitude. This made for 5 stars all lying in a line with the A-component in the middle. The refractor revealed the primary to be creamy-yellow, showing some diffraction rings.
- HJ 3945 (Winter Albireo) - 5.0/5.8 magnitudes @ 26.8 arc-seconds
This is a little beauty - widely separated, bright, orange primary and blue secondary, nice color contrast, good separation. There's a 3rd star out there about 2 times the A-B separation. Although the star images aren’t as nice as with the little refractor, the SCT does bring in a 4th star of around 13th magnitude.
- Zeta Cancri (Tegmine) - 5.3/6.2/5.8 magnitudes @ 1.2/6.2 arc-seconds
Due to poor seeing the refractor only showed the A-B pairing as an elongated image at same position image as shown by SkySafari. The big SCT at 320X had star images that were also a mess. But at times I could see two well-separated star images within the mayhem at the correct position angle. For both telescopes the C-component is well separated from the A-B pair.
When I first had a look at the next double it was quickly apparent that this was something special. The next two pairs are just the brightest stars in two separate clumps in the open cluster NGC 2169 in Orion.
- Σ 0844- 8.5/9.3/10.4 magnitudes @ 23.4/31.9 arc-seconds
Whoa, we've got a very interesting field here. The secondary is slightly orange-yellowish in the refractor. The SCT brings in the orange color of both primary and secondary. The C-component is in almost the opposite position angle as A-B and further out. In nearly the same PA is an 8th magnitude star further out at 3 times the A-C separation. There are at least 6 stars in this group. The reduced light-gathering power of the refractor (compared with the 11-inch SCT) makes it more difficult to see all the stars in this multiple system.
- Σ 0848- 7.3/8.1/11.7 magnitudes @ 2.5/15.6 arc-seconds
With the refractor the close pair is separated with some dark sky between 'em, good brightness contrast. At the same PA is another star at ~20 arc-seconds (the C-component). With the SCT the close pair is very easily seen. Along with the C-component there is added a 13-14 magnitude star in the opposite position angle. The 2-1/2 second pair forms one vertex of an almost equilateral triangle with 2 other stars.
- NGC 2169 (37- or LE-Cluster) – open cluster in Orion, 5.9 magnitude, 5.0 arc-minutes in diameter
With the little refractor at low power this cluster is a nice conglomeration of stars in 2 groups. The big SCT gave a better view at 55X and 160X. The extra light gathering power pulled in 6 bright stars in the group with Σ 0844 and 13 bright stars in the group containing Σ 0848. The cluster includes other very faint stars and a void in the middle with few stars.
So this cluster and its two multiple star groups were highlights of the evening. I wonder if Steve or David have any photos of this interesting group. Cloudbuster has posted some nice drawings recently. I also found the more colorful pairs to be enjoyable as well. Yet it was cold enough that just a couple of hours were enough to get my observing fix for the month.
I was able to touch up the collimation on the Schmidt-Cassegrain as well. Despite being careful not to bump or jostle that OTA, it just doesn’t hold perfect collimation for long. I do have the Bob’s Knobs adjustment screws very tight. I am considering replacing these screws with ones having allen-heads. This will allow keeping them tight, but also seeing very small rotations of the screws for fine tuning collimation.
Edited by Rustler46, 23 February 2019 - 11:05 PM.