Double Stars in October

Gearing up for observing season here in South Florida. Days are getting shorter, nights are getting less hot and muggy (still cloudy, though), and thinking about what’s to come. Here’s a post I originally put on sci.astro.amateur back in 2003, and, in anticipation of October skies, I thought I’d repost it here, adding links and expanding on a few shorthand notes for the benefit of those who might not speak astrogeek. I’ve upgraded my equipment since I wrote this post (in fact, I just finished work on a field battery similar to this one, so I can use my 8-inch scope again!), and am looking to see how much better my 60mm apochromatic scope does compare to the 80mm achromat I was using at the time… As I recall when I tested them side by side, the smaller scope was MUCH better on most observing tests.

After a long summer of clouds, rains, and mosquitoes, I (and many other  members of the Astronomical Society of the Palm Beaches) finally managed  to avoid the first two of the big three summer pests last weekend and get to a moderately dark site for some observing. [UPDATE: This summer was devoted to Daniel and sleep, in about that order. I’m looking forward to at least getting out to my back yard for the double-star portion of this observing plan.]

Date/Time: 18 October 2003, 0200-0515 UTC
Site: Jonathan Dickinson State Park, Jupiter, FL
Weather: mid-70s, mild breezes from time to time
Seeing: fairly poor
Transparency: no estimate (it’s been too long since I had good skies to estimate!)
Equipment: 80mmf6 refractor, 24mmTV Wide Angle, 20mm Meade RG Erfle,
15mm TV plossl, 7mm Siebert WA, 6mm UO ortho

The evening started off very nice, with nice weather and good people, although we arrived well after dark and had to set up blind. That initial condition of haste pervaded my entire observing program, and made it virtually certain that, as a series of low clouds interrupted the session, I would get completely off track. But I was successful at observing the globular cluster M30, which I had never seen before, and a host of double stars, and various familiar M objects.

I was testing my new Denver Observer’s chair, which worked well, but I had the same problem with it I had last week when I first built it—the stair tread adhesive failed, and it kept coming off the back! I have yet to figure out how to keep it on…

Anyway.

My observing list is based on the Autumn Double Star tour I found at P.J. Anway’s website, the Lookum Observatory (look it up if you’re interested). I added some deep-sky objects to his double star tour to compile my list, which was too ambitious by far for my first time back in a long while:

Alpha Capricorni (Algiedi)
Beta Capricorni (Dabih)
M30 (NGC 7099)
Gamma Delphini
Beta Delphini (Rotanev)
NGC 6905 (Blue Flash)
Epsilon Equulei
Epsilon Pegasi
M15
Zeta Aquarii
94 Aquarii
M2 (NGC 7089)
M72 (NGC 6981)
M74 (NGC 6994)
NGC 7009 (Saturn Nebula)
65 Piscium
Psi 1 Piscium
Zeta Piscium
M74 (NGC 628)
Gamma Arietis (Mesarthim)
Lambda Arietis
Alpha Piscium (Alrisha)
Gamma Andromedae (Almaak)
M31 (NGC 224)
M32 (NGC 221)
M110 (NGC 205)
Iota Trianguli
M33 (NGC 598)
Gamma Ceti (Kaffaljidhma)

First on the list were the wide doubles (alpha and beta) in Capricornus, which I had seen before, but I wanted to confirm their appearance through the 80mm refractor, as well as draw their separations and PAs. [Separation is the measure of how far apart the stars are, usually given in arcseconds; PA, position angle, is the direction the secondary star is from the primary, measured in degrees.] I have to practice this skill, because my results are still quite poor—I forget to note colors, and I never note estimated visual separation. I rely entirely on the published values, and not on my observations. I need to establish the true FOV of all my eyepieces in all my telescopes before I can do any real “observing.”

I used 80x with the UO ortho, and have a field sketch of Beta Cap showing the primary to the north, with two other stars in the field, one to the SE and the other to the SW, making a rouhgly equilateral triangle.

Next up, and not too far away, was M30, a nice globular cluster that I had never gotten around to observing. At 68.5 power (7mm Siebert), I was able to see the cluster with direct vision. It appeared highly
concentrated, falling off sharply with increasing distance from the center. It’s a Shapley Class V cluster (I being highly concentrated, XII being diffuse), which makes it slightly more concentrated than average, I suppose—I need to observe more globulars so I can make more informed judgments about this!

Gamma Delphini is a nice easy double, about 9.6 arcseconds separation according to published values. My field sketch at 80x, using the 6mm Ortho, shows a much brighter primary than companion, although it could be that I’m not very good at indicating relative brightness yet. I don’t differentiate systematically, and I don’t have a method for indicating colors.

Next up was Beta Delphini, a close double star named Rotanev, for reasons that have been known since Webb (I believe?) figured them out and published them. Sky and Tel had a note on them a while back. In any case, at no power I possessed could I observe separation or even elongation of this double.

NGC 6905 remained lost in an area of the sky with which I am unfamiliar. Maybe a bigger scope and less haste will help next time I attempt it.

After this I took a brief break from double stars, touring M31 (still have trouble finding M110 and M32 in the 80mm, although the nice wide field at powers from 12x up to 20x should have made this a snap.

I also observed M33, but could only see it through averted vision. I had hoped to see quite a few other galaxies, but the skies weren’t dark enough, the seeing wasn’t good enough, and (the real reason) I’m not
experienced and patient enough!

Back to the program of doubles:

Epsilon Equulei I was able to observe through the 80mm at 80x, and I saw the primary as being bluish and the companion as being yellow/orange. When I observed the same pair through an Edmunds 4 inch f15 refractor, I was able to see that this impression was completely backwards, and it is the primary that is yellow/orange and the companion that is bluish. I have no idea why the colors were reversed in the Stellarvue. When I went back to the Stellarvue, I was quickly able to confirm the true colors, and remain puzzled as to this optical illusion, other than to ascribe it to relative inexperience and marginal aperture. [One thing I have since learned is that higher magnification, which allows the diffraction disks of the component stars to be seen, is helpful in making color determinations. So with higher aperture and higher magnification, you should be able to see more true color.]

Clouds rolled in now, and I was unable to observe much for a while. When the stars came out again, the next object I observed was Gamma Arietis, a double star for which I have some particular affection, since I found out that it was the second double star ever recorded (Mizar being the first). My field sketch shows the primary due North of the secondary at 80x. My sources tell me that these stars are separated by approximately 8 arcseconds, 3 fewer than Epsilon Equ, yet they were much easier to see in terms of color “difference,” a fact which I attribute to their similarity in magnitude. While Eps Equ’s stars are mags 5.9 and 7.4, gamma arietis is 4.8 and 4.8, making them much easier to compare.

From gamma Arietis I went to Zeta Piscium, which I observed at 68.5x. This pair seems to be aligned E-W, with the primary to the west (unless I’m correcting for the star diagonal improperly). I made no comments on my sheet about them other than the power and the sketch.

On to gamma Andromedae, one of the best double stars of Autumn. This pair is just under 10 arcseconds apart, and over 3 magnitudes in difference, making them look much closer than they are. The m2.2 primary is N and a little E of the companion, again assuming I’m correcting for the mirror reversal properly. For some reason I thought that N was down on my sketches, and now I see that N was up, so I may have done the whole night upside down and backwards! I need to get some more tutelage!

At this point, it was getting rather late, and we all trundled into the car and drove home. And that was the longest and best session I’ve had since I moved to Florida 2 1/4 years ago. I’m not disappointed in my
lack of success, just motivated to improve. The fellow members of ASPB have been very helpful, but everyone has been so photon-deprived this summer that this was the first opportunity to try out their new tricks/programs, etc., that I didn’t want to take them away from their programs to participate in mine.

As always, organize, plan in advance, and hope to see at least 50% of the objects on your list! (I got to 12 out of 29, which is below my goal, but so what?)

Don’t know what kind of success I’ll have this time around, but I’m looking forward to giving it a try sometime in the next few weeks (full moon is on the 11th, though, so it’ll have to be some time close to Halloween).

Related Images: