I had this Great Plan.
It started with what strikes me as a rather uncanny, although not unique, aspect of Corona Borealis. Actually, a better word than uncanny is unheimlich, a German word that has an aura of the unexplainable about it, which fits the specifics in this instance.
And to be specific about the specifics, I don’t know how many Star Splitting sleuths have noticed it, but there seem to be an inordinate number of double stars in this half circle of a constellation that are tighter than the barrel of a 1.26″ inch eyepiece in a 1.25″ diagonal. I just happen to have a couple of those things, and they’ll actually fit in the eyepiece holder of a diagonal — but only if you hold your mouth the right way and refrain from swearing sweet nothings out loud — at least not loud enough to bother the neighbors at two in the morning.
Anyway, to be even more specific, consider this —- Theta (θ) CrB has a separation of 0.8″; Eta (η) is separated by 0.67″; Gamma (γ) is at 0.6″; Beta (β) is a claustrophobic 0.2″ —– notice a trend there?
“Aha!,” I hear you say, “but there’s Epsilon (ε), at a redeeming 2.0!” — yeah, sure, with magnitudes of 4.2 and 12.6, meaning the secondary, already almost invisible anyway, is a mere 1575 times fainter than the primary. Forget that one, too.
Now, to be fair to the Crown, there are exceptions. I ran into a neat pair some time ago, Zeta (ζ) and Σ 1964, which I wrote up here. But even the last of that pair features some separations of microscopic proportions. It does seem to be contagious, at the very least.
So my Great Plan was to write a post entitled “Close Encounters in Corona Borealis” — which I didn’t think would prove to be too difficult, provided of course I could find some stars I could split. And with a separation of 1.6″, Σ 1932 fit the bill perfectly. And so did Σ 1950, with a comparatively expansive separation of 3.3″. Except that it’s not in Corona Borealis. It’s barely across the border — three arc minutes across — in Serpens Caput. And that’s what happened to the Great Plan — it went kaput — another German word, meaning it ain’t gonna work.
And of course I discovered that after I did the sketch and started writing this post.
So in order to avoid jumping around in Corona Borealis like a ravenous jack rabbit chasing a desperately plump mouse, I threw in a non-claustrophobic double star that happened to be located halfway between the other two, h 2777, with what passes in this stellar neighborhood for an astronomically wide 43.9″ of separation. And changed the title to what you see above. And parked the close encounter theme over in Serpens Caput, which has it’s share, too. But we’ll get to that — one of these days, or actually, nights.
Meanwhile, back at the Crown, we’ve got some serious star splitting ahead of us, so let’s get busy before the clouds gather up the clear skies and and whisk them away once again. They do that a lot around here.
Σ 1932 HIP: 74893 SAO: 83756
RA: 15h 18.3m Dec:+26° 50′
Magnitudes: 7.3, 7.4
Position Angle: 264° (WDS 2010)
Distance: 117 Light Years
Spectral Classification: F6, F6
And a tight little devil it is, too, with only 1.6 arc seconds of distance between its two stars. But — fortunately — there’s only a tenth of a magnitude of difference between the pair, which gives us a reasonable chance of prying them apart without an unreasonable exertion of effort.
Now the only reason I was even patrolling this part of the sky was I found myself with an evening of particularly good seeing — easily a IV on this scale — which is certainly a rarity around these parts. By some strange conjunction of a random collection of rare circumstances, I also happened to have my six inch f/10 refractor under the stars. The poor thing hadn’t been out from underneath the roof of the house for about five months, so my timing couldn’t have been better. I swiveled its long white tube high up into the sky, turned on a small green laser I use for pointing, aimed it a point about halfway between Alpha (α) Coronae Borealis and Psi (ψ) Boötis, turned it off before the Coast Guard came looking for me, spied my prey in the finder, bent down and peered into the eyepiece — and holy orbiting orange photons! — two beads of very subdued light were winking back at me.
Actually, a better color description of each of these two stars is a light reddish-orange hue with a trace of white — at least for my eyes in that scope on that night. That really doesn’t match their F6 spectral classification very well, though — in fact, not at all. Sissy Haas did much better in that regard:
125mm, 200x: Grand! A bright and perfect figure-8 — a pair of identical stars, yellow-white in color, that are almost but not quite fully separated.”
(Double Stars for Small Telescopes, p. 61)
On the other hand, she quotes the Reverend T. W. Webb as having seen “green-white” in both stars. Friedrich Georg Wilhelm von Struve, who discovered this pair in 1831, described each of them as white. The reddish-orange hue I saw may have been the result of peering through an excess of atmospheric moisture, thanks to the nearby Pacific Ocean, but I have no idea how the green crept into Webb’s observation. Stars simply are not green — a rather unheimlich anomaly, to say the least — but certainly not unique.
There’s a chart here (scroll down a bit), based on Washington Double Star Catalog data, showing the 203 year orbit of Σ 1932. The two stars will be at their closest, three-tenths of an arc second apart, in 2133. So time’s a wastin’ — get out there and get a look — quick! You’ve only got 120 years before that happens. 😉
And, in addition to the two main stars, the primary is a double as well, cataloged as CHR 45 in the WDS. Good luck with that one, though — they’re only three-tenths of an arc second apart. According to the WDS notes, that observation was made with an adaptive optics system, which is a high-tech way of overcoming contagious claustrophobia.
Moving on, if you move your scope south one degree and look into your finder, you’ll find a row of three seventh and eighth magnitude stars. The one farthest to the east is our next target, h 2777. It also is the northernmost of a line of three north-south aligned stars, the other two being 6.4 magnitude HIP 75125 and 7.3 magnitude HIP 75163, as shown on the second chart above — or to make things easier, you can view it here.
h 2777 (HJ 2777) HIP: 75233 SAO: 83795
RA: 15h 22.4m Dec: +25° 37′
Magnitudes: 7.5, 10.4
Position Angle: 343° (WDS 2007)
Distance: 1500 Light Years
Spectral Classification: K1
Now you’ve got to look closely to see the secondarial light here. Even though these two stars are much farther apart at 43.9″ than those of Σ 1932, the secondary is sixteen times dimmer than the primary, and at a relatively dim magnitude of 10.4, it doesn’t throw out a lot of light anyway.
I found the primary more white than reddish orange, although there was a definite hint of the darker color present. That matches up reasonably well with the K1 spectral classification, so at least my imagination wasn’t hard at work imagining colors that weren’t there — this time. That secondary, though, really required some hard staring in order to maintain a good visual grasp on it. I thought I could detect a hint of bluish-white a couple of times, but if it was there, it was an elusive bluish-white. It was just too darn faint to be sure in the five inch refractor I was using.
There are two more suspicious looking stars in the field that I thought might be doubles, one pair halfway to the northeast edge of the field, another parked at the field’s west edge, but neither of them appears in the WDS or in MegaStar. I think I may keep an eye on these two for the next hundred years or so, just to see if they move — it’s possible I’ve got two discoveries here. 🙄
Sir John Herschel came across these two stars in 1830, but didn’t leave any notes on them that I can find, other than his measurements (30″ and 352.5 degrees). I did discover that h 2777 is also a variable star, cataloged as UV Coronae Borealis, with a very tight range of magnitudes, 7.15 to 7.40, just a bit difficult to detect visually.
And that takes us to our last pair, the one that seems to have wandered across the border into Serpens Caput without my permission. Σ 1950 lies about a degree and a half east of h 2777, so if you move your finder that short distance, you should see it just about centered in the cross hairs. Watch that you don’t accidentally land on 6.0 magnitude HIP 75674, though, which is barely to the southwest of it. It won’t split — I’ve tried that already. Here’s that chart again if you need it.
Σ 1950 HIP: 75883 SAO: 83852
RA: 15h 30.0 Dec: +25° 30′
Magnitudes: 8.1, 9.2
Separation: 3.3″ (WDS 2008)
Position Angle: 91°
Distance: 1600 Light Years
Spectral Classification: K4
After our two previous stellar targets, Σ 1950 is a welcome contrast since both stars are further apart than our first star, Σ 1932, and have less magnitude difference than our second star, h 2777 . Of course that’s merely a relative improvement, since the separation is still fairly tight, and the secondary is even a bit elusive.
In fact, when I first looked at this pair, I was really surprised at how much smaller the secondary was visually in comparison to the primary. With only 1.1 magnitudes of difference, I expected them to be similar in visual size. As a result, I discovered I needed a very precise focus to get that beady little secondary to appear as an individual dot of barely there light.
The primary appeared to be a faint shade of reddish orange in the 20mm TV Plössl (95x) I was using, and to the extent that I could see any color at all in the secondary, it seemed to be a very pale imitation of borrowed photons from the primary. More than likely that was caused by the deterioration in seeing — it was down to its customary level of II — and by transparency that could barely charitably be described as pure yuck. Still, even under those conditions, I found it radiated a delicate beauty that kept me hovering over it for ten or fifteen minutes after I finished the sketch.
F. G.W. von Struve first had this pair in his sights in 1830, and he came up with gold for the primary and blue for the secondary, which left me wondering if we were even looking at the same stars. But he measured a separation of 3.2 arc seconds, and a position angle of ninety-three degrees — almost identical to the most recent measurements of 2008 — so maybe the poor transparency I was peering through influenced the colors I observed. The K4 classification of the primary argues for yellow orange, though, so I was on the right track it appears.
And since we’re left at the end of this tour hanging in the extreme northern edge of Serpens Cauda, we’ll just stick around here and see what other close pairs we can pry away from the serpent while his head is turned. Stay tuned —- there’s more coming as soon as the fickle weather gods release their hold on the sky! 😎