OK, it’s time to put away the low power eyepieces and aperture-challenged optical devices and get serious about prying into the diabolically difficult and totally torturous realm of high Delta doubles. Those would be doubles with magnitude differences of roughly two magnitudes or more. And to keep things manageable and sane, we’ll stay away from any pairs fainter than fifteenth magnitude. 😉
But in reality we don’t need to go anywhere near that faint – not that we ever could anyway – because the two stars we’re going to look at here are more than capable of making us yearn for less challenging targets such as Albireo or Mizar. In fact, keep a bottle of aspirin handy – you may need to subdue a headache caused by high-frequency stellar spinning-hopping-and-twitching.
We’re going to start way up high in the northeastern corner of Hercules with an enticingly innocent 6.47 magnitude star dubbed OΣ 344 by its discoverer, Otto Struve, and then re-dubbed STT 344 by the Washington Double Star Catalog (WDS). If you didn’t know there was a tenth magnitude companion hovering near that 6.47 bundle of photons, you probably would skip right over it – which just goes to show there are times when ignorance can truly be bliss.
But since the fate of a double star addict is to be cursed with a surplus knowledge of numerical data, we’ve got no choice but to stop and take a peek.
Hang on tight.
OΣ 344 (STT 344) HIP: 88754 SAO: 47233
RA: 18h 07.1m Dec: +49° 43’
Magnitudes: 6.47, 10.31
Position Angle: 140° (WDS 2009)
Distance: 722 Light Years
Spectral Classification: “A” is A2
I was first made aware of the existence of OΣ 344 after wrestling two difficult high Delta pairs to a dubious draw in Ursa Major (namely Bu 1074 and Cou 1900) when Mark McPhee posted a comment about it – something like “If you’d like a taste of what Cou 1900 is supposed to offer, mosey over to STT 344 in Hercules – you won’t be disappointed.” Now that’s like waving a dog-eared first edition copy of Burnham’s 1906 double star catalog in front of me, but I had to wait until seeing conditions aligned with the stars, so to speak. It took most of a year, but I finally had my chance – and this is what things looked like on first approach:
So there I sat, parked permanently (at least it had begun to seem that way) in upper northeast Hercules, attempting to wrestle frantically wriggling white photons into a stationary image for long enough to visually grab that 10.31 magnitude secondary. Seeing conditions were OK – certainly not worth bowing to the sky gods for – but I had a hunch there was a chance. The image in a 10mm Radian (245x) didn’t divulge anything, but since the frantic wriggle wasn’t high frequency yet, I reached for what is usually my ace-in-the-hole ocular, an old Celestron 7.5mm Plössl (327x) . . . . . and the wriggle not only advanced into high frequency territory, the image turned to mush. Suddenly I couldn’t buy a sharp focus with that eyepiece for all the Plössls on planet Earth.
Sometimes, though, there’s a different world lurking on the other side of that realm where visual images turn to mushy photons, so I reached for another dependable tool, a 6mm Astro-Tech Plössl. That eyepiece has always done an excellent job at controlling the glare in very glaring situations, such as this one. And for who knows what reason, I was able to get its 408x image into focus – usually only briefly, but occasionally for several seconds at a time.
I sat patiently still, waiting and hoping for that magical secondarial sighting, while my tortured right eye grudgingly tolerated my obsession. After about fifteen minutes – I’m guessing since time becomes every bit as relative in this situation as Einstein predicted – I had an averted vision glimpse of something popping into view just inside the thick diffraction ring surrounding the primary.
Several times it leaped into sight and then slipped silently back into the primary’s high frequency twitch, and then re-appeared again. After several of those teasing episodes, I grabbed the secondarial light with direct vision and held it for a couple of seconds:
Seeing conditions seemed to be improving slightly – either that, or my eyepiece eye and a secret compartment in my brain were getting better at cooperating with each other. At one point, I had the secondary in direct view for about ten seconds. It was a bit more than a puff of light – it had to be in order to be seen in the primary’s throbbing glare – but not quite what you would call a splendidly solid beam of light. At times there was almost a thinly transparent, surreal, quality to it.
But it was there – definitely, undeniably, unquestionably there – which was more than I had been able to say about the secondaries of Bu 1074 and Cou 1900 the year prior.
And as I sat there, mesmerized into a stellar stupor, I remembered another Herculean challenge – Zeta. But by the time I tore myself loose from Otto Struve’s 344th pair, the clouds began moving in, turning the sky into a featureless dark ocean. So I had to wait until the following night . . . . . . . and having wrestled unsuccessfully with Zeta numerous times the prior year, I reached for the 9.25 inch edge once again.
BUT – before you move your scope, we really should pan over to one of F.G.W. Struve’s nearby discoveries, Σ 2290, for a quick peek – it’s located a mere 18’ to the north. If you move OΣ 344 to the south edge of the field of view, Σ 2290 will come into view just slightly west of the north corner of the field. You can use 8.79 magnitude SAO 47230 to guide you in the correct direction.
Σ 2290 HIP: 88713 SAO: 30749
RA: 18h 06.6m Dec: +50° 01’
Identifier Magnitudes Separation Position Angle WDS
Cou 2276 Aa, Ab: 9.77, 10.00 0.30” 13° 1993
STF 2290 AB: 8.90, 11.20 3.90” 352° 2009
STF 2290 AC: 8.90, 12.70 178.00” 69° 2003
Distance: 2233 Light Years (Simbad)
Spectral Classification: “A” is A5
Now that we have that one under our belts, we’ll move on to Zeta (ζ ) Herculis. If you’ve lost track of it, here’s the first chart once again.
Zeta (ζ) Herculis (40 Her) (Σ 2084) (H I 36)
HIP: 81693 SAO: 65485
RA: 16h 41.3m Dec: +31° 36’
Magnitudes: 2.95, 5.40
Position Angle: 145.5° (WDS 2014)
Distance: 35 Light Years
Spectral Classification: “A” is G0, “B” is G7
Note: Orbit and data can be seen here
I think it was Neil English, renowned guru of the long focus achromatic refractor, who first brought Zeta (ζ) Herculis to my attention — and here I was, attacking it with an SCT. However, without giving too much away, after the evening with the SCT, I returned to the refractor fold with my six inch f/10 to get this wide field view of Zeta (ζ):
To get back to the evening of June 23rd, I found the skies a couple of notches more cooperative, something close to a IV on this chart. I spent some time on other objects until close to midnight, which gave Zeta (ζ) plenty of time to get into position high in the sky and just west of the meridian. Once I located it and centered it in an 18mm Radian (136x), I went immediately to the 6mm Astro-Tech Plössl (408x) again. The image was more steady than the previous night, so it didn’t take long at all to realize the secondary was sitting out in the open, right at the outer edge of the first diffraction ring:
I was amazed at how easy it was! I had tried and failed to split Zeta several times the previous year and here it was, just like that, on the first try. But now that I had the secondary in sight, I realized last year’s tantalizing teases were the real thing. All those attempts had been under less than friendly seeing conditions, with so much jumping, whirling, spinning, and hopping that I could never be certain of what I saw.
When I returned to Zeta (ζ) a week later to get the wide field sketch with the 6 inch f/10 refractor, the seeing conditions were somewhere between the previous visit to Zeta (ζ) and the one to OΣ 344. I couldn’t resist the temptation to try again, so after I finished the 84x sketch, I reached for the 6mm AT Plössl (253x) once more to see what would happen. I had to look closely, but the secondary was definitely attempting to split off from the primary – what it needed was some help.
I grabbed a seldom-used 2.4x Dakin Barlow, slipped the 6mm AT Plössl into it, parked the whole thing in the diagonal, and then leaned over the unified pair and attempted to focus the blurred, vibrating image staring back at me. There’s one thing you just can’t miss when you blow up a yellowish 2.95 magnitude star to 608x – it’s dazzlingly bright. In fact, it seems to light up the whole field of view. With a very delicate touch on the two-speed focuser’s fine focus knob, I nudged the image toward what I hoped would be something resembling a focused star.
All the yellow-white light compressed into that diminutive five arc minute field was shimmering as though the star was about to erupt. Slowly, then suddenly, the image came into focus. I had to coax my eyepiece eye into reconnecting with the same secret compartment in my brain it had found on the night with OΣ 344, but after it re-established the connection, I could see through the glare to the secondary, sitting once more on the outer edge of the first diffraction ring with what looked like a mile of open space between it and the primary. OK – that’s a bit of an exaggeration caused by a temporary illusion and a very brief bout of insanity, but . . . . . . . . WOW! What a sight!
William Herschel came up with a great phrase to describe the suddenly obvious distance between the primary and secondary at very high magnifications: “the distance is, as it were, laid open to the view.” You can almost see that thought materializing in his mind as he describes his experience with Zeta (ζ) on July 18th, 1782 (source, scroll down to the sixth title):
There’s nothing like the thrill of peering into the dazzle of magnified starlight and catching sight of a smaller secondary, very clear and very distinct, with black space between it and the primary, each of them vibrating, spinning, hopping, and leaping in unison – and around both of them, a diffraction ring shimmering so rapidly it appears to be spinning. It’s an electrical thrill that causes every quark in you to quiver (and probably quite a few outside you), and reminds you the sketch is only a snapshot of an experience quite literally out of this world.
Gotta go grab a small glass of something strong to calm the optic nerves now . . . . . . .
Clear (and stable) Skies! 😎 (Next time, back to northern Hercules again).