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The Subtelties of Starlight in Cygnus, First Part: Upsilon Cygni (OΣ 433), OΣ 437, and Σ 2762

What we have planned this time out is a short excursion into a small area of Cygnus, which — despite its diminutive size — features an abundant collection of multiple points of starlight that have one quality in common: a delicate aesthetic appeal.

Now I know some folks prefer to have their eyeballs blasted with a sudden explosion of photons radiating from two luminescent dancing points of adjacent light.  I certainly include myself in that group — my knees knock and my focus fingers fidget when I see Porrima or Castor in the sky.  But it’s kind of like listening to the deafening roar of the ocean during a raging storm — it’s invigorating and awe inspiring; it makes the adrenalin rush and pulse through every square inch of you.  But but after an hour of that, you get tired of having your senses assaulted — you need a break.  So you walk away from it half a mile or so to a place where there’s total silence, and you find the sheer absence of sound is suddenly very soothing.

So what we’re going to do here is attempt to massage the soul with silence, while soaking up the subtle beauty of closely spaced pinpoints of silently pulsing starlight   ………….   which means we’re not in a hurry.  Get a hot cup of tea, put on a warm coat, pull up a chair, clear your head, and above all, make yourself comfortable.

Usually for a tour of this sort, it’s good to have an anchor point from which to start.  In this case, that would be Zeta (ζ) Cygni, an interesting star in its own right — and, as it turns out, also a binary.  But at a claustrophobically spaced four one hundredths  of an arcsecond from the primary — which translates into eight AU’s (an astronomical unit being the distance between the earth and the sun, about 93 million miles) — the components are about as close as they can get without being pulled into one another.  In fact, something similar to that actually took place many eons ago — you might want to take a look at Jim Kaler’s discussion of it.

Zeta (ζ) Cygni shines at a moderate magnitude of 3.2 in the Swan’s eastern wing. We’re going to wander through the area to the east and north of it, following in the footsteps of several observing greats: Sirs William Herschel and John Herschel, Sir James South, Admiral William Smyth, and another father-son duo,  Friedrich Georg Wilhelm von Struve and Otto von Struve. (Stellarium screen image with lots of Greek letters added, click for a larger view).

But let’s get started quickly before I’m tempted down the winding path of digression once more.  😉

One quick aside, though — all of the stars in this tour are best seen in a five or six inch refractor, although a four will do almost as well — but anything less will lose the effects I’m going to describe here.  If you’re using a reflector, I suspect a six inch would be a good place to start, as would a six inch SCT.  A moonless night is a big help, but if you can’t avoid it, you’ll do better with one of the larger apertures — and if the seeing and transparency aren’t average — what we call a III here — wait for a better night.

Our first star, Σ 2762, is found one degree directly west of Zeta (ζ) Cygni. It forms a neat little triangle with 5.75 magnitude HIP 104185 to its north and 6.5 magnitude HIP 104653 to its east. (Stellarium screen image with labels added, click on the chart for a larger view).

Σ 2762  (H II 97)  (S 775)  (H II 97 — AB only)        HIP: 104371    SAO: 70968
RA: 21h 08.6m   Dec: + 30° 12′
*****      Magnitudes       Separation       Position Angle        WDS Data
AB:           5.7,   8.1                  3.2″                      305°                      2010
AC:           5.7, 10.2               59.3″                      229°                      2007
AD:           5.7, 10.1               72.7″                        66°                      1999
Distance:  444 Light Years
Spectral Classifications:  B9 for all
Status:  AB gravitationally linked (Haas), “C” optical (Burnham), “D” undetermined

The first time I got a good look at Σ 2762 — it took about 30 seconds to register —  a loud thud echoed across my observing deck as I dropped like a rock into the seat of my observing chair.   I was captivated  —  completely.  And it has several subtle attractions which emerge slowly the longer you look at it.

First, you’ll find you need a bit of magnification to pull the 8.1 magnitude secondary away from the primary.  It’s a bit tight at 3.2″ — and don’t under-estimate the 2.4 magnitudes of difference — but it’s certainly not difficult to separate.  An 18mm Radian (118x) in my five inch Meade refractor separated the two very comfortably.  Once you pry the secondary free from the primary, you’ll notice the two stars flanking the AB pairing ninety degrees to either side, which are 10.2 magnitude “C” and 10.1 magnitude “D”.  And after you’ve picked those out, your eyes will be drawn to a neat little grouping of four stars just northeast of “D” — not part of this system, but just an added touch which improves the view.

“I was captivated — completely.” (East & west reversed to match the refractor view, click for a version without this caption).

So after you’ve had time to absorb the entire view, you find yourself staring at a rather attractive and eye-catching group of eight stars perched in the center of your eyepiece, with no competing starlight elsewhere in the field of view.  I’ve sat back and let this view calm my star-cluttered thoughts several times in the last month or so.

In the years since its photons first found their way into William Herschel’s twenty foot reflector on September 15th, 1783,  Σ 2762 has had a lot of attention.  After assigning it a catalog number of H II 97, Sir William described it as a “Treble. About 1 degree preceding Zeta, towards the 41st Cygni; a large star.  The two nearest extremely unequal.”

Sir James South added his observation of it (S 775) forty-one years later, on September 24th, 1824  —  “Double, 6th and 10th magnitudes; small, blue.”  —  on a night that apparently was a bit frustrating: “The dew is so intolerably troublesome, that I am obliged to discontinue the observations; and I do it with the greatest reluctance, for the night is unusually fine.”

F. G. W. von Struve, whose name is attached to this star, observed it in 1829 and described the colors as “greenish white and blue” — and also noted a third star at 225 degrees and a separation of 57.8″, which is a close match for where “C” is now.

And four years later, Admiral William Smyth added this: “A very neat double star, towards the tip of the Swan’s right wing [east], directly preceding Zeta (ζ) Cygni by about 1° ½ due west.  “A” 6 ½, dull white; “B” 9, pale lilac; and there is a third star in the sp  [south preceding] quadrant.”  (p. 497 of the The Bedford Catalog)

And then I happened to wander onto the scene a mere 178 years after the Admiral’s observation, on a night when the moon was about fifty percent full and hovering forty degrees to the east.  That moonlight had the effect of muting the colors quite a bit, and as a result the primary matched Smyth’s description of “dull white.”  On a darker night it picked up a weak tinge of yellow, and I detected just the slightest hint of blue in the secondary.  “C” was a bit difficult on that first night because of the moon’s reflected light, but under darker skies it recovered and reclaimed its position very distinctly.

That grouping of four stars to the north of the primary was also more obvious on a moonless night, and in fact was so enticing I just couldn’t resist putting them and the four Σ 2762 stars under my magical 7.5mm Celestron Plössl (157x).  All eight of those stars, shimmering at that magnification against a backdrop of black velvet sky, etched their way deeply into some secret corner of my memory.  As I look at the sketch, and that memory comes into sharp focus now, the peaceful silence of that night is just as real as if I was still sitting at the eyepiece.  You could have heard a pin drop a mile away.

But let’s ease out of this calm moment now and hop northeast about three degrees to one of Otto von Struve’s discoveries,  OΣ 437.  If you look at the second chart above, you’ll see that Σ 2762, 6.5 magnitude HIP 104653, and 7.3 magnitude HIP 104733 form a line that points almost directly at OΣ 437.  You’ll find it wedged between 7.1 magnitude HIP 105234 and 6.0 magnitude HIP 105432.

OΣ 437       HIP: 105390    SAO: 71230
RA:  21h 20.8m   Dec: +32° 27′
*****                      Magnitudes       Separation        Position Angle       WDS Data
AB:                             7.2,  7.4                  2.4″                       19°                      2010
AC:                            7.2, 11.2               79.9″                     142°                      1998
CD (POP 1232)    11.2, 11.2               15.0″                       21°                      1990
Distance:  239 Light Years
Spectral Classification: G4 for all except “D”
Status:  AB gravitationally linked (orbit available here), others undetermined

Now the AB pair of this triple star is noticeably tighter than the AB pairing of Σ 2762, but it’s more evenly matched in magnitude, making it just slightly easier to pry apart.  Still, it took some judicious application of magnification to get those two to relax their grip on one another.  But when you get it just right, you find yourself staring at two very small pinpoints of tangerine tinted light, right in the center of a dim field of view, notable for not having anything else available to lure your eyes away from the display at the center.

Stare deeply into those tangerine-tinted photons …………. (east & west reversed, click for the caption-less version).

My Meade AR-5 called back the 7.5mm Celestron Plössl (157x) for another round, which turned out be the perfect choice.  I could see the two stars trying to leap apart in a 10mm Radian (118x), but the additional magnification of the 7.5mm did the trick, settling down to just a bit more than a hair’s width apart.  A week later, on a night when the seeing was barely a I,  I managed to split them in my six inch Celestron f/8 refractor using a 5mm Radian (240x) — and discovered what two oscillating and vibrating tangerines surrounded by diffraction rings can do to your emotions.  All I can add is amazing, amazing, amazing  …………….   just totally incredible.

“C” was no contest in the AR-5 at 157x, but not particularly notable — except, that I could see a hint of duplicity in it.  At a distance of fifteen arc seconds apart, their twin 11.2 magnitudes of faint light should easily separate in a six inch refractor, based on my experience with similar dim pairs recently.  So I gave it a try the night I had the six inch Celestron under the skies, but both of them eluded my thirsty eyes.  They were just too faint for the poor seeing conditions that night — on a night with average seeing, though, they should be no contest in a six inch refractor, so I shall return.

The OΣ in this star’s designation refers to Friedrich Georg Wilhelm von Struve’s son, Otto Wilhelm von Struve, who recorded his first observation of the AB pair in 1845.  He measured the separation at 1.31″ and the position angle at 61.8 degrees.  Since that time, the two stars have slowly widened — an 1898 observation by Hussey (see the note on sources at the end of part two) put them at 1.64″ and 43.9 degrees.

I found two other recorded observations of OΣ 437, both of them in Haas’s book: “Hartung: ’75mm easily resolves this close orange-yellow pair.’  Heckman, 250mm, 185x: ‘Superb yellowish pair of equal magnitude.’ ”  That first observation in a 75mm scope surprises me — I’m going to have to try that with my 76mm Tasco.

My impression of the color in the AB pair was more tangerine than yellow, with a slight bit of white present — just enough to make those two stars seem a bit brighter than their 7.2 and 7.4 magnitudes.  I’ve noticed when there’s enough white in an otherwise colorful star, the overall color has what I can best describe as a metallic quality.  It seems to be impossible to reproduce that effect in a sketch or a photograph — the only way to experience it is visually.

But to get back to my comment in the first paragraph on this star, once you’ve succeeded in splitting this pair, in order to get it really right, give this view some time to work its magic — don’t give it a quick glance and then rush off to some other object.  You need to look at this pair for ten or fifteen minutes — and you most definitely need to do this on a dark, moonless night.

Get yourself situated comfortably, relax, look into the eyepiece, and let those orange-tinted photons massage your vision.  After several minutes, the mental chatter in your head will begin to calm down of its own accord, and you’ll soon find there’s something very appealing about the appearance of these two points of orangish-white light glowing all alone in the deep black void of interstellar space.  It was the view of these twin points of light that prompted the phrase “delicate aesthetics” to slip into my thoughts from the fathomless depths above.

And after that view is fixed firmly in your memory  ……………..   take a deep breath   ………………   and then we’ll wander up to Upsilon (υ).

We need to make a turn to the north here, and although there aren’t any guide stars along the way on our chart, you should have no problem seeing Upsilon (υ) lying two degrees north of OΣ 437.  It shines at a combined magnitude of 4.4, making it stand out from the much fainter background stars.

Upsilon (υ) Cygni (OΣ 433) (66 Cygni) (h 932)       HIP: 105138    SAO: 71173
RA: 21h 17.9m   Dec: +34°  54′
*****                  Magnitudes        Separation         Position Angle       WDS Data
AB:                       4.4, 10.0                 14.2″                       220°                    2008
AC:                       4.4, 10.0                 21.2″                       181°                    2008
AD:                       4.4, 12.0                 57.1″                       308°                    1998
AE (BU 9011)     4.4, 10.0                34.9″                          67°                    2000
Distance:  901 Light Years
Spectral Classification:  All B2 except for “E”
Status: AB optical (Burnham), others undetermined

Now you’ve got to do some digging here — the magic in this view requires concerted effort, and probably at least five inches of aperture to see all of it on a dark night, meaning the disappearing “D” and the very elusive “E.”

I was wielding my Meade AR-5 the first time I wandered north to Upsilon (υ), but it was on the same night as the fifty percent full moon described in my description above of Σ 2762.  In this case, because all of the companions were closer to the primary than those of Σ 2762, my attempt to see anything than other than the primary was pretty much hopeless.  I had just the faintest glimpses of “B” and “C” attempting to emerge into the moonlight from that primarial glare, but I finally gave up any attempt to sketch this one and just wrote “hopeless — need a darker night.”

But I could see that wasn’t going to happen for a while, so even though the moon was well on its way to full, I returned to the search again with an extra inch of aperture — and eventually a whole lot more magnification.  A 14mm Radian (109x) in my six inch f/10 refractor produced a primary with an intense yellow-white glow (metallic again), and the extra inch of aperture allowed “B” and “C” to come out of their dark hiding spots.  “E,” which is the same magnitude as those two, remained out of sight.  That was a result of a diffuse halo of light surrounding the primary, which was a bit stronger where “E” was supposed to be — and 12th magnitude “D” was nowhere to be seen.

Subtle starlight yielding to muscular magnification …………. (east & west reversed again, click to lose this caption).

So I decided to start increasing the magnification until I reached the point where the eyepiece began magnifying more glare than starlight.  Usually the glare wins that race, but I got lucky in this particular case — before I knew it I was peering into the pinhole-sized lens of a 4mm Astro-Tech Plössl (380x !!!) and found myself looking directly at the disappearing “D.”  I had already pried the elusive “E” out of the glare with the four millimeter’s slightly less powerful relative, a 6mm AT Plössl (253x), which had also given me an averted vision first glimpse of “D.”

Now your first impression might be that this was less a case of subtle starlight and more one of muscular magnification.   But  ……..   let us not be so hasty here.  There is something very haunting about the view of eight dancing points of starlight magnified three hundred and eighty times in the center of a pin-holed lensed Plössl.  Really.

At that magnification, there’s certainly a lack of sharpness, but its absence is more than made up for by the shimmering, almost ghost-like dance of those shapeless concentrations of light.  There’s a word for it in German — unheimlich — meaning uncanny, intangible, mysterious, elusive — in other words, a word for a quality that defies description.  If you can picture that, you know exactly what I mean.  If you can’t, you’ve got no choice but to go outside and try it.

I probably should come back here on a dark night with the AR-5 and see if I can do as well, and possibly recover some of the aesthetic appeal that I’m sure I didn’t see.  I suspect what I’ll find is that 250x on a dark night in a five inch refractor will match the 380x in the six inch under all that moonlight.  On the other hand, I don’t want to do anything to disturb that shimmering memory of dancing light right now.  I think I’ll just leave it this way.

John Herschel discovered this star in 1827, describing it as “Triple. L. white. Both the small ones red.” His measurements of distance seem to be well off the mark for AB and AC, but in looking at the data in the Lick publication mentioned in the source notes at the end of part two of this post, “B” and “C” have shown virtually no motion since the 1890’s.  I’m not sure how that red arrived in his eyepiece since all three stars are the same spectral class, B2 — but maybe a dark night will provide a hint.

And now we move on to part two, and a neat little triple star discovered by Sir John’s sometime observing partner, James South.


3 Responses

  1. I got a look at Σ 2762 this evening – under nearly full moon light – using the 8-inch SCT and the Orion binoviewers at 100x and 200X. Very nice – especially at 200X – but puzzling in one respect.

    The “D” component should be just a hair brighter than the C component – especially since C is actually closer to the primary. But this simply wasn’t the case. At first I had trouble seeing the D component at all. But at the higher power it was easy, though I would say at least a half magnitude fainter than C.

    That’s weird because you seemed to have just the opposite experience with these two.

    • Hmmm — that is weird. I think the sky gods are playing tricks on one of us.

      It shouldn’t have anything to do with differing colors, since both stars are the same spectral class, B9. I was just trying to look at it again last night with a four inch refractor, but the seeing was so poor I didn’t spend much time on it. I did catch brief glimpses of both “C” and “D”, but they never did quite come into focus.

      I’ll take another look in the next few nights and see what happens.

      • I had another look at Σ 2762 last night before a wave of low clouds whisked it away for a while, but my experience this time was the same as yours, Greg. “C” was very obvious, and “D” was definitely a bit harder to see — which is totally the reverse of my first experience with them.

        I checked my notes, on the chance that I had mixed up the references to the two stars, but apparently not: ” ‘C’ a bit difficult because of the moon (50% full, forty degrees to the east).”

        At any rate, “D” certainly does not appear to be the brighter of the two. I agree that it’s at least half a magnitude fainter, possibly a bit more.

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