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In the Realm of the Ophiuchan Triangle: 61, 67, and 70 Ophiuchi; and S 694

When you have a chance to catch a clear, dark, moonless evening in August, take a glance up into the southern sky at the brilliant blue and white beauty of first magnitude Altair.  Then follow the trail of the Milky Way southwest from it to the first, rather large, glowing cloud of stars you come to — which is known as the Scutum Star Cloud.  Make a fist with your right hand, hold it up to the right (west) of the cloud and turn it so it’s at a ninety degree angle to the line that runs back to Altair.  And — unless you have a HUGE hand — at the right edge of it you’ll see a distinctive triangle of stars formerly known as Poniatowski’ Bull.

Mark that location in your memory, go grab a telescope, and follow me  ……..  ’cause that’s where we’re going tonight.

The Scutum (SKOO-tum) Star Cloud is seen here glowing about twenty degrees southwest of Altair. A twenty degree hop to the northwest from the Cloud will land you in a triangle consisting of 70, 67,and 68 Ophiuchi. All three of these are multiple stars, but 68 (Bu 1125), a triple, is a bit beyond our reach with separations of .4″ and .5″. This Ophiuchan triangle doesn’t have the same sinister reputation that the more famous Bermuda triangle does, but it might still be a good idea to follow my directions closely to avoid slipping into oblivion in Ophiuchus. (Stellarium screen image with labels added, click for a larger view)

There are a group of stars which have become famous for their seeming ability to display a wide range of colors.  One of the better known is 95 Herculis, made famous in particular by Admiral William H. Smyth’s observation of “light apple green, cherry red” in 1857. Others on that list include Delta Herculis, Gamma Delphini, and Gamma Leonis, which is better known as Algieba.

There’s one more, though — and it goes by the name of 70 Ophiuchi.  Just by chance, that happens to be our first stop.

The three stars that form our triangle — 70, 67, and 68 Ophiuchi — were once part of a constellation known as Poniatowski’s Bull, which has since been relegated to “asterism” status. Also visible on this chart is the fast moving ninth magnitude Barnard’s Star, six light year distant from us, moving at the rate of 10.4 arcseconds each year.  (Stellarium screen image with labels added, click to enlarge)

Splitting Tools: And for binary binocular fans, two of the stars shown on the chart above and described below — 67 Ophiuchus (the AC pair) and S 694 — are easily split in mounted 15×70 binoculars — and provide great views in either a 50mm or 60mm scope as well.

70 Ophiuchi  (Σ 2272)  (H II 4 — AB only)           HIP: 88601    SAO: 123107
RA: 18h 05.5m   Dec: +02° 30′
Magnitudes   AB: 4.2, 6.2     AC: 4.2, 12.0    AV: 4.2, 10.8
Separations  AB: 3.4″           AC: 34.9″          AV: 143.9″
Position Angles  AB:  79° (WDS 2012)    AC: 282°  (WDS 1947)   AV: 275°  (WDS 2010)
Distance: 16.6 Light Years
Spectral Classifications  A: K0   B: K4

So what color are they, really?   If you go by the spectral classifications, “A” and “B” should be orange.  Sir William Herschel, who discovered this pair in 1779, apparently didn’t notice anything distinctive here since he didn’t leave us a comment on their colors.   Admiral Smyth saw “pale topaz and violet,” and Haas describes them as two “tangerine-orange” stars.  Others have seen yellow and gold, and Flammarion even described “B” as “rose-colored.”  In his chapter on Ophiuchus, Burnham writes that he always saw them as “golden and rusty-orange.”

Orange or gold? Topaz or violet? Maybe even rose colored? I saw various blends of orange and gold in several different scopes. (East & west reversed to match the refractor view, click to enlarge)

In my 60mm f/16.7 refractor, using a 20mm TV Plössl (50x), I saw a gold primary with a touch of orange in it, and the secondary was a pale version of the same thing.  Three weeks later, using a 102mm Celestron refractor and a 24mm Brandon (42x), I saw orange and orange.  But in my six inch f10 at low magnification, the gold won out over the orange.

So with a fair degree of certainty, I think you can more than likely, somewhat definitively, and even reasonably safely, say  ………..  either gold and/or orange. 😉

Whatever the colors, I’m sure you’ll notice this is a rather tight pair of stars.  I haven’t quite made up my mind yet whether I like the low power view which has them so close they’re barely apart, or the high powered view that includes a wedge of black sky between the two stars.  There’s a lot to be said for the delicate nature of the low power view, with that diminutive little secondary clinging to the edge of the brighter primary, illuminating the inside of your eyepiece with their gold or orange photons.  I do know they’re a great pair for a 60mm scope — just close enough together at 3.4 seconds of arc, and far enough apart in magnitude, to be a little bit of a challenge.  And the reward is well worth the small effort it takes to separate them.

Regardless of how or when you view them, I’ve found their most striking aspect (apart from the colors) is the way the two stars dominate the field of view.  In the 60mm refractor at 50x, “A” and “B” are just two orange/gold points of light shining at the center of a black void. They don’t have any competition at all in that dim field, which is probably fortunate, since there are only a handful of stars in the sky that can compete with them anyway.

At a mere distance of 16.6 light years, this pair is one of our nearest neighbors.  It’s also a fast orbiting twosome, with a period of 88.4 years — fast enough that a person could watch their positions gradually change over the course of a long life.  During that time, their elliptical orbit brings them as close as two arcseconds and as far apart as seven arcseconds.  Admiral Smyth’s Bedford Catalog has a very interesting discussion of 70 Ophiuchi (pp. 404 to 409), including tables showing their rapidly changing positions between 1799 and the early 1840’s.

And it appears this is a very complicated system.  The Washington Double Star Catalog shows a total of eleven  stars involved.  Quite a few of those eleven companions are in the 14th to 16th magnitude range, well beyond the reach of most of us.  I’ve included just two in the data shown above, “C” and “V,” but so far “V” is the only one I’ve managed to pry out of the inky darkness.  Because of the glare from the primary and secondary, that took some rather hard staring in the 60mm refractor using an 11mm TV Plössl (91x).  Larger apertures failed to find “C” hiding in its closer location to the primary.  Still, how many times can you lay claim to having seen the “V” component of a multiple star?  And in a 60mm scope even!!!

Now let’s move from the northeast corner of this triangle and over to the northwest side, a hop of a short degree or so, where 67 Ophiuchi lies waiting for us.

67 Ophiuchi  (Bu 1124)  (H VI 2)            HIP: 88192    SAO: 123013
RA: 18h 00.6m   Dec: +02° 56′
*****                  Magnitudes   Separation  Position Angle   WDS Data
AB: (Bu 1124)    4.0, 13.7             6.6″                196°                 1934
AC:  (H VI 2)       4.0,   8.1           55.9″                139°                 2009
AE: (Bu 634)      4.0, 11.0           45.7″                179°                 2002
CD:      ”               8.1, 12.5             7.7″                123°                 2002
CE:      ”               8.1, 11.0           33.2″                266°                 2002
Distance: 1418 Light Years
Spectral Classifications     A: B5   C: B2

“A” and “C,” the two stars you’ll see immediately when our goal glides into view in your eyepiece, were discovered by Sir William Herschel in 1779.  S.W. Burnham came on the scene in the 1870’s, and ferreted AB, AE, CD, and CE from the darkness, which gained his designations shown above, Bu 1124 and Bu 634.   Beyond any doubt, though, the main attraction is the pair discovered by Sir William.

60mm, 25x: Grand sight!  A bright lemon-yellow star with a little silvery dot beside it.  The pair looks about as wide as Albireo. Webb: ‘Yellowish, blue.’  Smyth: ‘Straw color; purple.’ ”  (Sissy Haas, Double Stars for Small Telescopes, p. 112 of 2006 edition)

You can always depend on Admiral Smyth to find some purple in a star, but he deserves some recognition for coming up with “straw colored.”  I didn’t see it, though.  What I did see in my 102mm Celestron f/10 was a bright white primary and a pale blue secondary.

67 Ophiuchi is woven into a very interesting field of 9th and 10th magnitude stars. Included here is the elusive eleventh magnitude “E” companion. (East & west reversed, click for a larger view)

But Sissy Haas’s “grand sight” in a 60mm scope is quite correct.  At 55.9″ apart, splitting the pair is no issue, although seeing the 8.1 magnitude “C” star can be a bit of a battle if the moon has been turned on and is flooding your skies with its surplus of reflected light.  I had to fall back on averted vision to avoid failure the first night I looked for it, but once the moon was out of the skies, its “silvery” personality popped into view.  Silver, or maybe gray, is what I saw in the 60mm f/15 mounted on the 102mm Celestron, since the sixty millimeter lens just couldn’t collect quite enough light to display any color.

I was determined to see one of S. W. Burnham’s stars, though, and again, the moon made it difficult.  After having no luck with my six inch f/10 just as the moon was rising, I decided to give an eight inch Celestron SCT a try the next night.  I had to be quick, though, since a last quarter moon was due on the horizon at 10:30 PM, about an hour after darkness set in.  “B” was out of the question because it’s faint 13.7 magnitudes of dim light would be lost in the glow of the fourth magnitude primary.  And 12.5 magnitude “D” was excluded because the 7.7″ separating it from “C” would also put it behind the glow caused by the 4.4 magnitudes of difference between the two stars.  So that left “E,” at a magnitude of 11.0, sitting 45.7″ from “A” and 33.2″ from “E.”

And sure enough, even though it took about twenty minutes before I spied it, that’s where it was — sitting between “A” and “C,” forming a very tight triangle with an eerie resemblance to the larger one formed by 70, 67, and 68 Ophiuchi.  It took a 15mm TV Plössl (133x) to find it, and even then it wanted to play hide and seek behind the glow of its brighter companions.  But it was soon gone again, receding into the much brighter glow of the sky as the moon began its climb into the northeastern sky.

And since it’s gone, we’ll go on.

A three degree hop to the west from 67 Ophiuchi will get us to 3.8 magnitude Gamma (γ) Ophiuchi, and another three quarters of a degree will bring us to our next star, 61 Ophiuchi. (Stellarium screen image with labels added, click for a larger view)

61 Ophiuchi  (Σ 2202)  (H IV 32 — AB only)          HIP: 86831    SAO: 122690
RA: 17h 44.6m   Dec: +02° 35′
Magnitudes    AB: 6.1, 6.5       BC: 6.5, 12.8
Separations:  AB: 20.6″           BC: 93.6″
Position Angles:  AB: 93°  (WDS 2010)         BC: 28°  (WDS 2005)
Distance: 460 Light Years
Spectral Classification: A1 (for “A”)

This time, we’ll turn the floor over to the Admiral:

A neat double star below β, on the Serpent-bearer’s left shoulder, where it is 2° south of the bright star β, Cebalrai, which lies about 7° south-by-east of α Ophiuchi.  A and B, both 7 ½, and both silvery white.”  (The Bedford Catalog, Willman-Bell: 1986, p. 396)

“A neat double star below β, on the Serpent-bearer’s left shoulder . . .” (East & west reversed again, click for a larger version)

Haas describes them as “straw-yellow” in a 60mm refractor at 25x, and what I saw in my five inch Meade was two pale white stars with a slight  tinge of yellow in them.  It’s not often that the three of us agree that closely on color!

After the proliferation of components listed for our two previous stars, 61 Ophiuchi is relatively unconfusing.  But that 12.8 magnitude “C” companion was lurking in the blackness of interstellar space, and I just couldn’t resist giving it a try.  Actually, after searching for the fainter companions of 70 and 67 Ophiuchi, this one wasn’t much of a struggle in the AR5.  The wide gap between it and the primary, over one and a half arcminutes, put it beyond the reach of the glow surrounding it’s two much brighter relatives.  Although it wanted to play hide-and-seek at first, with some persistence I could see it with direct vision for a few seconds at a time.

Interestingly enough, the primary and secondary have shown little motion over the years.  Smyth includes a table of observations made in 1834 by the Reverend R. Sheepshanks (and no, I did not make up that name!) showing a position angle of 93° 37′ and a separation of 20.75″, which measures up well against the WDS’s 93 degrees and 20.7″.

And now I hear James South calling to us, so let’s go see what he has up his sleeve.

S 694            HIP: 87448    SAO: 122847
RA: 17h 52.1m   Dec: +01° 07′
Magnitudes: 6.7, 7.3
Separation:  79.0″
Position Angle: 237°  (WDS 2003)
Distance: 465 Light Years
Spectral Classifications: K0, A0

To get where we’re going, we’ll use the chart above and move two degrees to the southeast — past 6.4 magnitude HIP 87224 and 5.9 magnitude HIP 87491 — and we’ll find Mr. South’s S 694 waiting patiently for us about a quarter of a degree to the southwest.

This one is simplicity itself — an old fashioned two star system far enough apart to easily be seen in a 60mm refractor at low magnification.   And after punishing my photonic receptors with searches for dim specks of light at or just beyond the limit of visibility, the change was more than welcome.

And this time, I’ll quote myself:

An old-fashioned two star system, but with a chameleon-like character to its color. (East and west reversed, click for a better view)

Bright pair in six inch f/10 with 12mm Radian (127x) — “A” is yellow white, “B” pale white.

Easy pair in 60mm f/15 with a 20mm TV Plössl (45x), HIP 87491 seen in the same field of view.”

August 1st, 2300 PDT, 2011.

Ah, but those colors again.  They’re up to their old tricks.

Haas used a 125mm scope at 50x, and she saw “pumpkin orange and the other greenish white.”  She quotes Rachal as having seen “yellowish orange, bluish white” in a 70mm.

So we’re back to a familiar question: What color are they, really?  With a spectral class of K, the same as 70 Ophiuchi, the primary should appear to be orange — but I sure didn’t see it, and I looked at it with several different scopes.  And the secondary is classified as A, which means it should appear as either white, or the bluish-white that Rachal observed.  But all three of us picked up some shade of white, so that makes the primary the primary offender.

What to do, what to do, what to do  …………….   I was tempted to ask the good Admiral, but I could clearly hear him reply:  “Lilac.”

What I did  do was go back and take another careful look at this pair, using my Celestron six inch refractor.  And darned if I didn’t see gold with a tint of orange in the primary, and just a hint of blue in the mainly white secondary.  In fact, at low magnifications, you can pull the well-behaved HIP 87491 into the field of view.  It’s a deeper orangish-gold color, which agrees well with it’s K5 classification, and it provides a wonderful contrast with the weaker orange-gold I saw in S 694’s primary.

So I’ll leave you to puzzle this one out for yourself — take a look and see what you can see.  Meanwhile, I think I’ll wander up north of Cebalrai and take a look at the well-scattered beauty of IC 4665, and them I might meander over to Poniatowski’s bull and hitch a ride through the southern reaches of the zodiac.

Clear Skies!

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5 Responses

  1. John! Got S694 last night! The conditions were a little tough with winds to 20 mph and high cirrus clouds tip-toeing through from time to time, but I BAGGED it! I’ll fire you off the sketch. The right Admiral would probably reply, “lilac” for the companion, but I’d say “light silvery blue/white” to cover my bases… The primary is an easy orange – golden, even. I got that HIP 87491 off to the north. Its quite near Collinder 350, a very sparse open cluster with a Struve double in it. I’d like to get a look at IC 4665 one of these nights.

    • Well, the Right Honorable Admiral would be right proud of you, Steve!

      This is another one of those pairs that seems to wanna wander back and forth along the color spectrum. Either the sky gods (or maybe the Admiral) are playing tricks on us, or our eyes just aren’t up to the task of extracting the true colors from these two distant suns of the galaxy. Might be a good idea for me to go back again on the next clear night and see what colors I can see this time.

      By all means, wander around in IC 4665 — it’s a beautiful open cluster meant to be viewed at low magnification. In fact, the entire area shown in the second chart above is well worth spending some exploration time in some clear evening. It should be a heck of a sight at the 10,000 feet above sea level where you have your scope parked in Hawaii!

      John

      • I wandered back into this triangular realm last night with a pair of binoculars and found it absolutely fascinating. There are two beautiful open clusters situated east of Cebalrai (Beta Ophiuchi). Scan east about nine degrees, skimming over the top of Poniatowski’s Bull and you’ll come to NGC 6633, a glowing ball of stars that brightens at the center. A further three degrees southeast of it you’ll find IC 4756, which is a beautiful stretched out sparking cloud of star dust. I was using a pair of 10×30 Canon IS, which is roughly equivalent to what you might see with a pair of hand-held 15×70’s. Here’s a binocular view of the area, with IC 4756 on the left and below center, and NGC 6633 on the right above center. Remove about half of the background stars and the scene would be equivalent to what I saw last night.

        I see two double stars in NGC 6633 marked on my copy of the S&T Pocket Atlas (chart 65), and two more on the southern fringes of IC 4756, plus a few more circling around it a short distance away. There’s a lot here to look at once you delve into it deeply. I’ve got some exploring to do!

        John

  2. John,
    I’m finally uploading my sketch of S 694 observed June, 2013 to My Gallery and the Cloudy Nights Double Star Forum. It’s such a wonderful pair and I’m beginning to think that atmosphere may have a lot to do with the color discrepancy. Since I’m down at the 21st Parallel and at 10,000 feet elevation, the object is higher in the sky with possibly less atmospheric accumulation.
    I know you’re quite busy these days, and I’d love to get into NGC 6633 as it’s in the sky these days.
    Looking UP,
    Steve McGee

    • Hi Steve,

      Just took a look at what the WDS shows for NCG 6633 and found four pairs that should be resolvable without too much problem:

      BU 464 AC (Magnitudes of 8.97 and 11.25, 25.9″, 86°, WDS 2011)
      (The AB components are a bit tight at 1″)
      STT 350 AB (7.79 and 9.39, 1.8″, 66°, WDS 2012)
      GCB 31 AB (9.5 and 9.5, 4.4″, 76°, WDS 2009)
      SCJ 17 AB (8.42 and 10.57, 51.4″, 352°, WDS 2012)

      That should keep a dedicated sketcher busy for at least an hour!

      John

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