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Horsing around in Equuleus One More Time: Beta (β) and Epsilon (ε) Equulei, S 781, and Σ2737 (Delphinus)

When we left Equuleus in November of last year as the fall rains began, little did I know that once it started raining, it wouldn’t be able to stop.  November had a total of 13 inches, followed by 17 inches in December, another 17 in January, and a mere six in February — only to be followed by 13.5 inches in March.  As much as I love the rich green beauty of the north coast of Oregon, by the middle of January I found myself casting a covetous eye towards the Sahara Desert.

But all that’s water under the bridge now, so to speak.  Let’s turn to the task ahead of us and steer a return course straight for Equuleus, the little horse hiding under the shadow of a much larger horse, Pegasus.  We left three doubles lingering in the southern half of it, one of which is a real gem that really deserves to be better known.  And I couldn’t resist adding another that’s barely across the border in Delphinus.

I also came across a pair of pleasant surprises, both of which were off the charts — or at least they weren’t on the charts I was using — and before I finished here, I found one more off-the-chart-surprise.

A horse is a horse of course, unless of course the name of that horse ………. is Pegasus, or even Equuleus. Wedged between the nose of Pegasus, marked by Enif, and the Dolphin’s tail hanging from it’s diamond-shaped asterism, Equuleus is dim enough to warrant the aid of a pair of binoculars to help locate it. (Stellarium screen image with labels added, click for a larger view)

We’ll start with Beta (β), which is suspended all by itself out to the east of the outline of this small constellation.

Beta (β) Equulei   (10 Equulei)   (h 3023)
HIP: 105570   SAO: 126749
RA: 21h 22.9m   Dec: 06° 49’

Identifier  Magnitudes  Separation  Position Angle   WDS
HJ 3023   AB:   5.16, 13.60      40.60″           259°    2012
HJ 3023   AC:   5.16, 11.60      74.00″           302°    2012
HJ 3023   AE:   5.16, 12.19      95.90″           273°    2012
Bu 1054  CD: 11.60, 12.60       5.10″           188°    2000
Distance: 331 Light Years (Simbad)
Spectral Classification: “A” is A3

The “A,” “C,” and “E” components, which make up this eye-catching little configuration of stars, were discovered in 1830 by Sir John Herschel.  You might also see them referred to as HJ 3023, which is how they’re listed in the Washington Double Star Catalog (WDS).  In a letter dated June 11th, 1831, to Admiral William Smyth, Sir John described them this way:

As you are testing your telescope, there is a pretty test object in β Equulei, which is a coarse triple, and one of the small stars itself is a pretty first-class double star.” (The Bedford Catalog: Willman-Bell, 1986, p. 501)

A bright white primary with a tinge of blue, bracketed by a pair of faint stars on opposite sides.  ALD 76, an 11.4 magnitude pair,  floats in a sea of black to the south.  (East & west reversed to match the refractor view, click to enlarge)

My first view of this system showed a bright white primary with a tinge of blue, bracketed by pairs of faint stars on opposite sides (east and west).  Even though the wider pair of stars on the east side of the primary are not part of the system, they add a little something extra to its visual appeal.  I was using a six inch Celestron refractor, and it easily brought 11.6 magnitude “C” and 12.1 magnitude “E” into view.  All of the companions were beyond the reach of my 60mm f/16.7 refractor, though, so this is not what you would call a 60mm friendly system.

The 13.6 magnitude “B” companion, which refused to come out from its hiding place behind the glare of the primary regardless of how long or how hard I looked, was discovered in 1878 by S. W. Burnham.   And Burnham is also credited with the discovery of the 12.6 magnitude “D” companion in 1877,  but based on Herschel’s comment above, it would seem he was already aware as early as 1830 that “C” had a companion.  Whatever the case, when I went in search of it with the six inch Celestron, I found it to be an elusive little devil.  Using an 8mm Radian (150x), I could tell there was something there because the pair wouldn’t come into sharp focus.  More magnification seemed to be the solution, but when I gave a 6mm Astro Tech Plössl a chance, I found there was just not enough light to work with.  With 5.2″ separating them, and a full magnitude of difference, it would seem this pair is just too dim and too close for six inches of aperture.  Nevertheless, Admiral Smyth states he “perceived the minute point of light,” which he measured at a distance of 3.0″ from “C.”  He called it “dusky,” and he was using a 5.9 inch refractor — which convinced me that maybe I better try again.

So I did, with my six inch f/10, which seems to do a bit better than the six inch Celestron.  And sure enough, at 152x in a 10mm Radian, I could get glimpses of two barely separated smudges of light.  I tried an 8mm Radian next (190x), and then a 6mm Radian as well as a 6mm Astro-Tech Plössl (253x).  The 6mm eyepieces were too much — all I got were unfocused blobs of very weak light — but the 8mm was able to collect enough photons that I could see two distinct light sources in moments of good seeing.

I wouldn’t call the view at all satisfying.  What I saw were two smears of light that weren’t quite merged, which for short periods would almost come into focus and then shift back to smear mode just as the image was improving.  Rather frustrating to say the least. I’ll call them “smudgy” instead of Smyth’s dusky.  I also tried once more to pull “B” out of the glare of “A” — and once again, no luck.

There’s another faint double, ALD 76, in the same field of view, which is identified in the inset of the sketch.  That one was easier to separate because the stars are both the same magnitudes, providing just enough of an edge to make it possible.  It was the 8mm Radian at 190x that did the best job on it also.  Credit for the 1908 discovery of that one  goes to H. L. Alden.

S 781 is located two degrees north of Alpha (α) Equulei, and forms a triangle with Alpha (α) and Beta (β). There is one source of confusion to be aware of here which can mislead you when locating S 781. Some charts run their constellation lines from Delta (δ) to Beta (β), then over to Alpha (α) and back up to Gamma (γ), and ignore Epsilon (ε). Others extend their lines from Delta (δ) to Alpha (α) to Epsilon (ε) and back to Gamma (γ), ignoring Beta (β) altogether, as in the case of the charts shown here. So look closely at your chart to avoid using the wrong stars for reference points, or you may find yourself lost in this small constellation, as unlikely as that might seem. (Stellarium screen image with labels added, click to enlarge)

S 781   HIP: 104767   SAO: 126625
RA: 21h 13.5m   Dec: 07° 13’

Identifier   Magnitudes   Separation   Position Angle    WDS
Bu 270     AB:    7.42,  9.40        0.60″          347°    2008
Bu 270  AB,C:    7.25, 14.01       31.10″            26°    2013
S 781    AB,D:    7.25,  7.17      186.10″          172°    2013
Distance: 312 Light Years (Simbad)
Spectral Classification: “A” is F0, “D” is A2

The pair you’ll see as they come into view in your eyepiece is the last of the three pairs listed above — AB-D — which was discovered in 1824 by James South.  W. S. Burnham added the AB pair in 1875, and the AB-C pair in 1898.  Both of those are well out of my range, and probably yours, so we’ll stay with South’s 1824 discovery.

S 781 is two widely separated white stars in a very sparse field. Two more faint doubles lurk to the southeast and west in this same field of view.  (East & west reversed, click for a larger view)

I first caught this wide pair in a 60mm f/16.7 refractor — two widely separated white stars in a very sparse field.  Haas describes them as blue-white and green-white in a 125mm scope, but my six inch (152mm) Celestron refractor failed to turn up any hint of color in either of the stars.  Actually, the field surrounding this pair is so sparse that I found the view in the larger scope wasn’t much different than in the 60mm.  I could see a few more stars in the six inch, but all of them were on the dim side of dim.

But — there were two surprises lurking within the circular confines of this photon challenged field of view.

In the six inch refractor I could see a pair of very closely spaced faint stars at the southeast edge of the field.  Curious as to whether they were a chance alignment or had been cataloged as a double, I checked my copy of MegaStar and found them listed as HJ  3015.  It turns out this pair was discovered in 1830 by Sir John Herschel — and they’re actually not difficult at all to split.  While they were beyond the reach of the 60mm scope, I was able to separate them easily in my 90mm Orion f/10 refractor using a 10.5mm Ortho (87x).  In fact, I could almost separate them at 54x in a 16.8mm Ortho.  I listed the usual data just below the inset at the right of the sketch above.  Faint thought they are, they’re close enough in magnitude and spaced far enough apart to give an inexperienced observer a good shot at splitting them — take a look and give it a try!

The second surprise was lurking on the opposite side of the field.  When I was looking at the MegaStar chart, I noticed it showed another double in the same field, which it identified as BRT 2189.  MegaStar thoughtfully includes a list of all the abbreviations used in double star prefixes, so I found the three letter designation referred to S. G. Barton, for whom I can find no information whatever.  In checking the WDS database to get the most current measurements for this pair (shown at the left of the sketch below the inset), I found it was discovered in 1908.

There wasn’t anything about the appearance of that star in the six inch Celestron that led me to suspect it might be a double, but then I really wasn’t looking for it at the time.  I tried a few nights later with my Antares 105mm f/14.3 and had no luck at all.  The following night I aimed my six inch f/10 refractor at it and started with an 18mm Radian (84x).  At that magnification it showed signs of being faintly elongated, and just a couple of steps up to a 14mm Radian (109x) yielded the first hint of a split.  So I reached for a 12mm Radian (127x) next, which produced a very dim hairsplit pair that became more definite at 152x in a 10mm Radian.  I worked up to a 6mm Radian (253x) for the sketch, and believe it or not, as dim as it was at that magnification, I could detect a very distinctive blue-white tinge to the brighter of the two stars.

You never really know what you’re going to find when you look closely at the field surrounding the main object of attraction — it pays to scrutinize it closely.  And if I hadn’t been curious enough to search for information about the first faint pair, I never would have known of the existence of the other pair.

And now we’ll move on to a real surprise, Epsilon (ε).  To get there from S 781, drop down to Alpha (α) Equulei and slide four degrees to the southwest.  And as it slips into view in your eyepiece, you’ll find your eyes locking onto the “AB-C” pair.

Epsilon Equulei  (Σ2737)  (BC is H III 21)   HIP: 103569   SAO: 126428
RA: 20h 59.1m   Dec: 04° 18’

Magnitudes   Separation Position Angle   WDS
AB:   5.96,  6.31        0.40″          284°    2012
AB,C:   5.30,  7.05       10.50″            67°    2013
AD:   5.96, 13.10       69.30″          293°    2013
BC:    6.31,  7.05       10.50″            67°    2012

Distance: 176 Light Years (Simbad)
Stellar Classifications: “A” is F5, “B” is F6, “C” is F4
Status:   AB is closing rapidly, and will be down to only 0.017″ apart in 2019, just a little beyond our reach (the understatement of the year).  Still, it’s kind of neat to see the orbital chart and data, which can be found here.

This one stunned me into silence for a few moments.   I had no idea this kind of beauty was hiding in Equuleus.  Haas describes it as a “fantastic triple” and Smyth’s description was “a most delicate triple star.”

It’s both.

A “fantastic triple” — “a most delicate triple star.” (East & west reversed to match the refractor view, click for a larger version)

You absolutely can-NOT miss the colors on this one.  Now I was looking at them on a moonless night with very good transparency, so under less favorable conditions you may find the colors are not as striking.  Whatever the case, they sure struck me — speechless.

In both a 60mm f/16.7 and my Orion 90mm f/10, the primary (“AB”) was a bright orange and its companion (“C”) was a twinkling blue.  Haas saw “AB” as a “bright straw yellow” and “C” as “dim silvery blue.”    Smyth is off on another page with white in “AB” and lilac in “C”, although I suppose you could construe a dark blue as lilac — maybe.

Even though I didn’t expect much from it, I took a hard look at the AB pair in the six inch f/10 refractor and could see some elongation at 190x in the 8mm Radian.  And I think I spotted the 13.1 magnitude “D” companion in the six inch, which is also included in the inset of the sketch — sorry, no guess on the color of that one.

If you’ve ever wondered whether the famous observers of the 19th century felt the same challenge we do today when it comes to ferreting dim specks of light out of the glare of a brighter companion, you’ll be interested in Admiral Smyth’s comments on the “AB” pair:

I . . . measured it as a double in 1833, without noticing the elongation of A.  But on receiving Professor Struve’s great Catalogue, and perceiving that he made the object to be triple, I attacked it again, with . . . success.”  (The Bedford Catalog, p. 491)

And attack is what we’re going to do next, by moving a bit less than a degree to the west with a slight bias to the north, crossing the invisible border into Delphinus, and coming to a rest on our final pair.

Σ 2735          HIP: 103301     SAO: 126373
RA: 20h 55.7m   Dec: +04° 32′
Magnitudes: 6.45, 7.54
Separation:  2.0″
Position Angle: 281°  (WDS 2011)
Distance: 462 Light Years (Simbad)
Spectral Classification: G6

This one was another surprise, but you have to look closely to see it.

Haas attacked this pair with a 125mm scope at 200x, and describes them as a

Grand sight!  This is a bright Sun-yellow star almost touched by a bright pearly white, and both stars shine vividly though they’re mildly unequal.”

A very tight, almost touching, pair of orangish stars — but Haas saw yellow and white.   (East and west reversed . . . click to enlarge)

I was using the six inch Celestron refractor when I first looked at this one, and was able to split it easily with a 10mm Radian (120x), and did a bit better at 150x with an 8mm Radian.  It’s two very close stars — I’ll call them orangish — with the secondary clearly smaller in appearance than the primary.  I didn’t see the white at all in the secondary, but it could be the orange of the primary is just too dominant.

I was also able to separate them in my Antares f/14.3 105mm refractor in seeing that wavered between categories II and III.  At 83x in an 18mm Radian I found myself looking at an elongated pair of stars, managed the slimmest of a hair split pair at 94x in a 16mm Astro-Tech Flat Field eyepiece, eked out a clean split at 107x in a 14mm Radian, and improved on that at 125x with a 12mm Radian.  The oscillating seeing made it hard to hold the image in focus in the 12mm Radian, but I noticed that problem pretty much went away using the 16mm eyepiece.  I’ve since pried this one apart in a 90mm scope, and I suspect with enough magnification and steady seeing, it will separate as well in eighty millimeters of aperture.

So  ………   I think between this tour and the previous one last year, we can say we’ve pretty much exhausted Equuleus from a double star standpoint, at least for apertures ranging from 60mm to 152mm, and maybe even just a bit beyond.

Gamma (γ) and 6 Equulei make a very attractive pair at low magnification, and if the field of view is wide enough, Σ 2765 can be pulled into it as a bonus. (Stellarium screen image with labels added, click for a larger view)

But Gamma (γ) is still lingering at the northwest corner of this equestrian configuration, so I may see if I can crack it on a night of steady seeing.  With magnitudes of 4.7 and 8.7, separated by 1.5 seconds of arc, it will be a tough one.  And truthfully, the view of 4.7 magnitude Gamma (γ) and 6.1 magnitude Six Equulei (this pair carries the designation Σ I 54), separated by about six arcminutes — with a reddish-orange 9.4 magnitude star between them — is darn hard to beat.

But then again, who can say no to a challenge like that.  😉

Clear Skies!

(WDS data updated 12/5/2014)


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