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A Pair of Double-Doubles in Pegasus: Σ 3012 and Σ 3013; Σ 3060 and Σ 3061; plus a Bonus Triple, Σ 3021

A strange thing happened while I was on the way to Cygnus . . . .  I found myself in Pegasus.   Now actually, that’s not as unlikely as it seems.   Even though we (or at least I) think of Cygnus as a summer constellation and Pegasus as an autumn constellation, they actually border on one another.   If that surprises you, look at a star atlas and you’ll find Mu (μ) Cgyni resting barely inside Cygnus’ northeastern border.

Stellarium screen image with additional labels, click to enlarge the view.

Stellarium screen image with additional labels, click to enlarge the view.

All it would take is a slight celestial nudge to push it into Pegasus.  In fact, by my measurements, Mu (μ) is a mere seventeen degrees from Beta (β) Pegasi and just a few furlongs further from Alpha (α) Pegasi at twenty-two degrees.

Now when I look at chart number six in The Cambridge Double Star Atlas, I don’t see a lot double stars in Pegasus, especially inside the area known as the Great Square.  In fact, within the area bounded by that slightly irregular rectangle there are only eight double stars identified by name.  And if you inspect all 240 square degrees of that area a bit closer, you’ll struggle to come up with even a half dozen more no-named pairs.  A veritable double-star desert, so to speak.

But as Chris Thuemen, who has photographically corralled a veritable herd of double stars in Pegasus, mentioned to me, you just have to look a bit deeper.  They’re there.  In fact, it was his photo of the Σ 3060-3061 pair that roped me into throwing a six inch refractor into the saddle of a large mount and taking a gander.  Chris, by the way, is the brains behind this site, which is devoted to photographing all the double stars within reach of the lens of his refractor.

But enough of this horse talk.   Let’s spur ourselves into action – we’ve got a heap of hedges to leap.

 As I mentioned, there are considerably more double stars in Pegasus than meet the eye focused on a star atlas.   In fact, of the four we’re going to look at, the only one shown in The Cambridge Double Star Atlas is Σ 3012.  (Stellarium screen image with labels added, click for a larger view).

As I mentioned, there are considerably more double stars in Pegasus than meet a pair of eyes focused on a star atlas. In fact, of the four we’re going to look at, the only one identified in The Cambridge Double Star Atlas is Σ 3012. (Stellarium screen image with labels added, click for a larger view).

We’ll begin at the southwest corner of the Great Square with Σ 3012 and 3013 and use Markab as a base from which to start.  There are two ways to get to where we’re going, both of them focused on navigating to 6.65 magnitude HIP 115288.   (Stellarium screen image with labels attached, click on the chart for a larger view).

We’ll begin at the southwest corner of the Great Square with Σ 3012 and 3013 and use Markab as a base from which to start. There are two ways to get to where we’re going, both of them focused on navigating to 6.65 magnitude HIP 115288. (Stellarium screen image with labels attached, click on the chart for a larger view).

From 2.45 magnitude Markab (this will open the chart above in a second window to make it easier to follow along), you can move three-fourths of a degree south to 7.10 magnitude HIP 114028, then go a degree due east to 6.50 magnitude HIP 114378.  From there, it’s a long northeast leap of four degrees to HIP 115288, which is parked just northeast of a distinctive arc of seventh and eighth magnitude stars easily seen in an 8×50 finder under reasonably dark skies.

Or, you can start at Markab and move a bit more than a degree north to 6.40 magnitude HIP 113994, then head northeast almost two degrees to 5.65 magnitude HIP 114449, and next go east with a slight tilt to the south a total of about two and a half degrees to HIP 115288.

From HIP 115288 if you look a degree and half to the southeast, you’ll see a parallelogram consisting of 7.45 magnitude HIP 116021, 7.95 magnitude HIP 116091, 7.10 magnitude HIP 115910, and at the northwest corner our faint targets, Σ 3012 and Σ 3013, looking for all the world like a single star.

Σ 3012/Σ 3013     HIP: 115800   SAO: 108618
RA: 23h 27.6m   Dec: 16° 38’
Identifier         Magnitudes         Separation      Position Angle      WDS
STF 3012    AB: 9.47,   9.82             2.80”                  190°                2012
STF 3012    AC: 9.47,   8.51           52.20”                    66°                2012
DOB 18       AD: 9.47, 10.20           49.50”                    64°                2012
STF 3013    BC: 9.82,   8.51           53.80”                    64°                2012
DOB 18       BD: 9.82, 10.20           51.40”                    62°                2012
STF 3013:   CD: 8.51, 10.20            3.10”                  277°                2012
Distance: 247 Light Years
Spectral Classification:  “A” and “C” are G0

And as you’ll quickly realize, you need to sit up straight in the saddle and get a firm grasp on the reigns in order to pry these two tight pairs apart:

Σ 3012 (AB in the data above) is a pair of very delicate puffs of subdued light, while Σ 3013 (CD in the data) offers up a contrast in stellar diameters.  Both primaries are very white.  (East & west reversed to match the refractor view, click on the sketch for a better view).

Σ 3012 (AB in the data above) is a pair of very delicate puffs of subdued light, while Σ 3013 (CD in the data) offers up a contrast in stellar diameters. Both primaries are very white. (East & west reversed to match the refractor view, click on the sketch for a much better view).

Now I gotta be honest – the first time I looked at this pair I couldn’t see any duplicity.  I think that was with a four inch refractor on a night when the seeing was shakier than the view from the top of a horse streaking for the finish line at the Grand Prix de Paris.  The 2.80” and 3.10” of separation is well within reach of a four inch refractor, but the dearth of starlight is really a heck of a hurdle to overcome, and unsteady seeing certainly doesn’t help matters.

Click on the image to enlarge it.

Click on the image to enlarge it.

I did better with a five inch refractor, and of course a six inch improved the view  –  although not by much.   But once you manage that first rewarding view of the delectable slices of black sky intervening between the AB and CD pairs, you might just find yourself returning again and again.   I can’t recall ever having seen a pair of stars in this configuration – the way they lean into each other is unique.

However, if the tight distances and faint photons cause your telescope to rear up on the hind legs of its mount in disgust, don’t despair.   If you take a look at this list of observations in Lewis’s compilation of Struve’s stars, you can see they’re slowly moving farther apart.   So give it a few hundred years and the view will improve.

While I was roaming around this area, I came across a rather interesting Struvian triple, Σ 3021, which had concealed itself as HIP 116691 a short degree to the southeast.   I made a mental note to return, and although it took almost a month, I finally found my way back.

Σ 3021     HIP: 116691   SAO: 108659
RA: 23h 31.4m   Dec: +16° 13’
Magnitudes   AB: 8.06, 9.26    AC: 8.06, 10.79
Separations  AB: 8.90”            AC: 118.50”
Position Angles   AB: 308°  (WDS 2012)   AC: 23°  (WDS 2012)
Distance: 727 Light Years
Spectral Classification:  “A” is F8

 Everything in this field of view was either white or gray except for a slight hint of orange in the secondary, which I also saw a few nights later in a six inch refractor.  The right triangle alignment of the three components of Σ 3021, plus the line of stars running below the primary from northeast to southwest, add a bit of visual spice to the view.   (East & west reversed again, click for a larger image).

Everything in this field of view was either white or gray except for a slight hint of orange in the secondary, which I also saw a few nights later in a six inch refractor. The right triangle alignment of the three components of Σ 3021, plus the line of stars running below the primary from northeast to southwest, add a bit of visual spice to the view. (East & west reversed again, click to improve the view considerably).

Once again, the seeing was poor when I got my first look at this triple delight.   I don’t know what was in the air, but in addition to the quivering image, I had the impression I was looking through a layer of mud.  It’s possible there are some dimmer stars to be seen in this field on a more transparent night, although considering the conditions, this turned out to be an interesting threesome of stars.  But what I wouldn’t give at times for a stall full of stable skies.

Now don’t yank your boots out of the stirrups just yet!  We’re going to trot over to the opposite side of the Great Square now for our second pair:

Stellarium screen image with labels added, click on the chart to enlarge it.

Stellarium screen image with labels added, click on the chart to enlarge it.

From 2.80 magnitude Algenib (here’s that second window again), move north about one and half degrees to 6.50 magnitude HIP 1057 and then bend northwest and move about the same distance to 5.55 magnitude 87 Pegasi.  In you finder you’ll see a skewed rectangle consisting of 87 Peg, 7.45 magnitude HIP 493, 6.55 magnitude HIP 258, and 7.05 magnitude HIP 759.   Move a distance of about three quarters of a degree across its north edge to HIP 493 and center it in your finder.  As you start to move your scope south, the first of our two stars that comes into view is Σ 3060 which is just nine arcminutes south of HIP 493.

Σ 3060    HIP: 495   SAO: 91707
RA: 00h 05.9m   Dec: + 18° 05’
Identifier          Magnitudes         Separation      Position Angle      WDS
STF 3060     AB: 9.32,   9.65              3.40”                  135°               2011
STF 3060     AC: 9.32, 12.15           66.50”                  272°               2011
LEP 1            AD: 9.32,   7.47         573.20”                  359°               2000
LEP 1            AE: 9.32, 16.58         999.90”                  267°               2000
Distance: 127 Light Years
Spectral Classification: “A” and “B” are K0; “D” is F8
Notes: AC is an optical pair; AD is also HJL 1001 and SHY 112; AD (“D” is HIP 493) is also probably a physically related pair, with both stars moving parallel to each other at the same apparent rate.

Here’s the first view:

The 12.15 magnitude “C” companion can be seen a short distance almost due west of the AB pair, and due north you’ll find the 7.47 magnitude “D” companion hovering at the edge of the field.  (East & west reversed, click on the sketch for a larger view).

The 12.15 magnitude “C” companion can be seen a short distance almost due west of the AB pair, and due north you’ll find the 7.47 magnitude “D” companion hovering at the edge of the field. (East & west reversed, click on the sketch to bring it to life).

And as you continue to move your scope south, you’ll see Σ 3061 come into view just 14 arcminutes away.

Σ 3061    HIP: 482   SAO: 91703
RA: 00h 05.7m   Dec: 17° 50’
Magnitudes: 8.40, 8.51
Separation:  7.6”
Position Angle: 149° (WDS 2009)
Distance: 548 Light Years
Spectral Classification: F2, F2

Another almost vacant field of stars with the exception of the two pairs mimicking each other at opposite ends of the field of view.  Note that we’ve lost HIP 493, the “D” component of Σ 3060, which is just out of view beyond the north edge of the field.  (East & west reversed again, click to enlarge).

Another almost vacant field of stars with the exception of the two pairs mimicking each other at opposite ends of the field of view. Note that we’ve lost HIP 493, the “D” component of Σ 3060, which is just out of view beyond the north edge of the field. (East & west reversed again, click on the sketch to improve the view 100%).

This pair of doubles is a bit easier to see than the first pair, thanks to wider separations.  I haven’t tried them in a four inch refractor, but neither pair should be out of reach under average seeing conditions considering how easily they separated with the five inch used for the two sketches.

Where this pair differs considerably from the first pair is in their rate of proper motion.  Σ 3060 in particular is sprinting through the galaxy as if it was a thoroughbred streaking for some imaginary celestial finish line.  In the notes I attached to the data above for Σ 3060 you’ll see a comment about the AD pair moving parallel to each other, which is quickly apparent in the Simbad plot below:

East and west are in their conventional positions on this chart and the two to follow.  Click on any of the charts to enlarge them.

East and west are in their conventional positions on this chart as well as the two that follow. Click on any of the charts to enlarge them.

And when we flip the Simbad switch and narrow the field of view from fifteen minutes of arc to five, we see the AB pair is moving parallel to each other as well:

Simbad Close-up of SFT 3060

The proper motions illustrated so well in the two charts for “A”, “B,” and “D” are:

STF 3060 A:  -146 RA, -146 Dec
STF 3060 B:  -154 RA, -155 Dec
STF 3060 D:  -149 RA, -151 Dec

Those figures represent thousandths of arcseconds per year (as in .146”), with the negative sign indicating westward motion in right ascension and southerly motion in declination.

That first chart also showed noticeable movement for the Σ 3061 pair, which is revealed more clearly when we zoom in three times closer:

Simbad Close-up of STF 3061

The proper motion for these two star is:

STF 3061 A:  +060 RA, -018 Dec
STF 3061 B:  +055 RA, -014 Dec

Now if you go back to the first of the three Simbad charts, you can see the Σ 3060 pair is moving southwest as the Σ 3061 pair moves almost due east.   So given enough time, they’ll eventually put enough distance between them that we’ll need a wide-angle eyepiece to keep them within the same field of view.   Maybe by then the optical magicians at Tele Vue will unlock the secret to providing eyepieces with apparent fields of view of two hundred degrees.

While you’re thinking about that possibility, I’m going to reign in my eastward motion and gallop off to the west.  I need to catch Cygnus before it flies out of sight for the season.

Clear Skies!  :cool:

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3 Responses

  1. What fun! I did a sketch of these two, STF 3060 & 3061 just last month, as you may have seen on the Double Stars Imaging Yahoo Group. I think I inadvertently got the “C” companion just to the west of STF 3060 and have HIP 493, (LEP 1), to the north at the edge of the F.O.V. in my sketch. What a beautiful pair of systems to observe. And THANK YOU for your well researched descriptions of the proper motions of the two pairs!! Again, a well written discussion on these two pairs. I observed yellow/tan for the A & B stars of STF 3060 and STF 3061 has a golden primary and a bluish companion. I call HIP 493 HD 101 in my sketch and observe it as slightly yellow with an optical companion to the WSW of it showing a slightly blue hue. Even though you’ve probably already seen my sketch, I’ll email it to you for giggles…
    Steve McGaughey, Haleakala Amateur Astronomers

  2. Thanks for another great article on my favourite subject. keep up the good work guys

    • Thanks for the comments Darren and Steve!

      You can see the sketch of STF 3060 and 3061 that Steve refers to in the first comment by clicking on this link.

      John

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