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A Complication of Stars in Delphinus, Part One: HO 131 and S 752/Bu 987/Fox 254

Father Time was approaching nine o’clock on a cool summer evening as I crested the top of a rise and paused to absorb the view.  Hanging in the west above the vast flat expanse of the Pacific was the reddish-orange glow of Arcturus, its color just beginning to deepen as darkness swallowed the last lingering glimmer of dusk.  When it gets about thirty degrees or so above the western horizon, Arcturus can transform itself into a flashing beacon that fires off strobe-like rays of red, green, and even white light.  When the air is particularly turbulent, I’ve even seen it appear to dart back and forth quickly and then hover.   If you didn’t know what you were looking at, you could easily be convinced the aliens were about to land.

But as I stood there and stared into the west, I realized Arcturus was shining as straight and steady as a light house beam – no twinkling, no dancing, no multi-colored flashes of light.  Suddenly I was overwhelmed by visions of an entire evening of spectacular seeing.  Anticipation began to build:  images of sub-arcsecond pairs flashed in front of my eyes; dazzling diffraction rings echoed and bounced around in my head; my focus fingers began to twitch; my feet began to itch.  I glanced down and saw fire in the eyes of my four-legged observing partner.  I knew that look –  it meant “Time’s a wastin’, pal – make tracks’!

So we spun around in the sand and sprinted for home.  He may be fourteen, but he can still run like the wind when the sky is calm.

** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** **

Tonight we’re heading for an amorphously distinct collection of stars I just happened to stumble over on the same evening I first tracked down Nova Delphini 2013.  It was the nova that was supposed to catch my eye (it did eventually), but it was this stellar assemblage of light that captured my visual attention first.

Here’s where we’re going . . . . . . . (Stellarium screen image with labels added, click on the chart for a larger view).

Here’s where we’re going (the circled area). . . . . . . (Stellarium screen image with labels added, click on the chart for a larger view).

. . . . . . .  and there are a couple of ways to get there.

The easiest is to draw a line from 5.1 magnitude Eta (η) Sagittae to 4.8 magnitude 29 Vulpeculae, aim your telescope two-thirds of that distance toward 29 Vul, and then take a peek into your finder.  You should see the circled asterism on the chart staring back at you.

If your skies are too bright for that, center Eta (η ) Sagittae in your finder, hop one and a half degrees northeast to 6.50 magnitude Theta (θ) and 6.20 magnitude HIP 99445, which form a distinctive pair of stars.  Continue northeast a similar distance to 6.1 magnitude 18 Sagittae and pause for breath.  Now move two degrees east with a slight bias to the south to 5.65 magnitude HIP 100754, which is shadowed by a 7.1 magnitude star on its northwest corner.  The splayed H-shape of the asterism will be parked distinctly in the southeastern corner of your field of view:

Close-up of Delphinian Asterism with connecting lines

Or if you prefer to have your asterisms unadorned, here it is again without the distraction of the arbitrary connecting lines:

Stellarium screen image (both this and the one above) with labels added, click to enlarge, click on either chart to enlarge it.

Stellarium screen image (both this and the one above) with labels added, click to enlarge, click on either chart to enlarge it.

We’re going to star this tour on the east side of the asterism with HO 131, which attracted me simply because of its strange identifying prefix (we’ll get back to that).  First locate 6.8 magnitude S 752, which you’ll find at the southeast corner of the splayed-H.  If you look closely and carefully into your finder, you’ll notice both of its stars are easy to see.  From there it’s a one degree southwest hop to HO 131’s 6.9 magnitude glow.

HO 131      HIP: 100970   SAO: 106138
RA: 20h 28.3m   Dec: +18° 46’
.     Magnitudes        Separation     Position Angle      WDS
AB: 6.97, 10.60              3.50”                  331°               2002
AC: 6.97, 11.39            70.00”                   72°                2001
AD: 6.97,  9.50             83.70”                   98°                2001
Distance: 122 Light Years
Spectral Classification: G3

Now when Herr Klaus and I arrived home after our half mile uphill sprint from the beach (neither of us the least bit out of breath of course), I decided to take advantage of the steady sky by putting my 9.25 inch SCT to work.  And it’s a good thing I did, because the night was certainly meant for it.

I used a 20mm Astro-Tech High Grade Plössl to find my way to HO 131 and very much to my surprise, even at the eyepiece’s relatively meager 123x, I could see the 10.60 magnitude “B” companion’s weak pulse of light hovering distinctly at the edge of its seventh magnitude parent.  I was so overwhelmed with whatever overwhelms you when a thing like that happens that I grabbed Klaus, sat him on the chair, watched him bend over the eyepiece, and stood there proudly as he raised his vocal cords to the sky and crooned a high-pitched song to the sky gods that would have caused even the coyotes to pause and aim a pointed ear admiringly into the air.

Still stunned and somewhat in disbelief, I replaced the 20mm Plössl with the 204 magnifying diameters of a 12mm Radian, and sure enough, that weak pulse of light was pulsing weakly and faintly right where the 20mm eyepiece said it was:

An image of rare beauty that only a night of spectacular seeing can provide! I don’t have resort to the artistic skills to show it, but the primary was surrounded by a perfectly round diffraction ring that was heart-rending. (East & west reversed, click on the sketch for a larger version).

An image of rare beauty that only a night of spectacular seeing can provide! I don’t have resort to the artistic skills to show it, but the primary was surrounded by a perfectly round diffraction ring that was heart-rending. (East & west reversed, click on the sketch for a larger version).

Now I’ve never been one to tout the virtues of the centrally-obstructed vision of an SCT for pairs of stars of dis-similar magnitudes – BUT – if you can achieve virtual collimated perfection, miracles can truly happen.  I’ll save it for a later post, but I actually used the diffraction rings of Delta Cygni to collimate this SCT, and it has paid such high dividends that even the most unethical junk bond trader would blush.  Throw in a touch of very good seeing – and the sky’s the limit.   Literally.

When Klaus and I finally calmed down, I went in search of “C” and “D”, which of course were right there all the time, just beyond the edge of my narrowly focused vision.  The primary was distinctly white, although I’ve been back several times with my six inch f/10 refractor and detected hints of yellow escaping from it.  In fact, the secondary was also on view in the six inch scope, although I had to resort to averted vision to catch it.

The HO in HO 131 stand for George W. Hough, who discovered a total of 648 double stars, most of them while serving as Director of the Dearborn Observatory in Evanston, Illinois, which was one of S. W. Burnham’s favorite haunts.  Judging from a quick look through his catalog of discoveries, Hough seems to have picked up Burnham’s habit of digging difficult pairs out of the celestial darkness.  He was also involved in ground-breaking work on the Great Red Spot on Jupiter.  You’ll find a detailed bibliography of his work at the link in the first sentence of this paragraph.

The headings in maroon on Hough’s observation are my addition to help clarify the data.  Click on the excerpts for a larger view.

The headings in maroon on Hough’s observation are my addition to help clarify the data. Click on the excerpts for a larger view.

HO 131 actually proves to be a very interesting star when you look at the data on it closely.  Attached at the right are two excerpts, the first being Hough’s original observation of HO 131, and the second (below) being observational data from the second volume of S.W. Burnham’s 1906 General Catalogue.   If you look at Hough’s averaged data for his three 1881 observations, 322.8 degrees and 4.54”, and compare it with Burnham and Eric Doolittle’s (Doo) data, you can see the position angle and separation beginning to change.  And when you compare the data of those three observers with the WDS data of 2002, you see a very noticeable change in position angle (eight degrees further north) and separation (a decrease of one full arcsecond).  And in fact, the proper motions numbers in the WDS reveal quite a bit of movement in the primary: .351” per year eastward in right ascension and .059” per year to the south in declination, which can be seen very clearly in the Simbad plot below:

 Ignore the "B" in the Simbad title -- the WDS data clearly shows it's the primary that has the high rate of proper motion, not the secondary.  (Click for a larger view).

Ignore the “B” in the Simbad title — the WDS data clearly shows it’s the primary that has the high rate of proper motion, not the secondary. (Click for a larger view).

There’s no data in the WDS on the proper motion of the secondary, but it appears it must be trailing along behind the primary in roughly the same direction at a lesser rate.  Otherwise, the relative change in positions of the two stars would be more rapid given the speedy proper motion of the primary.  What would be useful at this point is both an updated measure of the position angle and separation of the primary and secondary, as well as a measure of the secondary’s proper motion.  At any rate, this pair is closing somewhat rapidly, so you better get a look at them soon – they aren’t going to get any easier!

Now let’s move back north to S 752, which we so carefully ignored earlier (here’s the third chart once again).

S 752             HIP:101154   SAO: 106177
RA: 20h 30.2m   Dec: +19° 25’
Identifier         Magnitudes       Separation       Position Angle        WDS
Bu 987      AB: 6.80,  11.10             2.60”                    126°                1986
S 752        AC: 6.80,    7.30        106.70”                    288°                 2011
Fox 254    AE:  6.80, 13.00           21.10”                      70°                 2003
Fox 254    CD: 7.30, 15.30           35.00”                    302°                 2001
Distance:  “A” is 879 Light Years, “C” is 1199 Light Years
Spectral Classifications: “A”, “C”, and “E” are all B9

Now here’s a pair that is a bit easier on the eyes and requires a lot less aperture.  In fact, the two most visible components, “A” and “C”, were easy to separate in my Canon 10×30 image stabilized binoculars:

The primary (upper right) is white, and I saw a definite hint of blue in the secondary (lower left).  (East & west reversed, click on the image for a larger view).

The primary (upper right) is white, and I saw a definite hint of blue in the secondary (lower left). (East & west reversed, click on the image for a larger view).

If you paid close attention to the distance line in the data above for S 752, you’ll see there’s more than meets the eye here.  From our corner of the galaxy “A” and “C” appear to be close enough to be related, but in reality “C” is shining from a point located 320 light years beyond “A” – so it’s not likely there’s any interstellar commerce taking place between them.

And as the data above shows, this is also a complicated arrangement of stars, with three more potential members of the family arrayed around them.  I did my darnedest to avoid any thought of chasing down the AB pair, not only because of the 4.30 magnitude difference and 2.60” separation between them, but also because I knew what I was going to be in for when I saw the identifying label: Bu 987.  What I was going to be in for was visual torment.  But it was tempting — it always is.

Click on the image for a larger view.

Click on the image for a larger view.

While the thought of making an attempt at that close pair circulated through my double star cluttered mind, I turned to S. W. Burnham’s original 1880 observation (shown at left) to see what I could find.  The bad news: “discovered with the 18 ½ inch”, which refers to the 18 ½ inch Clark refractor at the University of Chicago, Dearborn.  The good news: well, there was a glimmer of it.  Burnham recorded a separation of 2.32” in 1880, and compared with the 2.60” listed in the WDS as of 1986, I could see the two stars at least weren’t moving closer to each other.  My math showed the pair should have moved about another one tenth of an arcsecond apart between 1986 and 2013 – certainly not a lot, but in those white-photon-blasted close quarters, every little bit would help.  I still had doubts, but after a tussle with another one of Mr. Burnham’s  delicately close pairs (coming up next), I decided to reach for the sky, so to speak.

It took a while – about thirty minutes or so – but as I wrestled with various magnifications and marginally cooperative seeing, I began to harvest hints of a faint glimmer of light buried in the white 6.80 magnitude primarial glare, which you can see in the inset added to the prior sketch:

East and west reversed once again, click to get a better view of the two faint companions in the inset.

East and west reversed once again, click to get a better view of the two faint companions in the inset.

It was averted vision all the way, but the faint glimmer of light was consistently there, fighting desperately to emerge from the white glare.  The 13th magnitude “E” member wasn’t any easier, even though it was more distant.  But despite my high hopes, I never did catch the first faint 15.30 magnitude hint of “D” – not that I thought it was likely, but you never know until you try.

Now on to part two, where we’ll tackle the Burnham just referred to, Bu 363.

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2 Responses

  1. Hi John!
    Really now…a 4-legged amateur astronomer…I like the image. Your asterism reminds me of an inverted “Crater”. Another fine read!
    Cheers, Chris.

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