Star-Splitters

In the early morning hours of August 25th, 1779, as the first glimmering rays of the new day are just beginning to cast their long, faint-fingered light into the eastern sky, William Herschel is bent over an eyepiece, waiting for his last star of the night to drift into view.  He’s been at this since nine o’clock the previous evening without a break.  The air is damp and cool, his coat is barely keeping up with the falling temperature, he’s hungry and tired, and his eyelids are beginning to sag as sleep begins its inevitable persistent tug at them.

As that last star finally begins to drifts lazily into view in the eyepiece, William suddenly sits up straight and erect in his chair ———- and in awed shock and surprise, his native language takes charge:

“Ach!  Eine enge Paar von Sternen!  Sie sind rot!  Nein, blau!  Nein, nein . . . . .
.         (A close pair of stars!  They’re red!  No, blue!  No, no . . . .)
the large one is red, the small one is blue!  It’s sky blue!  A light sky blue!
Ach, nein, it’s ‘inclining to green!’  It’s . . . . . it’s . . . . . ist eine . . . . . eine . . . . .
it’s. . . . . . . . ‘A most beautiful object!’ ”                              (p. 69 of the 1782 catalog)

He takes a quick measure of its separation, turns to his observation log, and writes: Class III, number 5.

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It’s November 29th, 1821.  Under a dome in London, the metallic creaks and wooden groans of a large equatorial mount echo from the walls as John Herschel and James South slough the five foot long tube of a 3.8” Dolland refractor to a right ascension of 1h 53m and a declination of +41° 28’.  Their target is Sir William’s “most beautiful object.”  Even though each of them has seen Almach several times before, their eyes are still riveted to it as they take turns at the eyepiece.

“What color do we ascribe to the large one, John?”
“Orange.”
“And the small one?”
“Mmmmm  ——-  let’s . . . . . . . . yes, let’s describe it as emerald green.”
“Anything else?”
“Yes, we have to include this: ‘very beautiful.’ “

And then at the top of the page, the future Sir James South adds their catalog number,  XXVI  . . . . . .  and leaps to the eyepiece.                       (p. 49 of Herschel/South Catalog)

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” . . . Among the best of all . . . is the last star of the string of bright beauties that helps make the constellation Andromeda, second magnitude (2.16) Almach, Andromeda’s Gamma star.” (Stellarium screen image with labels added, click to enlarge).

 Almach  (Σ 205)  (H III 5)  (SHJ 26)               HIP: 9640   SAO: 37735
RA: 02h 03.9m   Dec: +42° 20′
.                              Magnitudes       Separation      Position Angle        WDS
STF 205    A, BC: 2.31,   5.02              9.50″                     63°                  2011
BAR 22          AD: 2.31, 15.00            27.90″                  245°                  1898
STT 38           BC: 5.10,   6.30              0.17″                     96°                  2012
Distance: 355 Light Years
Spectral Classifications:  A is K3    C is B8
Status: A, BC is physically linked; BC is gravitationally linked, a view of the orbit can be seen here.

OK, you’ve just read the origins of the second and third numbers in parentheses above – and the question taking shape in your mind is this:  Is Almach really that good?

A sight that will stir your soul on a cold winter night! (East & west reversed to match the refractor view, click on the sketch for a larger version).

You bet your last little Ortho it is.

Look, even Jim Kaler waxes eloquently about it:

You take your new telescope to the back yard perhaps wondering what to examine. When finished with the Moon and the bright planets you turn to the stars, first perhaps to the grand Orion Nebula, next maybe to the magnificent Andromeda Galaxy. Then it is time for double stars. The sky abounds with them . . . Among the best of all . . . is the last star of the string of bright beauties that helps make the constellation Andromeda, second magnitude (2.16) Almach, Andromeda’s Gamma star.”

Almach’s gift to the visual observer is enticingly wrapped in its vividly contrasting colors.  You can’t fail to be impressed by them, regardless of what aperture you might happen to have hanging around your house, your back yard, or your observatory.

Of course there are other attractively tinted stars traveling every night through the clear skies above us, and every one of us has his or her favorite.  I’ll just say that Almach is very, very high on my very, very crowded list of favorites.  And I’ll add this: it’s contrasting red/orange and pale blue/emerald green is a sure cure for whatever ails your frazzled ocular nerves.

But as is frequently the case when confronting true beauty, there’s more than meets the eye.  Almach is not just another pretty pair of stars —–  it’s also a pretty complicated collection of stars.

If you look at the data line above, you’ll see three separate identifiers listed for Almach’s components.  The second of those, BAR 22, is a rather mysterious 15th magnitude star which was first observed in 1898 by Edward Emerson Barnard and hasn’t been observed since.  So we’ll set it aside for now while we look at the others —- although if you happen to have the aperture available to chase it down, please do.  I would be more than interested in hearing about it since E. E. Barnard was not well known for his double star discoveries.

Let’s focus instead on the BC pair, which you’ll see listed twice.  The first time is opposite STF 205, where you’ll see it included with the primary as “A, BC”; and the second time is opposite STT 38, where it’s listed separately – and with a very tight separation between “B” and “C” of 0.17 seconds of arc.

It was Otto Wilhelm von Struve who first pulled back the optical veil drawn over “B”.  His sighting of “C” took place in the autumn of 1842 when the two stars were separated by roughly 0.5 arc seconds, but it took a while for that information to filter through the slow-flowing astronomical channels of the era.

Let’s park ourselves in Admiral William H. Smyth’s parlor in the late spring of 1843 and listen to him describe history as it was taking place:

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. . . Mr. Baily put into my hand a letter which he had received from M. Struve, in October, 1842, announcing the unlooked for tidings that he had detected γ Andromedæ to be triple, and that the companion is composed of two stars of equal size, separated by an interval of less than 0″·5.  I lost no time in notifying this to my friend Mr. Dawes, who, as well as myself, had so repeatedly gazed at this, merely as a double star.  On the 1st of November, he informed me that he charged Mr. Bishop’s refractor with an excellent single lens magnifying 520 times, and when the star was best defined, became satisfied of an elongation sf and np [south following and north preceding] in the companion, making it look like a dumpyish egg.  By the measures he obtained, the angle of position was 125° 48’, and the distance of the centres was estimated at 0″·4.  I also received a letter from the Rev. J. Challis, under date of December 9th, 1842, after his attacking it with the Northumberland equatoreal, at my request, of which the following extract is most interesting.

‘I looked at γ Andromedæ the first opportunity after receiving your note, and was surprised to find that I could easily recognize the small star as being double.  I cannot say that I saw the components separated, but there was a decided elongation, and several measures which I took of position agree well with each other.  The distance is certainly not more than 0″·5.  My impression was, that the components are not equal.’

When I repaired to Hartwell, in February, 1843, I was baffled in my attempts to examine this object in the evening twilight.  But on returning thither in the spring I was enabled to catch some fine early views of it.  On the 1st of May, the morning atmosphere was perfectly diaphanous, and I teased γ under various powers from 118 to 600, until I fairly saw that the comes was not round, but elongated, in a direction np and sf  to the amount above estimated.  It was, however, so slightly oval, that, but for M. Struve’s unexpected announcement, I must assuredly have overlooked it.”
.                                                                            pp. 50-51 of The Bedford Catalog)

.

Now, when I first looked up the statistics for Almach in the Washington Double Star Catalog (WDS), the separation of the BC pair was listed at 0.51″, so my initial reaction was to forget about any telescopic attempt to see it.  But after reading of the Admiral’s experience, and taking into account the aperture of the instrument he used, I had second thoughts on the matter – and here’s why:

Admiral Smyth employed a 5.9” (150mm) f/17.3 Tulley refractor in his observatory – and normally I wouldn’t associate a six inch refractor with use on a pair of stars separated by only 0.5”  But even more surprising, the telescope referred to by the Reverend Dawes – Mr. Bishop’s refractor — employed a significantly smaller 3.75” (96.5mm) f/15.8 objective made by Dolland.  Those dimension, 96.5mm and f/15.8, also describe the telescope John Herschel and James South were using on Almach on November 29th, 1821, although they didn’t use enough magnification to glimpse an elongation of “B.”  But please take careful note –- these are early 18th century long focus achromatic doublets, very distant relatives to today’s short focus exotic-glassed apochromatic refractors – and obviously very capable double-star instruments.

So I aimed my six inch f/10 refractor at Almach a few nights later and stepped my way up to 1140x (a 3.2mm TMB Planetary eyepiece lodged in 2.4x Dakin Barlow), which is an absolutely unheard of magnification for either me or that scope.  And when I didn’t see the first hint of elongation – even though surprisingly the image was actually quite viewable – I decided I had better check the orbital elements data from the WDS.    And that’s when I discovered the 2012 separation for the BC pair  was actually a much tighter — and very much out of reach — 0.172 arc seconds.

So all I have to do now is wait until about 2045 for the separation to widen to 1.5”.  Stay tuned.  😉

There’s one more exotic addition to the Almach family that deserves momentary mention:  it seems that the “B” of the BC pairing is also double!  It took a spectrograph to detect it – and it revealed a very close and fast orbit of 2.7 days.

At any rate —– when your eyes light on Almach’s magnificently tinted rays, remember all that heavenly color is emanating in your direction from four stars, two of which are hidden from your sight – not to mention that 15th magnitude “D” companion, which may or may not exist in the dark depths of Almachian space.

In Jim Kaler’s words:  “The naked-eye star we know as Almach is thus quadruple, making it a feast for both the mind and for the eye.”

And as we’re about to see, a feast it most certainly is.

Filed under: 4. Choose a Constellation:, Andromeda |