For those not familiar with the name, the British astronomer John Flamsteed (1646-1719) is generally credited with the numerical designations assigned to the brighter stars of each constellation which are shown on a star atlas or star chart. Those numbers increase in each constellation as you move from west to east in right ascension, with a few exceptions caused by stars that have shifted positions since the numbers were assigned.
At any rate, as my eyes were roaming around a star chart of Cygnus one cloudy evening, I noticed a concentration of Flamsteed-numbered stars on the constellation’s northeast side, all arrayed along almost the same line of right ascension. Numbered 75, 76, 77, and 79, they provide a welcome line of illumination in what is otherwise a realm of faint starlight. That isn’t surprising since this area lies just a few degrees west of Lacerta, a constellation which has very little competition for the distinction of being the dimmest in the heavens.
As it turns out, all of those numbered stars are double or multiple stars, and two of them are shadowed by additional double or multiple stars. And since I’m not one to resist a stellar offering of that sort, I packed my telescopic bags and headed off to see what there was to see.
It’s easier to get where we’re going if we start with 79 Cygni and work our way north. To get there, we’ll need to negotiate a star-studded wilderness made more difficult by an absence of well illuminated stellar sign posts, so follow closely! Once we reach 79 Cygni, navigation becomes much easier.
To get started, you’ll need to locate Sigma (σ) and Tau (τ) Cygni. Probably the easiest way to do that is to start at Deneb and move four and a half degrees south and slightly east to 3.94 magnitude Nu (ν) Cygni. From there move four more degrees in the same direction but slightly further toward the east and you’ll find yourself at 4.91 magnitude Tau (τ), with Sigma (σ) gleaming just a couple of degrees north of it at a magnitude of 4.24. From Tau (τ) it’s another four degrees, this time due east, to our next landing point, 4.91 magnitude 72 Cygni. Two and a half degrees further east with a slight dip to the south will land you on our first target, 79 Cygni.
79 Cygni (S 799) HIP: 107253 SAO: 71643
RA: 21h 43.4m Dec: + 38° 17’
Identifier Magnitudes Separation Position Angle WDS
KU 109 Aa, Ab: 5.69, 11.10 1.50” 155° 1948
S 799 AB: 5.69, 7.00 149.10” 59° 2011
S 799 AC: 5.69, 10.24 135.30” 318° 2011
S 799 BD: 6.98, 13.90 33.70” 254° 2002
Distance: 273 Light Years
Spectral Classifications: Both “A” and “B” are A0
Note: AB is H VI 57
This is a wide pair first discovered by Sir William Herschel on October 1st, 1781, but not measured. Sir James South not only measured that pair in 1824, but also noted and measured the “C” component as can be seen below. His measures — 59° 21’ and 153” for AB, 320° 8’ and an estimated 150” for AC – are surprisingly close to the 2011 figures in the WDS, excepting his estimate for AC.
The arrival of the “D” companion to “B” is described on page 953 (catalogue number 11208) of the second volume of S.W. Burnham’s 1906 catalogue this way: “Espin measures a small star near “B”: 1905.93, 248.5°, 30.76”.” Which leaves the Aa,Ab pair, added by Karl Friedrich Küstner (1856-1936) at a later date, but not published until 1937.
And now that we know who did what, let’s see what 79 Cygni aka S 799 looks like:
Although the magnitudes and separations of the Aa, Bb pair should be within our reach, their 5.41 magnitude difference effectively cancels our hopes. Instead, I put quite a bit of effort into seeing Espin’s 1905 discovery, the “D” companion to “B”, but to catch it I had to call my 9.25 inch SCT into action. The result can be seen in the inset at the right of the sketch if you enlarge it and look very closely. At almost 14th magnitude, it took a determined application of averted vision to catch its faintly desperate glimmer behind the glare of “B”.
Now we’ll move two and a half degrees due north to another William Herschel-James South discovery, 76 Cygni, which can be seen in the same field with another of our targets, 77 Cygni and Bu 688.
76 Cygni (S 796) HIP: 107097 SAO: 51189
RA: 21h 41.6m Dec: +40° 48’
Magnitudes AB: 6.08, 9.47 AC: 6.08, 11.71
Separations AB: 58.20” AC: 133.20”
Position Angles AB: 234° (WDS 2012) AC: 282° (WDS 2002)
Distance: 456 Light Years
Spectral Classifications: “A” is A2, “B” is A0
Note: AB is H V 43
Sir William came across the AB pair of 76 Cygni on the same night he discovered 79 Cygni (October 1st, 1781), but missed the fainter “C” companion. That star eluded James South as well, but he did get measurements for the AB pair, which can be seen at the right, ending up with an average of 230° 52’ and 65.6”. Looking closely at his notes, you can see each of his observations includes a comment on the difficulty of measuring the separation because of the secondary’s comparative faintness, which is hinted at in the sketch below.
77 Cygni, a mid-sixth magnitude range pair, was discovered in 1937 by Gerard Kuiper, of planetary fame. It’s primary and secondary are separated by a claustrophobic two-tenths of an arc second:
77 Cygni (KUI 108) HIP: 107162 SAO: 51207
RA: 21h 42.4m Dec: +41° 05’
Magnitudes: 6.33, 6.72
Position Angle: 23.8° (WDS Ephemerides 2013)
Distance: 372 Light Years
Spectral Classification: “A” is A0
Status: Gravitationally linked, orbit can be seen here (orbital period is only 26.2 years)
Note: May be related to Bu 688, located 3’ to southeast
Although that pair is well beyond our telescopic range, it’s thought to be associated with Bu 688, a quadruple star with three companions whose starlight does lie within reach of my telescopes . . . . . . . but just barely:
Bu 688 HIP: 107177 SAO: 51212
RA: 21h 42.6m Dec: +41° 03’
Identifier Magnitudes Separation Position Angle WDS
Bu 688 AB: 8.10, 8.62 0.44” 200° 2008
Bu 688 AB,C: 7.50, 11.90 27.20” 30° 2002
Fox 9036 AB,D: 7.50, 13.10 46.40” 307° 2002
Distance: 370 Light Years
Spectral Classifications: “A” is F2
Status: Gravitationally linked, orbit can be seen here
It took a concerted concentration of visual effort to pry anything at all loose from the 7.50 magnitude primary of Bu 688. My first effort with the six inch refractor failed completely due to poor seeing. A second visit a few nights later resulted in the appearance of the 11.90 “C” component, but it was exclusively an averted vision affair.
The “D” companion, which apparently wasn’t added until 2000, was too much of a stretch for the six inch refractor, so I returned on a later night with a 9.25” Celestron Edge SCT. It took about ten minutes to get my first glimpse of it, but once I had it, I was able to keep it in sight with averted vision.
I needed to resort to a couple of tricks, though, to reach that point. The first was to find the correct magnification – too much simply magnified the surplus of white light being thrown around recklessly in the confined area between “D” and the primary. The second trick was to fix my gaze on “C” – when I did that, “D” popped into view with little problem.
The AB pair, again out of our reach with a separation of 0.44”, was discovered by S.W. Burnham in 1877 using the 18.5 inch Clark refractor at Dearborn Observatory in Chicago. The “C” component was added in 1914.
Next move is north again, a short two degrees, to 75 Cygni (here’s our last chart again).
75 Cygni HIP: 106999 SAO: 51167
RA: 21h 40.2m Dec: +43° 16’
Magnitudes AB: 5.28, 10.10 AC: 5.28, 10.26
Separations AB: 2.70” AC: 62.20”
Position Angles AB: 327° (WDS 2008) AC: 253° (WDS 2003)
Distance: 405 Light Years
Spectral Classifications: “A” is M2, “C” is K
Notes: AB is AC 20; AC is STTA 221
This is another pair that features a tight primary-secondary combination which proved a bit too tight for my seeing conditions. Even under ideal conditions, though, a 4.82 magnitude difference with a tight 2.70” separation would be right at the limit of what’s possible with the 9.25 inch SCT I normally use in a case like this. On the other hand, the “C” companion was no contest at all for the six inch refractor, thanks to the much wider separation, even though the magnitude difference was similar.
The AB pair, which is designated AC 20, was discovered in 1859 by Alvan Clark, of Clark Refractor fame, when he was observing from the Reverend Dawes’ observatory in England. As you can see in the excerpt below from Burnham’s 1906 catalog, it was Dawes (notice the Da abbreviation) who provided the first measures in 1860.
Also inconspicuously inhabiting the field is one of the Reverend’s discoveries, DA 14, also known by its variable star designation, UU Cygni. As of 2009, that 8.91 and 11.4 magnitude pair had a separation of 3.7” and a position angle of 351°. I didn’t realize it was a double star at the time I looked at 75 Cygni, so I didn’t try to separate it. It would be near the limits of a six inch refractor, but shouldn’t be too difficult in a 9.25 inch SCT.
The other pair, GIC 168, located at the bottom (southwest) of the sketch, which I was aware at the time I made the sketch, is dimmer (magnitudes of 12.3 and 12.8) but wider (6.8”, PA of 275° as of 2002). I had little problem prying it apart a few nights later with the 9.25 inch SCT.
And that’s it for Cygnus for this year — there’s a whole lot more worth exploring in this area that we’ll save for next year. But since we’re already this far north, we may as well wander over to Cassiopeia next. I’ve been given a tip about a colorful carbon star there that also happens to be an intriguing multiple star.
In the meantime, Clear Skies! 😎