If you’ve been hanging on for dear life at OΣ 302 since the last post (that would be part one, this is part two!), you can relax your grip now. I’m back again, and we’re going to forge forward once more as we continue bushwhacking our way through the Northern Marches of Corona Borealis.
Put your star-hopping cap on — next stop is Kappa (κ)!
Kappa (κ) Coronae Borealis (11 CrB) (BUP 163) Σ 1983
HIP: 77655 SAO: 64948 No HIP or SAO number
RA: 15h 51.2m Dec: +35° 39’ RA: 15h 52.0m Dec: +35° 28’
Magnitudes: 4.8, 11.55 Magnitudes: 10.19, 11.74
Separation: 109.1” Separation: 14.3”
Position Angle: 209° (WDS 2009) Position Angle: 64° (WDS 2009)
Distance: 102 Light Years Distance: ???
Spectral Classification: K0 Spectral Classification: K2
If you look at the magnitude difference between Kappa’s primary and secondary, you can see we’re dealing with a W-I-D-E spread of 6.75 magnitudes, which makes the secondary almost six hundred times fainter than the primary. Fortunately, though, it’s lurking far enough away from that glaring primary that it can be seen in a six inch refractor without too much problem. Cut that distance in half and you would be in for a real visual battle.
In fact, if you wait long enough, that’s exactly what will happen – that is, the distance will be cut in half! And no, I haven’t been out in the damp darkness without a hat so long that my cranial circuits have corroded. Not yet, anyway.
Take a look at the last identifier in the first line of the data above for Kappa (κ). BUP 163 comes from what is usually referred to as the Burnham Proper Motion Catalog (the actual title is Measures of Proper Motion Stars made with the 40 Inch Refractor of the Yerkes Observatory in the Years 1907 to 1912).
If you turn to page 48 of that catalog and look at the separation and position angle of Kappa (κ) when Burnham measured it in 1909, you’ll see a rather surprising change (click on the excerpt at right).
In exactly one hundred years (from Burnham’s 1909 measures to the 2009 data in the WDS) the primary has moved a very surprising thirty seconds of arc closer to the secondary! That speed demon-like motion led me back to the WDS to take a look at the proper motion numbers, and sure enough, they’re fleet of foot: -007 in RA and -347 in declination. Translated into understandable terms, the primary is moving .007 seconds of arc west and .347 seconds of arc south per year! Which is captured well in this plot of that motion from Simbad:
If you do the obvious and multiply .347 by 100, you get a total movement in declination of 34.7 seconds of arc in the interval between Burnham’s measure and that of the WDS, which is reasonably close to the thirty arc second change in separation shown by the data. The reason the numbers don’t match precisely is due to the slight westward motion in RA.
Before we move on, don’t skip over the much fainter Σ 1983 over in the south corner of the field. You’ll need at least five or six inches of aperture to see it, but it’s a subject well worth the test of your eyes and optics.
Now we’ll turn towards Zeta (ζ), but first let’s stop and pay a visit to another of F.G.W. Struve’s stars, Σ 1973, which is on our way. If you go back to our chart above (or here), with Kappa (κ) still centered in your finder, you’ll see Zeta (ζ) just a bit over two degrees to the northwest. Halfway between Kappa (κ) and Zeta (ζ) and slightly to the northeast you’ll see a weak point of light, which is what we’re going to take a gander at next.
Σ 1973 HIP: 77252 SAO: 64893
RA: 15h 46.4m Dec: +36° 27’
Magnitudes: 7.60, 8.79
Position Angle: 321° (WDS 2012)
Distance: 263 Light Years
Spectral Classification: F5
Notes: Also HN 32, SHJ 209, HJL 229, and SHY 685. Probably a physical pair based on SHY’s observations
Sir William Herschel was actually here first (May 1st, 1785), but didn’t measure this pair. His son John, and his temporary side-kick James South, paid a visit in 1823, followed by the senior Struve in 1829. As you can see in the excerpt at the left from Thomas Lewis’s compilation of Struve’s observations, Herschel and South (h and S) made two measures of the pair (their catalog number is SHJ 209), but nevertheless, Struve’s catalog number is now used to identify the star.
Unlike Kappa’s fast-moving primary, the two stars of Σ 1973 show little change from the time of Herschel and South’s first measurements up through 2012. I looked at the proper motion numbers in the WDS and found both stars are actually moving at a relatively modest rate. The primary shows motion of .103” west per year in RA and .057” north per year in declination, and the secondary is moving at a rate of .104” west per year and also .057” north per year in declination. In other words, they’re moving as though chained together, which is captured well in the Simbad plot once again:
Sorry to drag you into the intricacies of stellar proper motion again, but it’s interesting what you can detect with just a bit of delving into the detail. In this case, our quick look at the data provides some intriguing insight into why this pair is considered physically linked.
But enough of that now – let’s get back to the action at the eyepiece before we get lost in charts.
Zeta (ζ) is lurking just a bit more than a degree away from where we are now (here’s the chart again). In fact, if we’re careful about our approach to it, we’ll even catch Σ 1964 in the same field with it, which is what I did here:
Pour yourself a cup of tea now, pull up a chair, and make yourself comfortable – because there’s enough tea-sipping detail here to hold our attention for quite a while. We’ll start with the less complicated and slightly more colorful of the pair, Zeta (ζ).
Zeta (ζ) Coronae Borealis (Σ 1965) (H II 8) (SHJ 208)
HIP: 76669 SAO: 64384
RA: 15h 39.4m Dec: +36° 38’
Magnitudes: 4.96, 5.91
Position Angle: 306° (WDS 2012)
Distance: 225 Light Years
Spectral Classifications: B7, B9
This is a mellow-colored tight pair of stars that does well in a 60mm refractor. I’m not sure why, but I could see definite hints of yellow in both the primary and secondary, which shouldn’t have been there in two B class stars (almost A) that ought to be firmly locked into white. (A chart of spectral classes can be seen here).
Sir William Herschel stumbled onto these two stars on the first of October in 1779 and saw white in both of them, with a touch of red (a staple of his observations) in the secondary (Philosophical Transactions, 1782, p. 124 — scroll down to the twelfth title). John Herschel and James South paid several visits to Zeta (ζ) in 1821 and 1823 with slightly different results. They reported white for the primary, blue for the secondary on March 21st, 1821, but a month later (April 21st) they described both stars as blue “but the small one the deepest colour” (see thumbnail below).
The loquacious Admiral William H. Smyth gazed on Zeta (ζ) (“A fine double star, in the middle of the space over the wreath, and 10° north, a little easterly, from Gemma”) in 1831 and described the primary as “bluish white” and the secondary as “smalt blue” (pp.346-347 of The Bedford Catalog — Gemma, by the way, is another name for Alpha Coronae Borealis). The Reverend Webb left us with two descriptions, “greenish white, greenish” and “flushed white, bluish green” (p. 89). Meanwhile, Sissy Haas goes with “a very bright white and a modestly bright white” (p. 61).
From the standpoint of adhering to the spectral class, she wins and everyone else fails completely, especially me and my yellow. Think I better get a stronger cup of tea and go back and look again.
Getting back to Sirs John Herschel and James South, I’ve included the two pages of their observations of Zeta (ζ) from 1821 and 1823 at the right, which are interesting because they shows how much effort was put into their measurements (click on the thumbnail image at the right). Nevertheless, there’s still a pretty significant spread between the averages of their April 1821 and May 1823 observations – which just goes to show how difficult it was to get consistent measures back in their day. (Their catalog can be found here at the bottom of the page).
Let’s drift down to Σ 1964 in the southwest corner of our field of view now and take a look . I’ve already mentioned it’s a complicated star, which becomes obvious when you look at the numbers . . . . . . .
Σ 1964 HIP: 76563 SAO: 64821
RA: 15h 38.2m Dec: +36° 15’
Designation Magnitudes Separation Position Angle WDS
HV 1167 AB: 8.07, 9.87 1.16” 83° 2012
Σ 1964 AC: 8.07, 8.06 14.70” 86° 2012
Σ 1964 AD: 8.07, 9.02 15.20” 81° 2012
Σ 1964 CD: 8.06, 9.02 1.58” 17° 2012
WAK 1 CE: 8.06, 8.20 0.10” 82° 1970
Distance: 285.6 Light Years
Spectral Classifications: “A” is F5, “B” is G4, “C” is F5
Notes: AC is also H IV 61 and HJL 227
. . . . . . . and is just as obvious when you put it under moderate magnification and look very closely.
First, let’s save ourselves from pointless frustration and pass on the CE pair at .10” of separation – we’ll leave that for the folks with the speckle interferometers. Second, we’ll skip over the AB pair since the skies I was laboring under the night of the sketch weren’t quite up to it, although it should be possible to get that pair with six inches of aperture.
That leaves us with the two stars that are obvious when you first focus eyes (or one eye) on Σ 1964 – and that’s also where things turn complicatedly devious (here’s that sketch again for reference). The brighter of the two stars you see is actually the AB pair and the dimmer of the two is the CD pair.
So what you see on first glance is in really the alphabetically combined light of AB and CD. Now if you look very carefully at the inset at the lower right of the sketch you’ll see I was able to separate CD at a relatively modest 157x, thanks to the humble proficiency of that amazing little (and old) 7.5mm Celestron Halloween Plössl.
Which really shocked me.
Because I wasn’t looking for that at 157x.
I was merely testing the skies to see if they would take more magnification.
Suddenly, before I could stifle it, I found myself shouting in an unaccountable and unlikely blend of two languages, Greek (ancient) and German (modern), “εúρηκα, ich ‘hab es gefunden!”, meaning “Eureka, I’ve found it!”.
Now I know that’s saying the same thing twice, since Archimedes’ ancient Greek exclamation “Eureka” actually includes “I’ve found it” (ancient Greek is a curiously compact language). But I was so thrilled with what I saw in the confined space of that old chrome cylinder that clear thinking was out of the question. And anyway, the double emphasis seemed to suit the occasion.
About thirty seconds later I heard a window slide open. My neighbor leaned out and in a tolerantly irritated voice sighed, “John, do you know it’s past three o’clock in the morning???” Somehow I got the impression my enthusiasm was less than infectious.
But I did appreciate his thoughtfulness in providing me with the time.
However — for all of Σ 1964 ‘s complicated nature, there’s little color to be seen here. My notes say “dirty white, slight gray”, which about sums it up. The only spectroscopic hint of color is the yellow in “B” (G4), but if I could have seen “B”, I suspect its yellow would have been smothered by the white (F5) of “A”.
William Herschel discovered the AB-CD pairing (he only saw them as two stars) on July 18th, 1782 (p. 93 of 1784 catalog, sixth title from the top) but cautiously ignored their colors. James South took a look on May 7th, 1825, also saw only two stars, and also left no notations on color (p. 198 of Philosophical Transactions, 1826, V. 116). Nor was there a comment on color from the senior Struve, but Lewis did detect “yellowish” in AB and CD (pp. 427-28). Haas saw “gloss white” and described the two stars as “a fine easy pair” for a 60mm refractor (p. 61). Which they are.
And now, last on our tour, but certainly not least, is Lambda (λ), which can be found three degrees northeast of Zeta (ζ). In fact, it and Zeta (ζ) form a distinctive triangle in an 8×50 finder with Kappa (κ), as you can see from another look at our chart.
Lambda (λ) Coronae Borealis (12 CrB) (H VI 94)
HIP: 78012 SAO: 64974
RA: 15h 55.8m Dec: +37° 57’
Magnitudes: 5.47, 11.44
Position Angle: 67° (WDS 2002)
Distance: 135 Light Years
Spectral Classification: F0
Lambda (λ) is good place to give our eyes a break, although you may have to strain them slightly to scoop the 11.4 magnitude secondary out of the dark.
Fortunately it’s far enough away from the primary to cooperate – in the sketch you can see it just beyond and east of the primary’s circular radiance. And after the drab grays of Σ 1964 and the muted tones of Zeta (ζ), that primarial gold glow is rather soothing to the observing eye.
This is another William Herschel discovery, as you can see below (source — sixth title down):
And since Lambda (λ) has pretty well been neglected since Sir William first came across it (although not by us at least), that’s about it for this trip through Corona Borealis.
Next time out, we’ll head south and fly around the fringes of the Milky Way in search of duplicitous stars in and near open clusters.
‘Til then, CLEAR SKIES! 😎