Now we’ll continue out trek north, but this time with a new chart. (If you happened to land here without reading part one you can find it here).
And you might start by warming up your averted vision – you’re going to need it . . . . . .
Bu 363 HIP: 101213 SAO: 88783
RA: 20h 31.0m Dec: +20° 36’
Magnitudes AB: 6.18, 10.0 AC: 6.18, 13.0
Separation AB: 6.60” AC: 54.10”
Position Angle AB: 81° (WDS 2008) AC: 206° (WDS 2006)
Distance: 346 Light Years
Spectral Classification: A1
. . . . . . because this one was tough – and I do mean tough. Given that I cracked HO 131 at a mere 123x in the 9.25 inch SCT, I didn’t expect to have all that much problem on Bu 363. After all, according to the WDS data, the secondary was almost twice as far away (6.60” vs. HO 131’s 3.50”) and the magnitude difference was about the same (3.82 vs. HO 131’s 3.63). But it sure didn’t turn out that way, and I could swear I heard a couple of poorly stifled peals of Burnham-ian laughter from up on high as I struggled to come to terms with S.W. Burnham’s 1874 discovery.
Now if you’ll permit your eyes to roam to the inset at the right, the top half is an excerpt from Burnham’s 1900 catalog and it clearly says “Discovered with the six inch.” Which means with Burnham’s six inch f/15 Clark refractor . . . . . . which means I didn’t expect splitting this pair in my six inch f/10 refractor would be a big deal. But if you look just a bit closer at that entry, you’ll also see Burnham measured the separation in 1878 at 21.77”. Uh-oh . . . . . . we gotta problem here, Houston. We’ll circle back to it shortly.
So I sauntered out under the stars with my six inch f/10 and dived in with all the gusto I could muster . . . . . . . and failed spectacularly (better seeing would have really helped, though). Two nights later I leaped to the attack with the 9.25 inch SCT under marginally worse seeing conditions and lost the battle again. But holding out hope that the third time would really be a charm, I gave it a shot the next night, armed with not only the six inch refractor, but also category IV seeing.
I had to stretch my averted vision skills to the absolute limit, but with the maniacal concentration of a photon deprived double star addict, I finally pried both “B” and “C” out of the spectacularly white glare of the primary:
The tenth magnitude secondary was tucked in so closely to the primary that holding it with averted vision was an unrestrained battle. I kept seeing a dart of light shooting out of the primary, aimed directly at the secondary. I was reasonably sure I was seeing a faint wisp of light trying to wiggle into view where the WDS data said it should be, but in a case like this, you’re always haunted by the possibility your imagination has taken control of the observation without your being fully aware of it. So I gritted my teeth, reached deep into my arsenal of eyepieces, and pulled out both a 4mm TMB Planetary II and a 4mm Astro-Tech High Grade Plössl, each of which yielded up hair-raising and eye-punishing magnified diameters of 380.
Switching back and forth between the two implements of magnification, I finally settled on the 4mm TMB because of its wider field of view and better eye relief, which was a real breath of fresh air to my abused right eye. And fortunately the additional ocular amplification did what it was supposed to do: it removed the imagination factor completely from the observation:
Seeing the secondarial light escaping from “B” was still mainly an averted vision affair, but occasionally I was treated to glimpses of it with direct vision, many of them lasting for several seconds. Thirteenth magnitude “C” was still barely visible, almost nine times further out on the south side of the primary, but I gradually lost it as a rising moon slowly filled the sky with its rambunctiously uncontrolled flood of photons.
What really made this battle so darned-ably difficult was the sheer obnoxious glare of the primary’s very obnoxious white light. It carries an A1 spectral classification, which means it’s about as white as white can get. And it certainly showed. But I was bugged in the back of my mind by why Bu 363 proved to be so much more difficult than HO 131. Part of the reason for the unequal struggle may have been attributable to the color differences between the two primaries – HO 131 “A” was blessed with a soft yellow color, which certainly cast a more subdued circular glare into the surrounding stellar terrain.
But there was something else as well. If you go back to the two excerpts above from Burnham’s catalogs (click here to open them in a second window) and study the second one, you’ll find the separation between “A” and “B” narrowed from 21.77” in 1878 to 18.24” in 1905, which is a pretty rapid change. If you look at “A” and “C”, you’ll see a gradual increase in separation between 1892 and 1905 – and even though it’s not a lot, it’s still remarkable for a mere thirteen year period. If you return to the WDS figures in the data above for Bu 363, you’ll see both of those trends have continued: “B” has narrowed from 21.77” in 1878 to 6.60” in 2008, and “C” has widened from 44.14” in 1892 to 54.10” in 2006. Brian Mason at the U.S. Naval Observatory (USNO), home of the Washington Double Star Catalog (WDS), provided me with the historical observational data for both the AB and AC components of Bu 363, which I plotted on the chart below:
Back to the WDS I went once more to look up the proper motion data, and sure enough, the numbers there gave credence to the changes screaming out from the century of accumulated data. They show the primary is moving at the rate of .099” east per year in right ascension and .057” north per year in declination. There are no figures provided for the proper motion of either “B” or “C”, but it appears they must be pretty stationary, possibly indicating they’re located at some considerable distance from the primary.
Now if you look at my chart showing the relative changes in position of AB and AC, it appears as though “B” is moving closer to the primary and “C” is moving further away from it. Ah, but ’tis mere stellar sleight of hand! As the WDS proper motion numbers show, it’s the primary, “A”, which is responsible for the visual changes because it’s moving northeast – meaning the “A” is moving toward “B” and away from “C”. This Simbad plot shows it very well:
What all of this means is the secondary must be slightly closer to the primary in 2013 than it was in 2008. I did the math and got a change in separation of .117” per year, which means in the last five years “B” has moved .585” closer to the primary. That would put it at a distance of 6.015” as of the time I looked at it, or about nine percent closer. It doesn’t seem like a lot, but given the brilliant white glare of the primary, it was probably just enough to make Bu 363 distinctly more difficult than HO 131 was.
Still, in the back of my still bugged mind, I have a nagging suspicion the elusive tenth magnitude secondary has worked its way even closer to the primary than my math tells me it has. Given the glaring white glow of the primary, the weak tenth magnitude light of the secondary, and the 3.82 magnitudes of difference between primary and secondary, what we have here is the perfect stellar storm, a swirling combination of circumstances that complicates the life of a visual observer in ways that are difficult to measure.
In one unmeasured word: Arghhhhh!
But enough of this spectacular vision torturing spectacle – let’s go find something a bit more pleasing and soothing to our eyepiece eye.
We’re going to drop back down to 6.55 magnitude HIP 101070 (here’s the chart at the top of the page again), then slide westward across the connecting line of the splayed H, hopping across 6.85 magnitude HIP 100971 and 8.05 magnitude SAO 106126 to the west leg of the H. From there we’ll slide down the leg in a southwesterly direction to 6.45 magnitude HIP 100779 and then almost due south to 7.54 magnitude SAO 106092. That puts us at the eastern corner of a triangle formed by that star with 8.02 magnitude SAO 106076 and our goal, Σ 2679, which occupies the northwest corner of the triangle.
Σ 2679 HIP: 100638 SAO: 106068
RA: 20h 24.4m Dec: +19° 35’
Magnitudes AB: 7.88, 9.69 AC: 7.88, 12.30
Separations AB: 24.70” AC: 38.70”
Position Angles AB: 77° (WDS 2012) AC: 150° (WDS 2005)
Distance: 733 Light Years
Spectral Classifications: “A” is A2, “B” is F0
And let’s cut straight to the sketch:
And a welcome sight it is! – a delicately designed triangle of stars which draws your eye right to the center of the field. That 12.3 magnitude “C” component can be a bit tricky, but with a slight concentration of attention it’s easily seen in both a four inch and a five inch refractor.
The A-B pair was discovered in 1830 by Friedrich Georg Wilhelm von Struve, and the third companion was added in 1895, although by whom has eluded me so far. I suspect it was a Russian astronomer, Sergei Pavlovich von Glasenapp (1848-1937), who was based outside of St. Petersburg at Pulkovo, and is cited on page 890 of the second volume of Burnham’s 1906 Catalog. I’m still trying to track down his observations, but no luck so far. At any rate, the AB pair seems to be drifting apart very slowly. Struve’s 1830 observation recorded a position angle of 79.8 degrees and a separation of 21.90”, so the change has been very gradual.
And that’s it for this very exhaustive look at a very small section of Delphinian sky. Special thanks are due once again to Brian Mason at the WDS for supplying observational data to a confirmed Burnham devotee.
Our next tour takes place in nearby Sagitta, so don’t move from the edge of your seat until then! In the meantime, I’ll leave you to linger over this photo of S.W. Burnham’s six inch f/15 Clark refractor.
Clear Skies! 😎