If you find yourself roaming the southeastern sector of Perseus some dark and starry night, you’ll encounter some strangely named stars — such as Menkib and Atik — and some oddly named objects — such as B5 and LDN 1470 — not to mention the very extended, very ghostly, and pretty much very invisible California Nebula (at least to eyes without CCD implants).
And if you cast a chart-bound glance (chart 13 of the S&T Pocket Atlas, chart 7 of the Cambridge Double Star Atlas) about five degrees east and somewhat south of Menkib, you’ll find your eyes settling on a rather unlikely trio of north-south aligned stars — lined up like buttons on a coat, they are — beckoning for your attention. The two outer suns at the opposite ends of that alignment are multiple stars. Each of them is accompanied by an adjacent multiple system, one a little further north, the other a little farther south — and all of them are visible within a mere half-degree eyepiece field of view. And sitting right there in the middle is the fifth star mysteriously missing from the title above, 55 Persei, a 5.73 magnitude single blue-white (B8) star at a distance of 450 light years from us — sort of the glue for the whole view.
But instead of talking about them, let’s go look.
Let’s start by taking a look at photo of this area, which will give you a good idea of the relative positions of the four multiple stars we’re going to look at on this Persean sojourn:
And now we’ll take a look at a sketch of the area (and lose most of those background stars visible in the photo), tilted to match Perseus’ sliding-into-the-west-reclining-position:
We’ll start in the north and zero in on Σ 533 and MLB 1036:
Σ 533 (STF 533) (AB is H IV 72) HIP: 20570 SAO: 57211
RA: 04h 24.4m Dec: +34° 19’
Magnitudes AB: 7.30, 8.49 AC: 7.30, 12.0
Separations AB: 19.80” AC: 107.20”
Position Angles AB: 61° (WDS 2011) AC: 193° (WDS 2001)
Spectral Classification: A is B8, B is F2
MLB 1036 (No HIP or SAO numbers assigned)
RA: 04h 24.6m Dec: +34° 21’
Magnitudes: 11.0, 11.5
Position Angle: 217° (WDS 2007)
Spectral Classification: None assigned
You’ll find the AB pairing of Σ 533 is an easy split (visible even in an 8×50 finder), but you may have to stretch a bit to catch the twelfth magnitude “C” companion, depending on what aperture you’re using. The primary and secondary are both a very obvious blue-white, although Sir William Herschel, who was the first to record an observation of them (on September 7th, 1782), seems to have seen reddish-white in the primary and pale red in the secondary:
I suspect the speculum coating on his mirror had something to do with his perception of color, since both stars are a long way from red as far as their spectral class is concerned. You can see he also took note of the lineup of three stars in the field of view, but seems to have missed the primary-secondary configuration of OΣ 81, the southernmost of the three stars, since it’s absent from his 1784 catalog (scroll down the sixth title on the list).
One other puzzle I ran into was the absence of a distance for Σ 533. I searched all the usual sources (WDS, Simbad, Bright Star Catalog, Stellarium, Sky Safari) and came up with nothing, which is rather surprising for a seventh magnitude star.
MLB 1036, on the other hand, is as difficult to separate as Σ 533 is easy. In fact, the little devil defied me in three determined attempts to pry it apart — so much so that I began to doubt whether I was wrestling with the correct star. I finally had to go back and refer to the STScI photo above to make sure — and sure enough, when I enlarged the photo (at the right), I could see an elongation pointing somewhere close to the 217 degree position angle listed for it in the WDS. I’ve split fainter pairs in that five arc second range without much problem, but this pair was as uncooperative as a cloudy night. Maybe I was just holding my mouth the wrong way.
The letters MLB refer to the discoverer of this pair, W. Milburn, who we ran into this past autumn when looking at another of his discoveries, MLB 36, also a tough pair to wedge apart. You can see his original observation by clicking on the thumbnail at the right, which is from this source.
Let’s slide down to the south section of our field of view now and look at our other pair of multiple stars (and for reference, here’s that previous sketch of the whole field once again).
OΣ 81 (STT 81) (56 Per) HIP: 20591 SAO: 57216
RA: 04h 24.6m Dec: 33° 58’
. Magnitudes Separation Position Angle WDS
STT 81 AB: 5.84, 9.25 4.30” 16° 2007
BAS 4 Aa, Ab: 5.77, 9.00 0.40” 306° 1999
BAS 4 Ba, Bb: 9.60, 11.30 0.60” 292° 2002
Distance: 136 Light Years
Spectral Classification: F4
DOO 7 (No HIP or SAO numbers assigned)
RA: 04h 24.8m Dec: +33° 53’
Magnitudes AB: 10.71, 11.20 BC: 11.20, 11.70
Separations AB: 46.40” BC: 3.30”
Position Angles AB: 212° (WDS 2011) BC: 216° (WDS 2001)
Distance: 45 Light Years
Spectral Classification: A3
OΣ 81 is quite a bit tougher than Σ 533 to split — the senior Struve’s discovery surrenders without the least fight, but Otto’s eighty-first discovery (in 1847) forces you to come after it. I had no luck at all with the magnitude 9.25 secondary on the first night I looked at it, even in a six inch scope, because of atrocious seeing. There was so much vibration in the eyepiece even at low magnification that I could have sat there all night and never had the first hint of its duplicity. The second and third nights were much better, with the secondary hovering like a dust mote just out of the primary’s reach — really a pleasing view after the frustrations of the first night. I didn’t see any hint of a colorful hue creeping into the white primary here, which was the case with all the stars on our list tonight.
As for DOO 7, as the sketch shows, the 10.71 and 11.20 magnitude primary and secondary are very obvious. “C”, on the other hand, is just a plain pain. It’s only half a magnitude fainter than “B”, but it’s located claustrophobically close, especially when you consider the weak magnitudes we’re dealing with here. Fortunately the 216 degree position angle of BC is almost a perfect match for that of the AB pair at 212 degrees, which provides you with a pointer of sorts.
It took several attempts, but I finally managed a few very weak glimpses of “C” with a 6mm Astro-Tech Plössl (253x). There wasn’t much light left by the time I worked my way up to that magnification, though, so it was far from a satisfying view. It should be possible to do better when Perseus is positioned closer to the zenith, as opposed to the about halfway-to-the-horizon location I where I found it on that night. If you enlarge the STScI photo above considerably, as shown at the right, you’ll see a very, very slight elongation in the “B” companion.
This triple star was first discovered and measured in 1900 by Eric Doolittle when he was the Director of the University of Pennsylvania’s Flower Observatory in Philadelphia. In 1901 he published Measures of 900 Double and Multiple Stars made with the Eighteen Inch Refractor of the Flower Observatory (that link to the book will take about a minute to load) which included on page eight a list of twenty-two systems he discovered while compiling his measures. Number seven on that list, which can be seen at the right, is DOO 7.
The eighteen inch refractor he was using, which was equipped with the largest Brashear objective of that time, can be seen here, and a short history of the Flower Observatory can be found here. In the book referred to above, he mentions he was able to measure pairs with that refractor as faint as fourteenth magnitude, and on good nights could resolve stars as close as 0.21” . . . . . . . which should give you something to shoot for on a night when you’re looking for something to do.
In the meantime, some of the other Persean stars on Mr. Doolittle’s list have ignited a smoldering curiosity which should be bursting into flames six months from now, so I’ll see if I can work my way back again in late August or early September when Perseus returns to the zenith.
Meanwhile, Clear Skies! 😎