The northern tip of Perseus is a great location for tracking down several splendid multiple stars — and right at the top of the Persean peak is where you’ll find Eta (η) Persei.
My first look at it came on September 25th in a 90mm f/10 refractor. Using a 12.5mm eyepiece (73x), I found the primary was a splendid yellow-red, but couldn’t really detect any significant color in “B.” I was using the Haas book, which only lists data for the “A” and “B” components. But I noticed several faint stars rather close to the the primary, so I checked the Night Sky Observer’s Guide (scroll down a bit to see the reference) and sure enough, I found a third component listed there, “AC”. The data also includes a “CD” component, but at magnitudes of 9.8 and 10.3 with a separation of five arc seconds, I skipped them, deciding those two were very likely to be lost in the glare of the primary. (Note of 10/5/2014): The magnitudes of 9.8 and 10.3 for the CD pair turned out to be inaccurate — we’ll get to that in just a moment).
|Eta (η) Persei (Miram) (Σ 307) HIP: 13268 SAO: 23655|
|(AB is H IV 4, AC is H VI 21)|
|RA: 02h 50.7m Dec:+55° 54′|
|STF 307 AB:||3.76, 8.50||31.40″||295°||2012|
|STF 307 AC:||3.76, 11.61||64.00″||269°||2014|
|SHJ 34 AE:||3.76, 9.24||242.90″||297°||2012|
|WAL 19 AF:||3.76, 11.44||57.40″||24°||2012|
|WAR 1 CD:||11.61, 12.70||5.10″||116°||2012|
|Distance: 1331 Light Years|
|Spectral Classification: A: M3 or K3 B: A0 C: B E: A2|
So, back again on October 17th with the bright moon at my back – but doing it’s best to shine into my eyepieces – I went in search of “C” using a bit more aperture, a Meade five inch refractor. This time I found the primary had a dark golden hue tending toward red and “B” was clearly blue. I also noticed that “A” and “B” pointed to the middle of three stars which formed the top of a nice “T” just to the west of Eta (η) and its companions. The moon was illuminating a bright haze in the sky, so transparency was not the best. There was only one star near the primary that was close to the 9.8 magnitude listed for “C,” but in order to match up with the published data, the position angles of “B” and “C” would have to be reversed. Since there was nothing else to be seen in the right places, I felt pretty sure that was what had happened.
But not sure enough to bet the farm on it — or a telescope. So I went back the next night with the big gun, my six inch f/10 refractor, and took another look — the sky was still bright, but the haze was gone, so the transparency was much better. With averted vision, I could just barely detect a star very close to the published position angle for “C” — but it was a whole lot fainter than the 9.8 magnitude that was shown for it.
(Another note: This was written in October of 2010 when the magnitude for “C” was shown as 9.8. As of 10/5/2014, the WDS has updated the magnitude of “C” to 11.61, which is a much better match with what I saw in the six inch refractor. As a result, much of what follows no longer applies, but it’s still provides an interesting look at the process of discovery we all go through as we learn about double stars. There’s a message here: nothing stays the same forever, including stars! For another look at Eta Persei, read this post which was written two years later).
After checking various places to see what I could find, I found that the situation is about as clear as meandering mud in a Martian moraine. What it seems to come down to is that there isn’t a 9.8 magnitude star at a position angle of 268 degrees. I made a sketch which is reproduced here and have labeled the magnitudes of most of the stars in it. What it shows is a magnitude 11.5 star at about 280 degrees that is about thirty arc seconds past the 66.6″ shown for “C,” and a 13.4 magnitude star that is very close to the published 268 degrees and also is at about the correct distance.
So which one is the real “C”? Is it a variable star? Has its light been dimmed by a cloud of that ubiquitous dark matter that no one has been able to identify yet? 😉 I don’t know, but after reading Jim Kaler’s summary of Eta Persei, it appears that in all likelihood neither “B” or “C” are really gravitationally linked to the primary — “B” would have to be 11,500 Astronomical Units from the primary and would take 350,000 years to orbit it . And to complicate matters, there are also “E” and “F” stars, which probably really are not components because they’re probably really not gravitationally linked either. Clear as Martian mud.
Whatever the case, the “A” and “B” components of Eta (η) Persei are well worth taking a look at. Haas describes them as 60mm showpieces, which they certainly are, and describes the colors as “apricot orange and cobalt blue.”
Not content to leave things where they were, I rolled out of bed at 5 AM on the morning of October 20th with intentions of taking another look at Eta (η), but this time under dark skies. I was also after one last look at Comet Hartley-2 before the moon made it difficult to see for the next week. Using an 80mm AT f/6 to look at the comet first, I found it right in the middle of Auriga and studied it closely for about fifteen minutes. Then I pointed the scope up at Eta (η) Persei while the sky was dark, and again — with averted vision — I found the 11.5 magnitude star about where “C” was supposed to be, but again — it was too faint for me to be convinced it matched the 9.8 magnitudes listed for it. And I knew the 80mm scope wasn’t pulling in the 13.4 magnitude star shown on the sketch which I had seen in the six inch scope.
No doubt I’ll return to Eta (η) Persei when the skies are dark and the weather cooperates, but daylight was due soon, so I moved on to other things. I lingered over M42 and the Trapezium, swung up to the Pleiades, and could see that the sky was starting to brighten quite a bit. I packed everything up, took it in the house, and grabbed my four-legged companion’s leash, and the two of us took a short walk. Even though it was getting lighter, I couldn’t quit looking up at the sky because the crisp transparency made it absolutely irresistible. After about a fifteen minute walk, we came back into the drive and I stopped to look up once again. All the fainter stars were gone by that time, but all three of the stars in Orion’s belt could be seen, and I could still pick out about five stars in the Pleiades. I watched those fade rather quickly and turned back to Orion. Gradually each of the three belt stars were extinguished by our own star, then Betelgeuse became hard to see, and finally Rigel began to fade into the blue sky.
Daylight wasn’t going to be denied, but I really felt like I had been robbed of the stellar splendor of that beautifully transparent, star-filled sky I had spent the last two hours with. Blue and cloudless at it was, the daytime sky just couldn’t match the awe I had felt under that black sky glowing with stars.
The observations of Eta (η) Persei were made on September 25th, October 17th, 18th, and 20th, 2010, with several refractors – an 80mm f/6 AT-LE, an Orion 90mm f/10, a Meade 127mm f/9.3, and a custom built six inch f/10.