Xi ( ξ) Cephei (Kurhah)
RA: 22h 04m Dec: +64° 38′
Mag: 4.4, 6.4 Sep: 7.9″ PA: 275°
Dist: 100 ly
Spectral Classification: A3
ΟΣ461 in Cepheus
RA: 22h 04m Dec: +59° 49′
- AB Mag: 6.7, 11.4 Sep: 11.1″ PA: 297°
- AC Mag: 6.7, 10.0 Sep: 88.9″ PA: 41°
- AD Mag: 6.7, 7.8 Sep: 184.7″ PA: 73°
- AE Mag: 6.7, 11.4 Sep: 237″ PA: 38°
Note: Click image at right to see all the data on this complex system from the Washington Double Star Catalog.
Five star isn’t a quality rating -it’s how many visible stars there are in this combo – or perhaps more if you apply enough light grasp. But let’s start with Xi ( ξ). It’s a piece of cake to find and yummy, too!
Haas rates it a “showcase” double and it deserves the title. Xi ( ξ) is an easy split – a 4.4 lemon yellow star and a 6.4 violet companion almost 8 seconds apart. While a 60mm should handle it, I found it very easy with the 76mm, even at 38X – and just plain pretty when I used a 13mm Plossl delivering 92X. I found it with no trouble on the night of a full moon – in darker skies it would be even easier. Cepheus forms a crude “home plate” with five bright stars, the faintest approaching magnitude 4. In the middle of the square part of this figure is Xi which at 4.4 I couldn’t see in the moonlight, but it stood out easily in the finder scope with no competing stars of similar brightness to confuse me.
Xi( ξ) serves as a guide to our second prize in the interior of Cepheus, the five-star multiple known as ΟΣ461. Now this was more challenging with plenty of nearby stars to confuse, but the beauty of it is this: It lies right on the same hour circle – almost to the second – as Xi ( ξ). So if you’ve found Xi, all you have to do is move due south a bit less than 5 degrees. (Which way is south? It depends on the time of year and night – but simply find Polaris. Look at the direction to Polaris and move in the opposite direction. Your finder probably provides a rough five degree fov to act as a guide as to how much.)
That’s the easy part. Now you need to be careful about the identification because I found at least one field that seemed to be the right one, but the star pattern I saw was simply too large. You need to be aware of what you are looking for – the chart below should help – and you need to be aware of the field of view of your eyepiece. (I was using one with close to half a degree field of view.) This whole group of stars fits in about four minutes – so that meant it would take up a little more than one-eighth of the diameter of my eyepiece field. Armed with that information, you can make short work of finding this. Without it, I spent quite a bit of time and frankly, part of what was confusing me was a little piece of text in the Haas book. But first take a look at this chart.
Click on image for larger version.
My problem is Haas says:
“The shape is pretty – three white stars in a straight line, all exactly alike, with a smaller star off to one side.”
When she says “exactly alike” I take it to mean roughly the same magnitude – and what jumped out at me were the stars I have labeled A, E, and X seem to fit this description – but “X” is not part of the combination, it just fits her description. You could say she means A, C, and E – but E is so faint (mag 10) that I had to look hard for it under these conditions and a 3 magnitude drop doesn’t fit the wording “exactly a like.”)
Bottom line – whether Haas confused “X” as part of the multiple star or not, I think other observers might – I did, going on her description. It wasn’t until I started examining my notes and comparing them to Starry Nights Pro screen – which is where the image comes from, as well as the distances and PAs – that I noticed the problem.
In any event, ΟΣ461 is worth a second visit on a moonless night. This multiple is attractive – and once I got over the confusion, I liked including “X” in this equation – “X” makes for an especially pretty grouping whether it belongs to the gang or not 😉
Filed under: 4. Choose a Constellation:, Cepheus | Tagged: Cepheus, double stars, ΟΣ461, Xi Cephei |
John Nanson
Greg Stone
Star-Splitters 
I revisited ΟΣ461 with an 80mm scope tonight and didn’t have a bit of trouble locating it. Haas’ “three white stars in a straight line, all exactly alike,” is the key to identifying this multiple. The other is to keep in mind that those three stars are wide apart so this multiple “splits” easily at low power and makes a very distinctive asterism.
Well those stars split easily – and I still think one of the three is NOT part of the multiple – and the first combo – the AB does not split for me in the 80mm. These are 11 seconds apart – but with an almost five magnitude difference. I’m tired. maybe on another night…
As I reread my original post and first comment I don’t think I made it clear that I had a problem splitting AB on both nights. In each case I was seeing five stars only if I counted “X” in the mix and I don’t think it belongs.
Last night – under excellent conditions and using a new (to me) Orion 110mm ED refractor I was able to get a split of AB – just barely. I used a 5mm eyepiece yield about 154X.
This still is worth another visit – in fact, it could become a regular. This time I approached it simply by prowling around north of Herschel’s Garnet Star. That star really stands out, so it’s a good starting point. And this little asterism with three stars of even brightness in a row and one off tot he side really jumps out at you as well. The only real challenge is figuring out which star is which and then trying to make the split of AB.
Sept 28th, 2010
While I was doing some exploring in Cepheus, I saw Xi shining in the middle of the Cephean rectangle and couldn’t resist taking a look – one of those stars I have on my list but can never quite seem to get to.
And it was well worth it. In fact, fantastic is the first thing that came to mind as I looked at it for the first time. It’s a close pair, and definitely the showpiece that Haas considers it to be. The primary appeared white with a bit of yellow in it, and the secondary was white.
I was using two scopes on this particular night – a 127mm Meade AR-5, f9.3, and an Orion 90mm, f10.1. The view in the Meade with a 14mm Radian (84x) was one of two pinpoint sharp stars, but a better view was to be had in the 90mm scope armed with a 20mm Plossl (46x), mainly because the stars were a bit closer together, which just strikes me as a bit more pleasing.
October 3rd, 2010
Tonight I had an Antares 105mm f14.3 for exploring, with a 60mm f16.7 mounted on it. Clouds were moving in quickly, but I wanted to get a quick look at Xi before I lost it to the advancing wave of moisturizing marauders.
I took a quick look in the 105mm scope – just as pleasing as the view in the 127mm had been – but what I really wanted to do was catch it in the 60mm. I did, but just barely. The split was clean with a 20mm Plossl (50x) – two very sharp points of light very close together and clearly separate – just the way I like them.
The cloud attack was full of holes, so I sat there for about fifteen minutes watching the pair of stars pop into view, then fade into the clouds, and then emerge quickly again, almost as if someone was turning on two lights in the distance.
After a very satisfying but short observing session, I packed up and got everything inside before the drizzle that was forecast moved in.
This one is well worth repeated observations, so take a look at if you have the chance. Easy to find and easy to like.
Thanks for this; I had made the mistake of thinking the ‘fifth’ bright star was part of the system. Now I’ve got to go back to it! Still, at least I’ll know what I’m looking at – I couldn’t find a lot of info about O∑461. This blog was really useful!
You’re more than welcome, Andrew — glad you found this blog to be useful.
The whole area in and around Cepheus can keep a person busy from dusk until dawn. I was back there a few nights ago looking at Xi and Delta Cephei, and then slipped over to the opposite side and spent some time on Beta and Kappa. And although it’s not a double, the deep orange color of Mu Cephei is always worth a long lingering look as well.
John