This is a DSC-60 Project observation – for project details go here.
|]||Iota Cancri||08h 46m.7||+28° 46′||4.2, 6.6||30″||307°|
I was looking for what I thought was the “Winter Albireo” – Iota Cancri, which is in my eyes a good imposter of Albireo. I enjoyed it immensely – beautiful double, but the real fun started when I got back in the house, sat down with my notes and discovered I had not been looking at what others call the “Winter Albireo” at all. What’s more, I think I can make a case for my candidate – Iota Cancri, over the more popular one, h3945. But first, the background.
Iota is fascinating in its own right and quite easy to find on a spring evening since its one of the brighter stars in the dim region between Leo and Gemlni that we know as Cancer the Crab. If you can find the Beehive (M44) , a large and beautiful open star cluster, then Iota is the 4th magnitude star nearly due north about one fist -held at arms length – from M44..
This is one of the doubles featured by Guy Consolmagno and Dan Davis in their beautiful observing guide, “Turn Left at Orion.” The primary is a giant and while the two stars are gravitationally linked, they are quite far apart as doubles go. (Almost as far apart as the real Albireo and a bit farther apart than what others call the “Winter Albireo.”) Consolmagno and Davis note that if you were on a planet that orbited the primary star, you”would see its companion as a very bright star, about half as bright as the Full Moon. ” From a planet orbiting the secondary, the primary “would look about four times brighter than the Full Moon.” I love to carry images like that in my head to the telescope and ponder them as I observe.
But I’m getting side tracked. See, Iota Cancri looks so much like Albireo to me that I have written “Winter Albireo” in the margins of two of my observing books next to the Iota Cancri entry. When I saw those notes as I was planning this observing session, I assumed that was it’s accepted nickname – wrong! Seems like the only one calling Iota Cancri that is me. Or at least I can’t find any other reference to it as such. What I did find, as I said, is that another double I’ve never seen is called the “Winter Albireo” by many others and is generally regarded as too frequently neglected. Well, mark me down as “neglectful” – I’ve never seen Herschel 3945, but now I am really curious, so it has moved to the top of my “to be observed list!” And when I do observe it I may change my tune, but from what I’m reading I just don’t see how they give it this nickname while ignoring Iota Cancri.
I love Albireo. Nothing can replace it. My observations of it go back nearly half a century and I’ve never tired of looking at it. I always see it as gold and blue – very easy to split and with dramatic contrast.
And when I looked at Iota Cancri on this occasion I saw a wonderful yellow – pale yellow – primary and a beautiful, deep, sky-blue secondary. So I will readily admit that my idea of the “Winter Albireo” doesn’t quite measure up to the summer one, but it comes close. I confirmed this by getting a couple hours sleep, then getting up and observing the real Albireo while the memory of Iota Cancri was still fresh.
So when I got in to write this report I decided to check on the spectral types to see if that gave me a solid guide to these color differences. Guess what? It does – but it opens more questions. The Albireo primary is a K3, the Iota Cancri primary is G7.5. Look at the chart in the Star Colors post and you’ll see that we tend to perceive G stars like Iota Cancri as “yellowish white.” Whereas K stars, like the primary of Albireo, tend more towards the orange. So “pale yellow” for Iota and “gold” for Albireo seem to fit. The secondary’s also match the spectral classes. The Albireo secondary is B8 and the Iota Cancri secondary, A3 – that makes the Albireo secondary a somewhat richer blue, but they both tend towards blue.
Yes, this is splitting hairs because colors are so difficult to perceive, but having observed them within a matter of hours of one another, I did come away with just that impression – Iota Cancri makes a credible imitation of Albireo, but in the end Iota is just not as intense.
And what about the star so many do label the “Winter Albireo?” There my curiosity is really sparked. The h3945 primary is a K0 – so that pushes it over closer to the yellowish-orange of the real Albireo primary. So far so good. What throws me, though, is the spectrum of the secondary. It is listed as F0! That puts it in the white category in terms of our perception – or certainly a very,very pale blue. Not nearly so blue as the B8 of Albireo, or the A3 of the Iota Cancri secondary. These deductions based on spectral class also match the description in “Turn Left at Orion.”
Herschel 3945 gets attention under the “Also in the neighborhood” category of “Turn Left at Orion” – just not the neighborhood of Iota Cancri. They link it with observing an open cluster, NGC2362, in Canis Major. They note that the primary is a “distinct red, while it’s companion may appear white or yellow.” Huh?! Does that sound like Albireo to you? Red and white/yellow? What happened to gold and blue? I find their description in tune with the spectral classification, but out of tune with Albireo. Still, they note that this double is more popularly known as ‘The Winter Albireo.’ Indeed the color contrast and separation are reminiscent of Albireo…” Oh boy! Color contrast maybe, but not color. Now I really have to get a look at these stars!
So I’ll report back here after I’ve looked at h3945 and we’d love to hear from others on how they see these three stars. Here are the vital statistics for each.
|Beta Cygni||19h 30m.7||+27° 58′||3.1, 5.1||34.4″||54°||K3, B8|
|Iota Cancri||08h 46m.7||+28° 46′||4.2, 6.6||30″||307°||G7.5, A3|
|h3945 (Canis Major)||07h 16m.6||-23° 19′||5, 5.8||26.8“||52°||K0,F0|
Just looking at the stats, they do all look pretty similar until you get to spectral class and in that I would think Iota Cancri would be a better match.
And h3945? How does Sissy Haas see it? Well, she reports the stars “are bright citrus orange and royal blue: the colors are seen vividly and in strong contrast.”
And, of course, we have discussed many times the variables involved in seeing color differences – but there may be something special here in h3945. I can’t wait to see for myself.
Update: March 12, 2011
Conditions certainly could have been better, but seeing was just a bit below average and I found a hole through the bare tree branches where I had a clean shot at h3935 and guess what? It’s every bit as beautiful as folks say – but in my book it is not the “Winter Albireo.” In fact, the colors remind me more of Rasalgethi (Alpha [α] Herculi) – orange going to red with a blue companion. I think one thing that separates it from Albireo, besid the colors, is the primary just isn’t as dazzling. With Albireo you’re seeing a magnitude 3.1 primary, whereas h3945 is nearly two magnitudes fainter.
I would also say that I’m looking through a lot of atmosphere – I caught it when it was about 24 degrees above my southern horizon which is only a couple degrees lower than it is at transit, so I can’t do much better. I suspect that contributes to the redness however. Folks in the southern states have a better shot at this beauty. I used the Televue 60 with a 10mm Tak for 36X which to my taste gave very nice proportions. It was just as attractive in the TV85 with a 13mm Nagler – 46X.
Want to take a look for yourself? Here’s a finder for the “Winter Albireo” aka. h3945.
Now that said, the overall impression of the true ALbireo in a 60mm scope at 72X left me duly dazzled – and smiling broardly at the winter imposter. Oh Iota Cancri is nice. It is wonderful, really – it just isn’t Albireo. But it’s a darned good substitute on an early Spring evening. Hmmmm. . . and maybe that’s the solution. When I made this observation it was still winter and Iota was well placed at a reasonable hour. So i guess that makes it a winter star. But I have to admit, it feels more like a spring star. So maybe I should give the Big Dog his “Winter Albireo” regardless – and give the Crab a Spring Albireo!