• Choose a post by category or constellation

  • Learn the Night Sky

  • Search strategies

    Use the Search box below to find doubles by popular name, RA, or telescope size. For example, a search on "15h" will find all doubles we've reported on that have an RA of 15 hours. A search for "60mm" will find all doubles where we used that size telescope.

Captured by Color: The Multiple Thrills of Xi (ξ) Boötis

What in the world is it about some of these stars that keeps me glued to the eyepiece for more than an hour at a time?  This one I found to be irresistible, magnetic, stunning — heck, it was even charismatic in a chromacolor sort of way.  It really was that good.

Boötes, the Hunter, on the hunt for a colorful pair of stars. (Stellarium screen image with labels added, click on the image to enlarge)

I have no idea now where I first came across a reference to Xi (ξ) Boötis, but at a visual magnitude of 4.7, it’s one of the many gems of the sky that glow in the dim fourth and fifth magnitude range that escapes easy visual detection — yet it’s relatively easy to pick out of a reasonably dark sky once you’ve identified its location on a star chart.  I really wish I knew how many more are twinkling up there in relative obscurity — there must be hundreds.

Fairly easy to locate, it can be found about eight degrees due east of Arcturus, or about the same distance directly south of Izar, since it occupies one corner of an equilateral triangle anchored by all three stars.  I was going from memory when I aimed a TV85 at it, and I landed on Omicron (ο) Boötis instead, which absolutely would NOT split.  And for good reason, too — it’s only a single star.  🙂

But that dim light came on upstairs soon enough.  I looked at a chart,  moved a few degrees to the northeast — and when Xi (ξ) hovered into view, my hour of stellar bliss began.  Wow.

Xi (ξ) Boötis forms an equilateral triangle with Izar to its north, and Arcturus to its west. (Stellarium screen image with labels added, click for a larger view)

Xi (ξ) Boötis  (Σ 1888)        HIP: 72659    SAO: 101250
RA: 14h 51.4m    Dec: +19° 06′
*****     Magnitudes           Separation         PA         Latest Data
AB:      4.76,   6.95                 5.6″            302°        WDS 2015
AC:      4.76, 13.83                69.9″           342°        WDS 2015
AD:      4.76, 11.73              158.6″           286°        WDS 2015
AE:      4.76,   8.65              271.5″             98°        WDS 2015
AF:      4.76,   9.20              337.5″             37°        WDS 2015
Distance: 22.1 Light Years
Spectral Classification:  G8 (A), K5 (B)

NOTE: Magnitudes, separations, and PA updated to match current WDS as of 12/2/2016

My instrument of first approach was a 12mm Radian (50x), which prompted me to sit up straight and look closely.  At first glance, I saw only a single star, but with a bit of intense staring, the very small dot of the secondary revealed itself.

The larger one beams back at you with a soft and pale radiance, the smaller one gleams very intensely and richly . . . (East and west reversed to match refractor view — TIP: turn off the lights for a better view!)

This was really a splendid sight — the primary was a light shade of glowing red with a touch of orange, and there was just enough white mixed in to lighten up the overall color.  The secondary was an intense little spot of light virtually identical in color, but much richer.  The contrast between those two colors reeled me in so quickly I didn’t know I had been hooked.

The reported colors on this star have been all over the place.  In a 60mm at 25x, Haas describes it as a “bright white star touching a vivid little gray star.”  I haven’t seen it in a 60mm scope, but I’m curious as to whether I’ll see the same colors.  She credits Webb with “yellow, purplish red,” and Hartung with “yellow and deep orange,” which was at least closer to what I saw.  The always quote-worthy Admiral Smyth described it in The Bedford Catalogue as

“A binary star, in the left knee of Boötes; being the northernmost of the four stars forming his leg, and 10° east of Arcturus.  “A” 3 ½, orange; “B” 6 ½, purple; the colors in fine contrast.”   (p. 328)

And somewhere I saw a reference to it as red and blue.

In comparison to the sun, these two stars are somewhat of a rarity, having both less luminosity and less mass than our star.  It’s their relatively close proximity to us that keeps them from being out of reach of my telescope, and is responsible for the dazzling show I saw.  More on Xi (ξ) can be found here  on Jim Kaler’s Star Site.

But to get back to the current observation  —-  with the seeing wavering between average (III) and medium poor (II),  I couldn’t see any reason not to try a 10mm Radian (60x).  That pried the two stars apart just a slight bit more, leaving me hungry for a larger slice of dark sky, so I reached down into my eyepiece box and pulled out an 8mm Radian (75x).

Ahhhhhhh   …………   that went a long way toward curing my craving.  But as usually happens after appetite appeasement, I developed a strong thirst.  So my right arm reached down into the depths of the eyepiece box and came out with a 6mm Radian — and 100x.

What blessed bliss!  I traversed that field of view several times, lingering over every visible star in it, and in between traverses, I took another drink of those vibrant colors.

Located about five arc minutes east of the primary is a trio of ninth magnitude stars oriented on a north-south line which kept calling to me.  They reminded of me another stellar sight I’ve spent many an evening or morning with, Eta (η) Persei.  Like this one, it also has a distinctive reddish glow which is very appealing, and it also has a line of three stars spread out in a row opposite the primary, but on the west side instead.  And it’s a multiple star as well  ………….

……….  which I’ve neglected to mention so far.  Stunned as I was by the view, I still couldn’t help but suspect that some of the dim stars surrounding Xi (ξ) could be companions, but the data I had at that moment only provided the statistics for two stars.  So the next morning I checked that old standby, the Washington Double Star Catalog, and found Xi (ξ) had another four companions scattered around it!  I was able to go back to the sketch I had made and identify all of them except for “C.”  At a magnitude of 12.6, it might be within reach of the TV85, but I really think the separation of 71.6″ is close enough for it to drown in the glow of the primary.  Shouldn’t be any problem with four inches of aperture or more, though, so I’ll try again on the next clear night.  In a six inch scope, it should even be possible to detect some color in the “D,” “E,” and “F” companions.  (I did pry “C” free from the glare a few days later, and added the inset at the lower right to the sketch above — see the first comment below).

And I discovered something while I was sketching this star field.  I was using a red flashlight with an adjustable dimmer, but as I’ve found many times before, despite keeping the light as low as possible, it still affects my dark adaptation just a bit.  Not for long, but enough that when I leaned back over the eyepiece, it took about fifteen to thirty seconds to get back to normal.  What I noticed, though, was when I first looked into the eyepiece, the colors of the primary and secondary were richer and the background sky was blacker.  I suppose that’s not surprising, considering the slight loss in dark adaptation, but the effect is mesmerizing.  If I hadn’t been hooked already, I certainly was now.

So imagine a velvet black background that is as devoid of light as it can be.  Glowing at the center of it are two red-orange dots of light — the larger one beaming back at you with a soft and pale radiance, the smaller one gleaming very intensely and richly at very close to the same color.  Now try to pull yourself away from it and go on to another star.

I tried.

But I couldn’t.

Believe me, I tried about a dozen times — but every time I pulled back from the eyepiece and looked up at my next target, I was consumed with a craving for another round of those vibrant reddish-orange photons.  So back to the eyepiece again  …  and again   ……..   and again    …………..    and several more agains.

And when I finally did succeed in overcoming Xi’s (ξ) magnetic pull, it was to take a peek at Izar — another reddish-orange star.

What can I say  — I’m probably a few hundred thousand parsecs past hope.  😉

Advertisements

4 Responses

  1. July 9th, 2011, 1AM

    I had found an eight inch Celestron SCT, of all things, sitting at my door earlier in the day (which would be the afternoon of the 8th), and of course, I had no idea how or why it got there. But I did the normal thing anyone would do in that case — I opened the box. 🙂

    And inside was an immaculate black tube that was desperately in need of some starlight. Being an agreeable sort when it comes to that kind of thing, I was more than willing to help the poor thing out by installing it on a mount.

    Now, I’m not one to lean towards using SCT’s for double stars. Although …… I will say if they’re very well collimated, they can do a darn good job. This one was pretty close right out of the box, but it needed a bit of tweaking. After I was sure it had acclimated to the outside temperature, I pointed it at Polaris and found all was in good shape except for a very irritating spike of yellow-white light shooting out of the left edge of the Polarian primary and obliterating the secondary completely.

    Not good, or as someone I once knew used to say after shaking their head and clicking their teeth: “Very un-good.”

    It took about five minutes to get rid of that spike, and when I did, I found myself staring at an almost perfectly round yellow-white ball of light (the primary) with a pinpoint of white light (the secondary) dancing about 18.6″ arcseconds away from it — give or take a few tenths.

    Bingo! And sehr gut!

    And I knew where I was going next, too.

    Swiveling the scope around to the southwest, I spotted Xi (ξ) in the sky and went to work. (Note: Xi is pronounced Chi, as in sky — you need to know that to get the full effect of that sentence. 😉 )

    And I must say I was really impressed with the view at 63x with a 32mm Celestron Plössl — the colors were the same as I had seen in the post above in the TV85, and the primary and secondary were clearly distinct, separate globes of light. And everything else was where it was supposed to be, standing out nice and sharp against a dark background, despite a nearby waxing quarter moon about thirty degrees to the south and west.

    But “C” was missing — still. I worked up through several eyepieces, and finally I thought I saw it in an 11m TV Plössl (182x), but it was really elusive. I tried, but I just couldn’t hold it in view.

    A 9mm UO Ortho (222x) was a bit better, but that faint point of fleeing light just would not stay where I thought I saw it for more than a few micro-seconds. Just as I expected, it was a battle between the star’s weak light and the strength of the glare from the combined glow of the primary and secondary.

    But I wasn’t leaving Xi (ξ) high and dry. So I thought I would try something a bit different, a 7mm Faworski Ortho, in hopes of reducing some of the scatter from the glow. I don’t know if it made all that much difference, or if it was just the additional magnification (286x), but I found that by staring directly at the “A-B” pair, I could see “C” pop in and out of view about right where its PA of 340 degrees predicted it should be. Every now and then the atmosphere would cooperate for a few tenths of a second and I could spy “C” with direct vision, but mostly it was an averted vision affair.

    So there you have it. All six stars of the Xi (ξ) Boötis system — five wrestled out of the dark of night with a small 85mm refractor, and one with a 200mm SCT. And I have to hand it to the SCT — considering the moon was not making its chore easier, it did a stellar job of it.

  2. John,
    I was able to get XI Boo recently but NOT the “C” companion. I will try to get it next March or April with my refractor. I’ll work up this sketch and send it to you.
    Steve McG.

    • Hi Steve,

      I just took a look at the latest WDS data on Xi Boo and found the magnitudes for both the C and D components have been updated. C has been changed from 12.6 to 13.83, and D from 9.6 to 11.73. Both of those are considerable reductions in magnitude, and if both of the reductions are correct, that would account for why C is eluding you.

      I see in my comment above that I had a very tough time catching C in an eight inch SCT, which argues on the one hand that it’s fainter than the old magnitude of 12.6, but on the other it argues that it’s not as faint as the current magnitude of 13.83. So that magnitude is still suspect. Although . . . I just checked the UCAC4 magnitudes on C and they all point toward 13.83 as being correct. So now I’m wondering whether I actually saw C in the eight inch SCT — not likely if it’s at 13.83.

      D should be evident in the 9.25 inch SCT you were using, even at a magnitude of 11.73, so I would suggest applying a strong dose of averted vision to it. The UCAC4 data suggest that magnitude is correct, also.

      One thing worth noting, which I’ve pointed out before in several posts. It’s not uncommon for the published magnitudes of double or multiple stars that were first discovered between William Herschel’s era and the early 1900’s to be wrong. Many of those need updated. I’ve caught more than a few errors over the years, and I should have caught the errors in the C and D components of Xi Boo, except at the time I wasn’t aware how common those magnitude errors are.

      So, the moral of the story is, if you’re suspect a magnitude error, check the star against magnitude data in catalogs such as UCAC4 and URAT1.

      John

      • Thanks, John. That helps a LOT and I’ll “see what I can see” next time I have the opportunity. That’ll be next year – I’ll put it on my list.

        Steve McG.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: