A Lulu of an Alula Australis: Xi (ξ) Ursae Majoris

Now what kind of a title is THAT?  Well, I can explain.

But instead of rushing into THAT, why don’t we first divert our attention to some intriguing background, bearing in mind that a quick explanation is always the least interesting.

You’ll have to trust me on that one.  😉

So hang on, here we go  ……………………

There is nothing more unpredictable than a photon deprived Star Splitter.  You really can’t tell what one of these characters is likely to say or do or think or write.  The first sign is when one of ’em starts a reasonably rational sentence and then quite suddenly veers off into the most outlandish statement — and does it with a perfectly straight face.

I speak from experience.

When I was trading emails a few days ago with Greg about tripods, I found myself typing statements such as — “Tripods are a lot like humans.  Except they stand on three legs instead of two.”

The warning signs were clear.

The cure is well known.  It’s a simple process of activating a few synaptical switches in order to allow the flowing photons to nourish the neurons in the afflicted person’s mental matter .

But — for that you need clear skies.  Or at least slow-moving sucker holes.

Well, I was in luck — and probably none too soon.

Fortunately, between the NOAA infrared radar and the Clear Sky Chart for my location, I had a hint that the cloud covered skies above me would probably part for a short time shortly after midnight on March 25th.  So I set up my Celestron 102mm f10 refractor under cloudy skies and waited.  And by 1AM, holes began appearing in the sky, and at exactly 1:30 AM I was back on the road to something like sanity.

And I had an observing plan ready to go, too.  The thanks for that go to that distant Star Splitter and Guru of long focal length achromatic refractors, Neil English of Scotland.

Earlier this same evening, Neil had sent me a message describing several stars he had been chasing with his four inch f15 refractor, most of which I was familiar with.  But one new name jumped out at me:  Xi (ξ) Ursae Majoris.  I had heard of it, but had never looked at it.  I grabbed my Sky and Telescope Pocket Atlas, found it, and committed it’s location to memory.  Fortunately, despite the photon deprivation affliction, my memory was still functioning three hours later when the clouds cleared out.

It’s an easy one to find — another stroke of good fortune, because I knew the clearing wasn’t going to last for too long.  It shines at a magnitude of 3.8, just ten degrees north of Zosma, aka Delta (δ) Leonis — and Zosma can be found holding down the north corner of the distinctive triangle of stars that mark the location of Leo the Lion’s rear quarters.  I had just spent some time in this area a few weeks prior in search of photonic stimulation, so I knew it rather well.

A wide view of Ursa Major, The Big Bear, waving his three feet above an unsuspecting Leo the Lion, with a hapless Leo Minor caught in the middle. (Stellarium screen image with labels added – click on the chart for a larger view)

But back to that name — Alula Australis — and the overdue explanation.

Kaler credits the name with being derived from an Arabic phrase which means the “first spring” — as in leap or jump — and Australis refers to it as being the southernmost of a pair of stars.   The other star of the pair is Alula Borealis, located one and a half degrees to the north, a more challenging double with magnitudes of 3.5 and 10.1, separated by a very deceptive 7.1″.

This pair of stars — the northern and southern Alulas — represent one of the three feet at the end of the Big Bear’s legs which can be seen waving below his large body as he races in circles around the north celestial pole.  The chart above shows the three feet and the names of the corresponding stars.   As Greg just pointed out to me, the foot we’re after is the one closest to the rear of Leo Minor, the one that looks like it’s poised to give him a swift kick in the  — well — in the hind quarters.  Actually, there are several different ways to visualize the bear and his feet — take at look at these charts in another post Greg has done.

The twin Alulas poised above Leo’s rear quarters. (Stellarium screen image with labels added, click to enlarge)

And as for the “lulu” — after you feast your eyes on the ethereal double yellow glow of this pair of stars, you’ll understand.

Xi Ursae Majoris (Alula Australis)
(Σ 1523)      HIP: 55203    SAO: 62484
RA: 11h 18.2m   Dec: +31° 32′
Magnitudes: 4.3, 4.8
Separation:  1.6″
Position Angle: 196°  (WDS 2012, orbital info here)
Distance: 27 Light Years
Spectral Classifications: F9, G9

So I aimed the long black tube of my refractor ten degrees north of Zosma, looked in my finder, distinguished Alula Borealis (it’s reddish orange) from Alula Australis, centered that last one under the cross hairs, and sat down to see what I could see in a 20mm TV Plössl (50x).  And what I saw was a very distinctive yellow star.  Just one, not two —  it would be a bit of a stretch to call it elongated at that magnification.  But it did seem to be slightly oval.

Note how this wonderful sketch of Xi Ursae Majoris captures the unique yellow glow of this pair of stars! Used with the permission of Jeremy Perez. Click on the image for a larger view.

What caught my attention, though, was that yellow color.  I really can’t remember seeing a star anywhere close to that shade of yellow.  It wasn’t a bright yellow — as in dandelion yellow — but more of a very deep yellow, almost as if it was leaning in the direction of red or orange, but never quite able to get there.  The beautiful sketch shown here by Jeremy Perez captures it far better than I can describe it.   More of Jeremy’s stunning sketches can be see on his web site, The Belt of Venus.

After I got over being overwhelmed by the stunning color, I started up the magnification ladder to see if I could pry this star apart.  The seeing wasn’t particularly great — Roman numeral II on this chart pretty well covers it.

At 50x in the 20mm Plössl seeing wasn’t much of a factor, although there was some unsteadiness.  So I decided to give 80x a try with a 12.5mm Tak LE, and this time I could easily detect an elongated egg, or figure eight, shape.  A 10mm Tak gave me 100x and just the first hint of a hairline split — when it would hold steady.  But it was so close I could hardly call it satisfying.  Since the seeing looked like it would tolerate a bit more magnification, I decided to see what would happen at 133x with a 7.5mm Tak.

And, when it would stop bouncing up and down and from side to side — which wasn’t often, and often not for long — it was a very clean split.  And very impressive.

The best way to describe this pair of stars is to say they’re the same —  same color, same magnitude.  Even though there’s half a magnitude of difference between them, I couldn’t tell it.    And just going from memory — I didn’t have a chance to look at it on this particular night — it seemed to me the two stars were more delicate in appearance than the Porrima pair.  And they’re a fast moving pair, too — look at the orbital chart referenced in the data line above, and you’ll not only see that the position angle is changing rapidly, but the separation just happens to be at it’s closest from 2007 to 2013.

And there was that color again!  Based on their stellar classifications, there is a slight difference in color between the two components, although I certainly couldn’t detect it.  What I did see, though, was that ethereal yellow-leaning-toward-orange-but-not-quite-there-yet glow  —-  times two.  And I wanted more of it!

There it was — an ethereal yellow-leaning-toward-orange-but-not-quite-there-yet glow —- times two — and I couldn’t get enough of it! (East & west reversed to match the refractor view, click for a larger version).

So, considering that the image would hardly hold still at 133x, I recklessly reached for a 6.3mm Celestron Plössl, putting me at 159x.  And that was really at the limit of what my eyes would tolerate.

Now the poor seeing wasn’t helped in the least by a stream of wood chip trucks pounding their way north on U. S. 101, which lies about a quarter of a mile from my house.  There’s a rough spot in the road that they all hit, and when they do, the vibrations travel across that quarter mile, climb up the thick wooden posts that support my deck, and aim the remains of their energy directly into whatever eyepiece happens to be in the diagonal of my scope.

And the law of averages being what the law of averages is — unlawful and awful — every time the seeing would settle down in that 6.3mm Plössl, one of those, shall we say, darned :),  chip trucks would hit that rough spot.  So when the seeing wasn’t cooperating, the trucks were  — and when the seeing was, the trucks weren’t.

Still, despite all that aggravation and frustration, I had glimpses of a Star Splitter’s heaven a couple of times — two alluringly rich yellow globes of light split by a nice slice of black interstellar space.

But 159x was just too much to tolerate under those conditions.  I grabbed the 6.3mm Plössl’s partner, the 7.5mm Plössl, and gave it a try.  It seemed to really enhance the delicate quality of the pair of stars, so I stuck with it for about fifteen minutes, and then dropped back to the 10mm Tak at 100x.  Even though the split was barely visible, the rhythmic dancing caused by the trucks and the poor seeing was much more tolerable, so I let the yellow photons of that pair of stars nourish my neurons until I felt euphoria overtake me.

Or maybe it was the damp cold.

As I stood up to stretch and get some blood flowing through my cold fingers, I found myself staring at an army of low white clouds charging over the trees just south of my house.  After a few more – ahem – darns slipped from my lips, I stole another quick look in the eyepiece before Xi (ξ) was whisked away.

So I was able to collect almost an hour of that streaming photonic tonic with which to restore my sanity while sitting beneath an umbrella of black sky studded with stellar beauty.   And during that whole time — apart from peeking at Polaris when I was lining up the scope at the beginning of the session — I spent it admiring the ravishing Xi (ξ).

And even the clouds couldn’t erase the grin still spread beneath that damp Star Splitter’s hat.