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On the South Side of Tania Australis with Cou 1900 and HJ 2534

We’re back again in the domain of the Great Bear’s second foot, and we’re about to have more fun than a cluster of ocular addicts turned loose in an eyepiece warehouse.  The last time out we toured the stellar terrain north of Tania Borealis, and this time we’ll take a look at what can be seen in the domain south of its neighbor, the very attractive and very orange Tania Australis.

However – to protect the innocently uninitiated, as well as those who become wary when the subject is faint photons – this is mainly going to be an exercise in straddling the abyss-like border of the possible.  Or, to borrow a phrase from the last adventure, beyond the sane and simple.

How did I find myself in a black-hole-like-world where secondarial light rarely escapes?   T’weren’t easy – never is.

First, a look at where it happened:

We're back to our upside down bear once again. Focus your eyes on Mu (μ) Ursae Majoris (another name for Tania Australis), which is located on the right rear foot of the Great Bear . . . . . . . (Stellarium screen image with labels added, click for a larger view).

We’re back to our upside down bear once again. Focus your eyes on Mu (μ) Ursae Majoris (another name for Tania Australis), which is located on the right rear foot of the Great Bear . . . . . . . (Stellarium screen image with labels added, click for a larger view).

 . . . . . . . and now we'll zoom in on the Tania Australis/Tania Borealis pair. Our first target, Cou 1900, is located about one degree east (with a slight lean to the north) of Tania Australis. (Stellarium screen image with labels added, click to enlarge).

. . . . . . . and now we’ll zoom in on the Tania Australis/Tania Borealis pair. Our first target, Cou 1900, is located about one degree east (with a slight lean to the north) of Tania Australis. (Stellarium screen image with labels added, click to enlarge).

Tighten your seat strap now – we’re off!

Cou 1900        HIP: 51200   SAO: 43344
RA: 10h 27.5m   Dec: +41° 36’
Magnitudes: 6.0, 10.0
Separation:  2.4”
Position Angle: 304° (WDS 2010)
Distance: 216 Light Years
Spectral Classification: A2

This is where it all started.  Actually, it all started with Bu 1074 (covered in the middle of the last post), which will forever be linked in my photon deprived memory with Cou 1900.   Linked, that is, because I innocently and ignorantly considered them to be of equal difficulty.

They aren’t.

Let’s look at their deceptive numbers to discover why.

Bu 1074 is a pair of stars with magnitudes of 7.2 and 11.2, separated by 2.5 seconds of arc.  Its main characteristic is the four full magnitudes of difference between the primary and secondary.  And if you look at the numbers above for Cou 1900, you’ll see it boasts of a four full magnitudes of difference as well.  Even the separations of these two deceptive twins are so close – 2.4” and 2.5” –  that we can call that trait a tie.

Where the comparison takes a tortuous turn is in the difference in magnitudes of the respective primaries and secondaries.  On the one hand, the primary of Cou 1900 is a full 1.2 magnitudes brighter than that of Bu 1074 (6.0 vs. 7.2); while over there on the opposite hand, the secondary of Bu 1074 is a full 1.2 magnitudes fainter than that of Cou 1900 (10.0 vs. 11.2).

And there’s also a color difference here.  In one corner, we have Bu 1074’s primary radiating a weak orange light, while over in the opposite corner we find the primary of Cou 1900 overflowing with an almost obnoxious white light under moderate magnification.  Both of those colors match their respective spectral classifications, K2 and A2.

The reason I focus attention on the colors is they’re a primary factor in puzzling out what it is that sets these two stars apart in difficulty.  In the case of Bu 1074, an intent star splitter’s gaze is focused on seeing past a soft orange glow, whereas with Cou 1900, that gaze is frustrated by having to get past a harsh white glow which is also 1.2 magnitudes brighter.

So there are two interacting factors at work here hindering our attempt to mine faint photons from the primarial glows: one is the color of those glows, and the other is the marked difference between a 10.0 magnitude secondary and an 11.2 magnitude secondary (we’ll call that the faintness factor).  What I expected before I started down this stellar path to perdition was the overall brightness of the Cou 1900 pair would be offset by the overall faintness of the Bu 1074 pair, making them roughly of equal difficulty.

But it doesn’t work out that way.

Click for a full-sized view.

Click for a full-sized view.

While they both are certainly difficult, Cou 1900 is considerably more difficult.  Complicating the situation is the possibility its secondary may be in the neighborhood of 11.0 magnitudes, not the 10.0 number assigned to it currently in the WDS — although that could well be an illusion caused by the difficulty of seeing past the primary’s harsh white glow.  Still, there’s a persistence about that eleventh magnitude number since it was the figure originally determined by Paul Couteau when he discovered this pair in 1981 (see the thumbnail at the right – the source is here on the third page of the .pdf document).

Pardon the long explanation, but the apparent subtle differences in these two stars are very un-subtle when you actually get down on the mat and wrestle with both of them.

Now I would guess at this point I’ve easily invested at least three hours of rigid, locked-in-place, seat time in an effort to see the secondarial light in Cou 1900.  And all I can say after that all that eye-numbing effort is I think I saw it.  I’m pretty sure, even.  But there’s still a nagging doubt.

Here’s what I think I saw:

 If you have trouble picking out the secondary, click on the image to enlarge it and look at the eight o’clock position. (East & west reversed to match the refractor view).

If you have trouble picking out the secondary, click on the image to enlarge it and look at the eight o’clock position. (East & west reversed to match the refractor view).

I’ve tried also with a well-collimated 9.25 inch SCT armed with a two-speed external focuser, with about the same nagging results.  But most of my effort has been with the six inch f/10 refractor because it does a much better job of separating the drowning and gasping secondarial photons from the gleaming gray-white glow of the primary.  On my most recent attempt, I spent most of an hour looking into two four millimeter eyepieces (380x), an Astro-Tech Plössl and a TMB Planetary II, and had my best results yet.  Several times I saw a brief glimmer of whispering white light about where it should have been.  Once I even saw it for a couple of seconds, but just as I was about to leap out of my seat and yell I’ve got it!, it disappeared.

Rats and Arghhh!

It just didn’t feel solid.  I need something my eyes can latch onto, something they can grasp, feel, and touch.

Click to enlarge!

Update 4/22/2017: Speaking of something solid the eyes can latch onto, take a look at the photo at the right, which Mark McPhee sent me.  It shows beyond a shadow of a doubt that the elusive secondary is merely being elusive.  In other words, it’s really there.  Note that east is at the left in this image, north at the top.

So I think for now, at least in regard to visually separating this two stars, it’s best to say the jury is still undecided on this one.  I’m leaning toward declaring a secondarial sighting, but not with a lot of conviction.   To be continued – probably.


HJ 2534  (h 2534)           HIP: 51658   SAO: 43379
RA: 10h 33.2m   Dec: +40° 26’
Magnitudes: 4.75, 11.60
Separation:  16.9”
Position Angle: 358°  (WDS 2010)
Distance: 112 Light Years
Spectral Classification: A7
Status: Optical pair

Click on the image for a full-sized view.

Click on the image for a full-sized view.

And honestly, this isn’t a whole different – or easier, either.  In fact, a quick perusal of Sir John Herschel’s observation of this pair shows he estimated the magnitude of the secondary at sixteen, as shown at the right.  Now it isn’t that dim, as I now know, but it is hard to see in the glare of the 4.75 magnitude primary.

You can get to HJ 2534 (here’s the chart again) by making a one and a half degree leap in the dark southeast of Cou 1900, or you can hop to it by dropping south to 7.05 magnitude HIP 51222, then bending southeast to 7.0 magnitude HIP 51414, and turning east to reach our goal.

At least I can say I spied the secondary with certainty, although it didn’t happen on the first attempt.  That one was with my six inch f/10 refractor, and was on one of the same seeing-plagued, transparency impaired murky nights when I had been struggling with Cou 1900.  It took a week for another opportunity to open up in the heavens, and it was even murkier than the others, but the seeing was one level better, mainly being the difference between a II and a III.

For that attempt, I decided to give a newly acquired Celestron 9.25 inch SCT a try, although with considerable misgivings.  It wasn’t the SCT I suspected of misgiving, it’s what the heavens were handing me – a new level of murk.  Even though there was no moon, there were enough thin clouds and moisture in the air that I could swear the sky was almost the color of mud.  I found out later there was a strong display of northern lights that night, but I couldn’t see them from where I was.  It could have been that they contributed to increasing the brightness of the sky background, but I’m still leaning toward malicious murkiness as the cause.  Several times while I was attempting to pry the 11.60 magnitude secondary out of the primary’s glow, the image faded by a couple of magnitudes and then gradually returned to normal.  Whatever it was — clouds, murk, or northern lights — it made a real chore out of what should cause less strain on a more transparent night.

At any rate, my first sighting came in an old 10mm Celestron Plössl (245x), one of the variety that have recently been described as “Halloween” Plössls because of the black and orange lettering around the top of the barrels.  I was establishing my directional bearings by using the hand-controller to pin down north and west, and as I moved the image to the north, I caught a sudden brief glimpse of the secondary with averted vision.  The 10mm eyepiece was magnifying the primarial glare way too much, though, so I swapped a 12.5mm Astro-Tech High grade Plössl (196x) into the diagonal.  It cut through the glare immediately and provided a very dim direct vision view of the secondary.  Curious as to whether I would still be able to dig that faint stellar wisp of light out of the glare with less magnification, I gave a 15mm TV Plössl (163x) a trial run, found it did almost as well, and committed it’s vision to posterity below:

 The secondary is hiding in the glow on the left (north) side of the primary. There’s another (apparently) un-related star also to be seen slightly further away in the glow to the primary’s southwest. (East & west reversed, click to see a larger version).

The secondary is hiding in the glow on the left (north) side of the primary. There’s another (apparently) unrelated star also to be seen slightly further away in the glow to the primary’s southwest. (East & west reversed, click to see a larger version).

There are some other challenging pairs of stars circulating in the domain of Tania Australis, but since I’m losing this section of sky to the vaporous exhalations of the Pacific Ocean, I’ll probably have to put them on hold until they circulate around to the east again later in the year.  If you’re curious, here are three worth pursuing and perusing (these are identified on the chart we’ve been using):

HJ 2531: Magnitudes of 9.37 and 10.95, separated by 8.7”
OΣ 223 (STT 223): Magnitudes of 8.1 and 12.8, separated by 31.2”
Σ 1430 (STF 1430), AB: Magnitudes of 8.5 and 12.0, separated by 21.3”
                          and AC: Magnitudes of 8.5 and 10.7, separated by 23.0”

If I can catch them yet in the next month, I’ll be back with a report on them.

In the meantime . . . . . . .

In his 1782 essay, “On the Parallax of Fixed Stars”, Sir William Herschel penned the following paragraph in partial explanation of the six classifications he used for double star separations (see page four of The Cambridge Double Star Atlas), of which the closest were those of the first class he refers to below.  But his last two sentences could just as easily have been applied to Bu 1074, Cou 1900, and HJ 2534:

“I have divided the double stars into several different classes.  In the first I have placed all those which require indeed a very superior telescope, the utmost clearness of air, and every other favourable circumstance to be seen at all, or well enough to judge of them.  They seemed to me on that account to deserve a separate place, that an observer might not condemn his instrument or his eye if he should not be successful in distinguishing them.”
.                                                     Philosophical Transactions, Vol 72 (1782), p. 100.

He didn’t end there, though.  He included one more sentence:

“As these are some of the finest, most minute, and most delicate objects of vision I ever beheld, I shall be happy to hear that my observations have been verified by other persons, which I make no doubt the curious in astronomy will soon undertake.”
.                                                                                                                     (Same source)

So if you’re among the curious, you have some undertaking to do.   And we would be thrilled to hear about it, too.

To speed things along, I’ll order some Clear Skies!  😎


9 Responses

  1. Fantastic stuff, John.

    I love those comments from Herschel. Good to know our efforts with Bu1074 and COU 1900 are just the latest footsteps along a path few care to tread.

    Call me a masochist, but I will be checking in on these two again next cycle–something alluring about their difficulty. I also think of them as linked–partners in crime, stealing time away from other doubles.

    Fantastic blog!

    -MarkM (aka “Nucleophile”)

    • Hi Mark,

      Linked-partners in crime Bu 1074 and Cou 1900 certainly are. There’s something about the lure of the difficult that becomes addicting, which explains the attraction to those two double stars.

      I think William Herschel found it impossible to resist as well. In fact, I suspect he discovered more of a fascination with double stars than he ever dreamed of at the time he began looking at them in hopes of discovering indications of measurable parallax.

      Thanks for the compliment — it’s appreciated!


      • PS

        I checked in on COU1900 again tonight at the beginning of my session with the 15 inch and again saw the secondary. Once you’ve seen it once, well you know the rest.

        I have to say, the secondary may actually be fainter than mag 11 (like mag 11.5?) and closer than is reported.

        If you’d like a taste of what COU 1900 is supposed to offer, mosey over to STT 344 in HER — you won’t be disappointed.

  2. Just looked at the data for STT 344, Mark, and it looks rather interesting — magnitudes of 6.47 and 10.31 with a separation of 2.3″. With the primary’s A2 white light, it should be another challenge.

    I’ll give it a shot on the next clear night!


  3. Cou 1900, It seems a lot of folks have doubt that this is a double. John thinks he may have seen the secondary and even though I could not split this star with my 6 inch f/8 the night was steady and I was able to go really high power. And at over 600x I swear I caught an elongation.

    Don’t count this star out folks ……
    mike hyrczyk

    • On the night of June 1st, I observed the secondary of COU 1900 yet again with my 15″ reflector–it is definitely there, but I still think the secondary is a bit fainter than mag 10 and tighter than 2.4″.

      I then placed an 11 inch mask on this instrument and again detected the secondary in the same pa as mentioned above. It was decidedly harder to see the secondary with the 11 inch mask in place, however.

      I have not tried COU 1900 again this year with my 8 inch reflector and now have missed the window of opportunity from my observing site.


      • Hi Mark,

        I’ve had Cou 1900 on my list for this spring, but the seeing has been so poor I haven’t seen any point in attempting it. As soon as I get a cooperative night, I’ll point my 9.25″ Edge at it.

        I’ve also got the pair in Hercules, STT 344, on my list. I was near it a few nights ago but I was having problems splitting slightly wider pairs of the same magnitude, so I left it for another night.


  4. John:
    I recently succeeded in imaging and measuring both COU 1900AB and BU 1074. I made a composite picture of these along with STT 216 as a reference. Would you like a copy for this post?

    -Mark McPhee

    • Thanks for sending those excellent images, Mark. I’ll add each one of them to the posts on BU 1074, COU 1900, and STT 216. (Clicking on the names of the stars will take you to the respective posts).

      The composite image which includes all of these stars can be seen here.


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