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An Eclectic Collection in Aquila: Σ 2541, Σ 2545, Σ 2547, and LV 21

Now when you read the title of this post,  your natural inclination would be to expect a star hopping tour through Aquila.  But natural inclinations are like natural instincts — they’ll get you where you need to go in the vast majority of cases, but every now and then they’ll steer you down a perplexing path and leave you dangling at the edge of a perditious abyss.  So, no  —- this is not a four-starred star hopping expedition.   Instead, this is a tale of how I happened to capture four multiple stars within the cramped confines of a 32mm Celestron Plössl in a five inch f/15 refractor.

Still, even though I’ve saved you from the potentially hair-raising horror of a bottomless abyss, I feel compelled to warn you:  there may be moments in the adventure ahead where you’ll be inclined to pull a few hairs from your head.  My advice is to wear a hat.  Better yet, wear a helmet — and pull the chin strap tight.

How did I get myself into this torturous situation?  Wasn’t easy, I must say, but it happened about like this:

**** **** **** **** **** **** **** **** **** **** **** **** **** **** **** **** **** **** **** ****

(Stellarium screen image with labels added, click to enlarge)

I was calmly poring over chart 66 of Sky and Telescope’s Pocket Sky Atlas while plotting a navigational approach to 56 and 57 Aquilae for the post prior to this one — when just to their southwest I spotted an alluring triangle of stars at the northeast edge of 37 Aquilae.  One of the stars in that triangle even had the international symbol for a double star, that lovely horizontal line bisecting the center of it.  My natural inclinations took control — which should have set off clanging bells of alarm, but didn’t — and I found myself overwhelmed by a ravenous exploratory desire.

I began to feed it by consulting Chart 19 of The Cambridge Double Star Atlas, hoping it would show more detail than the S&T chart  —-  it didn’t.   Suddenly I felt the whirlpool-like pull of a frantic frenzy gaining control, so to keep it from forcing me into an extended internet research project, I flipped to page 20 of Haas’s book, and fortunately found this:

A low-power field, just northeast of 37 Aquilae, will show all three primary stars.  125mm: A hairsplit pair (Σ 2545), a slightly wider pair (Σ 2541), and a broad triplet that forms a straight line (Σ 2547).”

Three primary stars???  Three?????   Praise printed material!  My frantically ravenous frenzy was down to a mere rumble now.

However  —–  all of that was like a walk in the park in the twilight compared to what followed.  Now I had to identify those “three primary stars.”

(Stellarium screen image with labels added, click for a larger view).

After some judicious searching in MegaStar and Sky Safari, I was able to apply the identities as shown at the right — and you’ll notice there’s an addition to the three Struvian delights, the mysteriously and cryptically named LV 21.   I also discovered that when you include the non-duplicitous HIP 96479 with what were now four primary stars, they form an asterism remarkably similar to the Sagittarius teapot — heck, there’s even a spout arching off and up into the northwest!  And if you study it a bit more, you’ll find an uncanny resemblance to the dreaded House of Hyades as well.

So after all that Struvian sleuthing, it was time to turn a telescope to the sky and see what I could see.  And that’s when the twilight lit walk in the park came to a sudden crunching conclusion.

First, let’s step back and take a wide view in order to navigate our way to the target:

The easiest approach is to begin by drawing a line from Beta (β) Capricorni to Theta (θ) Aquilae, and from its midpoint, extend a perpendicular line six degrees slightly southwest to reach 56 and 57 Aquilae. Center those two stars in your finder, then pan two degrees south and very slightly west to reach 51 Aquilae, which will stand out as the brightest star in that two degree distance. Next pan slightly more than three degrees west to reach 37 Aquilae, which again is the brightest star you’ll see over the three degree distance. Once you have it, you’ll notice a triangle of three stars lying one degree to the northeast. You’ve arrived! (Stellarium screen image with labels added, click for a larger view).

Now that we’re here, I’ll show you what I saw:

You didn’t expect labels, did you? No, I was still lost in space at this point. East and west are reversed here to match what I saw in the telescope.

And when I looked in the eyepiece, I couldn’t make heads or tails, or doubles or triples, out of any of it.   Now the field above was the one I finally settled on after roving around this area for the better part of an hour, so what is obvious in the sketch was not at all obvious in the telescope.  Part of the problem was with the secondaries — they’re all faint, as in determinedly dim, and I didn’t see any of those I was looking for at first.  Another reason was there were several strings of three or more stars scattered around the field of view — think back to Haas’s comment: “a broad triplet that forms a straight line (Σ 2547).”

Where in the pulsating blue light of a blazar was Σ 2547?  Was it one of the three stars in the bottom right corner of the sketch??  Was it among the three at the top???   What were those three faint stars under the bright yellowish star at the top right center????  And what about the three stars at the bottom left?????   So many questions and no known answers!

I peered into the eyepiece, then looked at a rough sketch of relative positions I had in my hand, looked in the eyepiece again, then back at the data I had in my other hand, went back to the eyepiece once more  —-  I panned up, I panned down, I panned sideways, I stood on my head  —-  I imposed position angles where they wouldn’t work, I tried separations that weren’t separated enough  —–  I muttered words I didn’t know I knew, I conjured up all kinds of contorted and imaginative pairings . . . . . . . . . . .

Argggggggghhh!   Good thing I had a hat on my head.

So I broke a long standing ban on white light by going into the house, firing up the desktop computer that has MegaStar on it, and making a more detailed sketch of the area while blasting my night-adapted vision all to horrific Hades.  But I was finally able to finally pin down the location of Σ 2547 —  although it took several minutes for my vision to forgive me for that harsh treatment.

Σ 2547        HIP: 96646   SAO: 162847
RA: 19h 38.9m   Dec: -10° 20′
Magnitudes   AB: 8.1, 9.5    AC: 8.1, 11.1
Separation    AB: 20.8″        AC: 49.8″
Position Angles   AB: 331°  (WDS 2007)    AC: 142°  (WDS 2000)
Distance: 362 Light Years
Spectral Classifications   A: A0   B: F2    C: K1

It was in the bottom right corner!  Its three stars were not quite in a straight line, either, I must say — which was a key contribution to my confusion — but nevertheless, they still formed an eye-pleasing faint arrangement of triple delight.  (You can see full-sized versions of each of the sketches at the right by clicking on the image).

After achieving that hardly inconsiderable milestone, I had a point from which to navigate around the eyepiece.  I found Σ 2545 next, in the top right center, but only after I looked very, very carefully and found it’s 8.5 magnitude secondary.

Σ 2545  (AB is H I 13)        HIP: 96622    SAO: 162843
RA: 19h 38.7m   Dec: -10° 09′
Magnitudes   AB: 6.8, 8.5     AC: 6.8, 11.6
Separation    AB: 4.0″          AC: 25.4″
Position Angles   AB: 326°  (WDS 2008)    AC: 163°  (WDS 2000)
Distance: 263 Light Years
Spectral Classification: A9

After spying its dim light hiding behind the slight yellow-gold glow of the primary, it was as obvious as the moon at midnight.  Even so, the 11.6 magnitude “C” companion was easier to see, and it was one of a line of three faint stars that had confused me from the beginning.

And that led me up to LV 21, which I pinned down only after I confirmed the identity of the very faint and barely separated BC pair in my telescopic microscope.

LV 21         HIP: None listed    SAO: 162829
RA: 19h 37.7m   Dec: -09° 58′
Magnitudes   AB: 7.2, 10.2    BC: 10.2, 11.3
Separation    AB: 86.5″         BC: 4.1″
Position Angles   AB: 285°  (WDS 2010)  BC: 285°  (WDS 2002)
Distance:  ?????
Spectral Classification: A2

That BC pairing was a prime suspect from the start — all I needed was enough magnification (100x) in the five inch f/15 to pull them definitively apart, after which I could detect both stars easily enough at the 60x used for the first sketch above.  Again, it was part of a line of stars that had me roundly confused — there were four of them, and I had tried to break them down into either a group of three on the left or three on the right.   As it turned out, the star on the east edge of that string is an impostor hoping to convince an innocent visitor like me that it’s a member of the system.

So what happened to Σ 2541???  According to Haas, it was slightly wider than Σ 2545, which she described as “hairsplit.”

Σ 2541        HIP: 96471    SAO: 162814
RA: 19h 36.8m   Dec: -10° 27′
Magnitudes: 8.7, 10.1
Separation:  5.4″
Position Angle: 326°  (WDS 2010)
Distance: 99 Light Years
Spectral Classification: K2, K5

Well sure, Σ 2541 is slightly wider than Σ 2545, but the primary is also two magnitudes fainter to begin with, and its secondary is 1.5 magnitudes fainter than that of Σ 2545.  Add in the fact that both stars have a slight reddish-orange tint, which matches up well with their spectral classifications, and they’re even a bit fainter than if they were Class A stars like all of the others here.  All of which means Σ 2541 has elevated elusiveness to a Burnhamian level of difficulty — in fact, even in the six inch f/8 refractor I used for the sketch shown a few lines above, I had to look very, very closely to see the secondary.   I had looked right at this star several times on the first night I observed it and never once saw the first glimmer of secondarial light escaping from it.   But 100x did the trick again that first night — and again, once I had picked it out at that magnification, I could see it at 60x in the five inch f/15, but only if I was very precise with the focus.

So let’s look at that first sketch above again, and this time with labels:

And it’s a thing of beauty when all the key stars have identities! For a better view, turn out the lights, click on the image, and look closely to catch the faint secondarial pairings shown here, especially LV 21’s BC pair, and the secondary of Σ 2541. (East and west still are reversed!)

Now obviously this is not a task to be tackled with a small aperture scope — at least not if you want to pry into the tight spaces which are typical here. Five inches is probably the minimum of what will work (an optically perfect 100mm scope might work), six inches undoubtedly is a better choice, and anything over that should provide an outstanding view if you can keep all five stars in the same field.  The night I made all of the individual sketches shown above along the right edge of the data listings, I used my six inch Celestron f/8 — and due to persistent haze, I really didn’t do much better than I did on the earlier night with the five inch f/15 D&G.

One other thing before winding this sagacious saga up — actually another question, as if there haven’t been enough already:  What in the world does the LV in LV 21 stand for?

It stands for Leavenworth, as in Francis Preserved Leavenworth, who was director of the University of Minnesota Observatory for thirty-five years.  He published a book in 1930, Measures of Double Stars, and a review of it is available here.  I’ve searched the internet for that book and haven’t been able to find it, but it can be found in numerous libraries around the world — you can locate the closest one to you by going to World Cat at this address.  And one final touch:  a photo of F.P. Leavenworth

Let it never be said that I would leave a stone unturned somewhere.  😎

Next time out, we’ll move into northwest Aquila for a look at two very different stars —- but first, I need some CLEAR SKIES!!!!!!   And soon!


5 Responses

  1. Great fun! I wish the WX here was any calmer. Winds are >20 mph. I’ll try to get out my C925 soon and observe these as well as 56/57 Aql. You’ve done all the research for me. I wonder if that Leander McCormick Observatory w/ its 26″ refractor at the U of M still exists.

  2. I went back to these four stars last night with my Skylight f/13 100mm refractor to see what a good four inch could do, and it went pretty much as I expected.

    Σ 2547 was no problem — no surprise there. The BC component of LV 21 wouldn’t quite come apart, but I could tell there were two stars there because it was slightly extended. So again, no surprise.

    Σ 2545 proved to be the defining moment. Seeing was a III and transparency was about the same on the same scale. The secondary was very elusive in a 12mm Radian (108x), so I switched to a 12.5mm UO Ortho (104x) and it popped right into view. I could also hold it very clearly with a 12.5mm Siebert Star Splitter and a 12.5mm Astro-Tech (Sterling) Plössl.

    Was the view worth all that work??? You bet it was!!! The secondary was the faintest mere whisper of a phosphorescent white point of light, with a needle-thin slice of pure black interstellar space separating it from the primary — absolutely delicious!

    That left Σ 2541, which was just beyond reach for the conditions. If the seeing had been a IV or a V, I’m sure I could have separated the secondary from the primary. As it was, the pair was doing a high-frequency/low-frequency dance that looked like two pieces of salt water taffy spinning in a circle, stretching as they attempted to pull apart, and then snapping back together at the last second. I tried several times through the night, but the pair refused to settle down into a dull rhythm for long enough to materialize as anything other than an elongated blob of light.

    So I’ll stick with my comments in the post above — these four stars are well within reach of a five or six inch aperture refractor, and right at the limit of what can be seen in a very good 100mm model. If you want to work for the view, try the 100mm. On the other hand, if you want to enjoy the view for the subtle delights it offers, go with the larger apertures, sit back in your chair, and let your eyes rove around the field until they’re saturated with stardust.

    And if you want a truly excellent view, I can heartily recommend a C9.25 at 10,000 ft in Hawaii! 😉

  3. Hi John! Hi Steve!
    John…you are having far too much fun writing these reports!…LOL. I have this image of you sitting back with a fine scotch and a cigar…or maybe it’s a finally aged port. Whatever your crutch, keep them coming. It really does inspire one to get out and observe. I am curious, what is the reason for the significantly different results from the 12mm Radian and the UO 12.5 ortho? Are they providing pretty much the same field of view. This weeks Scutum submission will provide some real challenges. Next time I get out, this week I hope, I will meander into Aquila and look up the trio of fine doubles next to 37 Aquila and see if they will expose themselves on film, so to speak.

    Cheers, Chris.

    • Hi Chris,

      You caught the comparison between the Radian and the other eyepieces! That was probably the main surprise for the night, apart from a very diluted Perseid meteor shower — if there was a shower, I sure didn’t get drenched. But then I was bent over a telescope much of the time, too. I did see about a dozen over the course of the night.

      I’ve had pretty good luck lately with a few University Optics (UO) Orthos and some old Celestron Orthos that haven’t had much use — in particular, I noticed the image in an older 18mm Celestron Ortho was just a slight bit brighter than in an 18mm Radian. So when I couldn’t quite catch Σ 2545’s secondary in a 12mm Radian — and it was almost there a couple of times — I decided to fish a 12.5mm UO Ortho out of its box and see what it could do. And it did the trick without a milli-second of hesitation …… which surprised the socks right out of my shoes.

      I sat back, took a puff of my cigar, sipped my Port, and decided to see what a recently acquired 12.5mm Siebert Star Splitter could do — and it was a virtual carbon copy of the UO, with the added bonus of the same 60 degree field of the Radian (maybe more like 57 or 58 degrees — it’s not quite as wide). The Ortho by the way, is about fifty degrees — very noticeably restricted in comparison.

      So after a few more draws on the cigar, and another sip of Port, I pried myself off my chair, went in the house, and called to the Astro-Tech 12.5mm Plössl to climb out of its box. Of course, it didn’t — Plössls can be rather recalcitrant — so I reached in and pried it out, carried it outside, parked it in the diagonal, turned the focus knob slowly — and grinned as that delicately refined secondary hovered into view once more.

      Well, now ………….. a few more draws on the cigar, then a few more reflective sips of Port ……….. and I decided to call the 12mm Radian back into service — and I still couldn’t quite catch sight of that secondary in it.

      So ……….. that says a lot for the other eyepieces, none of which cost what the Radian did. On the other hand, the eye relief in the UO Ortho is atrociously poor, the field of view in the Siebert isn’t quite flat at the edges, and as for the Astro-Tech Plössl, other than the field of view being slightly smaller (55 degrees), it does well in the eye relief department and is as flat as a wafer-thin pancake all the way across.

      But the Radian is totally flat across the entire field and has very good eye relief. And, they’re ideal for studying a target for long periods of time, which is something I just cannot do with short relief eyepieces — for some reason, they tend to “gray-out” on me after a few minutes.

      Now even though I saw similar results on a few other targets during that same session, I wouldn’t rush to any conclusions. That’s one night and one telescope — and another night might yield totally different results, even with the same telescope. But I’ll make the comparisons again on five and six inch refractors eventually and see how it goes.

      As for the Port and cigars — the truth is, I love a good cigar and a beer in the afternoon, but they just don’t work at all when observing. A good cup of tea and a few cookies are better companions at the observing table. But at the end of a cold damp night, a few sips of Port will do wonders to restore lost body heat.

      Clear Skies ………. and Prost! 😎

  4. Hi John!
    I know there is an answer in there somewhere. I wouldn’t, for a minute, suggest that you consume any spirits during an observation session. The cigar and port was part of the image of you at your type-writer…remember those things…as you script your next post. Have a great evening. You know those 8 weeks of drought I was talking about…now, I may just need an ark…I think you have one started…if I recall correctly.

    Cheers, Chris.

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