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A Stellar Show on the North Shore of Leo: 54 Leonis and Σ 1521

It always amazes me what gems lurk in the dark of the night, waiting patiently for an unsuspecting Star Splitter’s unannounced visit.  I’ve been at this long enough now that it would seem there can’t be too many of those jewels left.  I won’t bet on it, though.  Every time I think I’ve rounded the last one up, another one drifts into view from wherever they drift into view from.

I usually start an observing session with one or two specific targets in mind and let the stellar muse take over from there.  Sometimes I’ll spend the whole night on one or two objects, other times I’ll finish up quickly with them and track down old favorites or neglected should-be-favorites.  And occasionally I’ll run through all of those and find myself with unexpected time on my hands.  That’s what happened on the night I discovered the two stars we’ll look at now.

I had exhausted my mental catalogue of stellar targets, as well as myself, so I took a break to brew a cup of tea and raid the cookie jar.  While the water was boiling, I picked up Sissy Haas’s book, flipped to Leo, and scanned through it to see what I could find north of the Lion’s back.  It wasn’t long before I came across this description of 54 Leonis on page ninety-two —  “Showcase pair.  60mm: A bright, easy pair with lovely contrast — a bright banana-yellow star and a smaller sapphire blue, split by hairs at 45x.  Webb: ‘Greenish white, blue.’ “ —  so I poured the tea, grabbed the cup, parked a couple of cookies in my pockets, and headed out into the dark of the night once more.

Let’s reach for the zenith tonight and see what kind of neck-aching beauty we can coax from the north Leonine shores.  One of our two gems hugs the border of the little lion, aka Leo Minor, and the other is just about a wide-field eyepiece view from being scooped up by Ursa Major.  (Stellarium screen image with labels added, click on the chart for a larger view).

Let’s reach for the zenith tonight and see what kind of neck-aching beauty we can coax from the north Leonine shores. One of our two gems hugs the border of the little lion, aka Leo Minor, and the other is just about a wide-field eyepiece view from being scooped up by Ursa Major. (Stellarium screen image with boundaries and labels added, click on the chart for a larger view).

54 Leonis  (STF 1487)  (Sh 117)  (H III 30)             HIP: 53417    SAO: 81584
RA: 10h 55.6m   Dec: +24° 45’
Magnitudes: 4.48, 6.30
Separation:  6.6”
Position Angle: 111°  (WDS 2012)
Distance: 289 Light Years
Spectral Classifications: A1, A2

If you look at the chart above (this will help), the easiest way to get to 54 Leonis is to follow the line that runs from Denebola [Beta (β) Leonis] to Zosma [Delta (δ) Leonis], then extend it about two-thirds of that length and incline it a slight bit to the north.  That will lead you directly to 54 Leonis, which conveniently forms a triangle with the two sixth magnitude stars above it, 48 and 50 Leonis Minoris.

54 Leonis is a classic example of the kind of trick a close pair of reasonably bright stars can play on your eyes. On first glance, I thought maybe I had taken a wrong turn — the “banana yellow’ and “sapphire blue” were absent without leave and white had taken their place.  According to their spectral classifications, these two stars should appear white or bluish-white to the critical Star Splitter eye.  And they do — sort of — or at least to start with — some of the time — usually.  What happened was that as I looked at them a little longer, I discovered a slight shift towards pale yellow taking place in the primary, and at the same time the secondary began picking up traces of a very subtle blue.  The colors seemed to creep in very gradually, as if some unseen creature was adjusting a color-control knob:

I went with a very subtle yellow and blue here, because most of the time that’s what they were, although occasionally they were capable of shining more vibrantly.  Note how barren the field is surrounding 54 Leonis.  (East & west reversed to match the refractor view, click on the sketch for a larger version).

I went with a very subtle yellow and blue here, because most of the time that’s what these two stars were, although occasionally they were capable of shining more vibrantly. Note how barren the field is surrounding 54 Leonis. (East & west reversed to match the refractor view, click on the sketch for a larger version).

The more I looked, the more colorful those colors became.  The energy for that increasing intensity of color seemed to be coming from a remarkable and very uncanny interaction of starlight dancing across, or in, or between, the gap separating the primary and secondary.

After I had written the description above, Pat Conlan posted a comment on 54 Leonis which led me to this post Greg wrote about it a couple of years ago, which I had totally forgotten about.  Normally we avoid repeating posts on the same star, but in this case, the experience the three of us had with the colors of 54 Leonis provides some very interesting, not to mention head-scratching, reading.

If you go back and read Greg’s post, you can see right away from his title he saw “whiter than white.”  And if you read further, he also saw yellow in the primary at 60mm’s of aperture (the secondary was a puffball), but in an eight inch SCT the primary went white and the secondary became pale blue.  Meanwhile, Pat was using an 80mm refractor and saw yellow in the primary and blue in the secondary using a 16mm Ortho — until he switched to a 10mm Ortho, which resulted in the primary shifting toward white and the blue becoming less blue.  And on an observation that took place a couple of nights later, the primary was now white in the 16mm Ortho, but then shifted to yellow in the same eyepiece with the same scope.

Hmmm — puzzling and perplexing.

OK, so what colors have others seen in this chameleon-like pair of stars?

As Haas mentions, the Reverend Webb saw greenish white and blue, so I looked up the observation on page 146 of his Celestial Objects for Small Telescopes and found other than those three words referring to the color, he had nothing else to say about 54 Leonis – which is surprising for a star as changeable as this one. But Thomas Lewis, who compiled an update of F.G. W. von Struve‘s catalog in 1906, also reported greenish white and blue.  The senior Struve, by the way, left no comment whatever on 54 Leonis’ color, but the always dependable Admiral Smyth reported white and gray.  And the discoverer of this pair, Sir William Herschel, described the primary as “brilliant white” and the secondary as “ash-colour, or greyish-white.”  If it means anything — and at this point I doubt that it does — Admiral Smyth was using a 5.9 inch achromatic doublet refractor, while Sir William was probably using a six inch reflector with a speculum coated mirror.

Click on the image for an enlarged view.

Click on the image for an enlarged view.

So that leads us to this question: when did the yellow make its first appearance?  Well actually, there was another pair of observations sandwiched between William Herschel’s and Admiral Smyth’s, which was that of Sirs John Herschel and James South in 1821 and 1822 (from their joint 1824 catalogue), and can be seen at the right.  They saw yellow in the primary (as well as green in the secondary), which leaves me wondering if theirs was the only recorded 19th century observation of primarial yellow.

Could it be the predominance of yellow in our current observations is a late-20th/early 21st century phenomenon caused by too much caffeine and/or sugar?  🙄

Rather than pry further into the inscrutable physical and physiological reasons for the weird and colorful transformations of this pair of stars, for now I’ll just call whatever it is that takes takes place between them an example of stellar sleight of hand, and accept it for what it is — ravishingly beautiful and marvelously mystifying.

Meanwhile, I think I’ll just linger here in the dark a while longer and bask in the magical aura of color.  Maybe if I look long enough the secondary will turn gray — or green.

And if that doesn’t happen, I’ll wander further north to our next star.

Σ 1521  (S 623)             HIP: 54967    SAO: 81740
RA: 11h 15.4m   Dec: +27° 34’
Magnitudes: 7.65, 8.06
Separation:  3.7”
Position Angle: 97°  (WDS 2010)
Distance: 418 Light Years
Spectral Classification: A5

This was another pair I found in Haas’s book on the night I was raiding the cookie jar, and even though it’s also in a sparsely populated stellar region of Leo, it was easy enough to find.

Going back to the chart above (for easy reference, click here), draw a line from Zosma [Delta (δ) Leonis] to Alula Borealis [Nu (ν) Ursae Majoris] and Alula Australis [Xi (ξ) Ursae Majoris], which is a distance of about ten degrees.  You’ll see the beautiful and very intriguing 72 Leonis a few degrees north of Zosma on that line, and you’ll find  Σ 1521 is slightly past the halfway point between 72 Leonis and Alula Australis.  With 7.60 magnitude HIP 55170 just east of Σ 1521, the two stars will be very conspicuous in your finder since there isn’t much else in the area to be seen.

Haas describes Σ 1521 as a “bright, easy, and attractively close binary” in a 125mm scope, “a pair of gloss-white stars, modestly unequal, that are split by hairs at 83x.” (page 92)

And at 109x in a 152mm refractor, that pretty well describes what I saw, although I lean toward pale white:

 This pair could easily be improved with about twice the magnification!  And once again, this is a very lonely section of the sky.  (East & west reversed, click on the sketch for a much better view).

This pair could easily be improved with about twice the magnification! And once again, this is a very lonely section of the sky. (East & west reversed, click on the sketch for a much better view).

Click on the image to see a larger view.

Click on the image to see a larger view.

The first recorded observation I can find of these two stars is that of Sir James South, which was published in his 1825 catalogue as number 623.  He was using a 96mm f/15.8 Dolland refractor at the time, which explains his description of the pair as very difficult when he first saw it on March 13th, 1824.  He recorded a second observation a few weeks later, on April 2nd, and had a slightly easier time of it under better seeing conditions.

Again, Herr von Struve, whose catalog number is now used to designate this pair, left no description of it, but Lewis, in his 1906 compilation, reported white and greenish white.  No guesses as to where the green came from, but it should be obvious by now that very strange things happen when stars are confined in a claustrophobic space.  The only thing definitive about star colors is there isn’t anything definitive about star colors — but maybe this will help a little.

Meanwhile, instead of sitting here and waiting for Σ 1521 to flash me with green, I think I’ll go back to 54 Leonis and see what color it is now.

Clear Skies!  :mrgreen:

8 Responses

  1. Hi John, enjoyed reading your post on 54 leonis, the way it changes
    colour is amazing when I next get a chance I will have a look with
    the 150mm reflector to see if that makes any difference.

    p.s. go easy on the cookies.

    Pat.

  2. Thanks, Pat. Let me know what happens with the 150mm reflector. I’ll be interested to find out if you see a gradual change in color similar to what I saw.

    54 Leonis really mystifies me. I’ve never seen a star change color gradually like that right in front of my eyes, so to speak. It’s always been my experience that an increase in aperture and/or an increase in magnification will tend to dilute color to some degree, but that principle doesn’t seem to apply here. It would really be interesting to find out which is the dominant factor — the primary and secondary’s proximity to one another (at least from where we view them), or the intensity of the colors. It could well be a combination of both, but it could just as well be something else entirely.

    Hopefully the cookies have nothing to do with it!

    John

    • Hi John! Hi Pat!
      Last night was a rare occasion. Instead of imaging, I thought I might, for a change of pace, do some conventional star splitting the old fashion way…at the eyepiece. I started out with the intent to track down some of the recent systems within Canis Minoris that I have been submitting to the “d_s_i” group recently. The obvious one to start with was Gomeisa. I had my 2 Stellarview 80mm scopes, Nighthawk II and the 80/9D. Given the turbulance in the air masses, I was under-powered, so I wandered around the southern sky until I remembered this post on 54 Leonis. 80mm at 100x (80/9D) was just right for this fine Struve pair. Colour was as both of you had experienced, soft yellow for the primary and just a hint of grey-blue in the secondary. Also, as John had indicated, my Nighthawk at 38x provided a slightly stronger colour rendering and still a clean split.
      For those who just happened to be checking out Jupiter last night, the Galilean moons, Europa and Ganymede were doing their best Struve double imitation last might. A beautiful pair of bright headlights. I never tire of the moons of Jupiter.

      Cheers, Chris.

    • Hi John, last night was the first chance I got to observe 54 Leonis
      with the 150mm reflector, using a 25mm plossel both stars looked
      white, I waited for 10 minutes but no change of colour I then changed
      to a 10mm plossel but still white even when I dropped in a 6mm ortho.
      they were still white. I left it then and moved to Zeta Cancri which I
      tried to split the A&B components with no luck after about 30 minutes
      I went back to 54 and using the 25mm again there seemed to be a bit
      of yellow in it at least it was not as white as when I first looked at it.
      It is a strange double alright when I used the 10 and 6 mm eyepieces
      the colour was gone, back to white. I will go back to the 80mm
      refractor tonight as the colours in it were very intense, hard to believe
      two scopes looking at the same stars would show such a difference
      in colour.

      Pat.

      • Hi Pat,

        I’m guessing the mirror of the reflector has something to do with seeing mainly white. My limited experience with mirrors is they introduce a harsher aspect to the color, meaning there’s more white present in most shades of color than what you typically see in a refractor. Still, the fact that you saw a bit of yellow is an indication of how stubbornly chameleon-like this pair is.

        I need to go back and get another look at it too as soon as the weather cooperates.

        John

  3. I observed 54 Leo with my SW 100ED on Apr 7 and visually the primary had a definite yellow cast to it but when I photographed it the primary showed bluish-white.

    Photo is posted on the Double Star Immaging News Group site.

    Steve

  4. Had another look at 54 Leo last night with my six inch f/10 and the results were slightly different. There was some yellow in the primary, but it was very weak — the blue in the secondary was rather pale, also, compared to what I saw in the post above. I did notice a very slight shift toward yellow in the primary the longer I looked at (84x with an 18mm Radian), but again, it was more pronounced in the observation described above.

    I had a 60m f/15 mounted on the six inch scope, and it showed a bit more yellow in the primary, but not much. The secondary was more gray than blue, but I expected that with the small aperture. (45x in a 20mm TV Plossl).

    I’ll call the primary white-leaning-toward-yellow-leaning-toward-white-leaing-toward-pale-yellow and leave it at that.

    John

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