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Cleaning up and Summing up in Serpens Caput: OΣ 300 and Σ 1987, plus a Short Summary of the Serpent’s Lair

I’ve been sleuthing and slithering around in the dark in this serpentine sector of the sky for what now seems like the better part of a long, long time — in reality, it’s only been for a couple of normal length months that were stretched into extra length months by a stubborn string of uncooperative spring weather.  Every time I’ve planned an exit from this region, I’ve heard the call or felt the lure of some new stellar delight, and there I am — stuck in the snake’s lair once more.  But one way or another, I’m sliding south from here when I get this post done, provided I can get the serpent to look the other way long enough.

The first of the stars in this short tour shares its field with a ghostly ethereal presence, while the other is accompanied by two additional faint pairs of double stars that only emerge from hiding when adequate aperture is applied.  Both were planned for appearances in other posts, but were shifted further back in the pecking order for various reasons, none of which I can remember any more.   At any rate, it’s time to make amends to each of them.

Serpens Caput is where we’re going, and if you haven’t been there, here’s a chart that will orient you in relation to the surrounding constellations.  Once you’ve carefully committed every star on that chart to short term memory (there might be a test before we get done here  😉 ), you’re ready to move on to the next chart, which we’ll use for hopping from the first star to the second:

To get where we’re going, start at Delta (δ) Serpentis, which is located midway along the serpent’s back. Move northeast two degrees and you’ll come to three stars which form a straight line, sitting about a degree south of Xi (χ) Serpentis. The eastern-most and brightest of those three stars is our goal. (Stellarium screen image with labels added, click for a larger view).

OΣ 300        HIP: 76733    SAO: 101673
RA: 15h 40.2m    Dec: +12° 03′
Magnitudes: 6.3, 10.1
Separation:  14.8″
Position Angle: 261°  (WDS 2008)
Distance: 1059 Light Years
Spectral Classification: G7.5

First of all, let’s take a look at a few observations that are notable for what they didn’t see, or at least mention.

Johann Heinrich Mädler first observed and measured this star in 1844, coming up with a separation of 15.43” and a position angle of 261.2 degrees.  Otto Struve was four years behind him in 1848, with measurements that averaged out to 15.20” and 261 degrees.  And W. J. Hussey, who recorded all of this data on p. 132 of this book, made three observations in 1898 that averaged out to 15.32” and 261.2 degrees.  Based on their position angles in comparison to the 2008 observation in the Washington Double Star Catalog (WDS), it’s obvious these two stars have barely moved relative to each other, if at all, since their 19th century observations.

Finally, Sissy Haas had this to say about OΣ 300: “125mm, 200x: Striking contrast for the separation!  A bright whitish peach star with a little vaporish bump on its edge.  At 50x, a bright white star [Chi (χ) Serpentis] is wide in the field.

And here’s what I saw:

What’s that wispy, ghost-like object over in the west corner of the field?????? (East & west reversed to match the refractor view, click for a larger view).

Now you’ll have to look at the southeast edge of the field to see OΣ 300 – it’s not at the center in this sketch.  I saw the secondary as a bit more than Haas’s “vaporish bump,” but then I was using another twenty-seven millimeters of aperture – which may also account for why I saw the primary as a light, pale yellow, with a slight lean in the direction of white.

And over on the opposite side of our circular field of view, you’ll see the ghost-like glow of a galaxy that goes by the name of NGC 5970.

Now I knew it was there when I went in search of OΣ 300, and in fact, it was part of the reason I wandered into this area.  But I wasn’t really sure I would see it.  For the record, it’s magnitude is listed at 11.4, but it’s surface brightness (SB) is listed at 13.1.  That last number is more significant since it measures the effect of spreading out the galaxy’s 11.4 magnitude light across it’s entire size, which is 3.0’ x 2.1’ – in other words, to the telescopically aided eye, the galaxy has the appearance of a 13.1 magnitude object, not an 11.4 magnitude object.

Even though I knew the galaxy was near OΣ 300, I wasn’t sure that I would be able to capture the two in the same field of view even if I did see it.  The first night I went in search of it, I was using my five inch f/15 D&G refractor, and thanks to very good transparency, I was able to easily catch sight of it.  After that, I caught it again in my six inch f/10 refractor, as well as in an eight inch Celestron Edge SCT.  But on those last two occasions there was a lot of murky moisture in the air, which made it a real struggle to pick the galaxy’s faint glow out of the sky background — it had actually been easier to see in the five inch refractor because the transparency was so much better that night.

To see it, you’ll need a dark, moonless night, and at least magnitude five skies.  I’m under magnitude six skies, and still I had to really look hard for it on the two nights of poor transparency.  Using the light blue beauty of 7.4 magnitude SAO 101663 (HD 139609) as a guide, look about ten arc minutes to the southwest of it – and it helps quite a bit to move your scope back and forth just a bit to get it to emerge from the background.  And use averted vision!  You’ll never see it by looking directly at it.

And now we return to our regularly scheduled double star program.  😉

Using the chart above, slide down the serpent’s back past Delta (δ) and Alpha (α) Serpentis until you reach Epsilon (ε).  Two degrees to its south, you’ll see Omega (ω).  You’ll find our next star, Σ 1987, sitting at the eastern corner of an equilateral triangle it forms with those two stars.

Σ 1987  (H III 103)  (Sh 212)       HIP: 78134    SAO: 121277
RA: 15h 57.2m    Dec:+ 03° 24′
Magnitudes: 7.3, 8.7
Separation:  10.7″
Position Angle: 320°  (WDS 2010)
Distance: 430 Light Years
Spectral Classification: A0

This is another star with a history, and like the previous one, it’s not standing alone in its field either – but this time, it’s a pair of double stars that provide the accompaniment, not a galaxy.

I first came across this pair when I was using an AT90mm f/6.7 refractor, which rewarded me with a delicate view of a light gold primary tinged with a bit of white, and a secondary that was a mere dot of  surprisingly blue light.  I didn’t expect either the color or the small visual size, mainly because there are only 1.4 magnitudes of difference between the two stars.  I was also able to pick both stars out of the sky with a 63mm Zeiss refractor and a 15mm TV Plössl, so it’s not a particularly difficult pair to see.

TOB 255 is at the center of this photo, and Σ 1987 is below it and to the left.  North is at the top, west at the left, matching the sketches below.   (Aladin DSS Image, click for a larger view)

But that night I also spied a pair of suspiciously close stars about four arc minutes northeast of our main attraction, which I eventually identified as TOB 255 (magnitudes of 12.0 and 12.9, 14.9”, and 198 degrees, WDS 2000).  In the process of establishing their identity, I also found there was a second pair of doubles about 11.5 arc minutes to the west of the Σ 1987 pair.  I had seen them as a single star in the ninety millimeter scope, so I returned with a six inch f/8 Celestron refractor in my hands and pried the dim little devils apart with the greatest of ease.  That pair is BAL 1410, shining weakly at magnitudes of 11.18 and 11.20, closely separated by 8.1”, and parked at a position angle of 68 degrees (WDS 2000).  Apparently they were just close enough that I couldn’t detect them as a pair in the 90mm scope at 60x.  What’s surprising is that I could split the first pair, which are a full magnitude fainter, in the 90mm scope, but not BAL 1410.  Either that extra six arc seconds of separation made a significant difference, or the first pair is brighter than the 12.0 and 12.9 magnitudes listed for it.

Just to provide a sense of the different perspectives provided by the two scopes, I’ve included sketches made with each of them:

It’s amazing what a few extra inches of aperture will do!    TOB 255 is just barely visible in the 90mm sketch, while BAL 2410 needed 152 millimeters (six inches)  to catch sight of both stars.  (East & west reversed, click on each sketch for a larger view).

And again, as with so many double stars, Sir William Herschel was here first.  He found the Σ 1987 pair on March 4th, 1783, measured them at 12.5” apart with a PA of 320 degrees, and described both as red, although he qualified that with this: “a dry fog, if I may call it, probably tinges them too deeply.”  (p. 197 of 1784 Catalog)

His son, John Herschel, and sometimes observing companion James South, observed the pair in 1823 on three occasions – May 21st, June 6th, and June 12th – and came up with 10.66” and 323 degrees, but left no comments on color.  Friedrich George Wilhelm von Struve observed them in 1831 (10.27”, 324 degrees) and described them as white and ash, and Admiral Smyth caught them in 1835 (10.5” and 324.7 degrees), and saw white and gray.  (Sources: Herschel/South Catalog, pp. 239-240 — scroll to the bottom of the linked page; Struve, p.434 of this book; Smyth, p. 350 of The Bedford Catalog)

Sissy Haas also had a look at these two stars in a 125mm scope and caught sight of the same colors I did: “A pretty pair that seems to jump out of an empty field.  It’s an amber yellow star with a tiny blue companion just a small gap apart.”

And so  ………….  I think that’s mainly about it for Serpens Caput for a while since I’ve been detained here longer than I ever thought was possible.  Although I’ve enjoyed every minute spent here, it’s time to move on — there are new paths calling to me from remote areas of the heavens not previously penetrated by me and my telescopic companions, and my focus fingers are twitching in anticipation.

But, but, but …………… before we go, it’s worth a short look back at this constellation.  I took a tour the other night of all the stars I’ve visited the last few months and found it was a very satisfying way to spend an evening.  I started at the southwest corner with a four inch refractor and picked off one star after another as I worked my way north and east, lingering over each until my eyes had their fill.  Altogether, I suppose I spent about an hour.

I’ve attached a chart below which shows all those stars, and beneath it I’ve listed each of them, including separate links to both the original post and the individual sketches, along with a comment on the minimum aperture needed to see them – depending on your sky conditions, you may need a little bit more or a little bit less.  There are two or three there that are beyond the reach of a four inch (100mm) refractor, but most of the others can be seen in apertures as small as 60mm.

So give it a try some evening.  It’s a great way to get acquainted with a small section of the sky, and experience a very enjoyable evening while doing it.  Highly recommended!

Think of this as your road map to a stellar double star tour (they’re all labeled in light blue). You can attack this from either the north or the south, but to impose some order, I began the list below by starting in the northeast corner with 49 Serpentis and then worked west and south.  Take them in whatever order works best for you, and take your time!!!!!  Give the millions of photons saturating all that starlight plenty of time to soak into your subconscious, where they can linger and work their magic. (Stellarium screen image with labels added, click for a larger view).

Clicking on the name of the star will get you to the post on it, and clicking on the minimum aperture will take you to a sketch of it:

49 Serpentis60mm for AB, probably at least 70mm for C
Σ 2007 (STF 2007):  60mm
OΣ 303 (STT 303):  127mm, maybe in a 100mm scope under ideal conditions
Σ 1988 (STF 1988):  100mm, but much less struggle in 127mm
39 Serpentis 80mm, but you can catch the secondary in a 60mm with averted vision
Beta Serpentis60mm (you’ll need to use averted vision for the AB pair)
OΣ 300 (STT 300):  70mm, possibly 60mm under ideal skies
Delta Serpentis 60mm
Σ 1987 (STF 1987):  60mm (Sketch 1; Sketch 2)
Σ 1930 (STF 1930) / 5 Serpentis):  70mm for AB, 60mm for C and D
Bu 32 / 6 Serpentis:  127mm
Bu 943152mm (on a night with stable seeing!)

Happy sleuthing, and Clear Skies!  😎


5 Responses

  1. Since I started following you blog, I find myself pausing at double stars more. A very enjoyable read! Would love to see photos of the equipment you use.

    • I just happen to have a review of one of the 80mm scopes I use coming up in the next post! Should have it up within the next couple of days. Thanks for the comment, and be careful — double stars can be addicting. 😉


  2. John, had a tough time getting this one. The wind was gusty. Tried to get TOB 255 but I think I only got one of the stars. The scope was dancing around like a humming bird. Fun, though. Here’s the sketch:

    Tried to research TOB 255 – made some notes on the bottom of the log. Don’t think I actually identified it positively. Spent about an hour on this as I knew it would be the only observation I’d make considering the conditions. Got a pretty close measurement with my Astrometric EP w/out a Barlow. Let me know any thoughts you may have…

    • You’ve definitely got the right star identified as TOB 255, Steve, but in that kind of wind it would have been darn hard to see both components. Being both faint and relatively close makes that a hard task under those conditions, even with the C9.25. Give it a try again on a better night and you shouldn’t have any problem at all with it. You should also be able to pick out that other pair to the west, BAL 2410, although it will be beyond the fields of view you show in the two sketches.

      I had a look at STF 1998 and 1999 a couple of nights ago under rather murky conditions, but even at that, it was a pleasing sight. I’ll do a post on it soon. If you have any info you want to add, let me know. I’ll send you a separate email on it so we can exchange thoughts on it.



      • Thanks, John. A real pleasure to participate. Yes, I’ll try again under more stable WX conditions. This is a great area of the sky at this location right now. We get a good view to the south. I just starting using SkySafari Pro on my MacBook connected to the scope. I know its cheating, but I have very little time when I’m at the summit. I’m quite good at star-hopping, having completed the Astro League Double Star, Messier and Carbon Star Club lists. All require star hopping. Now, I have only one night a week to observe and its a crap shoot for good WX conditions. Last night Struve 1987 was all I got to observe.
        I hope you can make it to the Maui Double Star Conference. It should be a great get-together for double star enthusiasts.
        In any case, we can exchange virtually. Looking forward to your post on Struve 1998 & 1999.
        Looking UP, Steve

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