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Draggin’ a Net through the Dragon (aka Draco), Part 2: Σ 2549, Σ 2509, Σ 2604, Σ 2573, Σ I 44

Draco, captured between Hercules and Ursa Minor (Stellarium screen image with labels added, click on the chart to enlarge)

After I left my net floating in Draco a few weeks ago, I found myself mired in the middle of a rain delay that continued for so long I was about to throw a tarp over the field and cancel the game.  But never fear, just when my neighbor pounded the last nail into his ark, the rain stopped, the clouds began to leave, and fair weather took over.  All those people who were lined up in pairs to get on the ark went home, but they’ll probably be back.  I have a hunch that thing will be afloat by the end of November.

At any rate, the skies are clear tonight, so time’s a-wastin’.  Grab hold of a corner of that net and bring your scope.  We’ve got a few more stars to catch before the rains return.

Starting at Xi (ξ) Draconis, which lies at the north corner of the parallelogram that outlines Draco’s head, we’ll make a hard turn to starboard and set a northwesterly course for third magnitude Delta (δ) Draconis. It lies about nine degrees from Xi (ξ), and anchors the opposite end of a section of sky notable for its scarcity of visible stars. (Stellarium screen image with labels added, click for a larger view)

At Delta (δ), we’re going to make a ninety degree turn to port and sail southwest into another relatively barren area of sky.  But lurking on the other side of the naked-eye threshold is a rather diverse collection of multiple starlight, much of it in multiple pairs, scattered throughout this stellar desert — and it’s just waiting to be re-discovered by us.  But first, we’ll pause at Pi (π) for some quick refreshment before we get started.  Grab me a piece of apple, if you can find it!

After the pause at Pi (π), which lies one degree southwest of Delta (δ), we’ll make a forty-five degree turn to the south, continue another degree and half, and then tie up at our first destination, Σ 2509. You can use 6.5 magnitude HIP 94993 to mark the halfway point to keep you on course. (Stellarium screen image, labels added, click to enlarge)

Σ 2509              HIP: 94760    SAO: 18257
RA: 19h 16.9m   Dec: +63° 12′
Magnitudes: 7.4, 8.2
Separation:  1.8″
Position Angle: 328°  (WDS 2010)
Distance: 267 Light Years
Spectral Classification: F6
Status: Undetermined

Claustrophobically tight, but not alone at least, with ES 2677 hovering to the east. (East and west reversed to match the refractor view, click to enlarge)

Now this is a tight little pair of stars, but surprisingly easy to split considering their claustrophobic separation of 1.8″.  I suspect that’s because they’re both relatively faint, which means less scattering of light to interfere with the dark sky between them.  Admiral Smyth had a tougher time with them, describing them as “a very difficult object” in his Bedford Catalog — but then his 1833 measurement put them at 0.5″ apart.  He also states that Struve came up with pretty much the same measurement in 1837 — 0.573″ if you want to be exactly exact.  So it would seem they’re moving apart slowly.

I got them easily in my Meade AR-5 at 118x using a 10mm Radian, and duplicated that a few weeks later in my four inch Celestron refractor at 100x, also with the 10mm Radian, although it was barely split by more than a hair.  The view I preferred was with the 7.5mm Celestron Plössl, shown in the inset of the sketch, which gave me 157x in the AR-5.  I saw both stars as white, as did Smyth.  It’s rare that we agree, so one of us must be right!

As I was looking around the field of view on that first night with the AR-5, I spotted another close pair to the east and slightly south of the Σ 2509 duo.  That turned out to be:

ES 2677      (No HIP or SAO numbers listed in Simbad)
RA: 19h 17m 26″   Dec: +63° 09′ 56″
Magnitudes: 11.3, 11.4
Separation:  14.0″
Position Angle: 90°  (WDS 2008)
Distance: ?????
Status: Undetermined

………  which gives us two pairs for the price of one, so to speak — and that turns out to not be at all usual around these dark parts.  Dim though they are, they’re far enough apart that they stand out distinctly.  First discovered in 1898 by T. E. Espin, as of the most recent WDS observation in 2008 no determination had been made as to whether this pair is gravitationally related or not.

Now we’ll change course and head for the next destination on our tour, Σ 2549, which lies about a degree west and slightly north of our current location.You’ll find it floating in a black sea about halfway between 6.4 magnitude HIP 95576 and 6.5 magnitude HIP 96297. (Stellarium screen image with labels added, click to enlarge)

Σ 2549            HIP: 95986    SAO: 18378  (HIP & SAO numbers refer to “D”)
RA: 19h 31.2m   Dec: +63° 19′
*****               Magnitudes         Separation          Position Angle        WDS Data
AB (Bu 655):    8.3, 12.0                  2.1″                     329°                   1991
AC:                  8.3,  9.3                28.0″                     284°                   2010
AD:                  8.3,  8.0                55.1″                     270°                   2010
AE: (GUI 24)     8.3, 10.5              152.6″                    241°                   1999
Distance: 1599 Light Years
Stellar Classification: All K0
Status: Undetermined

Now hang on to the arm of your chair — or if you’re standing, get a firm hold on something — because this one is a real visual treat.

The first thing that will strike you is the way the three most visible stars are lined up in a very gentle arc.  The next thing is the colors, which are subtle at first, but with a minimal amount of persistence, they become very obvious — although, as I discovered, a moonless night goes a long way toward giving the colors a chance to shine.

A beautiful arc of subtle color, with “E” extending the arc to a dim conclusion.  Turn out the lights for the full moonless night effect!  (East & west reversed, click for a version without this caption)

The first time I looked at this group of stars was in a four inch Celestron refractor on a very bright moonlit evening, so the colors totally escaped me.  But the second time, with a Meade AR-5 minus the moonlight, I got the full effect — no doubt with a little help from the extra one inch of aperture.  I saw just a shade of yellow in the primary, a tinge of red/orange in the middle star (“C”), and a bit of bluish-white in the last of the three stars, “D.”  The “D” star is a bit usual in that it’s the brightest of the three most visible stars of this grouping — normally the primary would lead the way.

In a 60mm scope, these three stars form a cool and compact little group.  Using the 60mm f/15 I have mounted on my C102, the middle of the three stars was difficult to see in a 20mm TV Plössl (45x) without the use of averted vision, but it was clear and obvious at 60x in a 15mm TV Plössl.

If you didn’t know “E” was a part of this group, it would probably escape your attention.  But once you realize it’s there, it’s not at all difficult to see, thanks to its distance from the trio of brighter stars.  It was first included with Σ 2549 in a 1911 observation made at an observatory in Lyons, France, by M.J. Guillaume, and was updated again in 1999 in the WDS.  In the intervening eighty-eight years, its position angle only changed by one degree, so the jury reached no conclusion as to whether it’s linked to the other stars gravitationally or is just floating past as an impartial observer.

I had no luck with splitting the AB pair because the seeing was never quite stable enough for it, but after reading in S. W. Burnham’s General Catalog of 1290 Double Stars Discovered from 1871 to 1899 that he detected it in 1878 with the 18 1/2 inch Clark refractor in use at Dearborn Observatory in Evanston, Illinois, I didn’t feel too badly. Given good seeing conditions, it should be visible in an eight inch SCT, and possibly in a six inch refractor.

Next, let’s increase our lean to the northwest a bit more and travel a degree and a half to Σ 2604. You can use Σ 2549 and HIP 96297 as pointers, since they’re aimed almost directly at our goal. (Stellarium screen image with labels added, click to enlarge)

Σ 2604          HIP: 97831    SAO: 18575
RA: 19h 52.8m   Dec: +64° 11′
Magnitudes: 6.9, 9.0
Separation:  27.9″
Position Angle: 183°  (WDS 2010)
Distance: 556 Light Years
Stellar Classification: G5
Status: Undetermined

Two pairs of stars in one field of view once again, making the dim field of view worth a longer look. (East & west reversed, click for a larger view)

This pair is pretty well in harmony with the lack of background stars that seems to characterize much of this southwest area of Draco.  The primary clearly dominates the surrounding sparse field, and even the ninth magnitude secondary seems to absorb some of that primary radiance.  Needless to say, I had no problem picking them out of the surrounding field in the four inch refractor I was using.  The secondary was a bit tougher in the 60mm f/15 mounted on the larger refractor — I needed to use averted vision to catch it at 45x in a 20mm TV Plössl, but it fought its way out of the glare and into direct vision at 60x in a 15mm TV Plössl.

I saw white when I looked at the primary, and couldn’t detect any color at all in the secondary.   Haas apparently didn’t look at this one, but she quotes Geertsen as seeing “light yellow with greenish” in a 100mm scope.  Hmmmm, maybe I better look again.

This is another case of two-for-one, with the much dimmer AG 394 located to the east of Σ 2604.  I had no problem seeing this pair, either, even though they’re faint.   But once again, they’re far enough apart at 22.1″ to make it easy.  This one was discovered in 1903 — the most recent observation, in 2010, shows it has moved a grand total of one tenth  of an arcsecond in the intervening 107 years.  As you would expect, with so little motion no determination has been made on it’s status.

Time to reverse directions, point our craft south and slightly east, and set sail for Σ 2573. We’ll use 6.7 magnitude HIP 97356 to make a slight mid-course correction by bending a bit more to the southeast, and then we’ll continue almost another full two degrees to get up close. (Stellarium screen image with labels added, click on the chart for a larger view)

Σ 2573                HIP: 96771    SAO: 18461
RA: 19h 40.2m   Dec:+ 60° 30′
Magnitudes: 6.5, 8.9
Separation:  18.1″
Position Angle: 26°  (WDS 2010)
Distance: 392 Light Years
Stellar Classification: A5
Status: Undetermined

An “aqua-marine” primary and a secondary with no color at all ……… (east & west reversed, click for a better view of the blue)

My first view of this one was in the Meade AR-5 on a breezy night flooded with moonlight, which meant both stars appeared to be white.  At the time, I thought it deserved a second look on a darker night, so I made a mental note to return.

I came back a few weeks later with my four inch Celestron and found a bit of blue in the primary that I had missed in the unforgiving moonlight.  The secondary remained in that strange color-less land of no color at all, not even gray — I guess the best you can say in those instances is it’s just there.  Haas’s observer for this one, Geertsen, who was using a 100mm scope, came up with a better description of the primary — “aqua-marine” — which fits it perfectly.

Again, in my 60mm f/15 that roosts on top of the 102mm refractor, I needed averted vision to catch the secondary.  That was at 45x with the 20mm TV Plössl.  And once more, the 15mm version of that same eyepiece cured the secondary of its disappearing act at 60x.

There are several close pairs in the surrounding field of view, but from what I could find, none of them have been cataloged as doubles — so no two-fers this time.

One last short hop of about half a degree southeast will get us to our final stellar docking point. With Σ 2573 centered in your finder, you should be able to see Σ I 44 burning at about the same brightness a little to its southeast. (Stellarium screen image, labels added, click to enlarge)

Σ I 44 (STFA 44 in WDS)           HIP: 96164    SAO: 18395
RA: 19h 33.2m   Dec: +60° 10′
Magnitudes: 6.5, 8.2
Separation:  75.5″
Position Angle: 288°  (WDS 2005)
Distance: 1204 Light Years
Stellar Classification: K4
Status: Physically related  (WDS, note Z)

A tangerine primary and the blue dot of a secondary make this one a memorable view. (East & west reversed, click … to … enlarge)

Ahhhhh ……. finally a bit of luscious color to liven up this area of the sky!  This pair is really a pleasing sight at first glance, and not a bad way to end our tour.

You can’t miss the glowing primary with it’s sharp tinge of orange — maybe tangerine is a better description — since nothing else in the field comes close to matching it for either brilliance or color.  The secondary has a very noticeable blue-white tinge to it, which provides a bit of contrast with the glowing primary.  That orange/tangerine glow was also very evident in the 60mm f/15 at 45x (20mm TV Plössl again) — a bit weaker in brilliance, and more compact, but all the more aesthetically pleasing because of that.

And for the third time on this trip, there’s another pair of stars lurking in the same field:

Σ 2554         HIP: 96216    SAO: 18402
RA: 19h 34.0   Dec: +60° 17′
Magnitudes: 9.1, 9.6
Separation:  18.8″
Position Angle: 195°   (WDS 2003)
Distance:  ?????
Stellar Classification: A2
Status: Undetermined

This pair of stars was obvious right away when I first peered into an eyepiece at the main attraction.  A bit too faint for any color to be seen, and not in possession of any particular qualities that will earn them a place in a stellar hall of fame, they nevertheless seem to provide a bit of comfort and company to the brighter pair at the center of the field of view.

It’s also an interesting pair of stars because the secondary seems to be moving away from the primary in a straight line.  Struve measured the separation at 15.0″ in 1831, which had widened to 18.8″ in 2003 according to the WDS data.  But the position angle has remained at 195 degrees during all that time.  So I presume that’s the reason no determination has been made as to the status of this pair.

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

And with that, we’ve finished a rather extensive exploration of the Draco-nian area lying southwest of a line running from Xi (ξ) to Delta (δ) Draconis.  Out of the ten main stars we’ve looked at, there are a couple that really deserve to be better known.  At the top of that list I would put  Σ 2549 and Σ I 44, both of which stand out on this tour — the first because of that delicate arc of three closely space stars, and the second because of the color of the primary.  And looking at the five in the first tour, I find I’m hard pressed to pick a favorite since some aspect of all five of those required some real effort.  But of all ten, I think  Σ 2549 is the most memorable — that trio of curving stars would stand out just about anywhere, but especially in this sparse area where there’s nothing to compete with it    ……..    so how about another quick look!

Σ 2549 in black and white! (STScI Photo, click for a larger view)

However ———————- there’s always a however ——————-

—————   there’s one more we haven’t looked at, even though we were camped right on top of it at the beginning of this tour.  So don’t go too far — it’s coming up next!

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