This is a continuation of a two part tour in southwestern Lyra, the first part of which looked at an area south and southwest of Sheliak (you can get to it by clicking on this link if you missed it). This time we’re going to strike out west of Sheliak and see what gems were found in the celestial darkness by F.G.W. Struve and his son, Otto.
First, if you’re not familiar with the area, let’s locate Sheliak:
And then we’ll zoom in on the immediate Sheliak environs and look at the chart we’re going to use for this tour:
We’ll start with Σ 2349, which is located due west of Sheliak at a distance of just under three arc minutes (2° 49’ to be exact). If you look on the chart (click here to open it in a second window), you’ll see two faint stars which straddle a line drawn from Sheliak to Σ 2349. HIP 91984, with a magnitude of 7.35, lies south of that line at a distance of one degree from Sheliak, and HIP 91563 (magnitude of 7.28) lies north of the line at a distance of two degrees from Sheliak. If you aim midway between those stars and continue due west, you’ll find Σ 2349 waiting patiently.
|Σ 2349 HIP: 91235 SAO: 67164|
|RA: 18h 36.6m Dec: +33° 28’|
|STF 2349 AB:||5.39, 9.40||7.40″||204°||2006|
|WAL 92 AC:||5.39, 12.10||32.90″||314°||1998|
|Distance: 522 Light Years|
|Spectral Classification: “A” is B8|
This is the most difficult of the three stars we’re going to look at due to it’s relatively tight separation, coupled with a sizable four magnitudes of difference:
It was 1830 when F.G.W. Struve first measured the AB pair at 205.5° and 7.33”, and as Thomas Lewis’s compilation of observations at the right shows, there was little change in the next seventy-four years which followed. The WDS measure in 2006 shows not much happening here with the passage of an additional 102 years. The proper motion numbers in the WDS show the primary crawling along at a rate of +004 +003 (.004”/year east, .003”/year north). No numbers are shown for “B”, but considering the absence of significant change in the AB pair, “B” appears to be following the primary at very close to the same pace.
The three letter identifier of WAL 92 belongs to A. Wallenquist, who apparently had a good look at this area since he also discovered the “E” and “F” components of Nu-1 Lyrae on our last excursion. According to the WDS data, he first measured the 12.10 magnitude “C” component of Σ 2349 in 1944 at 320° and 30”, and as you can see above, the most recent WDS measure for AC is 314° and 32.90”. But if you look carefully at the sketch above, you can see the position angle of AC is actually further north than 320 degrees.
I pulled up an image of Σ 2349 in Vizier to see what I could discover and found a star at that same location, which is labeled “1” in the image below:
I also used the UCAC4 catalog in Vizier to get the magnitudes of the stars on the northwest side of the primary in order to pin down the correct star. (Type UCAC4 — in upper case letters! — in the Vizier search box and then enter the WDS identification of 18366+3328 in the search box on the next screen. After the date comes up, click on the last option at the bottom of the data [optical image] to get the chart above. Click on any of the stars with red circles and its data will appear at the bottom of the chart.)
The only star that comes closes to the correct magnitude is the one I labeled with a “1”, which UCAC4 has at a magnitude of 12.561. Stars “2” and “3” are way too faint to be candidates. Next I put the Aladin/Vizier measuring software to work to get the position angle of star number “1” and came up with 341°, but then got a surprise when I found the separation measured 46”, quite an increase from the 1988 WDS separation of 32.90”. Just to check further, I measured the distance and position angle from the primary to star number “2” at 296° and 51.42”, and from the primary to star number “3” at 319.5° and 57.0”
So something is wrong somewhere. My observation and the photo don’t match at all with the first (1944) and last (1988) measurements in the WDS. Another celestial conundrum, once again.
Now we’ll reverse direction and head for one of Otto Struve’s discoveries, OΣΣ 172, which is located east and somewhat north of Σ 2349 at a distance of just under two degrees (1° 43’) – here’s our previous chart once again. You can use 7.28 magnitude HIP 91563, located not quite halfway to OΣΣ 172 at a distance of 48’, as a stepping stone. Or you can center your finder midway between Sheliak and Σ 2349 and you should be able to spot OΣΣ 172 northeast of that spot at about 40’ away. A good 8×50 finder will show both stars, similar to what’s shown on the chart, which makes it easier to locate.
OΣΣ 172 (STTA 172) HIP: 91940 SAO: 67311
RA: 18h 44.5m Dec: 34° 00’
Magnitudes: 7.91, 8.66
Position Angle: 6° (WDS 2012)
Distance: 176 Light Years in Simbad; 168 Light Years in Hipparcos
Spectral Classifications: “A” and “B” are F8
This is a bright and wide pair which should also be suitable for a 60mm refractor. On close examination, it’s a real beauty:
I didn’t catch it (not that I was looking for it) but S.W. Burnham mentioned seeing a faint star between the primary and secondary during one of the two observations he made of OΣΣ 172 in 1880 and 1905 (source):
Chances are it would have been buried in the glare, anyway, since according to the UCAC4 data it’s a 13.76 magnitude star:
Because this is a wide pair, I was curious about whether the primary and secondary are related. The WDS shows very similar proper motions for both the primary and secondary, which a chart from Simbad shows rather well:
In order to get a better picture of where the two stars are in relation to each other, it would be helpful to know the distance of the secondary (which also is identified as BD +33 3191 and SAO 67314), but several sources failed to show any data. Just to give you an idea of what’s available, I checked Hipparcos (available in Vizier by entering I/239/hip_main in the search box), Simbad, the Tokovinin Multiple Star Catalog, and the Yale Trigonometric Parallaxes (available in Vizier by entering I/238A/picat in the search box). It’s rather unusual for an 8.66 magnitude star not to have a published distance or parallax, so it could be both stars are at the same distance. Before I forget about it, many thanks to Bob Argyle and Neil English for the Tokovinin and Yale references.
Now let’s return to Σ 2349 in order to find our way to our last star, Σ 2333. If you look on our chart again, you’ll see we need to move southwest from Σ 2349 for about the same distance that separates Sheliak and Σ 2349, which is just under two degrees (1° 41’ in this case). You can use 7.60 magnitude HIP 90716 as a reference point since there’s nothing but a dark lane existing between Σ 2349 and Σ 2333.
|Σ 2333 (S 703) HIP: 90766
|RA: 18h 31.1m Dec: +32° 15’|
|STF 2333 AB:||7.82, 8.57||6.40″||333°||2007|
|STF 2333 AC:||7.82, 12.90||164.40″||35°||2002|
|STF 2333 AD:||7.82, 13.70||85.80″||339°||2002|
|STF 2333 BC:||8.57, 12.90||161.20″||37°||2002|
|Distance: 707 Light Years (Simbad)|
|Spectral Classification: “A” is A0|
Even though Struve’s name is assigned to this system, Sir James South actually arrived here first with his measuring tools, coming up with a position angle of 336° 9’ and a separation of 6.43” for the AB pair in 1825. If you look at his observation at the left, you’ll see he started out using n p (north preceding) on his first measures of June 9th, 1825, and then switched to s p (south preceding) a month later on July 13th, and continued with south preceding on his final averages. But the final figure of 66° 9’ south preceding translates into 203° 51’, which is obviously way off, whereas 66° 9’ north preceding results in a more harmonious 336° 9’ (compare with the measurements shown below at the right). If you’re wondering how I translate those figures, at the end of this post I’ve attached a chart I use which comes from page 428 of this version of Admiral Willam H. Smyth’s Bedford Catalogue. (The Bedford Catalogue is actually part two of a larger book, A Cycle of Celestial Objects, which is where that link takes you).
Six years later, when F.G.W. Struve arrived on the scene, he measured the position angle at 335.3° and the separation at 6.28”. After that, as the excerpt at the right from Lewis’s book shows, through 1904 the position angle averaged out to 334.6° and the separation to 6.38”. Comparing those numbers to the last WDS measure in 2007 shows little change occurring.
However, there’s an interesting difference in the proper motion numbers shown in the WDS and Simbad. The WDS has “A” and “B” moving at the same rate (.001”/year west, .002”/year south), while Simbad has “B” with a different rate and direction (.0065”/year west, .0036”/year north). The WDS also shows PM numbers for “C” and “D”, but Simbad shows nothing for either star.
|Proper Motions of Σ 2333|
|AB:||-001 -002||-001 -002 (006.5 +003.6 in Simbad)|
|AC:||-001 -002||-001 +002|
|AD:||-001 -002||+002 +016|
Simbad also has a plot of the AB pair, which looks like this when you zoom into a three arc minute view:
Considering how little change in separation and position angle has taken place, it looks like the WDS data is more reliable, although in either case the motion is very minimal.
Since I had been unable to see it, I was curious about “D”, so I pulled up an Aladin photo of Σ 2333 and used the UCAC4 catalog to see if the magnitude there was fainter than what was shown in the WDS. After using Aladin’s measuring software to pin down the location of “D”, I found UCAC4 listed the magnitude at 14.173, which may explain why I didn’t see it. On the other hand, even if the magnitude had been 13.70 per the WDS listing, it would have been tough to detect in the combined glare of the primary and secondary.
So at the end of this three star adventure, we’re left with two head scratching contradictions, one being the correct position angle and separation for Σ 2349 AC, and the other the correct proper motion for the secondary of Σ 2333. While you’re busy solving those two issues, I’m going to pay a visit to a small constellation I haven’t given enough attention to over the last few years. Meet me in Delphinus next!
Clear skies until then. 😎
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The Old Style Position Angle Chart
The numbers in the outer ring of this chart represent the current system of measuring position angles, while the numbers on the inside refer to the old style used above by James South (here’s his observation of Σ 2333 again). So if we take Sir James’ June 9th, 1825, position angle of 66° 23’ north preceding and look it up on the inside ring of the chart, we get a reading of 336° 23’ on the outer ring. If we use his July 13th, 1825, position angle of 65° 55’ south preceding, we find it equals 204° 05’ – which is nowhere close to Struve’s 1831 position angle of 333.3°.
The old style of measuring the position angle has the virtue of being more descriptive because it conveys the position angle in terms of the motion of a star through the eyepiece: preceding puts a secondary on the west side of a primary, following places a secondary on the east side of a primary. What stands out as rather odd, though, is the way south is placed at the top of the chart and north at the bottom. Although refractors were far more common in the early days of astronomy, star diagonals were apparently non-existent. Viewing an object without a diagonal in the eyepiece end of the tube results in all four directions being reversed, just as they are on the chart. That’s the most likely explanation for the reversal of north and south, but it may also have to do with the orientation of the image in a Newtonian reflector, although that telescope design didn’t get much attention until William Herschel began producing and using them. I haven’t been able to pin down the point at which the old style PA chart came into widespread use, but it’s possible Sir William had some influence since he was the first observer to produce a large number of double star measures, virtually all of which were done with Newtonian instruments.