During our last exploration we star-hopped our way through a distinctive area of Hercules south of Gamma (γ) Draconis, aka Eltanin, which is situated at the southeast corner of Draco’s head. For this excursion we’ll see what we can turn up in a seldom-traveled area of the sky beneath the southwest corner of the circuitous Dragon’s four-sided head, which is occupied by Beta (β) Draconis, aka Rastaban, aka Alwaid (scroll down to the middle of the page). It’s an eye-catching yellow-white third magnitude star which also just happens to carry a double star designation, Bu 1090. With magnitudes of 2.79 and 14.0 separated by 4.40”, it’s another one of S.W. Burnham’s vision tormenting pairs. I notice the most recent observation of that pair was in 1939, which apparently means others have had a hard time detecting the 14th magnitude secondary as well, especially since a third component was added as recently as 2012 (magnitude of 12.70 at 118.90”) without updating the measurements of the 14th magnitude star.
At any rate, to get where we’re going it’s much easier to start from Eltanin again and then drop south and work our way west through a rather dim and forlorn stretch of sky.
First, though, here’s a wide view of or we’re where going:
Stellarium screen image with labels added, click for a larger view.
And now we’ll zoom in on the area south of Eltanin and Rastaban:
Starting at second magnitude Eltanin, we’ll hop southwest almost a degree and a half (1° 23’) to fifth magnitude 30 Draconis. From there it’s a full degree further southwest to 7.0 magnitude HIP 86869, which is also double (TDT 485), although with a separation of .80” and 2.33 magnitudes of difference (7.29, 9.62) we’ll pass on it this time out. However, with HIP 86869/TDT 485 centered in your eyepiece, you’ll find Σ 2229, our first target, shining in the same field just 12’ northeast of it. (Stellarium screen image with labels added, click on the chart to enlarge it).
(You can also start at Rastaban and take this tour in reverse order (which is what I did originally) by following an arc of stars outlined in the chart above by 6.45 magnitude HIP 85268, 5.65 magnitude HIP 84950, 7.45 magnitude HIP 84511, 6.25 magnitude HIP 84021, 7.10 magnitude HIP 84072, and 6.45 magnitude HIP 83857, and on to Σ 2142. That’s a bit trickier, but it’s a good way to sharpen your star-hopping dexterity).
Σ 2229 No HIP SAO: 30555
RA: 17h 45.9m Dec: +50° 11’
Magnitudes: 8.31, 10.30
Position Angle: 338° ( WDS 2006)
Spectral Classification: “A” is K2
Note: Simbad shows “B” at a visual magnitude of 9.76
The seeing wasn’t cooperating at the time I was looking at this relatively tight pair, so I had to settle for a lowly magnified view in order to catch a firm glimpse of the secondary:
The primary had a very delicate and beautiful red-orange-white tint. Even in the wider field provided by the 26mm Plössl, the secondary, which was just a bit more than a spark of light, was clearly separated from the primary. (East and west reversed to match the SCT image, click on the sketch to get a better view of the secondary).
Shown in the southwest corner of the view is the star we used to locate Σ 2229, HIP 86869. As I mentioned above, it’s also a double star, TDT 485. The WDS shows magnitudes of 7.29 and 9.62, a separation of .80”, and a position angle of 328°, all based on 1991 data from the Tyco Double Star Catalog. That’s the only existing measure, so here’s a chance for someone with a well-developed photographic double star technique to make a contribution.
Click to enlarge.
It looks like there has been some change in the Σ 2229 pair since Struve’s first measurements, although not much. I added older WDS data I dug up to the excerpt at the right from Lewis’s compilation of Struve’s double stars and some distinctive irregularities are obvious. Mädler (Maed) shows a large increase in separation in 1843 to 6.72” which stands out from the rest of Lewis’s data, while the WDS data shows a 1931 separation of 5.3” which isn’t repeated by any of the other measurements. The WDS data also shows a surprising variation in position angles which don’t match the pattern of the data listed by Lewis.
Simbad shows a proper motion for the primary of -006 -010 (.006”/year west and .010”/year south) and -008 -007 for the secondary (.008”/year west and .007”/year south), which isn’t much, but it does mean the two stars should be separating slowly as the position angle decreases very gradually:
Click to enlarge the image.
Based on Simbad’s PM numbers, I would expect the 2006 WDS position angle is likely to be more accurate than the numbers shown from 1931 and 2002. The 2006 PA also matches the slowly decreasing trend in position angles from 1830 to 1905 shown in Lewis’s data. At any rate, here’s another opportunity for a photographic measurement.
Now on to our next pair, Fox 202 (here’s our last chart once more). From HIP 86869/TDT 485 move almost a full degree (52’) southwest to 6.60 magnitude HIP 86446, then another 40’ in the same direction to 7.5 magnitude HIP 86418, and then 32’ west and slightly south to 7.35 magnitude HIP 85880. Fox 202 lies 27’ northwest of it at the north end of two 9.5 magnitude stars that point almost directly to it.
Fox 202 HIP: 85769 SAO: 46777
RA: 17h 31.6m Dec: 49° 43’
Magnitudes: 8.1, 10.8
Position Angle: 237° (WDS 2003)
Distance: 937 Light Years (Simbad)
Spectral Classification: “A” is K0
The primary and secondary are located at the center of this field of view, competing for notice with a scattering of stars of slightly fainter magnitude to the southeast. I saw white in the primary and had to use averted vision to catch sight of the secondary. (East & west reversed to match the refractor view, click on the sketch and it’ll spring to life).
Also seen in the sketch above at the extreme east edge of the field of view is Hu 1282, a dim pair discovered in 1904 by W.J. Hussey. It’s just a bit tight and faint for my astronomical apparatus, with magnitudes of 10.3 and 11.3, a separation of 0.5”, and a PA of 142° (WDS 2010).
Click for a larger view.
Fox 202 was discovered by Philip Fox in 1909 with the observatory’s 18 ½ inch Clark Refractor (shown full size at the bottom of this piece) while he was employed at the architecturally intriguing Dearborn Observatory outside of Chicago.
It took a while, but I found Fox’s original observation of what was later cataloged as Fox 202 in a 1915 publication of Dearborn Observatory. Fox identified the pair with the primary’s BD (Bonner Durchmusterung) number, +49 2653, which I was able to cross-reference in Stelladoppie and Simbad with Fox 202.
Click to enlarge.
There’s a surprising difference between the 2003 data listed in the WDS and Fox’s observation. As the excerpt at the left shows, he made two measures, both of which were very consistent. Simbad shows a small amount of proper motion for the primary, +017 +005 (.017”/year east and .005”/year north), but none for the secondary. Since the small amount of motion of the primary is nowhere near enough to account for the ten arc seconds of change in separation from 1909 to 2003, I became curious about what measurements between those of Fox in 1909 and the WDS data of 2003 might show. Brian Mason at the USNO, home of the Washington Double Star Catalog (WDS), was kind enough to send me the text file for Fox 202, and I was surprised at what I found.
The WDS text files contain all known published measures of a given double star, which is always handy data to have in order to see how a pair of stars change over time. In the case of Fox 202, I found there was only one additional measure made between 1909 and 2003. But just as important, the text file also contains a bibliographical reference to the original source of each measurement. The reference for the only additional observation of Fox 202 led me to the Webb Society’s Double Star Circular Number 15:
As you can see, that data is much closer to Fox’s 1909 measures, and very close to what you would expect to see based on the proper motion of the primary. I also learned from the introductory material to the data that the measure was made on a digitized photographic plate by Tòfal Tobal at the Garraf Astronomical Observatory in Spain as part of a comprehensive program to measure what at the time was a long list of neglected double stars in the WDS – which explained why there were no measures of Fox 202 between 1909 and 1983.
As for the last (2003) measure listed in the WDS for Fox 202, the bibliographic information in the text file showed the source of those measures came from an unpublished manuscript connected with a 2003 project at Georgia State University. Given that the separation of 55.40” in that manuscript varies by over ten arc seconds from Fox and Tobal’s measurements, it’s quite likely a result of an error. Just to check a bit further, I turned to Vizier for the Aladin image of Fox 202 shown below and used Vizier’s measuring tools to come up with a separation of 45.22” and a position angle of 233.7 degrees, very close matches to Tobal’s 1983 data.
Click for a larger image.
As I mentioned at the outset, we’re in a seldom-traveled and neglected part of the sky, which we’ll find is the case again with our next pair, Σ 2167.
This one will require some careful navigating even though it isn’t far (here’s our chart again). There are two ways to get there. First, move due west to a pair of faint stars, magnitude 8.65 HIP 85430 and 8.55 magnitude SAO 46712 (no HIP number). The distance from Fox 202 to HIP 85430 is 40’, and from there it’s another 32’ southwest to Σ 2167. Because that pair of stars is faint and right at the limit of many finders, you might have better luck dropping back down to 7.35 magnitude HIP 85880 and then moving due west for a distance of 1° 25’ to reach Σ 2167.
Σ 2167 HIP: 85175 SAO: 46697
RA: 17h 24.4m Dec: +49° 31’
Magnitudes: 8.12, 10.67
Position Angle: 208° (WDS 2010)
Distance: 843 Light Years (WDS)
Spectral Classification: “A” is F5
Another faint Struve pair (in the center of the view) surrounded by an interesting scattering of stars. The primary was white and the secondary was almost an averted vision object because of the 2.5 magnitudes of difference. (East & west reversed, click on the sketch for a much better view).
In our last tour, we ran into a Struve pair, Σ 2293, which had been labeled as rejected (“rej.”) in Burnham’s 1906 catalog, and that was again the case with this pair.
Lewis also skipped over it in his collection of Struve observations, so I went back to Struve’s 1827 catalog and found he had described the pair as having a separation of between 4” and 8” (see p. X of Lewis for a breakdown of Struve’s Roman numeral categories), which obviously doesn’t match Espin’s observation of 18.24” in 1900 or the WDS observation of 20.8” in 2010 . . . . . which explains the “rej.” notation.
Curious as to whether any other observations might have existed between Struve’s in 1827 and Espin’s in 1900, I once again sent a request to Brian Mason at the WDS. And again, when I opened the text file I was surprised at what I found: not a single observation between 1827 and 1900. But I did find a series of observations made relatively quickly following Espin’s, which I collected from various sources based on the bibliographical information in the WDS text file. Among those were observations by Burnham in 1907 and Philip Fox in 1909. I also found a pair of observations from 1901 and 1902 by an Italian astronomer, A. Bemporad, which weren’t published until 1934, along with a 1919 observation by W.S. Franks.
Click for a larger view.
There’s a steady increase in separation in those measurements as well as the later ones in the WDS text file up through the most recent 2010 data, which is reflected in the proper motion numbers for the Σ 2167 pair. The primary is listed with a proper motion of -022 +040, meaning it’s moving west at the rate of .022” per year and north .040” per year, while the secondary is practically sitting still with motions of +001 (.001” east/year) and -004 (.004” south/year).
Our last stop is Σ 2142, which is due west of Σ 2167. Start by moving a long degree (1° 15’) due west to 7.50 magnitude HIP 84530 (here’s that chart again). Then continue due west for another 50’ and you’ll arrive at Σ 2142.
Σ 2142 HIP: 84108 SAO: 46561
RA: 17h 11.7m Dec: +49° 45’
Identifier Magnitudes Separation Position Angle WDS
STF 2142 AB: 6.18, 9.35 5.30” 109° 2006
KUI 78 AC: 6.18, 14.70 28.10” 107° 2003
Distance: 309 Light Years (Simbad)
Spectral Classification: “A” is A5
You have to look closely to see the weak ninth magnitude secondary overshadowed by a white primary three magnitudes brighter. With the 18mm Radian I used for the sketch, I needed averted vision to see the secondary (mainly because of poor seeing), but could detect it easily with direct vision using a 14mm Radian (109x). (East & west reversed once more, click on the sketch to improve the view).
There’s another double over at the east edge of the field of view, COU 1776. Magnitudes on that one are 10.5 and 11.0 (although Simbad shows the primary at 9.91) with a separation of 0.4” and a PA of 276 degrees (WDS 2008). Again, just a slight bit out of my reach.
To get some perspective on the Σ 2142 pair, I went to Lewis’s book on Struve’s double stars, which listed observations from 1830 to 1905. I added additional observations in red — a 1902 observation by W. J. Hussey that I found in Burnham’s 1906 catalog and some WDS observations I pulled from archived WDS lists.
As you can see, this pair of stars seems to be wobbling just a bit. With the exception of Mädler’s 1843 observation, the position angle decreases steadily through 1905, but then from 1958 to 2006 it bounces back and forth. Meanwhile, the separation is inconsistent throughout the whole range of dates. Again, in a situation like this one, proper motion is the best clue as to what’s taking place. The WDS shows proper motion for the primary at +018 +016 (.018”/year east, .016”/year north) and the secondary at +019 +019. Simbad shows the secondary at +019 +020, but surprisingly doesn’t show any data for the secondary. If the WDS data is correct for both primary and secondary, it would mean there’s no change taking place between the two stars.
Not finding any help there, I took a look at several photos of Σ 2142 in hopes of finding one I could measure, but the secondary was drowned out by the primary’s glare in all of them. What I did find, though, was the 14.7 magnitude “C” component, KUI 78, which I hadn’t been able to see in my six inch refractor. In fact, I initially mistook it for the secondary because its position angle is very close to that of the secondary (109° for “B”, 107° for “C”).
1955 POSSI photo, click to enlarge.
I’m not sure what to make of the inconsistent data on Σ 2142, but at a minimum it leaves one with the impression that for some reason it’s a difficult star to measure. Why that would be the case I couldn’t even begin to guess, but at any rate it fits in with the other odd characteristics of this short stretch of the sky we’ve just looked at – forlorn, neglected, and unpredictable.
Next time out we’ll head south to Sheliak, aka Beta (β )Lyrae, to see what stellar oddities are lurking there in the dark.
Clear skies until then! :cool:
Click for an even larger view!
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