Delphinus is another one of those small constellations which, like Lyra, promises more double and multiple star adventure than its small sector of allotted sky would lead a double star sleuther to expect. In the Lyre’s case, it’s a mainly a matter of quantity, as in sheer numbers of paired stars. But what the Dolphin offers is quality – not so much a refined quality (although there is certainly some of that with respect to Gamma (γ) Delphini), as an odd quality.
It didn’t take me long at all to realize mundane and average is not one of the Dolphin’s traits, as my prior discussion of 1 Delphini, aka Bu 63, has already shown. And we’re going to discover that again when the field of view surrounding the first star of this tour graces our eyepiece. But first, in case you’re not quite sure where to find Delphinus, let’s put it in context:
We’re going to start with Σ 2690, which lies near the base of the smiling Dolphin’s tail.
Σ 2690 is easy enough to find since it’s conveniently wedged between Epsilon (ε) Delphini and 1 Delphini/Bu 63, which we’ve perused previously. To help get a sense of scale, the actual distance between Epsilon (ε) and Σ 2690 is 30’.
Σ 2690 (15 Delphini) (A,BC is H III 16) (BC is STT 407)
HIP: 101235 SAO: 106196
RA: 20h 31.2m Dec: +11° 16’
|CHR 99 Aa, Ab:||7.10, ????||0.40″||137°||2005|
|STF 2690 A, BC:||7.12, 7.39||17.60″||255°||2013|
|HJ 269 AD:||7.12, 12.10||22.90″||106°||2000|
|DA 1 BC:||7.12, 8.00||0.20″||179°||2006|
|Distances: Aa, Bb is 1048 Light Years (Simbad); BC is 196 Light years (Simbad)|
|Spectral Classifications: “A” is B8, “B” is Am|
Hidden in the glares of “A” and “B” are two more stars, one designated as CHR 99 associated with “A”, and another designated as DA 1, associated with B, as in BC. Not hidden, but difficult to see without resorting to averted vision, was the faint and elusive 12.10 magnitude “D” component, designated as HJ 269. And lurking very faintly and innocently in the north corner of the field is LAU 4, which can be seen better in the inset at the upper right of the sketch.
As you can tell from that description, as well as by looking at the identifiers in the data for Σ 2690, a lot of people have spent some time in this corner of the sky: William Herschel (H III 16), F.G.W Struve (Σ 2690), John Herschel (HJ 269), the Reverend W.R. Dawes (DA 1), and the folks associated with the Center for High Angular Resolution for Astrometry (CHR 99), which includes William Hartkopf and Brian Mason of the USNO/WDS. And a quick look at Lewis’s data (source) on Σ 2690 (shown at the right) turns up several more familiar names, such as Giuseppe Piazzi, James South, and Otto Struve, the last having discovered the same close companion of “B” discovered by Dawes, resulting in another designation for the BC pair, OΣ 407. In fact, Lewis’s data is interesting not only for the quantity of measures it includes, but also because it provides a complete and well documented history of the additions to Σ 2690.
The most interesting among those additions is DA 1, the pair with the honor of initiating Reverend Dawes’ double star catalog. Dawes compiled a very complete record of his many observations of the BC pair of Σ 2690, which he first estimated at .60” apart with a surprisingly precise PA of 208.67°. I’ve included his notes below, which I found in his “Catalogue of Micrometrical Measurements of Double Stars”, published in the Memoirs of the Royal Astronomical Society in 1867. His descriptions of what he saw as he attempted to pry apart the BC pair will be very familiar to anyone who has wrestled with extracting a tight secondary from a bright primary under uncooperative seeing conditions.
Dawes recorded his observations over two pages, which I’ve put side by side here to make for easier reading. The first page consists primarily of data and the second page includes magnitudes, dates (1840 to 1854), and his comments. Each line is numbered, so as you read from left to right the line numbers on page 264 line up with those on page 265. The DA 1 pair begins on line 2180 and continues and ends at the bottom of the page at line 2194. As your read through Dawes’ comments, you’ll discover he never was able to definitively separate the BC pair, but did manage to distinguish their elongation several times, including several notched elongations. Line 2185 includes an observation of the AD pair, HJ 269.
Going back to the data at the beginning of this account of Σ 2690, if you look closely you’ll see two very different distances for the primary and secondary. The distance given for Aa, Ab is highly suspect since it’s based on a negative parallax, which is seldom reliable, while the distance for BC seems to be on a more solid foundation. On the other hand – and there’s always an other hand it seems in this business – Simbad, Hipparcos, and Tycho all have distinctly different values assigned for the parallaxes of both the primary and secondary. So in order to get some idea of how Aa,Ab and BC are related, we can turn to the proper motion plot in Simbad for each of these pairs, which fortunately provides a much clearer picture . . . . . . .
. . . . . . . and what we find is Aa, Ab is moving southwest at the same time BC is moving southeast. The actual numbers, taken from Simbad, are -013 -016 (.013”/year west, .016”/year south) for Aa, Ab and +010 -030 (.010”/year east, .030”/year south) for BC. So despite not having a firm grasp of their distance, we can be reasonably sure there’s no gravitational tug-of-war taking place between these two complicated stars.
As I mentioned at the outset, there’s nothing mundane about Delphinus. And in fact, we’re headed for some rather muddled and murky waters as we turn to . . . . . . .
The Strange Case of BRT 1344, or How S.G. Barton Got Tangled up with LAU 4
If you go back to the sketch above (or click here to open it in a second window), you’ll see LAU 4 trying to hide in the north corner. As I was sketching the field of view surrounding Σ 2690, my eyes kept returning to the north corner of the field because they were catching averted vision glimpses of faint stars on either side of what I later learned was the A-B pair of LAU 4 (actually, I caught the southernmost star several times with direct vision in a 10mm eyepiece). After identifying the pair the next day, I found this data in the WDS for it . . . . . . .
LAU 4 (20309+1126), No HIP/SAO
RA: 20h 30.9m Dec: +11° 26’
Magnitudes: 10.0, 11.26
Separation: 27.4” (WDS 2009)
Position Angle: 270°
Distance: 57 Light Years (Tycho)
Spectral Classification: “A” is F5
Meanwhile, as I was looking at the data in Simbad for LAU 4 “A”, I spied this designation among the identifiers listed — CCDM J20309+1126 – and also noticed those numbers match the WDS designation as well. That led me to Vizier, where I located the CCDM catalog (which stands for Catalog of Components of Double and Multiple stars), entered the coordinates for LAU 4, and came up with this screen:
And I not only found references to “C” and “D” components, but also something totally unexpected – a new identifier, BRT 1344, which by the way is also listed in Simbad (bottom left of screen). But as my perplexed staring at the numbers quickly revealed, there was a significant dearth of data, such as missing position angles (theta) and separations (rho). So in hopes the heavens would part and an explanatory light would suddenly cast an illuminating beam my way, I clicked on that last link at the bottom of the Vizier screen shown above (Optical image of this region with Aladin-Java) in anticipation of an exotic version of stellar fulfillment – and after a suitable period of time, this image of LAU 4 materialized on my computer screen:
Clicking on any of the red squares in the image retrieves the CCDM data for that particular star, which then appears at the bottom of the image. The labels I added to the stars in the image are the component designations assigned by the CCDM catalog as I clicked on the respective squares. The first star I clicked on was the one I’ve labeled AC, and I was more than a little surprised when the first two lines of data appeared simultaneously (which explains why both of those lines are labeled AC), but notice the absence of a position angle and separation. Clicking on the square I’ve labeled as “D” returned the third line of data, and clicking on the square labeled “B” returned the fourth line of data.
The measurements for LAU 4 are obvious in the fourth line of CCDM data, but it seems as though “A”, “C”, and “D” are all superimposed on a single star. And notice that neither of the two faint stars (northwest and southeast of “B”) which caught the attention of my averted vision are included in the CCDM listing.
But when all else fails, it’s always a good idea to go back to the original observation, so I located BRT 1344 in a 1935 issue of The Astronomical Journal, thanks to the incomparable SAO/NASA database.
The data in the yellow box above are measures made by S.G. Barton, whose name is represented by the BRT identifier used by the WDS. And it happens to be an exact match with the CCDM data . . . . . . . which really is less helpful than I had hoped.
BUT – it does contain one important morsel of information: the Bonner Durchmusterung number, BD +10 4305, which is assigned to the primary. (Bonner Durchmusterung is referred to today as DM, but in 1935 the initials BD were used). If you look back at the CCDM data above, you’ll find DM +10 4305.0 is identified with the primary in both the CCDM data chart and in the data at the bottom of the Aladin photo (click here to open it in a second window). So even though the rest of the picture is murky, we know for sure what primary Barton made his measure from – which of course is also the primary of LAU 4 – which is also DM +10 4305.
There’s one other tidbit of information in Barton’s observation, and that’s the “T” in front of DM +10 4305. That “T” stands for the Toulouse Catalogue (part of the much larger Cartes du Ciel project), which refers to the collection of photographic plates on which Barton made many of his measures, including BRT 1344. And if we could see the plate he was looking at (this is as close as I’ve come to locating it), we would have a chance of clearing this situation up. But since that’s not the case, it does introduce a question as to whether there was an artifact of some kind on the plate which misled Barton into thinking it was a star.
I enlarged the Aladin photo above, and using the Aladin/Vizier software to measure the separation and PA between the AC and D squares, came up with 3.03” and 224.3°, which is pretty darn close to Barton’s 3.1” and 223°. I’m not sure what to think of his magnitudes, 11.4 and 12.3, neither one of which matches the 10.0 magnitude assigned to the LAU 4 primary in the WDS (UCAC4 “f” puts the magnitude at 9.565). Nor does it seem likely that the 12.3 magnitude for his secondary refers to LAU 4 “B”, since the PA and separation of the LAU 4 secondary are nowhere close to Barton’s secondary.
However, here’s the same photo (not enlarged as much) with UCAC4 data shown at the bottom of it. The LAU 4 designations for “A” and “B” are labeled, and I also labeled the two fainter stars northwest and southeast of “B” as “3” and “4”.
The star labeled “4” is the only one anywhere near Barton’s PA of 223°. I measured to it from the primary and came up with a PA of 195.9°, and a separation of 38.74”. The UCAC4 “J” and “K” magnitudes for that star are 12.392 and 12.113, respectively, which are very close to what I saw visually since that’s the star I was able to detect several times with direct vision (which means the UCAC4 “f” magnitude of 13.381 is too faint). Could it be that Barton was measuring from “A” to “4” and made an error of some kind in transferring his data from one sheet of paper to another?
Of course it’s also possible Barton really was looking at a star, and not an artifact. If you look closely – as I did numerous times – at the enlarged Aladin photo shown with the CCDM data (here it is again), you’ll see a very slight elongation in the primary (it’s oriented northeast to southwest) which aligns with the 224.3° PA of the red “AC” and “D” squares on the photo.
As in the Aladin photo just referred to, there seem to be indications of an elongation poking out at about the 135 degree mark on several of the photos. I can see it most clearly in photos 1, 2, 4, 6, and 8. It seems to be most pronounced in photos 1, 6 and 8, so I increased the enlargement to 10x for those three images:
As I was looking at the primary, I also looked at the secondary carefully to see if there was any elongation in the same direction. While there is definitely some distortion in the secondary, it’s not in the same direction as the elongation in the primary. The last photo, the Hubble shot (8), shows very little distortion in the secondary, which no doubt is one of the advantages of not having an atmosphere to look through!
One other oddity I noticed in Simbad was this identifier: IDS 20261+1106. There’s nothing in the WDS at those coordinates, and when I searched the area around that location in Sky Tools 3, nothing turned up. BRT 1344, by the way, is not listed in the WDS, nor does it turn up in a search in Stelladoppie.
So while it’s possible there are two overlapping stars at the location of the LAU 4 primary which led Barton to the measurements that became BRT 1344, that leaves us with the confused identities in the CCDM. Its AC designation makes no sense whatever since it’s apparently applied to just one star, the LAU 4 primary. At most, there are three stars involved here: LAU 4 “A”and “B” and the star the CCDM identifies as “D”, which refers to the secondary measured by Barton.
So we’ll leave it there for now and move on to our last star, ENG 74, which is actually on the mundane side, although I did have a devil of a time locating it.
To get there, we’ll start from where we are, Σ 2690/LAU 4, and drop southwest to 1 Delphini/Bu 63, a place we’ve been before.
From there, we’re going to move due west into an area of faint stars. If you look on the chart, you’ll see 7.56 magnitude HIP 100547 (which is 1° 44’ west of 1 Delphini) lying a short distance (15’) west and slightly south of ENG 74. If you have problems locating HIP 100547, notice it’s in a line of stars formed by 6.32 magnitude HIP 100762, 6.70 magnitude HIP 100559, HIP 100547, and 6.63 magnitude HIP 100262. ENG 74 also lies just southwest of a pair of ninth magnitude stars, SAO 106075 and BD +10 04276, which point almost directly at it.
ENG 74 No HIP SAO: 106060
RA: 20h 24.2m Dec: +11° 13’
|Distance: 112 Light Years (Tycho)|
|Spectral Classification: “A” is G0|
And once you’re there, this is what you’ll see:
As I was looking at the data on ENG 74, I noticed the primary has a rather high rate of proper motion. Here’s an Aladin photo with Simbad’s data overlaid on it, showing the speed and direction of ENG 74 “A”:
You can see the proper motion numbers in the data at the bottom of the photo (PMRA and PMDEC), which show the primary moving west at the rate of .114” per year and south at the rate of .132” per year. At that rate, it’ll leave “B” and “C” in a cloud of interstellar dust within a few hundred years.
Next time out, we’ll go east from Epsilon (ε) Delphini in search of another three stars with questionable pasts.
Clear skies until then! 😎