As you can see from the title, Otto Wilhelm von Struve, aka OΣ, left his calling card at several locations in this part of the galaxy. In fact, a brief glance at a star atlas, such as the apparently out of print Cambridge Double Star Atlas, shows his footsteps all through Cassiopeia, especially the northeastern part of the constellation.
Depending on which source his observation comes from, you’ll find his stars identified with either an OΣ (or STT) or OΣΣ (or STTA) prefix. The OΣ designation represents the Greek letters assigned to the stars in Sir Otto’s first catalog, and are equivalent to the Arabic “OS”, while the STT designation is the WDS prefix now in more common use. Struve published an appendix of additional stars later in life, which are identified by the addition of the extra letter in the OΣΣ and STTA prefixes.
Both of his Pulkowa catalogs are non-existent on the internet, at least based on my repeated searches for them. Fortunately, the group of stars in his first catalog, including the original observational data, are all listed in W. J. Hussey’s 1901 Lick Observatory publication, Micrometrical Observations of the Double Stars Discovered at Pulkowa Made with the Thirty-Six Inch and Twelve Inch Refractors of the Lick Observatory, Together with the Mean Results of the Previous Observations of these Stars. I’ve searched high and low and everywhere in between for Struve’s appendix, but have yet to come up with a source. If anyone reading this is aware of an internet source for that appendix, I would be extremely grateful if he or she would contact me by adding a comment to this post.
As for ARY 33, there’s a tale there, but you’ll have to wait for a few paragraphs before we can get to it.
We’re going to start this four-starred tour at a familiar place, Beta Cassiopeiae, also known as Caph.
Stellarium screen image with labels added, click on the chart to enlarge it. The object at the right edge of the chart is M 31, the Andromeda galaxy.
Caph is located at the western tip of the Cassiopeian framework, which is shown above as it appears at about 8:30 PM in mid-October. Polaris is located to the left of Cassiopeia in this chart, which means north is to the left. West is at the top because Cassiopeia is rotating up and over Polaris. If that’s confusing, remember that astronomical west is always the direction of stellar motion through the sky. If that’s still confusing, here’s the same scene at the end of January at about 7:30 PM:
Stellarium screen image again with additional labeling, click to enlarge.
North still points to Polaris, which is now to the right of Cassiopeia. West is now down, because as Cassiopeia continues to rotate around Polaris it will pass beneath it. If I’ve confused you beyond all understanding, take a look at this excellent piece on astronomical direction written by Greg several years ago.
We’re going to explore an area near the western edge of Andromeda, and we’ll begin at Caph by projecting a line southwest that runs between fourth magnitude Sigma (σ) Cassiopeiae and 5.15 magnitude Rho (ρ) Cas. Extending that line further to the southwest will lead us to 5.35 magnitude 18 Andromedae. For scale, the distance from Caph to Sigma (σ) Cas is 3.4 degrees, and the Sigma (σ) Cas to 18 Andromedae distance is six degrees.
To get to our first star, we’ll zoom into the area with the chart below. This is how the scene appears at the end of January at about 7:30 PM. (If you decide to take this tour in the fall, here’s a chart showing the scene at about 8:30 PM in October).
Stellarium screen image with labels added, click on the chart for an easier to use version.
Using 18 Andromedae as a star base, we’ll prepare to move out to our first star, OΣ 498. You’ll notice three stars of about seventh magnitude arrayed in a line along the west edge of 18 And. Start by moving to the middle of those three stars, 6.87 magnitude HIP 116440. Move north one degree to 6.90 magnitude HIP 116418, and then move 38’ west with a slight tilt to the north to reach OΣ 498.
OΣ 498 HIP: 116082 SAO: 35501
RA: 23h 31.3m Dec: +52° 25′
Distance: 249 Light Years (Simbad)
Spectral Classification: “A” if F6
Note: Only one recorded observation of AC.
The field is rather sparse here, which may be because a 60% waxing moon was behind me. The primary was white. Also shown in the field is TDS 4085 with magnitudes of 11.47 and 11.56, separated by 0.7” at 271°. There’s only been one observation of that pair, which comes from the 1991 Tycho data. (East & west reversed to match the refractor view, click on the sketch to improve the view).
Click to enlarge.
Missing from the sketch is the mysterious “C” component, which is listed without a magnitude in both the WDS and Simbad. I also checked the UCAC4 and Nomad-1 catalogs in Vizier and came away empty-handed, although Nomad-1 includes a 13th magnitude star at a distance of 1.7” from the “B” component. I superimposed the distance and position angle for “C” on the Aladin photo at the right to identify where it should be according to the 1913 data, but I also noticed there hasn’t been an observation of that star since.
According the information in the WDS notes file (which can be seen here in Stelledoppie), at one time the “C” component was identified as Aa, Ab. That seems to have led to some confusion since Simbad shows CCDM designations of “C” and “D” for the components, and excludes “B”.
The AB pair appear to be physical linked by proper motion, which is clear from this 7.5 arc minute Simbad plot:
The proper motion shown here is +101 -030 for the primary (.101”/year east, .030”/year south) and +095 -037 for the secondary. (Click on the chart to enlarge it).
Click to enlarge.
Since the two stars appear to be moving in tandem at a similar rate, you would expect there to be little change in position angle and separation over the years. That appears to be the case, as can be seen in the excerpt at the left from Hussey’s book (referred to above).
Now let’s go back to our starting point, 18 Andromedae, before moving on to our next star, OΣΣ 248 (here’s our January chart again, and here’s the October version). It’s easy to navigate to since it’s located just slightly more than a degree (1° 7’) due east of 18 Andromedae. You’ll find it at the middle of an arc it forms with 7.72 magnitude HIP 117145 and 7.98 magnitude HIP 117231.
OΣΣ 248 HIP: 117224 SAO: 35742
RA: 23h 46.1m Dec: +50° 40′
|| 7.11, 11.10
|| 7.45, 9.82
|| 7.45, 12.20
Distance: 760 Light Years (Simbad)
Spectral Classification: “A” is K0
Considering the primary’s spectral class of K0, I was surprised to see a white star with only a trace of orange. The secondary was obvious, but colorless, and “C” was visible only with averted vision. 7.98 magnitude HIP 117231 marks the north edge of the field, which again is surprisingly sparse, most of which is probably attributable to the sky glow caused by the 60% full waxing moon at my back. (East & west reversed, click on the sketch to get a better look at “C”).
Based on the proper motions of the primary and secondary, they don’t appear to be related as this Simbad plot shows:
This is the same size plot as the previous one, which allows you to compare the rate of motion of the two stars. Note this is an erect image plot (as are the others shown for this tour), so east and west are opposite of what is shown in the sketch above. The proper motion of the primary is +041 +010 (.041”/year east, .010”/year north) and for the secondary -001 -002 (.001”/year west, .002”/year south). Both numbers come from Simbad (no data was shown for “C”). HIP 117231 is beyond the north edge of this chart.
Since Otto Struve’s appendix catalog isn’t available, a good source to turn to for information on OΣΣ 248 is the second part of S.W. Burnham’s 1906 General Catalogue of Double Stars Within 121° of the North Pole.
There are two measures each of the AB and AC pairs, which are about what would be expected given the proper motion of the primary. In other words, if you back up the position of the primary to either the 1883 or 1905 measures, you would see an increase in separation between “A” and “B”. You can visualize that by using a neat little tool available in Aladin, which allows you to move the Epoch, the measures (or positions) for a given year, forward and backward. In the case of OΣΣ 248, this is what you see when you compare Epoch 2000 with Epoch 1700:
Click to enlarge!
In this case, I backed up the position of the primary to the year 1700, resulting in the change in separation and position angle shown below each of the images. Also included at the bottom of the two images is the slider tool I used, which shows the two epochs, J2000 and J1700.
To get to our next star, which is another selection from Otto Struve’s appendix catalog, move from OΣΣ 251 to 7.98 magnitude HIP 117231 (which is included at the north edge of the sketch above), continue northeasterly to 7.49 magnitude HIP 117290, and then nudge your direction of travel a bit more to the east in order to reach 6.47 magnitude HIP 117551. Now move due east with a slight southern tilt to reach OΣΣ 251. The direct line distance from OΣΣ 248 to OΣΣ 251 is 1° 27’. (Here’s the January chart again, and the October chart).
OΣΣ 251 HIP: 117808 SAO: 35869
RA: 23h 53.6m Dec: +51° 31′
|| 6.89, 9.14
|| 6.89, 11.70
|| 6.89, 13.10
Distance: 580 Light Years (Simbad)
Spectral Classifications: “A” is K0, “B” is K5
This is an interesting quadruple combination, and it took some persistent application of averted vision to pry thirteenth magnitude “D” out of the combined glare of “A” and “B”. The primary had a slight yellow-gold tint, instead of the orange flavor promised by its K0 spectral classification. Much of the field is very faint, which again is partly attributable to the moon’s 60% full sky glow. (East & west reversed once more, click on the sketch to get a better look at “D”).
Again, when you look at Simbad’s proper motion plot of these two stars, you can see the primary and secondary are unrelated:
“A” is moving at the rate of +053 +004 (.053”/year east, .004”/year north) and “B” is creeping along at -015 -008 (.015”/year west, .008”/year south). Simbad didn’t list proper motion data for the other two components. Click to enlarge!
Now on to our last star, ARY 33. It’s easy to spot from our current location since it’s a bit more than a degree (1° 20’) southeast of OΣΣ 251. As was the case with OΣΣ 248, ARY 33 is also located at the center of an arc of stars, this one formed by 6.72 magnitude HIP 118162 and 7.19 magnitude HIP 118289. (Here’s the January chart, and here’s the October chart).
ARY 33 HIP: 118264 SAO: 35954
RA: 23h 59.2m Dec: 50° 32’
Magnitudes: 7.32, 8.12
Position Angle: 139° (WDS 2012)
Distance: “A” is 809 Light Years, “B” is 956 Light Years (from Simbad)
Spectral Classifications: “A” is G5, “B” is K2
This is the widest pair of this tour, and in fact if you look carefully, both components can be seen in an 8×50 finder. Both the primary and secondary are white, which again isn’t quite what you would expect from a G5 star (yellowish) and a K2 star (orangish). I’ll blame the moon again! (East & west reversed once again, click on the sketch for a more endearing view).
There are several faint, but obvious, stars surrounding this pair, two of which form an interesting parallelogram with “A” and “B”. Surprisingly, the 11.2 magnitude star just southwest of “A” has never been included in the system. On the other hand, the ARY pair wasn’t even cataloged until 2002, a fact which I stumbled across accidentally.
WDS Notes file info, click to enlarge.
As I usually do when looking up data on a double or multiple star, I entered ARY 33 into the Stelladoppie database of the WDS catalog . . . . . . . and found a surprise when I saw the WDS notes file referred to R.W. Argyle as the discoverer of the pair. Bob Argyle is known to many people as the editor of Observing and Measuring Visual Double Stars and is also Director of the Webb Society Double Star Section. The surprise resulted from the WDS’s date of first observation for the ARY 33 pair, 1903 . . . . . . . which is a bit before Bob’s time.
I turned up Bob Argyle’s observation on page five of The Webb Society Double Star Circular No. 11, which is shown below:
Click to enlarge
You can see his data at the end of the list, which is labeled “Anon”. He included a note of identification for the two stars at the end of his list of observations, which I added below the list. That information matches the BD designations in the WDS, which confirms his anonymous pair is the same as the pair identified as ARY 33 in the WDS. So how, where, and why does the 1903 date of first observation enter the picture?
Click to enlarge.
I had a hunch, but I requested the WDS text file from Bill Hartkopf at the USNO/WDS. In addition to containing all known published measures of a given double star, there’s also other interesting information coded into the file. As I suspected, the 1903 date is a photographic measure derived from Carte du Ciel plates (source), which was an international photographic attempt to catalog all stars brighter than eleventh magnitude. I found other measures which had also been made from photographic plates prior to Bob Argyle’s 2002 measurements, which are actually the first made with a micrometer. What caught my eye is how consistent all the measures are. The 1903 position angle (139.0°) and separation (101.386”) change very little up to Bob’s measurements (139.5°, 98.75”).
A look at the proper motions of the two stars shows why there’s been little change. I overlaid Simbad’s proper motion data on an Aladin photo of the ARY 33 pair, which provides a visual image of their motion:
Click to make the data at the bottom of the image more legible.
The proper motion shown there for “A” is +004 -012 (.004”/year east, .012”/year south); for “B” it’s -005 -002 (.005”/year west, .002”/year south). That data is shown in a slightly different and more precise format at the bottom of the photo: +004.17 -012.29 for “A”, -004.59 -001.77 for “B”. At any rate, as you can see, although these two stars are moving away from each other, the rate of motion is very slow.
Adding further to the case for this pair not being physically related are their distances. Simbad’s parallax data places “A” at 809 light years from us and “B” at 956 LY. Even granting the imprecision of parallax at those distances, when combined with the proper motion data, we can conclude with a high degree of certainty the ARY 33 pair are not gravitationally linked in any way.
Which is more than you knew when you sat down to read this. ;)
Thanks once again to Bill Hartkopf at the USNO/WDS for the informational support!
Next time out, we’ll turn to Taurus for a pair of star hopping adventures. Until then, clear and stable skies! :cool:
Filed under: 4. Choose a Constellation:, Cassiopeia | 4 Comments »