Floating in the sky northwest of the V-shaped asterism in Taurus which is home to the Hyades is a pair of stars that would probably be better known if fate hadn’t decreed they should occupy a stellar address within a few degrees of the Pleiades. Over-shadowed by the brilliant blue-white light and glowing nebulosity of the most dazzling naked eye open cluster in the heavens, 37 and 39 Tauri are ignored night after night by double star sleuthers.
But . . . . . . . not tonight!
Stellarium screen image with labels added, click for a larger view.
There are a couple of different paths to 37 and 39 Tauri, both starting from well-known objects. First, you can start at first magnitude Aldebaran and scoot across the northeast edge of the Hyades to 3.5 magnitude Epsilon (ε) Tauri (also known as Ain), a distance of about three degrees. From there, adjust your direction of travel very slightly to the south and leap another three degrees to fifth magnitude Omega (ω) Tauri, which sits just south of a trio of stars known as 56, 51, and 53 Tauri. Continue along the same line of travel another three and a half degrees and you’ll find yourself looking at 37 and 39 Tauri.
Stellarium screen image with labels added, click on the chart to enlarge it.
A shorter approach is to start from the Pleiades and move southeast a distance of 2.75 degrees to 5.6 magnitude 32 Tauri, and then correct your direction slightly to the north and hop another two degrees to reach 37 and 39 Tauri. That route is shorter, although you may find yourself mesmerized by the Pleiadic glow and forget what you came for.
Depending on how much aperture you’re wresting with, you’ll find yourself looking at either a double-double or a triple-triple:
37 Tau glows orangely on the left side of this mirror-image view, and 39 Tau gleams whitely on the right, but if you look carefully you can see a weak shade of orange in its secondary. The distance separating the two primaries is about 10’. The secondaries of both stars are obvious even in a 60mm refractor. However, to pry the 12.6 magnitude “C” components out of interstellar space you’ll need five to six inches of aperture. (East & west reversed to match the refractor image, click on the sketch for a better view).
Also shown to the south of 37 Tauri is SCA 30, with magnitudes of 9.54 and 12.92, separated by 42.6” at 345° (WDS 2000), which I was unaware of at the time I made the sketch. With some careful attention and averted vision, it should be possible to separate that pair with a six inch refractor.
37 Tau (OΣΣ 558) HIP: 19038 SAO: 76430
RA: 04h 04.7m Dec: +22° 05’
Distance: 187 Light Years (Simbad)
Spectral Classifications: “A” is K0, “B” is G0
37 Tauri captured my attention first because of its attractive orange tint. The tenth magnitude secondary shines south of it, and a careful perusal south and west of the secondary turned up the much weaker “C” companion, which is designated as STG 4. That three letter designation refers to Georg Hermann Struve, one of the lesser known members of the famous Struve family – more information on him can be found here.
39 Tau (OΣΣ 559) HIP: 19076 SAO: 76438
RA: 04h 05.3m Dec: +22° 01’
|| None listed
|| 5.97, 8.09
|| 5.97, 12.60
|| 8.09, 11.50
Distance: 55 Light Years (Simbad); also Simbad shows “B” at 797 LY
Spectral Classifications: “A” is G5, “B is K0
When you first look at the data on 37 and 39 Tauri, they seem to resemble each other because their three main components are all widely separated. But 39 Tauri includes an additional component, an elusive star of undetermined magnitude, CHR 158 (the CHR stands for Center for High Angular Resolution Astronomy). According to the WDS notes file, there were numerous attempt to resolve that companion between 1985 and 1998 that resulted in an “uncertain” resolution at a distance of 0.22”, followed by a successful attempt at resolution in 2003 at a distance of .41”.
Click to enlarge.
Both 37 and 39 Tauri have significantly high rates of proper motion, which are shown below in this Aladin photo with Simbad’s proper motion rates added as an overlay:
This is an erect image, so east and west are opposite of what’s shown in the sketch above. Click to enlarge the image. (All motions are east (“+”) and south (“-“); for example in the case of 39 Tau A, +172 -131 means motion of .172”/yr east and .131”/yr south).
At first glance, it appears there may be some relation between the primaries of 37 and 39 Tauri, but a look at their distances shows they’re much too far apart. Simbad has 37 Tau “A” at a distance of 187 light years and shows 39 Tau “A” quite a bit closer at 55 light years. None of the other components shown appear to have any relation to their primarial parents, and in fact, Simbad includes a distance for 39 Tau “B” of 797 light years, placing it much further away than its primary.
Our next star on this tour, Σ 479, is located about one and half degrees (1° 25’) northwest of 39 Tauri. (Here’s our last chart again). You can use 7.8 magnitude HIP 18833 as a stepping stone, which is a 40’ hop northwest of 37 Tau. Another short jump of 50’ more north than west will land you on Σ 479. HIP 18833 is also a double star, by the way, sporting an identification of LDS 5477 (magnitudes of 7.88 and 12.93, separated by 58.8” at a PA of 356° as of 2000).
Σ 479 (H N 93) (S 442) HIP: 18748 SAO: 76388
RA: 04h 00.9m Dec: +23° 12’
Magnitudes AB: 6.92, 7.76 AC: 6.92, 9.45
Separations AB: 7.20” AC: 57.40”
Position Angles AB: 127° (WDS 2013) AC: 242° (WDS 2012)
Distance: 1072 Light Years (Simbad)
Spectral Classifications: “A” is B9, “B” is A3, “C” is A5
This Struvian selection is a compact triple star with a yellow-white primary and a similarly colored secondary in which the hues are a bit less pronounced. Eleventh magnitude TYC 1813-981-1 sits a bit more than 2.5’ northwest of the AB pair of Σ 479. (East and west reversed once more, click on the sketch for a larger view).
William Herschel was the first person to come across what later became Σ 479. He found it on January 4th, 1793, and cataloged it as a double star, but seems to have made several errors in describing its location (source):
His “north preceding 36 (A.) Tauri 1 1/2°” is an error, since Σ 479 is located just over a degree southwest of 36 Tauri, not north (our chart again) – but it does precede 36 Tau. The distance separating the two stars is 1° 12’, so he’s sort of in the ballpark with his measure of 1 1/2°.
Click to enlarge.
Herschel also refers to Σ 479 and 36 Tauri as being “parallel to 54 (ν) and Pleiades.” 54 Tauri is Gamma (γ) Tauri, which is located at the point of the “V” at the southwest tip of Taurus (here’s our first chart, which has a wider view). Nu (ν) Tauri (also designated 38 Tauri) on the other hand, is located ten and half degrees southwest of Gamma (γ) Tauri and eighteen and a half degrees almost due south of the Pleiades. But if you look closely at the chart just mentioned, you’ll see Σ 494 and 36 Tauri are parallel with a line drawn from 54 Tauri (γ Tauri) to the Pleiades. So it appears Sir William confused Σ 494 and Σ 479. Must have been a bad night at the scope, and we’ve all had that happen.
In his book on F.G.W. Struve’s double stars, Thomas Lewis includes measures of both the AB pair and the BC pair (shown at right). James South seems to have been the first person to measure the AB pair in 1823, which would normally mean the star should carry his catalog number, S 442. Struve didn’t get to it until 1831, followed by Admiral William H. Smyth in 1835.
For the most part, all of the measures listed by Lewis for both the AB and BC pairs are remarkably consistent, with the exception of an 1861 measure of AB by Mädler. A look at the Aladin image below provides a visual clue as to why:
Click to make the data more legible — see the previous Aladin image of 37 and 39 Tau for an explanation of how to read the proper motion data. (Erect image once again).
It’s obvious all three components of Σ 479 are moving in the same direction, as well as at pretty close to the same speed, although “B” is lagging behind a bit. Unfortunately the only star we have a distance for is the primary, “A”, which Simbad shows at 1072 light years. Simbad lists radial velocities of +13.80 km/sec for the primary and +10 km/sec for secondary, but doesn’t list a number for “C”. So even though the stars appear to be physically related, there’s not enough data yet to be sure.
Our last star, Σ 494, is waiting patiently for us about two degrees (1° 50’) due east of our present location (here’s our second chart again). 8.3 magnitude HIP 19078 lies midway between the two, so it’s an ideal place to pause. That stars has a spectral classification of K0, so it’s worth taking a close look to see if you can detect any hint of orange in it. Simbad, by the way, shows a distance for it of 1468.5 light years.
Σ 494 (H N 17) (S 444) HIP: 19363 SAO: 76476
RA: 04h 08.9m Dec: +23° 06’
Magnitudes: 7.53, 7.65
Position Angle: 188° (WDS 2013)
Distance: 343 Light Years (Simbad)
Spectral Classifications: Both stars are A8
Nothing like an old fashioned pair of closely spaced stars similar in magnitude! Both stars were unmistakably white. Barely seen in the southwest corner of the view is Cou 152, with matched magnitudes of 10.70 for both the primary and secondary, spaced a claustrophic 0.30” apart at a PA of 40° (WDS 2008). Cou 152 also includes a 16th magnitude third component at a distance of 3.40” and a PA of 204° (WDS 1970) – all well out of my reach, unfortunately. The inset at the right shows another double star, GRV 206, which we’ll come back to shortly. (East and west reversed once more, click on the sketch to improve the view).
William Herschel was first on the scene of this pair of stars also, discovering it on November 16th, 1784 (source):
Click to enlarge.
Once again, Sir William’s directions are confusing. He seems to be saying 65 Tauri is preceding Σ 494 at a distance of 16’35” as well as being located north of 65 Tau at a distance of 0° 45’. I checked those measures against Sky Tools 3 and found the 0° 45’ measure is very close, but the other measure should be in the vicinity of 3.75°. (You can see 65 Tauri at the left middle edge of this chart). At any rate, his right ascension and polar distance (P.D.) numbers are correct.
Thomas Lewis’s entry (shown at right) on Σ 494 includes a long list of measurements, starting with that of James South in 1825, and including measures by Struve in 1828 and 1832, John Herschel (h) in 1829, and the Reverend W.R. Dawes in 1842 and 1860.
Starting with Mädler’s measures in 1844, the separation and position angle begin to be remarkably consistent (source).
And again, when we look at the proper motion numbers for the primary and secondary of Σ 494, that makes sense:
Erect image once again, click to see all the data more clearly. PMRA stands for proper motion right ascension and PMDEC is proper motion in declination.
Whoops – we got more than we bargained for here! Not only did we turn up a restless collection of stars, but we also uncovered another double I was unaware of at the time I did the sketch. GRV 206 (WDS ID 04086+2301) is a pair of stars with magnitudes of 12.56 and 13.39, separated by 41.2” at a PA of 44° (WDS 2013). I went back and looked at my sketch and found I captured the primary, but not the secondary, although it may have been there with some judicious use of averted vision.
The object with the 2MASS label is a star with a visual magnitude of 16.3 (determined by combining the J (14.033) and K (13.204) values). There’s no distance shown in Simbad for that star, but chances are that with the rate of proper motion it displays, it’s relatively close to us.
If you look closely at the overlay, you’ll see three circles super-imposed on the STF 494 pair. One of those circles belongs to HD 26128, which is an identification assigned to both stars. There are proper motion numbers for that designation, as well as for the identifications assigned to both “A” and “B”, which is confusing, to say the least. Simbad shows the data for HD 26128 is from 2007 (the shorter of three arrows), the data for “A” is from 2012 (the longest of the arrows), and the data for “B” is from 2000. At any rate, it appears STF 494 “A” and “B” may be physically related, although the only distance we have is for “A”, so more definitive information would be helpful.
That’s it for Taurus this year. Next time we’ll head east and see what there is to see in Leo Minor, a constellation known for being small, faint, and populated with about as many galaxies as double stars.
Clear Skies! :cool:
Filed under: 4. Choose a Constellation:, Taurus | Leave a comment »