It’s not distinctive, but it’s there if you look closely – Leo Minor, that is.
During the many hours I’ve spent in the larger Leo, perusing double stars and galaxies, I’ve always been aware of the smaller Leo to the north. Most atlases portray Leo Minor in a skewed diamond-shaped configuration, but the few times I’ve glanced up that way in a semi-serious search for it, I’ve never found anything but a wide scattering of faint and un-spectacular stars. Sooner or later I knew I would have to grab my Sky &Telescope Pocket Atlas, hold it up to the sky, and pin little Leo into place.
Sooner came later than I had planned, but at least it arrived.
Leo Minor is sandwiched between several somewhat dim, but discernible, reference points in a fairly faint part of the sky: Allula Australis, Allula Borealis, Tania Australis, Tania Borealis (all in Ursa Major), and Alpha (α) Lynicis, the brightest star in another faint constellation known for being spectacularly faint.
The easiest way to pin down Leo Minor is to begin by locating one of the Great Bear’s (Ursa Major’s) three distinctive feet. We’ll start at third magnitude Delta (δ) Leonis, also known as Zosma, which marks the rear of Leo the Lion’s back. Fourth magnitude Allula Australis, located at the south tip of the Great Bear’s rear leg, is eleven degrees due north of Zosma, where it sits linked to its slightly fainter neighbor, Allula Borealis, one and half degrees further north. From Allula Borealis, a five degree leap due west with a very slight tilt to the north will get you to 3.83 magnitude 46 Leonis Minoris. From there, it’s a matter of branching out both northwest and southwest about five and half degrees to reach 4.21 magnitude Beta (β) LMi and 4.74 magnitude 30 LMi. And from there, continue west and slightly north to pick out 4.49 magnitude 21 LMi and 4.56 10 LMi.
We’re going to start with fifth magnitude 42 Leonis Minoris, also known as S 612, which is four degrees south and slightly west of 46 LMi. On the chart, you can see it’s the southernmost of a line of three stars formed with 4.74 magnitude 30 LMi and 4.72 magnitude 37 LMi.
42 LMi (S 612) HIP: 52638 SAO: 62236
RA: 10h 45.9m Dec: +30° 41’
|S 612||AB:||5.34, 7.78||196.50″||174°||2012|
|ARN 3||AC:||5.34, 8.31||424.60″||94°||2012|
Distances A: 382 Light Years B: 661 LY C: 373 LY (Simbad)
Spectral Classifications “A” is A1, “B” is K2, “C” is F0
Sir South’s final position angle of 82° 36’ sf (south following) works out to a present day PA of 172° 36’ and when converted to arc seconds, his separation is 200.304”.
. . . . . . . and when the three measures are listed together, they show a gradual decrease in separation as well as a gradual change in PA toward the south, both of which are confirmed by the 2012 WDS measures which continue that trend:
A look at an Aladin photo of 42 LMi with Simbad’s proper motion data super-imposed on it clarifies why those changes are taking place:
The southerly motion of “A” towards “B” is obvious here, and given enough time, the two stars will probably appear to intersect. However, as the distances of “A” (382 LY) and “B” (661 LY) listed in the data lines above for 42 LMi indicate, there are 279 light years between the two star, so a stellar scale impact isn’t looming in the very distant future.
The “C” component (ARN 3), at 373 LY, is much closer to “A”, and is moving pretty close to parallel with it. But there’s enough difference in direction and rate of motion to cast doubt on a physical connection between the two stars, as well as the nine light years of distance between them. ARN 3 refers to Dave Arnold, who added the “C” component sometime around 2000 or 2001, as near as I can tell. At that time, he published his results in the Double Star Observer, which was succeeded in 2005 by the Journal for Double Star Observers, better known as the JDSO. I’ve had no luck with numerous internet searches for back issues of the Double Star Observer, so if anyone is aware of their existence, please leave a comment and I’ll follow up on it.
Next on our list is Σ 1432, a faint double located in a lonely part of the sky southwest of 42 LMi. To get there, we’ll need to negotiate a distance of almost four degrees (3° 45’) west and slightly south through relatively featureless terrain until we reach 6.61 magnitude HIP 51325 (here’s our last chart again). Σ 1432 is a faint dot of eighth magnitude light wedged between HIP 51325 on the east and 6.36 magnitude HIP 50904 on the west.
Σ 1432 HIP: 51158 SAO: 81347
RA: 10h 27.0m Dec: +29° 41’
Magnitudes: 7.84, 10.28
Position Angle: 121° (WDS 2012)
Distances A: 327 Light Years B: 399 LY (Simbad)
Spectral Classification: “A” is F2
This is one of F.G.W. Struve’s more challenging pairs, with a 2.44 magnitude difference between the primary and secondary. It’s not particularly difficult, but you have to look closely to catch the much fainter secondary’s diminutive dot of light.
There’s been a slight narrowing of the separation and a minor change in direction in the position angle since Struve’s first measures, which can be seen in the following fifty years of observations taken from Thomas Lewis’s book on Struve’s double star catalog:
That narrowing of separation and the slight PA change can be seen taking place in this Aladin photo, which shows the direction and rate of motion of both stars:
We can get a three-dimensional feel for what’s actually taking place here if we mentally super-impose the distances of “A” (327 light years) and “B” (399 light years) on the photo. Since it’s obvious in the photo that “A” is the brighter of the pair, it’s not difficult to perceive it as being in the foreground of the image. If you can pull it off, you’ll have an inkling of what a difference of 72 light years looks like!
Now we’ll move on to a pair that is wider, more colorful, and almost evenly matched in magnitude, OΣΣ 104. From Σ 1432, we’re going to move four degrees due north to 4.74 magnitude 30 LMi (our second chart once more). Once you have that star centered in your finder, you’ll see the twin glow of OΣΣ 104 a short 31’ to the northwest.
OΣΣ 104 HIP: 50951 SAO: 62021
RA: 10h 24.4m Dec: +34° 11’
Magnitudes: 7.21, 7.27
Position Angle: 287° (WDS 2012)
Distances A: 1028 Light Years B: 953 LY (Simbad)
Spectral Classifications: “A” is M4, “B” is K0
There’s a distance of 75 light years between the two stars of OΣΣ 104 according to Simbad’s data, so they’re purely a line of sight pair. They’re also moving away from each other as seen below:
The UCAC4 and NOMAD-1 data is included at the bottom of the photo above because I found a magnitude conflict with the AAVSO data. I stumbled on that discrepancy after discovering the primary of OΣΣ 104 is a variable star (Simbad labels it a semi-regular pulsating star). The AAVSO identifies the primary as UU LMi, with a magnitude range of 6.89 to 7.03. Since that magnitude range conflicts with the 7.21 magnitude assigned to the primary in the WDS, I checked the UCAC4 and NOMAD-1 catalogs and found visual magnitudes of 7.202 (UCAC4) and 7.048 (NOMAD-1) for the primary. So it’s possible the WDS magnitude for “A” is off slightly (although the similar UCAC4 Vmag value was probably generated by the AAVSO’s APASS data), but certainly not enough to be detectable visually unless you happen to have photometric cells in your eyes.
We’re not done with Leo Minor quite yet. On our next trip, we’ll wander to the west edge of little Leo for a look at three more stars.
In the meantime, Clear Skies! 😎