Star-Splitters

It’s long, it’s spread out, and it’s dim – all of which I suspect are reasons you never hear or read much about Lynx, as well as reasons most people don’t visit it. At any rate, it’s never been all that high on my list of locations for ferreting out sources of dueling photons. But I promised myself this would be the year to visit the lesser frequented constellations, and having already spent two sessions in Leo Minor (the first is here and second here), Lynx was a natural progression since the south end of it lies just west of the lesser Leo.

Stellarium screen image with labels added, click to enlarge.

Despite its dim nature, Lynx is not really all that difficult to pin down because it’s sandwiched between Ursa Major’s feet to the east and northeast (labeled on the map above), and Gemini’s Castor and Pollux to the southwest. From the southeast side of Lynx, a line drawn from Algieba in Leo through Mu (μ) Leonis will point you almost directly to Alpha Lyncis, which is where we’re going to start.

Here’s a close-up view which identifies two of the three stars we’re going to look at:

Don’t let that 10 UMa designation throw you. We’ll get to that in part two, but trust me, it’s correct! (Stellarium screen image with labels added, click for a larger view).

Alpha Lyncis  (40 Lyn)  (H IV 55)  (SHJ 369)     HIP: 45860   SAO: 61414
RA: 09h 21.3m   Dec: +34° 26’

Distance: 203 Light Years (Simbad)
Spectral Classifications: “A” is K7, “B” is A2
Notes:   BC is also H IV 55 and SHJ 369

The primary is a rather attractive shade of orange. The BC pair is obvious, but even in a six inch refractor, their duality is a bit elusive due to C’s faintness and the 2.27 magnitudes of difference between the two stars. (Click on the sketch to bring the image to life. East & west reversed to match the refractor view).

Also shown in the sketch is a faint and shadowy pair, GRV 784, with magnitudes of 12.78 and 13.62, separated by 20.2” at a PA of 98° (WDS 2001). I managed to latch onto the secondary with averted vision, so I suspect it may be a few tenths of a magnitude brighter than the WDS’s listing of 13.62.

I stumbled into a real maze of confusion in the historical literature on this star that took a short eon to sort out. It started with the discovery that William Herschel had identified H III 84 as 40 Lyn in his 1784 catalog of double stars (sixth title from top).  Meanwhile, in the second volume of his 1906 catalog, S.W. Burnham pointed out H III 84 actually refers to SHJ 369/Σ 1340, which is located fourteen degrees north of Alpha (40 Lyn) in Ursa Major. Compounding confusion with more confusion, in his entry for H IV 55 (which correctly refers to 40 Lyn) in the same 1784 catalog, Sir William described what is now the BC pair of Alpha (40 Lyn) as being “3 1/2 minutes north and following 41^st Lyncis.” But 41 Lyn is also in Ursa Major and is located eleven degrees north of Alpha Lyn (it’s also a double star, S 598). Both SHJ 369/Σ 1340 and S 598 are shown on the first chart above due north of Alpha (40 Lyn).  More than likely Herschel meant to refer to 40 Lyn, for which that description would be correct, instead of 41 Lyn.

Copies of Herschel’s and Burnham’s catalog entries are shown below, along with John Herschel and James South’s description of SHJ 369 in their 1824 catalog (last title on the page).

Click to enlarge!

As to what caused the error with H III 84, it’s possible the version of Flamsteed’s atlas which Herschel was using at the time had an error or at least was confusing. Also a possible source of the confusion is the fluid constellation boundaries in this area (in case you were wondering how 41 Lyn ended up in Ursa Major).  Another example of the changing boundaries is a star we’ll look at in part two of this tour, 10 UMa, which is firmly in Lynx now. James Kaler’s entry on 10 UMa contains a bit of information on boundary changes which took place in 1920.  And it’s also possible Herschel was tired and didn’t catch the mistakes, which is certainly something anyone who’s sat behind a telescope at 3 AM can understand.

One other aspect of Alpha Lyn (40 Lyn) worth noting is its proper motion, which is significant for a star located 203 light years from planet earth. The Simbad chart below shows the “C” component moving parallel to the primary, but at a much slower rate, while the “B” component is moving even more slowly on a slightly different path.

Rates of motion are A: -224 +015 (.224”/yr west. /.015”/yr north), B: -007 -004 (.007”/yr west, .004”/yr south), and C: -019 +002 (.019”/yr west, .002”/yr north). All data comes from Simbad, click to enlarge.

On to our next star, which requires a new chart because it’s dim and a bit elusive.

Stellarium screen image, click to enlarge.

To reach it, we’ll need to locate 5.98 magnitude HIP 45412, which is west and very slightly north of Alpha Lyn at a distance of 1° 13’.   A line drawn from Alpha Lyn to HIP 45412 will include HJ 2491 at about two-thirds of the distance to HIP 45412, or 54’.  There are two stars south of HJ 2491 which can be used to triangulate its location, 9.8 magnitude TYC 02496-0655 1 and 10.6 magnitude TYC 02496-1219 1.

HJ 2491     No HIP or SAO Numbers
RA: 09h 16.7m    Dec: +34° 31’
Magnitudes: 11.41, 11.50
Separation:  15.20”
Position Angle: 202°  (WDS 2012)
No distance or spectral class available

You have to look close (and enlarge the sketch!) to see this pair.  Six inches of aperture is ideal for these two stars, five should work, but resolution in a four inch refractor would be a tough task. As you can see, this is a very faint field and it didn’t help that clouds came in and interfered with the transparency as I was making this sketch. (East & west reversed again to match the refractor view).

John Herschel discovered this pair sometime around 1830 and was more descriptive with it than normal (source):

Click to enlarge.

There’s not much data on this pair of stars apart from what’s listed above and some proper motion statistics. The Aladin image below of HJ 2491 includes the PM data from both the NOMAD-1 and the UCAC-4 catalogs, which shows some slight differences, but overall indicates the possibility of some kind of physical relation between the two stars.  Simbad only shows the proper motion for A, which is why there’s a directional arrow for it and none for B.  If you look closely at the data, you’ll also see the Nomad and UCAC4 catalogs differ slightly on the direction and rate of movement of B in declination (pmDE).

Note this image has east and west in their normal places, as opposed to the refractor mirror image in my sketch. Click to enlarge the view.

We’ll move on to the third star in this tour, Σ 1333, which is slightly more than a degree (1° 7’) north and slightly west of Alpha (40 Lyn).   Here’s our second chart for reference.

Σ 1333  (H I 31)       HIP: 45661   SAO: 61387
RA: 09h 18.4m   Dec: +35° 22’
Magnitudes: 6.63, 6.69
Separation: 1.8”
Position Angle: 51°  (WDS 2013)
Distance: 283 Light Years (Simbad)
Spectral Classifications:  “A”is A8, “B” is A5

This is a tight pair, but not all that difficult to split because the two components are very close to being the same magnitude. Both stars are white. I was able to detect a hint of black space between them at 152x, but as the inset at the right shows, more magnification does an admirable job of putting space between them. (East & west reversed again, click on the sketch for a much better version).

This is another William Herschel discovery, dating to March 5^th, 1782, and again he refers to 41 Lyn when he means 40 Lyn. In fact, he also refers to 39 Lyn on the first line of his catalog entry (the Latin on the first line of the excerpt below translates as “Between 41 and 39 Lyncis”), which is obviously 38 Lyn on our chart.  So either the copy of the Flamsteed atlas Herschel was using had the wrong numbers assigned to the two stars or he used the wrong numbers by mistake (source for catalog excerpt below).

But then he throws in a mysterious reference to Eta (η) Ursae Majoris, which is the star at the east tip of the Big Dipper asterism’s handle, near the border with Boötes and Canes Venatici.  I’ve looked at two editions of Flamsteed’s Atlas Coelestis and in both of them there’s a star south of Kappa UMa (located above the center of our first chart on the Great Bear’s front paw) labeled “η”, which appears to be what is now referred to as 10 UMa – which is now in Lynx as a result of the change in constellation boundaries mentioned earlier.  There are no outlines of constellation boundaries in either of the atlases I looked at, so it’s difficult at times to tell what constellation a given star is part of — and no doubt that situation has caused some confusion in the past.

There’s one other aspect of this pair of stars which caught my attention as I was pulling together the data on it. Shown below is an Aladin image of STF 1333 with Simbad’s proper motion data attached at the bottom, and on the right of the image is a list of measures from Thomas Lewis’s book on Struve’s double stars:

Click to enlarge the image.

A close look at Simbad’s proper motion numbers shows both A and B with the same proper motion, yet as Lewis’s data shows the distance between the two stars is widening. The WDS also shows both stars with the same proper motion, while Nomad and UCAC4 only list proper motion data for A.

If you scan the measures in the excerpt from Lewis you’ll see some noticeable inconsistencies in both position angle and separation. Despite the inconsistency, it’s very apparent the two stars are moving relative to each other, which raises two questions: why doesn’t the proper motion data show that, and (stemming from the inconsistency in measures) is there some kind of gravitational interaction occurring between the two stars?

I sent a request to Bill Hartkopf at the USNO/WDS to get the text file for Σ 1333, which provided me with the additional measures made between the end of Lewis’s data in 1903 and the last WDS entry of 2014.  I discovered this pair of stars has received a lot of attention over the past two centuries – the total number of measures in the text file is 226, which provides a wealth of data.  I put both the position angle and separation measures on a graph and came up with this:

Click to enlarge.

As is evident from the jagged lines on both charts, the inconsistency in measures continued throughout the twentieth century.  A couple of things are obvious: first, the two stars are gradually moving farther apart, and second, if you ignore the peaks and valleys in the graphs, there appears to be a fairly consistent and small fluctuation in both PA and separation.

From the increasing separation of the stars, it’s clear the primary and secondary have slightly different proper motions.  And that wobble, or slight fluctuation in PA and separation, hints at either the possibility of an orbit, or at least, at some kind of physical interaction occurring between the two stars.  Bill ran a solution of the data which suggested an orbital period of approximately 3800 years, but also with a larger error range.  The actual chance of this being an orbital pair is actually very slight, but nevertheless, it’s a plausible explanation for the fluctuation visible in the graphs.

Along with all the data in the WDS text file for Σ 1333, there is also a large number of bibliographic references.  It’s possible that buried within all those references is a paper which addresses this issue.

Stellar mysteries!  Sometimes you need more tools and time than Sherlock Holmes ever even thought about!

Next time, we’ll continue moving north in Lynx, so until then,

Clear Skies!   😎

Filed under: 4. Choose a Constellation:, Lynx |