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A Stellar Stroll through Southern Lynx, Part 2: 38 Lyn, Σ 1338, and 10 UMa

When we last left Lynx, we were lingering over the mysterious tug-of-war taking place between the two components of Σ 1333.   Ahead of us, just a degree and a half north of that pair, a consecutively numbered mystery, Σ 1334 (aka 38 Lyncis), is impatiently beckoning us to investigate an issue of an entirely different magnitude.

Just to get you oriented before we start, here’s an overview of where we’re headed:

Stellarium screen image with labels added, click to enlarge the chart.

Stellarium screen image with labels added, click to enlarge the chart.

And here’s a close-up view of the area we’re going to tackle on this tour:

Stellarium screen image with labels added, click for a larger view.

All three of the stars for this tour are labeled in tantalizing turquoise.  Stellarium screen image with labels added, click for a larger view.

38 Lyn  (Σ 1334) (AB is H I 9)       HIP: 45688   SAO: 61391
RA: 09h 18.8m   Dec: +36° 48’

Identifier  Magnitudes Separation  PA WDS
STF 1334 AB:  3.92,   6.09       2.60″ 224°  2013
DRS 44 AE:  3.92, 14.70     99.50″   52°  2002
CHR 173 Ba, Bb:  6.09,  ????       0.20″ 266°  2004
STF 1334 BC:  6.09, 12.50     79.50″ 217°  2002
STF 1334 BD:  6.09, 12.46    174.50″ 261°  2002

Distance: 125 Light Years (Simbad)
Spectral Classifications:  “A” is A1,  “B” is A4,  “E” is A3

As the data above shows, this is a complicated star. We’re going to simplify it considerably, though, since two of the stars shown above, “E” and “Bb” are well beyond our reach.   That leaves us with “A” through “D”, which is still more than enough to keep us occupied for several paragraphs.

The primary was a color I’ll describe as “without-a-doubt white” and “C” and “D” were way to faint for detecting color in my six inch refractor ( I’ve lettered the components in the inset at the right). “C” was difficult to see because of the AB glare, but the wider separation of “D” allowed it to be seen with less effort.   The AB pair is barely separated at the low magnification shown here. (East & west reversed here to match the refractor view, click on the sketch to improve the view).

The primary was a color I’ll describe as “without-a-doubt white” and “C” and “D” were way too faint for detecting color in my six inch refractor ( I’ve lettered the components in the inset at the right). “C” was difficult to see because of the AB glare, but the wider separation of “D” allowed it to be seen with less effort. The AB pair is barely separated at the low magnification shown here. (East & west reversed here to match the refractor view, click on the sketch to improve the view).

The AB pair eluded me when I first looked at in the 84x view shown above, so I switched to a 253x view, resulting in the shimmering image shown below (the eyepiece view was nowhere near as crisp as the sketch).  As is frequently the case, once I had captured the difficult secondary at high magnification, I was able to go back and catch a glimpse of it at a lower magnification.

This is one of those views you dream about, mainly because they’re so rare, at least in my seeing-challenged neighborhood. The sight of that small white dot of vibrating secondarial light was thing of pure beauty. East & west reversed again, click to enlarge!

This is one of those views you dream about, mainly because they’re so rare, at least in my seeing-challenged neighborhood. The sight of that small white dot of vibrating secondarial light was a thing of pure beauty.  East & west reversed again, click to enlarge!

As you look at the two sketches, you can see “C” and “D” are similar in magnitude, which is reflected in the 12.50 and 12.46 magnitudes shown in the data above for the two stars.  But when I first looked at the two components, the WDS data showed “C” with a magnitude of 10.30.  I could clearly see that wasn’t the case, so I scrutinized the two stars carefully for a couple of nights and never could determine which of the two had the edge in brightness.  The “without-a-doubt-white” glare from the AB pair didn’t make the comparison any easier.

In a case like this, the first thing I do is go to the NOMAD-1 and UCAC4 catalogs to see if magnitudes are listed for the stars in question.  What I was hoping to find was a visual magnitude for “C”.

The 10.30 magnitude for “C” is outlined in red in the WDS data, which was current in early March of 2015. Click to enlarge the image in order to read the data more easily.   Note: this is a mirror image (refractor) view.

The 10.30 magnitude for “C” is outlined in red in the WDS data, which was current in early March of 2015. Click to enlarge the image in order to read the data more easily. Note: this is a mirror image (refractor) view.

There are three tables of data below the image, starting with the WDS data of early March, 2015, followed by the NOMAD-1 and UCAC4 data.  NOMAD-1 shows “C” with a Vmag of 12.520, whereas the UCAC4 table shows no Vmag listed for that component (both boxes are highlighted in yellow).  But UCAC4 shows an f.mag of 12.066 for “C”, so between that number and the NOMAD data, the most likely magnitude for “C” falls somewhere between 12.0 and 12.5.  It’s also possible to combine the UCAC4 J and K magnitude values in such a way as to produce a visual magnitude, so I ran that data through a spreadsheet used for that purpose and came up with a visual equivalent of 12.295 for “C”.

Armed with that data, I sent a message to Bill Hartkopf at the USNO/WDS.  After looking at his sources, Bill decided on the 12.5 Nomad-1 magnitude, which is now a part of the permanent data.  The old magnitude for “C” of 10.30 comes from an estimate made by S.W. Burnham in 1909, which leaves me in the uncomfortable position of having intervened in the work of an acknowledged master.  Just in case he’s watching, my apologies!

As long as we’re here, we may as well look at the proper motion data for 38 Lyn, which will explain another mystery I haven’t mentioned yet:

This is an erect image view -- click to enlarge!

This is an erect image view — click to enlarge!

If you were wondering why a 14.70 magnitude star at a distance of one and a half arc minutes from the primary was added to this system, the explanation lies in the similar proper motions of “A” and “E”.  No proper motion is shown in Simbad for “B”, but since past measures show very little change in the separation of the AB pair, there may be a physical link of some kind between the two stars.

We’re going to continue moving north now (with a slight tilt to the east), this time for a distance of 1° 27’, which will bring us to Σ 1338. As you move in that direction, 7.52 magnitude HIP 45788 helps to point the way. (Here’s our second chart again).   This is a difficult little devil, so bring some patience and a high-powered ocular!

Σ 1338          HIP: 45858   SAO: 61411
RA: 09h 21.0m   Dec: +38° 11’
Magnitudes   AB: 6.72, 7.08    AB,C: 6.12, 12.59
Separations  AB: 1.005”          AB,C: 144”
Position Angles   AB: 312.9° (WDS 2015 Ephemerides)   AB,C: 166° (WDS 2009)
Distance: 139 Light Years  (Simbad)
Spectral Classifications:  “A” is F2, “B” is F4

The tight separation of the AB pairing of this star makes it a real challenge, but fortunately each star is similar enough in magnification to offset part of the difficulty. After looking at the separation and realizing a low magnification would be pointless, I reached into my eyepiece box to grab a 6mm eyepiece and was rewarded with two glowing white globes separated by a slice of black sky.   “C” (south of the AB pair at the left edge of the sketch) was easy to see at 152x, but the AB pair was reduced to a shimmering figure-8 at that magnification.   (East & west reversed, click on the sketch for a better look).

The tight separation of “A” and “B” makes them a real challenge, but fortunately each star is similar enough in magnification to offset part of the difficulty.  After looking at the separation and realizing a low magnification would be pointless, I reached into my eyepiece box to grab a 6mm eyepiece (253x) and was rewarded with two glowing white globes separated by a slice of black sky.  “C” (south of the AB pair at the left edge of the sketch) was easy to see at 152x, but the AB pair was reduced to a shimmering figure-8 at that magnification. (East & west reversed, click on the sketch for a better look).

Friedrich Georg Wilhelm Struve discovered the AB pair in 1829 and over the ensuing years numerous measurements of it were made in an effort to determine whether they were an orbital pair.  The right hand column of the attachment below (from Thomas Lewis’s book on Struve’s double stars) lists a total of forty-five measurements made between Struve’s first one in 1829 and four separate measures in 1900.

Click to enlarge!

Click to enlarge!

The left side of the attachment, which comes from the second volume of S.W. Burnham’s 1906 double star catalog, includes an 1898 measure by Hussey as well as a 1903 measure.   Also shown is a plot by Burnham of the change in position angle and separation between 1829 and 1903.

Jumping ahead to 2015, we have the advantage of more data (not to mention improved technology) which results in enough time and precision to generate this orbital plot for the AB pair of Σ 1338:

Click to enlarge the image.

Click to enlarge the image.

Data from the WDS Ephemerides is shown at the left, and in the information at the top of the plot you can see the quality of the orbit is graded as a “3”, meaning it’s considered to be reasonably accurate.   That data also shows the two stars will be at their closest point in 2023 (periastron), although the change in separation between now and then will be minimal.

Last, but certainly not least, is the intriguing 10 UMa, now located in Lynx as a result of some not so subtle stellar shifting.   Our second chart shows it northwest of Σ 1338 at a distance of about five degrees (5° 18’ to be precise).

10 UMa         HIP: 44248   SAO: 42642
RA: 09h 00.6m    Dec: +41° 47’

Identifier Magnitudes Separation  PA WDS
KUI 37 AB: 4.18,   6.48       0.50″ 231°  2012
STT 566 AB,C: 4.03, 10.36     99.70″ 184°  2004
BUP 122 AB,D: 4.03, 12.08    173.00″ 104°  2013
STT 566 AB,E: 4.03, 11.19    260.40″ 101°  2012

Distance: 52 Light Years (Simbad)
Spectral Classifications:  AB is F3+K0V

You have to take some time to look at this array of stars because the primary has a tendency to overwhelm the surrounding companions.   But if you look closely, “C”, “D”, and “E” start to assert themselves, and as they do, the subtle beauty of the scene begins to capture you. As a bonus, there’s a faintly mysterious star wedged between “D” and “E” that has been neglected for some reason while the other members were added to this system. (East & west reversed once more, click on the sketch to get the full effect).

You have to take some time to look at this array of stars because the primary has a tendency to overwhelm the surrounding companions. But if you look closely, “C”, “D”, and “E” start to assert themselves, and as they do, the subtle beauty of the scene begins to capture you. As a bonus, there’s a faintly mysterious star wedged between “D” and “E” that has been neglected for some reason while the other members were added to this system. (East & west reversed once more, click on the sketch to get the full effect).

The first thing that needs to be said about this complex star is it needs another name.  Of course, like most stars, it has several identities, among them being HIP 44248, SAO 42642, HD 76943, HR 3579, and BD +42 1956 — none of which roll off the tip of your tongue – plus there are another forty-five designations (scroll towards the bottom of that page) in Simbad. A fourth magnitude star that’s easily visible in reasonably dark skies deserves a definite designation, so I suggest we call it STT 566 (OΣΣ 566) since that’s the first double star designation assigned to it as a consequence of Otto Wilhelm von Struve’s discovery of the AB,C pair in 1851.

Click to enlarge!

Click to enlarge!

That pair was the original AB pair until 1935, when Gerard Kuiper discovered the tight 6.48 magnitude companion of the primary. Herr von Struve also added what is now the “E” component in 1851 (at the time it was labeled “C”), and S.W. Burnham threw in the “D” companion in 1908 (he labeled it “a”), adding his measures to an earlier measure in 1893 by Donner.

As I was looking at the measurements for the various components in the excerpt from Burnham’s 1913 Proper Motion Catalog shown at the right, I noticed some rather surprising differences in separations and position angles from the current WDS numbers. For example, what is now the AB,C pair was measured by Struve in 1851 at 260.32° and 150.33”, whereas the 2012 WDS data is 184°and 99.70”.   Even Burnham’s 1908 measures of 119.74° and 141.87” for what is now the AB,D pair differs significantly from the 2012 WDS measures of 104° and 173”. All is not stationary in the heavens, as we’ve discovered on more than a few occasions.

Here’s why:

Click to enlarge.

Click to enlarge.

It seems the AB pair is in a real hurry to get to wherever it’s going. When you boil Simbad’s proper motion numbers (shown below the image) down to basics, they reveal AB is racing westward at the rate of .47” per year and toward the south at the rate of .2” per year. The net effect of those two components of motion is a straight line motion across the sky of approximately 2.5” per year – which adds up quickly in fifty and one hundred year periods.

Here’s the same chart as above, but this time with the position of AB shown in 1851, 1908, 2000, and 2030:

Click for the larger view.

Click for the larger view.

As you look at it, you can see why the separation of the AB,C pair was wider in 1851 when Otto Struve measured it, and also why the AB,D pair was closer in 1908 when S.W. Burnham applied a micrometer to it. Keeping in mind the distance of the AB pair from where we see it is 52 light years – rather close on a galactic scale – more than likely what we’re seeing is the motion of a foreground star against the backdrop of more distant stars.

The AB pair, by the way, has a reasonably well-defined 21 year orbit:

Click to enlarge.

Click to enlarge.

This is a WDS orbital diagram, which comes from the Stelledoppie page for 10 UMa.   If you look at that page, you’ll see another orbital plot above the WDS plot, as well as the WDS Ephemerides data from 2000 to 2030.

And to tie up the last intriguing thread, we’re left with the tale of how 10 UMa came to be in Lynx.  In his brief account of 10 UMa, James Kaler mentions a re-drawing of the constellation boundaries which occurred in the 1920’s.  One of the results was 10 UMa suddenly found itself lying in Lynx.  Actually, re-drawing is a misleading description of what took place. Until that time, the boundaries of the constellations were frequently vague and variable, depending on which atlas was being consulted.  Ian Ridpath has a more detailed explanation of what prompted the decision to re-plot the heavens here.

Update 6/01/2015: I had noticed the magnitudes listed in the WDS for “D” and “E” seemed a bit too bright, especially when compared with “C”, so I checked both the NOMAD-1 and UCAC4 catalogs and found fainter values listed for each of them that were more in line with what I saw.   I sent a message to Bill Hartkopf once again at the USNO/WDS, and he’s changed the magnitude of “D” from 10.80 to 12.082 and “E” has been changed from 10.50 to 11.186.   Those values are based on the APASS data for those two stars, which are the magnitudes listed under the heading “VMag” in the UCAC4 Catalog.   In the chart below, the WDS magnitudes are outlined in red, and the UCAC4 Vmag numbers are outlined in yellow.

Click to enlarge and make the data more legible.

Click to enlarge and make the data more legible.

That’s it for Lynx this year, but there’s a lot more in this faint and extended constellation worth tracking down, so look for more next year.   Not sure where the next tour will take us since the weather in these parts has been less than cooperative lately, so stay tuned.

Until then, Clear Skies!   😎

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2 Responses

  1. John as always a great report !! And your sketching has really taken a notch up . Not that they weren’t good before !! But they seem more realistic like I’m looking through my eyepiece.

  2. Thanks, MIke.

    One of these days I’ll animate one of the sketches done at high magnification to show the bouncing and gyrating we all encounter at the eyepiece. That’s an essential part of the experience that shouldn’t be neglected.

    Until then, there’s always these images that come from the Canadian Weather Service.

    John

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