• Choose a post by category or constellation

  • Learn the Night Sky

  • Search strategies

    Use the Search box below to find doubles by popular name, RA, or telescope size. For example, a search on "15h" will find all doubles we've reported on that have an RA of 15 hours. A search for "60mm" will find all doubles where we used that size telescope.

Splitting stars – for us and for you!

We are experienced amateur astronomers who especially enjoy viewing double stars with long-focus refractors.  This journal is a record of our observations, but we also hope it will serve as a guide to you to help you plan observing sessions and choose double stars you want to observe.  In the column to the left you’ll find a drop down menu listing the doubles in this blog by constellation – and to the right there’s a list of our 10 most recent observations. Finally, you have two other choices:

  • First, you can read  our observations of a double and leave your own observations of that same star as a comment.
  • Second, you can subscribe to this blog so that you get email notifications when we add a star to it. Just check out the links in the right-hand column.

We’d love to hear from you regarding your own observations of the same doubles.

A Stellar Stroll through Southern Lynx, Part 1: Alpha Lyn, HJ 2491, and Σ 1333

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.

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).

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’

Identifier Magnitudes Separation  PA WDS
STT   571 AB: 3.29,  8.83    222.20″  42° 2008
STF 1342 BC: 8.83, 11.10      16.60″ 313° 2012

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).

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 41st 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!

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.

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.

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 to see this pair!   Six inches of aperture is ideal for these two stars, five should work, but in a four inch refractor they would be difficult to resolve. 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, click on the image to improve the view).

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.

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.

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 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 5th, 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).

Wm. Herschel on STF 1333

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.

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.

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!   :cool:

A Book! Tales from the Golden Age of Astronomy

It gives me more than just a little pleasure — actually, to be honest, it thrills me right to the tips of my focus fingers — to announce that I’ll be combining with noted astronomy author Neil English on a new book which will be entitled Tales from the Golden Age of Astronomy: A Celebration of Visual Astronomers from Galileo to Moore.  We’ll cover the history of visual astronomy starting at roughly 1600 up through the late twentieth century.  Our focus will be on a few of the well known visual observers, many of whom are frequently referred to in this blog, and as we work our way through the book, we’ll bring in a cast of roughly forty or fifty supporting characters, many of whom have also been discussed at one time or another in this blog.   Completion is tentatively set for October of 2016, with publication sometime after that.

Neil and I wrote a piece on S.W. Burnham, certainly a major figure in visual astronomy, which appeared on his blog in September of 2013.   Reading it will give you an idea as to what we have in mind — it’s available at this link.

Among the titles of Neil’s books are Choosing and Using a Refracting Telescope (published in 2011), Choosing and Using a Dobsonian Telescope (2011), Classic Telescopes (2013), and Grab ‘n Go Astronomy (2014).   Neil also wrote The Guide to Mars for Pole Publications, which publishes the British astronomy magazine Astronomy Now, for which he has also written several articles.

As a preview, here’s a look at what will appear on the back cover:

From the first time humankind cast its collective gaze into the dark sky above, a never-ending fascination with the moon and stars has been a defining characteristic of our species.  Curiosity concerning the mysterious events and objects in the night sky led to constant speculation and conjecture, resulting in a diverse collection of myths and theories that became deeply woven into the fabric of our many cultures.

But for most of recorded history, mankind’s vision of the heavens was limited by the acuity of the naked eye.  That era reached its culmination with the Danish astronomer Tycho Brahe’s late sixteenth century attempts at a detailed catalog of the heavens based on systematic visual observation.  Brahe passed from the scene just as the seventeenth century began, only a few years before the first telescopic devices were being invented.

The first telescopes were inevitably crude devices, but that did not deter their enthusiastic use and their potential to revolutionize mankind’s visual reach ever further into the heavens.  As optical improvements began to take place, they created an insatiable desire for further improvements.  And as the telescope improved, so too did the skills and talents of the first people to utilize them.

Who these men and women were, the difficult conditions in which they frequently labored, and the many surprising – indeed, given the nature of their equipment, often amazing – discoveries they made, is the subject matter of this book.  It’s a fascinating allegory of dedication, insight, intuition, and perseverance, all of which were fueled by an unquenchable thirst to understand both the logic and the cycles of the heavens.  Well-known figures such as Galileo and William Herschel will receive the attention they so richly deserve, but the book also presents a large supporting cast of lesser known men and women.  Each of them played important roles in constructing the foundation of the noble science of astronomy as we recognize it today – and all of them employed the tools of visual astronomy to achieve their goals.

Cheers, Prost, and Clear Skies!

P.S — A little something to whet the appetite:

9.6 Inch Dorpat Refractor

Crowded Starlight in Leo: OΣ 215, OΣ 216, Σ 1417

For as large as Leo is, it’s a little light on double stars.  That’s not surprising since it lies north of the plane of the Milky Way, but it also explains why it’s a rich hunting ground for galaxies.  In fact, the eastern half of the constellation is something of a gateway leading to the large numbers of galaxies in Virgo, Coma Bernices, Canes Venatici, and Ursa Major.

Despite its relatively sparse allocation of multiple starlight, Leo at least can boast of being the home of one of the most dazzling double stars in the heavens, Algieba, aka Gamma (γ) Leonis. Less dazzling but at least as alluring is 54 Leonis, and then there’s the diabolically difficult Iota (ι) Leonis, which demands a night of good seeing in order to be seen.

And speaking of Leonine difficulties, I came across a pair of Otto Wilhelm von Struve’s pairs a couple of years ago, which managed to elude my numerous attempts to pry them apart.  In fact, I had so little luck I was never even sure I had located them. But in this line of endeavor persistence is a prerequisite, so I persisted, and finally the sky gods relented and ordered up the missing ingredient: a night of cooperative seeing.  Also eluding me elusively was a pair of stars discovered by the senior Struve (Friedrich George Wilhelm von Struve), which finally parted on that night to reveal a pair of dueling wisps of light.

One word of cautious warning: these three stars are challenging – which is a polite way of saying they can be difficult to the point of exasperation. The reason they’re challenging and difficult is because they’re relatively faint and unequivocally tight. But once you hook onto one of these impertinent pairs, you’re likely to find their subtle beauty absolutely irresistible.  Five to six inches of aperture and seeing equivalent to at least a III (average) on this scale will give you a fighting chance.

Here’s a wide view of where we’re headed:

Stellarium screen image with labels added, click to expand the view.

Stellarium screen image with labels added, click to expand the view.

And now we’ll zoom in to the vicinity of Algieba:

Since Algieba is near the three stars on our itinerary, we’ll start there and use it for a jumping off point to get to Σ 1417. (Stellarium screen image with labels added, click for better view).

Since Algieba is near the three stars on our itinerary, we’ll start there and use it for a jumping off point to get to Σ 1417. (Stellarium screen image with labels added, click for better view).

Located where Leo’s neck joins his back, Algieba is easy to locate – and as long as we’re starting with it, you might as well put it at the center of your eyepiece and enjoy its gleaming gold photons until you’re sublimely satiated. When – or if — you can tear yourself away from it, go back to your finder and move a short 22’ south and slightly west to 4.80 magnitude 40 Leonis and then turn to the southwest and move a bit more than a degree (1° 8’) to reach Σ 1417. Since it’s a weak ninth magnitude, you may have a problem seeing it in your finder, so while you have 40 Leonis centered, nudge your scope southwest just enough to put 40 Leonis about a quarter to a third of the way from the center of the finder’s field of view. That should put Σ 1417 somewhere in the field of view of your eyepiece.

Σ 1417      HIP: 50223   SAO: 99023
RA: 10h 15.1m   Dec: +19° 07’
Magnitudes: 9.24, 9.31
Separation:  2.2”
Position Angle: 77° (WDS 2013)
Distance: 767 Light Years (Simbad)
Spectral Classification: “A” is F2

Obviously these two stars aren’t a pair of Porrima-like dazzling white orbs, but they’re all the more impressive for their sheer delicacy. Notice how sparse the field is, which is a common characteristic of this part of the sky, and which adds immeasurably to the desolate beauty of the ninth magnitude pair. 9.23 magnitude HIP 50207, which is shown on the finder chart we just used, is seen here halfway to the southwest edge of the field of view (left in the sketch). East & west are reversed here to match the refractor view.

Obviously these two stars aren’t a pair of Porrima-like dazzling white orbs, but they’re all the more impressive for their sheer delicacy (you’ll have to enlarge the sketch by clicking on it to see this pair). Notice how sparse the field is, which is a common characteristic of this part of the sky, and which adds immeasurably to the desolate beauty of the ninth magnitude pair. 9.23 magnitude HIP 50207, which is shown on the finder chart we just used, is seen here halfway to the southwest edge of the field of view (left in the sketch). East & west are reversed here to match the refractor view.

This pair of stars was discovered and cataloged by F.G.W. Struve in 1830 when the separation was slightly wider. If you look carefully at the separations shown below (from Thomas Lewis’s book on Struve), you’ll see some significant fluctuations:

Click to enlarge

Click to enlarge

Curious about those numbers, I looked through some old WDS files and found two additional measures of Σ 1417, but I also discovered a dramatic change in position angles had taken place in 2005:

1997: 258°, 2.3”
2005:   77°, 2.1”

Because I had been looking at Lewis’s data and was seeing position angles ranging from 258° to 261°, it looked like an error had been made in 2005. But on a hunch, I subtracted 180° from the 1997 position angle of 258°, resulting in a figure of 78°. What has happened is the designations for “A” and “B” have been reversed once photometric data was able to identify which of the two stars is the brightest.

This pair of stars isn’t identified as an orbital pair, but in looking at Simbad’s proper motion data, it looks like there’s a pretty good possibility there’s some kind of bond between the two stars:

The proper motion numbers for Σ 1417 show the primary moving west in right ascension at the rate of .031” per year and south in declination at .005” per year, while the secondary is keeping pace at .034” per year west and .004” per year south. Click for a larger view.

The proper motion numbers for Σ 1417 show the primary moving west in right ascension at the rate of .031” per year and south in declination at .005” per year, while the secondary is keeping pace at .034” per year west and .004” per year south. Click for a larger view.

The proper motion for HIP 50207 is also shown above, illustrating once again the random and unpredictable nature of stellar motion which is frequently seen in our galaxy.

To get to our next star, OΣ 215, we’ll go back to Algieba and move south and very slightly west two degrees, using 40 Leonis as a pointer (here’s our last chart again). That move will put you midway between two stars: the one to the east is 6.85 magnitude HIP 50508 and the one to the west is our goal.

OΣ 215      HIP: 50305   SAO: 99032
RA: 10h 16.3   Dec: +17° 44’
Magnitudes:  7.25, 7.46
Separation:   1.558”
Position Angle: 178.4°  (WDS Ephemerides for 2015)
Distance: 373 Light Years (Simbad)
Spectral Classification:  “A” is A9

If this looks like déjà vu all over again, that’s because it almost is (you’ll have to click on the sketch to see the full-sized version).   Except that in this case the stars have a faint tint of orange in them – which is contrary to the white suggested by the primary’s A9 spectral classification – and, they’re significantly closer at 1.558”. The few background stars that were visible were very faint, almost to the point of being averted vision objects only.   The moon didn’t help, since it was about forty degrees to the west, waxing to about 30% of its full illumination.   (East & west reversed once more).

If this looks like déjà vu all over again, that’s because it almost is (you’ll have to click on the sketch to see the full-sized version). Except that in this case the stars have a faint tint of orange in them – which is contrary to the white suggested by the primary’s A9 spectral classification – and, they’re significantly closer at 1.558”. The few background stars that were visible were very faint, almost to the point of being averted vision objects only. The moon didn’t help, since it was about forty degrees to the west, waxing to about 30% of its full illumination. (East & west reversed once more).

This is a genuine orbital pair, but it didn’t quite start out that way.  The first series of measures over a span of sixty years was impeccably inconclusive, suggesting both orbital motion and straight line motion (the term used in the study of stellar motion is rectilinear). Just a glance at the two orbital diagrams below (from S.W. Burnham’s 1906 catalog and W.J. Hussey’s survey of Otto Struve stars) shows why it was hard to come to a conclusive decision.

Click to enlarge.

Click to enlarge and improve the clarity.

Burnham considered orbital motion to be a possibility, but leaned more towards rectilinear motion, while Hussey seems to have been inclined toward orbital motion, although it’s difficult to detect that in the spaghetti-like plot excerpted from his book.  A look at the measures shown beneath Burnham’s diagram shows the cause of the erratic motion of the secondary in the plots is an irregularity in the changes in position angle, which contrasts with fairly smooth changes in separation.

The initial guess as to orbital period was 107.94 years, which is mentioned at the top of Hussey’s diagram.  Further observation in the last one hundred plus years puts the orbital period at 620.27 years, but the WDS data grades that orbit as a 4, which is about halfway between definitive and indeterminate.  Not surprisingly, as the green lines in the most recent WDS orbital diagram (also available here) show, there is still some irregularity in the measures of this pair:

Click to enlarge.

Click to enlarge.

Our last star, OΣ 216, is a close relative, both numerically and spatially, since it’s located a short three degrees to the southeast of our present position. A quick glance at our second chart shows it’s easy to spot, shining a short 25’ north and slightly east of 6.16 magnitude 42 Leonis.

 OΣ 216      HIP: 50829   SAO: 99091
RA: 10h 22.7m   Dec: +15° 21’
Magnitudes: 7.38, 10.28
Separation:  2.230”
Position Angle: 231.2°  (WDS Ephemerides 2015)
Distance: 94 Light Years (Simbad)
Spectral Classification:  “A” is G5

Déjà all over again times two! Although this is the widest of the three stars we’ve looked at, it’s also the most difficult because of the 2.90 magnitudes of difference between the primary and secondary.   Again, you’ll have to click on the sketch to see the full-sized version.   The secondary was very elusive at 152x, but patient scrutiny at 304x was more successful. As is frequently the case, once I had confirmed the secondary at the higher magnification, it was easier to see at the lower magnification. (East & west reversed once more).

Déjà all over again times two! Although this is the widest of the three stars we’ve looked at, it’s also the most difficult because of the 2.90 magnitudes of difference between the primary and secondary. Again, you’ll have to click on the sketch to see the full-sized version. The secondary was very elusive at 152x, but patient scrutiny at 304x was more successful. As is frequently the case, once I had confirmed the secondary at the higher magnification, it was easier to see at the lower magnification. (East & west reversed once more).

This is another orbital pair, and just like its sibling, OΣ 215, the first sixty years of data was inconclusive and un-illuminating.   I went back to Burnham and Hussey again to get the first attempts at diagramming the motion of the two stars in relation to each other, and to quote Burnham, “The best of the measures have too much error to make it possible to decide as to the character of the motion.”

Click on the excerpts to enlarge them.

Click on the excerpts to enlarge them.

There was no attempt by either Burnham or Hussey to estimate an orbital period, but current WDS data puts that figure at 314.93 years and assigns it a grade of 4, which is the same as was assigned to OΣ 215. Here’s a look at the WDS orbital diagram, which can also be seen here.  Note the irregularities in motion shown by the green lines extending from the ellipse of the orbit:

Click for a larger view.

Click for a larger view.

Burnham describes the brighter of the two stars as having “considerable” proper motion, which is obvious in this plot based on Simbad’s data:

Click to enlarge the image (the circles at the lower right are a group of galaxies).

Click to enlarge the image (the circles at the lower right are a group of galaxies).

Simbad shows the proper motion of only one of the two stars, while the WDS lists proper motions for both stars.  A closer looks reveals the WDS data for the secondary is very similar to the Simbad data, which presumably refers to the primary:

Simbad proper motion data:       -261 -087   (.261”/year west, .087”/year south)
WDS proper motion data:   A =  -251 -101   B =  -262 -086

Regardless of which star the data refers to, what stands out is the relatively speedy motion of this pair through the galaxy.  Given their neighborly distance of 94 light years, that’s not too surprising.

And that’s it for the two Leos this season.   Our next tour will take us up to Leo Minor’s western relative, Lynx, where we’ll thread our way carefully through another barren and dim section of the sky.

Clear Skies until then!   :cool:

Leo in a Minor Key, Part Two: 7 LMi, 11 LMi, and Σ 1374

This excursion in Leo Minor will take us along the western edge of the constellation, close to its border with Lynx. (If you missed it, the first part of this tour is here).  All three of the stars we’re going to look at this time are aligned along a north-south line, so the chances of getting lost and disappearing into the starless black void typical of this area are pretty slim.

First, here’s an overview of where we’re headed (if you find Leo Minor difficult to track down because it’s frustratingly faint, the paragraphs above and below the first chart in part one describe how to locate it and trace its outline):

 Stellarium screen image with labels added, click to enlarge.

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

Here’s a closer look, which includes the three destinations for this tour, all of which are north or south of 10 LMi, and all of which are labeled in tantalizing turquoise:

Stellarium screen image with labels added, click to enlarge.

Stellarium screen image with labels added, click to enlarge.

Since 10 LMi is situated in the middle of our target area, we’ll start there and begin by moving north to Σ 1374, which is located three degrees north and slightly east of 10 LMi.   There’s a triangle of fifth magnitude stars (42 and 43 Lyn, and HIP 47029) just north of Σ 1374, which makes it easy to locate.

Σ 1374  (AC is ABT 7)      HIP: 47527   SAO: 61629
RA: 09h 41.4m   Dec: +38° 57’
Magnitudes   AB: 7.28, 8.65    AC: 7.28, 13.13
Separations  AB: 2.80”            AC: 307.60”
Position Angles   AB: 313° (WDS 2013)   AC: 10° (WDS 2002)
Distance:  167 Light Years (Simbad)
Spectral Classifications:  “A” is G3

This is what you might call a spatially diverse triple star. The secondary is close enough to hide in the primary’s glow produced, aided by the 1.37 magnitudes of difference between the two stars. At 152x the two stars were barely separated, but as the inset at the right shows, the view improved considerably at 253x. Both of those stars appeared white to my eyes, with no trace of the yellow hinted at by the G3 spectral classification of the primary. The “C” component is both very faint and very distant, and requires adequate aperture and a discerning eye to locate it.   (East & west reversed to match the refractor view, click on the sketch to get a better view).

This is what you might call a spatially diverse triple star. The secondary is close enough to hide in the primary’s glow, aided by the 1.37 magnitudes of difference between the two stars. At 152x the two stars were barely separated, but as the inset at the right shows, the view improved considerably at 253x. Both of those stars appeared white to my eyes, with no trace of the yellow hinted at by the G3 spectral classification of the primary. The “C” component is both very faint and very distant, and requires adequate aperture and a discerning eye to locate it. (East & west reversed to match the refractor view, click on the sketch to improve the view of one heck of a lot).

If you look closely (you’ll have to enlarge the sketch), you’ll see three very faint stars at the southwest (left) edge of the field.   By overlaying the WDS catalog on the Aladin image below, I was able to determine those three stars are not cataloged in the WDS.  I used the UCAC4 catalog to identify the three, which shows they’re all in the twelfth and thirteenth magnitude range.

Aladin image with UCAC4 data, click to enlarge.

Aladin image with UCAC4 data, click to enlarge.

The proper motions are also listed in the data at the bottom of the image and show some similarity in motion for the stars numbered “1” and “2”.  Considering how slight that motion is, the chances are the two stars are located quite a distance from us, which makes it difficult to come to any conclusion as to whether the pair is physically related.  Interestingly enough, the pair that are closest together visually, “2” and “3”, are moving away from each other.

But to get back to our main interest, the “A” and “B” components of Σ 1374 are a genuine orbital pair with a period of 1377 years (the orbit and data can be seen here).  The pair are in a phase of their orbit where they’re moving closer together, although at a very slow rate.  The WDS Ephemerides shows them with a separation and position angle of 2.778” and 314.2 degrees in 2030, so there’s no need to feel anxious about catching them before they get too close together to be caught.

As for “C”, why it was added to the Σ 1374 pair is something of a mystery (the ABT initials of ABT 7 refer to Giorgio Abetti).   At the bottom of the image above, I included the UCAC4 data on the three components of Σ 1374, which also include the proper motions of each of the stars.  It’s obvious “C” has no relation whatever to the AB pair of Σ 1374, and given that it’s over five arc minutes away from that pair, it’s hard to say what prompted Abetti’s inclusion of it in 1921 — possibly its position angle and separation were measured as a reference point for the proper motion of the AB pair.

Sometimes when you dig deep, the stellar puzzles seem to multiply at an astronomical rate.

Let’s go back south to 10 LMi now and take a look at a more difficult pair, 11 LMi, also known as HU 1128.   It’s easy to find since it’s parked just 39’ south and slightly east of 10 LMi (here’s our chart again).

11 LMi  (HU 1128)     HIP: 47080   SAO: 61586
RA: 09h 35.7m   Dec: +35° 49’
Magnitudes: 4.8, 12.5
Separation:  6.41”
Position Angle: 49.9° (WDS 2015 Ephemerides)
Distance: 37 Light Years (Simbad)
Spectral Classifications:  “A” is G8, “B” is M5

With just under eight magnitudes of difference between the primary and secondary, this is a very tough pair. I barely caught a glimpse of it at 152x in the glare of the yellow-white primary, and did a bit better at 253x.   (East & west reversed once again, click on the sketch to get a better view of the secondary).

With just under eight magnitudes of difference between the primary and secondary, this is a very tough pair. I barely caught a glimpse of it at 152x in the glare of the yellow-white primary, and did a bit better at 253x. (East & west reversed once again, click on the sketch to get a better view of the secondary).

Located 4.8′ north and slightly east of 11 LMi is ALI 357, with magnitudes of 12.5 and 12.6, separated by 7.60” at a PA of 96° (WDS 2002).  I didn’t notice them, probably because they were more closely spaced than the fainter pair of stars seen about 1.6’ southwest (left in the sketch) of the primary of 11 LMi.  That’s another pair which is not cataloged in the WDS, and as the data at the bottom of the image below shows, the two stars don’t appear to be linked by proper motion. The UCAC4 catalog data shows the northernmost of the pair with a magnitude of 13.5 and the southernmost at a magnitude of 12.98 — the separation is about 19″.

Click on the image to make the data more legible.

Click on the image to make the data more legible.

Click to enlarge.

Click to enlarge.

11 LMi, aka HU 1128, is also an orbital pair (here’s the orbit and data), with a relatively short period of 201 years.   The last date of observation in the WDS is 2006, but because the position of the two stars is changing significantly, I used the 2015 WDS Ephemerides for the data above, which is included in the chart at the right.  Notice it shows the stars will continue to widen over the next fifteen years.

The 11 LMi pair have a rather high rate of proper motion, which isn’t surprising considering they’re a short 37 light years from us:

Click to enlarge.

Click for a much better view.

Rounded off to three decimal figures, the column labeled PMRA shows motion of .729”/year west in right ascension and .260”/year south in declination, which means this pair are strolling across the sky at a rate of almost one arc second per year. There are two more stars in the photo above with significant proper motion (the data there is from Simbad also), neither of which are associated with 11 LMi.

The HU in HU 1128 refers to William Joseph Hussey, a prolific observer who spent much of his career at Lick Observatory in northern California.  When he first caught sight of this pair of stars in 1904, they were at a different point in their orbital waltz (source):

Click to enlarge.

Click to enlarge.

Let’s drop south and slightly west now for a distance of about two and half degrees to 7 LMi (here’s our chart once more).  You can use 5.39 magnitude 8 LMi as a reference point, which sits almost midway between the two stars and about 20’ west of the line which connects them.

7 LMI  (H V 69)  (HJ 1166)  (STTA 100)     HIP: 46652   SAO: 61529
RA: 09h 30.7m   Dec: +33° 39’
Magnitudes   AB: 5.97, 9.66    AC: 5.97, 11.58
Separations  AB: 61.30”          AC: 95.90”
Position Angles   AB:  125° (WDS 2011)   AC: 217° (WDS 2001)
Distance:  502 Light Years (Simbad)
Spectral Classifications:   “A” is G8, “B” is K0

We haven’t heard from the admirable Admiral William Smyth for a while, so let’s see what he has to say about 7 Leonis Minoris:

A wide double star, immediately under the animal’s right fore-paw. A 6, bluish white; B 11, livid. This object was registered 69 H V, in 1782, with a distance of 58.30”, but no angle of position; and it is No. 1116 of H.’s twenty-foot Sweeps. The companion is one of those minute and dusky objects which are best seen by averting the eye to the verge of the field; but there are many of much smaller magnitude, which shine quite sharply, and emit a strong blue ray. It may be found by carrying a line from Regulus close to the eastward of ε Leonis, and passing it exactly as far again into the north-north-west region.”   (The Bedford Catalogue, p. 217)

I’m not quite sure what the good Admiral meant with his description of “B” as livid, but I saw a hint of orange in it, and I saw yellow-orange in the primary instead of the Admiral’s bluish white.  “C”, which was added in 1912, was colorless, but no problem to see. The field of view is rather sparse, which has been typical of the stars we’ve looked at in this area.   (East & west reversed once more, click on the sketch to improve the view).

I’m not quite sure what the good Admiral meant with his description of “B” as livid, but I saw a hint of orange in it, and I saw yellow-orange in the primary instead of the Admiral’s bluish white. “C”, which was added in 1912, was colorless, but no problem to see. The field of view is rather sparse, which has been typical of the stars we’ve looked at in this area. (East & west reversed once more, click on the sketch to improve the view).

7 Leonis Minoris has had a lot of visitors, as is evident from the first line of data above.  William Herschel (H V 69), John Herschel (HJ 1166), and Otto Struve (STTA 100) — and of course, Admiral Smyth — all stopped here for a visit.  The father-son observations of the two Herschel’s are shown below (source for Wm. Herschel [six titles down), source for John Herschel):

Sir William’s work is at the top, Sir John’s is at the bottom. Click to enlarge.

Sir William’s work is at the top, Sir John’s is at the bottom. Click to enlarge.

As Admiral Smyth mentioned, William Herschel didn’t include a position angle in his notes, and in case you’re wondering, his Latin translates roughly as “in the extreme of the front foot.”  John Herschel’s 45° sf (south following) translates to 135°, which misses the 2001 WDS number by ten degrees, but since Sir John’s number was an estimate, we can call it in the ball park.  Their separations are considerably less than the 2001 WDS figure of 61.30”, and as was the case with Admiral Smyth’s magnitude estimates, their numbers are different from the 5.97 and 9.66 values shown in the WDS.

S.W. Burnham included another three measures in his 1906 catalog (the first is William Herschel’s original observation), which show gradual changes in both the position angle and separation:

Burnham on 7 LMi

Those numbers suggest the proper motions of the primary and secondary should show the two stars are gradually moving away from each other, and in fact that’s exactly what we see:

“A” is moving west at a rate of .023”/year and south at .048”/year, while “B” is moving west at .002”/year and south at a rate of .029”/year. Simbad doesn’t’ show any data on “C”, but the UCAC 4 catalog shows it moving due west at the rate of .051”/year with a very slight southern tendency of .0004”/year – in other words, it’s moving away from the other two stars as well. Notice the Simbad and UCAC4 proper motion for “A” and “B” are slightly different. (Click to enlarge the image).

Simbad’s data is shown in the top panel, UCAC4 is shown in the bottom one.  Click to make the date more legible!

“A” is moving west at a rate of .023”/year and south at .048”/year, while “B” is moving west at .002”/year and south at a rate of .029”/year. Simbad doesn’t show any data on “C”, but the UCAC 4 catalog shows it moving due west at the rate of .051”/year with a very slight southern tendency of .0004”/year – so it’s moving away from the other two stars as well.  Notice the Simbad and UCAC4 proper motions for “A” and “B” are slightly different.

And that should cover Leo Minor for a good while. Our next tour will take us down into the larger Leo for a look at some rather difficult stars, so order up some good seeing and break out the five and six inch scopes.

Clear Skies until then! :cool:

Leo in a Minor Key, Part One: 42 LMi, Σ 1432, and OΣΣ 104

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.

 Stellarium screen image with labels added, click to enlarge.

Stellarium screen image with labels added, click to enlarge.

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.

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

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

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’

Identifier Magnitudes Separation  PA WDS
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

A wide triple star that comes darn close to forming a perfect right angle triangle. “A” and “C” appeared white, and a careful look at “B” turned up a slight hint of orange, which dims it just enough to make it look about the same magnitude as “C”.   (East & west reversed to match the refractor view, click on the sketch for a better version).

A wide triple star that comes darn close to forming a perfect right angle triangle. “A” and “C” appeared white, and a careful look at “B” turned up a slight hint of orange, which dims it just enough to make it look about the same magnitude as “C”. (East & west reversed to match the refractor view, click on the sketch for a better version).

The AB pair was discovered by Sir James South on a frosty March night in 1825, which he describes rather well in this page from his 1826 catalog:

Frost prevention in the days before dew heaters and electrical power!

Frost prevention in the days before dew heaters!  Click to enlarge.

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”.

A look at S.W. Burnham’s 1906 double star catalog turns up two more observations of 42 LMi  . . . . . . .

Burnhan on 42 LMi

. . . . . . . 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:

South-Leiden-Burnham chart

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 motion here is south and west in this erect image version of 42 LMi (east and west are reversed in the mirror-image refractor sketch above). Decoded, the proper motion data for “A” means motion in arc seconds of .026”/year west and .037”/year south. The negative signs indicate westward motion in right ascension and southerly in declination.

The motion here is south and west in this erect image version of 42 LMi (east and west are reversed in the mirror-image refractor sketch above). Decoded, the proper motion data for “A” means motion in arc seconds of .026”/year west and .037”/year south. The negative signs indicate westward motion in right ascension and southerly in declination.

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
Separation:  28.5”
Position Angle: 121° (WDS 2012)
Distances   A: 327 Light Years   B: 399 LY (Simbad)
Spectral Classification:  “A” is F2

The field of view surrounding Σ 1432 is about as bleak and featureless as the terrain we navigated to get here. Apart from the ash white glow of the primary, the only other notable object is TDS 7264, a faint pair with magnitudes of 11.1 and 11.39 separated by 0.7” at a position angle of 134° as of 1991 – and well below the threshold of my detection.   (East & west reversed once more, click on the sketch to enlarge it).

The field of view surrounding Σ 1432 is about as bleak and featureless as the terrain we navigated to get here. Apart from the ash white glow of the primary, the only other notable object is TDS 7264, a faint pair with magnitudes of 11.1 and 11.39 separated by 0.7” at a position angle of 134° as of 1991 – and well below the threshold of my detection. (East & west reversed once more, click on the sketch to enlarge it).

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:

Lewis on STF 1432

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:

The motion shown here in this erect image is west and south, and the explanation of the numbers included in the Aladin-Simbad photo above of 42 LMi applies here as well.   Click for an improved version!

The motion shown here in this erect image is west and south, and the explanation of the numbers included in the Aladin-Simbad photo above of 42 LMi applies here as well. Click for an improved version!

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 104From 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
Separation:  209.4”
Position Angle: 287°  (WDS 2012)
Distances    A: 1028 Light Years   B: 953 LY  (Simbad)
Spectral Classifications:  “A” is M4, “B” is K0

The appearance of a pair of weakly tinted yellow-orange stars in the center of my eyepiece was a welcome change after the persistent white of our two previous objects. These two stars point almost due west on first glance, and the scene is improved by the intriguing parallelogram of three twelfth magnitude stars and one tenth magnitude star on the south side of the OΣΣ 104 pair.   (East & west reversed once more, click to enlarge).

The appearance of a pair of weakly tinted yellow-orange stars in the center of my eyepiece was a welcome change after the persistent white of our two previous objects. These two stars point almost due west on first glance, and the scene is improved by the intriguing parallelogram of three twelfth magnitude stars and one tenth magnitude star on the south side of the OΣΣ 104 pair. (East & west reversed once more, click to enlarge).

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:

“A” is moving east at .006”/yr (east is indicated by the plus sign) and south at the rate of .021”/year, while “B” is moving west at .005”/yr and south .014”/year.   Click to make the data more legible.

“A” is moving east at .006”/yr (east is indicated by the plus sign) and south at the rate of .021”/year, while “B” is moving west at .005”/yr and south .014”/year.  Notice the NOMAD-1 PM is slightly different.  Click to make the data more legible.

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!   :cool:

Double and Triple Stardom in Taurus: 37 and 39 Tau, Σ 479, and Σ 494

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.

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.

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).

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’

Identifier Magnitudes Separation  PA WDS
STT 558 AB: 4.46, 10.01    134.30″ 193°  2003
STG 4 AC: 4.46, 12.62    235.80″ 215°  2000

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’

Identifier  Magnitudes Separation  PA WDS
CHR 158 Aa, Ab:  None listed       0.40″ 252°  2003
STT 559 AB:  5.97,   8.09    176.80″ 359°  2003
STT 559 AC:  5.97, 12.60    148.80″   16°  2000
STT 559 BC:  8.09, 11.50      58.30″ 124°  2000

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.

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 -031 means motion of .172”/yr east and .031”/yr south).

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).

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):

Wm Herschel on STF 479

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.

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).

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
Separation:   5.3”
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 stars, GRV 206, which we’ll come back to shortly. (East and west reversed once more, click on the sketch to improve the view).

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):

Herschel on STF 494

Click to enlarge.

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.

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:

The Double Stars of Collinder 65, Part Two: OΣ 107, OΣ 108, HJ 3274, and HJ 3275

Now on to the last group of double stars in CR 65, which are located in the north part of the cluster.  If you missed part one, you can get to it by clicking on this link.

Here are our charts once again, starting first with a wide view:

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

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

And here are the finder views with the distances shown, starting with an erect image view:

This is an erect image chart, which will match the orientation you see in an RACI (right angle,correct image) 8x50 finder. (Stellarium screen image, labels added, click to enlarge).

This is an erect image chart, which will match the orientation you see in an RACI (right angle,correct image) 8×50 finder. (Stellarium screen image, labels added, click to enlarge).

And here’s the mirror-reversed image for use at the eyepiece of a refractor or SCT:

Stellarium screen image, labels added, click to enlarge:

Stellarium screen image, labels added, click to enlarge:

We’ll begin with an Otto Wilhlem von Struve discovery, OΣ 107. If you start at S 478, aka 111 Tauri, which is located near the middle of the west edge of CR 65, you’ll find OΣ 107 located 52’ to the northeast. If you have any influence with the sky guys and/or gals who control the seeing, give ‘em a call on the celestial night line – it’ll make things easier!

OΣ 107 (STT 107)         HIP: 25499    SAO: 94554
RA: 05h 27.2m    Dec: +17° 58’

Identifier  Magnitudes Separation  PA WDS
MCA 19 Aa, Ab:   5.80,  6.80      0.10″    89°  2007
STT 107 AB:   5.39, 10.10     10.30″  306°  1998
STT 107 AC:   5.39, 11.80     10.10″  346°  1998
STT 107 BC: 10.10, 11.80      7.00″    59°  2012

Distance: 549 Light Years (Simbad)
Spectral Classifications: “A” is B5, “B” is F8

On first glance, this scene reminded me of the alignment of Σ 697, which was the last star we looked at in part one. Alluring as the scene is, though, the two stars lined up to the west of the primary are not cataloged as part of OΣ 107.

In fact, you’ll have to look at the inset to see the “B” and “C” companions of the primary.   (East & west are reversed here to match the refractor image, click on the sketch for a better view of the close companions).

In fact, you’ll have to look at the inset to see the “B” and “C” companions of the primary.  Also shown here to the northwest of the primary is TDS 3195 with magnitudes of 10.6 and 10.98, separated by 0.4″ at 62 degrees (WDS 1991) — a bit beyond my reach!   (East & west are reversed here to match the refractor image, click on the sketch for a better view of the close companions).

I had a devil of a time prying both “B” and “C” out of the glare of the primary using the five inch refractor, but persistence finally paid off.  Not surprisingly, “B” popped into view first, and once I had it, patience added to more persistence finally resulted in “C” making an appearance.  The seeing was about average, although it was wavering between II and III on this chart.  The trick was to sit and wait for moments of good seeing and then to be quick with the eye.  It took several glimpses before I was convinced I was looking at “C”, and I went back later with a six inch refractor to confirm I had it.

Click to enlarge.

Click to enlarge.

There hasn’t been much change over the years in the measures of the AB and AC pairs, as can be seen in the excerpt at the right from William Hussey’s book on Otto Struve’s double star discoveries.  The position angle for AB measured in 1842 by Mädler (Ma) is at odds with the other measures, but otherwise, the PA’s average out to about 307°.

As for AC, it’s obvious from Hussey’s narrative the “C” component is difficult to measure (Otto Struve estimated the position angle), which probably is due to the glare caused by the primary. Hussey also found “C” was difficult because of its faintness, even with the twelve inch refractor at Lick Observatory. The most recent position angle in the WDS, 346°, seems to be at odds with the data in Hussey’s list, which probably is a further indication of the difficulty in measuring it.

I checked several photos of STT 107 in hopes I could get a measurement for both AB and AC, but the primary is so bright it blots out the “B” and “C” components.   There’s very little proper motion in the primary, +008 -021 (.008”/yr east, .021”/yr south), which corresponds with the minor change in the AB pair, but there’s no proper motion data on either “B” or “C”.

Now we’ll move on to OΣ 107’s sibling, OΣ 108, which is a short 39′ jaunt northeast from our current location.   Once you have it in view, you’ll find it’s accompanied by HJ 3275 to its northeast. (Here’s the erect image chart again, and the mirror-image chart).

OΣ 108 (STT 108)         HIP: 25702    SAO: 94586
RA: 05h 29.3m   Dec: +18° 22’
Magnitudes: 6.77, 10.42
Separation:  3.2”
Position Angle: 130° (WDS 1994)
Distance: 609 Light Years (Simbad)
Spectral Classification: “A” is A2

This is another tight pair which is made more difficult by a large magnitude difference, in this case a spread of 3.65 magnitudes.   I used the same procedure described above in order to catch a glimpse of the secondary with the five inch Meade, and made a second visit with a six inch refractor in order to confirm it.

This hand-full of scattered starlight includes all three of our remaining stars.   The secondary of OΣ 108 is visible in the upper inset on the right. The inset below, which is included for identification purposes, represents the same magnification as the larger sketch.   (East & west reversed once more, click on the sketch for a much better view).

This hand-full of scattered starlight includes all three of our remaining stars. The secondary of OΣ 108 is visible in the upper inset on the right. The inset below, which is included for identification purposes, represents the same magnification as the larger sketch. (East & west reversed once more, click on the sketch for a much better view).

Click to enlarge.

Click to enlarge.

Hussey’s 1898 observations of OΣ 108 are shown at the right, along with Otto Struve’s 1849 observation and four additional observations Hussey took from Burnham’s 1906 catalog.   Apart from Otto Struve’s 1849 position angles of 137.1° and 139.5°, the measures shown are pretty consistent.  Comparing that data with the 1994 position angle and separation in the WDS, it looks like this pair has moved slightly closer.  At the bottom of that page, I also included three later observations which come from R.G. Aitken’s 1932 New General Catalogue of Double Stars Within 120° of the North Pole, which continue the consistency in position angle and separation.

There isn’t much proper motion in the case of either star, but what stands out in the WDS data is the two stars are moving parallel to each other, with the primary moving at a rate of -015 -005 (.015”/yr west, .005”/yr south) and the secondary at a rate of -013 -004 (.013”/yr west, .004”/yr south).  That would indicate the measurable change in PA and separation should be negligible, or at least less than what the 1994 WDS measures indicate.  It’s possible the close proximity of the two stars, along with the wide magnitude difference, also makes this a tough pair to measure.  At any rate, since the last WDS date of measure is 1994, it looks like this pair could use an update.

Also included on the sketch above are two John Herschel discoveries, one of which was supplemented with additions by S.W. Burnham and Robert G. Aitken.

HJ 3275        HIP: 25745   SAO: 94589
RA: 05h 29.8m   Dec: +18° 25’

Identifier Magnitudes Separation  PA WDS
Bu 891 AB:  7.65, 13.60     10.60″ 128°  2000
HJ 3275 AC:  7.65,  8.22     56.30″   21°  2011
A 2433 CD:  8.22, 11.98      1.40″ 254°  1999

Distance: 567 Light Years (Simbad)
Spectral Classifications: “A” is A0, “C” is F

HJ 3274      No HIP or SAO Number
05h 29.7m   Dec: +18° 19’
Magnitudes: 11.04, 11.23
Separation:   5.3”
Position Angle: 107° (WDS 2000)
No distance or spectral classification in Simbad or WDS

Click to enlarge!

Click to enlarge!

John Herschel’s observations of HJ 3274 and HJ 3275 are shown at the left, but if you look at his data, you’ll see what appear to be estimates for HJ 3274 and no data at all, apart from magnitudes, on HJ 3275, which he describes as a “coarse double star” (probably a reference to their separation).   Also included on that page are his observations of Σ 697 and Σ 730, which were covered in part one of these posts on CR 65 (source).

HJ 3274 is the less impressive of the pair, and it takes an observant eye to catch the two faint stars. I wasn’t aware it of it when I first looked at this field, but as I was studying HJ 3275 I caught a hint of its duplicity out of the corner of my eye. When I gave it more attention, I was able to pry the secondary loose without too much effort.

HJ 3275 is the more interesting of the two, mainly because it’s been expanded from the two obvious components to include two more members, both of which are difficult to catch.

Click to enlarge.

Click to enlarge.

R.G. Aitken first caught sight of the tough CD pair in 1912, which was well beyond my seeing-limited reach on the two nights I looked for it.   I found that observation in his 1932 New General Catalogue, which includes measures for the AB pair (β 891) as well as the AC pair (h 3275), also referred to by Aitken as number 64 in Otto Struve’s appendix catalog. He expands the historical record even further when he refers to A 2433 as having been cataloged as JC 883. The JC refers to W.S. Jacob, whose observation I was unable to locate, although I did find several of his star catalogs. (Here’s more information on Jacob, who was an interesting observer in his own right).

S.W. Burnham was the first person to excavate the 13.60 magnitude “B” component from the 7.65 magnitude glare of the primary, using the 18 ½ inch refractor at Dearborn Observatory in 1879 (that observation is shown above in Aitken’s catalog).

Click to enlarge.

Click to enlarge.

If you compare Burnham and Aitken’s data, you’ll see the position angle of the AB pair meanders from 121.6° (1879) to 126.7° (1891) to 122.2° (1898) to 126.2° (1910) to 128.5° (1917), while the separation remains in the 10.6” range except for Burnham’s 1879 measure. More than likely the glare of the primary also makes this pair difficult to measure.

Burnham’s perceptive eye also detected an increase in separation taking place between “A” and “C”, which is confirmed by looking at the WDS proper motion numbers. This Aladin photo, with the aid of an overlay from Simbad, shows why the distance between the two stars is slowly increasing:

This is an erect image, so east and west are opposite of my sketch above.   Click for a better view.

This is an erect image, so east and west are opposite of my sketch above. Click for a better view.

There’s no proper motion data for the “B” component, but based on the 2000 WDS separation for AB at 10.60”, which is essentially the same as Burnham and Aitken’s data, it appears the two stars may be moving in tandem with each other.
_____________________________

There’s one other aspect of the Collinder 65 cluster worth looking at, which is the relation of the various stars to each other.  Normally an open cluster is a group of stars with similar distances, most of which are moving in the same direction.  For example, here’s a listing of the brighter stars in the Hyades cluster (the distances in black are members of the cluster), which is located fourteen degrees west of CR 65.  (That chart is included at end of this rollickingly informative post).

Compare that chart with this one showing the major luminaries of CR 65 . . . . . . .

Star    Dist (LY)      PM RV (km/s)
S 478          47
110 Tau        407
STT 107        549 +008 -021   +14.9
113 Tau        565 +001 -006   +27.2
HJ 3275        567 +003 -039     +1.0
STT 108        609  -015 -005
117 Tau        613 +017 -045
116 Tau        685
STF 697        874
STF 730      2991
 ———  ———-
122 Tau        158
120 Tau      1552
119 Tau      1791

. . . . . . . and you find the stellar distances are nowhere near as similar as those of the Hyades.   I highlighted three stars in red with similar distances, and another pair in green.   The three in red do in fact have similar proper motions, indicating a possible physical relation.  However, in order to get a three-dimensional view of what’s taking place, I included their radial velocities (RV), which tells us how fast the stars are moving towards us or away from us (in this case, away from us).   Adding that third dimension leads to the opposite conclusion.  As for the two stars in green, the proper motions are all we need to determine they’re unrelated.

I also expanded the boundary of CR 65 a bit to take in the last three stars at the bottom of the list, just to see if any of them might have distances similar to a few of those within the boundaries of the cluster – and it’s obvious they don’t.

So whatever criteria Collinder used for grouping this scattering of stars into a cluster, it apparently had nothing to do with their being physically related.  One more stellar mystery for the books!

Next tour will take us north of the Hyades to a small (non-clustered) group of four stars, two of which deserve to be better known than they presently are.

Clear Skies!  :cool:

Follow

Get every new post delivered to your Inbox.

Join 98 other followers