New Information on Sirius A and B

I just came across an interesting blog post on Sirius.  Among other things, the age of Sirius A is now estimated at 237 to 247 million years and Sirius B (the white dwarf companion) at 228 million years, with an uncertainty of about ten million years for each star.  Surprisingly, Sirius B is estimated to have begun the transition from a normal star to a white dwarf about 130 million years ago, which would mean it was only about a hundred million years old at the time.

This piece is written by Phil Plait, who writes a blog entitled Bad Astronomy.  Here’s the link:

Why so Sirus?

Four for Canis Major: S 537 and S 538, S 534, Nu1 (ν1)

I’m never sure where I’m headed next when I finish up in one area of the sky. Sometimes something in a star atlas will catch my eye and I’m off like a photon shot from a laser in hot pursuit, and other times I come across a book or internet reference to an intriguing multiple star that piques my curiosity.   There are other times, though, when an email lands squarely in the middle of my computer screen and grabs my full attention.

That’s what happened this time, and it led me on a chase down the same star-strewn path traveled by Sir James South almost two hundred years ago in Canis Major.   Whereas he was accompanied by a five inch f/16.8 refractor with a Tulley objective, I had the companionship of both a five inch f/9.3 Meade refractor and a six inch f/10 refractor equipped with a Jaeger’s objective – which is not to ignore the constant presence of Herr Klaus, the astro dog. I suspect the transparency of our skies was about the same, though – mine subdued with coastal moisture and his with the smoky murk of early nineteenth century Paris (the observatory he used for these observations was located at Passy).

And while I was roaming those star fields of two hundred years ago, my eye was caught by a distinctive trio of stars southwest of Sirius.   Those turned out to be the three members of the Nu (ν) family — ν¹, ν², and ν³ — one of which is a dazzling double star.

First, a look at the wide view of where we’re going:

You’ll find Nu-1 (ν1), the last star on our tour, three degrees southwest of Sirius, wedged between its stellar siblings, Nu-2 (ν2) to its south, and Nu-3 (ν3) to its north. But since I’m writing this in late April as Sirius sinks into the southwest, we’re going to start further south with S 537 and S 538, located west of Omicron-1 (o1) CMa, which is almost eight full degrees south and slightly east of Sirius. Hopefully by the time we work our way back up north, Nu-1 (ν1) will still be high enough for you to catch. (Stellarium screen image with labels added, click on the chart to enlarge it).

Here’s a close-up view of our star-studded hunting grounds with Omicron-1 (o1) parked down in the bottom left hand corner of the view. A short hop of three degrees due west from Omicron-1 will put both S 537 and S 538 in your field of view. If you have time, don’t neglect the ethereal starlight of M41. (Stellarium screen image with labels added, click on the chart for a larger view).

S 537/Bu 324           HIP: 32744   SAO: 172389
RA: 06h 49.7m   Dec:  -25° 05’
Identifier        Magnitudes       Separation     Position Angle      WDS
Bu 324    AB: 6.56,   7.93               1.80”                  211°               2008
S 537      AC: 6.56,   8.28             30.40”                 282°               2008
S 537      AD: 6.56, 13.00            30.60”                      3°               1999
Distance: 584.5 Light Years
Spectral  Classifications:  “A” is A0, “C” and “D” are A2

S 538                HIP: 32729   SAO: 172383
RA: 06h 49.6m    Dec:  -24° 09’
Magnitudes:  7.16, 7.18
Separation:   26.8”
Position Angle:  4°  (WDS 2007)
Distance: 622.4 Light Years
Spectral Classifications:  A6 and A2

Back to the email I referred to earlier, which is a description of S 537 and S 538:

A beautiful formation of two doubles and a single star. The top double is S 537 which is perpendicular to the line of stars, a bright and faint white double which is wide, then underneath (231″ away) is S 538, a faint and fainter white double slightly less wide, which is in line with the main line of stars, and finally adding to the overall beauty of the asterism is a faint star (mag. 8.4) which is CD-24 4476, about as away again (actually 253″). The main star of S 537 (BU 324) was resolved intermittently (‘popped out’) at 136x. The popping out was most odd. With rather poor seeing at the moment (the jet stream is very fast which makes the air turbulent) the main star was unresolved at first, then just as I was giving up, it suddenly ‘popped’ into being a pair, and then fell back to a single star again. I was rather doubtful but kept on looking and it happened again (but not thereafter).”

That picturesque description, written by Peter Morris from his London observing site, landed in my inbox on the Saturday afternoon of January 25^th (2014).   And at 9PM that night, I had S 537 and S 538 cornered in a 10mm Radian:

And there they were, exactly as Peter described them – S 537 at the top of the view, perpendicularly contrasting with the vertical symmetry of S 538, and at equal distance south of S 538 is the star Peter referred to as CD-24 4476, which also goes by SAO 172832, among other designations. The primaries, by the way, were all white. (East & west reversed to match the refractor view. Click on the sketch for a much better version).

S 537, click to enlarge the image.

My experience with trying to separate Bu 324 was uncannily similar to Peter’s. I had an elongated glimpse of it with the 10mm Radian (152x), which led me to see what I could coax from an Astro Tech 6mm Plössl (253x). The seeing was so poor that it wouldn’t come to focus, so I reluctantly went back to the 152x view and sat as still as rock, waiting for the elongation to transform itself into two distinct stars.

I eventually got the “popping out” effect Peter mentioned, but only briefly, and only twice.   Rats – foiled again by uncooperative skies. Bu 324, by the way, was discovered in 1875 by S.W. Burnham with his six inch f/15 Clark refractor. It was first measured at a separation of 1.88” in 1877, so it has changed little, if any, since.

S 538, click to enlarge.

The “S” designations are the result of several observations made by James South in February and March of 1825, which I’ve included at the right.  A close look at those numbers shows little change in the almost two hundred years since Sir James made his initial observations.

Translating his early nineteenth century position angles into present usage and leaving the separations as is, he measured what is now the AC pair of S 573 at 281° 51’ and 30.305” (the 2008 WDS numbers are 282° and 30.40”). For S 538, his final results were 3° 16’ and 27.806” (versus the 2007 WDS data of 4° and 26.8”).  The source for South’s observations shown at the right can be found here.

Click to enlarge.

It took some determined detective work, but I also tracked down the first measurement of what is now the AD component of S 537 on pages 46 and 47 of this source.   Eric Doolittle made that one in 1898 from the Flower Astronomical Observatory, which was associated with the University of Pennsylvania near Philadelphia.  The “Sh” designation Doolittle used in the page shown at the left is an error — it should be shown as S 537.  “Sh” was only used to refer to the joint John Herschel-James South catalog (scroll down to the last title) published in 1824, which we’ll get to when discussing Nu¹ (ν¹) CMa.  (The WDS has replaced “Sh” with “SHJ”).

The instrument used by Doolittle was an eighteen inch refractor with a Brashear objective, which he described as having “proved in every respect more than satisfactory.”   Again, there is little difference between his figures for the AD pair (2.45° and 30.27”) compared with the 1999 WDS figures (3° and 30.60”).

Now we’ll follow Sir South north by moving one degree northwest from S 537/538 to 6.0 magnitude HIP 32368 and then another degree northwest (slightly more north) to S 534 (here’s that earlier chart again).

S 534               HIP: 32144  SAO: 172204
RA: 06h 42.8m    Dec:  -22° 27’
Magnitudes:  6.27, 8.30
Separation:   18.2”
Position Angle:  144°  (WDS 2003)
Distance: 160 Light Years
Spectral Classifications:  “A” is F2
Note:  “A” is a variable star, V 350 CMa

You’ll find the field of view surrounding S 534 is quite a contrast to the dazzling white lights of S 537 and S 538:

In a five inch refractor S 534 is surrounded by a rather sparse field, although it compensates with an inner and outer arc of curving stars arrayed along its west edge. In fact, while sketching this idyllic scene I grew rather attached to that delicate arrangement of starlight. Once again, the only color visible here was the white light of the primary. (East & west reversed to match the refractor view, click on the sketch for a larger version).

The outer arc of stars guarding the west side of S 534 all have names, magnitudes, and even spectral classifications. From north to south they are SAO 172191 with a magnitude of 8.86 and a spectral classification of B9; SAO 172183, 8.12, B3; SAO 172181, 9.05, AO; and SAO 172187, 9.48, K5. That second star, SAO 172183, is also a double, designated as B 1963 (magnitudes of 8.10 and 10.98, 130°, 1.2”, WDS 1991), that would be an interesting challenge for a night of steady seeing.

S 534, click to enlarge.

James South paid three visits to the pair of stars he cataloged as S 534 around the same time he looked at S 537 and S 538. Those dates can be seen in his observation shown at the right. And again, when we compare the averaged measures made during his three observations (143° 13’ and 18.252”) with the most recent WDS measure of 2003 (144° and 18.2”), we see virtually no change in the relative positions of the primary and secondary.

The S 534 primary is also a variable, but depending on where you look you’ll find two different designations assigned to it.   Stelladoppie, which pulls its data from the WDS, lists it as V3181 (the AAVSO designation is NSV 3181), but I found the AAVSO site now lists that as obsolete.   Simbad uses the current designation, which is V 350 CMa.  The AAVSO web site shows a rather narrow magnitude range, 6.18 to 6.27, with a short period of .91041 days.

Meanwhile, on to our last star, which also has a connection to James South. Nu¹ (ν¹) CMa lies four degrees north and slightly east of S 534, but it’s actually easier to get there by starting at Sirius, which is impossible to miss with its -1.50 magnitudes of blazing white light.  Going back to our first chart (here), you’ll find the trio of Nu (ν) stars lying from two to three degrees southwest of Sirius.  Nu¹ (ν¹) is located halfway between Nu³ (ν³) and Nu² (ν²).

Nu¹ (ν¹) Canis Majoris  (6 CMa)  (H IV 81)  (SHJ 73)          HIP: 31564  SAO: 151694
RA: 06h 36.4m    Dec:  -18° 40’
Magnitudes:  5.79, 7.38
Separation:   17.8”
Position Angle:  264°  (WDS 2011)
Distance: 277 Light Years
Spectral Classifications:  “A” is G9

Another surprisingly sparse field, at least in a five inch refractor, but this time with what almost looks like a pair of headlights coming straight at you. There’s a very slight, but very noticeable, yellow-gold light streaming out of the primary. SAO 151712, over in the northeast corner, is a 7.83 magnitude K4 star. (East & west reversed, click on the sketch to improve the view).

Sir William Herschel had a look at this star on September 30^th, 1782, describing it with a mysterious Latin phrase “In dextro genu.”   I plugged that into the Google translator, which spit out “on the right knee” – and sure enough, that’s where Nu¹ (ν¹) CMa is (take a look at the first chart again).   Sir William measured the separation of the two stars at 18.32” but was more elusive with his position angle, describing it as “very near directly preceding”, which actually describes it reasonably well.

Click to enlarge.

I mentioned a connection between Nu¹ (ν¹) and James South, which is a result of a March 22nd, 1821, observation he made jointly with Sir John Herschel.   He felt there was an obvious change in position angle, a result of his measuring it at 17.24”, but with the 2011 WDS data falling almost exactly halfway between his measure and that of William Herschel forty years earlier, it’s hard to say who was closest to being correct.

As to whether those differences indicate orbital motion, or are just variations between observers, it’s possible to gain some insight by looking at the proper motions of the primary and secondary.   There’s a slight difference between the data listed in the WDS (-013 +018 for the primary, -009 +022 for the secondary) and Simbad (-010 +013 and -002 +006), but they both indicate the two stars are pretty much moving through interstellar space in parallel with each other, meaning there’s no indication of an orbital relation.   Here’s what that motion looks like on Simbad’s chart:

For those not familiar with proper motion numbers, the -013 +018 mentioned above for the primary means .013” per year west and .018” per year north, while -009 +022 for the secondary translates as .009” west per year and .022” north per year. (Click on the chart to enlarge it).

As for the position angle measurements by Wm. Herschel and the Herschel/South duo (their 10.8° south preceding translates to 259.2°), Sir James took issue with the senior Herschel’s description of the position angle, maintaining his “very near directly preceding” was “irreconcilable with a deviation of 10° from the parallel.”

And considering it was only an estimate, I actually thought Sir William had described it rather well.  Which just goes to show perception, as well as beauty, lies in the eye of the person at the eyepiece.

Off to the east again for the next tour as I race to catch sight of one more winter constellation before losing it to the western horizon.

Clear Skies! 😎

A Tale of Two Secondaries: Part Two — Tau (τ) Canis Majoris (h 3948)

If you wandered to this point without reading the first part of this two part post, you can get to part one by going  ➡   HERE.

Meanwhile, we’re leaving our former location east of Orion’s Betelgeuse and taking a trip to the warmer southern regions of Canis Major, where we’ll take a look at a complex multiple star basking in the center of a beautiful open cluster.

To reach (τ) from Delta (δ) Canis Majoris (aka Wezen), move three degrees due east to 4.85 magnitude HIP 35412 (aka 29 Canis Majoris). You can’t miss Tau (τ), which is about half a degree south of it surrounded by a shimmering glow.  Center it in your eyepiece and make yourself comfortable — we’re going to be here for a spell. (Stellarium screen image with labels added, click for a larger view).

Tau Canis Majoris  (h 3948)                          HIP: 35415         SAO: 173446
RA: 07h 17.8m   Dec: – 24° 57’
.                                    Magnitudes      Separation    Position Angle       WDS
.FIN 313      Aa, Ab     5.33,   4.89               0.1”                 129°                 2011
HJ 3948            AB     4.42, 10.20               8.6”                   93°                 2002
HJ 3948            AC     4.42, 11.20             14.2”                   87°                 2002
HJ 3948            AD     4.42,   8.22             84.8”                   77°                 2002
.TOK 42         Aa, E     5.33,   9.70               0.9”                   88°                 2011
Distance: 3198 Light Years
Spectral Classifications:  A is O9, D is B2

As you can see from the data above, this is a complicated multiple star.  In addition to the four components we’re going to look at, there are two more, at separations of 0.1” (Aa, Ab) and 0.9” (Aa, E), which are well beyond our reach.  But since Tau (τ) resides right in the middle of an eye-opening open cluster, NGC 2362, the complexity isn’t surprising.

East and west are reversed here to match my sketch. (STScI photo, click for a larger view).

As alluring as the cluster is, it creates a lot of star glow around Tau’s components, making it more difficult than it is anyway to pry them out of the glare.  In fact, there’s so much glare here from the cluster’s many stars, that in a four inch refractor or smaller it looks like Tau (τ) is immersed in nebulosity, which was precisely the impression it made on me when I first viewed it several years ago in a 102mm refractor.  Most of that nebulous impression is resolved into individual stars, though, in apertures of six inches or greater.

The photo above gives you some idea of the nature of the area, although nowhere near that many stars are visible even at ten inches of aperture.  And of course all those stars in the cluster have an additional effect:  they make it difficult to determine which stars belong to the cluster and which belong with Tau (τ).

Let’s start first by looking at my sketch:

I caught most of the stars in the field of view in this sketch, but since I only had thirty minutes before losing the view to a cluster of star-eating coastal pines, a few around the outer perimeter are missing. (East & west reversed, click on the sketch for a larger view).

Now the big question confronting us is this:  which stars are which components?  If you go back to the data above for Tau (τ), you can see from the position angles of the “B,” “C,” and “D” components that all three stars are lined up within sixteen degrees of each other.  It was obvious that “B” and “C” were going to be the tough ones, so I decided to start with “D” and work my way in to the primary from there.  With several stars competing for attention, I knew I had to pin down “D” precisely, so I put the plotting ability of Vizier to work on Tau and came up with this:

The line labeled 1.425” identifies “D”, which also matches it’s 77 degree position angle. (The software also plots that angle for you, but it isn’t visible here — click for a larger view).

I had hoped to identify the “B” and “C” companions with Vizier, but as you can see in the photo, they’re hopelessly buried in the primary’s glare.  But I did plot their positions as closely as possible (the 14.12″ and 9.401″ labels), and even though there aren’t any stars visible at the plotted locations, it gave me an idea of where exactly on my sketch to look for them.

 And this is where our experience with Bu 193’s secondary becomes invaluable.

With “D” now labeled, let’s look at my sketch again.  You’ll see two faint stars southeast of the primary (enclosed below in a box) which I found very intriguing.   Could they be “B” and “C”?

Same sketch as earlier, with “D” now labeled, and the possible “B” and “C” candidates boxed in. (East & west reversed, click for a full size view).

Something made me hesitate — I think it may have been S.W.’s voice warning me away from making a rash decision.  On the one hand, I was mystified by the fact that the position angles of those two stars are greater than the 87 and 93 degrees listed for them in the WDS figures from 2002 — and on the other, when I studied the relative position angles and distances between the two stars, I could see enough similarity to the WDS figures to slap “B” and “C” labels on them and call my chores done.

But think back to Bu 193 and the 19.5” separation of its secondary.  It was further out than the two companions of Tau that I was searching for (8.6” for “B” and 14.2” for “C”), and although it could only claim an anemic magnitude of 12.38 (compared to 10.20 and 11.20 for Tau’s “B” and “C” components), it wasn’t drowning in a sea of open cluster glare, either.  So I came to the reluctant conclusion that my “B” and “C” chores really weren’t done at all.  I knew where they were now, and they weren’t going to be easy to see.

I mulled over the wisdom of my next step — it had as much chance of succeeding as a marshmallow has in the middle of a bonfire — but I finally closed my eyes and leaped into the flames, telescope and all.  After waiting patiently for a clear night to arrive, I raced outside and set up my six inch f/10 refractor and pointed it into the middle of that glowing open cluster surrounding Tau (τ).  Unfortunately I was late in getting set up because dinner detained me longer than I had expected, which meant I lost about half of the thirty minute window I had for catching Tau (τ) while it was in the open sky between the coastal pines.

Once I had the primary centered in a wide angle eyepiece, I went for the murky heart of it right away with a 4mm Astro-Tech Plössl (380x).  And there were some heavy odds stacked against me: first, the seeing was poor to start with, and of course it was a whole lot worse at 380x; second, there was almost enough murk in the sky to make Sirius look like a second magnitude star; third, Tau was even lower in the thick atmosphere of the southern sky than Sirius; and fourth, there was all that white light rushing into the eyepiece from both the primary and the cluster’s glare.

Well aware that I was running a race against time, I persisted for about ten minutes, delicately tweaking the focuser’s fine focus knob first this way, then that way, then back again, pausing each time to see what would happen — and finally I had a glimpse of something.  I could feel the breath sucked out of me like a wandering star yanked into the heart of a black hole.  I became rigid as a rock, locked solidly into a frozen crouch, waiting to see what would happen next, and suddenly I caught another glimpse — two ghostly egg-shaped smears of light swimming in an overwhelming glare, desperately trying to break free of the primary’s glowing grasp — and then they were gone again, as fast as they had appeared.

I had one more tantalizing glimpse of them, then the trees swallowed everything, the view in the eyepiece went dark, and they vanished — probably forever.  And every bit as tantalizing as those glimpses was the thought that Tau’s “E” companion may have contributed it’s 9.70 magnitudes to that bleary egg-shaped smear of light.  Chalk one up for the marshmallow.

Those two ghostly stars were one of the most fantastic things I’ve ever seen.  Try to imagine looking through the blinding light at the center of a white-hot flame and suddenly catching sight of a wavering ghost-like face on the other side.  It disappears almost immediately, then it re-appears for a few tenths of a second longer, vanishes once again, and quickly flashes into existence once more for about as long as it takes you to blink your eyes in surprise — and then it’s gone.  Completely.  Everything goes dark.  And all you have to hold on to is a very brief, but amazingly vibrant, image of that bleared shimmering face being suffocated in a rush of white-hot flame.  You don’t quickly forget it.

** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** **

Now there’s one sure way to make the frustrations of identifying short-leashed secondaries less frustrating, and that’s to use the same scope all the time for all your searches of that kind.  That way an observer becomes familiar enough with distances at various magnifications that it’s possible to become reasonably adept at estimating both separations and magnitudes.  But I’m like a kid in a candy store when it comes to using refractors of different apertures — and removing the temptation from the candy store is like separating Laurel from Hardy.  It can’t be done — at least I can’t do it, anyway.

Speaking of which, I wonder if I can ferret Bu 193 “B” out of the primarial glare with a 90mm refractor?  Gotta go – I hear the candy rattling in the jar.

Clear Skies!  😎

UPDATE:  This recent photo (about March 20th, 2013) by Steve Smith captures both the “B” and “C” companions of Tau, which really is an amazing feat given the glare from the primary.  The glimpses I had of the two inner companions were nowhere near this clear, so feast your eyes on this carefully since it’s a beautiful, not to mention, rare view!  First, a view with the companions labeled:

Photo taken by Steve Smith through a 100mm refractor at prime focus, exposure of four seconds, ISO set at 200. I’ve flipped east and west to match my sketch and added the labels for the three companions, plus the directional indicator.  Click to enlarge both this and the photo below.

If you compare Steve’s photo with my labeled sketch above (here), you can see the two stars I had originally thought might be “B” and “C” are located in the photo to the right and below the primary at about a thirty-five degree angle.   The two inner companions are completely hidden in the primary’s glare in both my sketch and the STScI photo above.  Really, it’s remarkable to see those inner companions so clearly!

Here’s the photo once more, with the labels out of the way:

Photo again by Steve Smith, and used with his kind permission.

Post Script:  Thanks go to Steve McGee and Chris Thuemen for waving Bu 193 in front of me.  I probably never would have discovered it otherwise, and as unlikely as it seems, it led me back to Tau Canis Majoris, a trip I’ve had planned for the last couple of years, which also happened to be a favorite of theirs, too.  And many thanks to Steve Smith for permission to use the two photos above.   This has been a heck of collaborative effort, which has made it all the more enjoyable!

A John Herschel Odyssey in Canis Major: h 3934, h3938, and h 3945

So there we were, me and my 80mm Mizar, sitting quietly in the moonlight. The sky was magnificently crisp, the stars were twinkling with adolescent enthusiasm, a rapturous host of beautiful fluffy white clouds were arrayed randomly above me — and I was mentally preparing myself for an invigorating evening of sucker hole roulette.  You probably know the routine:  find the most wide open space of sky you can (get ready to spin the roulette wheel), aim your scope at a target in the middle of it (spin the wheel now), get lined up (it’s slowing down already), focus the image (it’s really slowing down now), and then guess how long it will be before the clouds invade your field of view (the wheel is barely moving at all now).  Usually it takes no more than a fraction of a second after you find the focus (yep, just heard the marble drop).  Fun stuff if you have the patience for being fleeced repeatedly.  (It doesn’t matter where the marble drops, you won’t win).

But as the evening wore on, the clouds became less common and the sucker holes began to get larger and more long-lasting.  So I stuck with it, zeroing in on a target and staying with it for as long as I could see it.  At some point – I think it was about the time my fingers had turned to ice and my toes were as hard as permafrost – I spied a huge swath of clear sky in Canis Major.  And that was when I remembered the Winter Albireo, thanks to a recent email and sketch from Steve McGee.

So I grabbed my well-worn copy of Sky and Telescope’s Pocket Sky Atlas, flipped to chart number 27, and star-hopped around the coastal pines to it.

I didn’t mention the coastal pines?  They’re a family of inter-woven and close-knit fir trees living across the street from my second story deck — there are about a dozen of them — that project eighty feet into the air, blocking most of my view of the southern sky below a declination of minus ten degrees or so. I keep waiting for a winter wind to take them down, but no luck so far. Anyway, since the Winter Albireo lies at a declination of minus twenty-three degrees, that meant I had replaced the art of sucker-hole-hopping with a challenging game of fir-tree-finesse.   So with mother earth escorting them through the lace-like framework of pine needle branches, I spent the next hour catching views of three of John Herschel’s 1837 discoveries.

** ** ** ** ** ** ** ** ** ** **** ** ** ** ** ** ** ** ** ** ** *** ** *** ** ** ** ** ** ** ** ** ** **

It was November 13^th, 1833 when Sir John, with firm intentions of completing a survey of the southern skies, packed up his astronomical hardware (including a five inch refractor and an 18.25” reflector) and boarded the East India Company’s Mount Stewart Elphinstone, bound for The Cape of Good Hope.  During his sojourn there, he made a large number of double star observations, which are preserved for posterity on pages 171 to 242 of the book that resulted from that trip, Results of Astronomical Observations Made During the Years 1834, 5, 6, 7, 8 at the Cape of Good Hope; Being the Completion of a Telescopic Survey of the Whole Surface of the Visible Heavens, Commenced in 1825. That long-titled book, which was published in London in 1847, has fortunately found its way into the public domain and can be found here.

And we’re here to take a look at three of those stars now, beginning with h 3945, sometimes referred to as the Winter Albireo.

One navigational method of carving a path through the sky to our first target is to triangulate your way to it by using Delta (δ) and Omicron-2 (O2) Canis Majoris. Another effective approach is to draw a line from Omicron-1 through Omicron-2 and extend it in the same direction for the same distance, which will bring you out just a few photons north of h 3945. (Stellarium screen image with labels added, click to enlarge).

h 3945    (BC is SHY 508)    HIP: 35210    SAO: 173349
RA: 07h 16.6m   Dec: – 23° 19’
Magnitudes   AB: 5.00, 5.84    BC: 5.84, 6.76
Separations  AB:26.40”           BC: 999.90”
Position Angle:  52° (WDS 2008)   165°  (WDS 1999)
Distance: 6273 Light Years
Spectral Classification: K4, A5

Before we get too far, I should mention you’ll find the stars catalogued by John Herschel carry a prefix of “HJ” in the Washington Double Star Catalog (WDS).  But the older lower case “h” is still used on many charts, so there’s no telling which style you’ll run across.  I prefer the historical aura of the lower case format, which was originally used to differentiate the younger Herschel (h), Sir John, from the senior Herschel (H), Sir William, an effective visual form of paternal recognition if ever there was one.

I first bumped into h 3945 by accident several years ago when I was exploring the star fields east of Canis Major for open clusters.  I think I had wandered north to it after ogling NGC 2362, a tight little cluster of stunning beauty surrounding Tau (τ) Canis Majoris which just happens to include another John Herschel discovery, h 3948.  That one is a complex quadruple star that also includes two additional sub-arc second companions, and with a bit of cooperation from the winter skies, it may be the subject of a another post.

But for now, let’s go see why h 3945 picked up the Winter Albireo designation:

And it should be obvious! This colorful sketch was done by Steve McGee and is used with his kind permission. The apparent field of view here is about 45’. (East and west are reversed here to match the refractor view, click for a larger version).

Outlined in yellow are all three of the Herschel stars described in this post. (Click to enlarge the view).

I don’t have the least clue as to who was first to describe h 3945 as the Winter Albireo, but as the colors in Steve’s sketch show, it was inevitable.  Haas describes it as “bright citrus orange” and “royal blue” (p. 38), and the Night Sky Observers’ Guide describes it as “intense orange and blue” (Vol 1, p. 88).  In his 1894 Celestial Objects for Common Telescopes, the Reverend T. W. Webb was considerably more impressed: “fiery red, greenish blue . . . Magnificent pair.” (64)  And even John Herschel, normally rather reticent with descriptive notes, recorded the colors he saw in two separate observations, as can be seen at the bottom of the page at the right:

Not only is h 3945 deserving of comparison to Albireo, it also measures up well with Almach — but despite that, it does disappoint on occasion.  I think it’s mainly a northern hemisphere thing, a result of the colorful pair’s relatively low position in the southern sky, which tends to diffuse the colors considerably when haze is present.

On the night I tracked it down with my 80mm Mizar, the sky was crisp and transparent, but the moon, waxing at about 60% of full, was bright enough to turn the orange tinge very pale, and the blue was barely detectable.  So if you’re not impressed, go back on a better night – and to give the color a chance to  work its magic, go with four inches of aperture or more if you can.  My first view of it was in a four inch refractor, and that initial image still flickers to life every now and then in my double-starred memory.

STScI Photo with labels added. (East & west reversed,

There’s supposed to be a 6.76 magnitude third component, SHY 508, which is shown in the data line above with a position angle of 165 degrees at a distance of 999.90” (16.7’).  The problem is it’s not there — not in Steve’s sketch, not in my copy of MegaStar, and not in the STScI photo at the left.

As you can see, I’ve labeled two possible candidates in the STScI photo.  The fainter of the two, GSC 6537:2093, is at the correct PA and distance, but at a magnitude of 10.8, it’s too dim.  The only star in the immediate area that comes close to matching the magnitude recorded for SHY 508 is 6.30 magnitude HIP 35132 / SAO 173319 / HD 56341, but at a PA of about 200 degrees and a distance of slightly less than 30 arc minutes, it’s in the wrong place.  So – another mystery for the books.  Or perhaps it’s just “SHY.”  🙄

Time to remove the mystery hat and clamber off to the north now, and to aid our navigation we’ll employ another chart:

As you can see, we don’t have far to go. In fact, with the Winter Albireo centered in your finder, our next star is easy to spot. Look for two stars of similar brightness about a degree to the northwest – the first is our next target, h 3938, and slightly beyond it in the same direction is 5.95 magnitude HIP 34914. (Stellarium screen image with labels added, click for a larger view).

h 3938                HIP: 34940   SAO: 173247
RA: 07h 13.8m   Dec: – 22° 54’
Magnitudes: 6.32, 9.10
Separation:  19.4”
Position Angle: 250°  (WDS 1999)
Distance: 1576 Light Years
Spectral Classification: B2, G5

Besides playing hide-and-seek with the interfering framework of pine needles, I was also contending with rather poor seeing once again, easily as bad as the worst shown on this chart.  And there were other factors of frustration as well.  The first was the 2.8 magnitude difference between the two stars, the second was the sunlight reflecting recklessly from 60% of the moon’s surface, and the third was the challenge the 9.1 magnitudes of secondarial light posed to an 80mm lens operating at 60x — more magnification just led to a muddled view.  So despite the reasonably wide separation of 19.4”, I had to look long and hard to corner my quarry — it was averted vision or no vision.   Fortunately, it didn’t take all that much visual averting to see the secondary, but it was very ghost-like at first.  It easily could have been a creation of my imagination on first sighting, so I kept coming back to it as I made my sketch:

You won’t need averted vision to see the secondary here, but clicking on the sketch will enlarge the view and make things easier. (East & west reversed to match the refractor view).

I really think this pair of stars is crying out for more aperture.  It was certainly a challenge with the 80mm scope — an additional twenty millimeters would be a much better choice.  Both stars were essentially colorless under the observing conditions I was contending with, but if you look up in the NNW corner of the sketch, you’ll see a sixth magnitude star that has a very pronounced orange tint to it – that’s HIP 34914, a class K4 star at a distance of 780 light years, which we saw earlier in our finder.

h 3934  (BC is RST 4840)    HIP: 34718   SAO: 173152
RA: 07h 13.3m   Dec: – 21° 48’
Magnitudes    A,BC: 6.91, 8.49     BC: 8.60, 10.80
Separations   A,BC: 13.7”      BC: 0.60”
Position Angles   A,BC: 235° (WDS 1999)   BC: 270° (WDS 1949)
Distance: ?????
Spectral Classification: B5, B9

Now, with our previous pair still centered in your finder, if you use HIP 34914 as a pointer (here’s the chart above), you’ll find h 3934 shining as a 6.9 magnitude star at three times the distance separating h 3938 and HIP 34914.

And again, I had to avert my vision to catch a glimpse of the 8.49 magnitude secondary (we’ll skip “C” since it’s well out of reach for 99.99% of us):

Very similar to the previous sketch, with a little less distance between the two stars. (East & west reversed, click for a larger view).

The magnitude difference is only 1.58 between this primary-secondary pair, but they’re six arc seconds closer than our previous Herschel duo, which pretty much gobbles up what would otherwise be an advantage.  In fact, the secondary here was every bit as eager to avoid my vision as that of h 3938.  Again, I heard a voice echoing in the moonlight – more aperture!  And sure enough, when I went looking for other observations of these two Herschel discoveries, I found Haas had come to the same conclusion:

h 3934: “150mm, 36x: Nice view.  A bright, easy pair at the end of a curved line of dim stars.  It’s a pure white star and an ash white, split by only a small gap.”

And our previous star —

h 3938: “125mm, 50x: Lovely combination. A bright white star with a small nebulous companion, split just wide enough for the companion to be easily seen while striking in contrast.”  (p. 38 for both)

** ** ** ** ** ** ** ** ** ** **** ** ** ** ** ** ** ** ** ** ** *** ** *** ** ** ** ** ** ** ** ** ** **

And that was about enough for me on this particular night.  Apparently intermission was over since the clouds were drifting back into their places in the sky in groups, the wind was winding itself up for another blustery show, and a persistent image of steaming hot tea was dancing in my head.

With any luck at all, next time out we’ll see if we can dig h 3948 out that open cluster surrounding Tau Canis Majoris.

Clear Skies!

DSC-60: Iota Cancri – in search of the real Winter Albireo!

This is a DSC-60 Project observation – for project details go here.

]

Iota Cancri

08h 46m.7

+28° 46′

4.2, 6.6

30″

307°

I was looking for what I thought was the “Winter Albireo” – Iota Cancri, which is in my eyes a good imposter  of Albireo. I enjoyed it immensely – beautiful double, but the real fun started when I got back in the house, sat down with my notes and discovered I had not been looking at what others call the “Winter Albireo” at all. What’s more, I think I can make a case for my candidate – Iota Cancri, over the more popular one, h3945. But first, the background.

Iota is fascinating in its own right and quite easy to find on a spring evening since its one of the brighter stars in the dim region between Leo and Gemlni  that we know as Cancer the Crab.  If you can find the Beehive (M44) , a large and beautiful open star cluster, then Iota is the 4th magnitude star nearly due north about one fist -held at arms length – from M44..

Your fist held at arms length covers about 10 degrees – just a bit more than the distance between the Beehive and Iota Cancri. (Prepared from Starry Night Pro screenshot.)

This is one of the doubles featured by Guy Consolmagno and Dan Davis in their beautiful observing guide, “Turn Left at Orion.” The primary is a giant and while the two stars are gravitationally linked, they are quite far apart as doubles go. (Almost as far apart as the real Albireo and a bit farther apart than what others call the “Winter Albireo.”)  Consolmagno and Davis note that if you were on a planet that orbited the primary star, you”would see its companion as a very bright star, about half as bright as the Full Moon. ” From a planet orbiting the secondary, the primary “would look about four times brighter than the Full Moon.” I love to carry images like that in my head to the telescope and ponder them as I observe.

But I’m getting side tracked.  See, Iota Cancri looks so much like Albireo to me that I have written “Winter Albireo” in the margins of two of my observing books next to the Iota Cancri entry.  When I saw those notes as I was planning this observing session, I assumed that was it’s accepted nickname – wrong!  Seems like the only one calling Iota Cancri that is me. Or at least I can’t find any other reference to it as such.   What I did find, as I said, is that another double I’ve never seen is called the “Winter Albireo” by many  others and is generally regarded as too frequently neglected. Well, mark me down as “neglectful” – I’ve never seen Herschel 3945, but now I am really curious, so it has moved to the top of my “to be observed list!” And when I do observe it I may change my tune, but from what I’m reading I just don’t see how they give it this nickname while ignoring Iota Cancri.

I love Albireo. Nothing can replace it. My observations of it go back nearly half a century and I’ve never tired of looking at it. I always see it as gold and blue – very easy to split and with dramatic contrast.

And when I looked at  Iota Cancri  on this occasion I saw a wonderful yellow – pale yellow – primary and a beautiful, deep, sky-blue secondary. So I will readily admit that my idea of the “Winter Albireo” doesn’t quite measure up to the summer one, but it comes close.  I confirmed this by getting a couple hours sleep, then getting up and observing the real Albireo while the memory of Iota Cancri was still fresh.

So when I got in to write this report I decided to check on the spectral types to see if that gave me a solid guide to these color differences.  Guess what? It does – but it opens more questions.  The Albireo primary is a K3, the Iota Cancri primary is G7.5.  Look at the chart in the Star Colors post and you’ll see that  we tend to perceive G stars like Iota Cancri as “yellowish white.” Whereas K stars, like the primary of Albireo, tend more towards the orange.  So “pale yellow” for Iota and “gold” for Albireo seem to fit. The secondary’s also match the spectral classes. The Albireo secondary is B8 and the Iota Cancri secondary, A3 – that makes the Albireo secondary a somewhat richer blue, but they both tend towards blue.

Yes, this is splitting hairs because colors are so difficult to perceive, but having observed them within a matter of hours of one another, I did come away with just that impression – Iota Cancri makes a credible imitation of Albireo, but in the end Iota is just not as intense.

And what about the star so many do label the “Winter Albireo?” There my curiosity is really sparked.  The h3945 primary is a K0 – so that pushes it over closer to the yellowish-orange of the real Albireo primary. So far so good.  What throws me, though, is the spectrum of the secondary. It is listed as F0! That puts it in the white category in terms of our perception – or certainly a very,very pale blue. Not nearly so blue as the B8 of Albireo, or the A3 of the Iota Cancri secondary.  These deductions based on spectral class also match the description in “Turn Left at Orion.”

Herschel 3945 gets attention under the “Also in the neighborhood” category of “Turn Left at Orion” – just not the neighborhood of Iota Cancri.  They link it with observing an open cluster, NGC2362, in Canis Major.  They note that the primary is a “distinct red, while it’s companion may appear white or yellow.” Huh?! Does that sound like Albireo to you? Red and white/yellow?  What happened to gold and blue? I find their description in tune with the spectral classification, but out of tune with Albireo.  Still, they note that this double  is more popularly known as ‘The Winter Albireo.’  Indeed the color contrast and separation are reminiscent of Albireo…” Oh boy! Color contrast maybe, but not color. Now I really have to get a look at these stars!

So I’ll report back here after I’ve looked at h3945 and we’d love to hear from others on how they see these three stars. Here are the vital statistics for each.

Beta Cygni

19h 30m.7

+27° 58′

3.1, 5.1

34.4″

54°

K3, B8

Iota Cancri

08h 46m.7

+28° 46′

4.2, 6.6

30″

307°

G7.5, A3

h3945 (Canis Major)

07h 16m.6

-23° 19′

5, 5.8

26.8“

52°

K0,F0

Just looking at the stats, they do all look pretty similar until you get to spectral class and in that  I would think Iota Cancri would be a  better match.

And h3945? How does Sissy Haas see it? Well, she reports the stars “are bright citrus orange and royal blue: the colors are seen vividly and in strong contrast.”

And, of course, we have discussed many times  the variables involved in seeing color differences – but there may be something special here in h3945. I can’t wait to see for myself.

Update: March 12, 2011

Conditions certainly could have been better, but seeing was just a bit below average and I found a hole through the bare tree branches where I had a clean shot at h3935 and guess what? It’s every bit as  beautiful as folks say – but in my book it is not the “Winter Albireo.” In fact, the colors remind me more of Rasalgethi  (Alpha [α] Herculi) – orange going to red with a blue companion. I think one thing that separates it from Albireo, besid the colors, is the primary just isn’t as dazzling. With Albireo you’re seeing  a magnitude 3.1 primary, whereas  h3945 is nearly two magnitudes fainter.

I would also say that I’m looking through a lot of atmosphere – I caught it when it was about 24 degrees above my southern horizon which is only a couple degrees lower than it is at transit, so I can’t do much better. I suspect that contributes to the redness  however. Folks in the southern states  have a better shot at this beauty. I used the Televue 60 with a 10mm Tak for 36X which to my taste gave very nice proportions.  It was just as attractive in the TV85 with a 13mm Nagler – 46X.

Want to take a look for yourself? Here’s a finder for the “Winter Albireo” aka. h3945.

Look for the triagle of bright stars south of Sirius. Atsra with Adhara and go to Wessen – consider that one step. Continue moving inthe same direction the smae amount (about 3.5° – and you willfind yourself at h3945.

Now that said, the overall impression of the true ALbireo in a 60mm scope at 72X left me duly dazzled  – and smiling broardly at the winter imposter. Oh Iota Cancri is nice. It is wonderful, really – it just isn’t Albireo. But it’s a darned good substitute on an early Spring evening.  Hmmmm. . . and maybe that’s the solution. When I made this observation it was still winter and Iota was well placed at a reasonable hour.  So i guess that makes it a winter star. But I have to admit, it feels more like a spring star. So maybe I should give the Big Dog his “Winter Albireo” regardless – and give the Crab a Spring Albireo!