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The Multiple Mysteries of Multiple Stars: OΣ 298 and KZA 105

There are double stars, and there are triple stars, and there are multiple stars . . . . . . . and then there are multiple stars.

Odd multiple stars . . . . . . . with attributes you would never think of attributing to multiple stars . . . . . . . with characteristics that are very uncharacteristic of multiple stars . . . . . . with odd quirks you would never in your wildest imagination imagine to be possible of multiple stars.

But that’s really all I can reveal in the first few paragraphs of this cryptic discussion.  Because in order to lure you further into the labyrinthine depths lurking beyond the bottom edge of this paragraph, I have to put a halt to the hints – except to say you’re in for a pair of uniquely unique surprises.

So if I’ve awakened your curiosity, and (or) if you’re harboring a stellar craving for adventure, follow me into the dark photonic wilderness . . . . . . . . . . . . . . .

Actually, we’ve been in this area before, but with a discretely zealous measure of zeal I left our intriguing targets unlabeled:

We’re returning to Nu-1 and Nu-2 (ν1 and ν2) in Boötes, so follow the line that runs northeast from Delta (δ) Boötis through Mu (μ) Boötis (Alkalurops) to ν1, ν2. (Stellarium screen image with labels added, click to enlarge).

We’re returning to Nu-1 and Nu-2 (ν1 and ν2) in Boötes, so follow the line that runs northeast from Delta (δ) Boötis through Mu (μ) Boötis (Alkalurops) to ν1, ν2. (Stellarium screen image with labels added, click to enlarge).

From Nu-1 and Nu-2 (ν1 and ν2), slide southeast one degree to 5.25 magnitude Phi (φ) Bootis, a pleasing yellowish G8 sun.  From there, reverse your direction ninety degrees to the southwest and drop less than half a degree to our goal, seventh magnitude OΣ 298 (STT 298).  (Stellarium screen image with labels added, click for a larger view).

From Nu-1 and Nu-2 (ν1 and ν2), slide southeast one degree to 5.25 magnitude Phi (φ) Bootis, a pleasing yellowish G8 sun. From there, reverse your direction ninety degrees to the southwest and drop less than half a degree to our goal, seventh magnitude OΣ 298 (STT 298). (Stellarium screen image with labels added, click for a larger view).

OΣ 298  (STT 298)              HIP: 76382   SAO: 64800
RA: 15h 36.0m   Dec: +39° 48’
.             Magnitudes        Separation        Position Angle         WDS
AB:         7.16,   8.44              1.167”                 181.8°                 2013
AB,C:     6.90,   7.75            121.50”                 328.0°                 2012
AB, D:    6.90, 13.94            167.40”                 224.0°                 2002
AB,E:     6.90, 12.07            456.00”                 335.0°                 1999
Distance: 71 Light Years
Hussey Orbital DiagramSpectral Classifications: “A” is K4, “B” is K5, “C” is K0
Notes:   
AB is a gravitationally attached pair, orbital data is available here.  (You can see an early attempt at determining an orbit by clicking on the thumbnail at the right).
AB is also LDS 798; AB,C is also HJL 225 and SHY 77
AB,C is physical
AB,D   ———   not yet!  We’ll get there, though . . . . . honest.  😉

OK, where to start . . . . . .

Let’s begin with the AB pair, which I should have tried to split, but overlooked completely because I was eager to get on to the three more distant members of this family of five.  With a separation of 1.167”, I should have been able to get it with the 9.25 inch SCT I was using that night.  In fact, it should be split-able with a six inch and probably a five inch refractor, the limiting factor being the 1.28 difference in magnitudes of the two stars.  But as I said, I was overcome with an irrational desire to meet the other members of this stellar troupe.

To be truthful, there was one member in particular I was searching for . . . . . . . ah, but I’m getting ahead of myself once again.  Pardon my lack of restraint.

Let’s stay with alphabetical order and proceed to AB,C, which isn’t difficult at all to find since it’s less than a magnitude fainter than the welded-together AB pair.  The orange tints of AB and AB,C (attributable to their spectral classifications of K4 and K5) are really worth pursuing on their own account since they add a decoratively tasteful touch to the sparse dark field in the eyepiece:

 East & west reversed to match the refractor view, click to enlarge the image.

East & west reversed to match the refractor view, click to enlarge the image.

Although Johann Heinrich von Mädler uncovered the AB pair in 1843, it was Otto Struve’s initials (the Greek letters OΣ) which were attached to it, possibly because Herr Otto added the 7.75 magnitude “C” component in 1867.  And if you look at the sketch, you’ll see that a line drawn from AB to “C” and extended toward the northwest edge of the field will also lead you to twelfth magnitude “E,” which was added in 1934 by G.V. Simonov, apparently while working at the Berlin Babelsberg Observatory.

And that – finally – leads us to where we’ve been headed since the first words of this piece: the mysterious and enigmatic “D”.

The 13.94 magnitudes of light listed in the Washington Double Star Catalog (WDS) for “D” is fainter than what it actually is, a fact I’m rather sure of for two reasons:  first, I had no problem seeing it in the 9.25 inch SCT, and second, I had no problem in discovering it’s true nature, which can be seen below in the inset I’ve added to the sketch of OΣ 298:

 A healthy application of averted vision was necessary to detect a definite “un-star-like” quality about the odd object in the inset.  (East & west reversed once again, click for a much better view of the inset).

A healthy application of averted vision was necessary to detect a definite “un-star-like” quality about the odd object in the inset. (East & west reversed once again, click for a much better view of the inset).

 Burnahm on STT 298As you can see in the inset at the bottom right of the sketch, there’s something rather fuzzy about that “D” component . . . . . which was also noted by S.W. Burnham in 1901 (click on the thumbnail attachment at the left).  In fact, if you read S.W.’s entry (the one in the yellow box) you’ll see this odd comment: “h 1930 is in the field; small, round, and not well defined for measurement.”  But S. W. Burnham being S.W. Burnham, he of course couldn’t resist measuring it.

 So now, what in the wonderfully weird world of multiple stars does “h 1930” refer to? Well, if you’re familiar with double star nomenclature, you would expect it to refer to number 1930 in Sir John Herschel’s Fourth Double Star Catalog of 1830-1831 (jump to p. 331 if Sir John’s essay doesn’t come up; his entry for h 1930 is near the top of page 378) – but that star happens to be way up north in Cassiopeia, where it’s twinkling under its current WDS designation, HJ 1930 – and if you recall, we’re still in Boötes.

J Herschel obsv of NGC 5966-h 1930Sir John also contributed a large catalog of deep sky objects (scroll two-thirds of the way down) which just happens to contain another object designated “h 1930”.  He described it this way: Faint, Small, gradually brighter in the middle (“F; S; R; g b M;”).  If you click on the thumbnail at the right, you’ll see his entry at the bottom of the page.   And if you look closely, you’ll see another number assigned to this object in the second column, the one labeled “Synonym,” which reads “III. 634”.  And darned if that doesn’t look like something  Sir John’s father, Sir William Herschel (who was fond of using Roman numerals in his double star designations), would use as a catalog number.

Wm. Herschel on III 634 aka NGC 5966As it turns out, Sir William was also a restless seeker of objects other than double stars, and “III. 634” is actually a catalog number from his second large catalog of deep sky objects (scroll to fifth title from the bottom).  You can see his observation by clicking on the thumbnail image at the left, where it’s described as very faint, very small (“vF. vS.”).  And, in fact, “III. 634” is now known by its number in the New General Catalog, NGC 5966.

Which is because it’s not a star – it’s a . . . . . . . galaxy.

STScI photo of OΣ 298 with labels added, east & west reversed to match the sketches.  Click on the photo for a larger view.

STScI photo of OΣ 298 with labels added, east & west reversed to match the refractor image. Click on the photo for a larger view.

To be more precise, NGC 5966, aka OΣ 298-D, is an elliptical galaxy, and may even be a quasar, although opinion on that is somewhat uncertain.  Quasars (short for quasi-stellar radio object) were first discovered in 1963, and are highly energetic sources of radio waves and visible light which are peculiarly out of proportion to their physical size.  According to the NGC/IC Project web site, the visual magnitude of NGC 5966 is 12.7, its surface brightness (a better measure of its visual brightness) is 13.4, and it measures 1.8’ x 1.2’ in size, all of which explains why I had little problem detecting its smudged appearance in the 9.25 inch SCT.   I have no idea what prompted the 13.94 magnitude listed for “D” in the WDS, but it’s clearly easier to see than that magnitude would lead one to believe.

M.G. Bigourdan on STT 298So how did a galaxy end up being cataloged as a member of a multiple star family?  Good question – and the only light I can shed on the topic is that this particular member of the group was added in 1886 by Guillaume Bigourdan, a French astronomer working out of the Paris Observatory.  Most likely he was using the great thirty-three inch Meudon Refractor, and if so, it’s surprising that he failed to realize this object wasn’t a star.  His observation can be seen by clicking on the thumbnail illustration at the right – the object now labeled as “D” is referred to in Bigourdan’s data as “AB/2 C”.  (The separation he lists matches Burnham’s information, but the position angle is off about 90 degrees, presumably an error that Burnham seems to have recognized, possibly because it was also made on one of the entries for AB).

In the meantime, as I was writing this, I was overcome with an unquenchable urge to return to OΣ 298 and see if I could break the weld on the AB pair.  And surprisingly, it was less difficult than I expected.  I suspect if I had been paying more attention to it on the night I made the first pair of sketches I would have detected a split in the two stars . . . . . . . because when I returned, I could clearly see each of them at 175x in a 14mm Radian.  The seeing was very jittery at the time, so I carefully worked my way up through 204x (a 12mm Radian) and 245x (a 10mm Radian).  I found myself encouraged enough by the 245x view to risk leaping into a magnified abyss with my trusty 7.5mm Celestron Halloween Plössl.  It very generously served up an eye-pleasing 327 diameters of shivering white light, as well as a splendid view of OΣ 298-D, aka h 1930, aka H III. 634, aka NGC 5966:

Notice the weak orange glow of the AB pair has surrendered to a weak shade of white under the increased magnification!  (East & west reversed again, click for a larger and better view).

Notice the pale orange glow of the AB pair has surrendered to a weak shade of white under the increased magnification! (East & west reversed again, click for a larger and better view).

So – an amazing multiple star with a galaxy as one of its members!

What could be stranger than that, you ask?

Well take a look at the upper right area of the eyepiece field of view in one of the first two sketches above (or take a peek here), and you’ll see a faint scattering of stars hanging on for dear life as they stretch from the north the edge of the field to the south edge.  That scattering of stars just happens to go by the collective name of KZA 105, and has a total of (ready for this?) . . . . . . . . nine members!

 KZA 105 data

.

One of the peculiarities that emerges quickly when you look closely at the table of data above is the individual members of this group of stars are assigned letters based on their increasing distance from the primary, which can also be seen in the labeled sketch below, although it’s not quite as obvious there:

 (East & west reversed to match the refractor view, click for a larger view).

East & west reversed to match the refractor view, click for a larger view.

And here’s the same sketch without the clutter caused by the labels:

The two bright stars down in the southwest corner are the AB and AB,C members of  OΣ 298.  East & west reversed again, click to enlarge.

The two bright stars down in the southwest corner are the AB and AB,C members of OΣ 298. East & west reversed again, click to enlarge.

Another peculiarity is that most of the measurements above were first made in 1982 (AI was added in 1984) with the exception of DF and HI, which were first measured in 1893 – and they just happen to also be the brightest members of the group.  My usual source for measurements from that period, S. W. Burnham’s A General Catalogue of Double Stars within 121° of the North Pole was no help, nor were other sources for that era.

In fact, tracking down information on KZA 105 resulted in several futile hours of research as there is virtually no information about this system available on line.  I did discover the initials KZA refer to S. M. Kazeza, who served as a member of the team that put the Hipparcos catalog together.  And, I found one article written by him which was published in 1984 in volume nine of the Bulletin of the Astronomical Observatoire Royale de Belgique, which is currently unavailable on line.

When you see this many stars listed as components in a system, and especially with such wide separations, it’s usually because they have similar proper motions.  Fortunately, the WDS provides the proper motion of all of the members of this group, which I included above (the numbers represent seconds of arc per thousand years, so inserting a decimal point at the beginning of each number will tell you how much each star moves in a single year).

The column labeled “First” refers to the first of a pair of stars, and the next column refers to the second of the pair.  In other words, in the case of the AB pair, the proper motion of “A” is -027 in RA and +001 in Dec, while “B” is -011 in RA and +002 in Dec.  A plus sign in front of a number indicates eastward motion in RA and northerly motion in declination; a negative sign means westward motion in RA and southerly in declination.

The table indicates a general slight motion to the west in RA and south in Dec for most of the individual stars (scan the numbers in the “Second” column).  “A” (in the “First” column) is a notable exception, moving due west at a considerably faster rate than the other members (-027 +001), “I” stands out because of its northwesterly motion (-023 +015), and “G” looks like it isn’t going anywhere at all (+000 -001).

So with the exception of “A”, “I”, and “G”, you could say there’s a general shared similarity in motion between this collection of stars.  That may partially explain why these nine stars were grouped together, but I suspect there’s more to this mystery lurking somewhere out there in the galactic darkness.

One thing, though, should be obvious from all of the above:  multiple stars can be mysterious beyond words – and they’re certainly not boring!

And before I forget about it, my thanks once again to Brian Mason at the U.S. Naval Observatory (home of the Washington Double Star Catalog) for providing me with data on both OΣ 298 and KZA 105.

Next time out we’ll take an old-fashioned star-hopping tour through the realm of the Nu twins in Corona Borealis.

Until then, Clear Skies!  😎

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2 Responses

  1. Hi John,

    I may have stumbled on an explanation for why M. Bigourdan added the OΣ 298-D component to his report.

    The astronomy software I use, Cartes du Ciel (a.k.a. Skycharts), suggests that M. Bigourdan was reporting an observation of a single star, and not the galaxy NGC 5966. I happened to zoom in on OΣ 298 until a small white dot appeared within the ‘boundaries’ of the galaxy.
    The dot is the star UCAC4-649-053372 and the software reports has a magnitude of 13.94, the same value reported in the WDS for the OΣ 298-D component.

    Terry

    • Hi Terry,

      Thanks for that info.

      There are actually two stars, one on either side (east and west) of NGC 5966 in the photo above, and if you look closely, there’s a faint star tucked in right against the east edge of the galaxy. MegaStar shows that one as GSC 3053:1207 with a magnitude of 13.8. It could well be the same star you came across in Carted du Ciel — these stars have too many designations!

      That would explain Bigourdan’s inclusion of it, but what puzzles me is the WDS refers to the “D” component as NGC 5966, which can be seen here if you scan down to the middle of the screen under NOTES.

      There are more strange twists and turns in this line of business than there in all the dimensions of String Theory!

      John

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