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Phi (φ) Cassiopeiae, Multiple Stars in NGC 457, and ET

It was a dark, damp, and murky Halloween-like night (minus the moon), but fortunately there was a window of relatively murk-free sky surrounding Cassiopeia, so I turned my four inch refractor in the Queen’s direction. On my list for the night was Phi (φ) Cassiopeia, a fifth magnitude multiple star embedded in NGC 457 and located two degrees south of Delta (δ) Cassiopeiae.

Phi (φ) Cas is shown here in radiant red. (Stellarium screen image with labels added, click to enlarge).

Phi (φ) Cas is shown here in radiant red. (Stellarium screen image with labels added, click to enlarge).

It only took one try to locate Phi (φ), and as I adjusted the focus for my first look at this five-part star, I had an uncanny feeling I had company – apart from my usual companion, Astro Dog Klaus. After I located all the members of Phi’s entourage, I started searching for the other multiple stars surrounding Phi (φ), but I couldn’t quite shake that eerie feeling – something was watching me.

Suddenly a charge of electricity rippled across the hair on the back of my neck and my focus fingers froze. I saw it: a two-eyed critter with arms and legs was staring back at me from inside my eyepiece.  I jerked my head back and leaped off my chair at the speed of light with a shout that shook every star in the murky sky. Astro Dog Klaus barely opened one eye in mock surprise, snorted in disgust at his weak-nerved master, and went back to sleep.

After recovering what was left of the dignity I had lost in front of my dog, curiosity got the best of me. Creeping cautiously back to the eyepiece, I approached its dark and forbidding rim with trembling trepidation, braced myself for the shock, hesitated for a moment, leaned over, and there it was again:  E.T. himself.

He even winked.

Argh!

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

OK – it wasn’t quite like that.   But there’s more to the story.

Phi (φ) Cassiopeiae sits in the middle of an open cluster of stars known as NGC 457, which also has a nickname: The ET Cluster.

East & west reversed to match refractor view, click to a better view.

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

Now I have to admit, I sure couldn’t see how that name had become attached to the cluster when I first looked at it. But if we rotate the sketch above about sixty degrees and turn up the contrast, it gets a bit easier:

Click to enlarge!

Click to enlarge!

Still don’t see it?   How about a crude visual aid, then:

Any better? (You probably better enlarge it). Can’t really tell if he/she/it has a helmet on or not.

Any better? (You probably better enlarge it). Can’t really tell if he/she/it is wearing a helmet or not.

Honestly, it wasn’t obvious at all to me until I saw this rendition of the critter.

NGC 457 also has another nickname, the Owl Cluster . . . . . . . apart from the eyes, I don’t get it.

On to serious stuff now.

Phi (φ) Cassiopeiae (H III 23)   HIP: 6242   SAO: 22191
Note: “A” is Phi-1, “C” is Phi-2
RA: 01h 20.1m   Dec: +58° 14’

    Magnitudes   Separation Position Angle WDS
AB: 5.07, 12.30       48.80″         209°  2010
AC: 5.07,   7.04     134.00″         231°  2012
AD: 5.07, 10.26     178.70″         288°  2010
AE: 5.07, 10.38     170.80″         239°  2010
CE: 7.04, 10.38      42.00″         265°  2010

Distance:  Rather uncertain – we’ll come back to it shortly
Spectral Classifications: “A” is F0; “C” is B6; “D” is B3; “E” is B5   (Simbad)


You can’t keep track of the players without a score card – or a chart – so this version identifies the various components of Phi (φ) Cassiopeiae. East & west are reversed here to match the refractor view, click to enlarge.

You can’t keep track of the players without a score card – or a chart – so this version identifies the various components of Phi (φ) Cassiopeiae. East & west are reversed here to match the refractor view, click to enlarge.

You can see a slight yellow-gold tinge in the primary, some of which may have been caused by the moisture in the air the night I made the sketch, although it does correspond reasonably well to the star’s F0 spectral classification (yellow-white). None of the additional four components were difficult to see, although I had to call on averted vision to catch my first glimpse of 12.30 magnitude “B” which was right at the limit of the four inch lens that night.

“A” and “C” make an interesting pair, and you have to wonder why they haven’t been cataloged as two separate double/multiple stars since each is surrounded by another companion or companions. But the two stars do show a similarity in proper motion, which suggests a tentative physical link.

Looking at the Simbad data, we find these two stars are moving very little in relation to our position in the galaxy.   In fact, you have to resort to five decimal places to begin to pick up the subtleties of their motion. The proper motion of “A” is -000.59 -001.59 (.00059”/year west and .00159”/year south), and for “C” we have -000.46 -000.79 (.00046”/year west and .00079”/year south). The only other companion for which I could find proper motion data is “E”, which is listed in Simbad at -006.50 -001.80 (.00650”/year west and .00180”/year south). So from those numbers it’s possible to conclude the three stars originated from the same cloud of gas, as Kaler points out.

None of which is surprising if Phi (φ) Cas is part of the NGC 457 cluster.   A look at a 7.5 arcminute resolution Simbad plot of the proper motion data for the cluster of stars surrounding Phi (φ) Cas shows the same subtlety of motion:

Click for a larger view.

Click for a larger view.

So all we need to know now is whether Phi (φ) Cas and its retinue are at the same distance as the other stars in NGC 457 . . . . . . . . but the judge and jury have called a recess until an improvement in distance technology (as in GAIA) resolves the conflicting data. By way of explanation for what follows, parallax-based distances (which means virtually all current star distances) are notoriously unreliable beyond about 450 light years, including those based on the 2007 Hipparcos revisions.  Hopefully that will change as data from GAIA begins to come in.

At any rate, going with what have at the moment, Jim Kaler refers to a distance of 7900 light years for NGC 457, while other sources place it as far away as 10,000 LY.  Kaler’s distance for Phi Cas “A” is 2300 light years, but he also mentions the error of that measurement is “perilously high”, and states there’s a significant chance of a distance of 4500 light years, as well as a possibility the star is at the same distance as the cluster.  Simbad’s parallax for Phi Cas “A” is little help, since it results in a distance of 12074 light years.  And it’s parallax for Phi Cas “C” results in a distance of 5344 light years.  So we may have to get some input from ET.

Meanwhile . . . . . . . Sir William Herschel discovered the pair in a less complicated era, namely on August 8th, 1780 (source — scroll down to the twelfth title):

Herschel on Phi Cas

But apparently the era was more complicated than I thought . . . . . . because it’s difficult to conclude from Herschel’s description that he was looking at Phi (φ) Cas.  The Flamsteed number (FL. 34) is correct, but after that the words resemble my normal observing conditions – murky.  “One of two telescopic stars” would seem to indicate Herschel was referring to “A” and “C”, but on the other hand his “Extremely unequal” description points to twelfth magnitude “B”. Couple that with his estimated distance of “12” or more” and we’re stuck in the murk again, because that separation doesn’t come anywhere close to resembling the current WDS distance between “A” and “B” of 48.80”, much less between “A” and “C” (134”).

Hoping for words of wisdom and some penetrating insight from my usual oracular source, I turned to S.W. Burnham’s 1906 catalog and found this:

Burnham on Phi Cas

His measures of AB and AC are very close to the current WDS data, which comes as no surprise since there’s very little proper motion taking place.  But on the first line he includes this statement: “Triple Cl. III and IV”.  That reads distinctly as if it was written by Sir William Herschel, but those words aren’t included in Herschel’s observation above.  Fortunately, Bill Hartkopf at the USNO/WDS came to the rescue when I sent him a request for the WDS text file on Phi (φ) Cas.  Among other things, the WDS text files include bibliographic references to the published source of the various observations listed in the file.

What I found there was a reference to an 1865-66 volume of Memoirs of the Royal Astronomical Society containing an article by Sir John Herschel entitled “A Synopsis of all Sir William Herschel’s Micrometrical Measurements and Estimated Positions and Distances of the Double Stars Described by him, together with a Catalogue of those Stars in order of Right Ascension, for the epoch 1880.0, so far as they are capable of identification.”   A rather long and very descriptive title for a publication I just happen to have been trying to find for quite some time.

On page 54, I found the entry for Phi (φ) Cas, aka H III 23:

This is a pasted together version of the title headings and the entry for H III 23 – the resolution for the entire page was too poor for reproduction.   Click to enlarge!

This is a pasted together version of the title headings and the entry for H III 23 – the resolution for the entire page was too poor for reproduction. Click to enlarge!

So that resolved the issue of the source for Burnham’s “Triple Cl. III and IV” quotation, but it didn’t clear up the murk.  In fact, with the addition of Herschel’s position angle for AC (271.85°) that wasn’t included in the 1782 catalog, it seems even more likely Herschel was looking at another star or simply made a mistake . . . . . . . which is supported by his estimated separation of 12” to 15” for AB, rather short of the current 48.80” and Burnham’s 48.61”.

Then there’s the matter of Herschel’s references to Classes III and IV. In Herschel’s language, Class III refers to separations of 5” to 15”, which would include his estimated separation of AB, and Class IV refers to separations of 15” to 30”, which doesn’t include any of the distances among the five stars of Phi (φ) Cas. And I’m also left wondering about his description of the star he described as being “Triple.” The 10.38 magnitude “E” component is obviously more obvious than the much fainter 12.30 magnitude “B” component, so “E” would have been a more likely inclusion than “B”.  But the separation between “C” and “E” is too wide at 42” to fit into Herschel’s Class III category, so that excludes any possibility that Wm. Herschel could have been referring to “E” when he made his measurements.

I suspect an error, maybe caused by poor weather or from being in a hurry, but the reality is there may be only one way to clear up this five-part stellar conundrum . . . . . . . ask E.T, again.

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

As for the other stars surrounding Phi (φ) Cas/aka H III 23 . . . . . . .

I was dubious about approaching NGC 457 with a four inch refractor – especially a $59 Celestron that was irresistibly on sale – because the entourage of stars surrounding Phi (φ) Cas are on the dim side.  But when I looked more closely at the faint secondaries, I realized they would probably be out of reach for my six inch refractor also.  So I stuck with my low cost experimental refractor, which actually turned out to be a very pleasant surprise.

Here’s the sketch again, this time with the additional stars in the field labeled:

Focus your attention on the inset at the left and click to enlarge!

None of this group of stars was particularly spectacular in the four inch refractor, although the grouping of ES 408 and STI 1560 struck me as being well worth a visit with a six inch or larger scope, so a year later I went back and took another look.  The seeing wasn’t the best, as usual, so I stuck with the 109x view shown in the inset at the left of the sketch above.  I did manage to pick out one additional pair, STI 1564, that wasn’t visible in the four inch scope.

As you can see, the small area within the inset is a complicated and congested area – almost every star in it is part of a double or multiple star system. In fact, if you care to count them all, you’ll come up with six different designations (there’s actually one more which isn’t shown because it wasn’t visible, BKO 1057) – not bad for an area that measures about 3.5’x 3.5’!  And it’s actually more complicated than that because there are components that were beyond my visual grasp.

You might call this a stellar traffic jam.   Make sure to click on the image so the labeling on the image and the data at the bottom are legible.   (Aladin image with WDS data overlay).

You might call this a stellar traffic jam. Make sure to click on the image so the labeling on the image and the data at the bottom are legible.  East and west are reversed here to match the view in a refractor.  (Aladin image with WDS data overlay).

Rather than include a long list of data here for all seven of the stars shown, I added it to the bottom of the image. The proper motion data is included as well, which for the most part indicates very little movement, in turn suggesting some of them may have a common origin.   Most are moving in the same general direction, west and south, although there are some exceptions.  The primaries of ES 408 and STI 1565 are moving in a northwesterly direction, while the secondary of ES 1808 stands out with a considerably higher rate of southwesterly motion.

[Quick course on proper motion numbers: the PM numbers listed below the image show the PM in right ascension (RA) and declination (DE) for the primary (pmRA1 and pmDE1) and in most cases for the secondary (pmRA2 and pmDE2) of each pair of components listed. Each number represents motion in thousandths of an arc second per year.   Using ES 408 AB as an example, the -10 and 23 shown there should be read as -.010”/year west and +.023”/year north, and the -3 and 3 should be read as -.003”/year west and +.003”/year north. A plus sign in front of the numbers indicates eastward motion in right ascension (RA) or northerly in declination (DE), and a negative sign means westward in RA or southerly in DE].

I discovered some of the proper motion data in Simbad conflicts quite noticeably with the WDS data shown above. For example, Simbad shows the primary of ES 1808 at +012 -015 (different direction and rate) and the primary of STI 1560 at -003 +003 (different direction). Still, there’s not much movement here, which again is characteristic of NGC 457.

There are also no distances shown for any of the seven primary stars or their components, so there’s really no way to know which stars are or aren’t part of NGC 457 . . . . . . .  except, of course, to ask E.T.

Thanks again to Bill Hartkopf for the assistance, and also thanks to Peter Morris, who I believe first mentioned Phi (φ) Cas to me. Thanks also are due to that on-sale $59 Celestron f/10 achromatic refractor, which is living proof you don’t have to invest a fortune in a telescope in order to delve deeply into double stars.

Next trip, we’ll return to Cassiopeiae for an Otto Struve odyssey.  Until then, clear skies! 😎

 

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2 Responses

  1. Ahh, one of my favorite areas of the late fall/winter sky! It’ll be lots of fun going back there again after having read this. Thanks!

    • Thanks, Mike — Cassiopeia is one of my favorite areas, too. I suspect a person could spend several years there and still not take it all in. I’ll be back with more on it again in a couple of weeks.

      John

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