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Zeta Cancri in 6"

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#1 Cotts

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Posted 29 March 2013 - 09:49 PM

Had a nice night of seeing tonight. Bagged Tegmine, also known as Zeta Cnc, a fine but challenging triple star. Using the 6" f/8 Intes Mak Newt on its new Teeter STS base i was able to take advantage of some very good seeing. I found the object with the 20mm Meade WA (60x) and it showed a clear split of the wider pair and the close 1.0" pair looked 'odd'. With the 5mm Nagler (240x) things were sorted out nicely. The closer pair showed a dark line between. For the crazy of it I threw in the 3-6 Nagler zoom and pushed things up to 400x. The triple sped across the field of view in about 10 seconds but there was clear dark space between the two close stars. They are at 1.0" these days so this was within the capability of the 6-inch.

It was interesting to note the seeing tonight. It was what I call "slow seeing". There was a clear diffraction pattern with one ring and occasionally two. The rings would slowly, over several second timespans, morph from one to two, appear mostly on one side of all three stars and then on the other (all three doing the same thing at the same time....) and then disappear slowly for a few seconds. There were moments when the pattern froze for a few seconds in the classic concentric display. 10/10!!!

Dave

#2 Rutilus

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Posted 30 March 2013 - 09:09 AM

Dave - Super observation of Zeta Cnc.
Here is a drawing I made of an observation some time back,with my 6 inch f/8 Achromat. I was using 320 and 480x
for the split of the closer pair.
My notes recorded the closer pair has having a slight yellow tint (maybe due to using an achromat at higher power?),
while the wider star had a slight bluish tint.

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#3 CelestronDaddy

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Posted 30 March 2013 - 09:41 AM

Dave - Nice report! Sounds like you had great seeing conditions :grin: Tony

#4 Ed Wiley

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Posted 30 March 2013 - 11:08 AM

Nice report, Dave. We get that kind of seeing in my area very rarely, glad you could take advantage of a great night. I am hoping for some good seeing at the TSP.

Ed

#5 astro4565

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Posted 30 March 2013 - 12:24 PM

A 6" scope is about the minimum to split that tight A-B pair, right? One of these days I will try it in my 15" scope.

#6 RAKing

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Posted 30 March 2013 - 12:42 PM

I think it depends on your seeing conditions. I can split them most of the time with my TEC 140 (0.83 Dawes Limit), but have a hard time with the 130mm refractor (0.89). I get a "peanut", but haven't been able to see the black line between them.

It's an easy job with my 8 inch Mak.

Ron

#7 buddyjesus

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Posted 30 March 2013 - 10:36 PM

beautiful triple star. don't think I could get it all, but do you guys think my 4" scope going at about 166x would get the B star?

#8 azure1961p

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Posted 30 March 2013 - 11:13 PM

It's been a while for me on this particular object(s) but in and of itself with good seeing and your 4" you ought to see merged airy patterns. Slight magnitude difference shouldn't prevent at least an elongation but I guessing a lopsided Dawes res.

It is a pretty multiple.

Pete

#9 Astrodj

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Posted 30 March 2013 - 11:51 PM

Thanks for the nice report, Dave.

I spent much of the same night observing several doubles and two carbon stars in Cancer with my SV80ed. Zeta was one of the doubles but of course no hope of the B component in that scope. I'll have to try it with my 8" SCT soon. I would have to have a near perfect night to get it with a 5", and I don't get those very often.

Question: In your Triple Star file you shared a while back, what were the criteria for the last two columns, Sep. Rank and Rank Points? I notice Zeta Cnc is the second star on the list.

Thanks,

#10 cildastun

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Posted 31 March 2013 - 02:44 AM

I tried Zeta Cnc again last night with my 5" Mak; conditions here were good, but not excellent. At x190, the close pair were clearly split in moments of good seeing with space between them, and appeared white, whereas the third component had a slightly blueish tint. Not easy, but certainly do-able.

Chris

#11 Cotts

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Posted 31 March 2013 - 10:01 AM

Here's a copy of the appropriate section of the article...

"Notes on the spreadsheet. Name -- I used the Bayer Greek letter as first choice, Flamsteed Number second and
the Washington Double Star Catalog (WDS) designation third.

RA and DEC -- checked and corrected for every entry so as to coincide with the WDS to enable anyone to look up the data for themselves especially in the future as some of the tight pairs will move significantly in just a few years.

Magnitudes, Mag Sum and Mag Sum Rank - checked, corrected and updated from the WDS. The ranking is simply sequential. In a few cases the WDS shows either the B component or the C component to be brighter than the A component. For these I took the liberty of altering the data so that M1 < M2 < M3 for all systems. The calculation of Mag. Range required this.
Mag. Range and Mag Range Rank -- In all cases this parameter was M3 - M1 so as to have a positive result. The ranking is, again, sequential.

Sep. AB, Sep AC and Sep. Rank -- The WDS gives clear AB and AC separations most of the time. In a few cases, when AB is a very tight pair the AB-C separation is given. I assigned these values to the Sep. AC column since it is the wider of AB and AC which is used to rank the systems. For example, if AB = 1.0” and AB- C is 52.0” then AC must be between 51.0” and 53.0” depending on the Position Angle of AB. This difference is too small to matter in my quite unscientific ranking. The AC value is used for ranking because it is always the larger of the two values and thus indicates the degree of &#699;closeness&#700; of the system as a whole.

Total Rank -- This is the sum of the Mag. Sum Rank, the Mag. Range Rank and the Sep. Rank. A lower &#699;total&#700; indicates a &#699;better&#700; triple star system. There is a vast range of total Ranks which is indicative of the great variety of triple star systems on the list.!"

Dave

#12 Karl Fabian

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Posted 31 March 2013 - 10:29 AM

Reviewing my observing notes the last time I viewed this triple was back on April 14,2004 using my 5 inch F9.3 achromat.(same scope as the Avatar). At the time I was testing the optics in good seeing. The close component was immediately obvious at first glance at 295X. Did not try lower powers. At the time the separation was .96" PA60deg according to WDS. It is now a little wider and should be easier. When the weather cooperates want to give it a try to see how low I can go on the mag.

#13 Astrodj

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Posted 31 March 2013 - 11:50 AM

Thanks for the detailed explanation of your table of triples. I just copied your reply and saved it with your previously downloaded table.

It is a nice resource for multiple star observers and I for one appreciate both the effort and your making it available.

Thanks again!

#14 R Botero

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Posted 31 March 2013 - 12:10 PM

Good post. Thank you bringing this beautiful multiple star up. I split it last night with my 6" f/7.5 Apo at 160x. I was using binoviewers and the close pair was coming in and out but at some moments the split was very clean. I may lose the binos tonight to crank up the power some more.
Roberto

#15 astro4565

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Posted 31 March 2013 - 09:36 PM

The 0.96" arc separation is exactly the Dawes limit of my 120mm f/7.5 refractor. I may be able to split the A-B pair. If I get a little higher than 2800 feet I may give it a shot. I'm glad that this pair has widened in the last few years. Seeing is usually better in the winter but I will keep an eye on the Clear Sky Clock in my area.

#16 fred1871

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Posted 01 April 2013 - 01:54 AM

Good report, Dave, and it's nice to be reminded of this triple, I'll seek it out again next clear night.

I looked it up in WDS - 2012 measure gives 1.1" for the AB close pair, which ties in well with the ephemeris (grade 1 orbit, so you'd hope so!). Should make it a Rayleigh "just splittable" pair for about a 5-inch scope.

The WDS listing includes mention of component 'C' being double as well - magnitudes 6.2 and 7.1 at 0.4" in 2009 (PA 261). Anyone want to try for it? :grin:

I last looked at Zeta Cancri (no way will I call it Tegmine - yet another of the hundreds of names that need an encyclopedia list to decipher) - in 2009, it was a neat double ABxC at 100x, and I skipped intermediate eyepieces and got a very close but clear split at 230x - this with 140mm refractor. 320x gave better separation, very clean discs. Seeing that night I recorded as very steady. Separation in 2009 was a tiny bit less than now in the 60 year orbit.

#17 Cotts

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Posted 01 April 2013 - 09:05 AM

The WDS listing includes mention of component 'C' being double as well - magnitudes 6.2 and 7.1 at 0.4" in 2009 (PA 261). Anyone want to try for it? :grin:


Thanks for pointing this out. When I get to the Texas Star Party I will throw my 16" Zambuto at it just for fun.

For my 16" Rayleigh is 0.34" and Dawes is 0.29". I'll need some fantastic seeing, though.....

Dave

#18 buddyjesus

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Posted 01 April 2013 - 02:13 PM

aw shucks. at least there are bigger scopes at star parties. this one looks like a must see!

#19 fred1871

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Posted 02 April 2013 - 11:58 PM

Follow-up on my recent note - clear sky for one night since, so I started with Zeta Cnc, again using the 140mm refractor. Seeing was not as good as on the night I observed it in 2009, but not bad. The close AB pair was a neat pair of points, just about touching, but not overlapping, at only 160x. As before, definite dark space between them at 230x; 285x made that dark space wider. And that's without 9/10 seeing conditions, which I did have in 2009. This time? - 7/10, best moments 8/10, fitfully.

It's a fine triple with this size scope. Not much colour effect, but I guess you can't have it all every time. :grin:

#20 OJS

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Posted 04 April 2013 - 09:45 AM

Have the orbital elements changed on the A-B pair? I generated this picture several years ago, and current separation in the graph looks more optimistic than the sub-arc sep. discussed here.

OJS

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#21 Cotts

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Posted 04 April 2013 - 09:59 AM

OJS, your graph looks ok for the AB pair -it shows about 1.1" for the AB pair for 2013 which agrees nicely with the WDS. The 'sub-arcsecond' pair is C. Actually Ca - Cb according to the WDS with a separation of about 0.4"

Dave

#22 ziridava

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Posted 11 April 2013 - 03:02 PM

Wednesday night, Zeta Cnc:
In my 125mm F/7 Dobsonian at 135x/Simetric Solid 12.8mm +2X Barlow the tight pair was visible in an eight shape,the distant companion was visible with no efort.Two nights ago the last one was seen in my 3 inch F/9.2 Newwtonian.
At 236x/Celestron ''orange'' Plossl 7.5mm+2x Barlow ,the tight pair of the triple star was also splitted,the companion being at about PA=70 degree.

Mircea

#23 Cotts

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Posted 11 April 2013 - 09:58 PM

Good work!

Dave

#24 azure1961p

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Posted 11 April 2013 - 10:37 PM

Mircea,

Good job. I love the figure eight doubles when the seeing allows for it to happen. Unforgettable on the best nights with the right pairs. Glad you found success here.

Pete

#25 ziridava

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Posted 12 April 2013 - 03:44 PM

Thank you Dave for pointing to this beautiful triple star,thank you Pete for encouragement.
Last night instead,the seeing was so bad,Zeta Cnc hardly seen as double star.
I still prefer this to the endless clouds...
Mircea






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