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Iota CAS in small refractors

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#1 gnowellsct

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Posted 25 July 2020 - 12:02 PM

Iota CAS is officially a quintuple star but for amateur purposes it is a triple and not a very hard one at that. Last night we were observing it under conditions that were robbing us of at least 2.5 magnitudes. The triple was obvious in the c14. In the 92 mm on the other hand it took more effort.

Only three out of four observers could detect the triple in the 92 mm even after looking at it in the c14. One problem is that the B component is significantly dimmer than the A component. The other problem is that the C component is very close to the A component.

We were using about 120X. At that magnification in the 92 mm the primary component shows as an airy disc with the C component as a little glowing nick to one side.

I have a feeling that under better sky conditions iota cas would not be too difficult in apertures under 100 mm. I'm wondering what people's experiences here and have been in both good and bad sky conditions.

Thanks, Greg N
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#2 Astrojensen

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Posted 25 July 2020 - 12:10 PM

I've seen it in my 63mm Zeiss under a reasonably dark sky. Can't remember the lowest possible magnification, but it's well seen at 125x (6.7mm ES82). 

 

 

Clear skies!
Thomas, Denmark


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#3 alnitak22

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Posted 25 July 2020 - 12:18 PM

Iota Cass is a favorite target in my TV85. Looks best to me in the 5 Radian at 120x,  on most nights. Have seen 3 stars at 85x in both a 7Nagler T6 and 7 UO ortho. My sky is not dark but consistently steady.


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#4 StarAlert

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Posted 25 July 2020 - 01:38 PM

I just put it on tonight’s to-do list.

 

Edit: I’ll be using a Tak 100DL from Bortle 7 skies. 


Edited by StarAlert, 25 July 2020 - 01:43 PM.


#5 Echolight

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Posted 25 July 2020 - 01:47 PM

I will try in my 6 achro if it's not too cloudy. Small compared to a c14.


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#6 alnitak22

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Posted 25 July 2020 - 01:56 PM

I've seen it in my 63mm Zeiss under a reasonably dark sky. Can't remember the lowest possible magnification, but it's well seen at 125x (6.7mm ES82). 

 

 

Clear skies!
Thomas, Denmark

Can’t remember if I ever got it in my 70mm Ranger. Will give it a try before long. 


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#7 alnitak22

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Posted 25 July 2020 - 02:09 PM

I just put it on tonight’s to-do list.

 

Edit: I’ll be using a Tak 100DL from Bortle 7 skies. 

Should be easy in a quality 4” apo in any sky.


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#8 barbie

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Posted 25 July 2020 - 02:47 PM

I've observed it in my Tak FC76 between 120X and 150X under my city sky during average seeing.


Edited by barbie, 25 July 2020 - 02:50 PM.

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#9 gnowellsct

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Posted 25 July 2020 - 02:51 PM

I will try in my 6 achro if it's not too cloudy. Small compared to a c14.

Yes but very large compared to a 92mm. (And 3 out of 4 of us saw it)  If you have to amp up the magnification I don't know whether/if chromatic aberration will interfere with the viewing.


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#10 gnowellsct

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Posted 25 July 2020 - 02:58 PM

Should be easy in a quality 4” apo in any sky.

I thought it was easy in the 92 but I'm not sure whether I would expect newbies to understand what they were looking at--in a 92.  My wife has a lot of experience, earlier that night she was able to see C/2017 T2 PANSTARRS in the C14.  That's one of the dozen or so other comets that are currently out and about.  It was a puffy smudge.  If you normalized for our poor transparency perhaps presenting as a mag 12.5 or 13 object   (It currently clocks in at 10, but as I say, the skies were robbing us of at least 2 magnitudes.  

 

Off hand I would have said that was a much more difficult detection.  But it was the triple star that evaded her.

 

I think in part she doesn't have much experience with doubles/triples that are showing the Airy in one or more components.  It is something of a novelty for the uninitiated.

 

Greg N


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#11 Echolight

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Posted 25 July 2020 - 03:10 PM

Yes but very large compared to a 92mm. (And 3 out of 4 of us saw it)  If you have to amp up the magnification I don't know whether/if chromatic aberration will interfere with the viewing.

Nah.. It'll be ok...I think?

 

I'll try and take a snapshot with my cheap phone to verify the split.

 

I thought I saw CA on Spica. But every picture I looked at after that had similar colors in it.

I saw something like this, from this article.

https://www.astronat...a-blue.html?m=1

Attached Thumbnails

  • Astronomy Science - Spica.jpg

Edited by Echolight, 25 July 2020 - 03:15 PM.


#12 John Fitzgerald

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Posted 25 July 2020 - 03:15 PM

I'll try it tonight in a 80mm f/6 triplet if it's not too cloudy.


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#13 StarAlert

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Posted 25 July 2020 - 04:06 PM

I've observed it in my Tak FC76 between 120X and 150X under my city sky during average seeing.

 

Should be easy in a quality 4” apo in any sky.

Okay.... I’ll bring out the TV76 instead... with my shortest FL eyepiece, a 4mm Delite. 


Edited by StarAlert, 25 July 2020 - 04:07 PM.

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#14 John Huntley

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Posted 25 July 2020 - 06:14 PM

It's a lovely and very well resolved in my 100mm Tak. Quite breathtaking in fact.

 

I was pleased that my little 90mm mak-cassegrain managed to split these as well. Took a bit more effort than with the Tak of course.

 

I can't recall quite managing this one with my Ranger 70mm when I had it ?


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#15 Uwe Pilz

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Posted 26 July 2020 - 01:00 AM

moved it to double stars.


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#16 flt158

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Posted 26 July 2020 - 07:40 AM

At 40X in my William Optics 158 mm F/7 apochromatic refractor I can only see 1 star of Iota Cassiopeiae. 

But at 112X, what a transformation: 3 stars!

 

One or 2 of you might check out another triple star nearby: Psi Cassiopeiae. 

 

Best regards and clear skies from Aubrey. 


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#17 nerich

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Posted 26 July 2020 - 10:31 AM

Greg, 

 

I know for sure that I observed this one with in 2016 with my 80mm refractor (I have a very distinct memory of being stunned at the sight of all three stars), but I can't seem to locate it in my notebooks, so I can't tell you what powers I was using. Based on the eyepieces I had available at the time, my guess is that I used 112x and 155x.

 

As soon as my skies allow, I'll grab another look at it with both the 80mm and 150mm and tell you what I see. 

 

Thanks for bringing this one up! A real jewel. 


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#18 MP173

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Posted 26 July 2020 - 10:54 AM

I observed STF 262 (iota Cas) on Oct 7, 2019 with my AT102ED

 

My comment was "oh boy, lots going on here."  I was able to pull all four components out with 9mm Plossl and 2x barlow - 158x.

 

With my 16mm Plossl - 88x the B component was not visible, but it did arrive at 158x.

 

 

Here is the data I had based on Stelle Doppie:

 

AB 4.6/6.9, 2.6" @ 227

C         9.0, 6.7" @ 117 

D         8.5, 210" @ 60 degrees

 

I live in Bortle 5 skys.

 

Ed


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#19 Bill Barlow

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Posted 26 July 2020 - 12:03 PM

I’ve seen it every time in my 76mm Tak from my white zone light polluted skies.  Always a nice sight.  
 

Bill


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#20 gnowellsct

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Posted 26 July 2020 - 02:15 PM

Just wait till I turn my 40mm 300x monocular telescope with mesoporous assembly technology on this little jewel of a triple star


Edited by gnowellsct, 26 July 2020 - 02:15 PM.

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#21 nerich

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Posted 26 July 2020 - 02:29 PM

Just wait till I turn my 40mm 300x monocular telescope with mesoporous assembly technology on this little jewel of a triple star

The old 40mm Starhawk. I read somewhere that with a set of Brandons, that thing will pick up the Horsehead on a clear night. Super low scatter owing to the straight-through design (although most owners sully the Starhawk with an aftermarket diagonal. Amateurs). 


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#22 nerich

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Posted 27 July 2020 - 12:50 AM

Hi Greg, 

 

I got a look at this one tonight at the end of my session. Luckily (or not), your observing conditions were recreated for me, with thin clouds in the northeast hampering the transparency. As an added bonus, the star was still low in my sky (around 12:25 am local time here in North Cackalacky), making for some groovy atmospheric wobbles. 

 

Anyway, here's approximately what it looked like in my 80mm at 94x: 

 

IotaCass.png

 

 

 

B and C were both visible, and B even had a distinct yellow tinge. The view in the 150mm Mak was similar, but slightly less cruddy. This will be a magnificent sight when it rises a little higher. 


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#23 Jon Isaacs

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Posted 27 July 2020 - 08:14 AM

Iota Cas is a favorite.  I have seen it scopes ranging from 80mm to 25 inches.  

 

The only problem with it is that from my backyard, until its at about 45 degrees, it tends to get hidden behind a power pole at the back of the yard.. ;)

 

Jon


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#24 StarAlert

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Posted 27 July 2020 - 08:31 AM

It finally cleared a single tree to the north just after midnight and was at about 28o. Using an 8.5mm XF was just enough power (106x) to see the triple. Very nice! I tried to increase the power a bit to get a better split, but it turned too mushy.

 

I’ll be putting this one on my favorites list and going back to it in a couple months when it’s higher.  
 

Thanks for the tip! 


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#25 Jon Isaacs

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Posted 27 July 2020 - 09:58 AM

It finally cleared a single tree to the north just after midnight and was at about 28o. Using an 8.5mm XF was just enough power (106x) to see the triple. Very nice! I tried to increase the power a bit to get a better split, but it turned too mushy.

 

I’ll be putting this one on my favorites list and going back to it in a couple months when it’s higher.  
 

Thanks for the tip! 

 

I think Iota Cas is a tricky one. If the seeing is unstable then too much magnification can make the fainter star disappear without being enough magnification to cleanly separate the closer, brighter companion.

 

Jon


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