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John_G
sage


Reged: 01/18/10

Re: Izar and Porrima new [Re: Bill Boublitz]
      #5886596 - 05/27/13 05:24 AM

I had a great look at Izar last night at 237x with my 90mm. I saw the blue/green companion on the first diffraction ring. Very nice colors.

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fred1871
professor emeritus


Reged: 03/22/09

Loc: Australia
Re: Izar and Porrima new [Re: Bill Boublitz]
      #5886604 - 05/27/13 06:00 AM

Bill, I think with some bright doubles the colours are better seen/more pronounced with less aperture. Almost as if the eye gets over-saturated with light in the manner of a camera sensor with larger telescopes. One I'm familiar with down here is Alpha Centauri, very very bright, and the colours (yellowish and deep yellow, contrasting) I find more obvious with 80mm than with 180mm or 235mm. The bigger telescopes tend to show it as near-white for both stars.

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Kon Dealer
professor emeritus


Reged: 01/05/11

Loc: Cambridge UK
Re: Izar and Porrima new [Re: fred1871]
      #5886620 - 05/27/13 06:53 AM

Quote:

Bill, I think with some bright doubles the colours are better seen/more pronounced with less aperture. Almost as if the eye gets over-saturated with light in the manner of a camera sensor with larger telescopes. One I'm familiar with down here is Alpha Centauri, very very bright, and the colours (yellowish and deep yellow, contrasting) I find more obvious with 80mm than with 180mm or 235mm. The bigger telescopes tend to show it as near-white for both stars.



That's my experience too. I get better colour in my Kson102ED, than my 6SE and 8SE.
What is more viewing is much less "seeing" dependent.
Had my 6SE out last night and Izar was a constantly seething mess. Swapped it for the Kson and instantly stable.


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Bill Boublitz
super member


Reged: 05/04/13

Re: Izar and Porrima new [Re: Kon Dealer]
      #5887755 - 05/27/13 07:37 PM

Fred, Kon, thanks for the input. Also, as Brian mentioned above, "Stopping down an instrument usually results in the optics becoming near perfect." I concur with this.

Not meaning to go off topic, but surveyed six doubles last night with the 60 mm aperture stop in place; 90 Leonis, 38 Lyncis, 65 Ursae Majoris, Struve 1881 in Virgo, 17 Draconis and Delta Serpentis. All wide pairs ranging from 2.5" to 4.0" in separation. I was stunned at the clarity of the images. The only pair that didn't hold up as well was Struve 1881. It was a split at x90, though x135 provided a pleasing view. At x225, the companion dissolved into a ghost like smudge. Had good sharp Airy on the primary, but a mere "cloud" in the P.A. of the companion.

I'm hooked. Every double star aficionado should experience stopping down an instrument they know well - especially a refractor.

So much to look at... so little time.


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WRAK
scholastic sledgehammer


Reged: 02/18/12

Re: Izar and Porrima new [Re: Bill Boublitz]
      #5888844 - 05/28/13 12:12 PM

Yes, my experience too - reducing the aperture with masks or iris diaphragms results in more saturated colors, better seeing and therefore crisper spurious disks. Overall higher aesthetic pleasure.
Wilfried


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labmand
sage
*****

Reged: 02/08/11

Loc: Michigan USA
Re: Izar and Porrima new [Re: WRAK]
      #5889502 - 05/28/13 06:30 PM

Was able to split Izar but not Porrima, when I tried to find the current PA I found 303, 11.1 and 10 for 2013 doing
a search and checking the WDS. The sep also came up with
1.9" and 4.5", please help me understand these numbers.

Edited by labmand (05/28/13 06:33 PM)


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Bill Boublitz
super member


Reged: 05/04/13

Re: Izar and Porrima new [Re: labmand]
      #5891048 - 05/29/13 05:31 PM

Lab .... When I check the current WDS, this is what I find for Porrima; Last measurement 2011, companion was then in Position Angle 319 degrees, the separation then was 1.6 arc-seconds between the components, magnitude of A was 3.48, that of B; 3.53.

If this doesn't help clarify, ask a more direct question. Many of us would be glad to help you in anyway we can. ~Bill


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labmand
sage
*****

Reged: 02/08/11

Loc: Michigan USA
Re: Izar and Porrima new [Re: Bill Boublitz]
      #5891255 - 05/29/13 08:10 PM

Thanks Bill,
When I go here (database for wds I think)
http://stelledoppie.goaction.it/index2.php?iddoppia=54650
I see 2013 pa as last=10 and also 303
sep shows 4.5"
so this is where I'm, a little confused.


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Bill Boublitz
super member


Reged: 05/04/13

Re: Izar and Porrima new [Re: labmand]
      #5891314 - 05/29/13 08:49 PM

Hi Dave! Well, an interesting website. A quick glance seems to indicate a lot of accurate data. It is not the WDS. The actual WDS doesn't list current information, as they monitor thousands of stars and review each submission for accuracy before entering.

Porrima is a quick moving binary (period 169 yrs.) so one can observe significant change well within a lifetime. It was closest in 2005 and all but unsplitable in amateur scopes. I first split it around 2006/2007 with a 4" aperture. It may be resolvable with 80 mm at this time. I don't know. Haven't looked in two years.

Here's the Washington Double Star Catalog; http://ad.usno.navy.mil/wds/

I'll be out hopefully tonight, definitely tomorrow night, so I'll give Porrima a look and report back. Good wishes, don't give up!


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fred1871
professor emeritus


Reged: 03/22/09

Loc: Australia
Re: Izar and Porrima new [Re: labmand]
      #5891347 - 05/29/13 09:06 PM

The WDS lists both the first measure of a double star, and the most recent. That appears to be where you've got confused. Porrima is a binary that's been changing quickly in recent years, so the numbers depend a lot on the date. Porrima was at 4.0" separation in 1980, 0.4" (!!) in 2004, and is now widening again.

The first good measure of it was by FGW Struve back in the early 1800s, and since then it's gone through more than a complete orbital revolution - the orbital period is listed at 169 years. And the orbit, as we see it from Earth, gives a huge variation in the separation of the stars.

The 2012 measure in the WDS is a separation of 1.7 arcseconds in PA 013 - just east of north. Because the pair are in the faster-moving part of their mutual orbit the numbers are changing quickly, and if I remember correctly the separation is now close to 2.0".

With this double as with others in the WDS, the summary line gives two time-slices - two dates of measures - which don't always provide a clear picture of what's happening. If you want more information on Porrima, the 6th Orbital Catalog, available on the USNO website along with the current WDS and other lists, has a diagram showing the measures superimposed on the calculated orbit - click on "P" on the far right of the data lines in the Orbit Catalog. There's also an ephemeris - presently, 2011-2015 - under "E" beside that.


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labmand
sage
*****

Reged: 02/08/11

Loc: Michigan USA
Re: Izar and Porrima new [Re: fred1871]
      #5891646 - 05/30/13 12:43 AM

Thanks Bill and Fred for the help, I had better luck tonight with my 8" sct 9.7mm x206, was able to split
Porrima, very tight, the pa does look to be about 10 degrees
I reread the posts in this thread and brianb11213 #5783938 - 04/07/13 02:33 PM post
"seperation increasing from 1.95 arc sec at the beginning of 2013 to 2.11 arc sec at the beginning of 2014,
with the position angle slowly decreasing from 11.1 deg to 8.4 deg"
Looks like good info to me.


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Jon Isaacs
Postmaster
*****

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Izar and Porrima new [Re: labmand]
      #5891894 - 05/30/13 07:48 AM

Sky Tools 3 computes the separation of short period binaries from the orbital data. Currently Porrima it reports Porrima at 2.02 arc-seconds. The Dawes limit for a 60mm is 1.93 arc-seconds, the Rayleigh Criterion is 2.3 arc-seconds, Porrima is near the Dawes limit for a 60mm, a tough split.

Monday night I had my 60mm x 800mm Asahi-Pentax refractor out in the backyard, I turned it toward Porrima and at 200x, I was able to catch glimpses of a split, the seeing wasn't steady but there were moments when I could see a slight line between the pair.

Izar has always been an easy split for that scope, the first time I pointed it at Izar, I was surprised to see the companion at 90x, I thought it must be an optical defect but increasing the magnification show it was real and I have split Izar many times with it since.

Other splits that evening were Xi Bootes at 5.8 arc-seconds and magnitudes 4.5-7, Pi Bootes at 5.5 arc-seconds and magnitudes 4.5 and 5.9. I also checked out Algieba.

Tuesday night I had out my NP-101, Porrima was a easy split. Alula Australis at 1.68 arc-seconds was doable but it was low over the house and quite unstable.

Jon


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Silver Bear
member


Reged: 04/02/13

Loc: Brazos Valley in Texas
Re: Izar and Porrima new [Re: fred1871]
      #5904464 - 06/05/13 06:09 PM

Have been busy, else I'd posted this yesterday!

Finally got a good seeing night here the other night, and was rewarded with my first splitting of of Porrima after several tries. Beautiful double, and had to go very high on magnification with this little telescope to get it...but it was rewarding.

Then, I thought I could split Izar...but I think I spent all my good opportunity on Porrima, as Izar was a no-go...again.


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labmand
sage
*****

Reged: 02/08/11

Loc: Michigan USA
Re: Izar and Porrima new [Re: Silver Bear]
      #5904832 - 06/05/13 10:07 PM

Ted, I too had a clear night, with my Meade 312 For me, Izar
was an easier split then Porrima, Had to use 2x barrlow
8mm =225, I tried using a mirror diag vs prism and a
raci diag, mirror and prism were close, maybe mirror
a little better, but with raci diag split was very faint.
Another thing I tried was using my Ultima 2x vs my Tele vue
1.8 barlow, The Ultima was winner by a mile.


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Silver Bear
member


Reged: 04/02/13

Loc: Brazos Valley in Texas
Re: Izar and Porrima new [Re: labmand]
      #5905004 - 06/05/13 11:34 PM

My 4" Nexstar is a Maksutov-Cassegrain style telescope, and has a usable magnification limit of ~200X. Of the eyepieces coming in the standard Celestron kit, the 6mm un-Barlowed hits 221X - I cannot use it without the image being affected.

If I run my 8mm eyepiece at a 2X Barlow, it nets me 330X - I see nothing but a blur. Hence, I can only run down to my 13mm eyepiece with my 2X Barlow for 203X - right at my workable limit.

At that magnification, I detected a split with Porrima's companion - but closely.

At this same magnification, I have yet to be able to split Izar, in spite of several attempts. But, hey! I'm still really new at this. I've seen others post above they've split Izar easily at ~165X magnification. For my own lack of results, though, I'm sure it must be an operator issue...

One day I'll see it, and like Porrima, it will just jump out at me like it was there all along.

Glad you had a really good night as well.


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labmand
sage
*****

Reged: 02/08/11

Loc: Michigan USA
Re: Izar and Porrima new [Re: Silver Bear]
      #5906197 - 06/06/13 02:47 PM

Ted,
Maybe try "reducing the aperture with masks or iris diaphragms results in more saturated colors, better seeing and therefore crisper spurious disks" as stated in this thread, I know 4" is not alot but may be worth a try.


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orion61

*****

Reged: 10/20/07

Loc: Birthplace James T Kirk
Re: Izar and Porrima new [Re: Rutilus]
      #5906389 - 06/06/13 04:34 PM

Anyone know what the min/max seperation of Izar is and how many years it takes to complete a revolution.

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Cepheus Elf
member


Reged: 08/01/10

Loc: Rainy, Cloudy Lancashire UK
Re: Izar and Porrima new [Re: orion61]
      #5906461 - 06/06/13 05:24 PM

The companion to Izar was the first star which actually appeared to be a true green colour to me. I had used 6" F13 SCT (Opticraft, British made)about 20 years ago. Subsequent views through a variety of other scopes have always shown it to be pale blue. I have often wondered if the fact the old SCT had an uncoated corrector had an impact on the star colours???? I have to say my favourite view was with the old SCT!!

Cheers,
Mick


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labmand
sage
*****

Reged: 02/08/11

Loc: Michigan USA
Re: Izar and Porrima new [Re: Cepheus Elf]
      #5906679 - 06/06/13 07:27 PM

orion61
fred1871's and Bill Boublitz
post "orbital period is listed at 169 years"
can't help ya with min/max


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fred1871
professor emeritus


Reged: 03/22/09

Loc: Australia
Re: Izar and Porrima new [Re: orion61]
      #5907313 - 06/07/13 02:57 AM

Separation - minimum was around 2005, less than 0.5", possibly only 0.3" - I'm away from my astro library at the moment so checking full details isn't possible. Max separation is nearly 6", to be reached again in the 2080s.

Previous time it reached minimum (mid-1830s) it was said that no telescope in the world could separate it. Obviously at maximum it's very easy; already it's back to being splittable in quite small telescopes.


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