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Izar and Porrima

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#26 Rutilus

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Posted 21 April 2013 - 03:30 PM

Last night I observed Izar with what I thought was a 60mm aperture mask on my 100mm f/13 Carton.
This morning I measured it again and found it to be 58mm. Still the companion was nicely seen with magnifications up to 260x.
The companion appeared to be extremely close to the inside edge of the first diffraction ring, with some light showing
up in the diffraction ring itself. Dark space clearly visible between the primary and companion.
Here is a quick drawing.

Attached Files



#27 fred1871

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Posted 21 April 2013 - 09:35 PM

Good drawing, Rutilus - nicely shows the pair. Interesting, as you and Bill (Bonco) have now resolved this one with ~60mm at not much more magnification than Sissy Haas recorded with her 60mm refractor, but both of you got a clean separation which her description doesn't suggest she did. Better optics? Better atmospheric conditions? Who knows ....

No doubt the 60mm has a benefit from the placement of the first diffraction ring just outside where the secondary star is located. Interesting. I'll try Izar (Epsilon Bootis) again when my local weather improves. Maybe with my 80mm refractor, then stop it down to 60mm to see the difference (and, I hope, the companion). I don't think it's optically good enough to manage Izar at 50mm - but my very good 140mm refractor might be worth stopping down that far. Hmmm. Think I can hear an experiment suggesting itself. :grin:

#28 brianb11213

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Posted 22 April 2013 - 03:20 AM

I don't think it's optically good enough to manage Izar at 50mm

Stopping down an instrument usually results in the optics becoming near perfect even if they were a bit iffy at full aperture. Especially as the effects of "pinching" by the objective cell will disappear when the outer part of the objective is obscured. Also increasing the working focal ratio is beneficial given the very short focal ratios which seem to be fashionable these days ... it takes a pretty good eyepiece to work well at f/6 & even the better (more complex, well engineered) designs seem to work better at f/7 - f/8 than at shorter focal ratios.

#29 SeptemberEquinox

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Posted 26 April 2013 - 08:28 AM

"diffraction ring"

what is diffraction ring? And in your photos what are those rings around the star?

I was able to split Epsilon Boo(Izar) at 220X ish clearly for the first time last night.

#30 Rutilus

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Posted 26 April 2013 - 05:53 PM

The diffraction ring - "Diffraction is an optical effect caused by the interference of light
waves in passing around or through any opening, such as a lens or your eye.
A point source is seen as a tiny disk, surrounded by one or more faint rings of light"

"This diffraction pattern consists (assuming a circular objective) of a central bright disc, termed
the spurious disc or Airy disc, surrounded by alternate concentric rings of light and darkness-
the diffraction rings and interspaces".

Quotes taken from from Sam brown's book All about Telescopes and Sidgwick's book Amateur
Astronomers Handbook.

The ring around the star in the drawing is the first diffraction ring. Only on nights of excellent seeing do
I see the ring as a solid circular patern. Usually due to the seeings conditions, the ring appears broken,
often appearing as arcs of light

#31 SeptemberEquinox

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Posted 26 April 2013 - 06:36 PM

So the light is playing trick to our eyes. it's an optical illusion or visual phenomenon?

Thank you for explaining :)

#32 Bonco

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Posted 27 April 2013 - 03:36 PM

So the light is playing trick to our eyes. it's an optical illusion or visual phenomenon?

Thank you for explaining :)

It's an artifact from the optical system. Bill

#33 Ain Soph Aur

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Posted 29 April 2013 - 09:11 PM

Izar nicely split tonight with the Carton 100mm f/13 aperture reduced to 50mm f/26. Companion cleanly split sitting on the first diffraction ring.

I have a nested aperture reduction system in 10mm increments from 90mm to 50mm, I kinda wish I had also had 40mm and 30mm reduction rings made too. 1.2" f/43 could be fun just to see what it is capable of splitting....

#34 BuffaloTri

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Posted 02 May 2013 - 09:29 AM

I took my first attempt at Izar last night with my CT 102mm f/11. The seeing was bad - Arcturus was twinkling to the naked eye, and I was in a white zone.

I tried it at 32x, 110x, and 220x. At 32x I wondered if I was on the right star because there wasn't even a hint of a split. There were occasional hints of the secondary at 110x. I had a clean split at 220x; the primary looked yellow/orange and the secondary was blue. It was not a crisp image because of the poor seeing. The primary itself was boiling and fragments of a diffraction ring would appear and disappear. Still, it was fun to split this double. Hopefully tonight I'll be able to try some magnifications in between 110-220 and find the minimum I need for a clean split.

I also like the idea of an aperture mask. I've always assumed I needed aperture to overcome the LP, but maybe that isn't the case.

#35 Bill Boublitz

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Posted 07 May 2013 - 10:47 PM

I saw your post and couldn't help responding. Izar is one of my favorites! Sort of like and old friend. It was the first double of any challenge I split through a scope. I view it almost every year. I have always seen the companion more grey-green than blue. But I attribute the color to the particular set of oculars I was given to work with. Most log the companion as blue. I first viewed it with a 101 mm refractor at x145. Truly beautiful object. I never tire of it. Happy to read your post! Thanks.

#36 aquariusnic

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Posted 12 May 2013 - 02:08 AM

Hi,

That was last may 7th, after seeing the double Algieba - very nice - in Leonis i had no problem splitting Porrima in Virgo on my balcony. The seeing was excellent (9/10) and my Tasco 60/900 showed it very well at 90X and better at 144X (12,5mm barlowed) like two close little diamonds. But I never saw the Izar companion with this.

#37 StarDusty

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Posted 12 May 2013 - 12:55 PM

I have not looked at Izar this year yet, but imaged it last summer. (Sorry, not in color.)

For a black and white image go here:

http://www.clearskyo...=popup&tmpl=...

#38 grom

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Posted 14 May 2013 - 02:32 PM

A few days ago, with good seeing. Porrima two Airy discs were touching or almost-touching in a 80mm APO.

#39 Silver Bear

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Posted 15 May 2013 - 06:55 PM

Two nights ago, I viewed Porrima, saw the color differences, but could not quite split the double under high magnification due to wind blowing against my light little telescope. Still, a very nice sight.

#40 Bill Boublitz

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Posted 22 May 2013 - 04:39 PM

My customary small instrument is a 101 mm refractor. Last night, I stopped it down to 60 mm with an aperture mask and split Izar quite easily. 1. The image was dimmer (than full aperture) 2. Colors seemed more vivid, more pronounced. 3. Prominent diffraction ring around primary - which is hardly noticeable at full aperture. Magnification was x225.

#41 John_G

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Posted 27 May 2013 - 04:24 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.

#42 fred1871

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Posted 27 May 2013 - 05:00 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.

#43 Kon Dealer

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Posted 27 May 2013 - 05:53 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.

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. :)

#44 Bill Boublitz

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Posted 27 May 2013 - 06:37 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.

#45 WRAK

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Posted 28 May 2013 - 11:12 AM

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

#46 labmand

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Posted 28 May 2013 - 05:30 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. :question:

#47 Bill Boublitz

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Posted 29 May 2013 - 04:31 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

#48 labmand

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Posted 29 May 2013 - 07:10 PM

Thanks Bill,
When I go here (database for wds I think)
http://stelledoppie....?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.

#49 Bill Boublitz

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Posted 29 May 2013 - 07:49 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!

#50 fred1871

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Posted 29 May 2013 - 08:06 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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