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A Fine Fall Challenge in Pegasus

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#1 rugby

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Posted 26 September 2019 - 11:46 PM

Pegasus abounds in beautful doubles. One such is BU 720 found roughly half way between Alpheratz and Scheat. This pair should climb to a perfect height around midnight on a crisp Autumn evening. I say perfect because I dont enjoy observing targets directly overhead. Instead I like 'em best as they clear the uppermost branches of tall neighbourhood trees. 

BU 720 is not for the faint of heart. The components are 5.7 and 6.1. Stella Doppie says the separation is a scant 0.6 seconds.

I attacked it first with a 120mm refractor using 300x and then with a ten-inch reflector at 460x. I had a very good night with steady seeing. 

So, how did I do?

Hard to tell. I believe the ten elongated the discs into a notched pair.  The PA was obvious. In the 120 I had a strong suspician of elongation east -west.

What a great test for eye and telescope.


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#2 aa6ww

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Posted 27 September 2019 - 12:59 AM

In using a program like Stellarium, what would I plug into the search  window to locate BU 720.

 

this is always the most confusing part of double star astronomy, the names are not familiar with the popular astronomy programs.

 

...Ralph                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        



#3 fred1871

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Posted 27 September 2019 - 07:47 AM

The popular astronomy programs (as I've commented previously) for unknown reasons don't seem to want to use the standard discoverer names for double stars. These are the long-time first labels. These programs don't seem to have a problem with NGC and IC and so on for galaxies, nebulae, clusters. But they use a smorgasbord of catalogues for double stars, and just about anything EXCEPT the standard namings will come up. Very unhelpful.

 

Personally, I've given up on these programs (including Sky Safari) for doubles. I use go-to or push-to with computer generated lists from WDS or (more often these days) Stelle Doppie and find the objects by RA and Dec. Surprisingly quick and easy. I've been doing it this way for about 25 years.

 

Doubles can be found by various means. The paper atlases (such as the Cambridge Double Star Atlas) also use the standard doubles labels. This kind of atlas can be used by star-hopping observers as well. I used to do that with scopes lacking go-to or digital circles; being older now and with a bad back I've stopped star-hopping, and I last longer at the scope (and with a happy back) by using the computer aids.

 

To each their own. But I do feel the popular programs are unhelpful for doubles.


Edited by fred1871, 27 September 2019 - 08:08 AM.


#4 fred1871

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Posted 27 September 2019 - 08:21 AM

Pegasus abounds in beautful doubles. One such is BU 720 found roughly half way between Alpheratz and Scheat. This pair should climb to a perfect height around midnight on a crisp Autumn evening. I say perfect because I dont enjoy observing targets directly overhead. Instead I like 'em best as they clear the uppermost branches of tall neighbourhood trees. 

BU 720 is not for the faint of heart. The components are 5.7 and 6.1. Stella Doppie says the separation is a scant 0.6 seconds.

I attacked it first with a 120mm refractor using 300x and then with a ten-inch reflector at 460x. I had a very good night with steady seeing. 

So, how did I do?

Hard to tell. I believe the ten elongated the discs into a notched pair.  The PA was obvious. In the 120 I had a strong suspician of elongation east -west.

What a great test for eye and telescope.

BU 720 (23340+3120 - gives the location) is a long period binary; measures in recent decades show PA increasing, with only very slow increase in separation. At present, based on speckle measures, separation is near enough 0.57". Should be good to nearest 0.01".

 

Orbital period is given as 492 years, but only a Grade 4 orbit, so future refinement can be expected.

 

The separation is about 0.5-Rayleigh for a 120mm scope, so the impression of elongation is likely real. For the 10-inch, this is a whisker easier than a Rayleigh split, and wider than a Dawes touching/tangent discs view.

 

I've seen BU 720 elongated with my 140mm refractor a few years ago (very little difference in separation from then to now), which I noted at the time as "definite elongation slightly off the E-W line" at 400x, confirmed at 570x.

 

BU 720 is marked on various star charts as 72 Pegasi. Another way to find it.


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#5 rugby

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Posted 27 September 2019 - 08:41 AM

Ran across a thread posted in CN regarding 72 Pegasi dated 2012. Interesting similarities. 



#6 Asbytec

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Posted 29 September 2019 - 07:34 PM

Ran across a thread posted in CN regarding 72 Pegasi dated 2012. Interesting similarities. 

Hey, an old friend. smile.gif

 

72 Pegasi.jpg



#7 rugby

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Posted 29 September 2019 - 08:29 PM

Thankyou Asbytec   My rough drawing of this pair is the same as yours just not as pretty. My ten-inch newt shows a deeper notch whereas the 120 refractor view is less elongated. I studied this pair for an hour on Sept 28 2019 with various eyepieces from a 3-6 zoom to a 4.7ES with 2x barlow. The latter combination gave 380x but the field disappeared from sight in a matter of seconds. The human eye is good at telling if something is assymetrical. I am far from separating this pair. I am only saying the image is not round.

Seeing is critical. I place my scope over grass not cement. I wait an hour for cool down and then view a high power out of focus image to see how large the seeing cells are. But also, I tap the scope gently with a finger nail

and just as the image settles I look away. Its in  that fraction of a second as the eye is moving away from the star that my sensation of elongation is strongest   


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#8 rugby

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Posted 29 September 2019 - 08:35 PM

Fred1871 Can you please tell me what eyepieces you used with the 140 to get to 570x and did you use a drive?



#9 gfeulner

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Posted 29 September 2019 - 09:07 PM

In using a program like Stellarium, what would I plug into the search  window to locate BU 720.

 

this is always the most confusing part of double star astronomy, the names are not familiar with the popular astronomy programs.

 

...Ralph                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        

BU 720 is SAO 73341. Stelle Doppie shows it as BU 720 and SAO 73341 and 72 Pegasi. You can search in Stellarium using SAO 73341 or 72 Pegasi.

Gerry


Edited by gfeulner, 29 September 2019 - 09:12 PM.


#10 fred1871

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Posted 29 September 2019 - 10:43 PM

Fred1871 Can you please tell me what eyepieces you used with the 140 to get to 570x and did you use a drive?

Driven mount, AZ-EQ6 in equatorial mode. Eyepiece was a 3.5mm Nagler 6 with 2.5x Powermate. Because the Petzval design gives a relatively short focal length to the scope, I frequently use the Powermate to give 2,000 mm focal length equivalent, at f/14.3 instead of f/5.7. With the native 800mm, I'd be using a 2.5mm eyepiece to get a mere 320x. The Powermate shows no optical degradation or issues - I'd say it improves the view for doubles (eyepieces like f/14 better than f/5.7 could be part of it).

 

I find that with double stars 400x (5mm with Powermate) shows everything the optics can produce, but for the tight elongated pairs I sometimes use 570x as confirmation. Airy disc at 570x is very neatly round on single stars in good seeing.

 

Most doubles will show at 285x with that aperture (Powermate with 7mm Pentax XW). 400x is for the very tightest ones. Limit for detection of "out of round" with equal pairs is about 0.47"/0.48" so far. I might try for slightly closer some time : see if I can get to 0.4-Rayleigh, which would be 0.39"/0.40" for 140mm aperture. Depends on getting a very steady night, not frequent where I live. 


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#11 azure1961p

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Posted 01 October 2019 - 11:08 AM

Pegasus abounds in beautful doubles. One such is BU 720 found roughly half way between Alpheratz and Scheat. This pair should climb to a perfect height around midnight on a crisp Autumn evening. I say perfect because I dont enjoy observing targets directly overhead. Instead I like 'em best as they clear the uppermost branches of tall neighbourhood trees. 

BU 720 is not for the faint of heart. The components are 5.7 and 6.1. Stella Doppie says the separation is a scant 0.6 seconds.

I attacked it first with a 120mm refractor using 300x and then with a ten-inch reflector at 460x. I had a very good night with steady seeing. 

So, how did I do?

Hard to tell. I believe the ten elongated the discs into a notched pair.  The PA was obvious. In the 120 I had a strong suspician of elongation east -west.

What a great test for eye and telescope.

Actually no. Pegasus is a letdown for doubles and after Cygnus' riches its a REAL letdown as we are now looking out of the galaxy into deep space and only a fraction of the milkyways stars are showing.  You are better off looking for abounding doubles in Cassiopeia rather then broadcast how little you know about double populations.   Alas, it also ushers in the season of galaxy observing and so thats a good thing.  But yes, move on to Cassiopeia . While there view WZ Cassiopeiae.  The carbon star in 8" and less aperture has true tinges of crimson.

 

Pete

 

 


Edited by azure1961p, 01 October 2019 - 11:09 AM.


#12 azure1961p

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Posted 01 October 2019 - 11:11 AM

Hey, an old friend. smile.gif

 

attachicon.gif 72 Pegasi.jpg

 

 

Yeah there are a few ok onrs, 72 Pegassi is actually a true fave with the 8" and that gentle candle yellow.  Incidentally last time I looked with the 8 it was 0.50 lol.

 

Pete


Edited by azure1961p, 01 October 2019 - 11:12 AM.

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#13 pugliano

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Posted 02 October 2019 - 05:41 PM

"You are better off looking for abounding doubles in Cassiopeia rather then broadcast how little you know about double populations."

 

How nice.


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#14 gfeulner

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Posted 02 October 2019 - 09:15 PM

"You are better off looking for abounding doubles in Cassiopeia rather then broadcast how little you know about double populations"

.

I don't think comments like that are necessary in this forum.

Gerry


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#15 CharlieB

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Posted 02 October 2019 - 09:38 PM

Gentlemen, let us keep thing civil.

 

Charlie


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#16 Nucleophile

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Posted 08 October 2019 - 09:05 PM

I will be revisiting Bu 720 shortly.

 

Here is a pic I took in 2016:

 

     Bu720_PEG.jpg

 

EDIT:  Last night I tried this one with the 8 inch at high power (627x) and noted it as decidedly elongated with a small difference in magnitude and color vs the primary.  I could not detect a 'notch but the seeing was not optimal--I will try again tonight.

 

 

Below are my notes from my 2016 post regarding this object.  These were written before I knew to look into the 4th Int Cat for historical data.  I agree with Fred re:  the likely current separation. I will endeavor to measure this one again with my current setup which is superior to the one used to make the image shown above.

 

[https://www.cloudyni...ab-and-16-vul/]

 

Bu 720, 72 Pegasi
magnitudes:  5.7, 6.1
position angle:  105 degrees
separation:  0.575” (orbital elements estimate); 0.505” (last precise measure; 2015)

 

The separation data are not in good agreement for this object.  This is, therefore, a good candidate for quantitative scrutiny.

 

Visual [15 inch reflector]
At 398x the object vacillated on the border between elongated and just resolved to two golden-orange disks of similar magnitude in the correct position angle; 569x proved sufficient to show the stars as different magnitude and clearly resolved (but not yet split); a final increase in magnitude to 798x showed the pair as split, again with a golden-orange color and a small difference in magnitude.  The ease of resolution at modest magnification led me to think the larger separation value [0.575”] was more accurate for Bu 720.

 

Photographic
Bu 720 was easily imaged using an exposure of 10 ms [gain = 320].  Four movies were made and separation was measured by three methods using REDUC:  cross correlation of the top 5% of frames using S4 filter; simple measure of a Registax composite; and simple measure of a composite generated in REDUC.  There was good agreement across these methods, giving a measured separation of 0.61”.


Edited by Nucleophile, 09 October 2019 - 08:46 AM.

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#17 Nucleophile

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Posted 11 October 2019 - 09:47 PM

I re-observed BU 720 last night with the 8 inch reflector under good seeing conditions (a 3+ out of 5 on the Danjon Scale) and made the following notes:

 

Viewed extensively at 627x:  20% of the time the image pushed past elongated/snowman shape to resolved showing two distinct discs with the secondary possessing a light orange tint versus the yellow primary.

 

I then installed an orange filter and observed again at 627x:  while the image was a bit sharper and a little smaller, the discs were not resolved at a greater frequency.  I decided I preferred the image without the filter.  Occasionally, the orange filter helps with difficult doubles--not so much this time.

 

BU 720 is perfectly placed in the sky for my imaging setup--looks like next weekend I may have a chance to get some video with the ASI290MM attached to the 15" reflector.  I will be sure to post any decent images thus obtained.


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