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Zeta Boo semi-major axis orientation?

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#1 entropy111

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Posted 22 April 2013 - 11:48 AM

How does one find out which way a double star system is aligned?

I was trying to split Zeta Boo; I think I did but I'm not sure. If I new which way they were aligned (the semi-major axis) then I might be sure.

Is semi major axis orientation a named thing?

Any help would be appreciated.

Thank you,

#2 brianb11213

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Posted 22 April 2013 - 12:33 PM

You're going to need a good scope & excellent seeing.

The 2013 British Astronomical Association gives parameters for Zeta Boo as follows:

2013.0, sep 0.49 arc sec, PA 292.3 deg
2014.0, sep 0.46 arc sec, PA 291.3 deg

So the system (which has a period of 124 years) is at present closing quite fast.

Semi major axis orientation would be the PA joining the periastron & apastron positions, which is irrelevant to observations though part of the orbital parameters needed to make predictions of position angle & seperation into the future.

#3 Cotts

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Posted 22 April 2013 - 12:36 PM

welcome aboard, entropy. What you want is the Position Angle (PA), measured eastward from north from 0 to 360 degrees. Currently Zeta Boo B is at 290 degrees relative to A with a separation of 0.6". So northwest, approximately. This info is readily available in every Double Star catalog out there. For the most authoritative listings you should become best friends with the Washington Double Star Catalog.

The Sixth Catalog of Orbits, part of the WDS gives the following ephemerides for Zeta Boo:
Year.. PA.... Sep.
2013. 292.3 0.486"
2014. 291.3. 0.458"
2015. 290.2. 0.427"

You,re going to need at least a 12 inch scope with perfect seeing to bag this one!

Good Luck

Dave

#4 entropy111

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Posted 22 April 2013 - 12:43 PM

Awesome. Thank you guys. Exactly the info I needed. I believe I saw Zeta Boo split last night.

Position Angle (PA) was the "thing" I needed.

#5 entropy111

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Posted 22 April 2013 - 01:03 PM

just realized wiki's pic of Bootis has Zeta Boo accurately labeled...

So, if I'm doing this right...... a PA of 300 degrees makes the semi-major axis about parallel to the line between Izar and Arcturus. (?)

for reference: http://upload.wikime.../Bo├Âtes_IAU.svg

#6 PJ Anway

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Posted 22 April 2013 - 07:03 PM

Here is the orbit - LINK

#7 fred1871

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Posted 22 April 2013 - 08:06 PM

Dave, I'll agree about needing a 12-inch telescope for getting a split on Zeta Bootis, but a lesser aperture will still show it elongated.

Back in mid-2011 I could still see a definite elongation of the double - a "rod" effect - with my 140mm refractor at 400x. At the time the WDS ephemeris, interpolated, would suggest 0.53" separation. And that's the Dawes Limit (as in, "barely split") for an 8.6-inch (218mm) aperture. Two years earlier, when the pair was somewhat wider, it was a notched image with the same telescope.

Currently, at about 0.47", I expect it'll be near enough a round image with 140mm - but given the 2011 observation, a 160mm refractor should give a similar "rod" to what I saw two years ago. Though it might need 500x or more to do it at present. :grin:

#8 fred1871

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Posted 22 April 2013 - 08:12 PM

Entropy, what size telescope are you using?

Regarding angle, a PA of 290 is just northerly from due west. It's mostly easy to work out directions from the E-W line - in alt-az/Dob and other undriven scopes W is the drift direction; equatorials give it, if driven, from moving on the RA axis.

#9 fred1871

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Posted 22 April 2013 - 08:27 PM

PJ, the Dibon Smith orbit you've provided a link to is slightly different when compared to orbit given in the WDS 6th orbit catalog, and with a slight difference of quoted period. The shape of the 6th orbit cat version is noticeably tighter around the line of sight periastron section. I guess we'll see over the next decade or so what happens - as with Gamma Virginis, the move through the closest part of the orbit allowed improvements in the orbit calculation. Currently, Zeta Boo has a mere grade 2 orbit, not yet a grade 1. :grin:

For now, the Dibon Smith version is fine and gives a nice overview of the orbit, with the benefit of dates for positions.

#10 entropy111

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Posted 22 April 2013 - 11:25 PM

Fred, using a 130mm reflector, with a customized apodizer.

I'm viewing it from my drive way in the northern CA. Generally very poor conditions due to light pollution, unfortunately.

Hoping to get back out there tonight or later this week.

#11 NewMoonTelescope

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Posted 06 May 2013 - 04:13 PM

I have been working on Zeta Boo for several nights. Using a 16", I have yet to make an honest split, but I attribute my woes to the horrible seeing here in upstate NY. Tonight seeing is supposed to get pretty sharp, so it may happen yet!
Congrats on the split!

Ryan

#12 NewMoonTelescope

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Posted 06 May 2013 - 09:08 PM

Tonight was the night. Clean split. As a casual double star observer this is always a nice start to the night.

#13 fred1871

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Posted 08 May 2013 - 11:25 PM

Ryan, what magnification for the clean split?

I had both clear sky and steady atmosphere late last night, so I tried Zeta Boo again, and had a clean split, though only just so, at 470x with C9.25. Two neat discs with a slight dark space between them, almost touching - as the Dawes Limit for that aperture is the same as the current separation (per ephemeris) it was fairly much as expected. But nice to get - not every night allows magnifications that high to be useful.

#14 WRAK

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Posted 10 May 2013 - 03:21 AM

Tried Zeta Boo mid July last year with my 140 refractor and got an egg pointing approximately to the position of the companion.
Wilfried

#15 Jason D

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Posted 11 May 2013 - 04:17 AM

I tried Zeta Boo tonight with my 10" reflector. I pushed magnification to 1200X. I observed two clear discs touching.
Jason

#16 Darren Drake

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Posted 17 May 2013 - 02:35 PM

I saw it was clearly 2 stars last night but seeing prevented a clean split with the 18 inch.

#17 Tom and Beth

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Posted 19 May 2013 - 05:09 PM

I tried Zeta Boo tonight with my 10" reflector. I pushed magnification to 1200X. I observed two clear discs touching.
Jason

:bawling: Missing nights like that. We've had a few nights where Doubles in the 0.7 or so range might be tried, but not steady enough for Zeta, which IIRC is just south of 0.5 now, and closing.

#18 azure1961p

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Posted 26 May 2013 - 11:53 PM

I used sky safari tonight in 4/10 seeing expecting to at least get a momentary split . They wrongly listed the sep at 1.1" . This makes total sense as the reflector in that seeing didn't give even the vaguest hint of duplicity which a 1.1" would be shown under these conditions.

Peye

#19 azure1961p

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Posted 26 May 2013 - 11:53 PM

I used sky safari tonight in 4/10 seeing expecting to at least get a momentary split . They wrongly listed the sep at 1.1" . This makes total sense as the reflector in that seeing didn't give even the vaguest hint of duplicity which a 1.1" would be shown under these conditions.

Pete

#20 C_Moon

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Posted 30 May 2013 - 09:37 PM

I had an nice observation of Zeta Boo last night. Finally a night with some pretty decent seeing.

On my first try I was unaware of the PA. I thought I saw an elongation in a direction I estimated to be 260 deg. After consulting my computer I realized I was off by 30 deg.

I decided to try some other easier targets and let the scope cool some more. After another 45 min or so I returned to Zeta. I now knew where to look (could be a bad thing, I guess). Anyway, I still couldn't quite make out a definitive sign of a double at a mag of about 320x. I upped the power to 500x and after some time adapting was rewarded with the classic "kissing" double. Really, this is the first time I've seen this (i.e., to stars touching but no split between them -- almost like a slot instead of a circle). The "slot" was oriented in the correct orientation (PA ~290 deg). I looked enough to know I was really seeing it and not just "filling in the blanks." Color was a deep white.

For kicks I looked at Izar at 500x and was impressed that the two points were steady and the color difference between them quite pronounced. At 500x Saturn did not look so hot ;)

#21 azure1961p

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Posted 01 June 2013 - 06:50 AM

Paul they sounds like a terrific observation. When doubles got this close AND the seeing complies and there's a color difference its one if the best sights in doue star observation I think. I want to make the call with my 8".

Pete






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