[Aavso-photometry] NU Cyg

[Gary Billings]

Hi Keith:  you may have just had a demonstration of why your 
observations are useful!  Eclipsing binaries change period, or the 
published elements may need to be refined.  Even a small period change, 
or error in the period, well to the right of the decimal point, will 
lead to a significant difference between the predicted and observed 
time of minimum after 100's or 1000's of cycles.

The Lichtenknecker database has some data for NU Cyg:  go to
http://www.bav-astro.de/LkDB/index_e.html
and enter NU Cyg.  You can retrieve all their datapoints via a button 
on the page that has displayed the O-C diagram.

The above database is the most comprehensive one that I know of, and 
it's maintainers try to glean data from all sources...  but there are 
others.  One place to check is to search recent issues of the IBVS for 
the name of your star.
http://www.konkoly.hu/IBVS/t.html

If you want to know the calculated / 'predicted' minimum for eclipses 
in the past, you can calculate it yourself.  The Cracow site you 
mentioned prints the elements on the same page as the computed times of 
upcoming eclipses.  You'll have to determine the "E" (cycle number) 
yourself.  Note that they use their own elements for predictions, not 
the elements from the GCVS.

If you need more details, just let me know...  I'm also an observer of 
eclipsing binaries, and am fascinated by how these beasts behave...

g.

P.S.  there are other possibilities re your 30 minute O-C (observed - 
calculated) value.  If that particular system had developed a very 
pronounced star-spot, it might lead a shift in the time of minimum 
light...  I don't know if 30 minutes is a possible value for this 
system, but spots *can* affect time of minimum light.


On 13 Nov, 2007, at 2:09 PM, Keith Graham wrote:

> Hi,
>
> I have run up against a brick wall and hope someone on this list can 
> point mein the right direction.
>
> I have been doing some TS photometry on the EB star NU Cyg. I am 
> detecting about a 30 minute time differential between the ephemeris 
> minima (both P & S) and my observed minima.  I began collecting data 
> for this star on JD 2454402. I need to get the calculated times for P 
> & S minima from that date forward. The only emphemeris I can even find 
> this star on is the one located at http://www.as.ap.krakow.pl/ephem/. 
> When I first began observing it, I did not record the calculated P & S 
> minima times from the ephemeris because I really was not looking for 
> any time differential.  But now that I appear to have detected an 
> approx 30 minute differential, I would like to verify it. So, does 
> anyone know where I might find past calculated minima for this star 
> (or any others, for that matter)? I have contacted Gerry Smolyk, but 
> he indicated that he had no data on this star.
>
> Thanks for any helpyou can offer.
>
> Cheers,
>
> Keith Graham
> GKA
>
>
>
>
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