[Aavso-photometry] Time seriess for GK Persei

[Gary Walker]

Hello Gianlucaros;



Since you are getting into error calculation, I would make one more suggestion.  Take a star that is supposed to be constant in your fields.  Measure the magnitude of it on each of the 5 frames.  Take a star that is close to the target star in magnitude and color if you can.  Then calculate the std dev of these 5 values.  This will give you a better representation of your total errors, and is much more representative than the 1/sn calculation which is usually a minor contributor to the real errors.  




You can repeat this on several different stars if you wish, taking the std dev on the 5 measurements.  The idea is this:  If these stars are constant, the repeatability that you get shows you just how much scatter you should expect in your target star.  1/sn is basically useless to see how you are doing.  




BTW:  you can discover potential variable stars this way.  If you take several constant stars, and find that the std dev is similar for them, but one is much larger, then it is suspect.  Remember, that the fainter stars will have slightly higher scatter.  Such a star requires additional followup.




I have seen constant stars using this method, that vary on some nights, and are constant on others.  If you see a trend in the data, one must remove the extinction to make sure that its not an air mass effect--but this comes later.




Thanks

Clear Skies
Gary Walker
Maria Mitchell Observatory
4 Vestal Street
Nantucket, Mass  02554


-----Original Message-----
From: gianlucaros at gmail.com
To: aavso-photometry at mira.aavso.org
Sent: Mon, 24 Mar 2008 6:42 am
Subject: Re: [Aavso-photometry] Time seriess for GK Persei








I am currently using Astroart to process the data.
Concerning my experiment on taking TS on GK Persei I used the formula 2.5Log
(1+1/SNR) to calculate uncertainty. The scale of my CCD/scope
combination is 1.67 arcsec per pixel and the FWHM and seeing of the 5 measures
was as follows:

FWHM =  2.56 = 4",27    SNR 27.7  err. 0.04
               3.28 = 5".48    SNR 22     err. 0.05
               2.26 = 3".77    SNR 35.5  err. 0.03
               2.35 = 3".92    SNR 37.7  err. 0.03
               2.35 = 3".92    SNR 47.7  err. 0.02

The TS were taken at 30 sec intervals and not 20 sec as I mistakenly
indicated in my previous e-mail.
Cheers
Gianluca

2008/3/23, aavso-photometry-request at mira.aavso.org
<aavso-photometry-request at mira.aavso.org>:
> Send Aavso-photometry mailing list submissions to
>         aavso-photometry at mira.aavso.org
_______________________________________________

Aavso-photometry mailing list
Aavso-photometry at mira.aavso.org
http://www.aavso.org/mailman/listinfo/aavso-photometry