[Aavso-photometry] Time series for GK Persei

[Tim Crawford]

Gianluca,


Are these filtered or unfiltered images?


With my 12" SCT and a "V" filter, I have to integrate for 45 - 60 seconds to get a good SNR on a 13.2 star.  If you are using a "V" filter, unless you have a scope larger than mine you are not integrating long enough and you probably also then have a poor SNR which will contribute to your scatter.
Unless dealing with a CV system in outburst, when a clear filter might be ok, all CCD obs should otherwise at least be with a "V" filter for the AAVSO.


Did you measure your seeing?  If you do not know how to measure seeing then please let me know and I will explain.  I ask this question because if your seeing was poor that would also contribute to scatter.


Now, having said all this, Intermediate Polars have some pretty rapid fluctuations; plus the fact that the GK per system's white dwarf has a pretty rapid spin value of just under 6 minutes;
 therefore, I think your obs are probably OK and reflective of the system you are measuring.


I would hope that any recently new observers reading this do not get concerned with variations this small, in a shot time period,  if you have a good SNR and a different target. 'taint no thang!  Lots of issues going on, including what the atmosphere is doing while you image.


TS, by the way, usually are over a several hour period to have significant  value.


While all data is welcome by AAVSO, I am not so sure that GK Per, an Intermediate Polar, TS data is all together that important when not in outburst unless you are wanting to attempt to calculate the spin period of the white dwarf portion of this binary CV system in which case you will need a good program like "Peranso" to process the photometric Light curve  data; don't misunderstand me, please; I am simply trying to point out that there are targets where the TS data can be more valuable than other targets; but don't let that stop you from doing a TS on anything you are comfortable with, especially while learning.


Right now, there are some bright targets (~10-12 mag) on the HMXB list that their is a demand for 2-3 hour filtered TS a few times/week; not sure if any are accessible from
 your location but you might take a look; by the way, most of these are very slow systems so unlikely that you will see much change, if any, in the short term.


http://homepage.usask.ca/~ges125/AAVSO_HMXB_Charts.html


In addition, here are two links from the Campaign page where TS are encouraged:


www.aavso.org/publications/alerts/alert351.shtml


www.aavso.org/publications/alerts/alert353.shtml


Campaign Page:


/www.aavso.org/news/campaigns.shtml


Also, here is a page with suggestion frequency of observation data for various types of targets.  This is not all-inclusive; often specific campaigns, alert notices, etc... will request TS data of specific targets.


www.aavso.org/aavso/about/howoften.shtml


'nough said for now


Per Ardua ad Astra


Tim Crawford CTX
Arch Cape Observatory




  




----- Original Message ----
From: "gianlucaros at gmail.com" <gianlucaros at gmail.com>
To: aavso-photometry at mira.aavso.org
Sent: Saturday, March 22, 2008 12:05:52 PM
Subject: [Aavso-photometry] Time series for GK Persei

 I  have  experimented  to  take  TS  of  GK  Persei  on  Feb  24th  to  see  if  I
can  detect  the  small  fluctuations  around  minimum.  I  have  actually
taken  5  consecutive  exposures  20  sec  each  and  done  the  calibration
with  both  darks  and  flats.  Since  I  get  5  different  mag  value  (13.19,
13.23,  13.13.27,13.22,13.23)  I  wonder  whether  such  measurements  are
indication  of  the  behaviour  of  the  star  rather  than  problems  in
accuracy.  Sorry  for  asking  a  question  that  could  be  trivial  to  answer.
Gianluca  (RGN)
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