[Aavso-photometry] Time series for GK Persei

[gianlucaros at gmail.com]

Hi Tim,
yes they are filter images as I always use a V filter with my CCD. I
have a fast Newtonian (8" F/4) which probably saturate faster than a
12" SCT but longer exposures are always better. I fully agree with you
that both the atmosphere and poor SNR do contribute to scatter. Thank
you for pointing out all the things you said as I have to learn and,
certainly, while I'm doing this I don't want to send wrong or useless
data to the AAVSO. By the way, can you explain how to properly measure
seeing, and the minimum SNR required for good photometry?
Clear skies
Gianluca (RGN)

2008/3/23, Tim Crawford <tcarchcape at yahoo.com>:
>
>
> 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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