[Aavso-photometry] Re: Questions on Henden sequences

[arne]

Alessandro Maitan wrote:

>I have the opportunity to partecipate to a programme to monitor symbiotic star magnitude variation. I am using Henden sequences to determine the transformation coefficients (I'm using only V & I since my camera is based on "old" KAF 400 chip) and therefore calculate the actual magnitude of the variable star. I'm finding very big differences in my photometry reduction, therefore I would like to get a piece of adivce on which could be the best way to face this situation considering that several star in the sequence are very red and the field I am worknig on (in Aql) is quite "croweded".
>For my reduction I'm using IRAF and the tasks of both the apphot and photcal packages.
>I understand that my question is too much generic, but I can't find a better way to ask unless writing a long amil detailing all the steps I did (obviously I can explain everything if necessary).
>Apologizing for my poor English and thanking everybody in advance, I remain.
>
>  
>
Are these the Henden/Munari sequences? (BTW, we have another 40 or so 
still to be published.)
The sequence stars are probably intrinsically normal-color, but reddened 
by interstellar
extinction.  The symbiotic star, on the other hand, is intrinsically 
red.  The two effects
are somewhat different and absolute, transformed photometry is a bit 
difficult.  I am
willing to help if you want to send me more details.
Arne