[vsnet-chat 73] Re: Times of minima (fwd)

[Taichi Kato <tkato@kusastro.kyoto-u.ac.jp>]

Forwarded message from W S G Walker:

From astroman@voyager.co.nz Fri Feb 14 17:32 JST 1997
Date: Fri, 14 Feb 1997 21:23:23 -0800
From: W S G Walker <astroman@voyager.co.nz>
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To: Rudolf Novak <rudolfn@physics.muni.cz>
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Subject: Re: [vsnet-chat 69] Times of minima
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Rudolf Novak wrote:
> 
> Dear vsnet-chat readers,
> Today I thought a bit about determining times of eclipsing binaries
> minimum. I found some program on VSNET HP but there were no documentation
> so I didn't use it. There are certainly many ways how to determine time of
> minimum but what shall I do if minimum is not symetric? And of course is
> there some alghoritm to determine time of RR Lyr, delta Sct or delta Cep
> time of maxima? I know that this question is not very suitable for many of
> readers but there are not just CVs :-)
> Of course this could be useful for some eclisping CVs or superhump's
> measuring analyze.
> So that's it. Would be very happy if some of you could wrote me a few
> sentences or recomend me some references I don't know ...
> Thank you very much and have a nice dreams or good breakfast
>                                                         Rudolf
> Greetings, Rudolf,

After coming back from Auckland I happened to see your note about 
determining times of maxima on VSNet. I do pep of EBs and DN, but 
in recent times mostly delta Cephei stars. For the latter two I find the 
best method is to make a master light curve from your own or someone 
else's measures then fit your measures - or someone else's - to this 
using a least squares method. Observations from about +/- 0.2 phase of 
the expected maximum are used. It also works for eclipsing binaries, but 
it's usually easy enough to fit these by eye to an expanded light curve. 

The method also works for visual observations of Mira stars, but you need 
rather more measures each season.

Perhaps you could background your enquiry a little. I'd really be 
interested to hear that you're observing cepheids, but I suppose that 
this was just a casual comment.

The method works well for asymmetric peaks such as you find with 
superhumps, although there is need to ensure that there is a reasonable 
distribution of measures on the rising and falling branches near the 
peak. Some scaling of the master light curve would be needed. I've got a 
lot of VW Hydri and other CV superhump measures from the 1970s and 80s 
and I've never thought of applying this - the inherent phase jitter of 
the superhumps makes eyeball estimates adequate. 

Regards,
Stan Walker

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