[Aavso-photometry] color photometry

[Stan Walker]

Hi Michael,

Recognising that there are sets is the first step in putting the colours 
back together. Still, if a user marked only the UBVRI boxes he'd get some 
idea of what was there. But reassembly is not as easy as it sounds - you 
have to sort to get the matching pairs or sets. I have this experience with 
Doug West's JH listings. If the colour sets are mixed with the odd single 
colour measure, as would usually be the case, it gets rather complex.

As for timing, it's normal to make the measures symmetrically. VBUUBV or 
similar would constitute a set timed at the moment midway in the U readings. 
The number and integration time in each filter is set by the type of target. 
In any case a slightly less than accurate time is not a problem in most 
cases - certainly not with Miras and Cepheids. CVs call for faster work but 
not many people are doing colour photometry of these - it was done 
extensively in the 70s and 80s and the colours behave much the same in most 
cases.

Regards,
Stan



----- Original Message ----- 
From: "Michael Koppelman" <lolife at bitstream.net>
To: "Stan Walker" <astroman at xtra.co.nz>
Cc: "AAVSO photometry" <aavso-photometry at aavso.org>
Sent: Saturday, March 24, 2007 4:17 AM
Subject: Re: [Aavso-photometry] color photometry


> Hey, Stan.
>
> You know, of course, that a researcher who downloads that data can  easily
> put it back in differential form. I totally see the economy of  storing
> the measurements in individual bandpasses separately. In  almost every
> case the individual measurements are taken at a slightly  different JD, as
> well, so the time window of the differential color  is preserved if the
> measurements are stores separately.
>
> I guess I don't see why this would cause you to withhold your
> observations.
>
> Best,
> M.
>
> PS - This was sitting unsent in my mail app. I hope I didn't send it
> twice!
>
>
> On Mar 15, 2007, at 4:05 PM, Stan Walker wrote:
>
>> At present I do not contribute data to the AAVSO for a different  reason.
>> I
>> have mentioned to Arne my concerns at the way the database is  arranged.
>> The
>> Star of the Season - RR Tauri - illustrates this point. In his article
>> Laszlo Kiss discussed the colour changes of this star when mentioning
>> 'blueing' and photometric measures. But if I send in UBV measures  of RR
>> Tauri (which can be observed from NZ) my V, B-V, U-B colour data  will be
>> separated into separate V B and U curves which are not nearly so
>> informative. In this area the historical methods of the AAVSO  hinder the
>> natural progress of something like colour photometry. One of his  themes
>> was
>> that by using a wide range of disciplines visual, pep, nir,  polarimetry,
>> spectroscopy, you get a fuller picture. So this is one area where  change
>> would be helpful.
>