[Aavso-photometry] Color Photometry

Wed Mar 28 17:25:31 EDT 2007

Hi Chuck,

I think that Jeff Hopkins has largely covered what you mentioned so no need
to say this again. The measures usually end up published somewhere but the
AAVSO professes to collect these in a more usable format than having to
refer to an old IBVS or some other publication. I just don't think that
separating out U B and V makes the measures more usable.

I was trying to get across the mesage that colour photometry gives
information about physical changes in a star during a cycle. Noone would
waste time doing time series photometry - which is largely what the AAVSO
database is all about - in U. So I was hoping that one day true colour
photometry could find a home in a database where it was instantly
recognisable.

A point that Jeff makes is that some time and effort has gone into
transforming UBV and JH into the international systems. Thus the measures
are very reliable. In contrast, Elizabeth Waagen, in her recent post about
LPV maxima and minima has commented about the disparities in CCD measures,
presumably not reduced to any standard system. So mixing them together does
a disservice to the people who provide very reliable measures.

I was looking at stars using the plotting procedures to see which were
interesting - no particular criteria for selection - and noticed some rather
startling differences in magnitude of the type that Elizabeth mentioned. Now
anyone submitting an R or I measure is not really contributing to the
classical TSP database but to a different one which is more related to the
physical nature, or changes in this, of the target star.

Taking this to its conclusion, the main database should include only visual
or pg and the equivalent V measures, whether by CCD or pep. Anything else 
should
be in a separate area or areas. Hopefully this will come in time.

Regards,
Stan

----- Original Message ----- 
From: "Chuck Pullen" <pullenc at gmail.com>
To: <aavso-photometry at mira.aavso.org>
Sent: Wednesday, March 28, 2007 4:10 AM
Subject: Re: [Aavso-photometry] Color Photometry

> Stan - while I fully give you that it is your data to send to
> whomever you want, who sees your data now if it isn't sent to an
> archive?  Who will see it in the future?
>
> I understand your concern, but I doubt anyone does much science with
> the presentations in the Quick View or the light curve generator.
> Anyone who is going to do much will ask for all the data on a given
> object from JD X to JD Y.  Your BVRI data will be there, and obvious
> to them, if that is what they are looking for.
>
> So while our advertising isn't so hot, I wouldn't use that as a
> reason for not contributing to the Int. Data Base.
>
> Chuck Pullen
>
>
> On Mar 27, 2007, at 9:00 AM, aavso-photometry-request at mira.aavso.org
> wrote:
>
>>
>>
>> Today's Topics:
>>
>>    1. Re: color photometry (Stan Walker)
>>
>>
>> ----------------------------------------------------------------------
>>
>> Message: 1
>> Date: Tue, 27 Mar 2007 15:15:09 +1200
>> From: "Stan Walker" <astroman at xtra.co.nz>
>> Subject: Re: [Aavso-photometry] color photometry
>> To: "Michael Koppelman" <lolife at bitstream.net>
>> Cc: AAVSO photometry <aavso-photometry at aavso.org>
>> Message-ID: <001101c7701e$9aaa4b90$345036d2 at your5139538146>
>> Content-Type: text/plain; format=flowed; charset="iso-8859-1";
>> reply-type=original
>>
>> 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.
>>>
>>
>>
>>
>> ------------------------------
>>
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>>
>> End of Aavso-photometry Digest, Vol 40, Issue 33
>> ************************************************
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