[Aavso-photometry] BVRI Program

[arne]

Brad Walter wrote:
>  Arne can you share the standard deviations for your Sonoita measurements of
> VX GEM?
> 
Crud.  You would catch me at that. :)
The standard deviations are available through VSP, if you select
the table option (since the SRO magnitudes are being reported rather
than the CCD chart magnitudes).  Typically they are 0.02-0.04, depending on
magnitude.  These are also quite conservative values.
Arne

> 
> Message: 2
> Date: Thu, 08 Nov 2007 16:35:12 -0500
> From: arne <arne at aavso.org>
> Subject: Re: [Aavso-photometry] BVRI Observing Program
> To: aavso Photometry <aavso-photometry at aavso.org>
> Cc: Keith Graham <kag at core.com>
> Message-ID: <47338110.5040501 at aavso.org>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
> 
> Good question.
> There are some holes in the current VSP/VSD update.  First, all stars with
> magnitudes more than 0.2mag different than their old chart values were not
> uploaded.  Second, all CCD charts, BVRI photometry charts, etc.
> had photometry listed on them that did not get copied into VSD.  This will
> happen during the January load.
> 
> The CCD BVRI program picked 8 stars to follow: S Per, U Ori, VX Gem, DH Dra,
> VX UMa, W Leo, RU Vir, and RR Boo.  Many of the comp stars were bright (some
> of these are bright Miras, after all), and those were filled in using Tycho2
> values during this initial load of the comp star database.  I'd recommend
> using the original BVRI charts and not VSP for these 8 stars until we
> properly populate the database.
> 
> On the other hand, a couple of those fields were observed by me for other
> reasons.  An example is VX Gem.  It is interesting to compare my 3-night
> BVRI calibration at Sonoita with the calibration on the BVRI chart:
> 
> 91, 94 101 and 104 are saturated at SRO, as our goal was accurate photometry
> from 11-15mag
> 
> ID     B       V      Rc      Ic
> 110  12.035  10.990  10.440   9.940 SRO
>       12.043  11.017  10.466   9.956 CCD
> 
> 115  12.172  11.509  11.134  10.780 SRO
>       12.155  11.509  11.138  10.776 CCD
> 
> 122  12.899  12.219  11.848  11.516 SRO
>       12.893  12.235  11.867  11.503 CCD
> 
> 127  13.266  12.715  12.384  12.079 SRO
>       13.284  12.746  12.412  12.095 CCD
> 
> 128  13.898  12.826  12.257  11.735 SRO
>       13.928  12.859  12.284  11.669 CCD
> 
> 139  14.428  13.940  13.624  13.324 SRO
>       14.478  13.989  13.673  13.196 CCD
> 
> You can see that, in general, the agreement is quite good.  As the stars get
> fainter, there appears to be a systematic offset for BVR, and a very obvious
> difference at Ic.  Who is right?  You might observe yourself and see which
> set of magnitudes comes closest to your own transformed values, using
> perhaps the 115 star as the zeropoint.
> I'd like to hear your answers!  The Howell, Mattei and Benson paper (1993,
> JAAVSO 22, 2) indicated that they had two clear nights and two partly cloudy
> nights, and that they covered 19 fields (of which
> 8 were used to create the BVRI program).  I don't know if the other
> 11 were finally processed.  They indicate that they did 3 measures on one
> night for each of the fields, and did not give the standard deviation of the
> measures in the paper.
> Arne
> 
> 
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