[vsnet-chat 5788] Re: [AAVSO-DIS] survey, pixy etc

[Arne Henden <aah@nofs.navy.mil>]

Brian found the Johnson et al. paper containing R,I "standards".
There is also a paper by Moffett and Barnes, and several catalogs
that contain Johnson R,I magnitudes (most notably Lanz).  There
are still a couple of observatories using Johnson filters
(the CAHA 0.8m comes to mind), and many of the SSP-3 photometers
came with Johnson filters.
   Regarding nomenclature, here are my preferences:
      R,I    before ~1990, the default assumption is that these
             are Johnson; after 1990, the default is Cousins.
             To avoid confusion, use one of the following two
             notations instead.
      Rc,Ic  Cousins (or Kron-Cousins)
      Rj,Ij  Johnson
      CR,CI  unfiltered ("clear"), zeropointed onto the Rc,Ic systems
             (the assumption is that you use the bandpass that most
             closely approximates the response of your unfiltered CCD)

Note that such filter system confusions are not restricted to past-century
photometry.  The Sloan Digital Sky Survey has *three* versions of its
filters:  the "standard" system published in AJ; the filters used by
the Photometric Monitor Telescope at Apache Point, and the filters used
by the 2.5m telescope itself.  These are referred to by various permutations
of the filter letters, such as ugriz, u'g'r'i'z', u*g*r*i*z* etc., and
differ by a few hundredths of a magnitude.
Arne

Brian Skiff wrote:
>      I found very recently that there is indeed a paper by Johnson where
> he actually says that the observations define the R,I and redder colors.
> It is:
> 
> 1964BOTT....3..305J
>   JOHNSON H.L.
>   Bol. Obs. Tonantz. Tacub., 3, 305-324 (1964)
>   The colors, bolometric corrections and effective temperature of the bright
>     stars.
> 
> Jean-Claude Mermilliod has a file with the UBVRI part of the data here:
> 
> http://obswww.unige.ch/gcpd/cgi-bin/getStars.cgi?Ref=3&Photo=08
> 
> In the abstract to the paper Johnson states in part:
> 
>      "Data for a total of 256 stars are given in this paper; of these 241 have
> complete observations in U,B,V,R,I,J, and K.....  For the R,I,J,K,L,M, and N
> systems, the data here should be regarded as the standard values for
> additional photometric work."
> 
>      However, one should note the systematic problems with V-R and R-I as
> a function of _Right_Ascension_, with star color, and with reddening for hot
> stars.  This in addition to the large accidental errors (~0.03 to 0.04 per
> star) make it a rather poorly defined system.  See Barry et al 1977
> (1977ApJ...212..462B) for discussion of the large internal errors, also
> Kunkel & Rydgren (1979AJ.....84..633K).  The problems with the RA errors
> was found by Cousins himself (1981MNSSA..40...37C).  Finally, se Taylor's
> more thorough analysis of the problems in 1986ApJS...60..577T.
> 
> \Brian
> 
>

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