[vsnet-chat 4051] Re: Color terms in visual observing

["Berto Monard" <Lagmonar@csir.co.za>]

I don't think here is much relevance on the topic. 

You cannot compare visual magnitudes with photographic ones. 
In the same way you cannot compare photo-electric V magnitudes with photo-electric B magnitudes. That will even give a larger discrepancy than the comparison of any of those two with visual estimates (not just for red stars..).

Visual light curves ought to ly between the V and B light curves. The precision will be lower (scattering due to different observers).

Regards,

Berto

>>> Stupendous Man <richmond@a188-l009.rit.edu> 02/02/01 04:04PM >>>

  [a previous version of this E-mail message -- with lots of garbage
   characters -- may have accidently been sent to vsnet-chat.  
   If so, I apologize.  MWR ]

  On the topic of visual magnitude estimates and color terms, let
me mention a small demonstration of the size of the effect.
A paper by Jacoby and Pierce, AJ 112, 723 (1996) discusses analysis
of the light curve of SN 1937C.  You can find this paper on-line at 

      http://adsabs.harvard.edu/cgi-bin/nph-bib_query? 
          bibcode=1996AJ....112..723J&db_key=AST&high=3a7abc557128029

  Pages 724-726 of this work address the question of visual measurements
of SN 1937C, and SN 1991T, and their relation to photographic or 
photoelectric measurements.  Figures 1 and 2 show clearly that there
_is_ a strong color term in visual estimates of Type Ia SN.  The magnitude
of the difference, (visual - photoelectric), changes by about 
0.7 magnitudes as the (B-V) color of the SN changes by 1.0 magnitudes.

                                       Michael Richmond

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