[vsnet-chat 5966] Re: Crude USNO B1.0 B1-R1 to B-V transformation

[Brian Skiff <Brian.Skiff@lowell.edu>]

     John's analysis looks fine.  Do remember that USNO-B1.0 B1 and R1 
will be derived from the contemporaneous POSS-I scans only north of about
-33 Dec (i.e. the -30 zone was the southernmost of the original series).
     Within the scatter likely from single-plate photometry (~0.2 mag rms),
the old POSS-I 103a-O plates will have negligible color term to transform
to Johnson B.  The POSS-I 103a-E plates will likewise have very small
color term to get to Cousins R (Johnson R has a redder effective wavelength).
The southern IIIa-J plates (and northern second-epoch plates) are centered
somewhat redward of Johnson B, so there will be a modest color term to get
to B.  The more recent IIIa-F plates should also have a quite small color
term to transform to Cousins R.  Again, with the fairly large scatter
expected, Sloan r' should be very similar to Cousins R.

\Brian

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