[vsnet-chat 5969] Re: Crude USNO B1.0 B1-R1 to B-V transformation

[Michael Linnolt <linnolt@hawaii.edu>]

On Mon, 10 Feb 2003, Taichi Kato wrote:

> USNO B1.0 is newly photometrically calibrated with respect to Tycho2
> BT and VT photometry.
>
> A linear fit gave B-V = 0.235 + 0.411(B1-R1) with correlation
> coefficient, R^2, of 0.59.
>
> Adopting a zero intercept gave B-V = 0.556(B1-R1) with a correlation
> coefficient, R^2, of 0.50.  (The white line in the graph).
>
> Personally, I feel this difference in fit is sufficiently small to
> feel happy about adopting the latter, considering the large scatter
> in any case.

This was a worthwhile effort, but to put things into perspective, consider
the analogous transformation from Tycho2 (Bt-Vt) to B-V [Bessell, PASP,112
(2000)]. A linear fit gives B-V = 0.83443(Bt-Vt) + .02 with R^2 = 0.96285
!!

Looking at that regression line is Ok, but not so good even at 0.96285, so
I can imagine how poor it must be for the USNO-B1 at 0.59...

Mike Linnolt (LMK)

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