[vsnet-chat 447] Re: SS Cyg: comparison between sequences

[Taichi Kato <tkato>]

Bruce Sumner wrote:

> Since Johnson V is derived from VT and BT, the assumption that Johnson V
> and VT share the same error would not be far from the truth. In
> actual fact BT error should also be incorporated with VT error to
> obtain a formal Johnson V error.

    Considering the Tycho passbands, both of which lie shortward to Johnson V,
I suspect V_J may have been calculated something like V_T - k(B_T-V_T), where
k may be large (near 1?).  If the errors given for V_T and (B-V) are
independent, I may assume V_err as sqrt(V_T_err^2 + (B-V)_err^2).
Am I correct?  Considering the B-bagnitudes for SS Cyg comparison stars
are reoughly close to the ground-based B, the error in V may be more
affected by the error in B-V, rather than by the original V_T.  So simply
adopting V_T_err may be misleading for these comparison purposes.

Regards,
Taichi Kato

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