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Spectral Type In Xephem And Tycho2

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Posted by Johannes Gajdosik on January 28, 2001 13:17:32 UTC

It seems to me that the only reason why there
is a spectral type in xephem is to draw star
colors: blue for O,B,A, yellow for F,G,K
and red for M. Notice that there are only 3
different colors.
There is no spectral type in tycho2, but
there is the Johnson color index B-V, which
describes the color of the star, and from which
the spectral type can be derived.

I have found some numbers on the internet:

And use them in my conversion utility:

const char *BvToSpectr(double b_v) {
static char sp[3];
if (b_v

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