temperatureFromColorIndex

Effective temperature from the B−V color index (Ballesteros 2012).

Derived by treating the star as a blackbody seen through the two Johnson filters, so it needs no calibration table and it is monotonic — which matters more here than the last hundred kelvin, because it is applied to 6,675 stars whose classifications came from a dozen different observers.

Outside roughly −0.3 < B−V < 2.0 it stops being meaningful, so the input is clamped rather than extrapolated: an unclamped B−V of 2.5 turns the denominator negative and returns a negative temperature.

colorIndexnumber

Undocumented