On the zero point constant of the bolometric correction scale

Abstract

Arbitrariness attributed to the zero-point constant of the V-band bolometric corrections (BCV) and its relation to ‘bolometric magnitude of a star ought to be brighter than its visual magnitude’ and ‘bolometric corrections must always be negative’ was investigated. The falsehood of the second assertion became noticeable to us after IAU 2015 General Assembly Resolution B2, where the zero-point constant of bolometric magnitude scale was decided to have a definite value CBol(W) = 71.197 425 ... . Since the zero-point constant of the BCV scale could be written as C2 = CBol − CV, where CV is the zero-point constant of the visual magnitudes in the basic definition BCV = MBol − MV = mbol − mV, and CBol > CV, the zero-point constant (C2) of the BCV scale cannot be arbitrary anymore; rather, it must be a definite positive number obtained from the two definite positive numbers. The two conditions C2 > 0 and 0 < BCV < C2 are also sufficient for LV < L, a similar case to negative BCV numbers, which means that ‘bolometric corrections are not always negative’. In sum it becomes apparent that the first assertion is misleading causing one to understand bolometric corrections must always be negative, which is not necessarily true.