Mbol zero point

[cayrel@opdas1....fr (Roger Cayrel)]

Dear Colleague,
In Kyoto, Commissions 25 and 36 of the IAU have appoved the following
definition of Mbol =0
It is the bolometric magnitude of a star radiating

L=3.055x10^28 W

(integrating over all frequencies of the electromagnetic spectrum)

I Allen A.Q. third edition the quoted value is

L = 2.97x10^28 W 
because he used 

Lsun= 3.826x10^33 erg/s

instead of the more accurate value 

Lsun = 3.846x10^33 erg/s

But the relationship

Mbol=4
Sorry ! I am correcting

Mbol =4.75-2.5log(L/Lsun)

is still exact. 

In practice it is the most useful as theoreticians express their bolometric
luminosities as L/Lsun.

The IAU commissions have decided that no reference to Lsun should be
used in the definition of the zero point of bolometric magnitude
but that the numerical value corresponding to a "nominal Sun" 
should be kept for ever.
So the value 3.055x10^28 will not be revised even when the Sun becomes a
giant star!
Best wishes,

Roger Cayrel