sign convention of bolometric correction

[phenolic]

Okay I realize that stars emit at least some radiation outside the visual range but I have seen stars with positive BC when I thought that most values are negative due to the radiant flux over all wavelengths being greater than its flux over a certain wavelength. Is the sign of the BC the same for any star? I think I am getting lost somewhere...any input? Thanks

[nicksauce]

Not an expert on the subject, but I found this: http://www.encyclopedia.com/doc/1O80-bolometriccorrection.html

The difference between the visual and bolometric magnitudes of an object. Two zero-points are in use, which differ by 0.07 mag. One defines the Sun to have zero bolometric correction. The other has its zero-point set so that bolometric corrections for all stars are positive; this is because other stars emit more energy than the Sun at non-visual wavelengths, either in the ultraviolet for hotter stars or the infrared for cooler stars. Confusingly, some authorities define bolometric correction as bolometric magnitude minus visual magnitude, which makes all values negative.

[phenolic]

Okay..the othermore straightforward question why is the bolometric correction always positive? Wouldn't the bolometric correction be negative since the bolometric magnitude is smaller than the visual magnitude

[nicksauce]

Well it just all depends on what sign convention people are using. And... it seems like different people use different things. For example, wikipedia uses BC = Mb - Mv, whereas scienceworld.wolfram.com uses BC = Mv - Mb. I don't know what the standard is generally in astronomy.