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.

 

[pmacias]

The sign convention of bolometric correction is a standardized way of representing the difference between a star's visual magnitude and its bolometric magnitude. This convention is based on the assumption that a star's visual magnitude is a good representation of its total luminosity, which is not always the case. Therefore, a bolometric correction is applied to adjust for the missing radiation outside the visual range.

In general, the bolometric correction is negative, meaning that a star's true luminosity is greater than its visual magnitude. This is because stars emit a significant amount of energy in the infrared and ultraviolet regions, which are not accounted for in the visual magnitude. However, there are cases where a star's bolometric correction is positive, meaning that its true luminosity is lower than its visual magnitude. This can happen for stars that emit less energy in the infrared and ultraviolet regions, such as white dwarfs.

The sign of the bolometric correction can vary for different stars, depending on their spectral type and temperature. It is not a fixed value and can change as a star evolves. It is important to note that the bolometric correction is not a measure of a star's brightness, but rather a correction factor to accurately determine its true luminosity.

If you are seeing stars with positive bolometric corrections, it could be due to various factors such as measurement errors, variability in a star's luminosity, or the specific characteristics of the star itself. It is always important to consider the spectral type and temperature of a star when interpreting its bolometric correction.

I hope this helps clarify the concept of bolometric correction. If you have further questions or concerns, please do not hesitate to reach out for more input and discussion.