Brown dwarfs and magnitude bands

[ajtribick]

Is there any way to get V-magnitudes from J,H,K magnitudes? I'm asking this because of this catalog of brown dwarfs which would be nice to implement in Celestia, but they tabulate JHK rather than V (presumably because most of the brown dwarfs are known through infrared surveys).

[MackTuesday]

Have you considered fitting the values to a blackbody spectrum, and then integrating the curve over the visible frequencies?

[ajtribick]

It's an idea I considered, however for brown dwarfs the spectrum is not very well approximated by a black body at all due to absorption lines, etc.

Whether there is some kind of empirical relationship that can be fit for these objects, I don't know.