Today Katie Breivik (Flatiron) asked me some technical questions about the bolometric correction. It's related to the difference between a relative magnitude in a bandpass and the relative magnitude you would get if you were using a very (infinitely) broad-band bolometer. Relative magnitudes are good things (AB magnitudes, in contrast, are bad things, but that's for another post): They are relative fluxes between the target and a standard (usually Vega). If your target is hotter than Vega, and you choose a very blue bandpass, the bandpass magnitude of the star will be smaller (relatively brighter) than the bolometric magnitude. If you choose a very red bandpass, the bandpass magnitude will be larger (relatively fainter) than the bolometric magnitude. That's all very confusing.
And bolometric is a horrible concept, since most contemporary detectors are photon-counting and not bolometric (and yes, that matters: the infinitely-wide filter on a photon-counting device gives a different relative magnitude than the infinitely-wide filter on a bolometer). I referred Breivik to this horrifying paper for unpleasant details.
No comments:
Post a Comment