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If one sets both the bolometric and visual luminosity of the Sun to 1 (and use a linear scale), can a star then have a higher visual than bolometric luminosity?

It makes sense that this will not be the case for most stars, as smaller stars will tend to radiate more of their energy as infrared, while larger go more into the ultraviolet. That is, this is inherently linked to what wavelengths the human eye has evolved sensitivity for. But are there exceptions? If there are, I would think they have parameters very close to the sun.

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  • $\begingroup$ The luminosity through any filter, or limited wavelength range, can ever be only a fraction of the total luminosity. So no. $\endgroup$ – AtmosphericPrisonEscape Jan 26 at 20:04
  • $\begingroup$ @AtmosphericPrisonEscape This is for normalised values, so the filtered wavelength range's fraction of sunlight is set to 1. $\endgroup$ – SE - stop firing the good guys Jan 26 at 21:23
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    $\begingroup$ So basically you're asking "Can a star emit a larger fraction of its total light in the visual that the Sun does"? The answer would depend on your exact definition of the V filter (i.e. width, central wavelength, and shape). Or maybe you're not interested in astronomical filters, but in the response function of the cones of the eye. I suppose the answer is "Yes, but the Sun is pretty close to maximal value in the visual". But we have probably evolved to maximal response of sunlight through the atmosphere, which is slightly more yellow than the Sun's intrinsic color. $\endgroup$ – pela Jan 27 at 10:31
  • $\begingroup$ @pela Exactly. Your way of putting it is much clearer, so I will edit the title. $\endgroup$ – SE - stop firing the good guys Jan 27 at 11:12
  • $\begingroup$ It is also worth noting that blackbody spectra at higher temperature have more power at all frequencies than blackbodies of a lower temperature, so the two ways for the answer to the question to be yes would be (1) better centred in the visible light range, or (2) having enough absorption to tweak the spectrum. Both cases sound like they would have to be very close to the solar spectrum unless there is a way of getting really wild absorption, which seems unlikely. $\endgroup$ – Anders Sandberg Jan 27 at 11:25
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Surely this is exactly what the V-band bolometric correction assesses. The numerically larger the bolometric correction, the more of a star's flux (as a fraction) is in the V-band.

The Sun's bolometric correction is about -0.06 to -0.11 mag, depending on which sources you look at. Cool stars and hot stars have numerically smaller BCs and emit a bigger fraction of their flux outside the V band.

Some sources put the BCs of A5-G0 stars as very slightly larger than the Sun's, by up to 0.1 mag (e.g. Pecaut & Mamajek 2013).

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