Department of Astronomy, Yale University, New Haven CT, USA
"IRRADIANCE OR LUMINOSITY CHANGES?"
Whereas a variation of the solar luminosity, L, will inevitably cause a
similar change of the total solar irradiance, S, the opposite is not true.
In fact, we can explain the bulk of the days to months variations of S
entirely in terms of the passage of active regions across the solar disk. In
this case, L remains essentially unchanged.
For the total irradiance variation observed over the solar cycle, the issue is more uncertain. One view explains this modulation primarily as a combined action of active regions and magnetic network. These components would be superposed to an otherwise unchanging photosphere. The other view suggests that the activity cycle modulation of S is primarily produced by a variation of L (both in terms of R and Teff) caused by structural readjustments of the interior of the Sun induced by a changing magnetic field. I will present evidence in support of this second interpretation, and a model for it. I will also present the S variations over the last 5 centuries implied by our model.