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How much of a star can be covered in starspots?

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Many stars, including the Sun, periodically display starspots, cooler areas of the surface associated with higher local concentrations of the stellar magnetic field. They can sometimes be a couple thousand Kelvin cooler than the surrounding regions of the stellar photosphere. My reasoning is that because surface flux from a star is proportional to $T^4$, with $T$ the photospheric temperature, if a large portion of the star was covered by starspots, we could see a significant reduction in flux, and I'm trying to use such a star in my universe.

The thing is, I don't know just how dramatic the effect could be. I can't say that I know much about starspots, and while Wikipedia claims that up to 30% of the surface of a star can be covered,

  • The claim is not backed up by a citation.
  • It's not clear if that's the theoretical limit or just the maximum value found in observations.
  • Wikipedia doesn't say in what type of stars this dramatic coverage is seen.
  • Another site claims a limit of at least 66%.

Therefore, what is the upper limit for the amount of a star's surface that can be covered by starspots at a given time? I'm hoping for main sequence stars of between $0.5M_{\odot}$ and $3M_{\odot}$, but I would be okay if we need to go outside those boundaries to cover a significant portion of the surface.

As a note, when I say "starspot", I'm looking for a region roughly $\sim1000\text{ K}$ to $2000\text{ K}$ cooler than the normal stellar photosphere outside the period of starspot activity. In other words, the spot is not necessarily substantially cooler than the regions around it at a given time, if it happens to be in a large region of magnetic activity, but it's cooler than the same location would be if there was no magnetic activity at all.

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