How much of a star can be covered in starspots?
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.
0 answers
0 comment threads