Kavli Affiliate: Robert Cameron
| First 5 Authors: Mayukh Panja, Robert Cameron, Sami K. Solanki, ,
| Summary:
There are no direct spatially resolved observations of spots on stars other
than the Sun and starspot properties are inferred indirectly through
lightcurves and spectropolarimetric data. We present the first self-consistent
3D radiative MHD computations of starspots on G2V, K0V and M0V stars, which
will help to better understand observations of activity, variability and
magnetic fields in late-type main-sequence stars. We used the MURaM code, which
has been extensively used to compute "realistic" sunspots, for our simulations.
We aim to study how fundamental starspot properties such as intensity contrast,
temperature and magnetic field strength vary with spectral type. We first
simulated in 2D, multiple spots of each spectral type to find out appropriate
initial conditions for our 3D runs. We find that with increasing stellar
effective temperature, there is an increase in the temperature difference
between the umbra of the spot and its surrounding photosphere, from 350K on the
M0V star to 1400K on the G2V star. This trend in our simulated starspots is
consistent with observations. The magnetic field strengths of all the starspot
umbrae are in the 3-4.5 kG range. The G2V and K0V umbrae have comparable
magnetic field strengths around 3.5 kG, while the M0V umbra has a relatively
higher field strength around 4 kG. We discuss the physical reasons behind both
these trends. All of the three starspots develop penumbral filament-like
structures with Evershed flows. The average Evershed flow speed drops from 1.32
km s$^{-1}$ in the G2V penumbra to 0.6 km s$^{-1}$ in the M0V penumbra.
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