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 .