Realistic MHD simulations of spots on cool main-sequence stars

by Mayukh Panja
Doctoral thesis
Date of Examination:2020-12-11
Date of issue:2021-08-09
Advisor:Prof. Dr. Sami Solanki
Referee:Prof. Dr. Sami Solanki
Referee:Prof. Dr. Ansgar Reiners
Referee:Dr. Matthias Dieter Rempel
Persistent Address: http://dx.doi.org/10.53846/goediss-8773

 

 

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Abstract

English

Sunspots are cool, dark features on the solar surface consisting of two distinct parts - the inner dark umbra and its surrounding brighter, filamentary penumbra. Strong, nearly vertical magnetic fields found in the umbra locally suppress overturning convective motion while the more inclined fields of the penumbra support the outward Evershed flow. The fine structure of sunspots has been studied in much detail with the help of both ground and space-based telescopes. Our knowledge about starspots, in comparison, is very limited. This is mainly because other stellar surfaces are at best poorly resolved. The fine structure of starspots is still unknown and how similar, or dissimilar, they are to spots on the Sun remains to be answered. In this thesis, I have attempted to make headway into these unsolved astrophysical problems through box-in-a-star realistic radiative magnetohydrodynamic simulations. Further, I synthesized spectral lines from the simulated starspot atmospheres. This allowed me to combine synthetic line profiles of umbrae, penumbrae, and quiet star regions calculated at various viewing angles to create disk integrated line profiles which I used to estimate the effects of spots on stellar radial velocity.
Keywords: sunspots; starspots; stellar physics
 
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