| Name: | Sowmya Krishnamurthy |
| Affiliation: | Max Planck Institute for Solar System Research |
| Conference ID : | ASI2024_274 |
| Title : | Starspot contribution to stellar Ca II H & K emission: lessons from sunspots |
| Authors : | K. Sowmya (1), A. I. Shapiro (1), L. H. M. Rouppe van der Voort (2,3), N. A. Krivova (1), S. K. Solanki (1) |
| Authors Affiliation: | 1 Max Planck Institute for Solar System Research
2 Institute of Theoretical Astrophysics, University of Oslo
3 Rosseland Centre for Solar Physics, University of Oslo |
| Mode of Presentation: | Oral |
| Abstract Category : | Stars, Interstellar Medium, and Astrochemistry in Milky Way |
| Abstract : | Ca II H & K emission, commonly characterized via the S-index, is sensitive to stellar magnetic activity. Even though this emission is routinely used as a proxy of stellar magnetic activity, its sources are not yet fully understood. Due to the absence of any information on the influence of spots on the S-index, the empirical and physics-based models assume faculae/plage to be the main source of Ca II emissions and thus neglect the contribution from spots. While this is a good approximation for old less-active stars such as the Sun, for young active stars with large surface coverages by spots, the role played by spots might become significant.
We use high quality sunspot observations in the Ca II H line from the Swedish Solar Telescope to determine the Ca II flux from chromospheres of sunspots. We find that spots are brighter than the surrounding quiet regions in the chromosphere. Using the sunspot flux computed from observations in our physics-based model which also accounts for the effect of faculae, we compute S-index for four solar activity cycles. We find that sunspots lead to an increase in the S-index, even though this increase is quite small to have a significant impact on the observed Ca II emission of the Sun. However, by considering stars which are more active than the Sun, we show that with increasing activity and hence spot area coverages, S-index increases strongly. This suggests that Ca II emissions of active stars might have a significant contribution from spots. |
