%0 Generic
%A Sadegi, Sepidehsadat
%C Heidelberg
%D 2023
%F heidok:34072
%R 10.11588/heidok.00034072
%T Investigating the Activity of M Dwarfs: Spectroscopic, Photometric, and Modelling Analyses
%U https://archiv.ub.uni-heidelberg.de/volltextserver/34072/
%X Stellar activity, characterised by various phenomena such as active regions, flares, coronal mass ejections (CME), etc., can be observed in low-mass stars, such as M-dwarfs. Understanding the activity of M-dwarfs is of paramount importance due to their suitability as hosts for exoplanets, including potentially habitable ones. By comprehending the activity of these stars, we not only enhance the accuracy of exoplanet detection but also gain crucial insights into the habitability of these associated exoplanets. Furthermore, studying activity in low-mass stars provides invaluable knowledge about their internal structure and sheds light on the dynamo processes that generate their magnetic fields. The primary objective of this PhD dissertation is to examine the impact of stellar activity on high-precision spectroscopic and photometric data. In pursuit of this goal, I utilised data from two highly successful exoplanet surveys, namely CARMENES and TESS.    For the first project, a sample of 58 highly active M dwarfs was carefully selected from the CARMENES survey. The aim was to examine the effect of active regions on the radial velocity (RV) measurements in these stars, using the chromatic index (CRX) as a robust parameter capable of capturing the wavelength-dependent RV signatures. The first part of this research focused on assessing the significance of the CRX-RV correlation in these stars, and its potential relationship with key stellar parameters such as mass, rotation period, v sin i, and others. In the second part, the investigation delved into the identification and analysis of periodic RV signals associated with the rotation period (or its harmonics) across the échelle orders of the visible-light (VIS) and near-infrared (NIR) channels of the CARMENES spectrograph.    The second project focused on studying the TESS light curves of the same group of stars, if available, to explore the potential correlation between their flare properties, stellar parameters, and chromospheric activity indices obtained from CARMENES. Given the well-established association between sunspots and flares, it was important to investigate whether a similar relationship exists among these magnetically connected phenomena on other stars. To achieve this, a semi-automated flare detection algorithm was developed to extract key flare characteristics such as amplitude, equivalent duration, and bolometric energy. To investigate the distribution of flares emitted at different energy levels, flare frequency diagrams (FFDs) were generated and parameterised to facilitate the observation of potential relationships.    The final project involved a comprehensive case study that focused on the detailed modelling of the stellar surface of V388 Cas. This was achieved by utilising high-resolution spectra obtained from CARMENES in conjunction with simultaneous TESS photometry. To accomplish this, we employed the powerful modelling tool, StarSim, to effectively simulate a rotating photosphere with spotted regions. The first step involved using the inverse method to retrieve the active regions of the star based on the simultaneous observations. Subsequently, we predicted the RV values across different wavelength ranges, matching the echelle spectrographs’ orders, and compared them to the observed RV values. This comparison allowed us to identify wavelength regions that were more susceptible to spot-induced signals in the absence of atmospheric and instrumental noise. In addition to this analysis, the TESS observations of V388 Cas were leveraged to conduct a study on the evolution of flares. Furthermore, we explored the possibility of a CME occurrence on the star by examining a blue asymmetry in the chromospheric lines of a spectroscopic observation taken 12 hours after a superflare event.