Speaker
Description
Understanding the stellar magnetic activity phenomena (such as spots, faculae, plages, flares) is very important for different fields of stellar and exoplanetary astrophysics, and for planetary climate studies. Studying magnetic activity on stars of different stellar parameters and activity levels provides an opportunity for detailed tests of stellar/solar dynamo models. From the exoplanetary side, it is well known that stellar active regions combined with the stellar rotation can induce signals in high-precision photometric and radial velocity (RV) observations. These activity-induced signals may lead to masking or mimicking an exoplanet signal. Moreover, these signals are one of the main limitations for the detection and the precise characterization of low mass/small radii planets, which is the major goal of future instruments.
Late-type stars commonly show flaring activities - unpredictable releases of energy. It is demonstrated that strong flares can significantly affect the properties (profile, flux, wavelength) of strong lines that appear in emission in the chromospheres. These energetic flares can also produce a significant,measurable RV shift for M dwarf stars. As a consequence, the spectra affected by flares are usually discarded in the RV observations. The number of discarded spectra can be significant for active M dwarfs, which is an obvious issue. Another, perhaps more important, issue related to flaring activity in exoplanet research is that the impact of weak flares on RV measurements is not quantified and is typically ignored. This, obviously, increases the level of ‘noise’ in the RV time-series.
The large number of ESPRESSO ultra-high quality observations should allow us to study the impact of flares (of different energies) on the line-profile variations even for relatively weak lines. The aim of this project is to first identify the signatures of flares in spectral lines and then to study their impact on the RV shift measured from lines with different properties (intensity, excitation potential etc).
