Stellar granulation generates fluctuations in photometric and spectroscopic data whose properties depend on the stellar type, composition and evolutionary state. Characterizing granulation is key for understanding stellar atmospheres and detecting planets. We aim at detecting the signatures of stellar granulation, linking spectroscopic and photometric signatures of convection for main-sequence stars, and testing predictions from 3D hydrodynamic models. For the first time, we observed two bright stars (Teff=5833K and 6205K) with high-precision observations taken simultaneously with CHEOPS and ESPRESSO. We analyzed the properties of the stellar granulation signal in each individual data set. We compared them to Kepler observations and 3D hydrodynamic models. While isolating the granulation-induced changes by attenuating/filtering the p-mode oscillation signals, we studied the relationship between photometric and spectroscopic observables. The signature of stellar granulation is detected and precisely characterized for the hotter F star in the CHEOPS and ESPRESSO observations. For the cooler G star, we obtain a clear detection in the CHEOPS dataset only. The TESS observations are blind to this stellar signal. Based on CHEOPS observations, we show that the inferred properties of stellar granulation are in agreement with both Kepler observations and hydrodynamic models. Comparing their periodograms, we observe a strong link between spectroscopic and photometric observables. Correlations of this stellar signal in the time domain (flux versus radial velocities) and with specific spectroscopic observables (shape of the cross-correlation functions) are however difficult to isolate due to signal-to-noise dependent variations. In the context of the upcoming PLATO mission and the extreme precision radial velocity surveys, a thorough understanding of the properties of the stellar granulation signal is needed. The CHEOPS and ESPRESSO observations pave the way for detailed analyses of this stellar process.

Cone search capability for table J/A+A/670/A24/tablef1 (Stellar and flicker characteristics of the targets)