Stellar pulsation and granulation as noise sources in exoplanet transit spectroscopy in the ARIEL space mission

Stellar variability from pulsations and granulation presents a source of correlated noise that can impact the accuracy and precision of multi-band photometric transit observations of exoplanets. This can potentially cause biased measurements in the transmission or emission spectrum or underestimation of the final error bars on the spectrum. ARIEL is a future space telescope and instrument designed to perform a transit spectroscopic survey of a large sample of exoplanets. In this paper we perform simulations to assess the impact of stellar variability arising from pulsations and granulation on ARIEL observations of GJ 1214b and HD 209458b. We take into account the correlated nature of stellar noise, quantify it, and compare it to photon noise. In the range 1.95-7.8 \textmu m, stellar pulsation and granulation noise has insignificant impact compared to photon noise for both targets. In the visual range the contribution increases significantly but remains small in absolute terms and will have minimal impact on the transmission spectra of the targets studied. The impact of pulsation and granulation will be greatest for planets with low scale height atmospheres and long transit times around bright stars.