Aims. Stellar activity produced by spots and plages affects the radial velocity (RV) signatures. Because even low activity stars would produce such a signal, it is crucial to determine how it influences our ability to detect small planetary signals such as those produced by Earth-mass planets in the habitable zone (HZ). In a recent paper, we investigated the impact of sunlike spots. We aim here to investigate the additional impact of plages. Methods. We used the spot and plage properties over a solar cycle to derive the RV that would be observed if the Sun was seen edgeon. The RV signal comes from the photometric contribution of spots and plages and from the attenuation of the convective blueshift in plages. We analyzed the properties of the RV signal at different activity levels and compared it with commonly used activity indicators such as photometry and the Ca index. We also compared it with the signal that would be produced by an Earth-mass planet in the HZ. Results. We find that the photometric contributions of spots and plages to the RV signal partially balance each other out, so that the residual signal is comparable to the spot signal. However, the plage contribution due to the convective blueshift attenuation dominates the total signal, with an amplitude over the solar cycle of about 8-10 m/s. Short-term variations are also significantly greater than the spot and plage photometric contribution. This contribution is very strongly correlated with the Ca index on the long term, which may be a way to distinguish between stellar activity and a planet. Conclusions. Providing a very good temporal sampling and signal-to-noise ratio, the photometric contribution of plages and spots should not prevent detection of Earth-mass planets in the HZ. However, the convection contribution makes such a direct detection impossible, unless its effect can be corrected for by methods that still need to be found. We show that it is possible to identify the convection contribution if the sensitivity is good enough, for example, by using activity indicators.

Context. Stellar activity induced by active structures such as stellar spots and faculae is known to have a strong impact on the radial velocity (RV) time series. It is therefore a strong limitation to the detection of small planetary RV signals, such as that of an Earth-mass planet in the habitable zone of a solar-like star. In a series of previous papers, we have studied the detectability of such planets around the Sun observed as a star in an edge-on configuration. For this purpose, we computed the RV, photometric and astrometric variations induced by solar magnetic activity, using all active structures observed over one entire cycle. Aims. Our goal is to perform similar studies on stars with different physical and geometrical properties. As a first step, we focus on Sun-like stars seen with various inclinations, and on estimating detection capabilities with future instruments. Methods. To do so, we first parameterize the solar active structures with the most realistic pattern so as to obtain results consistent with the observed ones. We simulate the growth, evolution and decay of solar magnetic features (spots, faculae and network), using parameters and empiric laws derived from solar observations and literature. We generate the corresponding structure lists over a full solar cycle. We then build the resulting spectra and deduce the RV and photometric variations, first in the case of a sun seen edge-on and then with various inclinations. The produced RV signal takes into account the photometric contribution of spots and faculae as well as the attenuation of the convective blueshift in faculae. We then use these patterns to study solar-like stars with various inclinations. Results. The comparison between our simulated activity pattern and the observed pattern validates our model. We show that the inclination of the stellar rotation axis has a significant impact on the photometric and RV time series. Radial velocity long-term amplitudes and short-term jitters are significantly reduced when going from edge-on to pole-on configurations. Assuming spin-orbit alignment, the best configuration for planet detection is an inclined star (i 45 • ).

Context. Stellar variability, at a variety of timescales, can strongly affect the ability to detect exoplanets, in particular when using radial velocity (RV) techniques. Accurately characterized solar variations are precious in this context to study the impact of stellar variations on planet detectability. Here we focus on the impact of small timescale variability. Aims. The objective of this paper is to model realistic RV time series due to granulation and supergranulation and to study in greater detail the impact of granulation and supergranulation on RV times series in the solar case. Methods. We have simulated a collection of granules and supergranules evolving in time to reproduce solar photometric and RV time series. Synthetic time series are built over the full hemisphere over one solar cycle. Results. We obtain intensity and RV rms due to solar granulation of respectively 0.8 m/s and 67 ppm, with a strong variability at timescales up to more than 1 h. The rms RV due to supergranulation is between 0.28 and 1.12 m/s. Conclusions. To minimize the effect of granulation, the best strategy is to split the observing time during the night into several periods instead of observing over a consecutive duration. However, the best strategy depends on the precise nature of the signal. The granulation RV remains large after even an hour of smoothing (about 0.4 m/s) while the supergranulation signal cannot be significantly reduced on such timescales: a reduction of a factor 2 in rms RV can for example be obtained over 7 nights (with 26 min/night). The activity RV variability dominates at larger timescales. Detection limits can easily be as high as 1 M Earth or above for periods of tens or hundreds of days. The impact on detection limits is therefore important and may prevent the detection of 1 M Earth planets for long orbital periods, while the impact is much smaller at small orbital periods. These results do not take the presence of pulsations into account.