The interior compositions of small rocky exoplanets cannot be observed directly but are expected to relate to the composition of the host star. Adibekyan et al. analyzed a sample of rocky exoplanets, inferring the planets' iron fractions by combining their masses and radii with an interior structure model. The iron fractions of the host stars were calculated from stellar elemental abundances. The two iron fractions, that of the planets and that of the stars, correlate with each other, but the slope is steeper than 1, indicating that planet formation processes modify the compositions of rocky planets.-KTS Stars and planets both form by accreting material from a surrounding disk. Because they grow from the same material, theory predicts that there should be a relationship between their compositions. In this study, we search for a compositional link between rocky exoplanets and their host stars. We estimate the iron-mass fraction of rocky exoplanets from their masses and radii and compare it with the compositions of their host stars, which we assume reflect the compositions of the protoplanetary disks. We find a correlation (but not a 1:1 relationship) between these two quantities, with a slope of >4, which we interpret as being attributable to planet formation processes. Super-Earths and super-Mercuries appear to be distinct populations with differing compositions, implying differences in their formation processes.

Context. Evidence exists in the 125-Myr Pleiades cluster, and more recently in the 5-Myr NGC 2264 cluster, to show that rotation plays a key role in lithium (Li) depletion processes among low-mass stars. Fast rotators appear to be less Li-depleted than equal-mass slow rotators. Aims. We intend to explore the existence of a Li depletion-rotation connection among the β Pictoris members at an age of about 24 Myr, and to use this correlation either to confirm or to improve age estimates based on the lithium depletion boundary (LDB) modeling. Methods. We photometrically monitored all the known members of the β Pictoris association with at least one lithium equivalent width (Li EW) measurement from the literature. Results. We measured the rotation periods of 30 members for the first time and retrieved the rotation periods for another 36 members from the literature, building a catalogue of 66 members with a measured rotation period and Li EW. Conclusions. We find that in the 0.3 < M < 0.8 M range, there is a strong correlation between rotation and Li EW. For higher mass stars, no significant correlation is found. For very low-mass stars in the Li depletion onset, at about 0.1 M , there are too few data to infer a significant correlation. The observed Li EWs are compared with those predicted by the Dartmouth stellar evolutionary models that incorporate the effects of magnetic fields. After decorrelating the Li EW from the rotation period, we find that the hot side of the LDB is well fitted by Li EW values that correspond to an age of 25 ± 3 Myr, which is in good agreement with independent estimates from the literature.