Abstract. We present the results of a 6.4 square degrees imaging survey of the Pleiades cluster in the I and Z-bands. The survey extends up to 3 degrees from the cluster center and is 90% complete down to I 22. It covers a mass range from 0.03 M to 0.48 M and yields 40 brown dwarf candidates (BDCs) of which 29 are new. The spatial distribution of BDCs is fitted by a King profile in order to estimate the cluster substellar core radius. The Pleiades mass function is then derived accross the stellar-substellar boundary and we find that, between 0.03 M and 0.48 M , it is well represented by a single power-law, dN/dM ∝ M −α , with an index α = 0.60 ± 0.11. Over a larger mass domain, however, from 0.03 M to 10 M , the mass function is better fitted by a log-normal function. We estimate that brown dwarfs represent about 25% of the cluster population which nevertheless makes up less than 1.5% of the cluster mass. The early dynamical evolution of the cluster appears to have had little effect on its present mass distribution at an age of 120 Myr. Comparison between the Pleiades mass function and the Galactic field mass function suggests that apparent differences may be mostly due to unresolved binary systems.

We report on the results of an i‐band time‐series photometric survey of NGC 2516 using the Cerro Tololo Inter‐American Observatory (CTIO) 4‐m Blanco telescope and 8k Mosaic‐II detector, achieving better than 1 per cent photometric precision per data point over 15 ≲i≲ 19. Candidate cluster members were selected from a V versus V−I colour–magnitude diagram over 16 < V < 26 (covering masses from 0.7 M⊙ down to below the brown dwarf limit), finding 1685 candidates, of which we expect ∼1000 to be real cluster members, taking into account contamination from the field (which is most severe at the extremes of our mass range). Searching for periodic variations in these gave 362 detections over the mass range 0.15 ≲M/M⊙≲ 0.7. The rotation period distributions were found to show a remarkable morphology as a function of mass, with the fastest rotators bounded by P > 0.25 d, and the slowest rotators for M≲ 0.5 M⊙ bounded by a line of P∝M3, with those for M≳ 0.5 M⊙ following a flatter relation closer to P∼ constant. Models of the rotational evolution were investigated, finding that the evolution of the fastest rotators was well reproduced by a conventional solid body model with a mass‐dependent saturation velocity, whereas core–envelope decoupling was needed to reproduce the evolution of the slowest rotators. None of our models were able to simultaneously reproduce the behaviour of both populations.

Aims. We conducted a search for brown dwarfs (BDs) and very low mass (VLM) stars in the 625 Myr-old Hyades cluster in order to derive the cluster's mass function across the stellar-substellar boundary. Methods. We performed a deep (I = 23, z = 22.5) photometric survey over 16 deg 2 around the cluster center and followed up with K-band photometry to measure the proper motion of candidate members and with optical and near-IR spectroscopy of probable BD and VLM members. Results. We report the discovery of the first 2 BDs in the Hyades cluster. The 2 objects have a spectral type early-T and their optical and near-IR photometry as well as their proper motion are consistent with them being cluster members. According to models, their mass is 50 Jupiter masses at an age of 625 Myr. We also report the discovery of 3 new very low mass stellar members of the cluster and confirm the membership of 16 others. We combine these results with a list of previously known cluster members to build the presentday mass function (PDMF) of the Hyades cluster from 50 Jupiter masses to 3 M . We find the Hyades PDMF to be strongly deficient in very low mass objects and BDs compared to the IMF of younger open clusters such as the Pleiades. We interpret this deficiency as the result of dynamical evolution over the past few 100 Myr, i.e., the preferential evaporation of low mass cluster members due to weak gravitational encounters. Conclusions. We thus estimate that the Hyades cluster currently hosts about 10−15 BDs, while its initial substellar population may have amounted to up to 150−200 members.

Context. The DANCe survey provides photometric and astrometric (position and proper motion) measurements for approximately 2 million unique sources in a region encompassing ∼80 deg 2 centered on the Pleiades cluster. Aims. We aim at deriving a complete census of the Pleiades and measure the mass and luminosity functions of the cluster. Methods. Using the probabilistic selection method previously described, we identified high probability members in the DANCe (i ≥ 14 mag) and Tycho-2 (V 12 mag) catalogues and studied the properties of the cluster over the corresponding luminosity range. Results. We find a total of 2109 high-probability members, of which 812 are new, making it the most extensive and complete census of the cluster to date. The luminosity and mass functions of the cluster are computed from the most massive members down to ∼0.025 M . The size, sensitivity, and quality of the sample result in the most precise luminosity and mass functions observed to date for a cluster. Conclusions. Our census supersedes previous studies of the Pleiades cluster populations, in terms of both sensitivity and accuracy.