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.

Aims. We take advantage of the second data release of the Gaia space mission and the state-of-the-art astrometry delivered from very long baseline interferometry observations to revisit the structure and kinematics of the nearby Taurus star-forming region. Methods. We apply a hierarchical clustering algorithm for partitioning the stars in our sample into groups (i.e., clusters) that are associated with the various molecular clouds of the complex, and derive the distance and spatial velocity of individual stars and their corresponding molecular clouds. Results. We show that the molecular clouds are located at different distances and confirm the existence of important depth effects in this region reported in previous studies. For example, we find that the L 1495 molecular cloud is located at d = 129.9 +0.4 −0.3 pc, while the filamentary structure connected to it (in the plane of the sky) is at d = 160.0 +1.2 −1.2 pc. We report B 215 and L 1558 as the closest (d = 128.5 +1.6 −1.6 pc) and most remote (d = 198.1 +2.5 −2.5 pc) substructures of the complex, respectively. The median inter-cloud distance is 25 pc and the relative motion of the subgroups is on the order of a few km/s. We find no clear evidence for expansion (or contraction) of the Taurus complex, but signs of the potential effects of a global rotation. Finally, we compare the radial velocity of the stars with the velocity of the underlying 13 CO molecular gas and report a mean difference of 0.04 ± 0.12 km/s (with r.m.s. of 0.63 km/s) confirming that the stars and the gas are tightly coupled.

COMMUNICATION 1700334 (1 of 7)

Context. The β Pictoris moving group is one of the most well-known young associations in the solar neighbourhood and several members are known to host circumstellar discs, planets, and comets. Measuring its age precisely is essential to the study of several astrophysical processes, such as planet formation and disc evolution, which are strongly age-dependent. Aims. We aim to determine a precise and accurate dynamical traceback age for the β Pictoris moving group. Methods. Our sample combines the extremely precise Gaia DR2 astrometry with ground-based radial velocities measured in an homogeneous manner. We use an updated version of our algorithm to determine dynamical ages. The new approach takes into account a robust estimate of the spatial and kinematic covariance matrices of the association to improve the sample selection process and to perform the traceback analysis. Results. We estimate a dynamical age of 18.5−2.4+2.0 Myr for the β Pictoris moving group. We investigated the spatial substructure of the association at the time of birth and we propose the existence of a core of stars that is more concentrated. We also provide precise radial velocity measurements for 81 members of β Pic, including ten stars with the first determinations of their radial velocities. Conclusions. Our dynamical traceback age is three times more precise than previous traceback age estimates and, more importantly, for the first time it reconciles the traceback age with the most recent estimates of other dynamical, lithium depletion boundaries and isochronal ages. This has been possible thanks to the excellent astrometric and spectroscopic precisions, the homogeneity of our sample, and the detailed analysis of binaries and membership.

Context. The distribution of member stars in the surroundings of an open cluster (OC) can shed light on the process of its formation, evolution, and dissolution. The analysis of structural parameters of OCs as a function of their age and position in the Galaxy constrains theoretical models of cluster evolution. The Gaia catalog is very appropriate for finding members of OCs at large distance from their centers. Aims. We revisit the membership lists of OCs from the solar vicinity, in particular, by extending these membership lists to the peripheral areas through Gaia EDR3. We then take advantage of these new member lists to study the morphological properties and the mass segregation levels of the clusters. Methods. We used the clustering algorithm HDBSCAN on Gaia parallaxes and proper motions to systematically search for members up to 50 pc from the cluster centers. We fit a King’s function on the radial density profile of these clusters and a Gaussian mixture model (GMM) on their two-dimensional member distribution to study their shape. We also evaluated the degree of mass segregation of the clusters and the correlations of these parameters with the age and Galactic position of the clusters. Results. Our method performs well on 389 clusters out of the 467 clusters we selected, including several recently discovered clusters that were poorly studied until now. We report the detection of vast coronae around almost all the clusters and report the detection of 71 OCs with tidal tails. This multiplies the number of these structures that are identified by more than four. The size of the cores is smaller for old clusters than for young ones on average. Moreover, the overall size of the clusters seems to increase slightly with age, but the fraction of stars in the halo seems to decrease. As expected, the mass segregation is more pronounced in the oldest clusters, but no clear trend with age is evident. Conclusions. OCs are more extended than previously expected, regardless of their age. The decrease in the proportion of stars populating the clusters halos highlights the different cluster evaporation processes and the short timescales they need to affect the clusters. Reported parameters such as cluster sizes or mass segregation levels all depend on cluster ages, but cannot be described as single functions of time.

Free-floating planets (FFPs) are the lightest products of star formation and they carry important information on the initial conditions of the environment in which they were formed. They were first discovered in the 2000s but still few of them have been identified and confirmed due to observational challenges. This is a review of the last advances in the detection of these objects and the understanding of their origin. Several studies indicate that the observed fraction of FFPs outnumbers the prediction of turbulent fragmentation and suggest that many were formed in planetary systems that were later abandoned. The JWST will certainly constitute a new step further in the detection and characterisation of FFPs. To interpret these new observations, precise ages for the nearby star-forming regions in which they were formed will be necessary.

Context. Chamaeleon is the southernmost low-mass star-forming complex within 200 pc from the Sun. Its stellar population has been extensively studied in the past, but the current census of the stellar content is not complete yet and deserves further investigation. Aims. We take advantage of the second data release of the Gaia space mission to expand the census of stars in Chamaeleon and to revisit the properties of the stellar populations associated to the Chamaeleon I (Cha I) and Chamaeleon II (Cha II) dark clouds. Methods. We perform a membership analysis of the sources in the Gaia catalogue over a field of 100 deg2 encompassing the Chamaeleon clouds, and use this new census of cluster members to investigate the 6D structure of the complex. Results. We identify 188 and 41 high-probability members of the stellar populations in Cha I and Cha II, respectively, including 19 and 7 new members. Our sample covers the magnitude range from G = 6 to G = 20 mag in Cha I, and from G = 12 to G = 18 mag in Cha II. We confirm that the northern and southern subgroups of Cha I are located at different distances (191.4−0.8+0.8 pc and 186.7−1.0+1.0 pc), but they exhibit the same space motion within the reported uncertainties. Cha II is located at a distance of 197.5−0.9+1.0 pc and exhibits a space motion that is consistent with Cha I within the admittedly large uncertainties on the spatial velocities of the stars that come from radial velocity data. The median age of the stars derived from the Hertzsprung-Russell diagram and stellar models is about 1−2 Myr, suggesting that they are somewhat younger than previously thought. We do not detect significant age differences between the Chamaeleon subgroups, but we show that Cha II exhibits a higher fraction of disc-bearing stars compared to Cha I. Conclusions. This study provides the most complete sample of cluster members associated to the Chamaeleon clouds that can be produced with Gaia data alone. We use this new census of stars to revisit the 6D structure of this region with unprecedented precision.

Context. Ruprecht 147 is the oldest (2.5 Gyr) open cluster in the solar vicinity (<300 pc), making it an important target for stellar evolution studies and exoplanet searches. Aims. We aim to derive a census of members and the luminosity, mass, and spatial distributions of the cluster. Methods. We used an astro-photometric data set including all available information from the literature together with our own observations. We processed the data with an updated version of an existent membership selection methodology. Results. We identify 259 high-probability candidate members, including 58 previously unreported. All these candidates cover the luminosity interval between G 6 mag and i 21 mag. The cluster luminosity and mass distributions are derived with an unprecedented level of details allowing us to recognize, among other features, the Wielen dip. The mass distribution in the low-mass regime drops sharply at 0.4 M even though our data are sensitive to stellar masses down to 0.1 M , suggesting that most very-low-mass members left the cluster as the result of its dynamical evolution. In addition, the cluster is highly elongated (ellipticity ∼0.5) towards the galactic plane, and mass segregated. Conclusions. Our combined Gaia+DANCe data set allows us to obtain an extended list of cluster candidate members, and to derive luminosity, mass, and projected spatial distributions in the oldest open cluster of the solar vicinity.