A proper motion study of the Lupus clouds using Virtual Observatory tools

Context. The Lupus dark cloud complex is a well-known, nearby low-mass star-forming region, probably associated with the Gould Belt. In recent years, the number of stellar and substellar Lupus candidate members has been remarkably increased thanks to the Cores to Disks (c2d) Spitzer Legacy Program and other studies. However, most of these newly discovered objects still lack confirmation that they belong to the dark clouds. Aims. By using available kinematical information, we test the membership of the new Lupus candidate members proposed by the c2d program and by a complementary optical survey. We also investigate the relationship between the proper motions and other properties of the objects, in order to get some clues about their formation and early evolution. Methods. We compiled a list of members and possible members of Lupus 1, 3, and 4, together with all available information on their spectral types, disks, and physical parameters. Using Virtual Observatory tools, we cross-matched this list with the available astrometric catalogues to get proper motions for our objects. Our final sample contains sources with magnitudes I < 16 mag and estimated masses greater than or similar to 0.1 M-circle dot. Results. According to the kinematic information, our sources can be divided into two main groups. The first one contains sources with higher proper motions in agreement with other Gould Belt populations and with spatial distribution, optical and near-infrared colours, and disk composition consistent with these objects belonging to the Lupus clouds. In the second group, sources have lower proper motions with random orientations, and they are mostly located outside the cloud cores, making their association with the Lupus complex more doubtful. We investigate the properties of the higher proper motion group, but cannot find any correlations with spatial location, binarity, the presence of a circumstellar disk, or with physical properties such as effective temperature, luminosity, mass, or age. Conclusions. We conclude that the lower proper motion group probably represents a background population or mixture of populations unrelated to the Lupus clouds. The higher proper motion group, on the other hand, has properties consistent with it being a genuine population of the Lupus star-forming region. More accurate proper motions and/or radial velocity information are required for a more detailed study of the kinematic properties of the Lupus stellar members.