Finding new members of the VelHel-4 stream

Abstract: According to the paradigm of lambda-CDM cosmology, the stellar halo ofour Galaxy has been built-up over time through the accretion of other galaxiesand star clusters. The remnants of some of these are still observable today asstellar streams, but are typically very faint and difficult to resolve amidst the farmore numerous foreground Milky Way stars. The VelHel-4 stream, discoveredby Helmi et al. [2017], consists of seven members selected based on their energiesand angular momenta. Further studies of these stars has shown evidence ofglobular cluster (GC) abundance patterns, suggesting that the stream originatedfrom a GC progenitor, but a larger sample is needed to verify this signature. Theobjective of this thesis is to find new candidate members of the VelHel-4 stellarstream in order to better characterize its properties and to confirm a possibleGC origin.The preliminary selection of stars was done kinematically, by computing theorbital actions and energies using astrometric data and radial velocities for abright subset of the Gaia DR3 database, and then analyzing the clustering ofstream members in different combinations of action space. The selected samplewas then cleaned by analyzing the positions of these stars in a colour-magnitudediagram. In total, 34 stars were included in the final selection. Follow-up high-resolution spectroscopy of these candidates is needed to study their stellar abun-dances and confirm the possible GC origin of this stream.