Bonifacio, P.P.BonifacioCaffau, E.E.CaffauSpite, M.M.SpiteSpite, F.F.SpiteFrançois, P.P.FrançoisZAGGIA, SimoneSimoneZAGGIAArenou, F.F.ArenouHaigron, R.R.HaigronLeclerc, N.N.LeclercMarchal, O.O.MarchalPanuzzo, P.P.PanuzzoPlum, G.G.PlumSartoretti, P.P.Sartoretti2022-07-152022-07-1520182515-5172http://hdl.handle.net/20.500.12386/32502The Gaia Data Release 2 provides a parallax of 0.734+/-0.073 mas for SDSS J102915+172927, currently the most metal-poor known object. This parallax implies that it is dwarf star, ruling out the scenario that it is a subgiant. The subgiant scenario had as a corollary that the star had been formed in a medium highly enriched in C, thus making line cooling efficient during the collapse, that was also highly enriched in Fe by Type Ia SNe. This scenario can also now be ruled out for this star, reinforcing the need of dust cooling and fragmentation to explain its formation.ELETTRONICOenArticle10.3847/2515-5172/aac0f4https://iopscience.iop.org/article/10.3847/2515-5172/aac0f42018RNAAS...2...19BFIS/05 - ASTRONOMIA E ASTROFISICAERC sectors::Physical Sciences and Engineering::PE9 Universe sciences: astro-physics/chemistry/biology; solar systems; stellar, galactic and extragalactic astronomy, planetary systems, cosmology, space science, instrumentation::PE9_6 Stars and stellar systems