J/A+A/702/A17ivo://CDS.VizieR/J/A+A/702/A17doi:10.26093/cds/vizier/bc-ny/lbhCDSGomez Maqueo Chew Y.Hebb L.Stempels H.C.Walter F.M.James D.J.,Feiden G.A.Petrucci R.Lister T.Baraffe I.Brodheim M.Faedi F.,Anderson D.R.Street R.A.Hellier C.Stassun K.G.2026-08-03T06:57:55Z2025-09-29T09:10:31ZCDS support team

CDS, Observatoire de Strasbourg, 11 rue de l'Universite, F-67000 Strasbourg, France

cds-question@unistra.freclipsing-binary-starsspectroscopic-binary-starsradial-velocityphotometryvisible-astronomyWe present the discovery of the eclipsing binary MML 48, which is a member of Upper Centaurus Lupus, has an associated age of 16 Myr, and is composed of two young, low-mass stars. We used space- and ground-based observations to characterize the system with both time-series photometry and spectroscopy. Given the extreme mass ratio between the stars, q_EB_=0.209+/-0.014, we modeled a single-lined spectroscopic and eclipsing binary system. Results. The orbital period, 2.0171068+/-0.0000004d, is measured from the highest precision light curves. We derive a primary mass of 1.2+/-0.07M_{sun}_ using stellar models, and with radial velocities we measured a secondary mass of 0.2509+/-0.0078M_{sun}_ . The radii are large, as expected for pre-main-sequence stars, and are measured as 1.574+/-0.026+/-0.050R_{sun}_ and 0.587+/-0.0095+/-0.050R_{sun}_ , for the primary and secondary stars, respectively. MML 48 joins the short list of known low-mass, pre-main-sequence eclipsing binaries (EBs), being one of only five systems with intermediate ages (15-25Myr), and the system with the most extreme mass ratio. The primary star is currently at the "fusion bump", undergoing an over-production of energy in the core due to the build-up of 3He before reaching its equilibrium abundance set by the proton-proton (p-p) I chain. MML 48 A is the first young star in an eclipsing system that has been found during its fusion bump. MML 48 is thus an important benchmark for low-mass stellar evolution at a time when the stars are rapidly changing, which allows for a tight constraint on the corresponding isochrone given the uneven mass ratio.2025A&A...702A..17Ghttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/702/A17CatalogResearchIsServedByTAP VizieR generic servicehttps://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/702/A17https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/702/A17http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/702/A17https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/702/A17https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/702/A17http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/702/A17GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapOpticaldefaultJ/A+A/702/A17/table1Light-curve data for MML 48recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintTimeBarycentric Julian Date (TDB) (BJD-2450000)dtime.epochdoubleindexedmagDifferential magnitude in Filtermagphot.magdoublee_magError in differential magnitude in Filtermagstat.error;phot.magdoubleTelTelescope namemeta.id;instr.telcharFilterFilter used (BVRI Ic zs TESS WASP)instr.setup;instr.filtercharJ/A+A/702/A17/table2Radial-velocity measurements for primary EB componentrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintTimeBarycentric Julian Date (TDB) (BJD-2450000)dtime.epochdoubleRVRadial velocitykm/sphys.veloc;pos.heliocentricdoublee_RVError in radial velocitykm/sstat.errorfloatInstInstrument name (CHIRON, FEROS or SOAR)meta.id;instrcharJ/A+A/702/A17/table3Time of minimum for full primary eclipses of MML 48recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintDatasetTelescope used and year of observationsmeta.id;meta.datasetcharFilterFilter used (BV Ic TESS WASP)instr.setup;instr.filtercharEpochTime of primary eclipse (TDB) (BJD-2450000)dtime.epochdoublee_EpochError in the time of the primary eclipse (TDB)dstat.error;time.epochdouble