cc-byRotaP BozzaV HundertmarkM BacheletE StreetR TsaprasY CassanA DominikM JaimesRF RybickiKA WambsganssJ WyrzykowskiL ZielinskiP BonavitaM HinseTC JorgensenUG KhaloueiE KorhonenH Longa-PenaP PeixinhoN RahvarS SajadianS SkottfeltJ SnodgrassC Tregolan-ReedJeremy Tregloanreed2025-06-052025-06-0520240004-6361https://hdl.handle.net/20.500.12740/22686Context. Gravitational microlensing is a method that is used to discover planet-hosting systems at distances of several kiloparsec in the Galactic disk and bulge. We present the analysis of a microlensing event reported by the Gaia photometric alert team that might have a bright lens. Aims. In order to infer the mass and distance to the lensing system, the parallax measurement at the position of Gaia21blx was used. In this particular case, the source and the lens have comparable magnitudes and we cannot attribute the parallax measured by Gaia to the lens or source alone. Methods. Since the blending flux is important, we assumed that the Gaia parallax is the flux-weighted average of the parallaxes of the lens and source. Combining this assumption with the information from the microlensing models and the finite source effects we were able to resolve all degeneracies and thus obtained the mass, distance, luminosities and projected kinematics of the binary lens and the source. Results. According to the best model, the lens is a binary system at 2.18 +/- 0.07 kpc from Earth. It is composed of a G star with 0.95 +/- 0.17 M-circle dot and a K star with 0.53 +/- 0.07 M-circle dot. The source is likely to be an F subgiant star at 2.38 +/- 1.71 kpc with a mass of 1.10 +/- 0.18 M-circle dot. Both lenses and the source follow the kinematics of the thin-disk population. We also discuss alternative models, that are disfavored by the data or by prior expectations, however. C1 [Rota, P.; Bozza, V.] Univ Salerno, Dipartimento Fis ER Caianiello, Via Giovanni Paolo II 132, I-84084 Fisciano, Italy. [Rota, P.; Bozza, V.] Ist Nazl Fis Nucl, Sez Napoli, I-80126 Naples, Italy. [Hundertmark, M.; Tsapras, Y.; Wambsganss, J.] Zentrum Astron Univ Heidelberg ZAH, Astron Rechen Inst, D-69120 Heidelberg, Germany. [Street, R.] Las Cumbres Observ, 6740 Cortona Dr,Suite 102, Goleta, CA 93117 USA. [Dominik, M.] Univ St Andrews, Ctr Exoplanet Sci, Sch Phys & Astron, St Andrews KY16 9SS, Scotland. [Jaimes, R. Figuera] Millennium Inst Astrophys MAS, Nuncio Monsenor Sotero Sanz 100,Of 104, Santiago, Chile. [Jaimes, R. Figuera] Pontificia Univ Catolica Chile, Fac Fis, Inst Astrofis, Av Vicuna Mackenna 4860, Santiago 7820436, Chile. [Cassan, A.] Sorbonne Univ, CNRS, UMR 7095, Inst Astrophys Paris, 98 Bis Bd Arago, F-75014 Paris, France. [Bachelet, E.] Caltech, IPAC, Mail Code 100-22,1200 E Calif Blvd, Pasadena, CA 91125 USA. [Wyrzykowski, L.] Univ Warsaw, Astron Observ, Al Ujazdowskie 4, PL-00478 Warsaw, Poland. [Rybicki, K. A.] Weizmann Inst Sci, Dept Particle Phys & Astrophys, IL-76100 Rehovot, Israel. [Zielinski, P.] Nicolaus Copernicus Univ Torun, Fac Phys Astron & Informat, Inst Astron, Grudziadzka 5, PL-87100 Torun, Poland. [Jorgensen, U. G.; Korhonen, H.] Univ Copenhagen, Niels Bohr Inst, Ctr ExoLife Sci, Oster Voldgade 5, DK-1350 Copenhagen, Denmark. [Sajadian, S.] Isfahan Univ Technol, Dept Phys, Esfahan 8415683111, Iran. [Khalouei, E.] Seoul Natl Univ, Astron Res Ctr, Res Inst Basic Sci, 1 Gwanak Ro, Seoul 08826, South Korea. [Peixinho, N.] Univ Coimbra, Inst Astrofis & Ciencias Espaco, P-3040004 Coimbra, Portugal. [Longa-Pena, P.] Univ Antofagasta, Unidad Astron, Av Angamos 601, Antofagasta, Chile. [Rahvar, S.] Sharif Univ Technol, Dept Phys, POB 11155-9161, Tehran, Iran. [Tregolan-Reed, J.] Univ Atacama, Inst Invest Astron & Ciencias Planetarias, Copiapo, Atacama, Chile. [Skottfelt, J.] Open Univ, Ctr Elect Imaging, Dept Phys Sci, Milton Keynes MK7 6AA, England. [Bonavita, M.; Snodgrass, C.; OMEGA Key Project] Univ Edinburgh, Royal Observ, Inst Astron, Edinburgh EH9 3HJ, Scotland. [Hinse, T. C.] Univ Southern Denmark, Dept Phys, SDU Galaxy, Campusvej 55, DK-5230 Odense M, Denmark. [Korhonen, H.] Max Planck Inst Astron, Heidelberg, Baden Wurttembe, Germany. C3 University of Salerno; Istituto Nazionale di Fisica Nucleare (INFN); Ruprecht Karls University Heidelberg; University of St Andrews; Pontificia Universidad Catolica de Chile; Centre National de la Recherche Scientifique (CNRS); CNRS - National Institute for Earth Sciences & Astronomy (INSU); Sorbonne Universite; California Institute of Technology; University of Warsaw; Weizmann Institute of Science; Nicolaus Copernicus University; University of Copenhagen; Niels Bohr Institute; Isfahan University of Technology; Seoul National University (SNU); Universidade de Coimbra; Universidad de Antofagasta; Sharif University of Technology; Universidad de Atacama; Open University - UK; University of Edinburgh; University of Southern Denmark; Max Planck Societyinfo:eu-repo/semantics/openAccessgravitationgravitational lensing: microcatalogsparallaxesproper motionsbinaries: generalAstronomy & AstrophysicsArticulo de revista10.1051/0004-6361/202347807