J/A+A/703/A141ivo://CDS.VizieR/J/A+A/703/A141CDSGuo Z.Lucas P.Yurchenko S.N.Kaminski T.Montesinos M.Nayakshin S.,Elbakyan V.Osses J.Caratti o Garatti A.Zhao H.Kurtev R.,Borissova J.Morris C.Minniti D.Alonso-Garcia J.Fermiano V.,Saito R.K.Miller N.Zsidi G.Muthu H.D.S.Briceno C.,Contreras Pena C.Lynas-Gray A.E.Tennyson J.Wang L.Yu L.,Benitez-Palacios D.Yang J.Kuhn M.Wang S.X.2026-03-02T06:25:50Z2025-11-13T09:14:53ZCDS support team

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

cds-question@unistra.frpre-main-sequence-starsinfrared-photometryOutburst phenomena are observed at different stages of stellar evolution, due to the enhancement of the mass accretion rate on protostars or even stellar merger events. In the case of a young stellar object (YSO), the episodic mass accretion event plays an important role in the pre-main- sequence stellar mass assembly. Here we investigate an infrared eruptive source (RA=16:53:44.38; DEC=-43:28:19.47), identified from the decade-long VISTA Variables in the Via Lactea survey (VVV). We named this target after a group of variable sources discovered by VVV, as VVV-WIT-13, where WIT stands for 'What is this?', due to its unique photometric variation behaviour and the mysterious origin of the outburst. This target exhibited an outburst with a 5.7mag amplitude in the Ks-band, remained on its brightness plateau for 3.5 years, and then rapidly faded to its pre-eruptive brightness afterwards. Our aim is to reveal the variable nature and outburst origin of VVV-WIT-13 by presenting our follow-up photometric and spectroscopic observations along with theoretical models. We gathered photo- metric time series in both near- and mid-infrared wavelengths. We obtained near-infrared spectra during the outburst and decaying stages on XSHOOTER/VLT and FIRE/Magellan, and then fitted the detected molecular absorption features using models from ExoMol. We applied 2D numerical simulations to re-create the observables of the eruptive phenomenon. We observe deep AlO absorption bands in the infrared spectra of VVV-WIT-13, during the outburst stage, along with other more common absorption bands (e.g. CO). Our best-fit model suggests a 600K temperature of the AlO absorption band. In the decaying stage, the AlO bands disappeared, whilst broad blue-shifted H_2_ lines arose, a common indicator of stellar wind and outflow. The observational evidence suggests that the CO and TiO features originate from an outflow or a wind environment. We find that VVV-WIT-13 is an eruptive young star with instability occurring in the accretion disk. One favoured theoretical explanation of this event is a disrupted gas clump at a distance of 3au from the source. If confirmed, this would be the first such event observed in real time.2025A&A...703A.141Ghttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/703/A141CatalogResearchIsServedByTAP VizieR generic servicehttps://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/703/A141https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/703/A141http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/703/A141https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/703/A141https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/703/A141http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/703/A141GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapInfrareddefaultJ/A+A/703/A141/table1Photometric data of VVV-WIT-13recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintMJDModified Julian Date of observationdtime.epochfloatBandPhotometric band (e.g. J, H, Ks, W1, W2, [24])instr.bandpasscharSurveyOrigin of the data (2MASS, GLIMPSE, VVV, NEOWISE, ALLWISE, SOFI, IRSF, REM, FIRE, etc.)meta.bibcharmagObserved magnitude in Band (Vega system)magphot.magfloate_magUncertainty of the magnitude measurementmagstat.error;phot.magfloatqflag[cp] Quality flag (c = catalogued; p = photometry)meta.code.qualchar