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The mass accretion rate is the fundamental parameter to understand theprocess of mass assembly that results in the formation of a low-mass star. Thisparameter has been largely studied in Classical TTauri stars in star-formingregions with ages of 1-10Myr. However, little is known about the accretionproperties of young stellar objects (YSOs) in younger regions and early stagesof star formation, such as in the Class0/I phases. We present new NIR spectraof 17 ClassI/Flat and 35 ClassII sources located in the young (<1Myr) NGC1333cluster, acquired with the KMOS instrument at the VLT. Our goal is to studywhether the mass accretion rate evolves with age, as suggested by the widelyadopted viscous evolution model, by comparing the properties of the NGC1333members with samples of older regions. We measured the stellar parameters andaccretion rates of our sample, finding a correlation between accretion andstellar luminosity, and between mass accretion rate and stellar mass. Bothcorrelations are compatible within the errors with the older Lupus star-formingregion, while only the latter is consistent with results from ChamaeleonI. TheClassI sample shows larger accretion luminosities with respect to the ClassIIstars of the same cloud. However, the derived accretion rates are notsufficiently high to build up the inferred stellar masses, assuming steadyaccretion during the ClassI lifetime. This suggests that the sources are not intheir main accretion phase and that most of their mass has already beenaccumulated during a previous stage and/or that the accretion is an episodicphenomenon. We show that some of the targets originally classified as Class Ithrough Spitzer photometry are in fact evolved or low accreting objects. Thisevidence can have implications for the estimated protostellar phase lifetimes.Further observations are needed to determine if this is a general result.

KMOS study of the mass accretion rate from Class I to Class II in NGC 1333