The relationship between accretion disc age and stellar age and its consequences for protostellar discs

Abstract

We show that for young stars which are still accreting and for which measurements of stellar aget*, disc massMdisc and accretion rateare available, nominal disc ageis approximately equal to the stellar aget*, at least within the considerable observational scatter. We then consider theoretical models of protostellar discs through analytic and numerical models. A variety of viscosity prescriptions including empirical power laws, magnetohydrodynamic turbulence and gravitational instability were considered within models describing the disc phenomena of dead zones, photoevaporation and planet formation. These models are generally poor fits to the observational data, showing values oftdisc which are too high by factors of 3-10. We then ask whether a systematic error in the measurement of one of the observational quantities might provide a reasonable explanation for this discrepancy. We show that for the observed systems only disc mass shows a systematic dependence on the value oftdisc/t*, and we note that a systematic underestimate of the value of disc mass by a factor of around 3-5 would account for the discrepancy between theory and observations. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.