We present new sub-arcsecond ( 0.7 ” ) Combined Array for Research in Millimeter-wave Astronomy ( CARMA ) observations of the 1.3 mm continuum emission from circumstellar disks around 11 low and intermediate mass pre-main sequence stars .
High resolution observations for 3 additional sources were obtained from literature .
In all cases the disk emission is spatially resolved .
We adopt a self consistent accretion disk model based on the similarity solution for the disk surface density and constrain the dust radial density distribution on spatial scales of about 40 AU .
Disk surface densities appear to be correlated with the stellar ages where the characteristic disk radius increases from 20 AU to 100 AU over about 5 Myr .
This disk expansion is accompanied by a decrease in the mass accretion rate , suggesting that our sample disks form an evolutionary sequence .
Interpreting our results in terms of the temporal evolution of a viscous \alpha -disk , we estimate ( i ) that at the beginning of the disk evolution about 60 % of the circumstellar material was located inside radii of 25–40 AU , ( ii ) that disks formed with masses from 0.05 to 0.4 M _ { \sun } and ( iii ) that the viscous timescale at the disk initial radius is about 0.1-0.3 Myr .
Viscous disk models tightly link the surface density \Sigma ( R ) with the radial profile of the disk viscosity \nu ( R ) \propto R ^ { \gamma } .
We find values of \gamma ranging from -0.8 to 0.8 , suggesting that the viscosity dependence on the orbital radius can be very different in the observed disks .
Adopting the \alpha parameterization for the viscosity , we argue that \alpha must decrease with the orbital radius and that it may vary between 0.5 and 10 ^ { -4 } .
From the inferred disk initial radii we derive specific angular momenta , j , for parent cores of ( 0.8 - 4 ) \times 10 ^ { -4 } km/s pc .
Comparison with the values of j in dense cores suggests that about 10 % of core angular momentum and 30 % of the core mass are conserved in the formation of the star/disk system .
We demonstrate that the similarity solution for the surface density for \gamma < 0 can explain the properties of some “ transitional disks ” without requiring discontinuities in the disk surface density .
In the case of LkCa 15 , a smooth distribution of material from few stellar radii to about 240 AU can produce both the observed SED and the spatially resolved continuum emission at millimeter wavelengths .
Finally we show that among the observed sample , TW Hya is the only object that has a disk radius comparable with the early solar nebula .