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The Submillimeter Array has opened a new window to study the innermost warmand dense regions of the envelopes and disks around deeply embedded protostars.This paper presents high-angular resolution (< 2'') submillimeter observationsof the class 0 young stellar object NGC1333-IRAS2A. Dust continuum emission andlines of complex organic molecules such as CH3OCH3 and CH3OCHO, high excitationCH3OH transitions, deuterated methanol CH3OD as well as lines of CO, HCN,H13CN, SO and SO2 are detected on < 200 AU scales. The observations areinterpreted using detailed radiative transfer models of the physical andchemical structure, consistent with both single-dish and interferometer data.The continuum emission is explained by an extended envelope and a compact butresolved component, presumably a circumstellar disk with a diameter of 200-300AU and a mass of a few times 0.01-0.1 M_sun. If related to the rotation of theenvelope, then the size of this disk suggests a centrifugal barrier of 200-300AU, which implies that the temperature in the envelope does not increase above100 K. Its large size also suggests that the build-up of disks proceeds rapidlythroughout the early protostellar stages. The smaller (< 100 AU) disks foundaround other deeply embedded protostars may be a result of tidal truncation.The high-resolution observations of SO can be explained with a simple constantabundance, ~1E-9, constrained through single-dish observations, whereas thoseof H13CN and the organic species require high abundances, increased by one totwo orders of magnitude, or an additional compact source of emission at smallscales. The compact molecular emission could originate in a hot core region ofthe inner envelope, but a more likely reservoir is the circumstellar disk.Comment: Accepted for publication in ApJ. 24 pages, 5 figure

Probing the Inner 200 AU of Low‐Mass Protostars with the Submillimeter Array: Dust and Organic Molecules in NGC 1333 IRAS 2A