In section 6. Interstellar and circumstellar medium
Interferometric view of the circumstellar envelopes of northern FU Orionis-type stars
The FU Ori stage of protostar formation is one of intense photometric and spectroscopic variability, lasting decades, and indicating a phase of enhanced mass transfer onto the forming protostar. The outbursts should also involve enhanced stellar outflows, This paper presents thefirst comprehensive spectrophotometric-interferometric millimeter wavelength study using the IRAM telescopes of the circumstellar environments of these stars including the peripheral regions of their accretion disks and the envelope in superb dynamical and spatial detailin two optically thin isotopes of CO. Outflow was detected in only three stars, but these were all well resolved. Compact structures were seen in 5/8 of the sample stars and the structures produced in channel maps. The combination of star and/or inner disk-like signatures and those of themore extended envelope are consistent with the picture of the FU Ori objects as the transition between completely enshrouded central objectsand the T Tau stage in which the central star dominates the disk.