Engineering topics
Publications and source records attributed to Terebey, S..
We investigate the question of disk formation during the protostar phase. We build on the results of Keene and Masson (1990) who analysis of L1551 showed themillimeter continuum emission comes from both an unresolved circumstellar conponent i.e. disk and an extended cloud core.
The VLA is used to search nearby very young low-mass stars for water maser emission. The sample consists of 26 low-luminosity IRAS sources embedded in dense molecular cores, a class of sources suspected to be newly forming low-mass stars on the order of a few hundred thousand years old. Three sources were detected. High spatial resolution maps show the region of maser emission is generally confined to an area smaller than about 0.5 arcsec near the star, and the velocities of individual components span intervals ranging from 20 to 40 km/s. It is inferred from the fact that the maser velocities are too large to be due to gravitational motions in at least two of the sources that the masers are associated with the winds from the young low-mass stars. A comparison of the high spatial resolution maser data to lower-resolution CO data shows no evidence for higher collimation close to the star; the stellar wind cavity appears to have similar collimation at 10 exp 15 cm as at 10 exp 7 to 10 exp 18 cm.
Near-infrared camera and Owens Valley millimeter interferometer data are presented that reveal the circumstellar environment of TMR-1 on scales of roughly 1000 AU. TMR-1 is a deeply embedded, young, low-mass star located in a rotating ring of material in the TMC-1/Heiles Cloud 2 region of the Taurus molecular cloud. The stellar wind cavity, as outlined by the extended infrared continuum emission at 2.2 microns, overlaps with the redshifted outflow detected in the (C-12)O data. High-density circumstellar material is seen in (C-13)O in emission and at 2.2 microns in absorption. The morphology suggests the high-density gas may either be part of a 1000 AU disk or may represent infalling material from the molecular cloud core. TMR-1 appears to be in an early wind-clearing phase of protostar formation.
Interferometer Maps with 2" to 6" resolution of a number of regions with active star formation (Orion A, W49, W51, SGRB2) show that the distribution of the molecule SO is very compact around stellar outflow sources. Both SO and SO2 were studied near three outflows, OrionA/IRc2 and two sources in W49. The two molecules have similar distributions and abundances. More than 95% of the emission comes from regions whose extents are only .05 to .2 pc., being larger around the more energetic sources. Their spectra are broad, 30 km/sec or more, suggesting that the oxide production is associated with the flows. The outflows are identified by water masers and by extended bipolar flows in SiO. Maps in other molecules, such as HCO+ and CS, which have similar collisional excitation requirements, have much greater spatial extent. Thus it appears that the SO and SO2 abundances are truly compact and are closely associated with the outflows.
The status of theoretical work on protostellar disks is reviewed. Accretion disk theory and its application to models of the solar nebula and protostellar disks are discussed. A unified view of the process of star formation is presented, starting from the evolution of molecular clouds, and leading naturally to the formation of protostellar disks. The models used to describe this process are idealized, but are believed to provide good prototypes that well represent the essential hydromagnetic phenomena involved in star and disk formation. Several possible evolutionary paths and final configurations are qualitatively discussed, showing how the outcomes depend on the relative efficiencies of various angular momentum transport processes.
A generalized model which accounts for the effects of initially uniform and slow rotation is defined for the spherical collapse of a singular isothermal sphere such as protosolar and binary nebulae. An initial unstable equilibrium state is described for a sound speed of 0.35 km/sec and a rotation rate of 10 to the -14th/sec for the molecular cloud surrounding the accreting core. The total angular momentum and mass of the inner cloud is set equal to solar system values. The evolution of the collapse is traced by applying a perturbation analysis to the similarity solution for a nonrotating condition, and matched asymptotic expansions solve the hydrodynamic equations. The model is concluded a valid tool for studying star and nebular disk formation.