The circumstellar envelopes around three protostars in Taurus

Abstract

We have investigated the distribution of circumstellar material around three Class I protostars in Taurus. TMC1 (IRAS 04381+2540), TMC1A (IRAS 04365+2535) and Haro 6-10 (IRAS 04263+2426) have all been mapped in 790-μm dust continuum emission using the James Clerk Maxwell Telescope, and TMC1A has also been imaged at λ1.1 mm. In addition, we present a 12CO J = 2-1 map of Haro 6-10 obtained using the Caltech Submillimeter Observatory. The dust emission from TMC1 is extended and is oriented perpendicular to its outflow, with little evidence for a compact disc component. The submillimetre emission from TMC1A is centrally peaked, with a weak extension in the direction of the outflow at both 790 μm and 1.1 mm. It is possible that the interaction of the outflow with the surrounding cloud is heating the dust. The emission from Haro 6-10 is oriented roughly perpendicular to the direction of several Herbig-Haro objects in the region. There is no clear bipolar molecular outflow structure in the CO(2-1) map, and the relatively low velocities observed in the line wings suggest that any such system must lie close to the plane of the sky. If the dust emission from the envelopes is optically thin and a temperature distribution can be specified, the broad-band spectral energy distribution (SED) can be used to constrain the density profile. We isolate the envelope SEDs for our sources by subtracting possible disc and wind components from the submillimetre flux densities, and use a simple model to derive the radial power-law dependence of the density in each case. We find that for a density distribution ρ ∝ r-p the values of p are 0.93 ± 0.25, 0.81 ± 0.30 and 1.22 ± 0.11 for TMC1, TMC1A and Haro 6-10 respectively, which for all but Haro 6-10 are considerably shallower than can currently be explained by collapse theory. We suggest that the envelopes around TMC1 and TMC1A may be rotationally supported, but that the Haro 6-10 envelope may still be infailing. The envelope masses are ∼0.02-0.03 M⊙ in all cases.