| Description |
scientific abstract: we propose to investigate with isocam the presence and properties of extended mid-infrared emission associated with energetic bipolar outflows and circumstellar dust halos around young stellar objects. the first part of this proposal deals with bipolar molecular outflows. recent array maps in the h2 s(1)(1-0) line at 2.12 microns often reveal shock emission regions along the flow axis, probably associated with a fast protostellar jet entraining the molecular gas. we expect that shocks of velocity greater than 60 km/s will have observable signatures in the isocam range in the form of neii emission at 12.8microns, while the uv radiation released in the shock front may excite a broad and faint halo of mid-infrared emission from small, heated dust grains. together with longer wavelength information from sws, lws, and phot, the spatially resolved information provided by isocam observations of these signatures will yield important constraints on true wind speeds, integrated mass-loss rates, and entrainment processes in protostellar winds, all of which are necessary for assessing the role of outflows in star formation and cloud evolution. in the second part of this proposal, we focus on a selected sample of young stellar objects in order to investigate their detailed geometry and emission properties of the isocam range. in particular we will search for extended 3-11micron emission from faint halos of small transiently heated dust particles. such a component has been invoked recently to explain the mid-infared excess of ysos, although scattering by large particles and non-spherical geometries offer other alternatives. our isocam observations will provide stronger constraints that should help develop coherent models of the circumstellar environment of these objects. observation summary: our sample of molecular flows concentrates on those with a well-defined bipolar appearance, high radial velocities in co lines, and/or evidence for shock activity (e.g. h2 or sio emission, temperature increase in co). in each flow, the high-velocity co extent will be raster-mapped in two cvf steps, one at the neii12.8micron line and the other in the neighbouring continuum. an independent estimate of line+continuum level will be obtained with a deeper map in lw10 (8-15micron) for comparison with cvf maps. a large scale map will be obtained with 6.. pfov to detect extended emission, and a smaller area covered with pfov 3.. to reveal bright small-scale structure (e.g. bow-shocks). a strip.. map across one outflow lobe will also be made in lw2 (pfov 6..), to search for a faint halo of small dust grains extending beyond the co contours down to a level of 2.5e-2 mjy/arcsec2 (5 sigma). in b335 (autumn) or l1448 (spring) a larger map will be made in both lw2 and lw3 for comparison with phot 60 and 100micron maps (tpray_infrabi proposal). our sample of young stellar objects includes embedded objects in the rho oph cloud with indications from earlier photometric measurements of excess 10 microns infrared emission at scales >10 (autumn), or similar objects in the cha i cloud as well as intermediate luminosity ysos with spectral evidence for very small grain emission or with outflow (spring). all objects are imaged with isocam in lw5, lw6, lw7, lw8 (to discriminate between scattered light and extended emission in the 7.7 and 11.3 bands), with pfov and sensitivity level indicated in tables 3 and 4. in addition, a subset of sources (gss30-irs1, s1, wl22, doar25, irs44, rho oph a / hd259431, lkha25, t32, t33a/b, t29, t41) will be mapped in sw2, sw6, and sw7 to search for the presence of extended 3.3micron feature emission and to sample the ice band. finally, a fully sampled cvf spectrum image from 5.5 to 8.5 micron will be taken of source 1 and gss30 (autumn) or t32 and hd259431 (spring). linked observations none fixed time observations none concatenation |
