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===================================================================== ==> In this proposal, more time is being requested for PANDRE.PA_PROTO ==> This proposal requests an upgrade from Priority 3 for PANDRE.PA_PROTO ===================================================================== A new class of very cold protostellar objects have recently been identified and designated `Class 0', which were all undetected by IRAS at 12 microns. These cold sources emit the bulk of their luminosity in the submillimeter range and correspond to the youngest protostars known to date (estimated age < 10^4 yr). They are still in the process of assembling the bulk of their final stellar mass, and direct evidence for gravitational infall has been found in some of them. Detailed studies of Class 0 protostars are thus of prime interest to constrain the physics of star formation. In the first round of ISO applications, we (PANDRE.PA_PROTO) proposed to use the high angular resolution of CAM to map the structure of these cold submm protostars at 7.75 and 15 microns, in absorption against a warmer diffuse cloud background. We obtained 14400 sec in Priority 2 for part of the 7.75 um observations (and 43200 sec in Priority 3 for the rest of our project). Some of these observations have now been taken, but we have not yet received the data. However, the CAM images of rho Oph (Abergel et al. 1996) demonstrate that our project is feasible. We therefore require more time to complete our 7.75 um observations (i.e., observe the `spring launch' sources). It is important to study a reasonably large number of sources in order to assess the importance of local environmental effects on the outer structure of protostars. In addition, we propose a detailed mapping at 4.5 um (LW1), 7.75 um (LW6), and 15 um (LW9) of the particularly promising protostellar core Oph-D, which is seen as a prominent absorption feature in the broad-band LW2/LW3 images of Abergel et al. (1996). The extinction curve is such that mapping at these wavelengths will allow us to penetrate at various depths within the core and to derive a complete spatial structure.