Infrared Structure of selected Planetary and Proto-Planetary Nebulae: II. Broad Band Imaging of the Dust Envelope

scientific abstract this is the second part of a proposal on planetary and protoplanetary nebulae that includes spectroimaging and large scale imaging of circumstellar envelopes. this part aims mainly to the study of the outer envelope. circumstellar envelopes of gas and dust around evolved stars can extend over several minutes, but become optically thin at short distance from the central star: using cam, we propose to map in several wide band filters the outer part of the envelope of a selection of a few archetypical objects through the thermal dust emission and the scattered light: this would give access to: a) the history of the massloss on a much larger time scale than presently known; b) the structure of the nonsymetric envelopes at a large distance. the second part, broadband imaging of a selection of pns, intends at completing the program of spectroimaging by tentative detection at longest wavelength of a dusty disk and envelope around pne and ppne. observation summary part 1: extended envelopes of ppns: sources: oh231.8+4.2: an oh source with very distinctive properties: an extended bipolar structure with a pronounced waist, a strong ice absorption feature at 3.05 microns, and a large terminal velocity of the outflow; iras 09371+1212 (frosty leo nebula): the most icy envelope known today, shows a disk and a weakly collimated very cold (t < 45k) bipolarity; crl 2688 (egg nebula): the prototype of a collimated extended bipolar nebula, with evidence for a bipolar cavity, and differing from the previous one by c/o > 1; cit6: a prototype of close carbon star with a thick envelope. proposed observations: aot: general observation : filter lw9, lw10, sw4, sw5. pfov 1.5 or 3 arcsec. complete integration time per filter: 15 to 30 min. the longer the integration time, the larger the radial distance of truncated! [truncated!, Please see actual data for full text]