| Description |
scientific abstract the iras fluxes for the calibration star vega (alpha lyrae, hr7001) showed that the star had excess flux over that expected for a normal main sequence star. the infrared excess has been interpreted as a dust disk left over from the formation of the star. several other main sequence stars show a similar excess in their iras fluxes. beta pic (hr2020) has been the only star around which the dust disk has been detected at shorter wavelengths and studied, and this disk is seen edge-on. isophot gives us the opportunity to investigate the structure of the dust disks around several of these stars, using multi-aperture and mapping observations, and to investigate deviations of the energy distribution from that expected from a black-body with multi-filter observations. spectra will be taken of all the stars, to look for dust features. observation summary the proposal is split into three parts, this is part 2. the times used in this proposal are calculated using the cookbook. the off positions (for background determination) may be adjusted later. p22 is executed with 7 filters, c_60, c_70, c_100, c_120, c_135, c_160, c_200. these observations are done with rectangular chopping, and a 32 second integration time. p40 is executed with 32 second integration. p04 is executed with the 16um filter for hr2020 (beta pic), hd98800, hd139614, hd169142, hd135344, hd142666, hd233517, hd144432, hd188037, hd139664, hd34700, hd143006. the rest are observed at 25um. p04 is executed at 60um for all stars. these oservations are not chopped, but a background field is observed near the star (64 sec integration time per filter). all the circular apertures from the diffraction limited aperture to 180 arcsec are used. p17 (with p18, p19) is executed for hr7001 (vega), hr2020 (beta pic), hr7828 (alpha psa), hd98800, hd139614, and hd34700. the background field is observed first and last, and 11 positions near the star avoiding the star itself, the 60um filter is used to combine resolution with flux from the cool dust. for two sources a 5 x 5 raster map will be performed with pht32, using an oversampling factor of 2, which results in a map area 258 x 138 being covered. an integration time of 2 seconds/chopper plateau is used, which means that the time per raster position is 26 seconds (13 chopper steps/raster position). |
