| Description |
we propose to observe the asteroids ceres, pallas, vesta, europa, amphitrite and herculina using the sws at grating resolution in aot6 mode to obtain spectra covering the full wavelength range between 5 and 45.3um. while sws calibration observations on these and other asteroids give clear hints as to their mineralogy and chemistry, higher s/n observations are necessary for proper characterisation. the proposed observations will complement the mineralogical studies of the asteroids ceres, pallas, vesta, europa, amphitrite and herculina and enable a database of all major asteroid types to be compiled. the comparison with laboratory data on meteorites, stratospheric interplanetary dust particles (idps) and other iso mineralogy studies on comets, zodiacal light, and circumstellar dust disks will give insight in evolution scenarios for dust in stellar systems and the place of asteroids in the evolution of our solar system. scientific justification ------------------------ iso-sws spectra from various programs have revealed a wealth of solid state features, allowing a detailed study of the mineral composition of the hosts. systematical studies across many different classes of objects contribute to a physical, chemical and evolutionary morphology for stellar systems, e.g. making the connection between oxygen rich dust in comets, debris disks around young stars, and dust shels around evolved stars. because the standard thermal model predicts a smooth mid-infrared spectrum for the asteroids ceres, pallas, vesta and juno, they were thought to be ideal sources for relative spectral responsivity calibration observations. however, our observations clearly showed a number of resolved features in basically all sws wavelength ranges, some of which could be identified as sulfates and olivines, demonstrating that detailed mineralogy studies on these asteroids are feasible with sws. the sws resolution and wavelength coverage are uniquely suited to systematically detect most of the expected grain species on these asteroids. the most prominent features caused by silicates (olivines, enstatite, . ), carbonates (calcite, dolomite), sulfides (pyrite), and oxides (hematite, goethite) are all located in the mid-infrared. however, most of these features cannot be seen by pht-s : the fwhm of most of the features below 12um is too small, and the most prominent olivine and non-silicate mineral features are at wavelengths longer than 12um. therefore the proposed observations are unique and do not overlap with existing programmes. the proposed observations will significantly increase the number of asteroid types observed by iso, leaving a database of asteroids with many different geological histories: 1 ceres g 2 pallas b 4 vesta v 29 amphitrite s 52 europa cf 532 herculina s asteroids are believed to be a primary source of the zodiacal dust near the earth. the transport of asteroidal particles from the main belt to the earth is very efficient because of the poynting-robertson light drag. detailed comparison of the mineralogy of the asteroids, iso spectra of the zodiacal light and lab data on meteorites and interplanetary dust particles (idps) will be of great value for this theory. comparison of these results with the composition of comets as determined from full sws spectra and circumstellar dust disks and shells around other stars at different stages in their evolution could contribute to iso.s view on the evolution of dust in stellar systems in general, and the evolution of our solar system in particular. requested observation time -------------------------- in order to obtain the needed observations on ceres, vesta, pallas, amphitrite, europa and herculina for a detailed and systematical mineralogy study, we ask for a total of 10 hours of observing time with the iso sws. it has been verified that the sources are still visible, as well as the fact that the proposed observations are not blocked by any other program. note that that amphitrite, europa and herulina are not in any current iso observing programmes. feasibility ----------- the six proposed objects are the brightest asteroids in the infrared wavelength range. the calibration observations mentioned before proove that a very good s/n can be obtained with the given flux densities of the targets. the biggest challenge of the proposed observations are the signal changes caused by the iso tracking algorithm for solar system objects. during one tracking leg, the source moves with respect to the slit, causing signal changes. the sidt has shown on existing observations that with the current knowledge of the sws beam profiles and the present accuracy of solar system object tracking, the signals can be succesfully rectified during the data reduction process by instrument experts. on request we can provide plots from the above mentioned sws calibration observations which demonstrate the technical feasibility of the proposed observations. |
