Abstract:
In the IRAS (12)-(25), (25)-(60) color-color diagram, RV Tauri stars are found to populate cooler temperature regions, distinctly different from those occupied by the oxygen and carbon Miras. The IRAS fluxes are consistent with the dust density in the envelope varying as the inverse square of the radial distance, implying that the grain formation processes in these objects are most probably continuous and not sporadic. It is found that the spectroscopic subgroups A and B are well-separated in the far-infrared two-color diagram, with group B objects having systematically cooler dust envelopes. Thyis is interpreted as being due to a difference in the nature of grains, including the chemical composition, in the two cases.
