SPECTRAL ENERGY-DISTRIBUTIONS AND PHYSICAL PARAMETERS OF THE ATMOSPHERES OF MAIN-SEQUENCE A STARS WITH INFRARED EXCESSES - COMPARISON WITH NORMAL STARS

For eight stars with infrared excesses greater than 0.5(m) in the IRAS bands, we obtained the energy distribution over the range 3200-7600 A ngstrom and measured their infrared JHKLM magnitudes. Similar observat ions were performed for 21 stars of various subclasses of the spectral type A with excesses no greater than 0.3(m). Based on the energy dist ribution derived from the response curves of the photometric UBV and W BVR systems, we computed the synthetic B-V color indices, which are in good agreement with the photometric observations. A comparison of the normalized energy distribution in the spectra of A stars with infrare d excesses greater than 0.5(m) in the IRAS bands and the mean energy d istribution for stars of the corresponding subclasses shows that the m aximum difference does not exceed 10% both in the ultraviolet (3200-40 00 Angstrom) and in the near infrared (up to 7600 Angstrom). In all of the stars studied, we detected no excesses in the JHKLM bands that we re greater than the accuracy of our measurements. Using the method of infrared fluxes and comparing the observed energy distribution with th eoretical models of Kurucz, we determined the effective temperatures a nd angular diameters of the stars. For three stars, we estimated the p arameters of their dust shells.