Gas—Dust Shells around Some Early-Type Stars with an IR Excess (of Emission)

Abstract

The results of an investigation of IR (IRAS) observations of 58 O—B—A—F stars of different luminosity classes, which are mainly members of various associations, are presented. The color indices of these stars are determined and two-color diagrams are constructed. The emission excesses at 12 and 25 mm (E12 and E25) are also compared with the absorption ΔA1640 of UV radiation. It is concluded that 24 stars (of the 58 investigated) are disk systems of the “Vega type,” to which Vega = N 53 also belongs. Eight known stars of the “Vega type” are also given in the figures for comparison. The remaining 34 stars may have gas—dust shells and/or shell—disks. The IR emission excesses of the 34 investigated stars and 11 comparison stars (eight of them are Be-Ae stars) are evidently due both to thermal emission from grains and to the emission from free—free transitions of electrons in the gas—dust shells of these stars.