2000A&A...354..965A

Seven Herbig Ae/Be stars were observed at mid- and far-infrared wavelengths with ISOPHOT, the photometer on-board the Infrared Space Observatory. At λ≤25µm, where the emission mainly arises from a compact circumstellar region, the observed spectral energy distributions can be described by power-law relationships between wavelength and flux density (F_ν∝ν^–n). The exponent of the power-law changes considerably among the stars, from n≃0 for MWC1080 to n≃2.3 in the case of LkHα234, with a typical value of around 1. Interpreting the observed power-law relationships in terms of circumstellar disks, in 5 out of 6 cases relatively shallow radial temperature distributions have to be assumed (T∝r^–q where 0.37≤q≤0.53). At longer wavelengths the observed emission is spatially extended, and in some cases significant discrepancy with IRAS was found due to beam size effects. The peak of the SEDs (in F_ν) is typically at 60-100µm, corresponding to temperatures of around 50K. At λ>100µm the emission observed by ISOPHOT is never dominated by the Herbig Ae/Be stars. The most likely sources of the far-infrared radiation are dust cores of about 1 arcminute in size. The dust cores are probably located in the vicinity of the stars, and may be related to the star forming process.