Optical, infrared and millimetre-wave properties of Vega-like systems - IV. Observations of a new sample of candidate Vega-like sources

Photometric observations at optical and near-infrared wavelengths are prese nted for members of a new sample of candidate Vega-like systems, or main se quence stars with excess infrared emission due to circumstellar dust. The o bservations are combined with IRAS fluxes to define the spectral energy dis tributions of the sources. Most of the sources show only photospheric emiss ion at near-IR wavelengths, indicating a lack of hot (similar to 1000 K) du st. Mid-infrared spectra are presented for four sources from the sample. On e of them, HD 150193, shows strong silicate emission, while another, HD 176 363, was not detected. The spectra of two stars from our previous sample of Vega-like sources both show UIR-band emission, attributed to hydrocarbon m aterials. Detailed comparisons of the optical and IRAS positions suggest th at in some cases the IRAS source is not physically associated with the visi ble star. Alternative associations are suggested for several of these sourc es. Fractional. excess luminosities are derived from the observed spectral energy distributions. The values found are comparable to those measured pre viously for other Vega-like sources.