Astron. Astrophys. 339, 134-140 (1998)

5. Summary and conclusions

We have presented in this paper mid-IR images and spectra of the pre-main-sequence star HD 97300 obtained with ISOCAM on board of ISO.

The images show extended emission, an elliptical ring structure of size about 0.0450.03 pc, and two peaks of emission, separated by about , displaced from the center of the ring in the NW direction. One of the two emission peaks is detected in the three filters at shorter wavelengths and coincides with the nominal position of the central star. The other peak is only visible in the two filters at longer wavelengths, and we suggest that it may be an embedded companion of HD 97300 similar to that seen in the 10µm images of Lagage et al. (1993) of the region around the younger Herbig AeBe star LkH198.

The CVF data reveal that the emission in this region is dominated by the IEBs. We fit the spectra in selected positions at increasing distance from the star with a dust model which includes PAHs, very small particles and large grains. At the spectral resolving power of ISOCAM a simple classical oscillator model is sufficient to account for the strengths and shapes of the infrared emission bands. Transiently heated species (PAHs and possibly very small grains) very likely produce also the continuum emission, clearly detected in the range 9-11µm and 14-16 µm, with contribution by large grains only at the longest wavelengths.

The elliptical ring has a mass of about 0.03 (from the model fits to the IEB intensity) and surrounds an almost empty cavity. We believe that its origin may be due to the interaction of the visible star HD 97300 with the surrounding matter. Two possible mechanisms can account for its properties; either a past mass-loss episode with rate  yr^-1 and duration yr, or radiation pressure. Both are consistent with the known properties of HD 97300. The off-center location of the star with respect to the ring may be the effect of a density gradient in the SE-NW direction in the outer region of the Chamalion I cloud where HD 97300 lies. The ring is reminiscent of the structure observed in scattered light around the Herbig Ae/Be star LkH198.

© European Southern Observatory (ESO) 1998

Online publication: September 30, 1998
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