A High Resolution Study of Circumstellar Matter

Physics

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Scientific paper

I present studies relating to the circumstellar matter in the vicinities of Young Stellar Objects (YSOs) and Planetary Nebulae (pn). With regard to YSOs, this work contains high resolution near infrared images and imaging polarimetry of a small sample of embedded, low mass sources in the Class I phase of protostellar evolution. The data are analysed by comparison with Monte Carlo simulations in scattered light: models are tailored to individual sources using all available data and multiple iterations constrain the structure of the circumstellar matter. The results support the view that we observe a circumstellar envelope with a bipolar cavity, but show that dust in outflows can also play a prominent role in the near infrared and that structures are very varied. The derived masses are in good agreement with estimates obtained from submillimetre observations of the thermal continuum. Smooth, continuous density profiles are indicated in the envelope, which obscures a physically thin inner disk. The very high (up to 80%) degrees of polarisation observed in the envelopes show that the scattering is dominated by small, interstellar-type dust grains. The morphologies and high polarisations of the cores show that the protostars are usually obscured at this phase of evolution, even at 3.7 microns. Observational methods for high resolution imaging are discussed. Spectra of the Unidentified Infrared bands in pn at 3 and 5 microns are presented. A relationship is proposed between the bands at 11.25, 5.25 and 3.4 microns in terms of combinations and overtones of C-H out-of-plane modes which may lead to a considerable simpification of the UIR-band spectrum. The 3.3 micron band is well correlated with C/O abundance and with the 3.4 micron band strength. The 3.4 micron band is found to be stronger in N-rich Type I pn, which are produced by relatively massive progenitor stars.

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