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Session 113 - Observations of the Circumstellar Environment of YSOs.
Oral session, Thursday, January 18
Corte Real, Hilton
Construction of the UCLA two-channel infrared camera was completed and commissioned in June, 1993. A polarization module was commissioned with the camera in December, 1993. The camera performs very well, giving good images at all specified wavebands between 1 and 4 \mum. The camera provides a scale of 0.675\arcsec per pixel on Lick Observatory's 3-m telescope, giving a total field of view of 3\arcmin \times 3\arcmin. The polarimetry system, designed for operation in the 1--2.5 \mum regime, has an efficiency of \sim93% at K^\prime (2.2 \mum), \sim91% at H (1.65 \mum), and \sim82% at J (1.2 \mum). The ability to double the effective telescope time by observing in two different wavebands simultaneously has resulted in some of the deepest polarimetry images ever obtained.
This camera was used to carry out extensive polarimetric observations of a selection of Young Stellar Objects (YSOs) identified in the literature. We selected a number of low-mass sources in the near-by Taurus and \rho Ophiuchi molecular clouds. We also observed the Cepheus A region as an example of a high mass YSO. The results of our polarization observations have been quite stunning. We concentrated on Cepheus A in particular because it is a well studied object but still not completely understood. Our results show that there is evidence for only a single source for the infrared reflection nebula, though other YSOs are detected in the field. We show good agreement with the radio continuum source #2 identified by Hughes amp; Wouterloot (1984, ApJ 276:204) as the illuminating source. Our data are also consistent with scattered light models by Whitney amp; Hartmann (1993, ApJ 402:605) though some foreground extinction is inferred. These results, as well as results for low-mass YSOs in the nearby molecular clouds, will be presented.
