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Session 47 - Circumstellar Disks & Shells.
Display session, Thursday, January 08
Roberts 22 (G284.2-0.8) is an Type II OH-IR star with strong OH maser emission. R22 consists of a bipolar reflection nebula illuminated by a hidden A2 Ie star. This non-standard association of an A2 star and strong maser emission (more ordinarily connected with late M stars) makes this object of particular interest. Following discovery in the radio, optical and IR observations of this object were made. Previous radio spectral line observations of R22 involved short duration observations at 1612 and 1666 MHz at lower spatial resolution. We present 28 hours of observations with the Australian Compact Array in three bands: 1612 MHz, 1665 MHz and 1667 MHz. High signal to noise allows us to locate the peak intensity at each velocity to high precision. The velocity of the emission runs from +11 km/s to -34 km/s. At 1612 and 1665 the peak of the maser emission in each channel traces out an arc segment, suggestive of a ellipse. Previous observers have suggested Roberts 22 may be an late evolution star with an expanding shell or, in contrast, a young star with an accreting disk. We present kinematic models that allow the qualitative features of the outflow to be determined, present disk and expanding ellipsoid models and discuss the impact they may have on the understanding of the evolutionary status of this object.
Program listing for Thursday