Discovery of a nebula around AS 201.

The discovery of a nebula surrounding AS 201 is presented. Previously classifed as symbiotic star and planetary nebula (PN), the object has always been regarded as an unresolved star. Here the author presents CCD images taken with the 3.5 m ESO New Technology Telescope which reveal a faint, somewhat elongated annular nebula of 9″5 by 12″5 surrounding the star. Spectroscopy is used to show that the nebula is mainly due to emission in the line of [N II] 6584 and is of low excitation. The author interprets the presence of this nebula as direct evidence that AS 201 is a PN. The energy distribution of AS 201 shows a strong far IR excess, indicating cool dust. The IRAS LRS spectrum shows a marginal 10 μm emission feature, implying the presence of silicates. Using the measured energy distribution and nebular density, together with the models of Schönberner (1981, 1983, 1989), the author estimates the fundamental parameters such as luminosity, distance and ionized mass of the object.