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Astron. Astrophys. 355, 720-724 (2000)

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1. Introduction

PC 11 (HD 149427 = IRAS 16336-5536 = PN G 331.1-05.7) is a peculiar object, classified as a planetary nebula (PN, hereafter) (Acker et al. 1992) but also as a D'-type symbiotic star (Allen 1982). The most recent analysis of the optical spectrum of PC 11 by Gutiérrez-Moreno & Moreno (1998, hereafter GMM98) concludes that it is a young low luminosity compact and dense PN with a central star having an energy balance temperature of 105,000 K. The classification of PC 11 as a PN and not as a symbiotic star is based on the low excitation observed in the optical spectrum and its location in the HR diagram.

From a preliminary analysis of the IUE UV spectra of PC 11 Parthasarathy et al. (1993) found variations in the strength of O III] and N III] lines. They also suggested that PC 11 is a PN and that the central star is a binary with a A-F type companion.

Discovering and studying binary central stars in PNe is important to understand the common-envelope evolutionary phase and also to get distance esimates to PNe. Binary central stars are relatively rare in PNe. There are about 15 close-binary central stars known (Bond & Livio 1990; Livio 1997). Some of them are among the hottest known central stars.

Milne & Aller (1982) made radio observations of PC 11 at 14.7 GHz and found a flux density of 41 mJy. Kenny et al. (1992) measured a flux density of 26 mJy at 5 GHz. The far-IR (IRAS) colours are similar to those usually observed in PNe (Parthasarathy & Bhatt 1989). We have obtained UV (IUE) spectra of PC 11 on six occasions and an analysis of these spectra is presented in this paper.

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© European Southern Observatory (ESO) 2000

Online publication: March 9, 2000