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Astron. Astrophys. 344, 143-150 (1999)

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1. Introduction

The orientation of stars, their outflows or their associated nebulae with respect to their environment, either local or global, may provide insights on their formation, life, and death in interrelation with the surrounding medium, i.e. their ecology.

Flows and jets from young objects are known to frequently align with the ambient interstellar magnetic field, a result of great importance for the theoretical interpretation of the flows as well as for star formation theory (e.g. Strom et al. 1988, Appenzeller 1989, and references therein).

At the other end of stellar evolution, the orientation of planetary nebulae with respect to the galactic plane has been studied by Grinin & Zvereva (1968), Melnick & Harwit (1975), and Phillips (1997). Considering a large sample of objects, all these authors found a significant alignment of planetary nebula major axes with the galactic plane, an effect which indicates a possible influence of the galactic magnetic field. Apparently, no clear theoretical modelling accounts for this phenomenon (cf. Phillips 1997).

Like planetary nebulae, which are ejected by evolved low-mass stars, nebulae are also ejected by the most massive stars in the late stages of their evolution. Such nebulae are detected around Luminous Blue Variables (LBV) and Wolf-Rayet (WR) stars. An alignment between the long axis of the nebulae surrounding the LBVs R127, AG Car and [FORMULA] Car and the direction of the local interstellar polarization -an indicator of the magnetic field local direction- has already been noticed by Schulte-Ladbeck et al. (1993, 1994) and Aitken et al. (1995). In fact, the position angles of the [FORMULA] Car, AG Car and HR Car nebulae (as reported in the literature, cf. Appendix A) are remarkably similar, possibly indicating a more global alignment effect.

The aim of the present paper is to study on a statistical basis the orientation of all known galactic LBV nebulae (plus a few ring nebulae associated with WR stars) with respect to the galactic plane and to the local direction of the interstellar polarization. LBV nebulae resolved in the Large Magellanic Cloud (LMC) are also considered and their orientation compared to the direction of the LMC magnetic field. In Sect. 2, the definition of the sample and the measurements of nebular position angles are described. Statistical analyzes and results are presented in Sect. 3, while discussion and conclusions form the last section.

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© European Southern Observatory (ESO) 1999

Online publication: March 10, 1999