Dissecting the AGB star L₂ Puppis: a torus in the making^⋆

¹ Institut für Astrophysik, Universität Wien, Türkenschanzstrasse 17, 1180 Wien, Austria
e-mail: foteini.lykou@univie.ac.at
² Institut d’Astronomie et d’Astrophysique, Université Libre de Bruxelles, CP 226, Boulevard du Triomphe, 1050 Bruxelles, Belgium
³ Jodrell Bank Centre of Astrophysics, Alan Turing Building, University of Manchester, Oxford Road, M13 9PL, Manchester, UK
⁴ UJF-Grenoble 1/CNRS-INSU, Institut de Planétologie et d’Astrophysique de Grenoble (IPAG), UMR 5274 Grenoble, France
⁵ Sydney Institute for Astronomy, University of Sydney, 44 Rosehill St, Redfern, NSW 2016, Sydney, Australia
⁶ Department of Astronomy, Uppsala Universitet, Box 516, 75120 Uppsala, Sweden
⁷ Department of Astronomy, Cornell University, 222 Space Sciences Building, Ithaca, NY 14853-6801, USA
⁸ Laboratoire Lagrange, UMR 7293, Université de Nice-Sophia Antipolis, CNRS, Observatoire de la Côte d’Azur, Bd de l’Observatoire, BP 4229, 06304 Nice Cedex 4, France
⁹ European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching, Germany
¹⁰ Onsala Space Observatory, Department of Earth and Space Sciences, Chalmers University of Technology, 439-92 Onsala, Sweden

Received: 10 October 2013
Accepted: 20 December 2014

Abstract

Aims. The circumstellar environment of L₂ Pup, an oxygen-rich semiregular variable, was observed to understand the evolution of mass loss and the shaping of ejecta in the late stages of stellar evolution.

Methods. High-angular resolution observations from a single 8 m telescope were obtained using aperture masking in the near-infrared (1.64, 2.30 and 3.74 μm) on the NACO/VLT, both in imaging and polarimetric modes.

Results. The aperture-masking images of L₂ Pup at 2.30 μm show a resolved structure that resembles a toroidal structure with a major axis of ~140 milliarcseconds (mas) and an east–west orientation. Two clumps can be seen on either side of the star, ~65 mas from the star, beyond the edge of the circumstellar envelope (estimated diameter is ~27 mas), while a faint, hook-like structure appear toward the northeast. The patterns are visible both in the imaging and polarimetric mode, although the latter was only used to measure the total intensity (Stokes I). The overall shape of the structure is similar at the 3.74 μm pseudo-continuum (dust emission), where the clumps appear to be embedded within a dark, dusty lane. The faint, hook-like patterns are also seen at this wavelength, extending northeast and southwest with the central, dark lane being an apparent axis of symmetry. We interpret the structure as a circumstellar torus with inner radius of 4.2 au. With a rotation velocity of 10 km s^-1 as suggested by the SiO maser profile, we estimate a stellar mass of 0.7 M_⊙.