The dust disk and companion of the nearby AGB star L₂ Puppis

SPHERE/ZIMPOL polarimetric imaging at visible wavelengths^⋆

¹ Unidad Mixta Internacional Franco-Chilena de Astronomía (UMI 3386), CNRS/INSU, France & Departamento de Astronomía, Universidad de Chile, Camino El Observatorio 1515, Las Condes, Santiago, Chile
e-mail: pkervell@das.uchile.cl
² LESIA (UMR 8109), Observatoire de Paris, CNRS, UPMC, Université Paris-Diderot, PSL Research University, 5 place Jules Janssen, 92195 Meudon, France
e-mail: pierre.kervella@obspm.fr
³ Institut de Radio-Astronomie Millimétrique, 300 rue de la Piscine, 38406 St Martin d’Hères, France
⁴ 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
⁵ National Optical Astronomy Observatories, 950 North Cherry Avenue, Tucson, AZ 85719, USA
⁶ European Southern Observatory, Alonso de Córdova 3107, Casilla 19001, Santiago 19, Chile
⁷ Instituto de Astronomía, Universidad Católica del Norte, Avenida Angamos 0610, Antofagasta, Chile
⁸ Universidad de Concepción, Departamento de Astronomía, Casilla 160-C, Concepción, Chile

Received: 27 March 2015
Accepted: 6 May 2015

Abstract

The bright southern star L₂ Pup is a particularly prominent asymptotic giant branch (AGB) star, located at a distance of only 64 pc. We report new adaptive optics observations of L₂ Pup at visible wavelengths with the SPHERE/ZIMPOL instrument of the VLT that confirm the presence of the circumstellar dust disk discovered recently. This disk is seen almost almost edge-on at an inclination of 82^◦. The signature of its three-dimensional structure is clearly observed in the map of the degree of linear polarization p_L. We identify the inner rim of the disk through its polarimetric signature at a radius of 6 AU from the AGB star. The ZIMPOL intensity images in the V and R bands also reveal a close-in secondary source at a projected separation of 2 AU from the primary. Identification of the spectral type of this companion is uncertain due to the strong reddening from the disk, but its photometry suggests that it is a late K giant with comparable mass to the AGB star. We present refined physical parameters for the dust disk derived using the RADMC-3D radiative transfer code. We also interpret the p_L map using a simple polarization model to infer the three-dimensional structure of the envelope. Interactions between the inner binary system and the disk apparently form spiral structures that propagate along the orthogonal axis to the disk to form streamers. Two dust plumes propagating orthogonally to the disk are also detected. They originate in the inner stellar system and are possibly related to the interaction of the wind of the two stars with the material in the disk. Based on the morphology of the envelope of L₂ Pup, we propose that this star is at an early stage in the formation of a bipolar planetary nebula.