Dissecting the AGB star L₂Puppis: a torus in the making

Abstract

Aims. The circumstellar environment of L 2 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 L 2 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 .

A disk asymmetry in motion around the B[e] star MWC158

“…Borges postulated the formation of a "one-armed spiral" due to matter ejection from a stellar hot spot. Asymmetric features were also observed in the circumstellar environment of the AGB star L 2 Puppis (Kervella et al 2014;Lykou et al 2015). Such a pattern is very likely generated by the interaction of a close companion (that we could not constrain around MWC158) with the strong stellar wind coming from the primary (van Winckel et al 2009).…”

Mass loss of stars on the asymptotic giant branch

“…Indeed, the presence of a disk has been inferred in a number of post-AGB objects (Bujarrabal et al 2013), while disks around AGB stars have remained elusive. However, clear evidence of a dust disk with an inner and outer edge lying at ≈ 6 and ≈ 13 au, respectively, has recently been found towards the M-star L 2 Pup Lykou et al 2015;Ohnaka et al 2015). This could be the first evidence of disk formation around a star at the end of its evolution on the AGB.…”

Fundamental parameters and infrared excesses of Tycho–Gaia stars

“…Strong asymmetries also exist in some evolved stars, either as clumps or discs (e.g. Richards et al 2014;Leão et al 2015;Lykou et al 2015;Kervella et al 2016). …”