An edge-on translucent dust disk around the nearest AGB star, L₂Puppis

Abstract

As the nearest known AGB star (d = 64 pc) and one of the brightest (m K ≈ −2), L 2 Pup is a particularly interesting benchmark object to monitor the final stages of stellar evolution. We report new serendipitous imaging observations of this star with the VLT/NACO adaptive optics system in twelve narrow-band filters covering the 1.0−4.0 µm wavelength range. These diffraction-limited images reveal an extended circumstellar dust lane in front of the star that exhibits a high opacity in the J band and becomes translucent in the H and K bands. In the L band, extended thermal emission from the dust is detected. We reproduced these observations using Monte Carlo radiative transfer modeling of a dust disk with the RADMC-3D code. We also present new interferometric observations with the VLTI/VINCI and MIDI instruments. We measured in the K band an upper limit to the limb-darkened angular diameter of θ LD = 17.9 ± 1.6 mas, converting to a maximum linear radius of R = 123 ± 14 R . Considering the geometry of the extended K band emission in the NACO images, this upper limit is probably close to the actual angular diameter of the star. The position of L 2 Pup in the Hertzsprung-Russell diagram indicates that this star has a mass of about 2 M and is probably experiencing an early stage of the asymptotic giant branch. We did not detect any stellar companion of L 2 Pup in our adaptive optics and interferometric observations, and we attribute its apparent astrometric wobble in the H data to variable lighting effects on its circumstellar material. However, we do not exclude the presence of a binary companion, because the large loop structure extending to more than 10 AU to the northeast of the disk in our L-band images may be the result of interaction between the stellar wind of L 2 Pup and a hidden secondary object. The geometric configuration that we propose, with a large dust disk seen almost edge-on, appears particularly favorable to test and develop our understanding of the formation of bipolar nebulae.

High-resolution IR and radio observations of AGB stars

“…The detailed mechanics driving mass loss is not well understood; nor is the reason why many planetary nebulae are very asymmetric while their AGB progenitors appear circularly symmetric. Recent findings on the closest Mira-type star L2 Puppis may shed light on new directions to investigate this (Kervella et al 2014). Perrin et al (2004) observed a number of Mira variables between 2.2 and 3.6 µm and derived large variations of the apparent size with wavelength.…”

Dissecting the AGB star L2Puppis: a torus in the making

“…L 2 Pup is therefore one of the few AGB stars with evidence for asphericities in their circumstellar material, and as the closest mass-losing AGB star, is ideally placed for resolving the details of the envelope structure. We note that the technique of aperture masking used here is different and complementary to the technique of direct adaptive optics imaging used by Kervella et al (2014), as discussed in detail in Sect. 4.5.…”

Evidence of a Mira-like tail and bow shock about the semi-regular variable V CVn from four decades of polarization measurements

“…However, time-averaged DIRBE IR colors are consistent with observations of other semi-regular variable and Mira stars (Smith 2003;Smith et al 2004), hence we cannot draw conclusions from the above mentioned observations about the presence of a disk structure about V CVn. Kervella et al (2014) present new IR images of L 2 Pup, which displays similar polarimetric behaviors as V CVn, and detect a circumstellar disk that is approximately edge-on. They also find evidence for circumstellar material beyond the disk, in Table 1.…”

“…Higher resolution observations will improve the situation and test our hypothesis for explaining the observed polarization. The extended asymmetric structure, observed at IR wavelengths by Kervella et al (2014), about L 2 Pup may also be interpreted as a stellar-wind bow shock. This idea is supported as the material is aligned in the north-east to south-west axis consistent with the star's direction of motion.…”