AMBER-NACO aperture-synthesis imaging of the half-obscured central star and the edge-on disk of the red giant L2 Pup

TL;DR

This study uses advanced interferometric imaging to resolve the inner circumstellar environment of the red giant L2 Pup, revealing a nearly edge-on dust disk likely responsible for its dimming event, contrasting with earlier spherical mass loss.

Contribution

First high-resolution aperture-synthesis imaging of L2 Pup's inner environment combining NACO speckle and VLTI data, revealing a disk structure linked to its dimming event.

Findings

Resolved a nearly edge-on dust disk around L2 Pup.

Detected severe obscuration of the star's southern hemisphere.

Observed a spherical envelope in earlier data, indicating a change in mass-loss geometry.

Abstract

The red giant L2 Pup started a dimming event in 1994, which is considered to be caused by the ejection of dust clouds. We present near-IR aperture-synthesis imaging of L2 Pup achieved by combining data from VLT/NACO speckle observations and long-baseline interferometric observations with the AMBER instrument of the Very Large Telescope Interferometer (VLTI). We also extracted an 8.7 micron image from the mid-IR VLTI instrument MIDI. Our aim is to spatially resolve the innermost region of the circumstellar environment. The diffraction-limited image at 2.27 micron obtained by bispectrum speckle interferometry with NACO with a spatial resolution of 57 mas shows an elongated component. The aperture-synthesis imaging combining the NACO speckle data and AMBER data (2.2--2.29 micron) with a spatial resolution of 5.6x7.3 mas further resolves not only this elongated component, but also the central star. The reconstructed image reveals that the elongated component is a nearly edge-on disk with a size of ~180x50 mas lying in the E-W direction, and furthermore, that the southern hemisphere of the central star is severely obscured by the equatorial dust lane of the disk. The angular size of the disk is consistent with the distance that the dust clouds that were ejected at the onset of the dimming event should have traveled by the time of our observations, if we assume that the dust clouds moved radially. This implies that the formation of the disk may be responsible for the dimming event. The 8.7 micron image with a spatial resolution of 220 mas extracted from the MIDI data taken in 2004 (seven years before the AMBER and NACO observations) shows an approximately spherical envelope without a signature of the disk. This suggests that the mass loss before the dimming event may have been spherical.