The curious case of II Lup: a complex morphology revealed with SAM/NACO and ALMA

Lykou, Foteini and Zijlstra, A. A. and Kluska, J. and Lagadec, E. and Tuthill, P. G. (2018) The curious case of II Lup: a complex morphology revealed with SAM/NACO and ALMA. MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 480 (1). pp. 1006-1021. ISSN 0035-8711

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Abstract

We present the first-ever images of the circumstellar environment of the carbon-rich asymptotic giant branch (AGB) star II Lup in the infrared and sub-mm wavelengths, and the discovery of the envelope's non-spherical morphology with the use of high angular resolution imaging techniques with the sparse aperture maskingmode on NACO/Very Large Telescope (which enables diffraction-limited resolution from a single telescope) and with the Atacama Large Millimeter/submillimeter Array (ALMA). We have successfully recovered images in Ks (2.18 mu m), L' (3.80 mu m), and M' (4.78 mu m) that revealed the non-spherical morphology of the circumstellar envelope around II Lup. The stellar surface of the AGB star is unresolved (i.e. <= 30 mas in Ks), however, the detected structure extends up to 110 mas from the star in all filters. Clumps have been found in the Ks maps, while at lower emission levels a hook-like structure appears to extend counterclockwise from the south. At larger spatial scales, the circumstellar envelope extends up to approximately 23 arcsec, while its shape suggests a spiral at four different molecules, namely CO, SiO, CS, and HC3N, with an average arm spacing of 1.7 arcsec that would imply an orbital period of 128 yr for a distance of 590 pc.

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