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New paper: Exploring the circumstellar disk-like structure of the B[e] supergiant LHA 120-S 73

Finally after almost a year, our proceedings paper on the B[e] supergiant LHA 120-S 73 is out! It is based on a poster (2015-58aaa-torres-s73) presented on the 58th Annual Meeting of the Argentinian Astronomical Society (La Plata, Argentina, Sep 14-18, 2015) and connected also with our last refereed paper.

Exploring the circumstellar disk-like structure of the B[e] supergiant LHA 120-S 73

Torres A. F., Cidale L., Kraus M., Arias M. L., Maravelias G., Borges Fernandes M., Vallverdú R.

The Large Magellanic Cloud hosts the peculiar B8-type star LHA 120-S 73. Belonging to the B[e] supergiant group, this star is surrounded by large amounts of material which forms a circumstellar disk-like structure, seen more or less pole-on. Within its dense and cool circumstellar disk, molecules form and dust condensates. Based on medium and high-resolution optical and infrared spectroscopic data, we study the structure, kinematics and physical properties of the disk using different tracers, as the emission lines of [Oi] and [Caii] for the innermost gaseous atomic region and the first-overtone bands of CO for the inner border of the molecular disk. We also analyze near-infrared mid-resolution spectra to search for the presence of other molecules and mid-infrared low-resolution spectroscopic observations to study the composition of the dust component.

NASA ADS: 2016BAAA…58..120T

New paper: Inhomogeneous molecular ring around the B[e] supergiant LHA 120-S 73

Inhomogeneous molecular ring around the B[e] supergiant LHA 120-S 73

M. Kraus, L.S. Cidale, M.L. Arias, G. Maravelias, D.H. Nickeler, A.F. Torres, M. Borges Fernandes, A. Aret, M. Cure, R. Vallverdu, R.H. Barba

We aim to improve our knowledge on the structure and dynamics of the circumstellar disk of the LMC B[e] supergiant LHA 120-S 73. High-resolution optical and near-IR spectroscopic data were obtained over a period of 16 and 7 years, respectively. The spectra cover the diagnostic emission lines from [CaII] and [OI], as well as the CO bands. These features trace the disk at different distances from the star. We analyzed the kinematics of the individual emission regions by modeling their emission profiles. A low-resolution mid-infrared spectrum was obtained as well, which provides information on the composition of the dusty disk. All diagnostic emission features display double-peaked line profiles, which we interpret as due to Keplerian rotation. We find that LHA 120-S 73 is surrounded by at least four individual rings of material with alternating densities (or by a disk with strongly non-monotonic radial density distribution). Moreover, we find that the molecular ring must have gaps or at least strong density inhomogeneities, or in other words, a clumpy structure. The mid-infrared spectrum displays features of oxygen- and carbon-rich grain species, which indicates a long-lived, stable dusty disk. We cannot confirm the previously reported high value for the stellar rotation velocity. The line profile of HeI 5876 A is strongly variable in both width and shape and resembles of those seen in non-radially pulsating stars. A proper determination of the real underlying stellar rotation velocity is hence not possible. The existence of multiple stable and clumpy rings of alternating density recalls ring structures around planets. Although there is currently insufficient observational evidence, it is tempting to propose a scenario with one (or more) minor bodies or planets revolving around LHA 120-S 73 and stabilizing the ring system, in analogy to the shepherd moons in planetary systems.

arXiv:1607.00152 | NASA ADS: 2016A&A…593A.112K