A Study of the Circumstellar Envelopes of \(\delta\) Centauri and \(\eta\) Centauri Based on H\(\alpha\) Line and Geometric Modeling Amandaru Taruna Mandala, Hakim L. Malasan
Institut Teknologi Bandung
Abstract
This study investigates the envelope dynamics of two southern Be stars, \(\delta\) Centauri and \(\eta\) Centauri, using observational data from the Bosscha Observatory and the BeSS database. \(\delta\) Centauri was identified as a binary star in 2008 via spectro-interferometry, while \(\eta\) Centauri exhibits rapid photometric and spectroscopic variability on timescales of hours to days. The findings of this study present an initial interpretation of the complex physical mechanisms involved, including possible binary interaction driving the variability in \(\delta\) Centauri and pulsation-driven mass ejections in \(\eta\) Centauri. High-resolution analysis of the H\(\alpha\) line reveals complex and distinct envelope dynamics in both stars. In \(\delta\) Centauri, a temporary profile change from a double-peak to a single-peak was observed, which is hypothesized to be a consequence of a polar mass ejection triggered by Non-Radial Pulsations (NRPs). The presence of perturbations on the line peaks also indicates a likely interaction with the companion star. For \(\eta\) Centauri, an increase in absorption strength, correlated with the E/C ratio, signifies a new injection of matter into the envelope. Supported by additional photometric data, this variability is consistent with a beat cycle mechanism (0.035 c/d) driven by NRPs, causing periodic mass ejections and the observed expansion of the gaseous disk. To support future studies, a preliminary qualitative 3D model depicting the geometry of the Be star^s circumstellar envelope has also been successfully developed.
Keywords: Be Star, Spectroscopy, H\(\alpha\), Modeling, Envelope, Binary, NRP
