Multi-epoch infrared spectroscopy of mu Centauri prior to outburst

AGUAYO; MENNICKENT, R.; OTERO; GRANADA, A.

Florianopolis

Congreso; XIV Latin American Regional IAU Meeting; 2013

IAU

We present 9 L-band spectra of the Be star μ Cen obtained with theVLT ISAAC distributed along 1 year during an epoch of relative photometric quiescence prior to a Δ V= 0.4 mag outburst. Visual estimates for the V magnitude obtained during the last 13 years are also presented. The L-band region from 2.9 to 4.1 microns contains import antdiagnostic Hydrogen lines that are sensitive to changes in the optical depth conditions of the star envelope. We chose μ Centauri as our target due to its brightness and short recurrence time of relatively well documented outbursts in order to study the evolution of the Be star envelope along time including matter ejection episodes. We measured line strengths, line widths and constructed a line flux ratio diagram as the one made by Lenorzer et al. (2002). Despite the fact that we found the star into a quiescence period, we observe significant and monotonic changes in emission line strength of Bracket-α and Pfund-γ lines relative to Humphreys series. We interpret this variability as changes in the opacity of the circumstellar envelope, moving from an optically thin to an optically thick condition just prior to a major outburst.