Spectroscopic variabilities in λ Pavonis

¹ Universidade Federal de São Paulo, Depto. Ciências Exatas e da Terra, Rua Prof. Artur Riedel, 275, Jd. Eldorado, CEP 09972-270, Diadema SP, Brazil
e-mail: ronaldo.levenhagen@gmail.com
² Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo, CEP 05508-900 São Paulo, SP, Brazil
³ Instituto de Física, Universidade de São Paulo, Cidade Universitária, CEP 05508-900 São Paulo, SP, Brazil

Received: 26 January 2011
Accepted: 14 July 2011

Abstract

Aims. We investigate the time-varying patterns in line profiles, V/R, and radial velocity of the Be star HD 173948 (λ Pavonis).

Methods. Time series analyses of radial velocity, V/R, and line profiles of He i, Fe ii, and Si ii were performed with the Cleanest algorithm. An estimate of the stellar rotation frequency was derived from the stellar mass and radius in the Roche limit by adopting an aspect angle i derived from the fittings of non-LTE model spectra affected by rotation. The projected rotation velocity, necessary as input for the spectral synthesis procedure, was evaluated from the Fourier transform of the rotation profiles of all neutral helium lines in the optical range.

Results. Emission episodes in Balmer and He i lines, as well as V/R cyclic variations, are reported for spectra observed in year 1999, followed by a relatively quiescent phase (2000) and then again a new active epoch (2001). From time series analyses of line profiles, radial velocities, and V/R ratios, four signals with high confidence levels are detected: ν₁ = 0.17  ±  0.02, ν₂ = 0.49  ±  0.05, ν₃ = 0.82  ±  0.03, and ν₄ = 1.63  ±  0.04 c/d. We interpret ν₄ as a non-radial pulsation g-mode, ν₃ as a signal related to the orbital timescale of ejected material, which is near the theoretical rotation frequency 0.81 c/d inferred from the fitting of the models taken into account for gravity darkening. The signals ν₁ and ν₂ are viewed as aliases of ν₃ and ν₄.