Extensive spectral observations of η Carinae over the last cycle, and particularly around the 2003.5 low‐excitation event, have been obtained. The variability of both narrow and broad lines, when combined with data taken from two earlier cycles, reveal a common and well‐defined period. We have combined the cycle lengths derived from the many lines in the optical spectrum with those from broad‐band X‐rays, optical and near‐infrared observations, and obtained a period length of Ppres= 2022.7 ± 1.3 d. Spectroscopic data collected during the last 60 yr yield an average period of Pavg= 2020 ± 4 d, consistent with the present‐day period. The period cannot have changed by more than ΔP/P= 0.0007 since 1948. This confirms the previous claims of a true, stable periodicity, and gives strong support to the binary scenario. We have used the disappearance of the narrow component of He i 6678 to define the epoch of the Cycle 11 minimum, T0= JD 245 2819.8. The next event is predicted to occur on 2009 January 11 (±2 d). The dates for the start of the minimum in other spectral features and broad‐bands are very close to this date, and have well‐determined time‐delays from the He i epoch.

A full description of the 5.5‐yr low excitation events in η Carinae is presented. We show that they are not as simple and brief as previously thought, but a combination of two components. The first, the slow variation component, is revealed by slow changes in the ionization level of circumstellar matter across the whole cycle and is caused by gradual changes in the wind–wind collision shock‐cone orientation, angular opening and gaseous content. The second, the collapse component, is restricted to around the minimum, and is due to a temporary global collapse of the wind–wind collision shock. High‐energy photons (E > 16 eV) from the companion star are strongly shielded, leaving the Weigelt objects at low‐ionization state for more than six months. High‐energy phenomena are sensitive only to the collapse, low energy only to the slow variation and intermediate energies to both components. Simple eclipses and mechanisms effective only near periastron (e.g. shell ejection or accretion on to the secondary star) cannot account for the whole 5.5‐yr cycle. We find anti‐correlated changes in the intensity and the radial velocity of P Cygni absorption profiles in Fe iiλ6455 and He iλ7065 lines, indicating that the former is associated to the primary and the latter to the secondary star. We present a set of light curves representative of the whole spectrum, useful for monitoring the next event (2009 January 11).

We explore the geometrical distortion and the stellar and circumstellar activity of α Eri (HD 10144), the brightest Be star in the sky. We present a thorough discussion of the fundamental parameters of the object for an independent determination of its rotational distortion. We used stellar atmosphere models and evolutionary tracks calculated for fast rotating early-type stars. If the star is a rigid rotator, its angular velocity rate is Ω/Ω c 0.8, so that its rotational distortion is smaller than the one inferred from recent interferometric measurements. We then discuss the stellar surface activity using high resolution and high S/N spectroscopic observations of He i and Mg ii lines, which concern a period of Hα line emission decline. The variations in the He i lines are interpreted as due to non-radial pulsations. Time series analysis of variations was performed with the cleanest algorithm, which enabled us to detect the following frequencies: 0.49, 0.76, 1.27 and 1.72 c/d and pulsation degrees ∼ (3−4) for ν = 0.76 c/d; ∼ (2−3) for ν = 1.27 c/d and ∼ (3−4) for ν = 1.72 c/d. The study of the absolute deviation of the He i λ6678 Å spectral line revealed mass ejection between 1997 and 1998. We conclude that the lowest frequency found, ν = 0.49 c/d, is due to the circumstellar environment, which is present even at epochs of low emission in the wings of He i λ6678 Å and Mg ii λ4481 Å line profiles, as well as during nearly normal aspects of the Hα line. This suggests that there may be matter around the star affecting some spectral regions, even though the object displays a B-normal like phase. The long-term changes of the Hα line emission in α Eri are studied. We pay much attention to the Hα line emission at the epoch of interferometric observations. The Hα line emission is modeled and interpreted in terms of varying structures of the circumstellar disc. We conclude that during the epoch of interferometric measurements there was enough circumstellar matter near the star to produce λ2.2 µm flux excess, which could account for the overestimated stellar equatorial angular diameter. From the study of the latest B Be phase transition of α Eri we concluded that the Hα line emission formation regions underwent changes so that: a) the low Hα emission phases are characterized by extended emission zones in the circumstellar disc and a steep outward matter density decline; b) during the strong Hα emission phases the emitting regions are less extended and have a constant density distribution. The long-term variations of the Hα line in α Eri seem to have a 14-15 year cyclic B Be phase transition. The disc formation time scales, interpreted as the periods during which the Hα line emission increases from zero to its maximum, agree with the viscous decretion model. On the other hand, the time required for the disc dissipation ranges from 6 to 12 years which questions the viscous disc model.

We present the results of a high-accuracy ( ) polarization monitoring of the Be star Achernar that was j ≈ 0.005% carried out between 2006 July 7 and November 5. Our results indicate that after a near-quiescent phase from 1998 to 2002, Achernar is currently in an active phase and has built a circumstellar disk. We detect variations both in the polarization level and position angle on timescales as short as 1 hr and as long as several weeks. Detailed modeling of the observed polarization strongly suggests that the short-term variations originate from discrete mass ejection events which produce transient inhomogeneities in the inner disk. Long-term variations, on the other hand, can be explained by the formation of an inner ring following one or several mass ejection events.

Spectroscopic monitoring of 141 southern field B type stars, 114 of them known to exhibit the Be phenomenon, allowed the estimation of their projected rotational velocities, effective temperatures and superficial gravities from both line and equivalent width fitting procedures. Stellar ages, masses and bolometric luminosities were derived from internal structure models. Without taking into account for the effects of gravity darkening, we notice the occurrence of the Be phenomenon in later stages of main sequence phase.Comment: 10 pages, 6 figure