Nelson Vani Leister

The periodicity of the η Carinae events

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 P pres = 2022.7 ± 1.3 d. Spectroscopic data collected during the last 60 yr yield an average period of P avg = 2020 ± 4 d, consistent with the present-day period. The period cannot have changed by more than AP/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, To = 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.

Spectroscopic analysis of southern B and Be stars

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 the effects of gravity darkening, we note the occurrence of the Be phenomenon in later stages of main-sequence phase.

ACHERNAR : RAPID POLARIZATION VARIABILITY AS EVIDENCE OF PHOTOSPHERIC AND CIRCUMSTELLAR ACTIVITY

We present the results of a high-accuracy (σ ≈ 0.005%) polarization monitoring of the Be star Achernar that was 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.

Fourier-Doppler Imaging of Line Profile Variations in ζ Ophiuchi

We present, for the first time, the Fourier-Doppler Imaging (FDI) analysis of periodic line profile variations in a ζ Oph-type star. For this purpose we obtained, in the period from 1996 May 3 to May 5, a total of 242 high-resolution, high signal-to-noise ratio spectra of the Be star ζ Oph itself. Using the FDI technique, we examine the variations in both time and wavelength and complement it with time series analysis. This kind of analysis is valid for both the nonradial pulsator model and the rotation modulation model, but we discuss the results in terms of the former model, considering it the more likely explanation for the observed line profile variability. Two distinct groups of modes are detected: medium (4 ≤ l ≈ |m| ≤ 8) and high-degree modes (which could be associated with 13 ≤ l ≈ |m| ≤ 17). It is shown that the high-frequency oscillations were strongly confined to an equatorial belt narrower than 20° and that the line profile variability was caused predominantly by sectoral modes, although tesseral modes |m| = l - 1 are not excluded in taking into account the effect of fast rotation. We discuss the modal nature of the waves with respect to the characteristic oscillation periods in the corotating frame and the high amplitude of the projected rotational velocity variations (≈20 km s-1).

The Remarkable Be+sdOB Binary HD 55606. I. Orbital and Stellar Parameters*

Prompted by peculiar spectroscopic variability observed in SDSS/APOGEE

The Viscosity Parameter's Dependence on the Profile of the Disk Scale Height

H

A multispectral view of the periodic events in η Carinae

-band spectra, we monitored the Be star HD 55606 using optical spectroscopy and found that it is an exotic double-lined spectroscopic binary (SB2) consisting of a Be star and a hot, compact companion that is probably an OB subdwarf (sdOB) star. Motion of the sdOB star is traced by its impact on the strong He~I lines, observed as radial velocity (

Solar diameter measurements at São Paulo Observatory

V_{r}

The periodicity of the ? Carinae events

) variable, double-peaked emission profiles with narrow central absorption cores. Weak He II 4686 A absorption associated with the companion star is detected in most spectra. Use of the emission peaks of low-ionization emission lines to trace the Be star

Physical parameters and chemical abundances of δ Ceti

V_{r}