A. M. van Genderen

The yellow hypergiant HR 5171 A: Resolving a massive interacting binary in the common envelope phase

We initiated long-term optical interferometry monitoring of the diameters of unstable yellow hypergiants (YHG) with the goal of detecting both the long-term evolution of their radius and shorter term formation related to large mass-loss events. We observed HR5171 A with AMBER/VLTI. We also examined archival photometric data in the visual and near-IR spanning more than 60 years, as well as sparse spectroscopic data. HR5171A exhibits a complex appearance. Our AMBER data reveal a surprisingly large star for a YHG R*=1315+/-260Rsun\ (~6.1AU) at the distance of 3.6+/-0.5kpc. The source is surrounded by an extended nebulosity, and these data also show a large level of asymmetry in the brightness distribution of the system, which we attribute to a newly discovered companion star located in front of the primary star. The companions signature is also detected in the visual photometry, which indicates an orbital period of Porb=1304+/-6d. Modeling the light curve with the NIGHTFALL program provides clear evidence that the system is a contact or possibly over-contact eclipsing binary. A total current system mass of 39^{+40}_{-22} solar mass and a high mass ratio q>10 is inferred for the system. The low-mass companion of HR5171 A is very close to the primary star that is embedded within its dense wind. Tight constraints on the inclination and vsini of the primary are lacking, which prevents us from determining its influence precisely on the mass-loss phenomenon, but the system is probably experiencing a wind Roche-Lobe overflow. Depending on the amount of angular momentum that can be transferred to the stellar envelope, HR5171 A may become a fast-rotating B[e]/Luminous Blue Variable (LBV)/Wolf-Rayet star. In any case, HR5171 A highlights the possible importance of binaries for interpreting the unstable YHGs and for massive star evolution in general.

The enigmatic WR46: A binary or a pulsator in disguise. II. The spectroscopy

We present spectroscopic monitoring of the Wolf-Rayet (WR) star WR 46 between 1989 and 1998, which has been obtained simultaneously with multicolour photometry (Veen et al. 2002a, Paper I). The spectroscopic monitoring data show that the radiative fluxes of the optical emission lines (O vi 3811/34, O vi 5290, N v 4944, N v 4604/20, He ii 4686, He ii 4859, He ii 5411, He ii 6560) vary in concert with the photometric single-wave (sw) frequency fsw (Paper I), and also the dierence of that period between 1989 and 1991. The line-flux variability does not provide obvious support for a short second period (Paper I). The radial-velocity variations show a remarkable behaviour: usually, they display a coherent single-wave on the time scale of the double-wave period, while during some nights the radial velocity appears surprisingly to stay constant (see also Marchenko et al. 2000). These so-called stand-stills may be related to the observed time-delay eects. A time-delay eect manifests itself in several phenomena. Firstly, the line flux shows small, but persistent, time-delays for lines originating from lower optical depths, the outer-wind lines (N v 4604/20 and He ii). Secondly, the radial-velocity variations display much larger time-delays than the line fluxes and their behaviour appears less consistent. Assuming that the double-wave period controls the radial velocity, the stand-still is observed to start when the radial motion is in anti-phase with the presumed orbital motion. Thirdly, the outer-wind lines are observed to enter a stand-still much later than the inner-wind lines. Fourthly, the radial-velocity variations of the peaks of the emission lines precede the radial-velocity variations of the wings of those lines. In addition to line-flux- and radial-velocity variability, the He ii 4686 emission line shows pronounced line-prole changes on a time scale of hours. Our monitoring is not sucient to study this in detail. Furthermore, we discern a flaring behaviour, i.e., an emission bump appeared on the blue wing of two Heii-lines (around 1700 km s 1 ) lasting less than 5 min. Finally, the line fluxes follow the observed brightenings, also on a time scale of years. We conclude that the short-term cyclic variability conrms the WR nature as established from the WR standard model analysis by Crowther et al. (1995; hereafter referred to as CSH). The various time-delay eects are consistent with the formation of the spectrum in a stratied stellar wind. The outer layers trail the inner ones. The variability is inconsistent with the formation of the spectrum in a stellar disc as proposed by Niemela et al. (1995) and Steiner & Diaz (1998). The long-term cyclic variability of the brightness and line fluxes is related to an increase of the mass-loss-rate, and, possibly, to the period changes. The interpretation of the nature of the variability is deferred to Veen et al. (2002b, Paper III).

Light variations of massive stars (

Multi-colour photometry (Walraven system) of five superand hypergiants in the LMC, viz. R 74, R 78, HD 34664, R 84 and R 116, is searched for variability and periods, and discussed. Apart from R 84, of which the claimed variability in the past must be due to a number of faint field stars at the edge of the apertures, all are variable. R 74 and HD 34664 are weak-active LBVs with superimposed microvariations. HD 34664 is the second known B[e] star which is also an LBV. The first reported one is R 4 in the SMC. This could alter some views on the evolutionary history of B[e] stars and LBVs. R 78 is anα Cyg variable, but presumably no LBV. R 116 appears to be a close counterpart of the galactic ex-/dormant LBV ζ1 Sco, also showing an intricate α Cyg-type multi-period microvariability.We discuss photometric monitoring (VBLUW system) of three B(e) supergiants. All three objects appear to be variable. They are subject to two (R 66 and R 126 in the LMC) and three (S 18 in the SMC) types of light oscillations which range from a few days to years, and are probably due to pulsations. We argue that a classication as Cyg variables is justied. Their classication as mixed B(e)/S Dor variables is less certain, though not impossible. Also based on other cases, a strong B(e){S Dor variable connection seems to be present.

\alpha

Photometric and spectroscopic monitoring campaigns of WR 46 (WN3p), as presented in Veen et al. (2002a,b; hereafter Papers I and II, respectively), yield the following results. The light- and colour variations reveal a dominant single-wave period of P 89

Cyg variables) - XVIII. The B[e] supergiants S 18 in the SMC and R 66 = HDE 268835 and R 126 = HD 37974 in the LMC

On the basis of new photometric observations and archived data published since 1907, we discuss the light variations of P Cygni. We conclude that there are α Cygni-type microvariations with a stable (pulsation) quasi-period of 17.3 days. There are also longer cycles of variation with

The enigmatic WR46 : A binary or a pulsator in disguise. III. Interpretation

P\sim

Cyclicities in the light variations of S Doradus stars - III. P Cygni

100 d, so-called 100 d-type micro-variations, and with

Wra751, a luminous blue variable developing an S Doradus cycle

P\sim 1500

η Carinae : The 1998 brightening and the smearing-out effect

-1600 d, a short S Dor-type phase.

η Carinae: A pulsating luminous blue variable

Aims. The object Wra 751 is a luminous blue variable that lately exhibits strong changes in light and color. We summarise the available photometry of Wra 751, present new photometric observations, and discuss these data with special attention on the systematic differences between the various data sources. In addition, we establish an empirical relationship between b − y and B −V for this class of stars. Methods. Wra 751 is a strong-active member of the S Dor class, and it exhibits very-long term S Doradus phases with an amplitude of about two magnitudes in V and a cycle length of several decades. The associated B − V colour-index amplitude is about 0.4 mag. At this moment this LBV, which is the reddest member of the class, is going through the bright (and red) stage of a long-term S Dor cycle. Results. The S Dor behaviour of this system shows some resemblence to the temporal characteristics of the Galactic LBV AG Car, because the time scales and amplitudes of light and colour variability are very similar.