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2002A&A...385..600V - Astronomy and Astrophysics, volume 385, 600-618 (2002/4-2)

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


Abstract (from CDS):

We present spectroscopic monitoring of the Wolf-Rayet (WR) star WR46 between 1989 and 1998, which has been obtained simultaneously with multicolour photometry (Veen et al., 2002A&A...385..585V, Paper I). The spectroscopic monitoring data show that the radiative fluxes of the optical emission lines (OVI 3811/34, OVI 5290, NV 4944, NV 4604/20, HeII 4686, HeII 4859, HeII 5411, HeII 6560) vary in concert with the photometric single-wave (sw) frequency fsw (Paper I), and also the difference 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., 2000AJ....120.2101M). These so-called stand-stills may be related to the observed time-delay effects. A time-delay effect 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 (NV 4604/20 and HeII). 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 HeII 4686 emission line shows pronounced line-profile changes on a time scale of hours. Our monitoring is not sufficient 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 confirms the WR nature as established from the WR standard model analysis by Crowther et al. (1995A&A...302..457C; hereafter referred to as CSH). The various time-delay effects are consistent with the formation of the spectrum in a stratified 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. (1995IAUS..163..245N) and Steiner & Diaz (1998PASP..110..276S). 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. (2002A&A...385..619V, Paper III).

Abstract Copyright:

Journal keyword(s): stars: Wolf-Rayet - stars: individual: WR 46 - stars: binaries: close - stars: variables: general - stars: oscillations

Status at CDS:  

Simbad objects: 7

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