The enigmatic WR46: A binary or a pulsator in disguise^*

II. The spectroscopy

¹ Leiden Observatory, Postbus 9513, 2300 RA Leiden, The Netherlands
² Department of Physics and Astronomy, University College London, Gowerstreet, London WC1E 6BT, UK
³ Space Research Organization Netherlands, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands

Corresponding author: A. M. van Genderen, genderen@strw.leidenuniv.nl

Received: 1 September 2000
Accepted: 5 November 2001

Abstract

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. [CITE], Paper I). The spectroscopic monitoring data show that the radiative fluxes of the optical emission lines ( 3811/34, 5290, 4944, 4604/20, 4686, 4859, 5411, 6560) vary in concert with the photometric single-wave (sw) frequency f_sw (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. [CITE]). 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 ( 4604/20 and ). 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 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 -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. ([CITE]; 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. ([CITE]) and Steiner & Diaz ([CITE]). 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. ([CITE], Paper III).