New Constraints on the Origin of the Short-Term Cyclical Variability of the Wolf-Rayet Star WR 46

The Wolf-Rayet star WR 46 is known to exhibit a very complex variability pattern on relatively short time scales of a few hours. Periodic but intermittent radial velocity shifts of optical lines as well as multiple photometric periods have been found in the past. Non-radial pulsations, rapid rotational modulation or the presence of a putative low-mass companion have been proposed to explain the short-term behaviour. In an effort to unveil its true nature, we observed WR 46 with FUSE (Far Ultraviolet Spectroscopic Explorer) over several short-term variability cycles. We found significant variations on a time scale of ~8 hours in the far-ultraviolet (FUV) continuum, in the blue edge of the absorption trough of the OVI {\lambda}{\lambda}1032, 1038 doublet P Cygni profile and in the SVI {\lambda}{\lambda}933, 944 P Cygni absorption profile. We complemented these observations with X-ray and UV light-curves and an X-ray spectrum from archival XMM-Newton (X-ray Multi-Mirror Mission - Newton Space Telescope) data. The X-ray and UV light-curves show variations on a time scale similar to the variability found in the FUV. We discuss our results in the context of the different scenarios suggested to explain the short-term variability of this object and reiterate that non-radial pulsations is the most likely to occur.Comment: 36 pages, 11 figures. Accepted for publication in Ap

The conspicuous absence of X-ray emission from carbon-enriched Wolf-Rayet stars

The carbon-rich WC5 star WR 114 was not detected during a 15.9 ksec XMM-Newton observation, implying an upper limit to the X- ray luminosity of L-X less than or similar to 2.5 x 10(30) erg s(-1) and to the X-ray to bolometric luminosity ratio of L- X/L(bo)l less than or similar to 4 x 10(-9). This confirms indications from earlier less sensitive measurements that there has been no convincing X-ray detection of any single WC star. This lack of detections is reinforced by XMM-Newton and Chandra observations of WC stars. Thus the conclusion has to be drawn that the stars with radiatively-driven stellar winds of this particular class are insignificant X-ray sources. We attribute this to photoelectronic absorption by the stellar wind. The high opacity of the metal-rich and dense winds from WC stars puts the radius of optical depth unity at hundreds or thousands of stellar radii for much of the X-ray band. We believe that the essential absence of hot plasma so far out in the wind exacerbated by the large distances and correspondingly high ISM column densities makes the WC stars too faint to be detectable with current technology. The result also applies to many WC stars in binary systems, of which only about 20% are identified X-ray sources, presumably due to colliding winds

Dynamic lighting in classrooms:a new interactive tool for teaching

Abstract This paper presents the results of a field study on the use of lighting as a tool to structure and support teaching and learning activities by teachers. In a Danish elementary school, a dynamic lighting technology with the option of choosing four different lighting scenarios was installed in classrooms. The teachers’ use of the lighting was studied combining qualitative research material from observations and interviews and quantitative data from the lighting control system which indicated the teachers’ choices for lighting scenarios. As a result, different types of motivations for interacting with lighting emerged in the analysis: Supporting and structuring learning activities; Communicating with lighting and involving students; Affecting students’ activity level and behavior; Creating atmosphere; and Supporting visual task and visual comfort. All these motivational aspects should be considered when designing dynamic lighting systems for learning environments, thus creating a new interactive tool for teachers