On θ orionis

The enigmatic radio emission from θ 1 Orionis A

The bright star θ1 Orionis A, the third most luminous OB star in the Orion Trapezium Cluster, is known as a strongly variable non-thermal radio source. The physical nature of the emission mechanism has been a matter of debate since almost two decades. In this contribution we re-analyse available radio data in combination with near-infrared observations to investigate the radio-emission mechanis...

Periodic X - ray Emission from the O 7 V Star θ 1 Orionis C

We report the discovery of large-amplitude, periodic X-ray emission from the O7 V star θ Orionis C, the central star of the Orion Nebula. Ten ROSAT HRI snapshots of the Trapezium cluster taken over the course of 21 days show that the count rate of θ Ori C varies from 0.26 to 0.41 counts s with a clear 15-day period. The soft X-ray variations have the same phase and period as Hα and He II λ4686 ...

Continuum optical circular polarisation in the young O star Θ 1 Orionis C ?

Recently, Donati & Wade (1999) have claimed rather spectacular, large, variable circular polarisation in the optical continuum of Θ1 Orionis C, obtained with the échelle spectropolarimeter MuSiCoS. However, based on experience with the William-Wehlau spectropolarimeter, a similar unit using two fiber feeds, we suggest that this is the spurious result of instrumental effects. We propose a remedy...

On the magnetic field and circumstellar environment of the young O 7 star θ 1 Orionis C ?

We present new circular spectropolarimetric observations of the young O-type star θ 1 Orionis C obtained with the MuSiCoSéchelle spectropolarimeter and the 2 m Télescope Bernard Lyot, in an attempt to detect the surface magnetic field structure invoked to explain the periodic variability of θ 1 Ori C at X-ray, UV and optical wavelengths. We obtain null detections with 250 G 1σ error bars for th...

On (θ, θ)-Derivations in Semiprime Rings