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Probing the structures of stellar winds is of prime importance for the understanding of massive stars. Based on their optical spectral morphology and variability, the stars of the Oef class have been suggested to feature large-scale structures in their wind. High-resolution X-ray spectroscopy and time-series of X-ray observations of presumably-single O-type stars can help us understand the physics of their stellar winds. We have collected XMM-Newton observations and coordinated optical spectroscopy of the O6Ief star lambda Cep to study its X-ray and optical variability and to analyse its high-resolution X-ray spectrum. We investigate the line profile variability of the He II 4686 and H-alpha emission lines in our time series of optical spectra, including a search for periodicities. We further discuss the variability of the broadband X-ray flux and analyse the high-resolution spectrum of lambda Cep using line-by-line fits as well as a code designed to fit the full high-resolution X-ray spectrum consistently. During our observing campaign, the He II 4686 line varies on a timescale of ~18 hours. On the contrary, the H-alpha line profile displays a modulation on a timescale of 4.1 days which is likely the rotation period of the star. The X-ray flux varies on time-scales of days and could in fact be modulated by the same 4.1 days period as H-alpha, although both variations are shifted in phase. The high-resolution X-ray spectrum reveals broad and skewed emission lines as expected for the X-ray emission from a distribution of wind-embedded shocks. Most of the X-ray emission arises within less than 2R* above the photosphere.
A tomographic method, aiming at probing velocity fields at depth in stellar atmospheres, is applied to the red supergiant star {mu} Cep and to snapshots of 3D radiative-hydrodynamics simulation in order to constrain atmospheric motions and relate them to photometric variability.
To help constrain the origin of the peculiar X-ray emission of gamma Cas stars, we conducted a simultaneous optical and X-ray monitoring of pi Aqr in 2018. At that time, the star appeared optically bright and active, with a very strong Halpha emissio
We study the chromosphere and corona of the ultra-fast rotator AB Dor A at high temporal and spectral resolution using simultaneous observations with XMM-Newton in the X-rays, VLT/UVES in the optical, and the ATCA in the radio. Our optical spectra ha
Very young open clusters are ideal places to study the X-ray properties of a homogeneous population of early-type stars. In this respect, the IC1805 open cluster is very interesting as it hosts the O4If$^+$ star HD15570 thought to be in an evolutiona
We present an optical and infrared (IR) study of IC 10 X-2, a high-mass X-ray binary in the galaxy IC 10. Previous optical and X-ray studies suggest X-2 is a Supergiant Fast X-ray Transient: a large-amplitude (factor of $sim$ 100), short-duration (ho