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B supergiants (BSGs) are evolved stars with effective temperatures between 10 to 30 kK and are important to understand massive star evolution. Located on the edge of the line-driven wind regime, the study of their atmospheres is helpful to understand phenomena such as the bi-stability jump. Key UV features of their spectra have so far not been reproduced by models for types later than B1. Here, we aim to remedy this situation via spectral analysis that accounts for wind clumping and X-rays. In addition, we investigate the evolutionary status of our sample stars based on the obtained stellar parameters. We determined parameters via quantitative spectroscopy using CMFGEN and PoWR codes. The models were compared to UV and optical data of four BSGs: HD206165, HD198478, HD53138, and HD164353. We also study the evolutionary status of our sample using GENEC and MESA tracks. When including clumping and X-rays, we find good agreements between synthetic and observed spectra for our sample stars. For the first time, we reproduced key lines in the UV. For that, we require a moderately clumped wind (f_infty > ~0.5). We also infer relative X-ray luminosities of ~10^-7.5 to 10^-8 -- lower than the typical ratio of 10^-7. Moreover, we find a possible mismatch between evolutionary and spectroscopic masses, which could be related to the mass-discrepancy problem present in other OB stars. Our results provide evidence that X-rays and clumping are needed to describe the winds of cool BSGs. However, their winds seem less structured than in earlier type stars. This aligns with observational X-rays and clumping constraints as well as recent hydrodynamical simulations. The BSGs' evolutionary status appears diverse: some objects are potentially post-red supergiants or merger products. The wind parameters provide evidence for a moderate mass-loss rate increase around the bi-stability jump. Abstract abridged, 27 pages, 22 figures, accepted for publication in A&A

We present the results from Chandra X-ray observations, and near- and mid-infrared analysis, using VISTA/VVV and Spitzer/GLIMPSE catalogs, of the high-mass star-forming region IRAS 16562-3959, which contains a candidate for a high mass protostar. We detected 249 X-ray sources within the ACIS-I field-of-view. The majority of the X-ray sources have low count rates (< 0.638 cts/ks), and hard X-ray spectra. The search for YSOs in the region using VISTA/VVV and Spitzer/GLIMPSE catalogs resulted in a total of 799 YSOs, with 66 Class I and 733 Class II YSOs. The search for near- and mid-infrared counterparts of the X-ray sources led to a total of 165 VISTA/VVV counterparts, and a total of 151 Spitzer/GLIMPSE counterparts. The infrared analysis of the X-ray counterparts allowed us to add an extra 123 YSOs associated with the region. We conclude that a total of 922 YSOs are associated with the region, with 67 Class I, 764 Class II, and 91 Class III YSOs. We also found that the region is composed of 11 subclusters. In the vicinity of the high-mass protostar, the stellar distribution has a core-halo structure. The subcluster containing the high-mass protostar is the densest and the youngest in the region, and the high-mass protostar is located at its center. The YSOs in this cluster appear to be substantially older than the high mass protostar.

X-ray emission from stars much more massive than the Sun was discovered only 35 years ago. Such stars drive fast stellar winds where shocks can develop, and it is commonly assumed that the X-rays emerge from the shock-heated plasma. Many massive stars additionally pulsate. However, hitherto it was neither theoretically predicted nor observed that these pulsations would affect their X-ray emission. Here we report the discovery of pulsating X-rays from the massive B-type star Xi1 Canis Majoris. This star is a variable of beta Cephei type and has a strong magnetic field. Our observations with the XMM-Newton telescope reveal X-ray pulsations with the same period as the fundamental stellar pulsation. This discovery challenges our understanding of stellar winds from massive stars, their X-ray emission, and their magnetism., Comment: manuscript draft. The revised paper is published in Nature Communications

The true mass-loss rates from massive stars are important for many branches of astrophysics. For the correct modeling of the resonance lines, which are among the key diagnostics of stellar mass-loss, the stellar wind clumping turned out to be very important. In order to incorporate clumping into radiative transfer calculation, 3-D models are required. Various properties of the clumps may have strong impact on the resonance line formation and, therefore, on the determination of empirical mass-loss rates. We incorporate the 3-D nature of the stellar wind clumping into radiative transfer calculations and investigate how different model parameters influence the resonance line formation. We develop a full 3-D Monte Carlo radiative transfer code for inhomogeneous expanding stellar winds. The number density of clumps follows the mass conservation. For the first time, realistic 3-D models that describe the dense as well as the tenuous wind components are used to model the formation of resonance lines in a clumped stellar wind. At the same time, non-monotonic velocity fields are accounted for. The 3-D density and velocity wind inhomogeneities show very strong impact on the resonance line formation. The different parameters describing the clumping and the velocity field results in different line strengths and profiles. We present a set of representative models for various sets of model parameters and investigate how the resonance lines are affected. Our 3-D models show that the line opacity is reduced for larger clump separation and for more shallow velocity gradients within the clumps. Our new model demonstrates that to obtain empirically correct mass-loss rates from the UV resonance lines, the wind clumping and its 3-D nature must be taken into account., Comment: Astronomy and Astrophysics, accepted for publication

�� Columbae is a prototypical weak-wind O-star for which we have obtained a high-resolution X-ray spectrum with the Chandra LETG/ACIS-S instrument and a low resolution spectrum with Suzaku. This allows us, for the first time, to investigate the role of X-rays on the wind structure in a bona fide weak-wind system and to determine whether there actually is a massive, hot wind. The X-ray emission measure indicates that the outflow is an order of magnitude greater than that derived from UV lines and is commensurate with the nominal wind-luminosity relationship for O-stars. Therefore, the ``weak-wind problem''---identified from cool wind UV/optical spectra---is largely resolved by accounting for the hot wind seen in X-rays. From X-ray line profiles, Doppler shifts, and relative strengths, we find that this weak-wind star is typical of other late O dwarfs. The X-ray spectra do not suggest a magnetically confined plasma---the spectrum is soft and lines are broadened; Suzaku spectra confirm the lack of emission above 2 keV. Nor do the relative line shifts and widths suggest any wind decoupling by ions. The He-like triplets indicate that the bulk of the X-ray emission is formed rather close to the star, within 5 stellar radii. Our results challenge the idea that some OB stars are ``weak-wind'' stars that deviate from the standard wind-luminosity relationship. The wind is not weak, but it is hot and its bulk is only detectable in X-rays., Accepted for publication in ApJ Letters

Some of the Wolf-Rayet stars are found to have very high bolometric luminosities (more than 1000000 solar). We employ the Potsdam Wolf-Rayet (PoWR) model atmospheres for their spectral analysis, which yields the bolometric corrections. Distance and interstellar reddening also enter the luminosity estimates. Among the Galactic stars, there is a group of very luminous WNL stars (i.e. WR stars of late subtype from nitrogen sequence with hydrogen being depleted in their atmospheres, but not absent). Their distances are often the major source of uncertainty. From K-band spectroscopy we found a very luminous star ($\log L/L_\odot = 6.5$) in the Galactic center region, which we termed the Peony Star because of the form of its surrounding dusty nebula. A similar group of very luminous WNL stars is found in the Large Magellanic Cloud (LMC). In the Small Magellanic Cloud (SMC) the majority of WR stars resides in binary systems. The single WNL stars in the SMC are not very luminous. We conclude that a significant number of very luminous WNL stars exist in the Galaxy and the LMC. With initial masses above 60$M_\odot$, they apparently evolved directly to the WNL stage without a prior excursion to the red side of the HRD. At the low metallicity of the SMC, the binary channel may be dominant for the formation of WR stars., Comment: 5 pages, Proceedings of the 39th Li\`ege Astrophysical Colloquium "The multi-wavelength view of hot, massive stars". Referee's comments included