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Identifying trends between observational data and the range of physical parameters of massive stars is a critical step to the still-elusive full understanding of the source, structure, and evolution of X-ray emission from the stellar winds, requiring a substantial sample size and systematic analysis methods. As of 2022, the Chandra data archive contains 37 high-resolution spectra of O, B, and WR stars, observed with the Chandra/HETGS, and of sufficient quality to fit the continua and emission-line profiles. Using a systematic approach to the data analysis, we explore morphological trends in the line profiles (i.e., O, Ne, Mg, and Si) and find that the centroid offsets of resolved lines versus wavelength can be separated in three empirically defined groups based on the amount of line broadening and centroid offset. Using Fe xvii (15.01, 17.05 Å) and Ne x α (12.13 Å) lines, which are prevalent among the sample stars, we find a well-correlated linear trend of increasing Full Width Half Maximum with faster wind terminal velocity. The H-like/He-like total line flux ratio for strong lines displays different trends with spectral class depending on ion species. Some of the sources in our sample have peculiar properties (e.g., magnetic and γ Cas-analog stars) and we find that these sources stand out as outliers from more regular trends. Finally, our spectral analysis is presented summarily in terms of X-ray spectral energy distributions in specific luminosity for each source, including tables of line identifications and fluxes. [ABSTRACT FROM AUTHOR]

WR 25 is a colliding-wind binary star system comprising a very massive O2.5If*/WN6 primary and an O-star secondary in an eccentric orbit with a 208 day period. These hot stars have strong, highly supersonic winds that interact to form a bright X-ray source from wind-collision shocks whose conditions change with stellar separation. Different views through the winds of Wolf–Rayet and O stars are afforded with orbital phase as the stars move about their orbits, allowing for exploration of wind structure in ways not easy or even possible for single stars. We have analyzed an on-axis Chandra/HETGS spectrum of WR 25 obtained shortly before periastron when the X-rays emanating from the system are the brightest. From the on-axis observations, we constrain the line fluxes, centroids, and widths of various emission lines, including He triplets of Si xiii and Mg xi. We have also been able to include several serendipitous off-axis HETG spectra from the archive and study their flux variation with phase. This is the first report on high-resolution spectral studies of WR 25 in X-rays. [ABSTRACT FROM AUTHOR]

Analysis of the recent long exposure Chandra X-ray observation of the early-type O star ζ Pup shows clear variability with a period previously reported in optical photometric studies. These 813 ks of HETGS observations taken over a roughly one-year time span have two signals of periodic variability: (1) a high-significance period of 1.7820 ± 0.0008 day, and (2) a marginal detection of periodic behavior close to either 5 days or 6 days. A BRITE-Constellation nanosatellite optical photometric monitoring (using near-contemporaneous observations to the Chandra data) confirms a 1.78060 ± 0.00088 day period for this star. The optical period coincides with the new Chandra period within their error ranges, demonstrating a link between these two wave bands and providing a powerful lever for probing the photosphere-wind connection in this star. The phase lag of the X-ray maximum relative to the optical maximum is ∼ ϕ = 0.45, but consideration of secondary maxima in both data sets indicates possibly two "hot" spots on the star with an X-ray phase lag of ϕ = 0.1 each. The details of this periodic variation of the X-rays are probed by displaying a phased and trailed X-ray spectrum and by constructing phased light curves for wavelength bands within the HETGS spectral coverage (ranging down to bands encompassing groups of emission lines). We propose that the 1.78 day period is the stellar rotation period and explore how stellar bright spots and associated corotating interaction regions (CIRs) could explain the modulation of this star's optical and X-ray output and their phase difference. [ABSTRACT FROM AUTHOR]

We investigate X-ray emission properties of the peculiar X-ray source θ2 On A in the Orion Trapezium region using more than 500 ks of HETGS spectral data in the quiescent state. The amount of exposure provides tight constraints on several important diagnostics involving O, Ne, Mg, and Si line flux ratios from He-like ion triplets, resonance line ratios of the H- and He-like lines, and line widths. Accounting for the influence of the strong UV radiation field of the 09.5V star, we can now place the He-like line origin well within two stellar radii of the O-star's surface. The lines are resolved with average line widths of 341 ± 38 km s-1. In the framework of standard wind models, this likely implies a rather weak wind with moderate post-shock velocities. The emission measure distribution of the X-ray spectrum, as reported previously, includes very high temperature components which are not easily explained in this framework. The X-ray properties are also not consistent with coronal emissions from an unseen low-mass companion nor with typical signatures from colliding wind interactions. The properties are more consistent with X-ray signatures observed in the massive Trapezium star θ1 On C which has recently been successfully modeled with a magnetically confined wind model. [ABSTRACT FROM AUTHOR]