Two equations in Ignace et al. (2019) have minor typos. The first correction is in Eq. (15). That expression has three lines. In the first line, there should be no multiplicative factor of R0 appearing. The correct equation is: (Formula Presented) The other two lines in Eq. (15) are correct. The second correction is in Eq. (19). As in Eq. (15), the appearance of R0 is in error. The correct expression is (Formula Presented) The mistakes appearing in Eqs. (15) and (19) are typos that have no bearing on the results appearing in the figures which were computed correctly, nor on the discussion or conclusions of the paper. (Equation Presented).

We report on both high-precision photometry from the Microvariability and Oscillations of Stars (MOST) space telescope and ground-based spectroscopy of the triple system δ Ori A, consisting of a binary O9.5II+early-B(Aa1 and Aa2) with P=5.7 days, and a more distant tertiary(O9 IV P 400 years). This data was collected in concert with X-ray spectroscopy from the Chandra X-ray Observatory. Thanks to continuous coverage for three weeks, the MOST light curve reveals clear eclipses between Aa1 and Aa2 for the first time in non-phased data. From the spectroscopy, we have a well-constrained radial velocity (RV)curve of Aa1. While we are unable to recover RV variations of the secondary star, we are able to constrain several fundamental parameters of this system and determine an approximate mass of the primary using apsidal motion. We also detected second order modulations at 12 separate frequencies with spacings indicative of tidally influenced oscillations. These spacings have never been seen in a massive binary, making this system one of only a handful of such binaries that show evidence for tidally induced pulsations.

A rather strong mean longitudinal magnetic field of the order of a few hundred gauss was detected a few years ago in the Of?p star CPD −28° 2561 using FORS2 (FOcal Reducer low dispersion Spectrograph 2) low-resolution spectropolarimetric observations. In this work, we present additional low-resolution spectropolarimetric observations obtained during several weeks in 2013 December using FORS 2 mounted at the 8-m Antu telescope of the Very Large Telescope (VLT). These observations cover a little less than half of the stellar rotation period of 73.41 d mentioned in the literature. The behaviour of the mean longitudinal magnetic field is consistent with the assumption of a single-wave variation during the stellar rotation cycle, indicating a dominant dipolar contribution to the magnetic field topology. The estimated polar strength of the surface dipole Bd is larger than 1.15 kG. Further, we compared the behaviour of the line profiles of various elements at different rotation phases associated with different magnetic field strengths. The strongest contribution of the emission component is observed at the phases when the magnetic field shows a negative or positive extremum. The comparison of the spectral behaviour of CPD −28° 2561 with that of another Of?p star, HD 148937 of similar spectral type, reveals remarkable differences in the degree of variability between both stars. Finally, we present new X-ray observations obtained with the Suzaku X-ray Observatory. We report that the star is X-ray bright with log LX/Lbol ≈ −5.7. The low-resolution X-ray spectra reveal the presence of a plasma heated up to 24 MK. We associate the 24 MK plasma in CPD −28° 2561 with the presence of a kG strong magnetic field capable to confine stellar wind.

1720 MHz OH masers have been detected towards a number of supernova remnants (SNRs) at the shock interface where the SNR slams into the interstellar medium. Models indicate that these masers are shock excited and can only be produced under tight constraints of the physical conditions. In particular, the masers can only form behind a C-type shock. Jets from newlyformed stars plow into the surrounding gas, creating nebulous regions known as Herbig Haro (HH) objects. Signatures of C-type shocks have been found in many HH objects. If conditions behind the shock fronts of HH objects are able to support 1720 MHz OH masers they would be a usefull diagnostic tool for star formation. A survey toward HH objects detected a number of 1720 MHz OH lines in emission, but future observations with arrays are required to confirm the presence of masers. / Physics / M.Sc. (Astronomy)

In this thesis, I present the properties of IRAS 19306+1407 central source and its sur- rounding circumstellar envelope (CSE), from the analysis of near-infrared (near-IR) polarimetry and integral field spectroscopy (IFS), with supporting archived HST im- ages and sub-millimetre (sub-mm) photometry. This is supported by axi-symmetric light scattering (ALS), axi-symmetric radiative transfer (DART) and molecular hy-drogen (H2) shock models. The polarimetric images show that IRAS 19306+1407 has a dusty torus, which deviates from axisymmetry and exhibits a ‘twist’ feature. The DART and ALS modelling shows that the CSE consists of Oxygen-rich sub-micrometre dust grains, with a range in temperature from 130±30 to 40±20 K at the inner and outer radius, respectively, with inner and outer radii of 1.9±0.1×1014 and 2.7±0.1×1015 m. The CSE detached 400±10 years ago and the mass loss lasted 5700±160 years, assuming a constant asymptotic giant branch (AGB) outflow speed of 15 km s−1. The dust mass and total mass of the CSE is 8.9±5×10−4 and 1.8±1.0×10 −1 M⊙, assuming a gas-to-dust ratio of 200. The mass loss rate was 3.4±2.1×10−5 M⊙ year−1. The central source is consistent with a B1I-type star with a radius of 3.8 ± 0.6 R⊙, luminosity of 4500 ± 340 L⊙ at a distance of 2.7 ± 0.1 kpc. A purpose built idl package (fus) was developed and used in the SINFONI IFS data critical final reduction steps. It also produced emission line, kinematic and line ratio images. The IFS observations show that H2 is detected throughout the CSE, located in bright arcs and in the bipolar lobes. The velocity of the H2 is greatest at the end of the lobes. Brγ emission originates from, or close, to the central source – produced by a fast jump (J) shock or photo-ionised atomic gas. The 1-0 S(1)/2- 1 S(1) and 1-0 S(1)/3-2 S(3) ratios were used as a diagnostic and determined that H2 was excited by bow shaped shocks; however, these shock models could not wholly explain the observed rotational and vibrational temperatures. The CDR values were fitted by combining continuous (C) or J-bow shock and fluorescence models, with a contribution from the latter, observed throughout the CSE (5–77 per cent). The majority of shock can be described by a C-bow shock model with B = 0.02 to 1.28 mG. Shocks are predominately seen in the equatorial regions. Polarimetry and IFS highlight a ‘twist’ feature, which could be due to an episodic jet undergoing a recent change in the outflow direction. The sub-arcsecond IFS observations reveal a flocculent structure in the south- east bright arc, consisting of several clumps interpreted as a fast-wind eroding an equatorial torus, possibly forming H2 knots seen in (some) evolved planetary nebulae (PNe). My analysis has effectively constrained the following: spectral type, stellar radius, luminosity and distance, chemistry, dust grain properties, geometry, age, mass loss, excitation mechanism and evolutionary state of the post-AGB star and its surrounding CSE. I conclude that IRAS 19306+1407 is a post-AGB object on the verge becoming a PN.

La diffusion atomique joue un rôle déterminant dans l'évolution d'étoiles de plusieurs types (Michaud 1970). Dans ces étoiles, la diffusion atomique est principalement régie par la compétition entre l'accélération gravitationnelle et les accélérations radiatives et peut par ce biais mener à de fortes anomalies d'abondances. À l'aide d'un modèle évolutif qui considère les accélérations radiatives de 28 espèces, il est possible de modéliser plusieurs types d'étoiles de Population I, incluant le Soleil (Turcotte et al. 1998a), les étoiles de type F (Turcotte et al. 1998b), les étoiles AmFm (Richer et al. 2000; Richard et al. 2001) et les étoiles de métallicité solaire ayant une masse entre 0.5 et 1.4 Msol (Michaud et al. 2004), ainsi que des étoiles de Pop II (Michaud et al. 2005). Cependant, les modèles qui ne considèrent que la diffusion atomique comme processus de transport dans les intérieurs stellaires génèrent des anomalies d'abondance plus grandes que celles observées pour les étoiles de type Am, Ap et HgMn. Dans ces étoiles, il y a donc un ou plusieurs autres processus qui peuvent influencer le transport de particules, tels la circulation méridionale, la turbulence et la perte de masse. L'objet de cet thèse est de contraindre l'importance de la perte de masse dans l'intérieur de plusieurs étoiles chimiquement particulières de Pop I et Pop II, tout en essayant de différencier ces effets par rapport à ceux reliés aux processus de mélange turbulents. / Atomic diffusion plays an important role in the evolution of many types of stars (Michaud 1970). In these stars, elemental migration is modulated by the competition between radiative accelerations and gravity, and can thus lead to important abundance anomalies both in the interior and at the surface of these stars. With a stellar evolution model which considers detailed particle transport with radiative accelerations for 28 elements, one can study the evolution of many types of stars of Pop II including the Sun (Turcotte et al. 1998a), F stars (Turcotte et al. 1998b), AmFm stars (Richer et al. 2000; Richard et al. 2001), as well as less massive stars (0.5 to 1.4 Msol) with solar metallicity (Michaud et al. 2004). Furthermore, such a model can also look into the evolution of Pop II chemically peculiar stars (Michaud et al. 2005). However, models which consider atomic diffusion as the sole process affecting particle transport lead to abundance anomalies which are greater than the ones observed. There is thus at least one macroscopic process which is preventing such large anomalies to appear at the surface. These processes include mass loss, meridional circulation and turbulence. The main goal of this thesis is to constrain the relative importance of mass loss in the interiors of many chemically peculiar stars of Pop I and Pop II, as well as to properly differentiate its effects from those generated by turbulent mixing processes.

L'eau est un constituant essentiel de l'atmosphère de supergéantes rouges (RSG), mais dont l'influence reste mal comprise. Le spectre observé de l'eau de ces étoiles ne peut être reproduit que par l'ajout d'une coquille de gaz moléculaire, les MOLsphères. Cependant, l'hypothèse des MOLsphères reste fragile et sujette à caution. Dans le but de mieux interpréter les spectres observés, la synthèse de spectres hors équilibre thermodynamique local est une approche potentiellement importante. Les effets hors ETL étant potentiellement fort, ils pourraient être en mesure de lever les problèmes de l'interprétation des raies de l'eau sans ajout de MOLsphère et impliquer un rôle important dans la dynamique de l'atmosphère. Pour cela, nous avons développé une méthode originale en mesure de résoudre l'équation de transfert pour les nombreuses transitions radiatives de l'eau sans approximationETL. Cette méthode a été mise en oeuvre via le développement d'un code de transfert radiatif parallèle. Les premiers résultats montrent que les effets hors ETL dans l'atmosphère des RSG, et leur impact sur le spectre comme sur certaines observables utilisées pour sonder ces étoiles, sont importants / Water is an important constituent of the atmosphere of red supergiant stars (RSG), which influence remains however poorly understood. The water spectrum of these stars can apparently be only reproduced through the addition of a detached shell of cool molecular gas, the so-called MOLspheres. However, this hypothesis is still cautious. In order to better interpret observed spectra, non local thermodynamic equilibrium (NLTE) spectrum synthesis may be potentially important. NLTE effects being potentially important, they may alleviate the problems in the interpretation of water spectra, and affect the atmosphere dynamics. We thus developed an original method to solve the radiative transfer equation, adapted to the numerous water transitions and without the LTE approximation. This method has been implemented in an original parallel code. Preliminary results show that NLTE effects in RSG atmospheres and their impact on observables such as the emergent spectrum are very important.

The influence of macroclumps for free–free spectral energy distributions (SEDs) of ionized winds is considered. The goal is to emphasize distinctions between microclumping and macroclumping effects. Microclumping can alter SED slopes and flux levels if the volume filling factor of the clumps varies with radius; however, the modifications are independent of the clump geometry. To what extent does macroclumping alter SED slopes and flux levels? In addressing the question, two specific types of macroclump geometries are explored: shell fragments (pancake-shaped) and spherical clumps. Analytic and semi-analytic results are derived in the limiting case that clumps never obscure one another. Numerical calculations based on a porosity formalism is used when clumps do overlap. Under the assumptions of a constant expansion, isothermal, and fixed ionization wind, the fragment model leads to results that are essentially identical to the microclumping result. Mass-loss rate determinations are not affected by porosity effects for shell fragments. By contrast, spherical clumps can lead to a reduction in long-wavelength fluxes, but the reductions are only significant for extreme volume filling factors.

The blue hypergiant Cyg OB2 12 (B3Ia+) is a representative member of the class of very massive stars in a poorly understood evolutionary stage. We obtained its high-resolution X-ray spectrum using the Chandra observatory. PoWR model atmospheres were calculated to provide realistic wind opacities and to establish the wind density structure. We find that collisional de-excitation is the dominant mechanism depopulating the metastable upper levels of the forbidden lines of the He-like ions Si xivand Mg xii. Comparison between the model and observations reveals that X-ray emission is produced in a dense plasma, which could reside only at the photosphere or in a colliding wind zone between binary components. The observed X-ray spectra are well-fitted by thermal plasma models, with average temperatures in excess of 10 MK. The wind speed in Cyg OB2 12 is not high enough to power such high temperatures, but the collision of two winds in a binary system can be sufficient. We used archival data to investigate the X-ray properties of other blue hypergiants. In general, stars of this class are not detected as X-ray sources. We suggest that our new Chandra observations of Cyg OB2 12 can be best explained if Cyg OB2 12 is a colliding wind binary possessing a late O-type companion. This makes Cyg OB2 12 only the second binary system among the 16 known Galactic hypergiants. This low binary fraction indicates that the blue hypergiants are likely products of massive binary evolution during which they either accreted a significant amount of mass or already merged with their companions.

Context. High spectral resolution and long exposure times are providing unprecedented levels of data quality of massive stars at X-ray wavelengths. Aims. A key diagnostic of the X-ray emitting plasma are the fir lines for He-like triplets. In particular, owing to radiative pumping effects, the forbidden-to-intercombination line luminosity ratio, R = f∕i, can be used to determine the proximity of the hot plasma to the UV-bright photospheres of massive stars. Moreover, the era of large observing programs additionally allows for investigation of line variability. Methods. This contribution is the second to explore how variability in the line ratio can provide new diagnostic information about distributed X-rays in a massive star wind. We focus on wind integration for total line luminosities, taking account of radiative pumping and stellar occultation. While the case of a variable stellar radiation field was explored in the first paper, the effects of wind variability are emphasized in this work. Results. We formulate an expression for the ratio of line luminosities f∕i that closely resembles the classic expression for the on-the-spot result. While there are many ways to drive variability in the line ratio, we use variable mass loss as an illustrative example for wind integration, particularly since this produces no variability for the on-the-spot case. The f∕i ratio can be significantly modulated owing to evolving wind properties. The extent of the variation depends on how the timescale for the wind flow compares to the timescale over which the line emissivities change. Conclusions. While a variety of factors can ellicit variable line ratios, a time-varying mass-loss rate serves to demonstrate the range of amplitude and phased-dependent behavior in f∕i line ratios. Importantly, we evaluate how variable mass loss might bias measures of f∕i. For observational exposures that are less than the timescale of variable mass loss, biased measures (relative to the time-averaged wind) can result; if exposures are long, the f∕i ratio is reflective of the time-averaged spherical wind.