Aims.
The study of the X-ray line profiles produced by massive colliding wind binaries is a powerful tool for the characterisation of the stellar winds. We built a self-consistent program for the ...computation of line profiles named LIFELINE. The resulting theoretical profiles can be compared to the line profile that will be observed with future high-resolution X-ray spectrographs to retrieve the characteristics of the stellar winds generating them.
Methods.
We considered a grid of 780 O-type binaries and computed, for each of them, the wind velocity distribution of each star, taking the impact of the radiation pressure and gravity force of the companion star into account. We then computed the characteristics of the wind shock region and followed the emitted photons towards the observer to compute their absorption. Finally, the Fe K line profiles near 6.7 keV were constructed from the distribution of the photons as a function of the radial velocities of their emitting region. LIFELINE can be used to compare the theoretical line profiles to the observed ones or to compute theoretical profiles for a new binary system.
Results.
We highlight the results for three systems. While the line profiles created in adiabatic wind collision regions are quite simple, the line profiles arising from regions in the radiative regime, as found in short-period binaries, are more sophisticated notably because of the Coriolis effect on the shape of the shock. The predicted differences in line morphology between systems with different wind properties are quite significant, allowing a detailed comparison between the theoretical profiles and those that will be observed with future high-resolution X-ray spectrometers.
Exocomets: A spectroscopic survey Rebollido, I.; Eiroa, C.; Montesinos, B. ...
Astronomy and astrophysics (Berlin),
07/2020, Letnik:
639
Journal Article, Web Resource
Recenzirano
Odprti dostop
Context.
While exoplanets are now routinely detected, the detection of small bodies in extrasolar systems remains challenging. Since the discovery of sporadic events, which are interpreted to be ...exocomets (falling evaporating bodies) around
β
Pic in the early 1980s, only ∼20 stars have been reported to host exocomet-like events.
Aims.
We aim to expand the sample of known exocomet-host stars, as well as to monitor the hot-gas environment around stars with previously known exocometary activity.
Methods.
We have obtained high-resolution optical spectra of a heterogeneous sample of 117 main-sequence stars in the spectral type range from B8 to G8. The data were collected in 14 observing campaigns over the course of two years from both hemispheres. We analysed the Ca
II
K&H and Na
I
D lines in order to search for non-photospheric absorptions that originated in the circumstellar environment and for variable events that could be caused by the outgassing of exocomet-like bodies.
Results.
We detected non-photospheric absorptions towards 50% of the sample, thus attributing a circumstellar origin to half of the detections (i.e. 26% of the sample). Hot circumstellar gas was detected in the metallic lines inspected via narrow stable absorptions and/or variable blue- and red-shifted absorption events. Such variable events were found in 18 stars in the Ca
II
and/or Na
I
lines; six of them are reported in the context of this work for the first time. In some cases, the variations we report in the Ca
II
K line are similar to those observed in
β
Pic. While we do not find a significant trend in the age or location of the stars, we do find that the probability of finding CS gas in stars with larger
v
sin
i
is higher. We also find a weak trend with the presence of near-infrared excess and with anomalous (
λ
Boo-like) abundances, but this would require confirmation by expanding the sample.
The colliding-wind binary HD 168112 Blomme, R.; Rauw, G.; Volpi, D. ...
Astronomy and astrophysics (Berlin),
07/2024, Letnik:
687
Journal Article, Web Resource
Recenzirano
Odprti dostop
Context. Radio surveys of early-type stars have revealed a number of non-thermal emitters. Most of these have been shown to be binaries, where the collision between the two stellar winds is ...responsible for the non-thermal emission. Aims. HD 168112 is a non-thermal radio emitter, whose binary nature has only recently been confirmed spectroscopically. We obtained independent spectroscopic observations to determine its orbit, in addition to radio observations to see if the thermal or non-thermal nature of the emission changes during the periastron passage. Methods. We monitored HD 168112 spectroscopically for a 13 yr time span. From these data, we determined the orbital parameters, which we compared to the previous results in the literature. The stellar parameters of both components were determined by comparing the spectra to TLUSTY models. From the spectral index of the radio observations, we found how the nature of the emission changes as the system goes through periastron. Combining our results with other literature data allowed us to further constrain the orbital and stellar parameters. Results. We find HD 168112 to have an orbital period of P = 512.17 −0.11 +0.41 days, an eccentricity of e = 0.7533 −0.0124 +0.0053 , and a mass ratio close to one. From our spectroscopic modelling, we derived the stellar parameters, but we had difficulty arriving at a spectroscopic mass ratio of one. The radio observations around periastron show only thermal emission, suggesting that most of the synchrotron photons are absorbed in the two stellar winds at that phase. Combining our data with the optical interferometry detection, we could constrain the inclination angle to i ~ 63°, and the mass of each component to ~26 M ⊙ . Conclusions. We have provided an independent spectroscopic confirmation of the binary nature of HD 168112. Although detected as a non-thermal radio emitter, near periastron the radio emission of this highly eccentric system is thermal and is mainly formed in the colliding-wind region. This effect will also occur in other colliding-wind binaries.
Context. The long-period O-star binary system HD 168112 and the triple O-star system HD 167971 are well-known sources of non-thermal radio emission that arises from a colliding wind interaction. The ...wind-wind collisions in these systems should result in phase-dependent X-ray emissions. The presence of a population of relativistic electrons in the wind interaction zone could affect the properties of the X-ray emission and make it deviate from the behaviour expected for adiabatic shocks. Aims. We investigate the X-ray emission of these systems with the goals of quantifying the fraction of the X-ray flux arising from wind interactions and determining whether these emissions follow the predictions for adiabatic wind-wind collisions. Methods. Six X-ray observations were collected with XMM-Newton. Three observations were scheduled around the most recent peri-astron passage of HD 168112. Spectra and light curves were analysed and compared with simple predictions of model calculations for X-ray emission from colliding wind systems. Results. The X-ray emission of HD 168112 varies as the inverse of the orbital separation, as expected for an adiabatic wind interaction zone. The relative contribution of intrinsic X-ray emission from wind-embedded shocks varies between 38% at periastron to 81% at apastron. The wind-wind collision zone remains adiabatic even around periastron passage. The X-ray emission of HD 167971 displays variations on the orbital timescale of the inner eclipsing binary. The existing data of this system do not allow us to probe variations on the timescale of the outer orbit. Conclusions. Shock modification due to the action of relativistic electrons does not seem to be efficiently operating in the HD 168112 system. In the existing observations, a significant part of the emission of HD 167971 must arise in the inner eclipsing binary. The origin of this emission is as yet unclear.
ABSTRACT
HD 165052 is a short-period massive eccentric binary system that undergoes apsidal motion. As the rate of apsidal motion is directly related to the internal structure constants of the binary ...components, its study allows getting insight into the internal structure of the stars. We use medium- and high-resolution spectroscopic observations of HD 165052 to provide constraints on the fundamental properties of the binary system and the evolutionary state of its components. We apply a spectral disentangling code to reconstruct artefact-free spectra of the individual stars and derive the radial velocities (RVs) at the times of the observations. We perform the first analysis of the disentangled spectra with the non-local thermodynamic equilibrium model atmosphere code CMFGEN to determine the stellar properties. We derive the first self-consistent orbital solution of all existing RV data, including those reported in the literature, accounting for apsidal motion. We build, for the very first time, dedicated stellar evolution tracks with the Clés code requesting the theoretical effective temperatures and luminosities to match those obtained from our spectroscopic analysis. The binary system HD 165052, consisting of an O6.5 V((f)) primary ($T_\text{eff,P}=37\, 500 \pm 1000$ K) and an O7 V((f)) secondary ($T_\text{eff,S}=36\, 000 \pm 1000$ K), displays apsidal motion at a rate of $(11.30^{+0.64}_{-0.49})^\circ$ yr−1. Evolutionary masses are compared to minimum dynamical masses to constrain the orbital inclination. Evolutionary masses $M_\text{ev,P}=24.8\pm 1.0\, \mathrm{M}_\odot$ and $M_\text{ev,S}=20.9\pm 1.0\, \mathrm{M}_\odot$ and radii $R_\text{ev,P}=7.0^{+0.5}_{-0.4}\, \mathrm{R}_\odot$ and $R_\text{ev,S}=6.2^{+0.4}_{-0.3}\, \mathrm{R}_\odot$ are derived, and the inclination is constrained to 22.1° ≤ i ≤ 23.3°. Theoretical apsidal motion rates, derived assuming an age of 2.0 ± 0.5 Myr for the binary, are in agreement with the observational determination. The agreement with theoretical apsidal motion rates enforces the inferred values of the evolutionary stellar masses and radii.
Context. We investigated the X-ray emission of HD 149404, a 9.81-day period O-star binary in a post-Roche lobe overflow evolutionary stage. X-ray emission of O-star binaries consists of the intrinsic ...emission of the individual O stars and a putative additional component arising from the wind-wind interaction. Aims. Phase-locked variations in the X-ray spectra can be used to probe the properties of the stellar winds of such systems. Methods. XMM–Newton observations of HD 149404 collected at two conjunction phases and a quadrature phase were analysed. X-ray spectra were extracted and flux variations as a function of orbital phase were inferred. The flux ratios were analysed with models considering various origins for the X-ray emission. Results. The highest and lowest X-ray fluxes are observed at conjunction phases respectively with the primary and secondary star in front. The flux variations are nearly grey with only marginal energy dependence. None of the models accounting for photoelectric absorption by homogeneous stellar winds perfectly reproduces the observed variations. Whilst the overall X-ray luminosity is consistent with a pure intrinsic emission, the best formal agreement with the observed variations is obtained with a model assuming pure windwind collision X-ray emission. Conclusions. The lack of significant energy-dependence of the opacity most likely hints at the presence of optically thick clumps in the winds of HD149404.
Context. The initial distribution of rotational velocities of stars is still poorly known, and how the stellar spin evolves from birth to the various end points of stellar evolution is an actively ...debated topic. Binary interactions are often invoked to explain the existence of extremely fast-rotating stars ( v sin i ≳ 200 km s −1 ). The primary mechanisms through which binaries can spin up stars are tidal interactions, mass transfer, and possibly mergers. However, fast rotation could also be primordial, that is, a result of the star formation process. To evaluate these scenarios, we investigated in detail the evolution of three known fast-rotating stars in short-period spectroscopic and eclipsing binaries, namely HD 25631, HD 191495, and HD 46485, with primaries of masses of 7, 15, and 24 M ⊙ , respectively, with companions of ∼1 M ⊙ and orbital periods of less than 7 days. These systems belong to a recently identified class of binaries with extreme mass ratios, whose evolutionary origin is still poorly understood. Aims. We evaluated in detail three scenarios that could explain the fast rotation observed in these binaries: it could be primordial, a product of mass transfer, or the result of a merger within an originally triple system. We also discuss the future evolution of these systems to shed light on the impact of fast rotation on binary products. Methods. We computed grids of single and binary MESA models varying tidal forces and initial binary architectures to investigate the evolution and reproduce observational properties of these systems. When considering the triple scenario, we determined the region of parameter space compatible with the observed binaries and used a publicly available machine-learning model to determine the dynamical stability of the triple system. Results. We find that, because of the extreme mass-ratio between binary components, tides have a limited impact, regardless of the prescription used, and that the observed short orbital periods are at odds with post-mass-transfer scenarios. We also find that the overwhelming majority of triple systems compatible with the observed binaries are dynamically unstable and would be disrupted within years of formation, forcing a hypothetical merger to happen so close to a zero-age main-sequence that it could be considered part of the star formation process. Conclusions. The most likely scenario to form such young, rapidly rotating, and short-period binaries is primordial rotation, implying that the observed binaries are pre-interaction ones. Our simulations further indicate that such systems will subsequently go through a common envelope and likely merge. These binaries show that the initial spin distribution of massive stars can have a wide range of rotational velocities.
Aims. Our goal is to determine the stellar and wind properties of seven O stars in the cluster NGC 2244 and three O stars in the OB association Mon OB2. These properties give us insight into the mass ...loss rates of O stars. They allow us to both check the validity of rotational mixing in massive stars and to better understand the effects of the ionizing flux and wind mechanical energy release on the surrounding interstellar medium and its influence on triggered star formation. Methods. We collected optical and UV spectra of the target stars that we analyzed by means of atmosphere models computed with the code CMFGEN. The spectra of binary stars were disentangled and the components studied separately. Results. All stars have an evolutionary age less than 5 million years, with the most massive stars being among the youngest. Nitrogen surface abundances show no clear relation with projected rotational velocities. Binaries and single stars show the same range of enrichment. This is attributed to the youth and/or wide separation of the binary systems in which the components have not (yet) experienced strong interaction. A clear trend toward greater enrichment in higher luminosity objects is observed, consistent with what evolutionary models with rotation predict for a population of O stars at any given age. We confirm the weakness of winds in late O dwarfs. In general, mass loss rates derived from UV lines are lower than mass loss rates obtained from Hα. The UV mass loss rates are even lower than the single-line driving limit in the latest type dwarfs. These issues are discussed in the context of the structure of massive stars winds. The evolutionary and spectroscopic masses are in agreement above 25 M⊙, but the uncertainties are large. Below this threshold, the few late-type O stars studied here indicate that the mass discrepancy still seems to hold.
Gamma Cas stars are early-type Be stars that exhibit an unusually hard and bright thermal X-ray emission. One of the proposed scenarios to explain these properties postulates the existence of a ...neutron star companion in the propeller stage, during which the magnetosphere of a rapidly rotating neutron star repels infalling material. To test this model, we examined the fluorescent Fe Kalpha emission line at $ 6.4$\,keV in the X-ray spectra of gamma Cas stars, which offers a powerful diagnostic of both the primary source of hard X-rays and the reprocessing material. We computed synthetic line profiles of the fluorescent Fe Kalpha emission line in the framework of the propelling neutron star scenario. Two reservoirs of material contribute to the fluorescence in this case: the Be circumstellar decretion disk and a shell of cool material that surrounds the shell of X-ray-emitting plasma around the putative propelling neutron star. We analysed the synthetic line profiles and expected equivalent widths of the lines for three well-studied gamma Cas stars. The predicted line strengths fall short of the observed values by at least an order of magnitude. Pushing the model parameters to reproduce the observed line strengths led to column densities towards the primary X-ray source that exceed the observationally determined values by typically a factor of 20, and would further imply a higher X-ray luminosity than observed. The strengths of the observed Fe Kalpha fluorescent emission lines in gamma Cas stars are inconsistent with the expected properties of a propeller scenario as proposed in the literature.
Context.
The eccentric massive binary HD 152248 (also known as V1007 Sco), which hosts two O7.5 III-II(f) stars, is the most emblematic eclipsing O-star binary in the very young and rich open cluster ...NGC 6231. Its properties render the system an interesting target for studying tidally induced apsidal motion.
Aims.
Measuring the rate of apsidal motion in such a binary system gives insight into the internal structure and evolutionary state of the stars composing it.
Methods.
A large set of optical spectra was used to reconstruct the spectra of the individual binary components and establish their radial velocities using a disentangling code. Radial velocities measured over seven decades were used to establish the rate of apsidal motion. We furthermore analysed the reconstructed spectra with the
CMFGEN
model atmosphere code to determine stellar and wind properties of the system. Optical photometry was analysed with the
Nightfall
binary star code. A complete photometric and radial velocity model was constructed in
PHOEBE 2
to determine robust uncertainties.
Results.
We find a rate of apsidal motion of (1.843
−0.083
+0.064
)° yr
−1
. The photometric data indicate an orbital inclination of (67.6
−0.1
+0.2
)° and Roche-lobe filling factors of both stars of about 0.86. Absolute masses of 29.5
−0.4
+0.5
M
⊙
and mean stellar radii of 15.07
−0.12
+0.08
R
⊙
are derived for both stars. We infer an observational value for the internal structure constant of both stars of 0.0010 ± 0.0001.
Conclusions.
Our in-depth analysis of the massive binary HD 152248 and the redetermination of its fundamental parameters can serve as a basis for the construction of stellar evolution models to determine theoretical rates of apsidal motion to be compared with the observational one. In addition, the system hosts two twin stars, which offers a unique opportunity to obtain direct insight into the internal structure of the stars.
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