1,336 research outputs found
X-ray and optical spectroscopy of the massive young open cluster IC1805
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 evolutionary stage intermediate between a normal O-star and a Wolf-Rayet
star. Such a star could provide a test for theoretical models aiming at
explaining the empirical scaling relation between the X-ray and bolometric
luminosities of O-type stars. We have observed IC1805 with XMM-Newton and
further collected optical spectroscopy of some of the O-star members of the
cluster. The optical spectra allow us to revisit the orbital solutions of
BD+60 497 and HD15558, and provide the first evidence of binarity for
BD+60 498. X-ray emission from colliding winds does not appear to
play an important role among the O-stars of IC1805. Notably, the X-ray fluxes
do not vary significantly between archival X-ray observations and our
XMM-Newton pointing. The very fast rotator BD+60 513, and to a lesser
extent the O4If star HD15570 appear somewhat underluminous. Whilst the
underluminosity of HD15570 is only marginally significant, its amplitude is
found to be compatible with theoretical expectations based on its stellar and
wind properties. A number of other X-ray sources are detected in the field, and
the brightest objects, many of which are likely low-mass pre-main sequence
stars, are analyzed in detail.Comment: Accepted for publication in Astronomy & Astrophysic
X-ray emission from interacting massive binaries: a review of 15 years of progress
Previous generations of X-ray observatories revealed a group of massive
binaries that were relatively bright X-ray emitters. This was attributed to
emission of shock-heated plasma in the wind-wind interaction zone located
between the stars. With the advent of the current generation of X-ray
observatories, the phenomenon could be studied in much more detail. In this
review, we highlight the progress that has been achieved in our understanding
of the phenomenon over the last 15 years, both on theoretical and observational
grounds. All these studies have paved the way for future investigations using
the next generation of X-ray satellites that will provide crucial information
on the X-ray emission formed in the innermost part of the wind-wind
interaction.Comment: Accepted for publication in a special issue of Advances in Space
Research on X-ray Emission from Hot Stars and their Wind
Some comments on the paper by Vink et al. 2009 (A&A, 505, 743 or arXiv:0909.0888)
In a recent paper, Vink et al. analyzed some spectropolarimetry data of
O-type stars. Here we comment on our disagreement with some points presented in
this paper, with the hope of helping to fully grasp the scientific implication
of these measurements.Comment: 3 page
Fe xxv line profiles in colliding wind binaries
Strong wind-wind collisions in massive binaries generate a very hot plasma
that frequently produces a moderately strong iron line. The morphology of this
line depends upon the properties of the wind interaction zone and its
orientation with respect to the line of sight. As the binary components revolve
around their common centre of mass, the line profiles are thus expected to
vary. With the advent of the next generation of X-ray observatories (Astro-H,
Athena) that will offer high-resolution spectroscopy above 6 keV, it will
become possible to exploit these changes as the most sensitive probe of the
inner parts of the colliding wind interaction. Using a simple prescription of
the wind-wind interaction in an early-type binary, we have generated synthetic
line profiles for a number of configurations and orbital phases. These profiles
can help constrain the properties of the stellar winds in such binary systems.Comment: Accepted for publication in New Astronom
The long-period massive binary HD~54662 revisited
HD54662 is an O-type binary star belonging to the CMa OB1 association. Due to
its long-period orbit, this system is an interesting target to test the
adiabatic wind shock model. The goal is to improve our knowledge of the orbital
and stellar parameters of HD54662 and to analyze its X-ray emission to test the
theoretical scaling of the X-ray emission with orbital separation for adiabatic
wind shocks. We applied a spectral disentangling code to optical spectra to
determine the radial velocities and the individual spectra of each star. The
individual spectra were analyzed using the CMFGEN model atmosphere code. We
fitted two X-ray spectra using a Markov Chain Monte Carlo algorithm and
compared them to the emission expected from adiabatic shocks. We determine an
orbital period of 2103.4days, a low orbital eccentricity of 0.11, and a mass
ratio m2/m1=0.84. Combined with the orbital inclination inferred in a previous
astrometric study, we obtain surprisingly low masses of 9.7 and 8.2Msun. From
the individual spectra, we infer O6.5 spectral types for both stars and a
brightness ratio of l1/l2~2. The softness of the X-ray spectra, the very small
variation of spectral parameters, and the comparison of the X-ray-to-bolometric
luminosity ratio with the canonical value for O-type stars allow us to conclude
that X-ray emission from the wind interaction region is quite low. We cannot
confirm the runaway status previously attributed to HD54662 and we find no
X-ray emission associated with the bow shock detected in the infrared. The lack
of hard X-ray emission from the wind-shock region suggests that the mass-loss
rates are lower than expected and/or that the pre-shock wind velocities are
much lower than the terminal wind velocities. The bow shock associated with
HD54662 possibly corresponds to a wind-blown arc created by the interaction of
the stellar winds with the ionized gas of CMa OB1. (abridged)Comment: Manuscript has been accepted. A&A, in pres
Quest for the tertiary component in Cyg OB2 #5
The Cyg OB2 #5 system is thought to consist of a short-period (6.6 d)
eclipsing massive binary orbited by an OB-star orbiting with a period of ~6.7
yr; these stars in turn are orbited by a distant early B-star with a period of
thousands of years. However, while the inner binary has been studied many
times, information is missing on the other stars, in particular the third star
whose presence was indirectly postulated from recurrent modulations in the
radio domain. Besides, to this date, the X-ray light curve could not be fully
interpreted, for example in the framework of colliding-wind emission linked to
one of the systems. We obtained new optical and X-ray observations of Cyg OB2
#5, which we combined to archival data. We performed a thorough and homogeneous
investigation of all available data, notably revisiting the times of primary
minimum in photometry. In the X-ray domain, XMM-Newton provides scattered
exposures over ~5000 d whilst Swift provides a nearly continuous monitoring for
the last couple of years. Although the X-ray light curve reveals clear
variability, no significant period can be found hence the high-energy emission
cannot be explained solely in terms of colliding winds varying along either the
short or intermediate orbits. The optical data reveal for the first time clear
signs of reflex motion. The photometry indicates the presence of a 2366 d (i.e.
6.5 yr) period while the associated radial velocity changes are detected at the
3 sigma level in the systemic velocity of the He II 4686 emission line. With
the revised period, the radio light curve is interpreted consistently in terms
of a wind interaction between the inner binary and the tertiary star. From
these optical and radio data, we derive constraints on the physical properties
of the tertiary star and its orbit.Comment: Accepted for publication in Astronomy & Astrophysic
Interacting winds in massive binaries
Massive stars feature highly energetic stellar winds that interact whenever two such stars are bound in a binary system. The signatures of these interactions are nowadays found over a wide range of wavelengths, including the radio domain, the optical band, as well as X-rays and even γ-rays. A proper understanding of these effects is thus important to derive the fundamental parameters of the components of massive binaries from spectroscopic and photometric observations
A multi-epoch XMM-Newton campaign on the core of the massive Cygnus OB2 association
peer reviewedContext. Cyg OB2 is one of the most massive associations of O-type stars in our Galaxy. Despite the large interstellar reddening towards Cyg OB2, many studies, spanning a wide range of wavelengths, have been conducted to more clearly understand this association. X-ray observations provide a powerful tool to overcome the effect of interstellar absorption and study the most energetic processes associated with the stars in Cyg OB2. Aims: We analyse XMM-Newton data to investigate the X-ray and UV properties of massive O-type stars as well as low-mass pre-main sequence stars in Cyg OB2. Methods: We obtained six XMM-Newton observations of the core of Cyg OB2. In our analysis, we pay particular attention to the variability of the X-ray bright OB stars, especially the luminous blue variable candidate Cyg OB2 #12. Results: We find that X-ray variability is quite common among the stars in Cyg OB2. Whilst short-term variations are restricted mostly to low-mass pre-main sequence stars, one third of the OB stars display long-term variations. The X-ray flux of Cyg OB2 #12 varies by 37%, over timescales from days to years, whilst its mean log L[SUB]X[/SUB]/L[SUB]bol[/SUB] amounts to - 6.10. Conclusions: These properties suggest that Cyg OB2 #12 is either an interacting-wind system or displays a magnetically confined wind. Two other X-ray bright O-type stars (MT91 516 and CPR2002 A11) display variations that suggest they are interacting wind binary systems. Based on observations collected with XMM-Newton, an ESA Science Mission with instruments and contributions directly funded by ESA Member States and the USA (NASA).Full Table 2 and Table 4 are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/536/A31</A
X-ray emission of massive stars and their winds
Most types of massive stars display X-ray emission that is affected by the
properties of their stellar winds. Single non-magnetic OB stars have an X-ray
luminosity that scales with their bolometric luminosity and their emission is
thought to arise from a distribution of wind-embedded shocks. The lack of
significant short-term stochastic variability indicates that the winds consist
of a large number of independent fragments. Detailed variability studies
unveiled a connection between the photosphere and the wind: well-studied O-type
stars exhibit a ~ 10% modulation of their emission on timescales consistent
with the rotation period, and a few early B-type pulsators display ~ 10%
modulations of their X-ray flux with the pulsation period. Unlike OB stars,
their evolved descendants (WR and LBV stars) lack a well-defined relation
between their X-ray and bolometric luminosities, and several subcategories of
objects remain undetected. These properties most likely stem from the combined
effects of wind optical depth and wind velocity. Magnetic OB stars display an
enhanced X-ray emission frequently modulated by the rotation of the star. These
properties are well explained by the magnetically confined wind shock model and
an oblique magnetic rotator configuration. Some massive binaries display
phase-dependent excess emission arising from the collision between the winds of
the binary components. Yet, the majority of the massive binaries do not show
such an emission, probably as a consequence of radiative cooling of the
shock-heated plasma. Finally, a growing subset of the Be stars, the so-called
gamma Cas stars, feature an unusually hard and strong thermal X-ray emission
that varies over a wide range of timescales. Several scenarios have been
proposed to explain these properties, but the origin of the phenomenon remains
currently one of the major unsolved puzzles in stellar X-ray astrophysics.Comment: Invited chapter of the Handbook of X-ray and Gamma-ray Astrophysic
X-ray properties of the young open clusters HM1 and IC2944/2948
Using XMM data, we study for the first time the X-ray emission of HM1 and
IC2944/2948. Low-mass, pre-main-sequence objects with an age of a few Myr are
detected, as well as a few background or foreground objects. Most massive stars
in both clusters display the usual high-energy properties of that type of
objects, though with log(Lx/Lbol) apparently lower in HM1 than in IC2944/2948.
Compared with studies of other clusters, it seems that a low signal-to-noise
ratio at soft energies, due to the high extinction, may be the main cause of
this difference. In HM1, the two Wolf-Rayet stars show contrasting behaviors:
WR89 is extremely bright, but much softer than WR87. It remains to be seen
whether wind-wind collisions or magnetically confined winds can explain these
emissions. In IC2944/2948, the X-ray sources concentrate around HD101205; a
group of massive stars to the north of this object is isolated, suggesting that
there exist two subclusters in the field-of-view.Comment: 29 pages in total with 10 figures (12 pages paper + supplementary
material), accepted by A&
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