266 research outputs found
The X-ray light curve of the massive colliding wind Wolf-Rayet + O binary WR21a
Our dedicated XMM-Newton monitoring, as well as archival Chandra and Swift
datasets, were used to examine the behaviour of the WN5h+O3V binary WR21a at
high energies. For most of the orbit, the X-ray emission exhibits few
variations. However, an increase in strength of the emission is seen before
periastron, following a 1/D relative trend, where D is the separation between
both components. This increase is rapidly followed by a decline due to strong
absorption as the Wolf-Rayet (WR) comes in front. The fitted local absorption
value appears to be coherent with a mass-loss rate of about 1x10^{-5} M_sol/yr
for the WR component. However, absorption is not the only parameter affecting
the X-ray emission at periastron as even the hard X-ray emission decreases,
suggesting a possible collapse of the colliding wind region near to or onto the
photosphere of the companion just before or at periastron. An eclipse may
appear as another potential scenario, but it would be in apparent contradiction
with several lines of evidence, notably the width of the dip in the X-ray light
curve and the absence of variations in the UV light curve. Afterwards, the
emission slowly recovers, with a strong hysteresis effect. The observed
behaviour is compatible with predictions from general wind-wind collision
models although the absorption increase is too shallow.Comment: Accepted for publication in Astronomy & Astrophysic
Studies of WR+O colliding-wind binaries
Two of the main physical parameters that govern the massive star evolution, the mass and the mass-loss rate, are still poorly determined from the observational point of view. Only binary systems could provide well constrained masses and colliding-wind binaries could bring some constraints on the mass-loss rate. Therefore, colliding-wind binaries turn out to be very promising objects. In this framework, we present detailed studies of basic observational data obtained with the XMM-Newton facility and combined with ground-based observations and other data. We expose the results for two particularly interesting WR+O colliding-wind binaries: WR22 and WR21a
An X-ray view of HD166734, a massive supergiant system
The X-ray emission of the O+O binary HD166734 was monitored using Swift and
XMM-Newton observatories, leading to the discovery of phase-locked variations.
The presence of an f line in the He-like triplets further supports a wind-wind
collision as the main source of the X-rays in HD166734. While temperature and
absorption do not vary significantly along the orbit, the X-ray emission
strength varies by one order of magnitude, with a long minimum state
(Delta(phi)~0.1) occurring after a steep decrease. The flux at minimum is
compatible with the intrinsic emission of the O-stars in the system, suggesting
a possible disappearance of colliding wind emission. While this minimum cannot
be explained by eclipse or occultation effects, a shock collapse may occur at
periastron in view of the wind properties. Afterwards, the recovery is long,
with an X-ray flux proportional to the separation d (in hard band) or to d^2
(in soft band). This is incompatible with an adiabatic nature for the collision
(which would instead lead to "F_X propto 1/d"), but could be reconciled with a
radiative character of the collision, though predicted temperatures are lower
and more variable than in observations. An increase in flux around phi~0.65 and
the global asymmetry of the light curve remain unexplained, however.Comment: accepted by A&
New X-ray detections of known Wolf-Rayet stars
Using XMM-Newton, we undertook a dedicated project to search for X-ray bright
wind-wind collisions in 18 WR+OB systems. We complemented these observations
with Swift and Chandra datasets, allowing for the study of two additional
systems. We also improved the ephemerides, for these systems displaying
photometric changes, using TESS, Kepler, and ASAS-SN data. Five systems
displayed a very faint X-ray emission () and
three a faint one (), incompatible with
typical colliding wind emission: not all WR binaries are thus X-ray bright. In
a few other systems, X-rays from the O-star companion cannot be excluded as
being the true source of X-rays (or a large contributor). In two additional
cases, the emission appears faint but the observations were taken with the WR
wind obscuring the line-of-sight, which could hide a colliding wind emission.
Clear evidence of colliding winds was however found in the remaining six
systems (WR19, 21, 31, 97, 105, 127). In WR19, increased absorption and larger
emission at periastron are even detected, in line with expectations of
adiabatic collisions.Comment: accepted by MNRAS - the arxiv version has figures in low-resolutio
Investigation of the stellar content in the western part of the Carina nebula
We obtained deep H photometric data of the field situated to
the west of the main Carina nebula and centered on WR~22. Medium-resolution
optical spectroscopy of a subsample of X-ray selected objects along with
archival data sets from , and 2MASS surveys were used for
the present study. Different sets of color-color and color-magnitude diagrams
are used to determine reddening for the region and to identify young stellar
objects (YSOs) and estimate their age and mass. Our spectroscopic results
indicate that the majority of the X-ray sources are late spectral type stars.
The region shows a large amount of differential reddening with minimum and
maximum values of as 0.25 and 1.1 mag, respectively. Our analysis
reveals that the total-to-selective absorption ratio is 3.7
0.1, suggesting an abnormal grain size in the observed region. We
identified 467 YSOs and studied their characteristics. The ages and masses of
the 241 optically identified YSOs range from 0.1 to 10 Myr and 0.3
to 4.8M, respectively. However, the majority of them are younger than 1
Myr and have masses below 2 M. The high mass star WR 22 does not seem
to have contributed to the formation of YSOs in the CrW region. The initial
mass function slope, , in this region is found to be -1.13 0.20
in the mass range of 0.5 < M/M < 4.8. The -band luminosity function
slope () is also estimated as 0.31 0.01. We also performed
minimum spanning tree analysis of the YSOs in this region, which reveals that
there are at least ten YSO cores associated with the molecular cloud, and that
leads to an average core radius of 0.43 pc and a median branch length of 0.28
pc.Comment: 23 pages, 19 figures, 4 tables, Accepted for publication in Astronomy
& Astrophysics [A&A]. arXiv admin note: text overlap with arXiv:0906.0201,
arXiv:1211.2995, arXiv:1103.3396 by other author
Simulations of observations with the Optical Monitor of the X-ray Multi-Mirror Satellite
peer reviewedThis paper addresses the question of the observations to be performed with the Optical Monitor (OM) of the X-ray Multi-Mirror Satellite (XMM) under several aspects. First, we discuss XMM-OM's photometric system and its colour transformations towards the standard U BV system. Second, we establish a set of procedures to determine the temperature and the amount of interstellar absorption affecting the observed stars. Last, we address the possibility of isolating quasars in multidimensional colour diagrams based on the XMM-OM filter set
Spectroscopic binaries as observed by the future Gaia space mission
peer reviewedThe future Gaia satellite will observe a large number of stars through its three main channels: astrometric, photometric and, for the brightest stars, spectroscopic. The satellite is equipped with the RVS spectrograph, which will provide medium-resolution spectra over a small wavelength range. These spectra should allow us to identify stars exhibiting a composite spectrum, either because of a chance alignment or a true binarity. We discuss the various aspects related to the data treatment of the binary candidates and describe the algorithms that are intended to be included in the processing pipeline
Colliding winds in WR21 and WR31 -- I. The X-ray view
WR21 and WR31 are two WR+O binaries with short periods, quite similar to the
case of V444 Cyg. The XMM-Newton observatory has monitored these two objects
and clearly revealed phase-locked variations as expected from colliding winds.
The changes are maximum in the soft band (0.5--2.keV, variations by a factor
3--4) where they are intrinsically linked to absorption effects. The increase
in absorption due to the dense WR wind is confirmed by the spectral analysis.
The flux maximum is however not detected exactly at conjunction with the O star
in front but slightly afterwards, suggesting Coriolis deflection of the
collision zone as in V444 Cyg. In the hard band (2.--10. keV), the variations
(by a factor of 1.5--2.0) are much more limited. Because of the lower orbital
inclinations, eclipses as observed for V444 Cyg are not detected in these
systems.Comment: accepted for publication by MNRA
Revisiting the orbital motion of WR 138
peer reviewedThe optical spectrum of WR 138 exhibits emission lines typical of a WN6o star and absorption lines from a rapidly-rotating OB star. Using a large set of spectroscopic data, we establish a new orbital solution of the WN6o star based on the radial velocities of highly-ionized nitrogen lines. We show that the WN6o star moves on a 4.3 yr orbit with a comparatively low eccentricity of 0.16. The radial velocities of the OB star display considerable scatter. Our best estimates of the velocities of He I absorption lines result in a mass-ratio of mWN6o/mOB=0.53±0.09. We disentangle the spectra of the two stars and derive a projected rotational velocity of vsini=350±10 km s−1 for the OB star. Our best orbital parameters, combined with the Gaia parallax of WR 138, are at odds with a previous interferometric detection of the companion, suggesting that there is either a bias in this detection or that WR 138 is actually a triple system
Preliminary results of an observational campaign aiming at the study of the binary system LSS3074
We present preliminary results of an observational campaign aiming at the study of the binary system LSS3074. A new lightcurve clearly indicates that the system is in contact. Recent spectroscopy broadly confirms the previous results and the rather low masses of both components (O4f[SUP]+[/SUP] and O6-7:(f):). We further analyse an XMM-Newton observation of the object that indicates a rather hard X-ray spectrum. This is partly due to the high interstellar extinction towards the object but also to the high plasma temperature (kT Ë 1.2-1.3 keV)
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