1,115 research outputs found
Observational signatures of past mass-exchange episodes in massive binaries: The case of LSS 3074
The role of mass and momentum exchanges in close massive binaries is very
important in the subsequent evolution of the components. Such exchanges produce
several observational signatures such as asynchronous rotation and altered
chemical compositions, that remain after the stars detach again. We
investigated these effects for the close O-star binary LSS 3074 (O4 f + O6-7
:(f):), which is a good candidate for a past Roche lobe overflow (RLOF) episode
because of its very short orbital period, P = 2.185 days, and the luminosity
classes of both components. We determined a new orbital solution for the
system. We studied the photometric light curves to determine the inclination of
the orbit and Roche lobe filling factors of both stars. Using phase-resolved
spectroscopy, we performed the disentangling of the optical spectra of the two
stars. We then analysed the reconstructed primary and secondary spectra with
the CMFGEN model atmosphere code to determine stellar parameters, such as the
effective temperatures and surface gravities, and to constrain the chemical
composition of the components. We confirm the apparent low stellar masses and
radii reported in previous studies. We also find a strong overabundance in
nitrogen and a strong carbon and oxygen depletion in both primary and secondary
atmospheres, together with a strong enrichment in helium of the primary star.
We propose several possible evolutionary pathways through a RLOF process to
explain the current parameters of the system. We confirm that the system is
apparently in overcontact configuration and has lost a significant portion of
its mass to its surroundings. We suggest that some of the discrepancies between
the spectroscopic and photometric properties of LSS 3074 could stem from the
impact of a strong radiation pressure of the primary
Evidence for a physically bound third component in HD 150136
Context. HD150136 is one of the nearest systems harbouring an O3 star.
Although this system was for a long time considered as binary, more recent
investigations have suggested the possible existence of a third component.
Aims. We present a detailed analysis of HD 150136 to confirm the triple nature
of this system. In addition, we investigate the physical properties of the
individual components of this system. Methods. We analysed high-resolution,
high signal-to-noise data collected through multi-epoch runs spread over ten
years. We applied a disentangling program to refine the radial velocities and
to obtain the individual spectra of each star. With the radial velocities, we
computed the orbital solution of the inner system, and we describe the main
properties of the orbit of the outer star such as the preliminary mass ratio,
the eccentricity, and the orbital-period range. With the individual spectra, we
determined the stellar parameters of each star by means of the CMFGEN
atmosphere code. Results. We offer clear evidence that HD 150136 is a triple
system composed of an O3V((f\ast))-3.5V((f+)), an O5.5-6V((f)), and an
O6.5-7V((f)) star. The three stars are between 0-3 Myr old. We derive dynamical
masses of about 64, 40, and 35 Msun for the primary, the secondary and the
third components by assuming an inclination of 49{\deg}. It currently
corresponds to one of the most massive systems in our galaxy. The third star
moves with a period in the range of 2950 to 5500 d on an outer orbit with an
eccentricity of at least 0.3. This discovery makes HD 150136 the first
confirmed triple system with an O3 primary star. However, because of the long
orbital period, our dataset is not sufficient to constrain the orbital solution
of the tertiary component with high accuracy.Comment: 13 pages, 11 figures, accepted at A&
A new investigation of the binary HD 48099
With an orbital period of about 3.078 days, the double-lined spectroscopic
binary HD 48099 is, still now, the only short-period O+O system known in the
Mon OB2 association. Even though an orbital solution has already been derived
for this system, few information are available about the individual stars. We
present, in this paper, the results of a long-term spectroscopic campaign. We
derive a new orbital solution and apply a disentangling method to recover the
mean spectrum of each star. To improve our knowledge concerning both
components, we determine their spectral classifications and their projected
rotational velocities. We also constrain the main stellar parameters of both
stars by using the CMFGEN atmosphere code and provide the wind properties for
the primary star through the study of IUE spectra. This investigation reveals
that HD 48099 is an O5.5 V((f))+O9 V binary with M_1 sin^3 i = 0.70 M_{\sun}
and M_2 sin^3 i = 0.39 M_{\sun}, implying a rather low orbital inclination.
This result, combined with both a large effective temperature and log g,
suggests that the primary star (v sini ~ 91 km s^-1) is actually a fast rotator
with a strongly clumped wind and a nitrogen abundance of about 8 times the
solar value.Comment: 12 pages, 7 figures, accepted by Ap
Apsidal motion in the massive binary HD152218
Massive binary systems are important laboratories in which to probe the
properties of massive stars and stellar physics in general. In this context, we
analysed optical spectroscopy and photometry of the eccentric short-period
early-type binary HD 152218 in the young open cluster NGC 6231. We
reconstructed the spectra of the individual stars using a separating code. The
individual spectra were then compared with synthetic spectra obtained with the
CMFGEN model atmosphere code. We furthermore analysed the light curve of the
binary and used it to constrain the orbital inclination and to derive absolute
masses of 19.8 +/- 1.5 and 15.0 +/- 1.1 solar masses. Combining radial velocity
measurements from over 60 years, we show that the system displays apsidal
motion at a rate of (2.04^{+.23}_{-.24}) degree/year. Solving the
Clairaut-Radau equation, we used stellar evolution models, obtained with the
CLES code, to compute the internal structure constants and to evaluate the
theoretically predicted rate of apsidal motion as a function of stellar age and
primary mass. In this way, we determine an age of 5.8 +/- 0.6 Myr for HD
152218, which is towards the higher end of, but compatible with, the range of
ages of the massive star population of NGC 6231 as determined from isochrone
fitting.Comment: Accepted for publication in Astronomy & Astrophysic
Constraining the fundamental parameters of the O-type binary CPD-41degr7733
Using a set of high-resolution spectra, we studied the physical and orbital
properties of the O-type binary CPD-41 7733, located in the core of \ngc. We
report the unambiguous detection of the secondary spectral signature and we
derive the first SB2 orbital solution of the system. The period is 5.6815 +/-
0.0015 d and the orbit has no significant eccentricity. CPD-41 7733 probably
consists of stars of spectral types O8.5 and B3. As for other objects in the
cluster, we observe discrepant luminosity classifications while using
spectroscopic or brightness criteria. Still, the present analysis suggests that
both components display physical parameters close to those of typical O8.5 and
B3 dwarfs. We also analyze the X-ray light curves and spectra obtained during
six 30 ks XMM-Newton pointings spread over the 5.7 d period. We find no
significant variability between the different pointings, nor within the
individual observations. The CPD-41 7733 X-ray spectrum is well reproduced by a
three-temperature thermal mekal model with temperatures of 0.3, 0.8 and 2.4
keV. No X-ray overluminosity, resulting e.g. from a possible wind interaction,
is observed. The emission of CPD-41 7733 is thus very representative of typical
O-type star X-ray emission.Comment: Accepted by ApJ, 15 pages, 9 figure
Evidence for a physically bound third component in HD 150136
Context. HD150136 is one of the nearest systems harbouring an O3 star.
Although this system was for a long time considered as binary, more recent
investigations have suggested the possible existence of a third component.
Aims. We present a detailed analysis of HD 150136 to confirm the triple nature
of this system. In addition, we investigate the physical properties of the
individual components of this system. Methods. We analysed high-resolution,
high signal-to-noise data collected through multi-epoch runs spread over ten
years. We applied a disentangling program to refine the radial velocities and
to obtain the individual spectra of each star. With the radial velocities, we
computed the orbital solution of the inner system, and we describe the main
properties of the orbit of the outer star such as the preliminary mass ratio,
the eccentricity, and the orbital-period range. With the individual spectra, we
determined the stellar parameters of each star by means of the CMFGEN
atmosphere code. Results. We offer clear evidence that HD 150136 is a triple
system composed of an O3V((f\ast))-3.5V((f+)), an O5.5-6V((f)), and an
O6.5-7V((f)) star. The three stars are between 0-3 Myr old. We derive dynamical
masses of about 64, 40, and 35 Msun for the primary, the secondary and the
third components by assuming an inclination of 49{\deg}. It currently
corresponds to one of the most massive systems in our galaxy. The third star
moves with a period in the range of 2950 to 5500 d on an outer orbit with an
eccentricity of at least 0.3. This discovery makes HD 150136 the first
confirmed triple system with an O3 primary star. However, because of the long
orbital period, our dataset is not sufficient to constrain the orbital solution
of the tertiary component with high accuracy.Comment: 13 pages, 11 figures, accepted at A&
Plaskett's Star: Analysis of the CoRoT photometric data
The SRa02 of the CoRoT space mission for Asteroseismology was partly devoted
to stars belonging to the Mon OB2 association. An intense monitoring was
performed on Plaskett's Star (HD47129) and the unprecedented quality of the
light curve allows us to shed new light on this very massive, non-eclipsing
binary system. We particularly aimed at detecting periodic variability which
might be associated with pulsations or interactions between both components. We
also searched for variations related to the orbital cycle which could help to
constrain the inclination and the morphology of the binary system. A
Fourier-based prewhitening and a multiperiodic fitting procedure were applied
to analyse the time series and extract the frequencies of variations. We
describe the noise properties to tentatively define an appropriate significance
criterion, to only point out the peaks at a certain significance level. We also
detect the variations related to the orbital motion and study them by using the
NIGHTFALL program. The periodogram exhibits a majority of peaks at low
frequencies. Among these peaks, we highlight a list of about 43 values,
including notably two different sets of harmonic frequencies whose fundamental
peaks are located at about 0.07 and 0.82d-1. The former represents the orbital
frequency of the binary system whilst the latter could probably be associated
with non-radial pulsations. The study of the 0.07d-1 variations reveals the
presence of a hot spot most probably situated on the primary star and facing
the secondary. The investigation of this unique dataset constitutes a further
step in the understanding of Plaskett's Star. These results provide a first
basis for future seismic modelling. The existence of a hot region between both
components renders the determination of the inclination ambiguous.Comment: Accepted in A&A, 13 pages, 7 figures, 2 table
Fragment Flow and the Nuclear Equation of State
We use the Boltzmann-Uehling-Uhlenbeck model with a momentum-dependent
nuclear mean field to simulate the dynamical evolution of heavy ion collisions.
We re-examine the azimuthal anisotropy observable, proposed as sensitive to the
equation of state of nuclear matter. We obtain that this sensitivity is maximal
when the azimuthal anisotropy is calculated for nuclear composite fragments, in
agreement with some previous calculations. As a test case we concentrate on
semi-central collisions at 400 MeV.Comment: 12 pages, ReVTeX 3.0. 12 Postscript figures, uuencoded and appende
Early-type stars in the young open cluster NGC 2244 and in the Mon OB2 association I. The multiplicity of O-type stars
Aims. We present the results obtained from a long-term spectroscopic campaign
devoted to the multiplicity of O-type stars in the young open cluster NGC2244
and in the Mon OB2 association. Methods. Our spectroscopic monitoring was
performed over several years, allowing us to probe different time-scales. For
each star, several spectral diagnostic tools are applied, in order to search
for line shifts and profile variations. We also measure the projected
rotational velocity and revisit the spectral classification. Results. In our
sample, several stars were previously considered as spectroscopic binaries,
though only a few scattered observations were available. Our results now reveal
a more complex situation. Our study identifies two new spectroscopic binaries
(HD46149 in NGC2244 and HD46573 in MonOB2). The first object is a long-period
double-lined spectroscopic binary, though the exact value of its period remains
uncertain and the second object is classified as an SB1 system with a period of
about 10.67 days but the time series of our observations do not enable us to
derive a unique orbital solution for this system. We also classify another star
as variable in radial velocity (HD46150) and we detect line profile variations
in two rapid rotators (HD46056 and HD46485). Conclusions. This spectroscopic
investigation places a firm lower limit (17%) on the binary fraction of O-stars
in NGC2244 and reveals the lack of short-period O+OB systems in this cluster.
In addition, a comparison of these new results with two other well-studied
clusters (NGC6231 and IC1805) puts forward possible hints of a relation between
stellar density and binarity, which could provide constraints on the theories
about the formation and early evolution of hot stars.Comment: 14 pages, 10 figures, 9 table
The XMM-LSS catalogue: X-ray sources and associated optical data. Version I
Following the presentation of the XMM-LSS X-ray source detection package by
Pacaud et al., we provide the source lists for the first 5.5 surveyed square
degrees. The catalogues pertain to the [0.5-2] and [2-10] keV bands and contain
in total 3385 point-like or extended sources above a detection likelihood of 15
in either band. The agreement with deep logN-logS is excellent. The main
parameters considered are position, countrate, source extent with associated
likelihood values. A set of additional quantities such as astrometric
corrections and fluxes are further calculated while errors on the position and
countrate are deduced from simulations. We describe the construction of the
band-merged catalogue allowing rapid sub-sample selection and easy
cross-correlation with external multi-wavelength catalogues. A small optical
CFHTLS multi-band subset of objects is associated wich each source along with
an X-ray/optical overlay. We make the full X-ray images available in FITS
format. The data are available at CDS and, in a more extended form, at the
Milan XMM-LSS database.Comment: 13 pages, 7 figures and 11 tables (fig. 1 and 6 are enclosed in
reduced resolution), MNRAS Latex, accepted by MNRA
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