601 research outputs found
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
Evidence for quasi-chemically homogeneous evolution of massive stars up to solar metallicity
Long soft gamma ray bursts (LGRBs) are usually associated with the death of
the most massive stars. A large amount of core angular momentum in the phases
preceding the explosion is required to form LGRBs. A very high initial
rotational velocity can provide this angular momentum. Such a velocity strongly
influences the way the star evolves: it is chemically homogeneously mixed and
evolves directly towards the blue part of the HR diagram from the main
sequence. We have shown that chemically homogeneous evolution (CHE) takes place
in the SMC, at low metallicity. We want to see if there is a metallicity
threshold above which such an evolution does not exist. We perform a
spectroscopic analysis of H-rich early-type WN stars in the LMC and the Galaxy.
We use the code CMFGEN to determine the fundamental properties and the surface
composition of the target stars. We then place the stars in the HR diagram and
determine their evolution. We show that both the LMC and Galactic WNh stars we
selected cannot be explained by standard stellar evolution. They are located on
the left of the main sequence but show surface abundances typical of CN
equilibrium. In addition, they still contain a large amount of hydrogen. They
are thus core-H burning objects. Their properties are consistent with CHE. We
determine the metallicity of the Galactic stars from their position and
Galactic metallicity gradients, and conclude that they have 0.6<Z<1.0. A
moderate coupling between the core and the envelope is required to explain that
stellar winds do not extract to much angular momentum to prevent a blueward
evolution. In view of the findings that some long gamma ray bursts appear in
solar environments, CHE may be a viable way to form them over a wide range of
metallicities.Comment: 10 pages, 10 figures. Accepted in Astronomy and Astrophysic
Fundamental parameters of massive stars in multiple systems: The cases of HD17505A and HD206267A
Many massive stars are part of binary or higher multiplicity systems. The
present work focusses on two higher multiplicity systems: HD17505A and
HD206267A. Determining the fundamental parameters of the components of the
inner binary of these systems is mandatory to quantify the impact of binary or
triple interactions on their evolution. We analysed high-resolution optical
spectra to determine new orbital solutions of the inner binary systems. After
subtracting the spectrum of the tertiary component, a spectral disentangling
code was applied to reconstruct the individual spectra of the primary and
secondary. We then analysed these spectra with the non-LTE model atmosphere
code CMFGEN to establish the stellar parameters and the CNO abundances of these
stars. The inner binaries of these systems have eccentric orbits with e ~ 0.13
despite their relatively short orbital periods of 8.6 and 3.7 days for
HD17505Aa and HD206267Aa, respectively. Slight modifications of the CNO
abundances are found in both components of each system. The components of
HD17505Aa are both well inside their Roche lobe, whilst the primary of
HD206267Aa nearly fills its Roche lobe around periastron passage. Whilst the
rotation of the primary of HD206267Aa is in pseudo-synchronization with the
orbital motion, the secondary displays a rotation rate that is higher. The CNO
abundances and properties of HD17505Aa can be explained by single star
evolutionary models accounting for the effects of rotation, suggesting that
this system has not yet experienced binary interaction. The properties of
HD206267Aa suggest that some intermittent binary interaction might have taken
place during periastron passages, but is apparently not operating anymore.Comment: Accepted for publication in A&
A spectroscopic investigation of the O-type star population in four Cygnus OB associations. II. Determination of the fundamental parameters
Aims. Having established the binary status of nineteen O-type stars located
in four Cygnus OB associations, we now determine their fundamental parameters
to constrain their properties and their evolutionary status. We also
investigate their surface nitrogen abundances, which we compare with other
results from the literature obtained for galactic O-type stars. Methods. Using
optical spectra collected for each object in our sample and some UV data from
the archives, we apply the CMFGEN atmosphere code to determine their main
properties. For the binary systems, we have disentangled the components to
obtain their individual spectra and investigate them as if they were single
stars. Results. We find that the distances of several presumably single O-type
stars seem poorly constrained because their luminosities are not in agreement
with the "standard" luminosities of stars with similar spectral types. The ages
of these O-type stars are all less than 7 Myrs. Therefore, the ages of these
stars agree with those, quoted in the literature, of the four associations,
except for CygOB8 for which the stars seem older than the association itself.
However, we point out that the distance of certain stars is debatable relative
to values found in the literature. The N content of these stars put in
perspective with N contents of several other galactic O-type stars seems to
draw the same five groups as found in the "Hunter" diagram for the O and B-type
stars in the LMC even though their locations are obviously different. We
determine mass-loss rates for several objects from the Halpha line and UV
spectra. Finally, we confirm the "mass discrepancy" especially for O stars with
masses smaller than 30 Msun. .Comment: 11 pages, and 26 pages of Appendix. A&A in pres
Long-term in vitro 3D hydrogel co-culture model of inflammatory bowel disease
The in vitro study of the pathogenesis of inflammatory bowel disease (IBD) requires a cell model which closely reflects the characteristics of the in vivo intestinal epithelium. This study aimed to investigate the application of L-pNIPAM hydrogel as a scaffold to develop a long-term 3D co-culture model of Caco-2 and HT29-MTX cells under conditions analogous to inflammation, to determine its potential use in studying IBD. Monocultures and co-cultures were layered on L-pNIPAM hydrogel scaffolds and maintained under dynamic culture conditions for up to 12 weeks. Treatments with IL-1β, TNFα, and hypoxia for 1 week were used to create an inflammatory environment. Following prolonged culture, the metabolic activity of Caco-2 monoculture and 90% Caco-2/10% HT29-MTX co-cultures on L-pNIPAM hydrogels were increased, and finger-like structures, similar in appearance to villi were observed. Following treatment with IL-1β, TNFα and hypoxia, ALP and ZO-1 were decreased, MUC2 increased, and MUC5AC remained unchanged. ADAMTS1 was increased in response to hypoxia. Caspase 3 expression was increased in response to TNFα and hypoxic conditions. In conclusion, L-pNIPAM hydrogel supported long-term co-culture within a 3D model. Furthermore, stimulation with factors seen during inflammation recapitulated features seen during IBD
Phase resolved X-ray spectroscopy of HDE228766: Probing the wind of an extreme Of+/WNLha star
HDE228766 is a very massive binary system hosting a secondary component,
which is probably in an intermediate evolutionary stage between an Of
supergiant and an WN star. The wind of this star collides with the wind of its
O8 II companion, leading to relatively strong X-ray emission. Measuring the
orbital variations of the line-of-sight absorption toward the X-ray emission
from the wind-wind interaction zone yields information on the wind densities of
both stars. X-ray spectra have been collected at three key orbital phases to
probe the winds of both stars. Optical photometry has been gathered to set
constraints on the orbital inclination of the system. The X-ray spectra reveal
prominent variations of the intervening column density toward the X-ray
emission zone, which are in line with the expectations for a wind-wind
collision. We use a toy model to set constraints on the stellar wind parameters
by attempting to reproduce the observed variations of the relative fluxes and
wind optical depths at 1 keV. The lack of strong optical eclipses sets an upper
limit of about 68 degrees on the orbital inclination. The analysis of the
variations of the X-ray spectra suggests an inclination in the range 54 - 61
degrees and indicates that the secondary wind momentum ratio exceeds that of
the primary by at least a factor 5. Our models further suggest that the bulk of
the X-ray emission arises from the innermost region of the wind interaction
zone, which is from a region whose outer radius, as measured from the secondary
star, lies between 0.5 and 1.5 times the orbital separation
The mass of the very massive binary WR21a
We present multi-epoch spectroscopic observations of the massive binary
system WR21a, which include the January 2011 periastron passage. Our spectra
reveal multiple SB2 lines and facilitate an accurate determination of the orbit
and the spectral types of the components. We obtain minimum masses of
and for the two components of
WR21a. Using disentangled spectra of the individual components, we derive
spectral types of O3/WN5ha and O3Vz~((f*)) for the primary and secondary,
respectively. Using the spectral type of the secondary as an indication for its
mass, we estimate an orbital inclination of and
absolute masses of and , in
agreement with the luminosity of the system. The spectral types of the WR21a
components indicate that the stars are very young (12 Myr), similar to the
age of the nearby Westerlund 2 cluster. We use evolutionary tracks to determine
the mass-luminosity relation for the total system mass. We find that for a
distance of 8 kpc and an age of 1.5 Myr, the derived absolute masses are in
good agreement with those from evolutionary predictions.Comment: 7 pages, 4 figures; accepted for publication in MNRA
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
A modern study of HD166734: a massive supergiant system
Aims. HD166734 is an eccentric eclipsing binary system composed of two
supergiant O-type stars, orbiting with a 34.5-day period. In this rare
configuration for such stars, the two objects mainly evolve independently,
following single-star evolution so far. This system provides a chance to study
the individual parameters of two supergiant massive stars and to derive their
real masses. Methods. An intensive monitoring was dedicated to HD166734.We
analyzed mid- and high-resolution optical spectra to constrain the orbital
parameters of this system. We also studied its light curve for the first time,
obtained in the VRI filters. Finally, we disentangled the spectra of the two
stars and modeled them with the CMFGEN atmosphere code in order to determine
the individual physical parameters. Results. HD166734 is a O7.5If+O9I(f)
binary. We confirm its orbital period but we revise the other orbital
parameters. In comparison to what we found in the literature, the system is
more eccentric and, now, the hottest and the most luminous component is also
the most massive one. The light curve exhibits only one eclipse and its
analysis indicates an inclination of 63.0{\deg} 2.7{\deg}. The
photometric analysis provides us with a good estimation of the luminosities of
the stars, and therefore their exact positions in the Hertzsprung-Russell
diagram. The evolutionary and the spectroscopic masses show good agreement with
the dynamical masses of 39.5 Msun for the primary and 33.5 Msun for the
secondary, within the uncertainties. The two components are both enriched in
helium and in nitrogen and depleted in carbon. In addition, the primary also
shows a depletion in oxygen. Their surface abundances are however not different
from those derived from single supergiant stars, yielding, for both components,
an evolution similar to that of single stars.Comment: 13 pages, 13 figures, A&A accepte
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