286 research outputs found
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&
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&
GCIRS16SW: a massive eclipsing binary in the Galactic Center
We report on the spectroscopic monitoring of GCIRS16SW, an Ofpe/WN9 star and
LBV candidate in the central parsec of the Galaxy. SINFONI observations show
strong daily spectroscopic changes in the K band. Radial velocities are derived
from the HeI 2.112 um line complex and vary regularly with a period of 19.45
days, indicating that the star is most likely an eclipsing binary. Under
various assumptions, we are able to derive a mass of ~ 50 Msun for each
component.Comment: 4 pages, 4 figures, ApJ Letters accepte
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 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
A quantitative study of the O stars in NGC 2244
peer reviewedAbstract. NGC2244 located in the Rosette Nebula is a young open cluster composed of
seven O-type stars. A first paper focused on the multiplicity of these stars, revealed only one
binary system out of the seven studied stars. The minimum binary fraction of this cluster
(~ 14%) diff ers to the average fraction measured on the nearby clusters (~ 44%). In order to
better constrain this discrepancy, an analysis based on the determination of the stellar and wind
parameters of these stars with the CMFGEN atmosphere code was performed. The main results
con rfim that all the stars have an age between 0 and 5 Myr, and that the N surface abundance
appears to be consistent with the evolutionary models for a population of stars of the same age.
Moreover, this investigation exhibits the existence of dynamical interactions inside this young
open cluster sufficiently strong to eject the hottest component from its centre
Early-type stars in the core of the young open cluster Westerlund2
Aims. The properties of the early-type stars in the core of the Westerlund2
cluster are examined in order to establish a link between the cluster and the
very massive Wolf-Rayet binary WR20a as well as the HII complex RCW49.
Methods. Photometric monitoring as well as spectroscopic observations of
Westerlund2 are used to search for light variability and to establish the
spectral types of the early-type stars in the cluster core.
Results. The first light curves of the eclipsing binary WR20a in B and V
filters are analysed and a distance of 8kpc is inferred. Three additional
eclipsing binaries, which are probable late O or early B-type cluster members,
are discovered, but none of the known early O-type stars in the cluster
displays significant photometric variability above 1% at the 1-sigma level. The
twelve brightest O-type stars are found to have spectral types between O3 and
O6.5, significantly earlier than previously thought.
Conclusions. The distance of the early-type stars in Westerlund2 is
established to be in excellent agreement with the distance of WR20a, indicating
that WR20a actually belongs to the cluster. Our best estimate of the cluster
distance thus amounts to 8.0pm1.4kpc. Despite the earlier spectral types, the
currently known population of early-type stars in Westerlund2 does not provide
enough ionizing photons to account for the radio emission of the RCW49 complex.
This suggests that there might still exist a number of embedded early O-stars
in RCW49.Comment: 11 pages, 8 figures (figs 1, 3 and 5 in jpg), accepted for
publication by A&
The LMC transition star R84 and the core of the LH 39 OB association
On the basis of sub-arcsecond optical imaging we resolve and study the core
components of the LMC OB association LH 39. The central star of the
association, the rare transition object R84, is also investigated using CASPEC
echelle spectroscopy. A new, powerful image restoration code that conserves the
fluxes allows us to obtain the magnitudes and colors of the components. We
bring out some 30 stars in a ~16"x16", area centered on R84. At a resolution of
0.19", the closest components to R84 are shown to lie at 1.1" NW and 1.7" NW
respectively of the transition star. One of these stars is the reddest star of
the field after R84 but turns out to be too faint to correspond to the red M2
supergiant previously reported to contaminate the spectrum of R84. If the
late-type spectrum is due to a line-of-sight supergiant with a luminosity
comparable to R84, it should lie closer than 0.12" to R84. The transition star
shows spectral variability between 1982 and 1991. We also note some slight
radial velocity variations of the Of emission lines over timescales of several
years. Furthermore, we discuss the apparent absence of O type stars in this
association.Comment: 14 pages, LaTex file + postscript figures, Accepted for publication
in AA main journa
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
High resolution optical spectroscopy of Plaskett's star
We present here the analysis of an extensive set of high resolution optical
spectra of Plaskett's star (HD 47129). We use a disentangling method to
separate the individual spectra of each star. We derive a new orbital solution
and discuss the spectral classification of both components. A Doppler
tomography technique applied to the emission lines H alpha and He II 4686
yields a Doppler map that illustrates the wind interactions in the system.
Finally, an atmosphere code is used to determine the different chemical
abundances of the system components and the wind parameters. HD 47129 appears
to be an O8 III/I + O7.5 III binary system in a post RLOF evolutionary stage,
where matter has been transferred from the primary to the secondary star. The
He overabundance of the secondary supports this scenario. In addition, the N
overabundance and C underabundance of the primary component confirm previous
results based on X-ray spectroscopy and indicate that the primary is an evolved
massive star. Furthermore, the secondary star has a large rotational velocity
that deforms its surface, leading to a non-uniform distribution in effective
temperature. This could explain the variations in the equivalent widths of the
secondary lines with phase. We suggest that the wind of the secondary star is
confined near the equatorial plane because of its high rotational velocity,
affecting the ram pressure equilibrium in the wind interaction zone.Comment: Accepted in A &
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