120 research outputs found
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
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
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
The Massive Binary System 9 Sgr Revisited: New Insights into Disentangling Methods
Disentangling techniques are often needed to obtain the spectra of the
individual components of binary or multiple systems. A thorough analysis of the
shift-and-add algorithm of Marchenko, Moffat, & Eenens (1998) reveals that in
many cases the line fluxes are poorly reproduced and spurious wings appear. The
causes of these discrepancies are discussed and a new disentangling package,
QER20, is presented which significantly reduces these errors and vastly
increases the performance. When applied to the massive binary 9 Sgr, our new
code yields line fluxes which are notably different from those previously
published and lead us to revise the spectral classification to slightly earlier
subtypes: O3V((f +)) for the primary and O5V((f)) for the secondary. We show
that with the MME98 algorithm the classification of massive stars in binaries
can be off by several subtypes whilst there are no such errors when the QER20
package is used.Comment: Accepted for publication in Astronomical Notes, 12 pages, 10 figure
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
New insight into the massive eccentric binary HD 165052: self-consistent orbital solution, apsidal motion, and fundamental parameters
HD165052 is a short-period massive eccentric binary system that undergoes
apsidal motion. As the rate of apsidal motion is directly related to the
internal structure constants of the binary components, its study allows to get
insight into the internal structure of the stars. We use medium- and
high-resolution spectroscopic observations of HD165052 to provide constraints
on the fundamental properties of the binary system and the evolutionary state
of its components. We apply a spectral disentangling code to reconstruct
artefact-free spectra of the individual stars and derive the radial velocities
(RVs) at the times of the observations. We perform the first analysis of the
disentangled spectra with the non-LTE model atmosphere code CMFGEN to determine
the stellar properties. We derive the first self-consistent orbital solution of
all existing RV data, including those reported in the literature, accounting
for apsidal motion. We build, for the very first time, dedicated stellar
evolution tracks with the Cl\'es code requesting the theoretical effective
temperatures and luminosities to match those obtained from our spectroscopic
analysis. The binary system HD165052, consisting of an O6.5V((f)) primary and
an O7V((f)) secondary, displays apsidal motion at a rate of
(11.30+0.64-0.49)yr. Evolutionary masses are compared to minimum
dynamical masses to constrain the orbital inclination. Evolutionary masses
Mev,P=24.81.0M and Mev,S=20.91.0M and radii
Rev,P=7.0+0.5-0.4R and Rev,S=6.2+0.4-0.3R are derived, and the
inclination is constrained to 22.1. Theoretical apsidal
motion rates, derived assuming an age of 2.0+/-0.5 Myr for the binary, are in
agreement with the observational determination. The agreement with theoretical
apsidal motion rates enforces the inferred values of the evolutionary stellar
masses and radii.Comment: 17 pages. arXiv admin note: text overlap with arXiv:2205.1120
Near IR Spectroscopic monitoring of WR 140 during the 2001 periastron passage
We present new spectra of WR 140 (HD 193793) in the JHK bands with some
covering the 1.083-micron He I emission line at higher resolution, observed
between 2000 October and 2003 May to cover its 2001 periastron passage. The WC7
+ O4-5 spectroscopic binary WR 140 is the prototype of colliding-wind, episodic
dust-making Wolf-Rayet systems which also show strong variations in radio and
X-ray emission. The JHK spectra showed changes in continuum and in the
equivalent widths of the WC emission lines, consistent with formation of dust
starting between 2001 January 3 and March 26 (orbital phases 0.989 and 0.017)
and its subsequent fading and cooling. The 1.083-micron He I line has a P-Cygni
profile which showed variations in both absorption and emission components as
WR 140 went through periastron passage. The variation of the absorption
component yielded tight constraints on the geometry of the wind-collision
region, giving theta = 50 +/- 8 degrees for the opening semi-angle of the
interaction `cone', indicating a wind-momentum ratio of the O to the WR
star=0.1, about three times larger than previously believed. As the system
approached periastron, the emission component showed the appearance of a
significant sub-peak, movement of which across the profile was seen to be
consistent with its formation in wind material flowing along the contact
discontinuity between the two stellar winds and the changing orientation of the
colliding wind region. The flux carried in the sub-peak exceeded the X-ray
fluxes measured at previous periastron passages. This additional source of
radiative cooling of the shock-heated gas probably causes it to depart from
being adiabatic around periastron passage, thereby accounting for the departure
of the X-ray flux from its previously expected -dependency.Comment: Accepted for publication in MNRAS - 13 Pages, 10 figure
The Stellar Content of Obscured Galactic Giant H II Regions
Near infrared images of the Galactic giant HII region W43 reveal a dense
stellar cluster at its center. Broad band JHK photometry of the young cluster
and K-band spectra of three of its bright stars are presented. The 2 micron
spectrum of the brightest star in the cluster is very well matched to the
spectra of Wolf-Rayet stars of sub-type WN7. Two other stars are identified as
O type giants or supergiants by their NIII and CIV emission. The close spatial
clustering of O and the hydrogen WN type stars is analogous to the intense star
burst clusters R136 in the Large Magellanic Cloud and NGC3603 in the Galaxy.Comment: 22 pages (LaTex), including 7 figures (eps
First orbital solution for the non-thermal emitter Cyg OB2 #9
After the first detection of its binary nature, the spectroscopic monitoring
of the non-thermal radio emitter Cyg OB2 #9 (P=2.4yrs) has continued, doubling
the number of available spectra of the star. Since the discovery paper of 2008,
a second periastron passage has occurred in February 2009. Using a variety of
techniques, the radial velocities could be estimated and a first, preliminary
orbital solution was derived from the HeI5876 line. The mass ratio appears
close to unity and the eccentricity is large, 0.7--0.75. X-ray data from 2004
and 2007 are also analyzed in quest of peculiarities linked to binarity. The
observations reveal no large overluminosity nor strong hardness, but it must be
noted that the high-energy data were taken after the periastron passage, at a
time where colliding wind emission may be low. Some unusual X-ray variability
is however detected, with a 10% flux decrease between 2004 and 2007. To clarify
their origin and find a more obvious signature of the wind-wind collision,
additional data, taken at periastron and close to it, are needed.Comment: 15 pages, 4 figures, accepted by Ap
A downward revision to the distance of the 1806-20 cluster and associated magnetar from Gemini near-Infrared spectroscopy
We present H- and K-band spectroscopy of OB and Wolf-Rayet (WR) members of
the Milky Way cluster 1806-20 (G10.0-0.3), to obtain a revised cluster distance
of relevance to the 2004 giant flare from the SGR 1806-20 magnetar. From GNIRS
spectroscopy obtained with Gemini South, four candidate OB stars are confirmed
as late O/early B supergiants, while we support previous mid WN and late WC
classifications for two WR stars. Based upon an absolute Ks-band magnitude
calibration for B supergiants and WR stars, and near-IR photometry from NIRI at
Gemini North plus archival VLT/ISAAC datasets, we obtain a cluster distance
modulus of 14.7+/-0.35 mag. The known stellar content of the 1806-20 cluster
suggests an age of 3-5 Myr, from which theoretical isochrone fits infer a
distance modulus of 14.7+/-0.7 mag. Together, our results favour a distance
modulus of 14.7+/-0.4 mag (8.7^+1.8_-1.5 kpc) to the 1806-20 cluster, which is
significantly lower than the nominal 15 kpc distance to the magnetar. For our
preferred distance, the peak luminosity of the December 2004 giant flare is
reduced by a factor of three to 7 X 10^46 erg/s, such that the contamination of
BATSE short gamma ray bursts (GRB's) from giant flares of extragalactic
magnetars is reduced to a few percent. We infer a magnetar progenitor mass of
~48^+20_-8 Msun, in close agreement with that obtained recently for the
magnetar in Westerlund 1.Comment: 6 pages, 4 figures, accepted for MNRAS Letter
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