The presence of a nearby companion alters the evolution of massive stars in binary systems, leading to phenomena such as stellar mergers, x-ray binaries, and gamma-ray bursts. Unambiguous constraints ...on the fraction of massive stars affected by binary interaction were lacking. We simultaneously measured all relevant binary characteristics in a sample of Galactic massive O stars and quantified the frequency and nature of binary interactions. More than 70% of all massive stars will exchange mass with a companion, leading to a binary merger in one-third of the cases. These numbers greatly exceed previous estimates and imply that binary interaction dominates the evolution of massive stars, with implications for populations of massive stars and their supernovae.
Context.
The eccentric massive binary HD 152248 (also known as V1007 Sco), which hosts two O7.5 III-II(f) stars, is the most emblematic eclipsing O-star binary in the very young and rich open cluster ...NGC 6231. Its properties render the system an interesting target for studying tidally induced apsidal motion.
Aims.
Measuring the rate of apsidal motion in such a binary system gives insight into the internal structure and evolutionary state of the stars composing it.
Methods.
A large set of optical spectra was used to reconstruct the spectra of the individual binary components and establish their radial velocities using a disentangling code. Radial velocities measured over seven decades were used to establish the rate of apsidal motion. We furthermore analysed the reconstructed spectra with the
CMFGEN
model atmosphere code to determine stellar and wind properties of the system. Optical photometry was analysed with the
Nightfall
binary star code. A complete photometric and radial velocity model was constructed in
PHOEBE 2
to determine robust uncertainties.
Results.
We find a rate of apsidal motion of (1.843
−0.083
+0.064
)° yr
−1
. The photometric data indicate an orbital inclination of (67.6
−0.1
+0.2
)° and Roche-lobe filling factors of both stars of about 0.86. Absolute masses of 29.5
−0.4
+0.5
M
⊙
and mean stellar radii of 15.07
−0.12
+0.08
R
⊙
are derived for both stars. We infer an observational value for the internal structure constant of both stars of 0.0010 ± 0.0001.
Conclusions.
Our in-depth analysis of the massive binary HD 152248 and the redetermination of its fundamental parameters can serve as a basis for the construction of stellar evolution models to determine theoretical rates of apsidal motion to be compared with the observational one. In addition, the system hosts two twin stars, which offers a unique opportunity to obtain direct insight into the internal structure of the stars.
Context. HD 150136 is a triple hierarchical system and a non-thermal radio emitter. It is formed by an O3−3.5 V + O5.5−6 V close binary and a more distant O6.5−7 V tertiary. So far, only the inner ...orbital properties have been reliably constrained. Aims. To quantitatively understand the non-thermal emission process, accurate knowledge of the physical and orbital properties of the object is crucial. Here, we aim to investigate the orbital properties of the wide system and to constrain the inclinations of the inner and outer binaries, and with these the absolute masses of the system components. Methods. We used the PIONIER combiner at the Very Large Telescope Interferometer to obtain the very first interferometric measurements of HD 150136. We combined the interferometric observations with new and existing high-resolution spectroscopic data to derive the orbital solution of the outer companion in the three-dimensional space. Results. The wide system is clearly resolved by PIONIER, with a projected separation on the plane of the sky of about 9 milli-arcsec. The best-fit orbital period, eccentricity, and inclination are 8.2 yr, 0.73, and 108°. We constrain the masses of the three stars of the system to 63 ± 10, 40 ± 6, and 33 ± 12 M⊙ for the O3−3.5 V, O5.5−6 V, and O6.5−7 V components. Conclusions. The dynamical masses agree within errors with the evolutionary masses of the components. Future interferometric and spectroscopic monitoring of HD 150136 should allow one to reduce the uncertainties to a few per cent only and to accurately constrain the distance to the system. This makes HD 150136 an ideal system to quantitatively test evolutionary models of high-mass stars as well as the physics of non-thermal processes occurring in O-type systems.
Context.
Luminous blue variables (LBVs) are characterised by strong photometric and spectroscopic variability. They are thought to be in a transitory phase between O-type stars on the main sequence ...and the Wolf-Rayet stage. Recent studies also evoked the possibility that they might be formed through binary interaction. Only a few are known in binary systems so far, but their multiplicity fraction is still uncertain.
Aims.
We derive the binary fraction of the Galactic LBV population. We combine multi-epoch spectroscopy and long-baseline interferometry to probe separations from 0.1 to 120 mas around confirmed and candidate LBVs.
Methods.
We used a cross-correlation technique to measure the radial velocities of these objects. We identified spectroscopic binaries through significant radial velocity variability with an amplitude larger than 35 km s
−1
. We also investigated the observational biases to take them into account when we established the intrinsic binary fraction. We used
CANDID
to detect interferometric companions, derive their flux fractions, and their positions on the sky.
Results.
From the multi-epoch spectroscopy, we derive an observed spectroscopic binary fraction of 26
−10
+16
%. Considering period and mass ratio ranges from log(
P
orb
) = 0 − 3 (i.e. from 1 to 1000 days),
q
= 0.1 − 1.0, and a representative set of orbital parameter distributions, we find a bias-corrected binary fraction of 62
−24
+38
%. Based on data of the interferometric campaign, we detect a binary fraction of 70 ± 9% at projected separations between 1 and 120 mas. Based on the derived primary diameters and considering the distances of these objects, we measure for the first time the exact radii of Galactic LBVs to be between 100 and 650
R
⊙
. This means that it is unlikely that short-period systems are included among LBV-like stars.
Conclusions.
This analysis shows for the first time that the binary fraction in the Galactic LBV population is large. If they form through single-star evolution, their orbit must be large initially. If they form through a binary channel, the implication is that either massive stars in short binary systems must undergo a phase of fully non-conservative mass transfer to be able to sufficiently widen the orbit to form an LBV, or that LBVs form through merging in initially binary or triple systems. Interferometric follow-up would provide the distributions of orbital parameters at more advanced stages and would serve to quantitatively test the binary evolution in massive stars.
ABSTRACT
Our main aim is to test the non-variability of the radial velocity (RV) of a sample of 2351 standard stars used for wavelength calibration of the Radial Velocity Spectrometer (RVS) ...instrument onboard Gaia. In this paper, we present the spectroscopic analysis of these stars with the determination of their physical parameters by matching observed and synthetic spectra. We estimate the offset between different instruments after determining the shift between measured and archived RVs since the instrument pipelines use various numerical masks. Through the confirmation of the stability of the target RVs, we find 68 stars with a long-term variation having an acceleration that exceeds $10 \, \rm {m\, s^{-1}\,yr^{-1}}$. This suggests a barycentric reflex motion caused by a companion. As activity phenomena may be the source of periodic and trend-like RV variations in stars with putative planetary companions, we analysed various activity indicators in order to check their correlations to the RV changes. Among the trend stars, 18 have a trend model scatter greater than $100 \, \rm {m\, s^{-1}}$ over a time span from 10 to 12 yr. We also confirm that six stars with known substellar companions have a total model scatter, 3σ, exceeding the threshold set by Gaia, that is, $300 \, \rm {m\, s^{-1}}$. In addition, TYC8963-01543-1, an SB2 star, has data scatter $\sigma = 176.6\, \rm {m\, s^{-1}}$. Four more other stars are revealed to be variable after combining data from different instruments. Despite the presence of low-amplitude changes, a very large fraction of our sample (98.8 per cent) appears suitable as RV calibrators for Gaia RVS.
Aims. HD 166734 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 HD 166734. 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. HD 166734 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° ± 2.7°. 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 M⊙ for the primary and 33.5 M⊙ 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.
Aims. We examine the dependence of the wind-wind collision and subsequent X-ray emission from the massive WR+O star binary WR 22 on the acceleration of the stellar winds, radiative cooling, and ...orbital motion. Methods. Three dimensional (3D) adaptive-mesh refinement (AMR) simulations are presented that include radiative driving, gravity, optically-thin radiative cooling, and orbital motion. Simulations were performed with instantaneously accelerated and radiatively driven stellar winds. Radiative transfer calculations were performed on the simulation output to generate synthetic X-ray data, which are used to conduct a detailed comparison against observations. Results. When instantaneously accelerated stellar winds are adopted in the simulation, a stable wind-wind collision region (WCR) is established at all orbital phases. In contrast, when the stellar winds are radiatively driven, and thus the acceleration regions of the winds are accounted for, the WCR is far more unstable. As the stars approach periastron, the ram pressure of the WR’s wind overwhelms the O star’s and, following a significant disruption of the shocks by non-linear thin-shell instabilities (NTSIs), the WCR collapses onto the O star. X-ray calculations reveal that when a stable WCR exists the models over-predict the observed X-ray flux by more than two orders of magnitude. The collapse of the WCR onto the O star substantially reduces the discrepancy in the 2–10keV flux to a factor of ≃ 6 at φ = 0.994. However, the observed spectrum is not well matched by the models. Conclusions. We conclude that the agreement between the models and observations could be improved by increasing the ratio of the mass-loss rates in favour of the WR star to the extent that a normal wind ram pressure balance does not occur at any orbital phase, potentially leading to a sustained collapse of the WCR onto the O star. Radiative braking may then play a significant rôle for the WCR dynamics and resulting X-ray emission.
Using an extended set of multi-epoch high-resolution high signal-to-noise ratio optical spectra, we readdress the multiplicity properties of the O-type stars in IC 2944 and in the Cen OB2 ...association. We present new evidence of binarity for five objects and we confirm the multiple nature of another two. We derive the first orbital solutions for HD 100099, HD 101436 and HD 101190 and we provide additional support for HD 101205 being a quadruple system. The minimal spectroscopic binary fraction in our sample is f
min= 0.57. Using numerical simulations, we show that the detection rate of our observational campaign is close to 90 per cent, leaving thus little room for undetected spectroscopic binary systems. The statistical properties of the O-star population in IC 2944 are similar, within the uncertainties, to the results obtained in the earlier papers in this series despite the fact that sample size effects limit the significance of the comparison. Using newly derived spectroscopic parallaxes, we reassess the distance to IC 2944 and obtained 2.3 ± 0.3 kpc, in agreement with previous studies. We also confirm that, as far as the O stars are concerned, the IC 2944 cluster is most likely a single entity.
ABSTRACT Using an extended set of multi-epoch high-resolution high signal-to-noise ratio optical spectra, we readdress the multiplicity properties of the O-type stars in IC2944 and in the CenOB2 ...association. We present new evidence of binarity for five objects and we confirm the multiple nature of another two. We derive the first orbital solutions for HD100099, HD101436 and HD101190 and we provide additional support for HD101205 being a quadruple system. The minimal spectroscopic binary fraction in our sample isfmin= 0.57. Using numerical simulations, we show that the detection rate of our observational campaign is close to 90 per cent, leaving thus little room for undetected spectroscopic binary systems. The statistical properties of the O-star population in IC2944 are similar, within the uncertainties, to the results obtained in the earlier papers in this series despite the fact that sample size effects limit the significance of the comparison. Using newly derived spectroscopic parallaxes, we reassess the distance to IC2944 and obtained 2.3 ± 0.3kpc, in agreement with previous studies. We also confirm that, as far as the O stars are concerned, the IC2944 cluster is most likely a single entity. PUBLICATION ABSTRACT
Based on a set of over 100 medium- to high-resolution optical spectra collected from 2003 to 2009, we investigate the properties of the O-type star population in NGC 6611 in the core of the Eagle ...Nebula (M16). Using a much more extended data set than previously available, we revise the spectral classification and multiplicity status of the nine O-type stars in our sample. We confirm two suspected binaries and derive the first SB2 orbital solutions for two systems. We further report that two other objects are displaying a composite spectrum, suggesting possible long-period binaries. Our analysis is supported by a set of Monte Carlo simulations, allowing us to estimate the detection biases of our campaign and showing that the latter do not affect our conclusions. The absolute minimal binary fraction in our sample is fmin= 0.44 but could be as high as 0.67 if all the binary candidates are confirmed. As in NGC 6231 (see Paper I), up to 75 per cent of the O star population in NGC 6611 are found in an O+OB system, thus implicitly excluding random pairing from a classical IMF as a process to describe the companion association in massive binaries. No statistical difference could be further identified in the binary fraction, mass-ratio and period distributions between NGC 6231 and NGC 6611, despite the difference in age and environment of the two clusters.
PDF
