TY  - JOUR
A1  - Parkin, E. R.
A1  - Broos, Patrick  S.
A1  - Townsley, L. K.
A1  - Pittard, J. M.
A1  - Moffat, Anthony F. J.
A1  - Naze, Y.
A1  - Rauw, G.
A1  - Oskinova, Lida
A1  - Waldron, W. L.
T1  - X-RAY EMISSION FROM THE DOUBLE-BINARY OB-STAR SYSTEM QZ CAR (HD 93206)
JF  - ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES
N2  - X-ray observations of the double-binary OB-star system QZ Car (HD 93206) obtained with the Chandra X-ray Observatory over a period of roughly 2 years are presented. The respective orbits of systems A (O9.7 I+b2 v, P-A = 21 days) and B (O8 III+o9 v, P-B = 6 days) are reasonably well sampled by the observations, allowing the origin of the X-ray emission to be examined in detail. The X-ray spectra can be well fitted by an attenuated three-temperature thermal plasma model, characterized by cool, moderate, and hot plasma components at kT similar or equal to 0.2, 0.7, and 2 keV, respectively, and a circumstellar absorption of similar or equal to 0.2 x 10(22) cm(-2). Although the hot plasma component could be indicating the presence of wind-wind collision shocks in the system, the model fluxes calculated from spectral fits, with an average value of similar or equal to 7x10(-13) erg s(-1) cm(-2), do not show a clear correlation with the orbits of the two constituent binaries. A semi-analytical model of QZ Car reveals that a stable momentum balance may not be established in either system A or B. Yet, despite this, system B is expected to produce an observed X-ray flux well in excess of the observations. If one considers the wind of the O8 III star to be disrupted by mass transfer, the model and observations are in far better agreement, which lends support to the previous suggestion of mass transfer in the O8 III+o9 v binary. We conclude that the X-ray emission from QZ Car can be reasonably well accounted for by a combination of contributions mainly from the single stars and the mutual wind-wind collision between systems A and B.
KW  - hydrodynamics
KW  - stars: early-type
KW  - stars: individual (QZ Carinae)
KW  - stars: massive
KW  - stars: winds, outflows
KW  - X-rays: stars
Y1  - 2011
U6  - https://doi.org/10.1088/0067-0049/194/1/8
SN  - 0067-0049
VL  - 194
IS  - 1
PB  - IOP PUBLISHING LTD
CY  - BRISTOL
ER  - 
TY  - JOUR
A1  - Hainich, Rainer
A1  - Pasemann, Diana
A1  - Todt, Helge Tobias
A1  - Shenar, Tomer
A1  - Sander, Andreas Alexander Christoph
A1  - Hamann, Wolf-Rainer
T1  - Wolf-Rayet stars in the Small Magellanic Cloud I. Analysis of the single WN stars
JF  - Astronomy and astrophysics : an international weekly journal
N2  - Context. Wolf-Rayet (WR) stars have a severe impact on their environments owing to their strong ionizing radiation fields and powerful stellar winds. Since these winds are considered to be driven by radiation pressure, it is theoretically expected that the degree of the wind mass-loss depends on the initial metallicity of WR stars.
 Aims. Following our comprehensive studies of WR stars in the Milky Way, M31, and the LMC, we derive stellar parameters and mass-loss rates for all seven putatively single WN stars known in the SMC. Based on these data, we discuss the impact of a low-metallicity environment on the mass loss and evolution of WR stars.
 Methods. The quantitative analysis of the WN stars is performed with the Potsdam Wolf-Rayet (PoWR) model atmosphere code. The physical properties of our program stars are obtained from fitting synthetic spectra to multi-band observations.
 Results. In all SMC WN stars, a considerable surface hydrogen abundance is detectable. The majority of these objects have stellar temperatures exceeding 75 kK, while their luminosities range from 10(5.5) to 10(6.1) L-circle dot. The WN stars in the SMC exhibit on average lower mass-loss rates and weaker winds than their counterparts in the Milky Way, M31, and the LMC.
 Conclusions. By comparing the mass-loss rates derived for WN stars in different Local Group galaxies, we conclude that a clear dependence of the wind mass-loss on the initial metallicity is evident, supporting the current paradigm that WR winds are driven by radiation. A metallicity effect on the evolution of massive stars is obvious from the HRD positions of the SMC WN stars at high temperatures and high luminosities. Standard evolution tracks are not able to reproduce these parameters and the observed surface hydrogen abundances. Homogeneous evolution might provide a better explanation for their evolutionary past.
KW  - stars: Wolf-Rayet
KW  - Magellanic Clouds
KW  - stars: early-type
KW  - stars: atmospheres
KW  - stars: winds, outflows
KW  - stars: mass-loss
Y1  - 2015
U6  - https://doi.org/10.1051/0004-6361/201526241
SN  - 1432-0746
VL  - 581
PB  - EDP Sciences
CY  - Les Ulis
ER  - 
TY  - JOUR
A1  - Surlan, B.
A1  - Hamann, Wolf-Rainer
A1  - Kubat, Jirij
A1  - Oskinova, Lida
A1  - Feldmeier, Achim
T1  - Three-dimensional radiative transfer in clumped hot star winds I  influence of clumping on the resonance line formation
JF  - Astronomy and astrophysics : an international weekly journal
N2  - Context. The true mass-loss rates from massive stars are important for many branches of astrophysics. For the correct modeling of the resonance lines, which are among the key diagnostics of stellar mass-loss, the stellar wind clumping has been found to be very important. To incorporate clumping into a radiative transfer calculation, three-dimensional (3D) models are required. Various properties of the clumps may have a strong impact on the resonance line formation and, therefore, on the determination of empirical mass-loss rates.
 Aims. We incorporate the 3D nature of the stellar wind clumping into radiative transfer calculations and investigate how different model parameters influence the resonance line formation.
 Methods. We develop a full 3D Monte Carlo radiative transfer code for inhomogeneous expanding stellar winds. The number density of clumps follows the mass conservation. For the first time, we use realistic 3D models that describe the dense as well as the tenuous wind components to model the formation of resonance lines in a clumped stellar wind. At the same time, we account for non-monotonic velocity fields.
 Results. The 3D density and velocity wind inhomogeneities show that there is a very strong impact on the resonance line formation. The different parameters describing the clumping and the velocity field results in different line strengths and profiles. We present a set of representative models for various sets of model parameters and investigate how the resonance lines are affected. Our 3D models show that the line opacity is lower for a larger clump separation and shallower velocity gradients within the clumps.
 Conclusions. Our model demonstrates that to obtain empirically correct mass-loss rates from the UV resonance lines, the wind clumping and its 3D nature must be taken into account.
KW  - stars: winds, outflows
KW  - stars: mass-loss
KW  - stars: early-type
Y1  - 2012
U6  - https://doi.org/10.1051/0004-6361/201118590
SN  - 0004-6361
VL  - 541
PB  - EDP Sciences
CY  - Les Ulis
ER  - 
TY  - JOUR
A1  - Hainich, Rainer
A1  - Ruehling, Ute
A1  - Todt, Helge Tobias
A1  - Oskinova, Lida
A1  - Liermann, A.
A1  - Graefener, G.
A1  - Foellmi, C.
A1  - Schnurr, O.
A1  - Hamann, Wolf-Rainer
T1  - The Wolf-Rayet stars in the Large Magellanic Cloud - A comprehensive analysis of the WN class
JF  - Astronomy and astrophysics : an international weekly journal
N2  - Context. Massive stars, although being important building blocks of galaxies, are still not fully understood. This especially holds true for Wolf-Rayet (WR) stars with their strong mass loss, whose spectral analysis requires adequate model atmospheres. Aims. Following our comprehensive studies of the WR stars in the Milky Way, we now present spectroscopic analyses of almost all known WN stars in the LMC.
 Methods. For the quantitative analysis of the wind-dominated emission-line spectra, we employ the Potsdam Wolf-Rayet (PoWR) model atmosphere code. By fitting synthetic spectra to the observed spectral energy distribution and the available spectra (ultraviolet and optical), we obtain the physical properties of 107 stars.
 Results. We present the fundamental stellar and wind parameters for an almost complete sample of WN stars in the LMC. Among those stars that are putatively single, two different groups can be clearly distinguished. While 12% of our sample are more luminous than 10(6) L-circle dot and contain a significant amount of hydrogen, 88% of the WN stars, with little or no hydrogen, populate the luminosity range between log (L/L-circle dot) = 5.3 ... 5.8.
 Conclusions. While the few extremely luminous stars (log (L/L-circle dot) > 6), if indeed single stars, descended directly from the main sequence at very high initial masses, the bulk of WN stars have gone through the red-supergiant phase. According to their luminosities in the range of log (L/L-circle dot) = 5.3 ... 5.8, these stars originate from initial masses between 20 and 40 M-circle dot. This mass range is similar to the one found in the Galaxy, i.e. the expected metallicity dependence of the evolution is not seen. Current stellar evolution tracks, even when accounting for rotationally induced mixing, still partly fail to reproduce the observed ranges of luminosities and initial masses. Moreover, stellar radii are generally larger and effective temperatures correspondingly lower than predicted from stellar evolution models, probably due to subphotospheric inflation.
KW  - stars: Wolf-Rayet
KW  - Magellanic Clouds
KW  - stars: early-type
KW  - stars: atmospheres
KW  - stars: winds, outflows
KW  - stars: mass-loss
Y1  - 2014
U6  - https://doi.org/10.1051/0004-6361/201322696
SN  - 0004-6361
SN  - 1432-0746
VL  - 565
PB  - EDP Sciences
CY  - Les Ulis
ER  - 
TY  - JOUR
A1  - Miller, Amy E.
A1  - Cioni, Maria-Rosa L.
A1  - de Grijs, Richard
A1  - Sun, Ning-Chen
A1  - Bell, Cameron P. M.
A1  - Choudhury, Samyaday
A1  - Ivanov, Valentin D.
A1  - Marconi, Marcella
A1  - Oliveira, Joana M.
A1  - Petr-Gotzens, Monika
A1  - Ripepi, Vincenzo
A1  - van Loon, Jacco Th.
T1  - The VMC survey - XLVII. Turbulence-controlled hierarchical star formation in the large magellanic cloud
JF  - Monthly notices of the Royal Astronomical Society
N2  - We perform a statistical clustering analysis of upper main-sequence stars in the Large Magellanic Cloud (LMC) using data from the Visible and Infrared Survey Telescope for Astronomy survey of the Magellanic Clouds. We map over 2500 young stellar structures at 15 significance levels across similar to 120 square degrees centred on the LMC. The structures have sizes ranging from a few parsecs to over 1 kpc. We find that the young structures follow power-law size and mass distributions. From the perimeter-area relation, we derive a perimeter-area dimension of 1.44 +/- 0.20. From the mass-size relation and the size distribution, we derive two-dimensional fractal dimensions of 1.50 +/- 0.10 and 1.61 +/- 0.20, respectively. We find that the surface density distribution is well represented by a lognormal distribution. We apply the Larson relation to estimate the velocity dispersions and crossing times of these structures. Our results indicate that the fractal nature of the young stellar structures has been inherited from the gas clouds from which they form and that this architecture is generated by supersonic turbulence. Our results also suggest that star formation in the LMC is scale-free from 10 to 700 pc.
KW  - methods: statistical
KW  - stars: early-type
KW  - stars: formation
KW  - galaxies: individual: Magellanic Clouds
KW  - galaxies: stellar content
KW  - galaxies: structure
Y1  - 2022
U6  - https://doi.org/10.1093/mnras/stac508
SN  - 0035-8711
SN  - 1365-2966
VL  - 512
IS  - 1
SP  - 1196
EP  - 1213
PB  - Oxford Univ. Press
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Almeida, Leonardo A.
A1  - Sana, H.
A1  - Taylor, W.
A1  - Barbá, Rodolfo
A1  - Bonanos, Alceste Z.
A1  - Crowther, Paul
A1  - Damineli, Augusto
A1  - de Koter, A.
A1  - de Mink, Selma E.
A1  - Evans, C. J.
A1  - Gieles, Mark
A1  - Grin, Nathan J.
A1  - Hénault-Brunet, V.
A1  - Langer, Norbert
A1  - Lennon, D.
A1  - Lockwood, Sean
A1  - Maíz Apellániz, Jesús
A1  - Moffat, A. F. J.
A1  - Neijssel, C.
A1  - Norman, C.
A1  - Ramírez-Agudelo, O. H.
A1  - Richardson, N. D.
A1  - Schootemeijer, Abel
A1  - Shenar, Tomer
A1  - Soszyński, Igor
A1  - Tramper, Frank
A1  - Vink, J. S.
T1  - The tarantula massive binary monitoring
BT  - I. Observational campaign and OB-type spectroscopic binaries
JF  - Astronomy and astrophysics : an international weekly journal
N2  - Context:
Massive binaries play a crucial role in the Universe. Knowing the distributions of their orbital parameters is important for a wide range of topics from stellar feedback to binary evolution channels and from the distribution of supernova types to gravitational wave progenitors, yet no direct measurements exist outside the Milky Way.
Aims:
The Tarantula Massive Binary Monitoring project was designed to help fill this gap by obtaining multi-epoch radial velocity (RV) monitoring of 102 massive binaries in the 30 Doradus region.
Methods: 
In this paper we analyze 32 FLAMES/GIRAFFE observations of 93 O- and 7 B-type binaries. We performed a Fourier analysis and obtained orbital solutions for 82 systems: 51 single-lined (SB1) and 31 double-lined (SB2) spectroscopic binaries.
Results: 
Overall, the binary fraction and orbital properties across the 30 Doradus region are found to be similar to existing Galactic samples. This indicates that within these domains environmental effects are of second order in shaping the properties of massive binary systems. A small difference is found in the distribution of orbital periods, which is slightly flatter (in log space) in 30 Doradus than in the Galaxy, although this may be compatible within error estimates and differences in the fitting methodology. Also, orbital periods in 30 Doradus can be as short as 1.1 d, somewhat shorter than seen in Galactic samples. Equal mass binaries (q> 0.95) in 30 Doradus are all found outside NGC 2070, the central association that surrounds R136a, the very young and massive cluster at 30 Doradus’s core. Most of the differences, albeit small, are compatible with expectations from binary evolution. One outstanding exception, however, is the fact that earlier spectral types (O2–O7) tend to have shorter orbital periods than later spectral types (O9.2–O9.7).
Conclusions: 
Our results point to a relative universality of the incidence rate of massive binaries and their orbital properties in the metallicity range from solar (Z⊙) to about half solar. This provides the first direct constraints on massive binary properties in massive star-forming galaxies at the Universe’s peak of star formation at redshifts z ~ 1 to 2 which are estimated to have Z ~ 0.5 Z⊙.
KW  - stars: early-type
KW  - stars: massive
KW  - binaries: spectroscopic
KW  - binaries: close
Y1  - 2017
U6  - https://doi.org/10.1051/0004-6361/201629844
SN  - 1432-0746
VL  - 598
PB  - EDP Sciences
CY  - Les Ulis
ER  - 
TY  - JOUR
A1  - Liermann, A.
A1  - Hamann, Wolf-Rainer
A1  - Oskinova, Lida
T1  - The Quintuplet cluster III. Hertzsprung-Russell diagram and cluster age
JF  - Astronomy and astrophysics : an international weekly journal
N2  - The Quintuplet, one of three massive stellar clusters in the Galactic center (GC), is located about 30 pc in projection from Sagittarius A*. We aim at the construction of the Hertzsprung-Russell diagram (HRD) of the cluster to study its evolution and to constrain its star-formation history. For this purpose we use the most complete spectral catalog of the Quintuplet stars. Based on the K-band spectra we determine stellar temperatures and luminosities for all stars in the catalog under the assumption of a uniform reddening towards the cluster. We find two groups in the resulting HRD: early-type OB stars and late-type KM stars, well separated from each other. By comparison with Geneva stellar evolution models we derive initial masses exceeding 8 M-circle dot for the OB stars. In the HRD these stars are located along an isochrone corresponding to an age of about 4 Myr. This confirms previous considerations, where a similar age estimate was based on the presence of evolved Wolf-Rayet stars in the cluster. We derive number ratios for the various spectral subtype groups (e.g. N-WR/N-O, N-WC/N-WN) and compare them with predictions of population synthesis models. We find that an instantaneous burst of star formation at about 3.3 to 3.6 Myr ago is the most likely scenario to form the Quintuplet cluster. Furthermore, we apply a mass-luminosity relation to construct the initial mass function (IMF) of the cluster. We find indications for a slightly top-heavy IMF. The late-type stars in the LHO catalog are red giant branch (RGB) stars or red supergiants (RSGs) according to their spectral signatures. Under the assumption that they are located at about the distance of the Galactic center we can derive their luminosities. The comparison with stellar evolution models reveals that the initial masses of these stars are lower than 15 M-circle dot implying that they needed about 15 Myr (RSG) or even more than 30 Myr (RGB) to evolve into their present stage. It might be suspected that these late-type stars do not physically belong to the Quintuplet cluster. Indeed, most of them disqualify as cluster members because their radial velocities differ too much from the cluster average. Nevertheless, five of the brightest RGB/RSG stars from the LHO catalog share the mean radial velocity of the Quintuplet, and thus remain highly suspect for being gravitationally bound members. If so, this would challenge the cluster formation and evolution scenario.
KW  - stars: late-type
KW  - Hertzsprung-Russell and C-M diagrams
KW  - infrared: stars
KW  - stars: early-type
KW  - open cluster and associations: individual: Quintuplet
Y1  - 2012
U6  - https://doi.org/10.1051/0004-6361/201117534
SN  - 0004-6361
VL  - 540
PB  - EDP Sciences
CY  - Les Ulis
ER  - 
TY  - JOUR
A1  - Leto, Paolo
A1  - Trigilio, C.
A1  - Oskinova, Lida
A1  - Ignace, R.
A1  - Buemi, C. S.
A1  - Umana, G.
A1  - Cavallaro, Francesco
A1  - Ingallinera, A.
A1  - Bufano, F.
A1  - Phillips, N. M.
A1  - Agliozzo, Claudia
A1  - Cerrigone, L.
A1  - Todt, Helge Tobias
A1  - Riggi, S.
A1  - Leone, Francesco
T1  - The polarization mode of the auroral radio emission from the early-type star HD 142301
JF  - Monthly notices of the Royal Astronomical Society
N2  - We report the detection of the auroral radio emission from the early-type magnetic star HD142301. New VLA observations of HD142301 detected highly polarized amplified emission occurring at fixed stellar orientations. The coherent emission mechanism responsible for the stellar auroral radio emission amplifies the radiation within a narrow beam, making the star where this phenomenon occurs similar to a radio lighthouse. The elementary emission process responsible for the auroral radiation mainly amplifies one of the two magneto-ionic modes of the electromagnetic wave. This explains why the auroral pulses are highly circularly polarized. The auroral radio emission of HD142301 is characterized by a reversal of the sense of polarization as the star rotates. The effective magnetic field curve of HD142301 is also available making it possible to correlate the transition from the left to the right-hand circular polarization sense ( and vice versa) of the auroral pulses with the known orientation of the stellar magnetic field. The results presented in this letter have implications for the estimation of the dominant magneto-ionic mode amplified within the HD142301 magnetosphere.
KW  - masers
KW  - polarization
KW  - stars: early-type
KW  - stars: individual: HD142301
KW  - stars: magnetic field
KW  - radio continuum: stars
Y1  - 2018
U6  - https://doi.org/10.1093/mnrasl/sly179
SN  - 0035-8711
SN  - 1365-2966
VL  - 482
IS  - 1
SP  - L4
EP  - L8
PB  - Oxford Univ. Press
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Hubrig, Swetlana
A1  - Kholtygin, A.
A1  - Ilyin, Ilya
A1  - Schöller, M.
A1  - Oskinova, Lida
T1  - THE FIRST SPECTROPOLARIMETRIC MONITORING OF THE PECULIAR O4 Ief SUPERGIANT zeta PUPPIS
JF  - The astrophysical journal : an international review of spectroscopy and astronomical physics
N2  - The origin of the magnetic field in massive O-type stars is still under debate. To model the physical processes responsible for the generation of O star magnetic fields, it is important to understand whether correlations between the presence of a magnetic field and stellar evolutionary state, rotation velocity, kinematical status, and surface composition can be identified. The O4 Ief supergiant zeta Pup is a fast rotator and a runaway star, which may be a product of a past binary interaction, possibly having had an encounter with the cluster Trumper 10 some 2 Myr ago. The currently available observational material suggests that certain observed phenomena in this star may be related to the presence of a magnetic field. We acquired spectropolarimetric observations of zeta Pup with FORS 2 mounted on the 8 m Antu telescope of the Very Large Telescope to investigate if a magnetic field is indeed present in this star. We show that many spectral lines are highly variable and probably vary with the recently detected period of 1.78 day. No magnetic field is detected in zeta Pup, as no magnetic field measurement has a significance level higher than 2.4 sigma. Still, we studied the probability of a single sinusoidal explaining the variation of the longitudinal magnetic field measurements.
KW  - stars: atmospheres
KW  - stars: early-type
KW  - stars: individual (zetaPup)
KW  - stars: magnetic field
KW  - stars: variables: general
Y1  - 2016
U6  - https://doi.org/10.3847/0004-637X/822/2/104
SN  - 0004-637X
SN  - 1538-4357
VL  - 822
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Pillitteri, Ignazio
A1  - Wolk, Scott J.
A1  - Reale, Fabio
A1  - Oskinova, Lida
T1  - The early B-type star Rho Ophiuchi A is an X-ray lighthouse
JF  - Astronomy and astrophysics : an international weekly journal
N2  - We present the results of a 140 ks XMM-Newton observation of the B2 star rho Oph A. The star has exhibited strong X-ray variability: a cusp-shaped increase of rate, similar to that which we partially observed in 2013, and a bright flare. These events are separated in time by about 104 ks, which likely correspond to the rotational period of the star (1.2 days). Time resolved spectroscopy of the X-ray spectra shows that the first event is caused by an increase of the plasma emission measure, while the second increase of rate is a major flare with temperatures in excess of 60 MK (kT similar to 5 keV). From the analysis of its rise, we infer a magnetic field of >= 300 G and a size of the flaring region of similar to 1.4-1.9 x 10(11) cm, which corresponds to similar to 25%-30% of the stellar radius. We speculate that either an intrinsic magnetism that produces a hot spot on its surface or an unknown low mass companion are the source of such X-rays and variability. A hot spot of magnetic origin should be a stable structure over a time span of >= 2.5 yr, and suggests an overall large scale dipolar magnetic field that produces an extended feature on the stellar surface. In the second scenario, a low mass unknown companion is the emitter of X-rays and it should orbit extremely close to the surface of the primary in a locked spin-orbit configuration, almost on the verge of collapsing onto the primary. As such, the X-ray activity of the secondary star would be enhanced by its young age, and the tight orbit as in RS Cvn systems. In both cases rho Oph would constitute an extreme system that is worthy of further investigation.
KW  - stars: activity
KW  - stars: individual: Rho Ophiuchi
KW  - stars: early-type
KW  - stars: magnetic field
KW  - starspots
KW  - X-rays: stars
Y1  - 2017
U6  - https://doi.org/10.1051/0004-6361/201630070
SN  - 1432-0746
VL  - 602
PB  - EDP Sciences
CY  - Les Ulis
ER  -