Suchergebnisse

We have used (i) Hubble Space Telescope Advanced Camera for Surveys imaging and Space Telescope Imaging Spectrograph spectroscopy, (ii) ground-based Precision Integrated-Optics Near-infrared Imaging ExpeRiment/Very Large Telescope long-baseline interferometry, and (iii) ground-based spectroscopy from different instruments to study the orbit of the extreme multiple system HD 93 129 Aa,Ab, which is composed of (at least) two very massive stars in a long-period orbit with e > 0.92, which will pass through periastron in 2017/2018. In several ways, the system is an ¿ Car precursor. Around the time of periastron passage, the two very strong winds will collide and generate an outburst of non-thermal hard X-ray emission without precedent in an O+O binary since astronomers have been able to observe above Earth's atmosphere. A coordinated multiwavelength monitoring in the next two years will enable a breakthrough understanding of the wind interactions in such extreme close encounters. Furthermore, we have found evidence that HD 93 129 Aa may be a binary system itself. In that case, we could witness a three-body interaction which may yield a runaway star or a stellar collision close to or shortly after the periastron passage. Either of those outcomes would be unprecedented, as they are predicted to be low-frequency events in the Milky Way. ; JMA acknowledges support from the Spanish Government Ministerio de Economía y Competitividad (MINECO) through grant AYA2013-40 611-P and from HST GO programs 10205, 10602, and 10898. RHB acknowledges support from FONDECYT Projects1 140 076 and11 121 550. The HST data were obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555.

Context. Binarity and multiplicity appear to be a common outcome in star formation. In particular, the binary fraction of massive (OB-type) stars can be very high. In many cases, the further stellar evolution of these stars is affected by binary interactions at some stage during their lifetime. The origin of this high binarity and the binary parameters are poorly understood because observational constraints are scarce, which is predominantly due to a dearth of known young massive binary systems. Aims. We aim to identify and describe massive young binary systems in order to fill in the gaps of our knowledge of primordial binarity of massive stars, which is crucial for our understanding of massive star formation. Methods. We observed the two massive young stellar objects (MYSOs) PDS 27 and PDS 37 at the highest spatial resolution provided by VLTI/PIONIER in the H-band (1.3 mas). We applied geometrical models to fit the observed squared visibilities and closure phases. In addition, we performed a radial velocity analysis using published VLT/FORS2 spectropolarimetric and VLT/X-shooter spectroscopic observations. Results. Our findings suggest binary companions for both objects at 12 mas (30 au) for PDS 27 and at 22-28 mas (42-54 au) for PDS 37. This means that they are among the closest MYSO binaries resolved to date. Conclusions. Our data spatially resolve PDS 27 and PDS 37 for the first time, revealing two of the closest and most massive (>8 M·) YSO binary candidates to date. PDS 27 and PDS 37 are rare but great laboratories to quantitatively inform and test the theories on formation of such systems. © 2019 ESO. ; European Research Council, ERC ; Russian Science Foundation, RSF: 18-72-10132 ; Horizon 2020 Framework Programme, H2020: 743029 ; Acknowledgements. We would like to thank the anonymous referee for providing helpful comments and suggestions that improved the paper. S.K. acknowledges support from an ERC Starting Grant (Grant Agreement No. 639889). A.C.G. has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement No. 743029). P.B. acknowledges support by the Russian Science Foundation (grant 18-72-10132).

Context. Massive stars like company. However, low-mass companions have remained extremely di cult to detect at angular separations ( ) smaller than 1" (approx. 1000-3000 au considering typical distance to nearby massive stars) given the large brightness contrast between the companion and the central star. Constraints on the low-mass end of the companions mass-function for massive stars are however needed, for example to help distinguishing between various scenarios for the formation of massive stars. Aims. To obtain statistically significant constraint on the presence of low-mass companions beyond the typical detection limit of current surveys ( mag . 5 at . 1"), we initiated a survey of O and Wolf-Rayet stars in the Carina region using the SPHERE coronagraphic instrument on the VLT. In this first paper, we aim to introduce the survey, to present the methodology and to demonstrate the capability of SPHERE for massive stars using the multiple system QZ Car. Methods. We obtained VLT-SPHERE snapshot observations in the IRDIFS_EXT mode, which combines the IFS and IRDIS subsystems and simultaneously provides us four-dimension data cubes in two di erent field-of-view: 1.73" 1.73" for IFS (39 spectral channels across the YJH bands) and 12" 12" for IRDIS (two spectral channels across the K band). Angular- and spectral-di erential imaging techniques as well as PSF-fitting were applied to detect and measure the relative flux of the companions in each spectral channel. The latter are then flux-calibrated using theoretical SED models of the central object and are compared to a grid of ATLAS9 atmosphere model and (pre-)main-sequence evolutionary tracks, providing a first estimate of the physical properties of the detected companions. Results. Detection limits of 9 mag at > 200 mas for IFS and as faint as 13 mag at > 10:08 for IRDIS (corresponding to sub-solar masses for potential companions) can be reached in snapshot observations of only a few minutes integration times, allowing us to detect 19 sources around the QZ Car system. All but two are reported here for the first time. With near-IR magnitude contrasts in the range of 4 to 7.5 mag, the three brightest sources (Ab, Ad and E) are most likely physically bound, have masses in the range of 2 to 12 M and are potentially co-eval with QZ Car central system. The remaining sources have flux contrast of 1:5 105 to 9:5 106 ( K 11 to 13 mag). Their presence can be explained by the local source density and they are thus probably chance alignments. If they are members of the Carina nebula, they would be sub-solar-mass pre-main sequence stars. Conclusions. Based on this proof of concept, we showed that VLT/SPHERE allows us to reach the sub-solar mass regime of the companion mass function. This paves the way for this type of observation with a large sample of massive stars to provide novel constraints on the multiplicity of massive stars in a region of the parameter space that has remained inaccessible so far. ; European Southern Observatory 096.C-0510(A) French National Research Agency (ANR) ANR10 LABX56 FWO-Odysseus program G0F8H6N European Research Council under European Union's Horizon 2020 research programme 772225 European Research Council under European Union's Seventh Framework Program (ERC Grant) 337569 Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES) Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP) BELgian federal Science Policy Office (BELSPO) through PRODEX grant Gaia BELgian federal Science Policy Office (BELSPO) through PRODEX grant PLATO Australian Research Council DP180104235

Context. The innermost astronomical unit (au) in protoplanetary disks is a key region for stellar and planet formation, as exoplanet searches have shown a large occurrence of close-in planets that are located within the first au around their host star. Aims. We aim to reveal the morphology of the disk inner rim using near-infrared interferometric observations with milli-arcsecond resolution provided by near-infrared multitelescope interferometry. Methods. We provide model-independent reconstructed images of 15 objects selected from the Herbig AeBe survey carried out with PIONIER at the Very Large Telescope Interferometer, using the semi-parametric approach for image reconstruction of chromatic objects. We propose a set of methods to reconstruct and analyze the images in a consistent way. Results. We find that 40% of the systems (6/15) are centrosymmetric at the angular resolution of the observations. For the rest of the objects, we find evidence for asymmetric emission due to moderate-to-strong inclination of a disk-like structure for similar to 30% of the objects (5/15) and noncentrosymmetric morphology due to a nonaxisymmetric and possibly variable environment (4/15, similar to 27%). Among the systems with a disk-like structure, 20% (3/15) show a resolved dust-free cavity. Finally, we do not detect extended emission beyond the inner rim. Conclusions. The image reconstruction process is a powerful tool to reveal complex disk inner rim morphologies, which is complementary to the fit of geometrical models. At the angular resolution reached by near-infrared interferometric observations, most of the images are compatible with a centrally peaked emission (no cavity). For the most resolved targets, image reconstruction reveals morphologies that cannot be reproduced by generic parametric models (e.g., perturbed inner rims or complex brightness distributions). Moreover, the nonaxisymmetric disks show that the spatial resolution probed by optical interferometers makes the observations of the near-infrared emission (inside a few au) sensitive to temporal evolution with a time-scale down to a few weeks. The evidence of nonaxisymmetric emission that cannot be explained by simple inclination and radiative transfer effects requires alternative explanations, such as a warping of the inner disks. Interferometric observations can therefore be used to follow the evolution of the asymmetry of those disks at an au or sub-au scale. ; French National Research Agency (ANR) ANR-10-BLAN-0511 European Union (EU) SH-06192 Philip Leverhulme Prize PLP-2013-110 KU Leuven C14/17/082 National Science Foundation (NSF) 1210972 1616483 European Research Council (ERC) 639889 European Union (EU) 284405 French National Research Agency (ANR) ANR-16-CE31-0013 Australian Research Council FT170100040 DP180104235 Universite Joseph Fourier (UJF, Grenoble) through its Pole TUNES Universite Joseph Fourier (UJF, Grenoble) through its Pole SMING Institut de Planetologie et d'Astrophysique de Grenoble French National Research Agency (ANR) French National Research Agency (ANR) Institut National des Science de l'Univers (INSU) via the "Programme National de Physique Stellaire" Institut National des Science de l'Univers (INSU) via "Programme National de Planetologie"