Suchergebnisse

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. While exoplanets are now routinely detected, the detection of small bodies in extrasolar systems remains challenging. Since the discovery of sporadic events, which are interpreted to be exocomets (falling evaporating bodies) around β Pic in the early 1980s, only ∼20 stars have been reported to host exocomet-like events. Aims. We aim to expand the sample of known exocomet-host stars, as well as to monitor the hot-gas environment around stars with previously known exocometary activity. Methods. We have obtained high-resolution optical spectra of a heterogeneous sample of 117 main-sequence stars in the spectral type range from B8 to G8. The data were collected in 14 observing campaigns over the course of two years from both hemispheres. We analysed the Ca » II K&H and Na » I D lines in order to search for non-photospheric absorptions that originated in the circumstellar environment and for variable events that could be caused by the outgassing of exocomet-like bodies. Results. We detected non-photospheric absorptions towards 50% of the sample, thus attributing a circumstellar origin to half of the detections (i.e. 26% of the sample). Hot circumstellar gas was detected in the metallic lines inspected via narrow stable absorptions and/or variable blue- and red-shifted absorption events. Such variable events were found in 18 stars in the Ca » II and/or Na » I lines; six of them are reported in the context of this work for the first time. In some cases, the variations we report in the Ca » II K line are similar to those observed in β Pic. While we do not find a significant trend in the age or location of the stars, we do find that the probability of finding CS gas in stars with larger v sin i is higher. We also find a weak trend with the presence of near-infrared excess and with anomalous (λ Boo-like) abundances, but this would require confirmation by expanding the sample. ; With funding from the Spanish government through the "María de Maeztu Unit of Excellence" accreditation (MDM-2017-0737)

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"