Search

We report the discovery of a new example of the rare class of highly magnetized, rapidly rotating, helium enhanced, early B stars that produce anomalously wide hydrogen emission due to a centrifugal magnetosphere (CM). The star is Trumpler 16-26, a B1.5 V member of the Trumpler 16 open cluster. A CM was initially suspected based on hydrogen Brackett series emission observed in SDSS/APOGEE $H$-band spectra. Similar to the other stars of this type, the emission was highly variable and at all times remarkable due to the extreme velocity separations of the double peaks (up to 1300 km s$^{-1}$.) Another clue lay in the TESS lightcurve, which shows two irregular eclipses per cycle when phased with the likely 0.9718115 day rotation period, similar to the behavior of the well known CM host star $\sigma$ Ori E. To confirm a strong magnetic field and rotation-phase-locked variability, we initiated a follow-up campaign consisting of optical spectropolarimetry and spectroscopy. The associated data revealed a longitudinal magnetic field varying between $-3.1$ and $+1.6$ kG with the period found from photometry. The optical spectra confirmed rapid rotation ($v \sin i=195$ km s$^{-1}$), surface helium enhancement, and wide, variable hydrogen emission. Tr16-26 is thus confirmed as the 20$^{\rm th}$ known, the fourth most rapidly rotating, and the faintest CM host star yet discovered. With a projected dipole magnetic field strength of $B_{\rm d}>11$ kG, Tr16-26 is also among the most magnetic CM stars.

Multiplicity is a ubiquitous characteristic of massive stars. Multiple systems offer us a unique observational constraint on the formation of high-mass systems. Herschel 36 A is a massive triple system composed of a close binary (Ab1-Ab2) and an outer component (Aa). We measured the orbital motion of the outer component of Herschel 36 A using infrared interferometry with the AMBER and PIONIER instruments of ESO's Very Large Telescope Interferometer. Our immediate aims are to constrain the masses of all components of this system and to determine if the outer orbit is co-planar with the inner one. Reported spectroscopic data for all three components of this system and our interferometric data allow us to derive full orbital solutions for the outer orbit Aa-Ab and the inner orbit Ab1-Ab2. For the first time, we derive the absolute masses of mAa = 22.3 +/- 1.7 M_sun, mAb1 = 20.5 +/- 1.5 M_sun and mAb2 = 12.5 +/- 0.9 M_sun. Despite not being able to resolve the close binary components, we infer the inclination of their orbit by imposing the same parallax as the outer orbit. Inclinations derived from the inner and outer orbits imply a modest difference of about 22 deg. between the orbital planes. We discuss this result and the formation of Herschel 36 A in the context of Core Accretion and Competitive Accretion models, which make different predictions regarding the statistic of the relative orbital inclinations., Comment: accepted to be published by MNRAS, 8 pages, 5 figures

The O9.7 V star HD 54879 is currently the only massive magnetic star whose magnetic field geometry and rotation period are not constrained. Over the last three years, we gathered additional observations of this star, obtained using various instruments at several astronomical facilities with, the aim to constrain the rotation period and the magnetic field geometry. The new data include the first full Stokes vector observations with the PEPSI spectropolarimeter, installed at the Large Binocular Telescope. The acquired spectropolarimetric observations show a very slow magnetic field variability related to the extremely slow rotation of HD 54879, which is also indicated in a dynamical spectrum, displaying variability of the H$\alpha$ line. The most intriguing result of our study is the discovery of differences in longitudinal magnetic field strengths measured using different LSD masks containing lines belonging to different elements. It is the first time that such a differential analysis of the field strength in dependence of the used lines is carried out for a magnetic O-type star. Since the LSD Stokes $I$ profiles of the studied O, Si, and He line masks remain stable over all observing epochs, we conclude that the detection of different field strengths using lines belonging to these elements is related to the different formation depths, with the He lines formed much higher in the stellar atmosphere compared to the silicon and the oxygen lines, and NLTE effects. Our numerical magnetospherical model suggests the presence of enhanced gas density that fills the volume inside the field lines close to the star., Comment: This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society Published by Oxford University Press on behalf of the Royal Astronomical Society

Altough both components of the bright eclipsing binary $\alpha$ Dra having been resolved using long baseline interferometry and the secondary component shown to contribute some 15\% of the total flux, a spectroscopic detection of the companion star was so far unsuccessful. To achieve our goals, we use a combined data set from interferometry with the Navy Precision Optical Interferometer (NPOI), photometry with the TESS space observatory, and high-resolution spectroscopy with the HERMES fibre-fed spectrograph at the La Palma observatory. We use the method of spectral disentangling to search for the contribution of a companion star in the observed composite HERMES spectra, to separate the spectral contributions of both components, and to determine orbital elements of the $\alpha$ Dra system. TESS light curves are analysed in an iterative fashion with spectroscopic inference of stellar atmospheric parameters to determine fundamental stellar properties and their uncertainties. Finally, NPOI interferometric measurements are used for determination of the orbital parameters of the system and angular diameters of both binary components. We report the first firm spectroscopic detection of the secondary component in $\alpha$ Dra and deliver disentangled spectra of both binary components. The inferred near-core mixing properties of both components do not support a dependence of the convective core overshooting on the stellar mass. At the same time, the $\alpha$ Dra system provides extra support to hypothesise that the mass discrepancy in eclipsing spectroscopic double-lined binaries is associated with inferior atmospheric modelling of intermediate- and high-mass stars, and less so with the predictive power of stellar structure and evolution models as to the amount of near-core mixing and mass of the convective core. (abridged abstract), Comment: 23 pages, 15 figures, 8 tables, accepted for publication in Astronomy & Astrophysics

Context:Optical interferometry is at a key development stage. ESO's VLTI has established a stable, robust infrastructure for long-baseline interferometry for general astronomical observers. The present second-generation instruments offer a wide wavelength coverage and improved performance. Their sensitivity and measurement accuracy lead to data and images of high reliability. Aims:We have developed MATISSE, the Multi AperTure mid-Infrared SpectroScopic Experiment, to access high resolution imaging in a wide spectral domain and explore topics such: stellar activity and mass loss; planet formation and evolution in the gas and dust disks around young stars; accretion processes around super massive black holes in AGN. Methods:The instrument is a spectro-interferometric imager covering three atmospheric bands (L,M,N) from 2.8 to 13.0 mu, combining four optical beams from the VLTI's telscopes. Its concept, related observing procedure, data reduction and calibration approach are the product of 30 years of instrumental research. The instrument utilizes a multi-axial beam combination that delivers spectrally dispersed fringes. The signal provides the following quantities at several spectral resolutions: photometric flux, coherent fluxes, visibilities, closure phases, wavelength differential visibilities and phases, and aperture-synthesis imaging. Results:We provide an overview of the physical principle of the instrument and its functionalities, the characteristics of the delivered signal, a description of the observing modes and of their performance limits. An ensemble of data and reconstructed images are illustrating the first acquired key observations. Conclusion:The instrument has been in operation at Cerro Paranal, ESO, Chile since 2018, and has been open for science use by the international community since April 2019. The first scientific results are being published now., Comment: 24 pages, 26 figures, submitted to Astronomy & Astrophysics

We present the results of a multiplicity survey for a magnitude-limited sample of 31 classical Be stars conducted with the Navy Precision Optical Interferometer and the Mark III Stellar Interferometer. The interferometric observations were used to detect companions in ten previously known binary systems. For two of these sources (66 Oph and $\beta$ Cep) new orbital solutions were obtained, while for a third source ($\upsilon$ Sgr) our observations provide the first direct, visual detection of the hot sdO companion to the Be primary star. Combining our interferometric observations with an extensive literature search, we conclude that an additional four sources (o Cas, 15 Mon, $\beta$ Lyr, and $\beta$ Cep) also contain wider binary components that are physical companions to the narrow binaries, thus forming hierarchical multiple systems. Among the sources not previously confirmed as spectroscopic or visual binaries, BK Cam was resolved on a number of nights within a close physical proximity of another star with relative motion possibly suggesting a physical binary. Combining our interferometric observations with an extensive literature search, we provide a detailed listing of companions known around each star in the sample, and discuss the multiplicity frequency in the sample. We also discuss the prospects for future multiplicity studies of classical Be stars by long baseline optical interferometry., Comment: 58 pages, 14 figures, 8 tables

Carbon is one of the most abundant components in the Universe. While silicates have been the main focus of solid phase studies in protoplanetary discs (PPDs), little is known about the solid carbon content especially in the planet-forming regions ($\sim $0.1 to 10 au). Fortunately, several refractory carbonaceous species present C-H bonds (such as hydrogenated nano-diamond and amorphous carbon as well as polycyclic aromatic hydrocarbons (PAHs)), which generate infrared (IR) features that can be used to trace the solid carbon reservoirs. The new mid-IR instrument MATISSE, installed at the Very Large Telescope Interferometer (VLTI), can spatially resolve the inner regions ($\sim$ 1 to 10 au) of PPDs and locate, down to the au-scale, the emission coming from carbon grains. Our aim is to provide a consistent view on the radial structure, down to the au-scale, as well as basic physical properties and the nature of the material responsible for the IR continuum emission in the inner disk region around HD 179218. We implemented a temperature-gradient model to interpret the disk IR continuum emission, based on a multiwavelength dataset comprising a broadband spectral energy distribution (SED) and VLTI H-, L-, and N-bands interferometric data obtained in low spectral resolution. Then, we added a ring-like component, representing the carbonaceous L-band features-emitting region, to assess its detectability in future higher spectral resolution observations employing mid-IR interferometry.

The Bp star HD94660 is a single-lined spectroscopic binary. Some authors have suggested that the unseen companion of at least 2M_sun may be a compact object. We intend to study this multiple system in detail, especially to learn more about the so-far unseen companion. We have collected and analyzed PIONIER H-band data from the Very Large Telescope Interferometer, TESS visible photometric data, and X-ray observations with Chandra of HD94660. Using PIONIER, we were able to detect the companion to HD94660, which is absent from high quality spectra at visible wavelengths, with a magnitude difference of 1.8 in the H band at a separation of 18.72mas. The TESS light curve shows variations with a period of 2.1d and also flaring. The Chandra spectrum is well described by emission from hot thermal plasma, yet might include a non-thermal component. The X-ray properties are compatible with a magnetically active companion, while some magnetospheric contribution from the primary is also possible. We can rule out that the companion to HD94660 is a compact source. It is also very unlikely that this companion is a single star, as the estimated mass of more than 2M_sun, the magnitude difference of 1.8 in the H band, and its non-detection in visible spectra are difficult to realize in a single object. One alternative could be a pair of late F stars, which would also be responsible for the detected photometric variations. Interferometric observations over the full binary orbit are necessary to determine the real mass of the companion and to add constraints on the overall geometry of the system., Comment: 6 pages, 1 table, 4 figures, accepted for publication in A&A

The first FORS2 spectropolarimetric observation of the longitudinal magnetic field of HD54879 of the order of -600G with a lower limit of the dipole strength of ~2kG dates back to 2014. Since then observations showed a gradual decrease of the absolute value of the mean longitudinal magnetic field. In the course of the most recent monitoring of HD54879 using FORS2 spectropolarimetric observations from 2017 October to 2018 February, a longitudinal magnetic field strength change from about -300G down to about -90G was reported. A sudden increase of the absolute value of the mean longitudinal magnetic field and an accompanying spectral variability was detected on 2018 February 17. New FORS2 spectropolarimetric data obtained from 2018 December to 2019 February confirm the very slow magnetic field variability, with the field decreasing from about 150G to -100G over two months. Such a slow magnetic field variability, related to the extremely slow rotation of HD54879, is also confirmed using high-resolution HARPSpol and ESPaDOnS spectropolarimetry. The re-analysis of the FORS2 polarimetric spectra from 2018 February indicates that the previously reported field increase and the change of the spectral appearance was caused by improper spectra extraction and wavelength calibration using observations obtained at an insufficient signal-to-noise ratio. The presented properties of HD54879 are discussed in the context of the Of?p spectral classification., Comment: 8 pages, 2 tables, 11 figures, accepted for publication in MNRAS

Context. Colliding winds in massive binaries are able to accelerate particles up to relativistic speeds as the result of the interaction between the winds of the different stellar components. HD 167971 exhibits this phenomenology which makes it a strong radio source. Aims. We aim at characterizing the morphology of the radio emission and its dependence on the orbital motion, traced independently by NIR-interferometry, of the spectroscopic binary and the tertiary component that conforms HD 167971. Methods. We analyze 2006 and 2016 very long baseline interferometric data at C and X bands. We complement our analysis with a geometrical model of the wind-wind collision region, and with an astrometric description of the system. Results. We confirm that the detected non-thermal radio emission is associated with the wind-wind collision region of the spectroscopic binary and the tertiary component in HD 167971. The wind-wind collision region changes orientation in agreement with the orbital motion of the tertiary around the spectroscopic binary. The total intensity also changes between the two observing epochs in a way inversely proportional to the separation between the SB and T, with a negative-steep spectral index typical of an optically thin synchrotron emission possibly steepened by an inverse Compton cooling effect. The wind-wind collision bow-shock shape and its position with respect to the stars indicates that the wind momentum from the spectroscopic binary is stronger than that of the tertiary. Finally, the astrometric solution derived for the stellar system and the wind-wind collision region is consistent with independent Gaia data., Comment: Accepted for publication in Astronomy and Astrophysics, 7 pages, 6 figures

Eta Car is one of the most intriguing luminous blue variables in the Galaxy. Observations and models at different wavelengths suggest a central binary with a 5.54 yr period residing in its core. 2D and 3D radiative transfer and hydrodynamic simulations predict a primary with a dense and slow stellar wind that interacts with the faster and lower density wind of the secondary. The wind-wind collision scenario suggests that the secondary's wind penetrates the primary's wind creating a low-density cavity in it, with dense walls where the two winds interact. We aim to trace the inner ~5-50 au structure of Eta Car's wind-wind interaction, as seen through BrG and, for the first time, through the He I 2s-2p line. We have used spectro-interferometric observations with GRAVITY at the VLTI. Our modeling of the continuum allows us to estimate its FWHM angular size close to 2 mas and an elongation ratio of 1.06 +/- 0.05 over a PA = 130 +/- 20 deg. Our CMFGEN modeling helped us to confirm that the role of the secondary should be taken into account to properly reproduce the observed BrG and He I lines. Chromatic images across BrG reveal a southeast arc-like feature, possibly associated to the hot post-shocked winds flowing along the cavity wall. The images of He I 2s-2p served to constrain the 20 mas structure of the line-emitting region. The observed morphology of He I suggests that the secondary is responsible for the ionized material that produces the line profile. Both the BrG and the He I 2s-2p maps are consistent with previous hydrodynamical models of the colliding wind scenario. Future dedicated simulations together with an extensive interferometric campaign are necessary to refine our constraints on the wind and stellar parameters of the binary, which finally will help us predict the evolutionary path of Eta Car., Comment: 32 pages, 27 figures (14 in the main body, 13 in the appendices), accepted for publication in AA

We report the detection of weak mean longitudinal magnetic fields in the Herbig Ae double-lined spectroscopic binary AK Sco and in the presumed spectroscopic Herbig Ae binary HD95881 using observations with the High Accuracy Radial velocity Planet Searcher polarimeter (HARPSpol) attached to the European Southern Observatory's (ESO's) 3.6m telescope. Employing a multi-line singular value decomposition (SVD) method, we detect a mean longitudinal magnetic field =-83+-31G in the secondary component of AK Sco on one occasion. For HD95881, we measure =-93+-25G and =105+-29G at two different observing epochs. For all the detections the false alarm probability is smaller than 10^-5. For AK Sco system, we discover that accretion diagnostic Na I doublet lines and photospheric lines show intensity variations over the observing nights. The double-lined spectral appearance of HD95881 is presented here for the first time.

To investigate the inner regions of protoplanetary disks, we performed near-infrared interferometric observations of the classical TTauri binary system S CrA. We present the first VLTI-GRAVITY high spectral resolution ($R\sim$4000) observations of a classical TTauri binary, S CrA (composed of S CrA N and S CrA S and separated by $\sim$1.4"), combining the four 8-m telescopes in dual-field mode. Our observations in the near-infrared K-band continuum reveal a disk around each binary component, with similar half-flux radii of about 0.1 au at d$\sim$130 pc, inclinations ($i=$28$\pm$3$^o$\ and $i=$22$\pm$6$^o$), and position angles (PA=0$^o\pm$6$^o$ and PA=-2$^o\pm$12$^o$), suggesting that they formed from the fragmentation of a common disk. The S CrA N spectrum shows bright HeI and Br$\gamma$ line emission exhibiting inverse P-Cygni profiles, typically associated with infalling gas. The continuum-compensated Br$\gamma$ line visibilities of S CrA N show the presence of a compact Br$\gamma$ emitting region the radius of which is about $\sim$0.06 au, which is twice as big as the truncation radius. This component is mostly tracing a wind. Moreover, a slight radius change between the blue- and red-shifted Br$\gamma$ line components is marginally detected. The presence of an inverse P-Cygni profile in the HeI and Br$\gamma$ lines, along with the tentative detection of a slightly larger size of the blue-shifted Br$\gamma$ line component, hint at the simultaneous presence of a wind and magnetospheric accretion in S CrA N., Comment: Accepted by A&A

Characterization of the dynamics of massive star systems and the astrophysical properties of the interacting components are a prerequisite for understanding their formation and evolution. Optical interferometry at milliarcsecond resolution is a key observing technique for resolving high-mass multiple compact systems. Here we report on VLTI/GRAVITY, Magellan/FIRE, and MPG2.2m/FEROS observations of the late-O/early-B type system HD 93206 A, which is a member of the massive cluster Collinder 228 in the Carina nebula complex. With a total mass of about 90 M_sun, it is one of the most compact massive-quadruple systems known. In addition to measuring the separation and position angle of the outer binary Aa - Ac, we observe BrG and HeI variability in phase with the orbital motion of the two inner binaries. From the differential phases analysis, we conclude that the BrG emission arises from the interaction regions within the components of the individual binaries, which is consistent with previous models for the X-ray emission of the system based on wind-wind interaction. With an average 3-sigma deviation of ~15 deg, we establish an upper limit of p ~ 0.157 mas (0.35 AU) for the size of the BrG line-emitting region. Future interferometric observations with GRAVITY using the 8m UTs will allow us to constrain the line-emitting regions down to angular sizes of 20 uas (0.05 AU at the distance of the Carina nebula)., Comment: 17pages, 12 figures Accepted for publication in ApJ

GRAVITY is a new instrument to coherently combine the light of the European Southern Observatory Very Large Telescope Interferometer to form a telescope with an equivalent 130 m diameter angular resolution and a collecting area of 200 m$^2$. The instrument comprises fiber fed integrated optics beam combination, high resolution spectroscopy, built-in beam analysis and control, near-infrared wavefront sensing, phase-tracking, dual beam operation and laser metrology [...]. This article gives an overview of GRAVITY and reports on the performance and the first astronomical observations during commissioning in 2015/16. We demonstrate phase tracking on stars as faint as m$_K$ ~ 10 mag, phase-referenced interferometry of objects fainter than m$_K$ ~ 15 mag with a limiting magnitude of m$_K$ ~ 17 mag, minute long coherent integrations, a visibility accuracy of better than 0.25 %, and spectro-differential phase and closure phase accuracy better than 0.5{\deg}, corresponding to a differential astrometric precision of better than 10 microarcseconds ({\mu}as). The dual-beam astrometry, measuring the phase difference of two objects with laser metrology, is still under commissioning. First observations show residuals as low as 50 {\mu}as when following objects over several months. We illustrate the instrument performance with the observations of archetypical objects for the different instrument modes. Examples include the Galactic Center supermassive black hole and its fast orbiting star S2 for phase referenced dual beam observations and infrared wavefront sensing, the High Mass X-Ray Binary BP Cru and the Active Galactic Nucleus of PDS 456 for few {\mu}as spectro-differential astrometry, the T Tauri star S CrA for a spectro-differential visibility analysis, {\xi} Tel and 24 Cap for high accuracy visibility observations, and {\eta} Car for interferometric imaging with GRAVITY., Comment: Accepted for publication in A&A, 23 pages, 23 figures, corresponding author: F. Eisenhauer

Context. Mercury-manganese (HgMn) stars are a class of slowly rotating chemically peculiar main-sequence late B-type stars. More than two-thirds of the HgMn stars are known to belong to spectroscopic binaries. Aims. By determining orbital solutions for binary HgMn stars, we will be able to obtain the masses for both components and the distance to the system. Consequently, we can establish the position of both components in the Hertzsprung-Russell diagram and confront the chemical peculiarities of the HgMn stars with their age and evolutionary history. Methods. We initiated a program to identify interferometric binaries in a sample of HgMn stars, using the PIONIER near-infrared interferometer at the VLTI on Cerro Paranal, Chile. For the detected systems, we intend to obtain full orbital solutions in conjunction with spectroscopic data. Results. The data obtained for the SB2 system 41 Eridani allowed the determination of the orbital elements with a period of just five days and a semi-major axis of under 2 mas. Including published radial velocity measurements, we derived almost identical masses of 3.17 +/- 0.07 M_Sun for the primary and 3.07 +/- 0.07 M_Sun for the secondary. The measured magnitude difference is less than 0.1 mag. The orbital parallax is 18.05 +/- 0.17 mas, which is in good agreement with the Hipparcos trigonometric parallax of 18.33 +/- 0.15 mas. The stellar diameters are resolved as well at 0.39 +/- 0.03 mas. The spin rate is synchronized with the orbital rate., Comment: 5 pages, 4 figures

Context. The mass loss from massive stars is not understood well. Eta Car is a unique object for studying the massive stellar wind during the LBV phase. It is also an eccentric binary with a period of 5.54 yr. The nature of both stars is uncertain, although we know from X-ray studies that there is a wind-wind collision whose properties change with orbital phase. Methods. Observations of Eta Car were carried out with the ESO VLTI and the AMBER instrument between approximately five and seven months before the August 2014 periastron passage. Velocity-resolved aperture-synthesis images were reconstructed from the spectrally dispersed interferograms. Interferometric studies can provide information on the binary orbit, the primary wind, and the wind collision. Results. We present velocity-resolved aperture-synthesis images reconstructed in more than 100 different spectral channels distributed across the Br Gamma 2.166 micrometer emission line. The intensity distribution of the images strongly depends on wavelength. At wavelengths corresponding to radial velocities of approximately -140 to -376 km/s measured relative to line center, the intensity distribution has a fan-shaped structure. At the velocity of -277 km/s, the position angle of the symmetry axis of the fan is ~ 126 degree. The fan-shaped structure extends approximately 8.0 mas (~ 18.8 au) to the southeast and 5.8 mas (~ 13.6 au) to the northwest, measured along the symmetry axis at the 16% intensity contour. The shape of the intensity distributions suggests that the obtained images are the first direct images of the innermost wind-wind collision zone. Therefore, the observations provide velocity-dependent image structures that can be used to test three-dimensional hydrodynamical, radiative transfer models of the massive interacting winds of Eta Car.

We present interferometric observations of the sigma Orionis triple system using the CHARA Array, NPOI, and VLTI. Using these measurements, we spatially resolve the orbit of the close spectroscopic binary (Aa,Ab) for the first time and present a revised orbit for the wide pair (A,B). Combining the visual orbits with previously published radial velocity measurements and new radial velocities measured at CTIO, we derive dynamical masses for the three massive stars in the system of M_Aa = 16.99 +/- 0.20 Msun, M_Ab = 12.81 +/- 0.18 Msun, and M_B = 11.5 +/- 1.2 Msun. The inner and outer orbits in the triple are not coplanar, with a relative inclination of 120-127 deg. The orbital parallax provides a precise distance of 387.5 +/- 1.3 pc to the system. This is a significant improvement over previous estimates of the distance to the young sigma Orionis cluster., Comment: Accepted by the Astronomical Journal. 23 pages, 11 figures, 11 tables

MATISSE is the second-generation mid-infrared spectrograph and imager for the Very Large Telescope Interferometer (VLTI) at Paranal. This new interferometric instrument will allow significant advances by opening new avenues in various fundamental research fields: studying the planet-forming region of disks around young stellar objects, understanding the surface structures and mass loss phenomena affecting evolved stars, and probing the environments of black holes in active galactic nuclei. As a first breakthrough, MATISSE will enlarge the spectral domain of current optical interferometers by offering the L and M bands in addition to the N band. This will open a wide wavelength domain, ranging from 2.8 to 13 um, exploring angular scales as small as 3 mas (L band) / 10 mas (N band). As a second breakthrough, MATISSE will allow mid-infrared imaging - closure-phase aperture-synthesis imaging - with up to four Unit Telescopes (UT) or Auxiliary Telescopes (AT) of the VLTI. Moreover, MATISSE will offer a spectral resolution range from R ~ 30 to R ~ 5000. Here, we present one of the main science objectives, the study of protoplanetary disks, that has driven the instrument design and motivated several VLTI upgrades (GRA4MAT and NAOMI). We introduce the physical concept of MATISSE including a description of the signal on the detectors and an evaluation of the expected performances. We also discuss the current status of the MATISSE instrument, which is entering its testing phase, and the foreseen schedule for the next two years that will lead to the first light at Paranal., Comment: SPIE Astronomical Telescopes and Instrumentation conference, June 2016, 11 pages, 6 Figures

The formation of massive stars and their arrival on the zero-age main-sequence occurs hidden behind dense clouds of gas and dust. In the giant Hii region NGC 3603, the radiation of a young cluster of OB stars has dispersed dust and gas in its vicinity. At a projected distance of 2:5 pc from the cluster, a bright mid-infrared (mid-IR) source (IRS 9A) had been identified as a massive young stellar object (MYSO), located on the side of a molecular clump (MM2) of gas facing the cluster. We investigated the physical conditions in MM2, based on APEX sub-mm observations using the SABOCA and SHFI instruments, and archival ATCA 3 mm continuum and CS spectral line data. We resolved MM2 into several compact cores, one of them closely associated with IRS 9A. These are likely infrared dark clouds as they do not show the typical hot-core emission lines and are mostly opaque against the mid-IR background. The compact cores have masses of up to several hundred times the solar mass and gas temperatures of about 50 K, without evidence of internal ionizing sources. We speculate that IRS 9A is younger than the cluster stars, but is in an evolutionary state after that of the compact cores.

For about three years, it was known that precision spectrophotometry with FORS2 suffered from systematic errors that made quantitative observations of planetary transits impossible. We identified the Longitudinal Atmospheric Dispersion Compensator (LADC) as the most likely culprit, and therefore engaged in a project to exchange the LADC prisms with the uncoated ones from FORS1. This led to a significant improvement in the depth of FORS2 zero points, a reduction in the systematic noise, and should make FORS2 again competitive for transmission spectroscopy of exoplanets., Comment: To appear in the March issue of the ESO Messenger

Contemporary theory holds that massive stars gather mass during their initial phases via accreting disk-like structures. However, conclusive evidence for disks has remained elusive for the most massive young objects. This is mainly due to significant observational challenges. Incisive studies, even targeting individual objects, are therefore relevant to the progression of the field. NGC 3603 IRS 9A* is a young massive stellar object still surrounded by an envelope of molecular gas. Previous mid-infrared observations with long-baseline interferometry provided evidence for a disk of 50 mas diameter at its core. This work aims at a comprehensive study of the physics and morphology of IRS 9A at near-infrared wavelengths. New sparse aperture masking interferometry data taken with NACO/VLT at Ks and Lp filters were obtained and analysed together with archival CRIRES spectra of the H2 and BrG lines. The calibrated visibilities recorded at Ks and Lp bands suggest the presence of a partially resolved compact object of 30 mas at the core of IRS 9A, together with the presence of over-resolved flux. The spectroastrometric signal of the H2 line shows that this spectral feature proceeds from the large scale extended emission (300 mas) of IRS 9A, while the BrG line appears to be formed at the core of the object (20 mas). This scenario is consistent with the brightness distribution of the source for near- and mid-infrared wavelengths at various spatial scales. However, our model suffers from remaining inconsistencies between SED modelling and the interferometric data. Moreover, the BrG spectroastrometric signal indicates that the core of IRS 9A exhibits some form of complexity such as asymmetries in the disk. Future high-resolution observations are required to confirm the disk/envelope model and to flesh out the details of the physical form of the inner regions of IRS 9A., Comment: Accepted to be published in Astronomy & Astrophysics, 13 pages, 14 figures

Context: Massive stars are extremely important for the evolution of the galaxies; there are large gaps in our understanding of their properties and formation, however, mainly because they evolve rapidly, are rare, and distant. It may well be that almost all massive stars are born as triples or higher multiples, but their large distances require very high angular resolution to directly detect the companions at milliarcsecond scales. Aims: Herschel36 is a young massive system located at 1.3 kpc. It has a combined smallest predicted mass of 45 M_sun. Multi-epoch spectroscopic data suggest the existence of at least three gravitationally bound components. Two of them, system Ab, are tightly bound in a spectroscopic binary, and the third one, component Aa, orbits in a wider orbit. Our aim was to image and obtain astrometric and photometric measurements of components Aa and Ab using, for the first time, long-baseline optical interferometry to further constrain its nature. Methods: We observed Herschel 36 with the near-infrared instrument AMBER attached to the ESO VLT Interferometer, which provides an angular resolution of approx. 2 mas. We used the code BSMEM to perform the interferometric image reconstruction. We fitted the interferometric observables using proprietary IDL routines and the code LitPro. Results: We imaged the Aa+Ab components of Herschel 36 in H and K filters. Component Ab is located at a projected distance of 1.81 mas, at a position angle of approx. 222 deg. east of north, the flux ratio between components Aa and Ab is close to one. The small measured angular separation indicates that system Ab and Ab may be approaching the periastron of their orbits. These results, only achievable with long-baseline near-infrared interferometry, constitute the first step toward a thorough understanding of this massive triple system., Comment: accepted for publication by A&A, 4 pages, 4 figures