Spectroscopic and interferometric signatures of magnetospheric accretion in young stars

Methods. We use the code MCFOST to solve the non-LTE problem of line formation in non-axisymmetric accreting magnetospheres. We compute the Br{\gamma} line profile originating from accretion columns for models with different magnetic obliquities. We also derive monochromatic synthetic images of the Br{\gamma} line emitting region across the line profile. This spectral line is a prime diagnostics of magnetospheric accretion in young stars and is accessible with the long baseline near-infrared interferometer GRAVITY installed at the ESO Very Large Telescope Interferometer. Results. We derive Br{\gamma} line profiles as a function of rotational phase and compute interferometric observables, visibilities and phases, from synthetic images. The line profile shape is modulated along the rotational cycle, exhibiting inverse P Cygni profiles at the time the accretion shock faces the observer. The size of the line's emission region decreases as the magnetic obliquity increases, which is reflected in a lower line flux. We apply interferometric models to the synthetic visibilities in order to derive the size of the line-emitting region. We find the derived interferometric size to be more compact than the actual size of the magnetosphere, ranging from 50 to 90\% of the truncation radius. Additionally, we show that the rotation of the non-axisymmetric magnetosphere is recovered from the rotational modulation of the Br{\gamma}-to-continuum photo-centre shifts, as measured by the differential phase of interferometric visibilities

Grown-up stars physics with MATISSE

MATISSE represents a great opportunity to image the environment around massive and evolved stars. This will allow one to put constraints on the circumstellar structure, on the mass ejection of dust and its reorganization , and on the dust-nature and formation processes. MATISSE measurements will often be pivotal for the understanding of large multiwavelength datasets on the same targets collected through many high-angular resolution facilities at ESO like sub-millimeter interferometry (ALMA), near-infrared adaptive optics (NACO, SPHERE), interferometry (PIONIER, GRAVITY), spectroscopy (CRIRES), and mid-infrared imaging (VISIR). Among main sequence and evolved stars, several cases of interest have been identified that we describe in this paper.Comment: SPIE, Jun 2016, Edimbourgh, Franc

The extreme colliding-wind system Apep : resolved imagery of the central binary and dust plume in the infrared

The recent discovery of a spectacular dust plume in the system 2XMM J160050.7–514245 (referred to as ‘Apep’) suggested a physical origin in a colliding-wind binary by way of the ‘Pinwheel’ mechanism. Observational data pointed to a hierarchical triple-star system, however, several extreme and unexpected physical properties seem to defy the established physics of such objects. Most notably, a stark discrepancy was found in the observed outflow speed of the gas as measured spectroscopically in the line-of-sight direction compared to the proper motion expansion of the dust in the sky plane. This enigmatic behaviour arises at the wind base within the central Wolf–Rayet binary: a system that has so far remained spatially unresolved. Here, we present an updated proper motion study deriving the expansion speed of Apep’s dust plume over a 2-year baseline that is four times slower than the spectroscopic wind speed, confirming and strengthening the previous finding. We also present the results from high angular resolution near-infrared imaging studies of the heart of the system, revealing a close binary with properties matching a Wolf–Rayet colliding-wind system. Based on these new observational constraints, an improved geometric model is presented yielding a close match to the data, constraining the orbital parameters of the Wolf–Rayet binary and lending further support to the anisotropic wind model

SPHERE view of Wolf-Rayet 104. Direct detection of the Pinwheel and the link with the nearby star

Context. WR104 is an emblematic dusty Wolf-Rayet star and the prototypical member of a sub-group hosting spirals that are mainly observable with high-angular resolution techniques. Previous aperture masking observations showed that WR104 is likely to be an interacting binary star at the end of its life. However, several aspects of the system are still unknown. This includes the opening angle of the spiral, the dust formation locus, and the link between the central binary star and a candidate companion star detected with the Hubble Space Telescope (HST) at 1′′. Aims. Our aim was to directly image the dusty spiral or “pinwheel” structure around WR104 for the first time and determine its physical properties at large spatial scales. We also wanted to address the characteristics of the candidate companion detected by the HST. Methods. For this purpose, we used SPHERE and VISIR at the Very Large Telescope to image the system in the near- and mid-infrared, respectively. Both instruments furnished an excellent view of the system at the highest angular resolution a single, ground-based telescope can provide. Based on these direct images, we then used analytical and radiative transfer models to determine several physical properties of the system. Results. Employing a different technique than previously used, our new images have allowed us to confirm the presence of the dust pinwheel around the central star. We have also detected up to five revolutions of the spiral pattern of WR104 in the K band for the first time. The circumstellar dust extends up to 2 arcsec from the central binary star in the N band, corresponding to the past 20 yr of mass loss. Moreover, we found no clear evidence of a shadow of the first spiral coil onto the subsequent ones, which likely points to a dusty environment less massive than inferred in previous studies. We have also confirmed that the stellar candidate companion previously detected by the HST is gravitationally bound to WR104 and herein provide information about its nature and orbital elements

The Near Infrared Imager and Slitless Spectrograph for the James Webb Space Telescope -- IV. Aperture Masking Interferometry

The James Webb Space Telescope's Near Infrared Imager and Slitless Spectrograph (JWST-NIRISS) flies a 7-hole non-redundant mask (NRM), the first such interferometer in space, operating at 3-5 \micron~wavelengths, and a bright limit of $\simeq 4$ magnitudes in W2. We describe the NIRISS Aperture Masking Interferometry (AMI) mode to help potential observers understand its underlying principles, present some sample science cases, explain its operational observing strategies, indicate how AMI proposals can be developed with data simulations, and how AMI data can be analyzed. We also present key results from commissioning AMI. Since the allied Kernel Phase Imaging (KPI) technique benefits from AMI operational strategies, we also cover NIRISS KPI methods and analysis techniques, including a new user-friendly KPI pipeline. The NIRISS KPI bright limit is $\simeq 8$ W2 magnitudes. AMI (and KPI) achieve an inner working angle of $\sim 70$ mas that is well inside the $\sim 400$ mas NIRCam inner working angle for its circular occulter coronagraphs at comparable wavelengths.Comment: 30 pages, 10 figure

Locating dust and molecules in the inner circumstellar environment of R Sculptoris with MATISSE

Stars and planetary system

The extended atmosphere and circumstellar environment of the cool evolved star VX Sagittarii as seen by MATISSE

Stars and planetary system

First MATISSE L-band observations of HD 179218: is the inner 10 au region rich in carbon dust particles?

Stars and planetary system

MATISSE, the VLTI mid-infrared imaging spectro-interferometer

GalaxiesStars and planetary systemsInstrumentatio