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The Wolf–Rayet (WR) binary system WR140 is a close (0.9–16.7 mas; ref. 1 ) binary star consisting of an O5 primary and WC7 companion 2 and is known as the archetype of episodic dust-producing WRs. Dust in WR binaries is known to form in a confined stream originating from the collision of the two stellar winds, with orbital motion of the binary sculpting the large-scale dust structure into arcs as dust is swept radially outwards. It is understood that sensitive conditions required for dust production in WR140 are only met around periastron when the two stars are sufficiently close 2 – 4 . Here we present multiepoch imagery of the circumstellar dust shell of WR140. We constructed geometric models that closely trace the expansion of the intricately structured dust plume, showing that complex effects induced by orbital modulation may result in a ‘Goldilocks zone’ for dust production. We find that the expansion of the dust plume cannot be reproduced under the assumption of a simple uniform-speed outflow, finding instead the dust to be accelerating. This constitutes a direct kinematic record of dust motion under acceleration by radiation pressure and further highlights the complexity of the physical conditions in colliding-wind binaries. Multiepoch imagery of the circumstellar dust shell in WR140 is modelled to trace the expansion of the dust plume, which seems to be subject to radiation-driven acceleration.

The dust shells of three intermediate-mass stars are observed to lie remarkably close to the photosphere and to be composed of unexpectedly large grains, consistent with mass loss from such stars occurring by means of ejection of this dust by photon scattering rather than as a result of radiation pressure. Last gasp of a red giant Towards the ends of their lives, intermediate-mass stars lose much of their mass in the form of gas and dust ejected in a slow, dense wind. The underlying processes driving these outflows are poorly understood, owing in part to difficulties in observing such ejected material. Norris et al . use an innovative technique that combines interferometric imaging with high-precision differential polarimetry to observe three red giants. Their images reveal circumstellar dust shells with remarkably small radii (less than two times the radius of the star), made up of unexpectedly large dust grains approximately 300 nanometres in radius. The authors suggest that these observations support a wind-driving model based on acceleration of dust grains by the scattering, rather than absorption, of starlight. An intermediate-mass star ends its life by ejecting the bulk of its envelope in a slow, dense wind 1 , 2 , 3 . Stellar pulsations are thought to elevate gas to an altitude cool enough for the condensation of dust 1 , which is then accelerated by radiation pressure, entraining the gas and driving the wind 2 , 4 , 5 . Explaining the amount of mass loss, however, has been a problem because of the difficulty of observing tenuous gas and dust only tens of milliarcseconds from the star. For this reason, there is no consensus on the way sufficient momentum is transferred from the light from the star to the outflow. Here we report spatially resolved, multiwavelength observations of circumstellar dust shells of three stars on the asymptotic giant branch of the Hertzsprung–Russell diagram. When imaged in scattered light, dust shells were found at remarkably small radii (less than about two stellar radii) and with unexpectedly large grains (about 300 nanometres in radius). This proximity to the photosphere argues for dust species that are transparent to the light from the star and, therefore, resistant to sublimation by the intense radiation field. Although transparency usually implies insufficient radiative pressure to drive a wind 6 , 7 , the radiation field can accelerate these large grains through photon scattering rather than absorption 8 —a plausible mass loss mechanism for lower-amplitude pulsating stars.

Characterisation of exoplanets is key to understanding their formation, composition and potential for life. Nulling interferometry, combined with extreme adaptive optics, is among the most promising techniques to advance this goal. We present an integrated-optic nuller whose design is directly scalable to future science-ready interferometric nullers: the Guided-Light Interferometric Nulling Technology, deployed at the Subaru Telescope. It combines four beams and delivers spatial and spectral information. We demonstrate the capability of the instrument, achieving a null depth better than 10 −3 with a precision of 10 −4 for all baselines, in laboratory conditions with simulated seeing applied. On sky, the instrument delivered angular diameter measurements of stars that were 2.5 times smaller than the diffraction limit of the telescope. These successes pave the way for future design enhancements: scaling to more baselines, improved photonic component and handling low-order atmospheric aberration within the instrument, all of which will contribute to enhance sensitivity and precision. Nulling interferometry is a technique combining lights from different telescopes or apertures to observe weak sources nearby bright ones. The authors report the first nulling interferometer implemented in a photonic chip doing spectrally dispersed nulling on several baselines, simultaneously.

Optical cross-correlation is a technique that can achieve both high specificity and high sensitivity when deployed as the basis for a sensing technology. Offering significant gains in cost, size and complexity, it can also deliver significantly higher signal-to-noise ratios than traditional approaches such as absorption methodologies. In this paper, we present an optical cross-correlation technology constructed around a bespoke customised Fiber Bragg Grating (FBG). Exploiting the remarkable flexibility in design enabled by multiple aperiodic Bragg gratings, optical filters are devised that exactly mimic the absorption features of a target gas species (for this paper, acetylene C 2 H 2 ) over some waveband of interest. This grating forms the heart of the sensor architecture described here that employs modulated optical cross-correlation for gas detection. An experimental demonstration of this approach is presented, and shown to be capable of differentiating between different concentrations of the C 2 H 2 target gas. Furthermore these measurements are shown to be robust against interloper species, with minimal impact on the detection signal-to-noise arising from the introduction of contaminant gases. This represents is a significant step toward the use of customised FBGs as low-cost, compact, and highly customisable photonic devices for deployment in gas detection.

Wolf-Rayet (WR) stars are luminous, massive blue stars thought to be the immediate precursors to some supernovae. The existence of dust shells around such stars has been enigmatic since their discovery about 30 years ago, as the intense ultraviolet radiation from the star should be inimical to dust survival 1 . Although dust creation models, including those involving interacting stellar winds 2 , have been put forward to explain these dust shells, the high-resolution observations needed to distinguish between the models have hitherto been lacking. Here we present images of the dust outflow around WR104, obtained using a technique that allows us to resolve detail on scales of about 40  au at the distance of the star. Our images—taken at two epochs—show that the dust forms a spatially confined stream that follows precisely a linear (or archimedian) spiral trajectory with a rotation period of 220 ± 30 days. These results prove that, in this case, a binary companion is responsible for the creation of the circumstellar dust. Moreover, the spiral plume makes WR104 the prototype of a new class of circumstellar nebulae, which are unique to systems with interacting winds.

A star forms when a cloud of dust and gas collapses. It is generally believed that this collapse first produces a flattened rotating disk 1 , 2 , through which matter is fed onto the embryonic star at the centre of the disk. When the temperature and density at the centre of the star pass a critical threshold, thermonuclear fusion begins. The remaining disk, which can still contain up to 0.3 times the mass of the star 3 , 4 , 5 , is then sculpted and eventually dissipated by the radiation and wind from the newborn star. But this picture of the structure and evolution of the disk remains speculative because of the lack of morphological data of sufficient resolution and uncertainties regarding the underlying physical processes. Here we present images of a young star, LkHα101, in which the structure of the inner accretion disk is resolved. We find that the disk is almost face-on, with a central gap (or cavity) and a hot inner edge. The cavity is bigger than previous theoretical predictions 6 , and we infer that the position of the inner edge is probably determined by sublimation of dust grains by direct stellar radiation, rather than by disk-reprocessing or viscous-heating processes as usually assumed 29 .

We report on the observations of the circumstellar envelope of the AGB star II Lup in the near- and mid-infrared with the use of direct imaging and interferometric techniques. Our findings indicate that the circumstellar envelope is not spherically symmetric and that the majority of the emission originates within 0.5 arcsec from the star.

The origin of red supergiant mass loss still remains to be unveiled. Characterising the formation loci and the dust distribution in the first stellar radii above the surface is key to understand the initiation of the mass loss phenomenon. Polarimetric interferometry observations in the near-infrared allowed us to detect an inner dust atmosphere located only 0.5 stellar radius above the photosphere of Betelgeuse. We modelled these observations and compare them with visible polarimetric measurements to discuss the dust distribution properties.

Direct images of protoplanets embedded in disks around infant stars provide the key to understanding the formation of gas giant planets such as Jupiter. Using the Subaru Telescope and the Hubble Space Telescope, we find evidence for a Jovian protoplanet around AB Aurigae orbiting at a wide projected separation (~93 au), probably responsible for multiple planet-induced features in the disk. Its emission is reproducible as reprocessed radiation from an embedded protoplanet. We also identify two structures located at 430–580 au that are candidate sites of planet formation. These data reveal planet formation in the embedded phase and a protoplanet discovery at wide, >50 au separations characteristic of most imaged exoplanets. With at least one clump-like protoplanet and multiple spiral arms, the AB Aur system may also provide the evidence for a long-considered alternative to the canonical model for Jupiter’s formation, namely disk (gravitational) instability. Images from the Subaru Telescope and the Hubble Space Telescope reveal an embedded protoplanet at a wide separation around the star AB Aurigae. The system provides evidence for a long-considered alternative mechanism for forming Jupiter-like planets.