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Very low-mass stars (those <0.3 solar masses) host orbiting terrestrial planets more frequently than other types of stars, but the compositions of those planets are largely unknown. We use mid-infrared spectroscopy with the James Webb Space Telescope to investigate the chemical composition of the planet-forming disk around ISO-ChaI 147, a 0.11 solar-mass star. The inner disk has a carbon-rich chemistry: we identify emission from 13 carbon-bearing molecules including ethane and benzene. We derive large column densities of hydrocarbons indicating that we probe deep into the disk. The high carbon to oxygen ratio we infer indicates radial transport of material within the disk, which we predict would affect the bulk composition of any planets forming in the disk., Comment: Published, 36 pages, 8 figures

Our purpose is to study the effect of binary companions located within the first 10 stellar radii from the primary AGB star. In this work, we target the mass-losing carbon star V Hydrae (V Hya), looking for signatures of its companion in the dust forming region of the atmosphere. The star was observed in the L- and N-bands with the VLTI/MATISSE instrument at low spectral resolution. We reconstructed images of V Hya's photosphere and surroundings using the two bands and compared our interferometric observables with VLTI/MIDI and VISIR archival data. To constrain the dust properties, we used DUSTY to model the spectral energy distribution. The star is dominated by dust emission in the L- and N- bands. The VISIR image confirms the presence of a large-scale dusty circumstellar envelope surrounding V Hya. The MATISSE reconstructed images show asymmetric and elongated structures in both infrared bands. In the L-band, we detected an elongated shape of approximately 15 mas, likely to be of photospheric origin. In the N-band, we found a 20 mas extension North-East from the star, and perpendicular to the L-band elongated axis. The position angle and the size of the N-band extension match the prediction of the companion position at MATISSE epoch. By comparing MATISSE N-band with MIDI data, we deduce that the elongation axis in the N-band has rotated since the previous interferometric measurements 13 years ago, supporting the idea that the particle enhancement is related to the dusty clump moving along with the companion. The MATISSE images unveil the presence of a dust enhancement at the companion position, opening new doors for further analysis on the binary interaction with an AGB component., Comment: Accepted for publication in Astronomy & Astrophysics

Context. Rocky planets form by the concentration of solid particles in the inner few au regions of planet-forming disks. Their chemical composition reflects the materials in the disk available in the solid phase at the time the planets were forming. Aims. We aim to constrain the structure and dust composition of the inner disk of the young star HD 144432, using an extensive set of infrared interferometric data taken by the Very Large Telescope Interferometer (VLTI), combining PIONIER, GRAVITY, and MATISSE observations. Methods. We introduced a new physical disk model, TGMdust, to image the interferometric data, and to fit the disk structure and dust composition. We also performed equilibrium condensation calculations with GGchem. Results. Our best-fit model has three disk zones with ring-like structures at 0.15, 1.3, and 4.1 au. Assuming that the dark regions in the disk at ~0.9 au and at ~3 au are gaps opened by planets, we estimate the masses of the putative gap-opening planets to be around a Jupiter mass. We find evidence for an optically thin emission ($\tau<0.4$) from the inner two disk zones ($r<4$ au) at $\lambda>3\ \mu$m. Our silicate compositional fits confirm radial mineralogy gradients. To identify the dust component responsible for the infrared continuum emission, we explore two cases for the dust composition, one with a silicate+iron mixture and the other with a silicate+carbon one. We find that the iron-rich model provides a better fit to the spectral energy distribution. Conclusions. We propose that in the warm inner regions ($r<5$ au) of typical planet-forming disks, most if not all carbon is in the gas phase, while iron and iron sulfide grains are major constituents of the solid mixture along with forsterite and enstatite. Our analysis demonstrates the need for detailed studies of the dust in inner disks with new mid-infrared instruments such as MATISSE and JWST/MIRI., Comment: 29 pages, 24 figures

Terrestrial and sub-Neptune planets are expected to form in the inner ($<10~$AU) regions of protoplanetary disks. Water plays a key role in their formation, although it is yet unclear whether water molecules are formed in-situ or transported from the outer disk. So far Spitzer Space Telescope observations have only provided water luminosity upper limits for dust-depleted inner disks, similar to PDS 70, the first system with direct confirmation of protoplanet presence. Here we report JWST observations of PDS 70, a benchmark target to search for water in a disk hosting a large ($\sim54~$AU) planet-carved gap separating an inner and outer disk. Our findings show water in the inner disk of PDS 70. This implies that potential terrestrial planets forming therein have access to a water reservoir. The column densities of water vapour suggest in-situ formation via a reaction sequence involving O, H$_2$, and/or OH, and survival through water self-shielding. This is also supported by the presence of CO$_2$ emission, another molecule sensitive to UV photodissociation. Dust shielding, and replenishment of both gas and small dust from the outer disk, may also play a role in sustaining the water reservoir. Our observations also reveal a strong variability of the mid-infrared spectral energy distribution, pointing to a change of inner disk geometry., Comment: To appear in Nature on 24 July 2023. 21 pages, 10 figures; includes extended data. Part of the JWST MINDS Guaranteed Time Observations program's science enabling products. Spectra downloadable on Zenodo at https://zenodo.org/record/7991022

Carbon is an essential element for life but how much can be delivered to young planets is still an open question. The chemical characterization of planet-forming disks is a crucial step in our understanding of the diversity and habitability of exoplanets. Very low-mass stars ($<0.2~M_{\odot}$) are interesting targets because they host a rich population of terrestrial planets. Here we present the JWST detection of abundant hydrocarbons in the disk of a very low-mass star obtained as part of the MIRI mid-INfrared Disk Survey (MINDS). In addition to very strong and broad emission from C$_2$H$_2$ and its $^{13}$C$^{12}$CH$_2$ isotopologue, C$_4$H$_2$, benzene, and possibly CH$_4$ are identified, but water, PAH and silicate features are weak or absent. The lack of small silicate grains implies that we can look deep down into this disk. These detections testify to an active warm hydrocarbon chemistry with a high C/O ratio in the inner 0.1 au of this disk, perhaps due to destruction of carbonaceous grains. The exceptionally high C$_2$H$_2$/CO$_2$ and C$_2$H$_2$/H$_2$O column density ratios suggest that oxygen is locked up in icy pebbles and planetesimals outside the water iceline. This, in turn, will have significant consequences for the composition of forming exoplanets., Comment: version submitted to Nature Astronomy

SPHERE+ is a proposed upgrade of the SPHERE instrument at the VLT, which is intended to boost the current performances of detection and characterization for exoplanets and disks. SPHERE+ will also serve as a demonstrator for the future planet finder (PCS) of the European ELT. The main science drivers for SPHERE+ are 1/ to access the bulk of the young giant planet population down to the snow line ($3-10$ au), to bridge the gap with complementary techniques (radial velocity, astrometry); 2/ to observe fainter and redder targets in the youngest ($1-10$\,Myr) associations compared to those observed with SPHERE to directly study the formation of giant planets in their birth environment; 3/ to improve the level of characterization of exoplanetary atmospheres by increasing the spectral resolution in order to break degeneracies in giant planet atmosphere models. Achieving these objectives requires to increase the bandwidth of the xAO system (from $\sim$1 to 3\,kHz) as well as the sensitivity in the infrared (2 to 3\,mag). These features will be brought by a second stage AO system optimized in the infrared with a pyramid wavefront sensor. As a new science instrument, a medium resolution integral field spectrograph will provide a spectral resolution from 1000 to 5000 in the J and H bands. This paper gives an overview of the science drivers, requirements and key instrumental trade-off that were done for SPHERE+ to reach the final selected baseline concept., Comment: To appear in the Proceedings of the SPIE Astronomical Telescopes + Instrumentation (2022), 13 pages, 6 figure

The disk of FU Orionis is marginally resolved with MATISSE, suggesting that the region emitting in the thermal infrared is rather compact. An upper limit of $\sim1.3\pm0.1$ mas (in $L$) can be given for the diameter of the disk region probed in the $L$ band, corresponding to 0.5 au at the adopted Gaia EDR3 distance. This represents the hot, gaseous region of the accretion disk. The $N$-band data indicate that the dusty passive disk is silicate-rich. Only the innermost region of said dusty disk is found to emit strongly in the $N$ band, and it is resolved at an angular size of $\sim5$ mas, which translates to a diameter of about 2 au. The observations therefore place stringent constraints for the outer radius of the inner accretion disk. Dust radiative transfer simulations with RADMC-3D provide adequate fits to the spectral energy distribution from the optical to the submillimeter and to the interferometric observables when opting for an accretion rate $\dot{M}\sim 2\times 10^{-5}\, M_\odot$ yr$^{-1}$ and assuming $M_*=0.6\, M_\odot$. Most importantly, the hot inner accretion disk's outer radius can be fixed at 0.3 au. The outer radius of the dusty disk is placed at 100 au, based on constraints from scattered-light images in the literature. The dust mass contained in the disk is $2.4\times10^{-4}\, M_\odot$, and for a typical gas-to-dust ratio of 100, the total mass in the disk is approximately 0.02 $M_\odot$. We did not find any evidence for a nearby companion in the current interferometric data, and we tentatively explored the case of disk misalignment. For the latter, our modeling results suggest that the disk orientation is similar to that found in previous imaging studies by ALMA. Should there be an asymmetry in the very compact, inner accretion disk, this might be resolved at even smaller spatial scales ($\leq1$ mas)., Comment: 17 pages, 14 figures, to be published in Astronomy & Astrophysics

Context. VX Sgr is a cool, evolved, and luminous red star whose stellar parameters are difficult to determine, which affects its classification. Aims. We aim to spatially resolve the photospheric extent as well as the circumstellar environment. Methods. We used interferometric observations obtained with the MATISSE instrument in the L (3 to 4 {\mu}m), M (4.5 to 5 {\mu}m), and N (8 to 13 {\mu}m) bands. We reconstructed monochromatic images using the MIRA software. We used 3D radiation-hydrodynamics (RHD) simulations carried out with CO5BOLD and a uniform disc model to estimate the apparent diameter and interpret the stellar surface structures. Moreover, we employed the radiative transfer codes Optim3D and Radmc3D to compute the spectral energy distribution for the L, M, and N bands, respectively. Results. MATISSE observations unveil, for the first time, the morphology of VX Sgr across the L, M, and N bands. The reconstructed images show a complex morphology with brighter areas whose characteristics depend on the wavelength probed. We measured the angular diameter as a function of the wavelength and showed that the photospheric extent in the L and M bands depends on the opacity through the atmosphere. In addition to this, we also concluded that the observed photospheric inhomogeneities can be interpreted as convection-related surface structures. The comparison in the N band yielded a qualitative agreement between the N band spectrum and simple dust radiative transfer simulations. However, it is not possible to firmly conclude on the interpretation of the current data because of the difficulty in constraing the model parameters using the limited accuracy of our absolute flux calibration. Conclusions. MATISSE observations and the derived reconstructed images unveil the appearance of the stellar surface and circumstellar environment across a very large spectral domain for the first time., Comment: Accepted for publication on Astronomy and Astrophysics

Context: FS Canis Majoris (FS CMa, HD 45677) is an unclassified B[e] star surrounded by an inclined dust disk. The evolutionary stage of FS CMa is still debated. Perpendicular to the circumstellar disk, a bipolar outflow was detected. Infrared aperture-synthesis imaging provides us with a unique opportunity to study the disk structure. Aims: Our aim is to study the intensity distribution of the disk of FS CMa in the mid-infrared L and N bands. Methods: We performed aperture-synthesis imaging of FS CMa with the MATISSE instrument (Multi AperTure mid-Infrared SpectroScopic Experiment) in the low spectral resolution mode to obtain images in the L and N bands. We computed radiative transfer models that reproduce the L- and N-band intensity distributions of the resolved disks. Results: We present L- and N-band aperture-synthesis images of FS CMa reconstructed in the wavelength bands of 3.4-3.8 and 8.6-9.0 micrometer. In the L-band image, the inner rim region of an inclined circumstellar disk and the central object can be seen with a spatial resolution of 2.7 milliarcsec (mas). An inner disk cavity with an angular diameter of 6x12mas is resolved. The L-band disk consists of a bright northwestern (NW) disk region and a much fainter southeastern (SE) region. The images suggest that we are looking at the bright inner wall of the NW disk rim, which is on the far side of the disk. In the N band, only the bright NW disk region is seen. In addition to deriving the inclination and the inner disk radius, fitting the reconstructed brightness distributions via radiative transfer modeling allows one to constrain the innermost disk structure, in particular the shape of the inner disk rim., Comment: accepted for publication in A&A

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

Context. Spiral arms in protoplanetary disks could be shown to be the manifestation of density waves launched by protoplanets and propagating in the gaseous component of the disk. At least two point sources have been identified in the L band in the MWC 758 system as planetary mass object candidates. Aims. We used VLT/SPHERE to search for counterparts of these candidates in the H and K bands, and to characterize the morphology of the spiral arms . Methods. The data were processed with now-standard techniques in high-contrast imaging to determine the limits of detection, and to compare them to the luminosity derived from L band observations. Results. In considering the evolutionary, atmospheric, and opacity models we were not able to confirm the two former detections of point sources performed in the L band. In addition, the analysis of the spiral arms from a dynamical point of view does not support the hypothesis that these candidates comprise the origin of the spirals. Conclusions. Deeper observations and longer timescales will be required to identify the actual source of the spiral arms in MWC 758., Comment: Accepted for publication in Astronomy and Astrophysics

In this era of spatially resolved observations of planet forming disks with ALMA and large ground-based telescopes such as the VLT, Keck and Subaru, we still lack statistically relevant information on the quantity and composition of the material that is building the planets, such as the total disk gas mass, the ice content of dust, and the state of water in planetesimals. SPICA is an infrared space mission concept developed jointly by JAXA and ESA to address these questions. The key unique capabilities of SPICA that enable this research are (1) the wide spectral coverage 10-220 micron, (2) the high line detection sensitivity of (1-2) 10-19 W m-2 with R~2000-5000 in the far-IR (SAFARI) and 10-20 W m-2 with R~29000 in the mid-IR (SMI, spectrally resolving line profiles), (3) the high far-IR continuum sensitivity of 0.45 mJy (SAFARI), and (4) the observing efficiency for point source surveys. This paper details how mid- to far-IR infrared spectra will be unique in measuring the gas masses and water/ice content of disks and how these quantities evolve during the planet forming period. These observations will clarify the crucial transition when disks exhaust their primordial gas and further planet formation requires secondary gas produced from planetesimals. The high spectral resolution mid-IR is also unique for determining the location of the snowline dividing the rocky and icy mass reservoirs within the disk and how the divide evolves during the build-up of planetary systems. Infrared spectroscopy (mid- to far-IR) of key solid state bands is crucial for assessing whether extensive radial mixing, which is part of our Solar System history, is a general process occurring in most planetary systems and whether extrasolar planetesimals are similar to our Solar System comets/asteroids. ... (abbreviated), Comment: accepted for publication in PASA

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 direct imaging of rocky exoplanets is one of the major science goals for upcoming large telescopes. The contrast requirement for imaging such planets is challenging. However, the mid-IR (InfraRed) regime provides the optimum contrast to directly detect the thermal signatures of exoplanets in our solar neighbourhood. We aim to exploit novel fast chopping techniques newly developed for astronomy with the aid of adaptive optics to look for thermal signatures of exoplanets around bright stars in the solar neighbourhood. We use the upgraded VISIR (Very Large Telescope Imager and Spectrometer for the mid-InfraRed) instrument with high contrast imaging (HCI) capability optimized for observations at 10~$\mu$m to look for exoplanets around five nearby ($d$ < 4 pc) stars. The instrument provides an improved signal-to-noise (S/N) by a factor of $\sim$4 in the N-band compared to standard VISIR for a given S/N and time. In this work we achieve a detection sensitivity of sub-mJy, which is sufficient to detect few Jupiter mass planets in nearby systems. Although no detections are made we achieve most sensitive limits within $<2''$ for all the observed targets compared to previous campaigns. For $\epsilon$ Indi A and $\epsilon$ Eri we achieve detection limits very close to the giant planets discovered by RV, with the limits on $\epsilon$ Indi A being the most sensitive to date. Our non-detection therefore supports an older age for $\epsilon$ Indi A. The results presented here show the promise for high contrast imaging and exoplanet detections in the mid-IR regime., Comment: Accepted for publication in A&A

The nature of circumstellar envelopes (CSE) around Cepheids is still a matter of debate. The physical origin of their infrared (IR) excess could be either a shell of ionized gas, or a dust envelope, or both. This study aims at constraining the geometry and the IR excess of the environment of the long-period Cepheid $\ell$ Car (P=35.5 days) at mid-IR wavelengths to understand its physical nature. We first use photometric observations in various bands and Spitzer Space Telescope spectroscopy to constrain the IR excess of $\ell$ Car. Then, we analyze the VLTI/MATISSE measurements at a specific phase of observation, in order to determine the flux contribution, the size and shape of the environment of the star in the L band. We finally test the hypothesis of a shell of ionized gas in order to model the IR excess. We report the first detection in the L band of a centro-symmetric extended emission around l Car, of about 1.7$R_\star$ in FWHM, producing an excess of about 7.0\% in this band. In the N band, there is no clear evidence for dust emission from VLTI/MATISSE correlated flux and Spitzer data. On the other side, the modeled shell of ionized gas implies a more compact CSE ($1.13\pm0.02\,R_\star$) and fainter (IR excess of 1\% in the L band). We provide new evidences for a compact CSE of $\ell$ Car and we demonstrate the capabilities of VLTI/MATISSE for determining common properties of CSEs. While the compact CSE of $\ell$ Car is probably of gaseous nature, the tested model of a shell of ionized gas is not able to simultaneously reproduce the IR excess and the interferometric observations. Further Galactic Cepheids observations with VLTI/MATISSE are necessary for determining the properties of CSEs, which may also depend on both the pulsation period and the evolutionary state of the stars., Comment: 13 pages, 8 figures, accepted in Astronomy and Astrophysics

Mid-infrared imaging traces the sub-micron and micron sized dust grains in protoplanetary disks and it offers constraints on the geometrical properties of the disks and potential companions, particularly if those companions have circumplanetary disks. We use the VISIR instrument and its upgrade NEAR on the VLT to take new mid-infrared images of five (pre-)transition disks and one circumstellar disk with proposed planets and obtain the deepest resolved mid-infrared observations to date in order to put new constraints on the sizes of the emitting regions of the disks and the presence of possible companions. We derotate and stack the data to find the disk properties. Where available we compare the data to ProDiMo (Protoplanetary Disk Model) radiation thermo-chemical models to achieve a deeper understanding of the underlying physical processes within the disks. We apply the circularised PSF subtraction method to find upper limits on the fluxes of possible companions and model companions with circumplanetary disks. We resolve three of the six disks and calculate position angles, inclinations and (upper limits to) sizes of emission regions in the disks, improving upper limits on two of the unresolved disks. In all cases the majority of the mid-IR emission comes from small inner disks or the hot inner rims of outer disks. We refine the existing ProDiMo HD 100546 model SED fit in the mid-IR by increasing the PAH abundance relative to the ISM, adopting coronene as the representative PAH, and increase the outer cavity radius to 22.3 AU. We produce flux estimates for putative planetary-mass companions and circumplanetary disks, ruling out the presence of planetary-mass companions with $L > 0.0028 L_{\odot}$ for $a > 180$ AU in the HD 100546 system. Upper limits of 0.5 mJy-30 mJy are obtained at 8 $\mu$m-12 $\mu$m for potential companions in the different disks., Comment: Accepted in A&A

Giant exoplanets on wide orbits have been directly imaged around young stars. If the thermal background in the mid-infrared can be mitigated, then exoplanets with lower masses can also be imaged. Here we present a ground-based mid-infrared observing approach that enables imaging low-mass temperate exoplanets around nearby stars, and in particular within the closest stellar system, Alpha Centauri. Based on 75-80% of the best quality images from 100 hours of cumulative observations, we demonstrate sensitivity to warm sub-Neptune-sized planets throughout much of the habitable zone of Alpha Centauri A. This is an order of magnitude more sensitive than state-of-the-art exoplanet imaging mass detection limits. We also discuss a possible exoplanet or exozodiacal disk detection around Alpha Centauri A. However, an instrumental artifact of unknown origin cannot be ruled out. These results demonstrate the feasibility of imaging rocky habitable-zone exoplanets with current and upcoming telescopes., Comment: 29 pages, 11 figures, published in Nature Communications

T Tauri has long been the prototypical young pre-main-sequence star. However, it has now been decomposed into a triple system with a complex disk and outflow geometry. We aim to measure the brightness of all three components of the T Tauri system (T Tau N, T Tau Sa, T Tau Sb) in the mid-infrared in order to obtain photometry around the $\sim 9.7~\mu m$ silicate feature. This allows us to study their variability and to investigate the distribution of dust and the geometry of circumstellar and circumbinary disks in this complex system. We observe T Tauri with the VLT/VISIR-NEAR instrument. With kernel phase interferometry post-processing of the data, and using the astrometric positions of all three components from VLT/SPHERE, we measure the three components' individual brightnesses (including the southern binary at an angular separation down to $\sim 0.2~\lambda/D$) and obtain their photometry. In order to validate our methods, we simulate and recover mock data of the T Tauri system using the observed reference point-spread function of HD 27639. We find that T Tau N is rather stable and shows weak silicate emission, while T Tau Sa is highly variable and shows prominent silicate absorption. T Tau Sb became significantly fainter compared to data from 2004 and 2006, suggesting increased extinction by dust. The precision of our photometry is limited by systematic errors, which is consistent with previous studies using kernel phase interferometry. Our results confirm the complex scenario of misaligned disks in the T Tauri system that had been observed previously, and they are in agreement with the recently observed dimming of T Tau Sb in the near-infrared. Our mid-infrared photometry supports the interpretation that T Tau Sb has moved behind the dense region of the Sa-Sb circumbinary disk on its tight orbit around Sa, therefore suffering increased extinction., Comment: 14 pages, 7 figures, accepted for publication in Astronomy & Astrophysics

Vortex coronagraphs have been shown to be a promising avenue for high-contrast imaging in the close-in environment of stars at thermal infrared (IR) wavelengths. They are included in the baseline design of METIS. To ensure good performance of these coronagraphs, a precise control of the centering of the star image in real time is needed. We previously developed and validated the quadrant analysis of coronagraphic images for tip-tilt sensing estimator (QACITS) pointing estimator to address this issue. While this approach is not wavelength-dependent in theory, it was never implemented for mid-IR observations, which leads to specific challenges and limitations. Here, we present the design of the mid-IR vortex coronagraph for the new Earths in the $\alpha$ Cen Region (NEAR) experiment with the VLT/VISIR instrument and assess the performance of the QACITS estimator for the centering control of the star image onto the vortex coronagraph. We use simulated data and on-sky data obtained with VLT/VISIR, which was recently upgraded for observations assisted by adaptive optics in the context of the NEAR experiment. We demonstrate that the QACITS-based correction loop is able to control the centering of the star image onto the NEAR vortex coronagraph with a stability down to $0.015 \lambda/D$ rms over 4h in good conditions. These results show that QACITS is a robust approach for precisely controlling in real time the centering of vortex coronagraphs for mid-IR observations., Comment: Published in JATIS. This version is the manuscript resubmitted before acceptance, 30 pages, 14 figures

Context. The inner few au region of planet-forming disks is a complex environment. High angular resolution observations have a key role in understanding the disk structure and the dynamical processes at work. Aims. In this study we aim to characterize the mid-infrared brightness distribution of the inner disk of the young intermediate-mass star HD 163296, from VLTI/MATISSE observations. Methods. We use geometric models to fit the data. Our models include a smoothed ring, a flat disk with inner cavity, and a 2D Gaussian. The models can account for disk inclination and for azimuthal asymmetries as well. We also perform numerical hydro-dynamical simulations of the inner edge of the disk. Results. Our modeling reveals a significant brightness asymmetry in the L-band disk emission. The brightness maximum of the asymmetry is located at the NW part of the disk image, nearly at the position angle of the semimajor axis. The surface brightness ratio in the azimuthal variation is $3.5 \pm 0.2$. Comparing our result on the location of the asymmetry with other interferometric measurements, we confirm that the morphology of the $r<0.3$ au disk region is time-variable. We propose that this asymmetric structure, located in or near the inner rim of the dusty disk, orbits the star. For the physical origin of the asymmetry, we tested a hypothesis where a vortex is created by Rossby wave instability, and we find that a unique large scale vortex may be compatible with our data. The half-light radius of the L-band emitting region is $0.33\pm 0.01$ au, the inclination is ${52^\circ}^{+5^\circ}_{-7^\circ}$, and the position angle is $143^\circ \pm 3^\circ$. Our models predict that a non-negligible fraction of the L-band disk emission originates inside the dust sublimation radius for $\mu$m-sized grains. Refractory grains or large ($\gtrsim 10\ \mu$m-sized) grains could be the origin for this emission., Comment: accepted for publication in A&A

Context. Planet formation is expected to take place in the first million years of a planetary system through various processes, which remain to be tested through observations. Aims. With the recent discovery, using ALMA, of two gaseous spiral arms inside the 120 au cavity and connected to dusty spirals, the famous protoplanetary disk around AB Aurigae presents a strong incentive for investigating the mechanisms that lead to giant planet formation. A candidate protoplanet located inside a spiral arm has already been claimed in an earlier study based on the same ALMA data. Methods. We used SPHERE at the Very Large Telescope (VLT) to perform near-infrared (IR) high-contrast imaging of AB Aur in polarized and unpolarized light in order to study the morphology of the disk and search for signs of planet formation. Results. SPHERE has delivered the deepest images ever obtained for AB Aur in scattered light. Among the many structures that are yet to be understood, we identified not only the inner spiral arms, but we also resolved a feature in the form of a twist in the eastern spiral at a separation of about 30 au. The twist of the spiral is perfectly reproduced with a planet-driven density wave model when projection effects are accounted for. We measured an azimuthal displacement with respect to the counterpart of this feature in the ALMA data, which is consistent with Keplerian motion on a 4-yr baseline. Another point sxce is detected near the edge of the inner ring, which is likely the result of scattering as opposed to the direct emission from a planet photosphere. We tentatively derived mass constraints for these two features. Conclusions. The twist and its apparent orbital motion could well be the first direct evidence of a connection between a protoplanet candidate and its manifestation as a spiral imprinted in the gas and dust distributions., Comment: accepted in Astronomy and Astrophysics, 8 pages, 5 figures

A large fraction of stars is found to be part of binary or higher-order multiple systems. The ubiquity of planets found around single stars raises the question if and how planets in binary systems may form. Protoplanetary disks are the birthplaces of planets, and their characterization is crucial in order to understand the planet formation process. Our aim is to characterize the morphology of the GG Tau A disk, one of the largest and most massive circumbinary disks, and trace evidence for binary-disk interactions. We obtained observations in polarized scattered light of GG Tau A using the SPHERE/IRDIS instrument in the H-band filter. We analyze the observed disk morphology and substructures. We run 2D hydrodynamical models simulating the evolution of the circumbinary ring over the lifetime of the disk. The disk, as well as the cavity and the inner region are highly structured with several shadowed regions, spiral structures, and streamer-like filaments, some of them detected for the first time. The streamer-like filaments appear to connect the outer ring with the northern arc. Their azimuthal spacing suggests that they may be generated by periodic perturbations by the binary, tearing off material from the inner edge of the outer disk once during each orbit. By comparing observations to hydrodynamical simulations we find that the main features, in particular the gap size, as well as the spiral and streamer filaments, can be qualitatively explained by the gravitational interactions of a binary with semi-major axis of $\sim$35 au on an orbit coplanar with the circumbinary ring., Comment: Accepted for publication in A&A

Spectro-photometry of debris disks in total intensity and polarimetry can provide new insight into the properties of the dust grains therein (size distribution and optical properties). We aim to constrain the morphology of the highly inclined debris disk HD 32297. We also intend to obtain spectroscopic and polarimetric measurements to retrieve information on the particle size distribution within the disk for certain grain compositions. We observed HD 32297 with SPHERE in Y, J, and H bands in total intensity and in J band in polarimetry. The observations are compared to synthetic models of debris disks and we developed methods to extract the photometry in total intensity overcoming the data-reduction artifacts, namely the self-subtraction. The spectro-photometric measurements averaged along the disk mid-plane are then compared to model spectra of various grain compositions. These new images reveal the very inner part of the system as close as 0.15". The disk image is mostly dominated by the forward scattering making one side (half-ellipse) of the disk more visible, but observations in total intensity are deep enough to also detect the back side for the very first time. The images as well as the surface brightness profiles of the disk rule out the presence of a gap as previously proposed. We do not detect any significant asymmetry between the northeast and southwest sides of the disk. The spectral reflectance features a "gray to blue" color which is interpreted as the presence of grains far below the blowout size. The presence of sub-micron grains in the disk is suspected to be the result of gas drag and/or "avalanche mechanisms". The blue color of the disk could be further investigated with additional total intensity and polarimetric observations in K and H bands respectively to confirm the spectral slope and the fraction of polarization.

SPICA, the cryogenic infrared space telescope recently pre-selected for a `Phase A' concept study as one of the three remaining candidates for ESA's fifth medium class (M5) mission, is foreseen to include a far-infrared polarimetric imager (SPICA-POL, now called B-BOP), which would offer a unique opportunity to resolve major issues in our understanding of the nearby, cold magnetized Universe. This paper presents an overview of the main science drivers for B-BOP, including high dynamic range polarimetric imaging of the cold interstellar medium (ISM) in both our Milky Way and nearby galaxies. Thanks to a cooled telescope, B-BOP will deliver wide-field 100-350 micron images of linearly polarized dust emission in Stokes Q and U with a resolution, signal-to-noise ratio, and both intensity and spatial dynamic ranges comparable to those achieved by Herschel images of the cold ISM in total intensity (Stokes I). The B-BOP 200 micron images will also have a factor ~30 higher resolution than Planck polarization data. This will make B-BOP a unique tool for characterizing the statistical properties of the magnetized interstellar medium and probing the role of magnetic fields in the formation and evolution of the interstellar web of dusty molecular filaments giving birth to most stars in our Galaxy. B-BOP will also be a powerful instrument for studying the magnetism of nearby galaxies and testing galactic dynamo models, constraining the physics of dust grain alignment, informing the problem of the interaction of cosmic rays with molecular clouds, tracing magnetic fields in the inner layers of protoplanetary disks, and monitoring accretion bursts in embedded protostars., Comment: Accepted for publication in PASA; 37 pages, 16 figures

We present new observations of the edge-on debris disk around HD 15115 (F star at 48.2 pc) obtained in the near-IR. We search for observational evidence for a second inner planetesimal ring in the system. We obtained total intensity and polarimetric data in the broad bands J and H and processed the data with differential imaging techniques achieving an angular resolution of about 40 mas. We observe an axisymmetric planetesimal belt with a radius of $\sim$2$''$, an inclination of $85.8^{\circ} \pm 0.7^{\circ}$ and position angle of 278.9$^{\circ} \pm 0.1^{\circ}$. A grid of models describing the spatial distribution of the grains in the disk is generated to constrain the geometric parameters of the disk and to explore the presence of a second belt. We perform a photometric analysis of the data and compare disk brightness in two bands in scattered and in polarized light. The analysis shows that the west side is $\sim$2.5 times brighter in total intensity than the east side in both bands, while for polarized light in the J band this ratio is only 1.25. The maximum polarization fraction is 15--20% at $r\sim$2.5$''$. We also find that the J - H color of the disk appears to be red for the radial separations $r\lesssim2''$ and is getting bluer for the larger separations. This apparent change of disk color from red to blue with an increasing radial separation could be explained by the decreasing average grain size with distance. The presence of an additional inner belt slightly inclined with respect to the main planetesimal belt is suspected from the polarized intensity image but the analysis and modeling presented here cannot establish a firm conclusion due to the faintness of the disk and its high inclination., Comment: 23 pages, 21 figures typos corrected

MWC758 is a young star surrounded by a transitional disk. Recently, a protoplanet candidate has been detected around MWC758 through high-resolution $L'$-band observations. The candidate is located inside the disk cavity at a separation of $\sim$111 mas from the central star, and at an average position angle of $\sim$165.5 degrees. We have performed simultaneous adaptive optics observations of MWC758 in the H$_{\alpha}$ line and the adjacent continuum using SPHERE/ZIMPOL at the Very Large Telescope (VLT). We aim at detecting accreting protoplanet candidates through spectral angular differential imaging observations. The data analysis does not reveal any H$_{\alpha}$ signal around the target. The derived contrast curve in the B_Ha filter allows us to derive a 5$\sigma$ upper limit of $\sim$7.6 mag at 111 mas, the separation of the previously detected planet candidate. This contrast translates into a H$_{\alpha}$ line luminosity of $L_{\rm H_{\alpha}}\lesssim$ 5$\times$10$^{-5}$ $L_{\odot}$ at 111 mas, and an accretion luminosity of $L_{acc} <$3.7$\times$10$^{-4}\,L_{\odot}$. For the predicted mass range of MWC758b, 0.5-5 $M_{\rm Jup}$, this implies accretion rates of $\dot M \lesssim$ 3.4$\times$(10$^{-8}$-10$^{-9})\,M_{\odot}/yr$, for an average planet radius of 1.1 $R_{\rm Jup}$. Therefore, our estimates are consistent with the predictions of accreting circumplanetary accretion models for $R_{\rm in} = 1 R_{\rm Jup}$. In any case, the non-detection of any H$_{\alpha}$ emitting source in the ZIMPOL images does not allow us to unveil the true nature of the $L'$ detected source., Comment: 5 pages, accepted for publication in A&A letters

We present an overview of the scientific potential of MATISSE, the Multi Aperture mid-Infrared SpectroScopic Experiment for the Very Large Telescope Interferometer. For this purpose we outline selected case studies from various areas, such as star and planet formation, active galactic nuclei, evolved stars, extrasolar planets, and solar system minor bodies and discuss strategies for the planning and analysis of future MATISSE observations. Moreover, the importance of MATISSE observations in the context of complementary high-angular resolution observations at near-infrared and submillimeter/millimeter wavelengths is highlighted., Comment: SPIE Astronomical Telescopes and Instrumentation conference, June 2016, 20 pages, 6 Figures

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

Transition disks correspond to a short stage between the young protoplanetary phase and older debris phase. Along this evolutionary sequence, the gas component disappears leaving room for a dust-dominated environment where already-formed planets signpost their gravitational perturbations. We endeavor to study the very inner region of the well-known and complex debris, but still gas-rich disk, around HD 141569A using the exquisite high-contrast capability of SPHERE at the VLT. Recent near-infrared (IR) images suggest a relatively depleted cavity within ~200 au, while former mid-IR data indicate the presence of dust at separations shorter than ~100 au. We obtained multi-wavelength images in the near-IR in J, H2, H3 and Ks bands with the IRDIS camera and a 0.95-1.35 micrometers spectral data cube with the IFS. Data were acquired in pupil-tracking mode, thus allowing for angular differential imaging. We discovered several new structures inside 1", of which the most prominent is a bright ring with sharp edges (semi-major axis: 0.4") featuring a strong north-south brightness asymmetry. Other faint structures are also detected from 0.4" to 1" in the form of concentric ringlets and at least one spiral arm. Finally, the VISIR data at 8.6 micrometers suggests the presence of an additional dust population closer in. Besides, we do not detect companions more massive than 1-3 mass of Jupiter. The performance of SPHERE allows us to resolve the extended dust component, which was previously detected at thermal and visible wavelengths, into very complex patterns with strong asymmetries ; the nature of these asymmetries remains to be understood. Scenarios involving shepherding by planets or dust-gas interactions will have to be tested against these observations., Comment: Accepted by A&A. 10 pages, 8 figures

The young star beta Pictoris is well known for its dusty debris disk, produced through the grinding down by collisions of planetesimals, kilometre-sized bodies in orbit around the star. In addition to dust, small amounts of gas are also known to orbit the star, likely the result from vaporisation of violently colliding dust grains. The disk is seen edge on and from previous absorption spectroscopy we know that the gas is very rich in carbon relative to other elements. The oxygen content has been more difficult to assess, however, with early estimates finding very little oxygen in the gas at a C/O ratio 20x higher than the cosmic value. A C/O ratio that high is difficult to explain and would have far-reaching consequences for planet formation. Here we report on observations by the far-infrared space telescope Herschel, using PACS, of emission lines from ionised carbon and neutral oxygen. The detected emission from C+ is consistent with that previously reported being observed by the HIFI instrument on Herschel, while the emission from O is hard to explain without assuming a higher-density region in the disk, perhaps in the shape of a clump or a dense torus, required to sufficiently excite the O atoms. A possible scenario is that the C/O gas is produced by the same process responsible for the CO clump recently observed by ALMA in the disk, and that the re-distribution of the gas takes longer than previously assumed. A more detailed estimate of the C/O ratio and the mass of O will have to await better constraints on the C/O gas spatial distribution., Comment: Accepted by A&A; 6 pages including 3 figures

The study of dynamical processes in protoplanetary disks is essential to understand planet formation. In this context, transition disks are prime targets because they are at an advanced stage of disk clearing and may harbor direct signatures of disk evolution. In this paper, we aim to derive new constraints on the structure of the transition disk MWC 758, to detect non-axisymmetric features and understand their origin. We obtained infrared polarized intensity observations of the protoplanetary disk MWC 758 with SPHERE/VLT at 1.04 microns to resolve scattered light at a smaller inner working angle (0.093") and a higher angular resolution (0.027") than previously achieved. We observe polarized scattered light within 0.53" (148 au) down to the inner working angle (26 au) and detect distinct non-axisymmetric features but no fully depleted cavity. The two small-scale spiral features that were previously detected with HiCIAO are resolved more clearly, and new features are identified, including two that are located at previously inaccessible radii close to the star. We present a model based on the spiral density wave theory with two planetary companions in circular orbits. The best model requires a high disk aspect ratio (H/r~0.20 at the planet locations) to account for the large pitch angles which implies a very warm disk. Our observations reveal the complex morphology of the disk MWC758. To understand the origin of the detected features, the combination of high-resolution observations in the submillimeter with ALMA and detailed modeling is needed., Comment: Accepted by A&A Letters

Planets are thought to form in the gas and dust disks around young stars. In particular, it has been proposed that giant planets can form through the gravitational instability of massive extended disks around intermediate-mass stars. However, we still lack direct observations to constrain this mechanism. We have spatially resolved the 8.6 and 11.2 $\mu$m emission of a massive protoplanetary disk seen edge on around an A star, Gomez's Hamburger (GoHam), using VISIR at the Very Large Telescope. A compact region situated at a projected distance of $350\pm50$ AU south of the central star is found to have a reduced emission.This asymmetry is fully consistent with the presence of a cold density structure, or clump, identified in earlier CO observations, and we derive physical characteristics consistent with those observations: a mass of 0.8-11.4 Jupiter masses (for a dust-to-gas mass ratio of 0.01), a radius of about 10$^2$ astronomical units, and a local density of about $10^{7}$ cm$^{-3}$. Based on this evidence, we argue that this clump, which we call GoHam b, is a promising candidate for a young protoplanet formed by gravitational instability that might be representative of the precursors of massive planets observed around A stars, such as HR 8799 or Beta pictoris. More detailed studies at high angular resolution are needed to better constrain the physical properties of this object to confirm this proposal., Comment: 7 Pages, accepted for publication as a Letter in A&A

The discovery of almost 2000 exoplanets has revealed an unexpectedly diverse planet population. Observations to date have shown that our Solar System is certainly not representative of the general population of planets in our Milky Way. The key science questions that urgently need addressing are therefore: What are exoplanets made of? Why are planets as they are? What causes the exceptional diversity observed as compared to the Solar System? EChO (Exoplanet Characterisation Observatory) has been designed as a dedicated survey mission for transit and eclipse spectroscopy capable of observing a large and diverse planet sample within its four-year mission lifetime. EChO can target the atmospheres of super-Earths, Neptune-like, and Jupiter-like planets, in the very hot to temperate zones (planet temperatures of 300K-3000K) of F to M-type host stars. Over the next ten years, several new ground- and space-based transit surveys will come on-line (e.g. NGTS, CHEOPS, TESS, PLATO), which will specifically focus on finding bright, nearby systems. The current rapid rate of discovery would allow the target list to be further optimised in the years prior to EChO's launch and enable the atmospheric characterisation of hundreds of planets. Placing the satellite at L2 provides a cold and stable thermal environment, as well as a large field of regard to allow efficient time-critical observation of targets randomly distributed over the sky. A 1m class telescope is sufficiently large to achieve the necessary spectro-photometric precision. The spectral coverage (0.5-11 micron, goal 16 micron) and SNR to be achieved by EChO, thanks to its high stability and dedicated design, would enable a very accurate measurement of the atmospheric composition and structure of hundreds of exoplanets., Comment: 50 pages, 30 figures. Experimental Astronomy

We aim at unveiling the observational imprint of physical mechanisms that govern planetary formation in young, multiple systems. In particular, we investigate the impact of tidal truncation on the inner circumstellar disks. We observed the emblematic system GG Tau at high-angular resolution: a hierarchical quadruple system composed of low-mass T Tauri binary stars surrounded by a well-studied, massive circumbinary disk in Keplerian rotation. We used the near-IR 4-telescope combiner PIONIER on the VLTI and sparse-aperture-masking techniques on VLT/NaCo to probe this proto-planetary system at sub-AU scales. We report the discovery of a significant closure-phase signal in H and Ks bands that can be reproduced with an additional low-mass companion orbiting GG Tau Ab, at a (projected) separation rho = 31.7 +/- 0.2mas (4.4 au) and PA = 219.6 +/- 0.3deg. This finding offers a simple explanation for several key questions in this system, including the missing-stellar-mass problem and the asymmetry of continuum emission from the inner dust disks observed at millimeter wavelengths. Composed of now five co-eval stars with 0.02 <= Mstar <= 0.7 Msun, the quintuple system GG Tau has become an ideal test case to constrain stellar evolution models at young ages (few 10^6yr)., Comment: 5pages, 3 figures, 1 appendix (online material)

Context: The dusty debris disk around the $\sim$20 Myr old main-sequence A-star {\beta} Pictoris is known to contain gas. Evidence points towards a secondary origin of the gas as opposed to being a direct remnant form the initial protoplanetary disk, although the dominant gas production mechanism is so far not identified. The origin of the observed overabundance of C and O compared to solar abundances of metallic elements, e.g. Na and Fe, is also unclear. Aims: Our goal is to constrain the spatial distribution of C in the disk, and thereby the gas origin and its abundance pattern. Methods: We used the HIFI instrument onboard Herschel to observe and spectrally resolve CII emission at 158 $\mu$m from the {\beta} Pic debris disk. Assuming Keplerian rotation, we use the spectrally resolved line profile to constrain the spatial distribution of the gas. Results: We show that most of the gas is located around $\sim$100 AU or beyond. We estimate a total C gas mass of $1.3\times10^{-2}$ M$_\oplus$. The data suggest that more gas is located on the southwest side of the disk than on the northeast side. The data are consistent with the hypothesis of a well-mixed gas (constant C/Fe ratio throughout the disk). Assuming instead a spatial profile expected from a simplified accretion disk model, we found it to give a significantly worse fit to the observations. Conclusions: Since the bulk of the gas is found outside 30 AU, we argue that the cometary objects known as "falling evaporating bodies" are unlikely to be the dominant source of gas; production from grain-grain collisions or photodesorption seems more likely. The incompatibility of the observations with a simplified accretion disk model could favour a preferential depletion explanation for the overabundance of C and O. More stringent constraints on the spatial distribution will be available from ALMA observations of CI at 609 $\mu$m., Comment: 10 pages, 7 figures, published in A&A. v2: Revised section 5.4 and figure 6, results unchanged. Changed x- and y-axis of figure 5. Some other minor changes. Fixed typos v3, v4: Language correction, some typos

Protoplanetary disks around young stars harbor many structures related to planetary formation. Of particular interest, spiral patterns were discovered among several of these disks and are expected to be the sign of gravitational instabilities leading to giant planets formation or gravitational perturbations caused by already existing planets. In this context, the star HD100546 presents some specific characteristics with a complex gas and dusty disk including spirals as well as a possible planet in formation. The objective of this study is to analyze high contrast and high angular resolution images of this emblematic system to shed light on critical steps of the planet formation. We retrieved archival images obtained at Gemini in the near IR (Ks band) with the instrument NICI and processed the data using advanced high contrast imaging technique taking advantage of the angular differential imaging. These new images reveal the spiral pattern previously identified with HST with an unprecedented resolution, while the large-scale structure of the disk is mostly erased by the data processing. The single pattern at the southeast in HST images is now resolved into a multi-armed spiral pattern. Using two models of a gravitational perturber orbiting in a gaseous disk we attempted to bring constraints on the characteristics of this perturber assuming each spiral being independent and we derived qualitative conclusions. The non-detection of the northeast spiral pattern observed in HST allows to put a lower limit on the intensity ratio between the two sides of the disk, which if interpreted as forward scattering yields a larger anisotropic scattering than derived in the visible. Also, we found that the spirals are likely spatially resolved with a thickness of about 5-10AU. Finally, we did not detect the candidate forming planet recently discovered in the Lp band, with a mass upper limit of 16-18 MJ., Comment: Accepted for publication in Astronomy and Astrophysics, 10 pages, 8 figures

GASPS is a far-infrared line and continuum survey of protoplanetary and young debris disks using PACS on the Herschel Space Observatory. The survey includes [OI] at 63 microns, as well as 70, 100 and 160um continuum, with the brightest objects also studied in [OI]145um, [CII]157um, H2O and CO. Targets included T Tauri stars and debris disks in 7 nearby young associations, and a sample of isolated Herbig AeBe stars. The aim was to study the global gas and dust content in a wide disk sample, systemically comparing the results with models. In this paper we review the main aims, target selection and observing strategy. We show initial results, including line identifications, sources detected, and a first statistical study. [OI]63um was the brightest line in most objects, by a factor of ~10. Detection rates were 49%, including 100% of HAeBe stars and 43% of T Tauri stars. Comparison with published dust masses show a dust threshold for [OI]63um detection of ~1e-5 M_solar. Normalising to 140pc distance, 32% with mass 1e-6 - 1e-5 M_solar, and a small number with lower mass were also detected. This is consistent with moderate UV excess and disk flaring. In most cases, continuum and line emission is spatially and spectrally unresolved, suggesting disk emission. ~10 objects were resolved, likely from outflows. Detection rates in [OI]145um, [CII]157um and CO J=18-17 were 20-40%, but [CII] was not correlated with disk mass, suggesting it arises instead from a compact envelope. [OI] detection rates in T Tauri associations of ages 0.3-4Myr were ~50%. ~2 stars were detectable in associations of 5-20Myr, with no detections in associations of age >20Myr. Comparing with the total number of young stars, and assuming a ISM-like gas/dust ratio, this indicates that ~18% of stars retain a gas-rich disk of total mass >1M_Jupiter for 1-4Myr, 1-7% keep such disks for 5-10Myr, and none remain beyond 10-20Myr., Comment: Accepted for PASP

Some planetary systems harbour debris disks containing planetesimals such as asteroids and comets. Collisions between such bodies produce small dust particles, the spectral features of which reveal their composition and, hence, that of their parent bodies. A measurement of the composition of olivine crystals has been done for the protoplanetary disk HD100546 and for olivine crystals in the warm inner parts of planetary systems. The latter compares well with the iron-rich olivine in asteroids (x<0.29). In the cold outskirts of the Beta Pictoris system, an analogue to the young Solar System, olivine crystals were detected but their composition remained undetermined, leaving unknown how the composition of the bulk of Solar System cometary olivine grains compares with that of extrasolar comets. Here we report the detection of the 69-micrometre-wavelength band of olivine crystals in the spectrum of Beta Pictoris. Because the disk is optically thin, we can associate the crystals with an extrasolar proto-Kuiper belt a distance of 15-45 astronomical units from the star (one astronomical unit is the Sun-Earth distance), determine their magnesium-rich composition (x=0.01+/-0.001) and show that they make up 3.6+/-1.0 per cent of the total dust mass. These values are strikingly similar to those for the dust emitted by the most primitive comets in the Solar System, even though Beta Pictoris is more massive and more luminous and has a different planetary system architecture.

Fomalhaut is a young, nearby star that is suspected to harbor an infant planetary system, interspersed with one or more belts of dusty debris. We present far-infrared images obtained with the Herschel Space Observatory with an angular resolution between 5.7 and 36.7 arcsec at wavelengths between 70 and 500 micrometer. The images show the main debris belt in great detail. Even at high spatial resolution, the belt appears smooth. The region in between the belt and the central star is not devoid of material; thermal emission is observed here as well. Also at the location of the star, excess emission is detected. We use a dynamical model together with radiative-transfer tools to derive the parameters of the debris disk. We include detailed models of the interaction of the dust grains with radiation, for both the radiation pressure and the temperature determination. Comparing these models to the spatially resolved temperature information contained in the images allows us to place strong constraints on the presence of grains that will be blown out of the system by radiation pressure. We use this to derive the dynamical parameters of the system. The appearance of the belt points towards a remarkably active system in which dust grains are produced at a very high rate by a collisional cascade in a narrow region filled with dynamically excited planetesimals. Dust particles with sizes below the blow-out size are abundantly present. The equivalent of 2000 one-km-sized comets are destroyed every day, out of a cometary reservoir amounting to 110 Earth masses. From comparison of their scattering and thermal properties, we find evidence that the dust grains are fluffy aggregates, which indicates a cometary origin. The excess emission at the location of the star may be produced by hot dust with a range of temperatures, but may also be due to gaseous free-free emission from a stellar wind., Comment: 9 pages, 6 figures

HD 181327 is a young F5/F6V star belonging to the Beta Pictoris moving group (12 Myr). It harbors an optically thin belt of circumstellar material at 90 AU. We aim to study the dust properties in the belt in details, and to constrain the gas-to-dust ratio. We obtained far-IR observations with the Herschel/PACS instrument, and 3.2 mm observations with the ATCA array. The geometry of the belt is constrained with newly reduced HST/NICMOS images that break the degeneracy between the disk geometry and the dust properties. We use the radiative transfer code GRaTer to compute a large grid of models, and we identify the grain models that best reproduce the Spectral Energy Distribution through a Bayesian analysis. We attempt to detect the [OI] and [CII] lines with PACS spectroscopy, providing observables to our photochemical code ProDiMo. The HST observations confirm that the dust is confined in a narrow belt. The continuum is detected in the far-IR with PACS and the disk is resolved with both PACS and ATCA. A medium integration of the gas spectral lines only provides upper limits on the line fluxes. We show that the HD 181327 dust disk consists of micron-sized grains of porous amorphous silicates and carbonaceous material surrounded by an important layer of ice, for a total dust mass of 0.05 M\oplus (up to 1 mm). We discuss evidences that the grains are fluffy aggregates. The upper limits on the gas lines do not provide unambiguous constraints: only if the PAH abundance is high, the gas mass must be lower than 17 M\oplus. Despite the weak constraints on the gas disk, the age of HD 181327 and the properties of the dust disk suggest that it has passed the stage of gaseous planets formation. The dust reveals a population of icy planetesimals, similar to the primitive Kuiper Belt, that may be a source for the future delivery of water and volatiles onto forming terrestrial planets., Comment: 17 pages, 12 figures. Accepted for publication in Astronomy & Astrophysics (2011 december 7)

A dedicated mission to investigate exoplanetary atmospheres represents a major milestone in our quest to understand our place in the universe by placing our Solar System in context and by addressing the suitability of planets for the presence of life. EChO -the Exoplanet Characterisation Observatory- is a mission concept specifically geared for this purpose. EChO will provide simultaneous, multi-wavelength spectroscopic observations on a stable platform that will allow very long exposures. EChO will build on observations by Hubble, Spitzer and groundbased telescopes, which discovered the first molecules and atoms in exoplanetary atmospheres. EChO will simultaneously observe a broad enough spectral region -from the visible to the mid-IR- to constrain from one single spectrum the temperature structure of the atmosphere and the abundances of the major molecular species. The spectral range and resolution are tailored to separate bands belonging to up to 30 molecules to retrieve the composition and temperature structure of planetary atmospheres. The target list for EChO includes planets ranging from Jupiter-sized with equilibrium temperatures Teq up to 2000 K, to those of a few Earth masses, with Teq ~300 K. We have baselined a dispersive spectrograph design covering continuously the 0.4-16 micron spectral range in 6 channels (1 in the VIS, 5 in the IR), which allows the spectral resolution to be adapted from several tens to several hundreds, depending on the target brightness. The instrument will be mounted behind a 1.5 m class telescope, passively cooled to 50 K, with the instrument structure and optics passively cooled to ~45 K. EChO will be placed in a grand halo orbit around L2. We have also undertaken a first-order cost and development plan analysis and find that EChO is easily compatible with the ESA M-class mission framework., Comment: Accepted for publication in Experimental Astronomy, 23 pages, 15 figures

We report on a sensitive search for H2 1-0 S(1), 1-0 S(0) and 2-1 S(1) ro-vibrational emission at 2.12, 2.22 and 2.25 micron in a sample of 15 Herbig Ae/Be stars employing CRIRES, the ESO-VLT near-infrared high-resolution spectrograph, at R~90,000. We detect the H2 1-0 S(1) line toward HD 100546 and HD 97048. In the other 13 targets, the line is not detected. The H2 1-0 S(0) and 2-1 S(1) lines are undetected in all sources. This is the first detection of near-IR H2 emission in HD 100546. The H2 1-0 S(1) lines observed in HD 100546 and HD 97048 are observed at a velocity consistent with the rest velocity of both stars, suggesting that they are produced in the circumstellar disk. In HD 97048, the emission is spatially resolved and it is observed to extend at least up to 200 AU. We report an increase of one order of magnitude in the H2 1-0 S(1) line flux with respect to previous measurements taken in 2003 for this star, which suggests line variability. In HD 100546 the emission is tentatively spatially resolved and may extend at least up to 50 AU. Modeling of the H2 1-0 S(1) line profiles and their spatial extent with flat keplerian disks shows that most of the emission is produced at a radius >5 AU. Upper limits to the H2 1-0 S(0)/ 1-0 S(1) and H2 2-1 S(1)/1-0 S(1) line ratios in HD 97048 are consistent with H2 gas at T>2000 K and suggest that the emission observed may be produced by X-ray excitation. The upper limits for the line ratios for HD 100546 are inconclusive. Because the H2 emission is located at large radii, for both sources a thermal emission scenario (i.e., gas heated by collisions with dust) is implausible. We argue that the observation of H2 emission at large radii may be indicative of an extended disk atmosphere at radii >5 AU. This may be explained by a hydrostatic disk in which gas and dust are thermally decoupled or by a disk wind caused by photoevaporation., Comment: Accepted by A&A. 16 pages, 7 figures

The recent findings of gas giant planets around young A-type stars suggest that disks surrounding Herbig Ae/Be stars will develop planetary systems. An interesting case is HD142527, for which previous observations revealed a complex circumstellar environment and an unusually high ratio of infrared to stellar luminosity. Its properties differ considerably from other Herbig Ae/Be stars. This suggests that the disk surrounding HD142527 is in an uncommon evolutionary stage. We aim for a better understanding of the geometry and evolutionary status of the circumstellar material around the Herbig Ae/Be star HD142527. We map the composition and spatial distribution of the dust around HD142527. We analyze SEST and ATCA millimeter data, VISIR N and Q-band imaging and spectroscopy. We gather additional relevant data from the literature. We use the radiative transfer code MCMax to construct a model of the geometry and density structure of the circumstellar matter, which fits all of the observables satisfactorily. We find that the disk of HD142527 has three geometrically distinct components separated by a disk gap running from 30 to 130 AU. There is a geometrically flat inner disk running from 0.3 AU up to 30 AU; an optically thin halo-like component of dust in the inner disk regions; and a massive self-shadowed outer disk running from 130 AU up to 200 AU. We derived a total dust mass in small grains of 10^-3 M0 and a vertical height of the inner wall of the outer disk of h = 60 AU. ...., Comment: 13 pages, 17 figures. Accepted by A&A 14 January 2011

The Mid Infra Red Instrument (MIRI) is one of the four instruments onboard the James Webb Space Telescope (JWST), providing imaging, coronagraphy and spectroscopy over the 5-28 microns band. To verify the optical performance of the instrument, extensive tests were performed at CEA on the flight model (FM) of the Mid-InfraRed IMager (MIRIM) at cryogenic temperatures and in the infrared. This paper reports on the point spread function (PSF) measurements at 5.6 microns, the shortest operating wavelength for imaging. At 5.6 microns the PSF is not Nyquist-sampled, so we use am original technique that combines a microscanning measurement strategy with a deconvolution algorithm to obtain an over-resolved MIRIM PSF. The microscanning consists in a sub-pixel scan of a point source on the focal plane. A data inversion method is used to reconstruct PSF images that are over-resolved by a factor of 7 compared to the native resolution of MIRI. We show that the FWHM of the high-resolution PSFs were 5-10% wider than that obtained with Zemax simulations. The main cause was identified as an out-of-specification tilt of the M4 mirror. After correction, two additional test campaigns were carried out, and we show that the shape of the PSF is conform to expectations. The FWHM of the PSFs are 0.18-0.20 arcsec, in agreement with simulations. 56.1-59.2% of the total encircled energy (normalized to a 5 arcsec radius) is contained within the first dark Airy ring, over the whole field of view. At longer wavelengths (7.7-25.5 microns), this percentage is 57-68%. MIRIM is thus compliant with the optical quality requirements. This characterization of the MIRIM PSF, as well as the deconvolution method presented here, are of particular importance, not only for the verification of the optical quality and the MIRI calibration, but also for scientific applications., Comment: 13 pages, submitted to SPIE Proceedings vol. 7731, Space Telescopes and Instrumentation 2010: Optical, Infrared, and Millimeter Wave

We obtained Herschel PACS and SPIRE images of the thermal emission of the debris disk around the A5V star {\beta} Pic. The disk is well resolved in the PACS filters at 70, 100, and 160 {\mu}m. The surface brightness profiles between 70 and 160 {\mu}m show no significant asymmetries along the disk, and are compatible with 90% of the emission between 70 and 160 {\mu}m originating in a region closer than 200 AU to the star. Although only marginally resolving the debris disk, the maps obtained in the SPIRE 250 - 500 {\mu}m filters provide full-disk photometry, completing the SED over a few octaves in wavelength that had been previously inaccessible. The small far-infrared spectral index ({\beta} = 0.34) indicates that the grain size distribution in the inner disk (<200AU) is inconsistent with a local collisional equilibrium. The size distribution is either modified by non-equilibrium effects, or exhibits a wavy pattern, caused by an under-abundance of impactors which have been removed by radiation pressure., Comment: Accepted for publication in Astronomy&Astrophysics, Herschel First Results special issue

Context - Circumstellar discs are ubiquitous around young stars, but rapidly dissipate their gas and dust on timescales of a few Myr. The Herschel space observatory allows for the study of the warm disc atmosphere, using far-infrared spectroscopy to measure gas content and excitation conditions, and far-IR photometry to constrain the dust distribution. Aims - We aim to detect and characterize the gas content of circumstellar discs in four targets as part of the Herschel science demonstration phase. Methods - We carried out sensitive medium resolution spectroscopy and high sensitivity photometry at lambda ~60-190 micron using the Photodetector Array Camera and Spectrometer instrument on the Herschel space observatory. Results - We detect [OI] 63 micron emission from the young stars HD 169142, TW Hydrae, and RECX 15, but not HD 181327. No other lines, including [CII] 158 and [OI] 145, are significantly detected. All four stars are detected in photometry at 70 and 160 micron. Extensive models are presented in associated papers., Comment: Comments: 5 pages, 2 Postscript figures, accepted for publication in the A&A Herschel special issue

The Herschel GASPS Key Program is a survey of the gas phase of protoplanetary discs, targeting 240 objects which cover a large range of ages, spectral types, and disc properties. To interpret this large quantity of data and initiate self-consistent analyses of the gas and dust properties of protoplanetary discs, we have combined the capabilities of the radiative transfer code MCFOST with the gas thermal balance and chemistry code ProDiMo to compute a grid of 300 000 disc models (DENT). We present a comparison of the first Herschel/GASPS line and continuum data with the predictions from the DENT grid of models. Our objective is to test some of the main trends already identified in the DENT grid, as well as to define better empirical diagnostics to estimate the total gas mass of protoplanetary discs. Photospheric UV radiation appears to be the dominant gas-heating mechanism for Herbig stars, whereas UV excess and/or X-rays emission dominates for T Tauri stars. The DENT grid reveals the complexity in the analysis of far-IR lines and the difficulty to invert these observations into physical quantities. The combination of Herschel line observations with continuum data and/or with rotational lines in the (sub-)millimetre regime, in particular CO lines, is required for a detailed characterisation of the physical and chemical properties of circumstellar discs., Comment: 5 pages, 4 figures, accepted for publication in the A&A Herschel special issue