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ESO is in the process of upgrading one of the two FORS (FOcal Reducer/low dispersion Spectrograph) instruments - a multi-mode (imaging, polarimetry, long-slit, and multi-object spectroscopy) optical instrument mounted on the Cassegrain focus of Unit Telescope 1 of ESO's Very Large Telescope. FORS1 was moved from Chile to Trieste, and is undergoing complete refurbishment, including the exchange of all motorised parts. In addition, new software is developed, based on the Extremely Large Telescope Instrument Control Software Framework, as the upgraded FORS1 will be the first instrument in operations to use this framework. The new Teledyne e2V CCD has now been procured and is undergoing testing with the New Generation Controller at ESO. In addition, a new set of grisms have been developed, and a new set of filters will be purchased. A new internal calibration unit has been designed, making the operations more efficient., Comment: This paper is dedicated to the memory of our former colleague, Mario Nonino, who passed away prematurely. Proceedings for the SPIE Astronomical Telescopes and Instrumentation 2024

The nature of dust in the diffuse interstellar medium can be best investigated by means of reddening curves where only a single interstellar cloud lies between the observer and the background source. Published reddening curves often suffer from various systematic uncertainties. We merge a sample of 895 reddening curves of stars for which both FORS2 polarisation spectra and UVES high-resolution spectra are available. The resulting 111 sightlines toward OB-type stars have 175 reddening curves. For these stars, we derive their spectral type from the UVES high-resolution spectroscopy. To obtain high-quality reddening curves we exclude stars with composite spectra in the IUE/FUSE data due to multiple stellar systems. Likewise, we omit stars that have uncertain spectral type designations or stars with photometric variability. We neglect stars that show inconsistent parallaxes when comparing DR2 and DR3 from GAIA. Finally, we identify stars that show differences in the space and ground-based derived reddening curves between $0.28\,\mu$m and the $U$-band or in $R_V$. In total, we find 53 stars with one or more reddening curves passing the rejection criteria. This provides the highest quality Milky Way reddening curve sample available today. Averaging the curves from our high-quality sample, we find $R_V = 3.1 \pm 0.4$, confirming previous estimates. A future paper in this series will use the current sample of precise reddening curves and combine them with polarisation data to study the properties of Dark Dust., Comment: Recommended to acceptance by A&A

We present a general framework on how the polarization of radiation due to scattering, dichroic extinction, and birefringence of aligned spheroidal dust grains can be implemented and tested in 3D Monte Carlo radiative transfer (MCRT) codes. We derive a methodology for solving the radiative transfer equation governing the changes of the Stokes parameters in dust-enshrouded objects. We utilize the M\"uller matrix, and the extinction, scattering, linear, and circular polarization cross sections of spheroidal grains as well as electrons. An established MCRT code is used and its capabilities are extended to include the Stokes formalism. We compute changes in the polarization state of the light by scattering, dichroic extinction, and birefringence on spheroidal grains. The dependency of the optical depth and the albedo on the polarization is treated. The implementation of scattering by spheroidal grains both for random walk steps as well as for directed scattering (peel-off) are described. The observable polarization of radiation of the objects is determined through an angle binning method for photon packages leaving the model space as well as through an inverse ray-tracing routine for the generation of images. We present paradigmatic examples for which we derive analytical solutions of the optical light polarization by spheroidal dust particles. These tests are suited for benchmark verification of MCpol and other such codes, and allow to quantify the numerical precision reached. We demonstrate that MCpol is in excellent agreement to within 0.1% of the Stokes parameters when compared to the analytical solutions., Comment: A&A accepted by Editor

The paper describes profile broadening and peak wavelength variation of diffuse interstellar bands (DIBs) measured for 46 lines of sight, probably caused by physical properties of intervening clouds. Full width at half maximum of four studied diffuse bands (5780, 5797, 6196 and 6614 \AA) demonstrate strong variability sometimes doubling the features' width. Despite the high magnitude of the effect, our current analysis is restricted to the strongest diffuse bands because the weaker ones require a much higher S/N ratio. The profile broadening in the studied DIBs moves the profile's centers towards longer wavelengths, probably due to the excitation of higher levels of the P branch of the unknown molecular carrier. Moreover, diffuse bands are broader in clouds with abundantly populated vibrationally excited states of the hydrogen molecules, i.e. DIB's broadening correlates with the rotational temperature estimated on H$_2$ $\nu$=2 vibrational level. However, objects demonstrating extremely broadened profiles of DIBs are scarce. The extreme peculiarity of DIBs' profiles was detected in Herschel~36. Here we show the gradual growths of the widths of diffuse bands, confirmed in spectra from different instruments., Comment: 8 pages, 9 figures

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

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

The FORS Upgrade project (FORS-Up) aims at bringing a new life to the highly demanded workhorse instrument attached to ESO's Very Large Telescope (VLT). FORS2 is a multimode optical instrument, which started regular science operations in 2000 and since then, together with its twin, FORS1, has been one of the most demanded and most productive instruments of the VLT. In order to ensure that a FORS shall remain operational for at least another 15 years, an upgrade has been planned. This is required as FORS2 is using technology and software that is now obsolete and cannot be put and maintained to the standards in use at the Observatory. The project - carried out as a collaboration between ESO and INAF-Astronomical Observatory of Trieste - aims at bringing to the telescope in 2023/2024 a refurbished instrument with a new scientific detector, an upgrade of the instrument control software and electronics, a new calibration unit, as well as additional filters and grisms. The new FORS will also serve as a test bench for the Extremely Large Telescope (ELT) standard technologies (among them the use of programmable logic controllers and of the features of the ELT Control Software). The project aims at minimising the downtime of the instrument by performing the upgrade on the currently decommissioned instrument FORS1 and retrofitting the Mask Exchange Unit and polarisation optics from FORS2 to FORS1., Comment: Author version of a paper presented at SPIE Ground-based and Airborne Instrumentation for Astronomy VIII; corrected one statement

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

The precise characteristics of clouds and the nature of dust in the diffuse interstellar medium can only be extracted by inspecting the rare cases of single-cloud sightlines. In our nomenclature such objects are identified by interstellar lines, such as K I, that show at a resolving power of $\lambda /\Delta \lambda \sim 75,000$ one dominating Doppler component that accounts for more than half of the observed column density. We searched for such sightlines using high-resolution spectroscopy towards reddened OB stars for which far-UV extinction curves are known. We compiled a sample of 186 spectra, 100 of which were obtained specifically for this project with UVES. In our sample we identified 65 single-cloud sightlines, about half of which were previously unknown. We used the CH/CH$^+$ line ratio of our targets to establish whether the sightlines are dominated by warm or cold clouds. We found that CN is detected in all cold (CH/CH$^+ >1$) clouds, but is frequently absent in warm clouds. We inspected the WISE ($3-22\, \mu$m) observed emission morphology around our sightlines and excluded a circumstellar nature for the observed dust extinction. We found that most sightlines are dominated by cold clouds that are located far away from the heating source. For 132 stars, we derived the spectral type and the associated spectral type-luminosity distance. We also applied the interstellar Ca II distance scale, and compared these two distance estimates with GAIA parallaxes. These distance estimates scatter by 40%. By comparing spectral type-luminosity distances with those of GAIA, we detected a hidden dust component that amounts to a few mag of extinction for eight sightlines. This Dark Dust is populated by $\ge 1 \mu$m large grains and predominately appears in the field of the cold interstellar medium., Comment: acceppted by A&A

The search for extrasolar planets has driven rapid advances in instrumentation, resulting in cameras such as SPHERE at the VLT, GPI at Gemini South and SCExAO at Subaru, capable of achieving very high contrast ($\sim10^{6}$) around bright stars with small inner working angles ($\sim 0\farcs{1}$). The optimal exploitation of data from these instruments depends on the availability of easy-to-use software to process and analyse their data products. We present a pure-python pipeline, {\sc precision}, which provides fast, memory-efficient reduction of data from the SPHERE/IRDIS near-infrared imager, and can be readily extended to other instruments. We apply {\sc precision} to observations of the extreme red supergiant VX~Sgr, the inner outflow of which is revealed to host complex, asymmetric structure in the near-IR. In addition, optical polarimetric imaging reveals clear extended polarised emission on $\sim0.5^{\prime\prime}$ scales which varies significantly with azimuth, confirming the asymmetry. While not conclusive, this could suggest that the ejecta are confined to a disc or torus, which we are viewing nearly face on, although other non-spherical or clumpy configurations remain possible. VX~Sgr has no known companions, making such a geometry difficult to explain, as there is no obvious source of angular momentum in the system., Comment: 13 pages, 5 figures. Accepted by MNRAS

RefPlanets is a guaranteed time observation (GTO) programme that uses the Zurich IMaging POLarimeter (ZIMPOL) of SPHERE/VLT for a blind search for exoplanets in wavelengths from 600-900 nm. The goals of this study are the characterization of the unprecedented high polarimetic contrast and polarimetric precision capabilities of ZIMPOL for bright targets, the search for polarized reflected light around some of the closest bright stars to the Sun and potentially the direct detection of an evolved cold exoplanet for the first time. For our observations of Alpha Cen A and B, Sirius A, Altair, Eps Eri and Tau Ceti we used the polarimetric differential imaging (PDI) mode of ZIMPOL which removes the speckle noise down to the photon noise limit for angular separations >0.6". We describe some of the instrumental effects that dominate the noise for smaller separations and explain how to remove these additional noise effects in post-processing. We then combine PDI with angular differential imaging (ADI) as a final layer of post-processing to further improve the contrast limits of our data at these separations. For good observing conditions we achieve polarimetric contrast limits of 15.0-16.3 mag at the effective inner working angle of about 0.13", 16.3-18.3 mag at 0.5" and 18.8-20.4 mag at 1.5". The contrast limits closer in (<0.6") depend significantly on the observing conditions, while in the photon noise dominated regime (>0.6"), the limits mainly depend on the brightness of the star and the total integration time. We compare our results with contrast limits from other surveys and review the exoplanet detection limits obtained with different detection methods. For all our targets we achieve unprecedented contrast limits. Despite the high polarimetric contrasts we are not able to find any additional companions or extended polarized light sources in the data that has been taken so far., Comment: 23 pages, 17 figures, 2 table, Accepted for publication in A&A

Observations of circumstellar environments to look for the direct signal of exoplanets and the scattered light from disks has significant instrumental implications. In the past 15 years, major developments in adaptive optics, coronagraphy, optical manufacturing, wavefront sensing and data processing, together with a consistent global system analysis have enabled a new generation of high-contrast imagers and spectrographs on large ground-based telescopes with much better performance. One of the most productive is the Spectro-Polarimetic High contrast imager for Exoplanets REsearch (SPHERE) designed and built for the ESO Very Large Telescope (VLT) in Chile. SPHERE includes an extreme adaptive optics system, a highly stable common path interface, several types of coronagraphs and three science instruments. Two of them, the Integral Field Spectrograph (IFS) and the Infra-Red Dual-band Imager and Spectrograph (IRDIS), are designed to efficiently cover the near-infrared (NIR) range in a single observation for efficient young planet search. The third one, ZIMPOL, is designed for visible (VIR) polarimetric observation to look for the reflected light of exoplanets and the light scattered by debris disks. This suite of three science instruments enables to study circumstellar environments at unprecedented angular resolution both in the visible and the near-infrared. In this work, we present the complete instrument and its on-sky performance after 4 years of operations at the VLT., Comment: Final version accepted for publication in A&A

We present results of the analysis of a sample of 22 stars of spectral types from O7 to B5 and luminosity classes I-V for which Spitzer/IRS spectra are available. The IRS spectra of these stars are examined for signs of excess infrared (IR) emission by comparison with stellar atmospheric spectra. We find that the spectra of half of the studied stars are dominated by excess emission in the far-IR, including all six super- and bright giants. In order to examine the origin of the far-IR excess, we supplement the Spitzer data with optical high-resolution echelle spectroscopy ($\lambda/\Delta \lambda \sim 10^5$), near-IR high-contrast coronagraphic imaging taken with the SPHERE instrument at VLT with a spatial resolution of 0.05", and WISE and Herschel photometry. In the optical region, we detect various absorption and emission lines (H$\alpha$, CIII, and NIII) irrespective of the far-IR excess. Pfund($\alpha$) and Humphrey($\alpha$) lines are observed at the same time as the far-IR excess. These lines are stronger in stars with far-IR excess than in stars without excess. A scattered-light disk in the central r < 2.5" region of the far-IR excess stars HD149404, HD151804, and HD154368 can be excluded from H band imaging down to a 1$\sigma$ contrast of $F(r)/F_{*} \sim 10^{-6}$. The far-IR excess is fit either by a free-free component from ionized gas as for the winds of hot stars or a large (1pc) circumstellar dust shell. The putative dust envelopes required to explain the excess have a visual extinction as low as a few hundred $\mu$-mag., Comment: A&A accepted, 10 pages, 6 Figures, HR spectra availabe at CDS

We describe the Zurich Imaging Polarimeter (ZIMPOL), the visual focal plane subsystem of the SPHERE "VLT planet finder", which pushes the limits of current AO systems to shorter wavelengths, higher spatial resolution, and much improved polarimetric performance. We provide new benchmarks for the performance of high contrast instruments, in particular for polarimetric differential imaging. We have analyzed SPHERE/ZIMPOL point spread functions and measure the peak surface brightness, the encircled energy, and the full width half maximum (FWHM) for different wavelengths, atmospheric conditions, star brightness, and instrument modes. Coronagraphic images are described and analized and the performance for different coronagraphs is compared with tests for the binary alpha Hyi with a separation of 92 mas and a contrast of 6 mag. For the polarimetric mode we made the instrument calibrations using zero polarization and high polarization standard stars and here we give a recipe for the absolute calibration of polarimetric data. The data show a small <1 mas but disturbing differential polarimetric beam shifts, which can be explained as Goos-H\"ahnchen shifts from the inclined mirrors, and we discuss how to correct this effect. The polarimetric sensitivity is investigated with non-coronagraphic and deep, coronagraphic observations of the dust scattering around the symbiotic Mira variable R Aqr. SPHERE/ZIMPOL achieves imaging performances in the visual range with unprecedented characteristics, in particular very high spatial resolution and very high polarimetric contrast. This instrument opens up many new research opportunities for the detailed investigation of circumstellar dust, in scattered and therefore polarized light, for the investigation of faint companions, and for the mapping of circumstellar Halpha emission., Comment: 38 pages with 33 figurs, accepted for publication in Astron. Astrophys

It is well known that the dust properties of the diffuse interstellar medium exhibit variations towards different sight-lines on a large scale. We have investigated the variability of the dust characteristics on a small scale, and from cloud-to-cloud. We use low-resolution spectro-polarimetric data obtained in the context of the Large Interstellar Polarisation Survey (LIPS) towards 59 sight-lines in the Southern Hemisphere, and we fit these data using a dust model composed of silicate and carbon particles with sizes from the molecular to the sub-micrometre domain. Large (> 6 nm) silicates of prolate shape account for the observed polarisation. For 32 sight-lines we complement our data set with UVES archive high-resolution spectra, which enable us to establish the presence of single-cloud or multiple-clouds towards individual sight-lines. We find that the majority of these 35 sight-lines intersect two or more clouds, while eight of them are dominated by a single absorbing cloud. We confirm several correlations between extinction and parameters of the Serkowski law with dust parameters, but we also find previously undetected correlations between these parameters that are valid only in single-cloud sight-lines. We find that interstellar polarisation from multiple-clouds is smaller than from single-cloud sight-lines, showing that the presence of a second or more clouds depolarises the incoming radiation. We find large variations of the dust characteristics from cloud-to-cloud. However, when we average a sufficiently large number of clouds in single-cloud or multiple-cloud sight-lines, we always retrieve similar mean dust parameters. The typical dust abundances of the single-cloud cases are [C]/[H] = 92 ppm and [Si]/[H] = 20 ppm., Comment: A&A accepted

Polarimetric studies of light transmitted through interstellar clouds may give constraints on the properties of the interstellar dust grains. Traditionally, broadband linear polarisation (BBLP) measurements have been considered an important diagnostic tool for the study of the interstellar dust, while comparatively less attention has been paid to spectropolarimetric measurements. However, spectropolarimetry may offer stronger constraints than BBLP, for example by revealing narrowband features, and by allowing us to distinguish the contribution of dust from the contribution of interstellar gas. Therefore, we have decided to carry out a Large Interstellar Polarisation Survey (LIPS) using spectropolarimetric facilities in both hemispheres. Here we present the results obtained in the Southern Hemisphere with the FORS2 instrument of the ESO Very Large Telescope. Our spectra cover the wavelength range 380--950\,nm at a spectral resolving power of about 880. We have produced a publicly available catalogue of 127 linear polarisation spectra of 101 targets. We also provide the Serkowski-curve parameters, as well as the wavelength gradient of the polarisation position angle for the interstellar polarisation along 76 different lines of sight. In agreement with previous literature, we found that the best-fit parameters of the Serkowski-curve are not independent of each other. However, the relationships that we obtained are not always consistent with what was found in previous studies., Comment: Accepted by A&A (replaced on 12 October 2017 simply to correct a Metadata error)

We present observations of the known edge-on debris disk around HIP 79977 (HD 146897, F star in Upper Sco, 123 pc), taken with the ZIMPOL differential polarimeter of the SPHERE instrument in the Very Broad Band filter ($\lambda_c=735$ nm, $\Delta\lambda=290$ nm) with a spatial resolution of about 25 mas. We measure the polarization flux along and perpendicular to the disk spine of the highly inclined disk for projected separations between 0.2" (25 AU) and 1.6" (200 AU) and investigate the diagnostic potential of such data with model simulations. The polarized flux contrast ratio for the disk is $F_{pol}/F_\ast= (5.5 \pm 0.9) 10^{-4}$. The surface brightness reaches a maximum of 16.2 mag arcsec$^{-2}$ at a separation of $0.2"-0.5"$ along the disk spine with a maximum surface brightness contrast of 7.64 mag arcsec$^{-2}$. The polarized flux has a minimum near the star $<0.2"$ because no or only little polarization is produced by forward or backward scattering in the disk section lying in front of or behind the star. The data are modeled as a circular dust belt with an inclination $i=85(\pm 1.5)^\circ$ and a radius between $r_0$ = 60 AU and 90 AU. The radial density dependence is described by $(r/r_0)^{\alpha}$ with a steep power law index $\alpha=5$ inside $r_0$ and a more shallow index $\alpha=-2.5$ outside $r_0$. The scattering asymmetry factor lies between $g$ = 0.2 and 0.6 adopting a scattering angle-dependence for the fractional polarization as for Rayleigh scattering. Our data are qualitatively very similar to the case of AU Mic and they confirm that edge-on debris disks have a polarization minimum at a position near the star and a maximum near the projected separation of the main debris belt. The comparison of the polarized flux contrast ratio $F_{pol}/F_{\ast}$ with the fractional infrared excess provides strong constraints on the scattering albedo of the dust., Comment: Corrected typos, changed affiliation

We present polarisation spectra of seven stars in the lines-of-sight towards the Sco OB1 association. Our spectra were obtained within the framework of the Large Interstellar Polarization Survey carried out with the FORS instrument of the ESO VLT. We have modelled the wavelength-dependence of extinction and linear polarisation with a dust model for the diffuse interstellar medium which consists of a mixture of particles with size ranging from the molecular domain of 0.5 nm up to 350 nm. We have included stochastically heated small dust grains with radii between 0.5 and 6 nm made of graphite and silicate, as well as polycyclic aromatic hydrocarbon molecules (PAHs), and we have assumed that larger particles are prolate spheroids made of amorphous carbon and silicate. Overall, a dust model with eight free parameters best reproduces the observations. Reducing the number of free parameters leads to results that are inconsistent with cosmic abundance constraints. We found that aligned silicates are the dominant contributor to the observed polarisation, and that the polarisation spectra are best-fit by a lower limit of the equivolume sphere radius of aligned grains of 70 - 200nm., Comment: Planetary and Space Science, Planetary and Space Science, DOI:10.1016/j.pss.2017.05.007

R Aqr is a symbiotic binary system consisting of a mira variable, a hot companion with a spectacular jet outflow, and an extended emission line nebula. We have used R Aqr as test target for the visual camera subsystem ZIMPOL, which is part of the new extreme adaptive optics (AO) instrument SPHERE at the Very Large Telescope (VLT). We compare our observations with data from the Hubble Space Telescope (HST) and illustrate the complementarity of the two instruments. We determine from the Halpha emission the position, size, geometric structure, and line fluxes of the jet source and the clouds in the innermost region (<2") of R Aqr and determine Halpha emissivities mean density, mass, recombination time scale, and other cloud parameters. Our data resolve for the first time the R Aqr binary and we measure for the jet source a relative position 46+/-1 mas West of the mira. The central jet source is the strongest Halpha component. North east and south west from the central source there are many clouds with very diverse structures. We see in the SW a string of bright clouds arranged in a zig-zag pattern and, further out, more extended bubbles. In the N and NE we see a bright, very elongated filamentary structure and faint perpendicular "wisps" further out. Some jet clouds are also detected in the ZIMPOL [OI] and He I filters, as well as in the HST line filters for Halpha, [OIII], [NII], and [OI]. We determine jet cloud parameters and find a very well defined anti-correlation between cloud density and distance to the central binary. Future Halpha observations will provide the orientation of the orbital plane of the binary and allow detailed hydrodynamical investigations of this jet outflow and its interaction with the wind of the red giant companion., Comment: 24 pages, 14 figures (accepted for publication in Astronomy and Astrophysics)

We present high-angular (0.17$-$0.35 arcsec) resolution imaging polarimetric observations of Mrk 231 in the 3.1 $\mu$m filter using MMT-Pol on the 6.5-m MMT, and in the 8.7 $\mu$m, 10.3 $\mu$m, and 11.6 $\mu$m filters using CanariCam on the 10.4-m Gran Telescopio CANARIAS. In combination with already published observations, we compile the 1$-$12 $\mu$m total and polarized nuclear spectral energy distribution (SED). The total flux SED in the central 400 pc is explained as the combination of 1) a hot (731 $\pm$ 4 K) dusty structure, directly irradiated by the central engine, which is at 1.6 $\pm$ 0.1 pc away and attributed to be in the pc-scale polar region, 2) an optically-thick, smooth and disk-like dusty structure (`torus') with an inclination of 48 $\pm$ 23$^{\circ}$ surrounding the central engine, and 3) an extinguished (A$_{\mbox{V}} =$ 36 $\pm$ 5 mag) starburst component. The polarized SED decreases from 0.77 $\pm$ 0.14 per cent at 1.2 $\mu$m to 0.31 $\pm$ 0.15 per cent at 11.6 $\mu$m and follows a power-law function, $\lambda^{\sim0.57}$. The polarization angle remains constant ($\sim$108$^{\circ}$) in the 1$-$12 $\mu$m wavelength range. The dominant polarization mechanism is explained as scattering off hot dust grains in the pc-scale polar regions., Comment: 9 pages, 2 figures. Accepted for publication in MNRAS

Context: In the last years, there have been many studies on the omnipresence and structures of filaments in star-forming regions, as well as their role in the process of star formation. Those filaments are normally identified as elongated fibres across the plane of the sky. But how would we detect filaments that are inclined? Aims: We aim to learn more about whether, and how, total column density or dust temperature change with respect to the line of sight. Such variations would enable observers to use dust observations to identify and study filaments at any inclination and gain more insight on the distribution and orientations of filaments within the Galactic plane. Methods: As a first step, we perform numerical calculations on simple cylindrical models to evaluate the influence of filament geometry on the average flux density. After that, we apply our three-dimensional Monte Carlo dust radiative transfer code on two models of star-forming regions and derive maps of effective total column density and dust temperature at different viewing angles. Results: We see only slight changes of average flux density for all cylinders we study. For our more complex models, we find that the effective dust temperature is not sensitive to viewing angle, while the total column density is strongly influenced, with differences exceeding an order of magnitude. The variations are not injective with the viewing angle and depend on the structure of the object. Conclusions: We conclude that there is no single quantity in our analysis that can uniquely trace the inclination and three-dimensional structure of a filament based on dust observations alone. However, observing wide variations in total column density at a given effective dust temperature is indicative of inclined filaments., Comment: 19 pages, 20 figures, accepted by A&A

Massive stars live short lives, losing large amounts of mass through their stellar wind. Their mass is a key factor determining how and when they explode as supernovae, enriching the interstellar medium with heavy elements and dust. During the red supergiant phase, mass-loss rates increase prodigiously, but the driving mechanism has proven elusive. Here we present high-contrast optical polarimetric-imaging observations of the extreme red supergiant VY Canis Majoris and its clumpy, dusty, mass-loss envelope, using the new extreme-adaptive-optics instrument SPHERE at the VLT. These observations allow us to make the first direct and unambiguous detection of submicron dust grains in the ejecta; we derive an average grain radius $\sim$ 0.5 $\mu$m, 50 times larger than in the diffuse ISM, large enough to receive significant radiation pressure by photon scattering. We find evidence for varying grain sizes throughout the ejecta, highlighting the dynamical nature of the envelope. Grains with 0.5 $\mu$m sizes are likely to reach a safe distance from the eventual explosion of VY Canis Majoris; hence it may inject upwards of 10$^{-2}$ M$_\odot$ of dust into the ISM., Comment: 5 pages, 3 figures. Accepted as a letter to A&A. Press release available at: http://www.eso.org/public/news/eso1546/

(abridged) The dust content of the universe is primarily explored via its interaction with stellar photons, producing interstellar extinction. However, owing to the physical extension of the observing beam, observations may detect scattered photons, resulting in a change in the observed (or effective) extinction, depending on the spatial distribution of the dust and the resolution of the instrument. We investigate the influence of clumpy dust distributions on effective extinction toward embedded sources and those in the diffuse ISM. We use Monte Carlo radiative transfer to examine effective extinction for various geometries. By varying the number, optical depth and volume-filling factor of clumps in models of spherical shells and the diffuse ISM, we explore the evolution of extinction. Depending on the number of scattering events in the beam, the extinction curve steepens in homogeneous media and flattens in clumpy media. As a result, clumpy dust distributions can to reproduce extinction curves with arbitrary R_v, the effective ratio of total-to-selective extinction. The flattening `washes out' the 2175 \AA bump and shifts the peak to shorter wavelengths. The mean R_v of a shell correlates with the optical depth of an individual clump and the wavelength at which a clump becomes optically thick. Similar behaviour is seen for edge-on discs or tori. However, at grazing inclinations the combination of extinction and strong forward scattering results in chaotic behaviour. Caution is therefore advised when measuring extinction in, for example, AGN tori or toward SNIa or GRB afterglows. In face-on discs, the shape of the scattered continuum changes with clumpiness, however, unlike absorption features, individual features in the scattering cross-sections are preserved. Finally, we show that diffuse interstellar extinction is not modified by scattering on scales of a few kpc., Comment: 12 pages, 15 figures; A&A, accepted

We present Herschel (PACS and SPIRE) far-infrared (FIR) photometry of a complete sample of z>1 3CR sources, from the Herschel GT project The Herschel Legacy of distant radio-loud AGN (PI: Barthel). Combining these with existing Spitzer photometric data, we perform an infrared (IR) spectral energy distribution (SED) analysis of these landmark objects in extragalactic research to study the star formation in the hosts of some of the brightest active galactic nuclei (AGN) known at any epoch. Accounting for the contribution from an AGN-powered warm dust component to the IR SED, about 40% of our objects undergo episodes of prodigious, ULIRG-strength star formation, with rates of hundreds of solar masses per year, coeval with the growth of the central supermassive black hole. Median SEDs imply that the quasar and radio galaxy hosts have similar FIR properties, in agreement with the orientation-based unification for radio-loud AGN. The star-forming properties of the AGN hosts are similar to those of the general population of equally massive non-AGN galaxies at comparable redshifts, thus there is no strong evidence of universal quenching of star formation (negative feedback) within this sample. Massive galaxies at high redshift may be forming stars prodigiously, regardless of whether their supermassive black holes are accreting or not., Comment: 30 pages, 13 figures, 4 tables. Accepted for publication in A&A

We present Gran Telescopio CANARIAS CanariCam 8.7$\mu$m imaging and 7.5-13$\mu$m spectroscopy of six local systems known to host an active galactic nucleus (AGN) and have nuclear star formation. Our main goal is to investigate whether the molecules responsible for the 11.3$\mu$m polyclyclic aromatic hydrocarbon (PAH) feature are destroyed in the close vicinity of an AGN. We detect 11.3$\mu$m PAH feature emission in the nuclear regions of the galaxies as well as extended PAH emission over a few hundred parsecs. The equivalent width (EW) of the feature shows a minimum at the nucleus but increases with increasing radial distances, reaching typical star-forming values a few hundred parsecs away from the nucleus. The reduced nuclear EW are interpreted as due to increased dilution from the AGN continuum rather than destruction of the PAH molecules. We conclude that at least those molecules responsible for the 11.3$\mu$m PAH feature survive in the nuclear environments as close as 10pc from the AGN and for Seyfert-like AGN luminosities. We propose that material in the dusty tori, nuclear gas disks, and/or host galaxies of AGN is likely to provide the column densities necessary to protect the PAH molecules from the AGN radiation field., Comment: Accepted for publication in MNRAS, 19 pages, 13 figures

We present a revised model for the infrared emission of the hyperluminous infrared galaxy IRAS F10214+4724 which takes into account recent photometric data from Spitzer and Herschel that sample the peak of its spectral energy distribution. We first present and discuss a grid of smooth active galactic nucleus (AGN) torus models computed with the method of Efstathiou & Rowan-Robinson and demonstrate that the combination of these models and the starburst models of Efstathiou and coworkers, while able to give an excellent fit to the average spectrum of Seyfert 2s and spectra of individual type 2 quasars measured by Spitzer, fails to match the spectral energy distribution of IRAS F10214+4724. This is mainly due to the fact that the nuSnu distribution of the galaxy falls very steeply with increasing frequency (a characteristic that is usually indicative of heavy absorption by dust) but shows a silicate feature in emission. Such emission features are not expected in sources with optical/near-infrared type 2 AGN spectral signatures. The Herschel data show that there is more power emitted in the rest-frame 20-50um wavelength range compared with the model presented by Efstathiou which assumes three components of emission: an edge-on torus, clouds (at a temperature of 610 and 200K) that are associated with the narrow-line region (NLR) and a highly obscured starburst that dominates in the submillimetre. We present a revised version of that model that assumes an additional component of emission which we associate with NLR clouds at a temperature of 100K. The 100K dust component could also be explained by a highly obscured hot starburst. The model suggests that the NLR of IRAS F10214+4724 has an unusually high covering factor (>= 17%) or more likely the magnification of the emission from the NLR clouds is significantly higher than that of the emission from the torus., Comment: MNRAS accepted. The AGN torus and starburst models used here and in 1309.7005 are available on request

We present a model for the diffuse interstellar dust that explains the observed wavelength-dependence of extinction, emission, linear and circular polarisation of light. The model is set-up with a small number of parameters. It consists of a mixture of amorphous carbon and silicate grains with sizes from the molecular domain of 0.5 up to about 500nm. Dust grains with radii larger than 6nm are spheroids. Spheroidal dust particles have a factor 1.5 - 3 larger absorption cross section in the far IR than spherical grains of the same volume. Mass estimates derived from submillimeter observations that ignore this effect are overestimated by the same amount. In the presence of a magnetic field, spheroids may be partly aligned and polarise light. We find that polarisation spectra help to determine the upper particle radius of the otherwise rather unconstrained dust size distribution. Stochastically heated small grains of graphite, silicates and polycyclic aromatic hydrocarbons (PAHs) are included. We tabulate parameters for PAH emission bands in various environments. They show a trend with the hardness of the radiation field that can be explained by the ionisation state or hydrogenation coverage of the molecules. For each dust component its relative weight is specified, so that absolute element abundances are not direct input parameters. The model is confronted with the average properties of the Milky Way, which seems to represent dust in the solar neighbourhood. It is then applied to four specific sight lines including the reflection nebula NGC2023. For these sight lines, we present linear and circular spectro-polarimetric observations obtained with FORS/VLT. Using prolate rather than oblate grains gives a better fit to observed spectra; the axial ratio of the spheroids is typically two and aligned silicates are the dominant contributor to the polarisation., Comment: accepted by A&A Editor

We present observations and models for one of these MYSO candidates, NGC3603 IRS 9A. Our goal is to investigate with infrared interferometry the structure of IRS 9A on scales as small as 200AU, exploiting the fact that a cluster of O and B stars has blown away much of the obscuring foreground dust and gas. Observations in the N-band were carried out with the MIDI beam combiner attached to the VLTI. Additional interferometric observations which probe the structure of IRS 9A on larger scales were performed with an aperture mask installed in the T-ReCS instrument of Gemini South. The spectral energy distribution (SED) is constrained by the MIDI N-band spectrum and by data from the Spitzer Space Telescope. Our efforts to model the structure and SED of IRS 9A range from simple geometrical models of the brightness distribution to one- and two-dimensional radiative transfer computations. The target is resolved by T-ReCS, with an equivalent (elliptical) Gaussian width of 330mas by 280mas (2300 AU by 2000 AU). Despite this fact, a warm compact unresolved component was detected by MIDI which is possibly associated with the inner regions of a flattened dust distribution. Based on our interferometric data, no sign of multiplicity was found on scales between about 200AU and 700AU projected separation. A geometric model consisting of a warm (1000 K) ring (400 AU diameter) and a cool (140 K) large envelope provides a good fit to the data. No single model fitting all visibility and photometric data could be found, with disk models performing better than spherical models. While the data are clearly inconsistent with a spherical dust distribution they are insufficient to prove the existence of a disk but rather hint at a more complex dust distribution., Comment: 8 pages, 11 figures. Accepted for publication in A&A

We present a technique to synthesise telluric absorption and emission features both for in-situ wavelength calibration and for their removal from astronomical spectra. While the presented technique is applicable for a wide variety of optical and infrared spectra, we concentrate in this paper on selected high-resolution near-infrared spectra obtained with the CRIRES spectrograph to demonstrate its performance and limitation. We find that synthetic spectra reproduce telluric absorption features to about 2%, even close to saturated line cores. Thus, synthetic telluric spectra could be used to replace the observation of telluric standard stars, saving valuable observing time. This technique also provides a precise in-situ wavelength calibration, especially useful for high-resolution near-infrared spectra in the absence of other calibration sources., Comment: 11 pages, 11 figures, accepted for publication in A&A (updated version)

Using the Spitzer Space Telescope, we have obtained rest frame 9-16mu spectra of 11 quasars and 9 radio galaxies from the 3CRR catalog at redshifts 1.0

Mid-infrared imaging at resolutions of 300 mas of the central kpc region of 13 nearby, well-known active galaxies is presented. The bulk of the mid-IR emission is concentrated on an unresolved central source within a size of less than 5 to 130 pc, depending on the object distance. Further resolved emission is detected in 70% of the sample in the form of circumnuclear star-forming rings or diffuse nuclear extended emission. In the three cases with circumnuclear star formation, the stellar contribution is at least as important as that of the AGN. In those with extended nuclear emission -- a third of the sample -- this emission represents a few per cent of the total measured; however, this contribution may be underestimated because of the chopped nature of these observations. This extended emission is generally collimated in a preferential direction often coinciding with that of the extended ionized gas or the jet. In all cases, the nuclear fluxes measured at 11.8 and 18.7 micron represent a minor contribution of the flux levels measured by large aperture IRAS data at the nearest energy bands of 12 and 25 micron. This contribution ranges from 30% to less than 10%. In only three cases do the AGN fluxes agree with IRAS to within a factor of 2. In the AGNs with strong circumnuclear star formation, this component can well account for most of the IRAS flux measured in these objects. But in all other cases, either a low surface brightness component extending over galactic scales or strong extra-nuclear IR sources -- e.g. HII regions in spiral arms -- have to be the main source of the IRAS emission. In either case, the contribution of these components dwarfs that of the AGN at mid-IR wavelengths., Comment: 17 pages, 10 figures. Accepted for publication in MNRAS

Using the Spitzer Space Telescope, we have obtained 3.6--24 micron photometry of 38 radio galaxies and 24 quasars from the 3CR catalog at redshift 1

Dust enshrouded activity can ideally be studied by mid-infrared (MIR) observations. In order to explore the AGN versus star forming origin of the nuclear MIR emission of galaxies, observations of high spatial resolution are required. Here we report on 11.3mic. observations with VISIR at the VLT, reaching 0.35'' spatial resolution (FWHM). During the scientific verification of VISIR we have observed a sample of 36 nearby galaxies having a variety of optically classified nuclear activity: 17 black hole driven active galactic nuclei (AGN), 10 starbursts (SBs) and 9 quiet spirals. 16/17 AGN are detected and unresolved, 5/10 SBs are detected and resolved with structured emission up to a few arcsec, while for 5/10 SB and all 9 quiet nuclei low upper limits are provided. The morphology of the resolved SB nuclei follows that seen at radio frequencies. The compactness of AGN and the extent of the SB nuclei is consistent with predictions from radiative transfer models and with MIR spectra of lower spatial resolution. We explore the nuclear MIR surface brightness as a quantitative measure. While AGN and SB cannot be distinguished with MIR data from 4m class telescopes, our data provide evidence that, up to a distance of 100 Mpc, AGN and SB can well be separated by means of MIR surface brightness when using 8m class telescopes., Comment: accepted by A&A: 14 pages, 5 Figures; rsiebenm@eso.org

We present a refined orbital solution for the components A, B, and C of the nearby late-M type multiple system LHS 1070. By combining astrometric datapoints from NACO/VLT, CIAO/SUBARU, and PUEO/CFHT, as well as a radial velocity measurement from the newly commissioned near infrared high-resolution spectrograph CRIRES/VLT, we achieve a very precise orbital solution for the B and C components and a first realistic constraint on the much longer orbit of the A-BC system. Both orbits appear to be co-planar. Masses for the B and C components calculated from the new orbital solution (M_(B+C) = 0.157 +/- 0.009 M_sun) are in excellent agreement with theoretical models, but do not match empirical mass-luminosity tracks. The preliminary orbit of the A-BC system reveals no mass excess for the A component, giving no indication for a previously proposed fourth (D) component in LHS 1070., Comment: published in A&A, 2008, 484, 429; added CFHT acknowledgement

In the course of the NIR/MIR AGN search combining the 6.7 mu ISOCAM Parallel Survey and 2MASS we have discovered 24 type-1 quasars about a third of which are too red to be discriminated by optical/UV search techniques. Here we report on a detailed case study of the reddest type-1 quasar of our sample (J2341) at redshift z=0.236 with M_K=-25.8 and J-K=1.95. We performed spectroscopy in the optical with VLT/FORS1 and in the MIR with Spitzer as well as NIR imaging with ISPI at CTIO. The optical and NIR observations reveal a star forming emission-line galaxy at the same redshift as the quasar with a projected linear separation of 1.8 arcsec (6.7 kpc). The quasar and its companion are embedded in diffuse extended continuum emission. Compared with its companion the quasar exhibits redder optical-NIR colours, which we attribute to hot nuclear dust. The MIR spectrum shows only few emission lines superimposed on a power-law spectral energy distribution. However, the lack of strong FIR emission suggests that our potentially interacting object contains much less gas and dust and is in a stage different from dust reddened ULIRG-AGN like Mrk 231. The optical spectrum shows signatures for reddening in the emission-lines and no post-starburst stellar population is detected in the host galaxy of the quasar. The optical continuum emission of the active nucleus appears absorbed and diluted. Even the combination of absorption and host dilution is not able to match J2341 with standard quasar templates. While the BLR shows only a rather moderate absorption of E_(B-V)=0.3, the continuum shorter than 4500 AA requires strong obscuration with E_(B-V)=0.7, exceeding the constraints from the low upper limit on the 9.7 mu silicate absorption. This leads us to conclude that the continuum of J2341 is intrinsically redder than that of typical quasars., Comment: 8 pages, 9 figures

OO Serpentis is a deeply embedded pre-main sequence star that went into outburst in 1995 and gradually faded afterwards. Its eruption resembled the well-known FU Orionis-type or EX Lupi-type outbursts. Since very few such events have ever been documented at infrared wavelengths, our aim is to study the temporal evolution of OO Ser in the infrared. OO Ser was monitored with the Infrared Space Observatory starting 4 months after peak brightness and covering 20 months. In 2004-2006 we again observed OO Ser from the ground and complemented this dataset with archival Spitzer obsevations also from 2004. We analysed these data with special attention to source confusion and constructed light curves at 10 different wavelengths as well as spectral energy distributions. The outburst caused brightening in the whole infrared regime. According to the infrared light curves, OO Ser started a wavelength-independent fading after peak brightness. Later the flux decay became slower but stayed wavelength-independent. The fading is still ongoing, and current fading rates indicate that OO Ser will not return to quiescent state before 2011. The outburst timescale of OO Ser seems to be shorter than that of FUors, but longer than that of EXors. The outburst timescale and the moderate luminosity suggest that OO Ser is different from both FUors and EXors, and shows similarities to the recently erupted young star V1647 Ori. Based on its spectral energy distribution and bolometric temperature, OO Ser seems to be an early class I object, with an age of < 10^5 yr. The object is probably surrounded by an accretion disc and a dense envelope. Due to the shorter outburst timescales, the viscosity in the circumstellar disc of OO Ser is probably an order of magnitude higher than usual for FUors., Comment: 12 pages, 7 figures, accepted for publication in A&A

Context: A long-standing challenge of observational AGN research is to find type 2 quasars, the luminous analogues of Seyfert-2 galaxies. Aims: We search for luminous narrow-line type 2 AGN, characterise their properties, and compare them with broad-line type 1 AGN. Methods: Combining the ISOCAM parallel survey at 6.7 mu with 2MASS, we have selected AGN via near-mid-infrared colours caused by the hot nuclear dust emission. We performed spectroscopy in the optical and, for a subset of the sample, also in the mid-infrared with Spitzer. Results: We find nine type 2 AGN at redshift 0.10.5 we did not find type 2 AGN, probably because the hottest dust emission, still covered by the NIR filters, is obscured. The optical spectra of the type 2 host galaxies show young and old stellar populations. Only one object is an ultraluminous infrared galaxy with starburst. The 5-38 mu spectra of the two type 2 sources observed show a strong continuum with PAH emission in one case and silicate absorption in the other case. Conclusions: The near-mid-infrared selection is a successful strategy to find luminous type 2 AGN at low z. The objects exhibit a large range of properties so that it is difficult to infer details by means of popular SED fitting with simple average templates., Comment: Accepted for publication in A&A

We investigate the morphology and the evolutionary stage of the hypercompact HII region M17-UC1 using observations at infrared wavelengths and NIR radiative transfer modeling. For the first time, this region is resolved into two emission areas separated by a dark lane reminiscent of an obscuring silhouette of a circumstellar disk. So far, the observational data as well as model calculations suggest that M17-UC1 is surrounded by a disk of cool dust. This direct direct detection of a circumstellar disk candidate around a hypercompact HII region is in agreement with the expectations of the disk accretion model for high-mass star formation., Comment: 4 pages, 3 figures, ApJL emulate style (accepted 19 Jan. 2007) to appear in 2007 ApJ Letters 656, No. 2

We present a high-resolution (R~16,000) spectrum and a narrow-band image centered on the [NeII]12.8 micron line of the central kpc region of the starburst/Seyfert2 galaxy NGC 7582. The galaxy has a rotating circum-nuclear starburst disk, shown at great detail at a diffraction-limited resolution of 0.4 arcsec. The high spatial resolution allows us to probe the dynamics of the [NeII] gas in the nuclear regions, and to estimate the mass of the central black hole. We construct models of gas disks rotating in the combined gravitational potential from the stellar bulge and a central black hole, and derive a black hole mass of 5.5 x 10^7 solar masses with a 95% confidence interval of [3.6,8.1] x 10^7 solar masses. The black hole mass combined with stellar velocity dispersion measurements from the literature shows that the galaxy is consistent with the local M-sigma relation. This is the first time that a black hole mass in a galaxy except our own Milky Way system has been estimated from gas dynamics in the mid-infrared. We show that spatially resolved mid-infrared spectroscopy may be competitive with similar techniques in the optical and near-infrared, and may prove to be important for estimating black hole masses in galaxies with strong nuclear dust obscuration. The high spectral resolution allows us to determine the heliocentric systemic velocity of the galaxy to between 1614 and 1634 km/s. The mid-infrared image reveals several dense knots of dust-embedded star formation in the circum-nuclear disk, and we briefly discuss its morphology., Comment: 11 pages, 7 figures, accepted for publication in A&A

We combined the ISOCAM Parallel Mode Survey at 6.7 micron (LW2 filter) with the Two Micron All Sky Survey in order to obtain a powerful tool to search for AGN independent of dust extinction. Using moderate colour criteria H-K>0.5 and K-LW2>2.7 we have selected a sample of 77 AGN candidates in an effective area of about 10 square degrees. By means of optical spectroscopy we find 24 (30%) type-1 QSOs at redshifts 0.10.8. About one third of the ISO-2MASS QSOs show so red optical colours, that they are missed in optical and UV AGN surveys like SDSS, 2DF, or HES. With a surface density of about 2 deg^(-2) down to R<18 mag the ISO-2MASS QSOs outnumber the 1.35 deg^(-2) of the SDSS quasar survey by 50%; we find a combined optical-IR QSO surface density of 2.7 deg^(-2). Since only two of the ISO-2MASS QSOs have also J-K>2, the inclusion of the ISO mid-infrared photometry significantly extends the capabilities of the pure 2MASS red AGN survey. We suggest that the newly found red AGN resemble young members of the quasar population, and that quasars spend much of their lifetime in a dust enshrouded phase., Comment: 5 pages, 5 figures, accepted for publication as A&A Letter

We present ISO mid-infrared spectrophotometry and far-infrared photometry of galaxies with Hidden Broad Line Regions (HBLR). We also present radiative transfer models of their spectral energy distributions which enable us to separate the contributions from the dusty disc of the AGN and the dusty starbursts. We find that the combination of tapered discs (discs whose thickness increases with distance from the central source in the inner part but stays constant in the outer part) and starbursts provide good fits to the data. The tapered discs dominate in the mid-infrared part of the spectrum and the starbursts in the far-infrared. After correcting the AGN luminosity for anisotropic emission we find that the ratio of the AGN luminosity to the starburst luminosity, L(AGN)/L(SB), ranges from about unity for IRAS14454-4343 to about 13 for IRAS01475-0740. Our results suggest that the warm IRAS colours of HBLR are due to the relatively high L(AGN)/L(SB). Our fits are consistent with the unified model and the idea that the infrared emission of AGN is dominated by a dusty disc in the mid-infrared and starbursts in the far-infrared., Comment: A&A accepeted, 8pages 2 Figures, final version

According to the unified scheme, AGN are surrounded by a dust-torus, and the observed diversity of AGN properties results from the different orientations relative to our line of sight. The strong resonance of silicate dust at 10 micron is therefore, as expected, seen in absorption towards many type-2 AGN. In type-1 AGN, it should be seen in emission because the hot inner surface of the dust torus becomes visible. However, this has not been observed so far, thus challenging the unification scheme or leading to exotic modifications of the dust-torus model. Here we report the discovery of the 10 micron silicate feature in emission in two luminous quasars with the Infrared Spectrograph of the Spitzer Space Telescope., Comment: accepted A&A Letters: 2 Fig., 4 pages

We have imaged $\epsilon$ Indi B, the closest brown dwarf binary known, with VISIR at the VLT in three narrow-band mid-infrared bandpasses located around 8.6$\mu$m, 10.5$\mu$m and 11.3$\mu$m. We are able to spatially resolve both components, and determine accurate mid-infrared photometry for both components independently. In particular, our VISIR observations probe the NH$_3$ feature in the atmospheres of the cooler and warmer brown dwarfs. For the first time, we can disentangle the contributions of the two components, and find that % our photometry of $\epsilon$ IndiBb is in good agreement with recent ``cloud-free'' atmosphere models having an effective temperature of $T_\mathrm{eff}=800$ K. With an assumed age of 1 Gyr for the $\epsilon$ Indi system, component Ba agrees more with $T_\mathrm{eff} \approx 1100$ K rather than with $T_\mathrm{eff}=1200$ K, as suggested by SPITZER spectroscopic observations of the combined $\epsilon$ Indi B system (Roellig et al., 2004). Even higher effective temperatures appear inconsistent with our absolute photometry, as they would imply an unphysical small size of the brown dwarf $\epsilon$ IndiBa., Comment: 4 pages, 2 figures

We compare three 3CR samples of 11 FR1 galaxies, 17 FR2 galaxies and 18 lobe-dominated quasars contained in the ISO Data Archive. In contrast to the powerful FR2 galaxies with edge-brightened lobes, the low radio power FR1 galaxies in our sample do not exhibit any high MIR or FIR dust luminosity, which is typical for a buried, intrinsically more luminous AGN. This consolidates the fact already inferred from optical studies that their AGNs have only a relatively low luminosity. Also the FR1 galaxies show a high FIR/MIR luminosity ratio, compared to quasars, suggesting that their FIR luminosity is substantially powered by the interstellar radiation field (ISRF) of the giant elliptical hosts. Finally, we discuss the FR1-FR2 morphological dichotomy. FR1 galaxies do not have more interstellar matter (ISM) than FR2s as traced -- on the large scale -- by the cool FIR emitting dust and -- in the nuclear region -- by the warm MIR emitting dust. Due to the lack of central gas we suggest that the black holes of our FR1 galaxies are fed at a lower accretion rate than those of the FR2 galaxies., Comment: 4 pages 3 figures Letter accepted by A&A