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, α Centauri. Based on 75-80% of the best quality images from 100 h of cumulative observations, we demonstrate sensitivity to warm sub-Neptune-sized planets throughout much of the habitable zone of α 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 α 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.
Context. Observations at various wavelengths of late B-type stars exhibiting strong atmospheric overabundances of the chemical elements Hg and Mn indicate that these stars are frequently found in ...binary and multiple systems. Aims. We intend to study the multiplicity of this type of chemically peculiar stars, looking for visual companions in the range of angular separation between 0″̣05 and 8″. Methods. We carried out a survey of 56 stars using diffraction-limited near-infrared imaging with NAOS-CONICA at the VLT. Results. Thirty-three companion candidates in 24 binaries, three triples, and one quadruple system were detected. Nine companion candidates were found for the first time in this study. Five objects are likely chance projections. The detected companion candidates have K magnitudes between 5ṃ95 and 18ṃ07 and angular separations ranging from < 0″̣05 to 7″̣8, corresponding to linear projected separations of 13.5–1700 AU. Conclusions. Our study clearly confirms that HgMn stars are frequently members of binary and multiple systems. Taking into account companions found by other techniques, the multiplicity fraction in our sample may be as high as 91%. The membership in binary and multiple systems seems to be a key point to understanding the abundance patterns in these stars.
We describe the design, development, and performance of HAWK-I, the new High-Acuity Wide-field K-band Imager for ESO's Very Large Telescope, which is equipped with a mosaic of four 2 k $\times$ 2 k ...arrays and operates from 0.9-2.4 μm over $7.5\arcmin \times 7.5\arcmin$ with 0.1´´ pixels. A novel feature is the use of all reflective optics that, together with filters of excellent throughput and detectors of high quantum efficiency, has yielded an extremely high throughput. Commissioning and science verification observations have already delivered a variety of excellent and deep images that demonstrate its high scientific potential for addressing important astrophysical questions of current interest.
We present near-infrared multi-object spectroscopy and JHKsubs imaging of the massive stellar content of the Galactic star-forming region W3 Main, obtained with LUCI at the Large Binocular Telescope. ...We confirm 15 OB stars in W3 Main and derive spectral types between 05V and B4V from their absorption line spectra. Three massive young stellar objects are identified by their emission line spectra and near-infrared excess. The color-color diagram of the detected sources allows a detailed investigation of the slope of the near-infrared extinction law toward W3 Main. From our spectrophotometric analysis of the massive stars and the nature of their surrounding H II regions, we derive the evolutionary sequence of W3 Main and we find evidence of an age spread of at least 2-3 Myr. We have detected the photospheres of OB stars from the more evolved diffuse H II region to the much younger UCH II regions, suggesting that these stars have finished their formation and cleared away their circumstellar disks very fast.
Many galaxies are thought to have supermassive black holes at their centres-more than a million times the mass of the Sun. Measurements of stellar velocities and the discovery of variable X-ray ...emission have provided strong evidence in favour of such a black hole at the centre of the Milky Way, but have hitherto been unable to rule out conclusively the presence of alternative concentrations of mass. Here we report ten years of high-resolution astrometric imaging that allows us to trace two-thirds of the orbit of the star currently closest to the compact radio source (and massive black-hole candidate) Sagittarius A*. The observations, which include both pericentre and apocentre passages, show that the star is on a bound, highly elliptical keplerian orbit around Sgr A*, with an orbital period of 15.2 years and a pericentre distance of only 17 light hours. The orbit with the best fit to the observations requires a central point mass of (3.7 ± 1.5) × 106 solar masses (M ). The data no longer allow for a central mass composed of a dense cluster of dark stellar objects or a ball of massive, degenerate fermions.
We use HAWK-I, the recently-commissioned near-IR imager on Yepun (VLT- UT4), to obtain wide-field, high-resolution images of the X-ray luminous galaxy cluster XMMU J2235.3-2557 in the J and K s ...bands, and we use these images to build a colour-magnitude diagram of cluster galaxies. Galaxies in the core of the cluster form a tight red sequence with a mean J-K s colour of 1.9 (Vega system). The intrinsic scatter in the colour of galaxies that lie on the red sequence is similar to that measured for galaxies on the red sequence of the Coma cluster. The slope and location of the red sequence can be modelled by passively evolving the red sequence of the Coma cluster backwards in time. Using simple stellar population (SSP) models, we find that galaxies in the core of XMMU J2235.3-2557 are, even at z =1.39, already 3 Gyr old, corresponding to a formation redshift of z_{f} sim 4. Outside the core, the intrinsic scatter and the fraction of galaxies actively forming stars increase substantially. Using SSP models, we find that most of these galaxies will join the red sequence within 1.5 Gyr. The contrast between galaxies in the cluster core and galaxies in the cluster outskirts indicates that the red sequence of XMMU J2235.3-2557 is being built from the dense cluster core outwards.
•The optical chain mockup of ITER spectroscopy was manufactured, aligned and tested.•The measured spatial resolution at the object plane is 6.8–9 mm.•The system keeps the required image quality under ...shift/tilt of vacuum components.•Calibration of the optical path can be carried out with additional optical fiber.
H-alpha and Visible Spectroscopy is one of the ITER first-plasma diagnostics providing full poloidal coverage of plasma scrape-off layer near the first wall. There are two poloidal-view channels in Equatorial Port Plug 11 (EPP11), one tangential-view channel in Equatorial Port Plug 12 (EPP12), and one divertor-view channel in Upper Port Plug 02 (UPP02). At the moment, the final design phase is ongoing, requiring proper testing of design solutions to identify the realistic optical parameters and the problems related to the manufacturing, alignment, calibration and stability issues. A full-scale mockup of the whole optical chain has been built for this purpose. It comprises the most important units starting from the in-vessel optical front-end (First Mirror Unit) to the Interspace relay optics (Long-Focus Spectral Telescope), and to the Optical Bench Assembly located in the Port Cell, where the collected light is coupled to the imaging cameras and to the complex optical fiber bundle transmitting it to the various detectors and spectrometers to be located in the ITER Diagnostic Building. The detailed optical design, analyses, benchmarking and test results are reported with a main focus on the alignment/calibration issues, and on the spatial resolution measured. The measurements have been performed in the wide spectral range 450–700 nm, which is required for the monitoring of the H-alpha, Beryllium and other impurity emission line profiles with probable local peaks considered as the most important ITER safety-relevant task for the passive visible spectroscopy diagnostics.
We use HAWK-I, the recently-commissioned near-IR imager on Yepun (VLT-UT4), to obtain wide-field, high-resolution images of the X-ray luminous galaxy cluster XMMU J2235.3-2557 in the J and Ks bands, ...and we use these images to build a colour-magnitude diagram of cluster galaxies. Galaxies in the core of the cluster form a tight red sequence with a mean $J-K\mathrm{s}$ colour of 1.9 (Vega system). The intrinsic scatter in the colour of galaxies that lie on the red sequence is similar to that measured for galaxies on the red sequence of the Coma cluster. The slope and location of the red sequence can be modelled by passively evolving the red sequence of the Coma cluster backwards in time. Using simple stellar population (SSP) models, we find that galaxies in the core of XMMU J2235.3-2557 are, even at $z=1.39$, already 3 Gyr old, corresponding to a formation redshift of $z_{\rm f} \sim 4$. Outside the core, the intrinsic scatter and the fraction of galaxies actively forming stars increase substantially. Using SSP models, we find that most of these galaxies will join the red sequence within 1.5 Gyr. The contrast between galaxies in the cluster core and galaxies in the cluster outskirts indicates that the red sequence of XMMU J2235.3-2557 is being built from the dense cluster core outwards.
Context. Pluto has five known satellites with diameters ranging from ~1200 km down to ~40 km, a possible outcome of a collisional origin. Smaller objects probably exist and may maintain tenuous ...rings, thus representing hazards during the New Horizons flyby of July 2015. Aims. The goal is to provide an upper limit for the numbers of unseen small bodies and/or equivalent widths of putative Pluto rings. Methods. We use a Pluto stellar appulse on April 10, 2006, and a stellar occultation by the dwarf planet on June 14, 2007, to scan Pluto’s surroundings. Results. Our best data set places a 3σ upper limit of 0.3 km for the radius of isolated moonlets that we can detect. In the absence of detection, we derive an upper limit of 15 000 for the number of such bodies at distances smaller than ~70 000 km from Pluto’s system barycenter. We place a 3σ upper limit of typically 30−100 m for the equivalent width of ring material at barycentric distances ranging from 13 000 to 70 000 km. This limit applies for narrow rings only, i.e. less than about 10 km in width.
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