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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. Imaging of low-mass exoplanets can be achieved once the thermal background in the mid-infrared (MIR) wavelengths can be mitigated. Here, the authors present a ground-based MIR observing approach enabling imaging low-mass temperate exoplanets around nearby stars.

Many galaxies are thought to have supermassive black holes at their centres 1 —more than a million times the mass of the Sun. Measurements of stellar velocities 2 , 3 , 4 , 5 , 6 , 7 and the discovery of variable X-ray emission 8 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) × 10 6 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.

Charon among the stars Stellar occultations, when a Solar System object passes between us and a star and blocks its light, are eagerly awaited by astronomers as they provide a chance to make measurements that are not normally possible. It had been 25 years since a solitary observation of a stellar occultation by Pluto's moon Charon. But on 11 July 2005 another occurred and this time observatories across South America were ideally placed to track it. The resulting haul of data has been used to obtain an accurate measure of Charon's radius, of close to 605 km, and to establish an upper limit (a rather low one) on the density of its atmosphere. Visit tinyurl.com/9c56s for a QuickTime movie of the event. Pluto and its satellite, Charon (discovered in 1978; ref. 1 ), appear to form a double planet, rather than a hierarchical planet/satellite couple. Charon is about half Pluto's size and about one-eighth its mass. The precise radii of Pluto and Charon have remained uncertain, leading to large uncertainties on their densities 2 . Although stellar occultations by Charon are in principle a powerful way of measuring its size, they are rare, as the satellite subtends less than 0.3 microradians (0.06 arcsec) on the sky. One occultation (in 1980) yielded a lower limit of 600 km for the satellite's radius 3 , which was later refined to 601.5 km (ref. 4 ). Here we report observations from a multi-station stellar occultation by Charon, which we use to derive a radius, R C = 603.6 ± 1.4 km (1 σ ), and a density of ρ = 1.71 ± 0.08 g cm -3 . This occultation also provides upper limits of 110 and 15 (3 σ ) nanobar for an atmosphere around Charon, assuming respectively a pure nitrogen or pure methane atmosphere.

All large telescopes in the world are now equipped with adaptive optics systems. These systems are usually used for near‐infrared imaging, spectroscopy, and/or coronography. Their efficiency in terms of spatial resolution improvement is now globally accepted. But no study has been made so far about the (in)efficiency of such systems in terms of telescope observing time, i.e., effective integration times used for scientific observations (shutter time). This is the aim of this paper. For the very first time, adaptive optics observations, over 3 years, are studied in detail: the relative scientific shutter efficiency is found to be between 10% and 35%, significantly below the average for other infrared instrumentation, i.e., between 50% and 80%. This study also shows that the use of adaptive optics observation preparation tools together with smart observing templates will dramatically increase the average shutter efficiency for many adaptive optics programs. The observational experience of the users also influences the (in)efficiency: users with more experience in the operation of the system are in general more efficient in using the allocated observing time. Scheduling of service‐mode observation programs should be preferred in the future.

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.

Observations at various wavelengths of late B-type stars exhibiting strong overabundances of the chemical elements Hg and Mn in their atmospheres indicate that these stars are frequently found in binary and multiple systems. 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\". We carried out a survey of 56 stars using diffraction-limited near-infrared imaging with NAOS-CONICA at the VLT. 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 5.95m and 18.07m and angular separations ranging from <0.05\" to 7.8\", corresponding to linear projected separations of 13.5-1700 AU. 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 present near-infrared multi-object spectroscopy and JHKs 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 O5V 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 towards W3 Main. Analysis of the Hertzsprung Russell diagram suggests that the Nishiyama extinction law fits the stellar population of W3 Main best (E(J-H)/E(H-Ks) = 1.76 and R_(Ks) = 1.44). From our spectrophotometric analysis of the massive stars and the nature of their surrounding HII regions we derive the evolutionary sequence of W3 Main and we find evidence of an age spread of at least 2-3 Myr. While the most massive star (IRS2) is already evolved, indications for high-mass pre-main-sequence evolution is found for another star (IRS N1), deeply embedded in an ultra compact HII region, in line with the different evolutionary phases observed in the corresponding HII regions. We derive a stellar mass of W3 Main of (4 +- 1) 10^3 Msun, by extrapolating from the number of OB stars using a Kroupa IMF and correcting for our spectroscopic incompleteness. We have detected the photospheres of OB stars from the more evolved diffuse HII region to the much younger UCHII regions, suggesting that these stars have finished their formation and cleared away their circumstellar disks very fast. Only in the hyper-compact HII region (IRS5), the early type stars seem to be still surrounded by circumstellar material.