Aims. We investigate the star formation activity in a young star forming cluster embedded at the edge of the RCW 41 H ii region. As a complementary goal, we aim to demonstrate the gain provided by wide-field adaptive optics (WFAO) instruments to study young clusters. Methods. We used deep, JHK s images from the newly commissioned Gemini-GeMS/GSAOI instrument, complemented with Spitzer IRAC observations, in order to study the photometric properties of the young stellar cluster. GeMS is a WFAO instrument that delivers almost diffraction-limited images over a field of ∼2 across. The exquisite angular resolution allows us to reach a limiting magnitude of J ∼ 22 for 98% completeness. The combination of the IRAC photometry with our JHK s catalog is used to build color−color diagrams, and select young stellar object (YSO) candidates. The JHK s photometry is also used in conjunction with pre-main sequence evolutionary models to infer masses and ages. The K-band luminosity function is derived, and then used to build the initial mass function (IMF) of the cluster. Results. We detect the presence of 80 YSO candidates. Those YSOs are used to infer the cluster age, which is found to be in the range 1 to 5 Myr. More precisely, we find that 1/3 of the YSOs are in a range between 3 to 5 Myr, while 2/3 of the YSO are ≤3 Myr. When looking at the spatial distribution of these two populations, we find evidence of a potential age gradient across the field that suggests sequential star formation. We construct the IMF and show that we can sample the mass distribution well into the brown dwarf regime (down to ∼0.01 M ). The logarithmic mass function rises to peak at ∼0.3 M , before turning over and declining into the brown dwarf regime. The total cluster mass derived is estimated to be 78 ± 18 M , while the ratio derived of brown dwarfs to star is 18 ± 5%. When comparing it with other young clusters, we find that the IMF shape of the young cluster embedded within RCW 41 is consistent with those of Trapezium, IC 348, or Chamaeleon I, except for the IMF peak, which happens to be at higher mass. This characteristic is also seen in clusters like NGC 6611 or even Taurus. These results suggest that the medium-to-low mass end of the IMF possibly depends on environment.

Aims. The formation and properties of star clusters at the edge of H II regions are poorly known, partly due to limitations in angular resolution and sensitivity, which become particularly critical when dealing with extragalactic clusters. In this paper we study the stellar content and star-formation processes in the young N159W region in the Large Magellanic Cloud. Methods. We investigate the star-forming sites in N159W at unprecedented spatial resolution using JHK s -band images obtained with the GeMS/GSAOI instrument on the Gemini South telescope. The typical angular resolution of the images is ∼100 mas, with a limiting magnitude of H ∼22 mag (90% completeness). Photometry from our images is used to identify candidate young stellar objects (YSOs) in N159W. We also determine the H-band luminosity function of the star cluster at the centre of the H II region and use this to estimate its initial mass function (IMF). Results. We estimate an age of 2 ± 1 Myr for the central cluster, with its IMF described by a power-law with an index of Γ = −1.05 ± 0.2, and with a total estimated mass of ∼1300 M . We also identify 104 candidate YSOs, which are concentrated in clumps and subclusters of stars, principally at the edges of the H II region. These clusters display signs of recent and active star-formation such as ultra-compact H II regions, and molecular outflows. This suggests that the YSOs are typically younger than the central cluster, pointing to sequential star-formation in N159W, which has probably been influenced by interactions with the expanding H II bubble.

Detecting orbital magnetism Graphene’s electronic structure has been predicted to lead to an unusual orbital response to magnetic fields. However, detecting this orbital magnetism is difficult because it is usually masked by the signal stemming from spins. Vallejo Bustamante et al . managed to capture this response by placing two giant magnetoresistance detectors below a sample of graphene sandwiched by layers of hexagonal boron nitride. These detectors picked up a strong diamagnetic response from an undoped sample, consistent with theoretical predictions. The technique may be useful in the investigation of other two-dimensional materials. —JS

Whether is ground-based or space-based, any optical instrument suffers from some amount of optical geometric distortion. Recently, the diffraction-limited image quality afforded by space-based telescopes and by Adaptive Optics (AO) corrected instruments on ground basedtelescope, have increased the relative importance of the error terms induced by optical distortions. In particular, variable distortions present in Multi-Conjugated Adaptive Optics (MCAO) data are limiting the astrometry and photometry accuracy of such high resolution instruments. From there, the ability to deal with those phenomenon had become a critical issue for highprecision studies. We present in this paper an optimal method of distortion correction for high angular resolution images. Based on a prior-knowledge of the static distortion the method aims to correct the dynamical distortions specifically for each observation set and each frame. The method follows an inverse problem approach based on the work done by Gratadour et al. (2005) on image re-centering, and we aim to generalized it to any kind of distortion mode. The complete formalism of a Weighted Least Square minimization, as well as a detailed characterization of the error budget are presented. In particular we study the influence of different parameters such as the number of frames and the density of the field (sparse or crowed images), of the noise level, and of the aliasing effect. Finally, we show the first application of the method on real observations collected with the Gemini MCAO instrument, GeMS/GSAOI. The performance as well as the gain brought by this method are presented.

of the RR Lyrae star UW Gru are presented. The variable clearly belongs to the Bailey ab-type on the basis of the shape of the light and color curves, with a period of 0.548210 day and a mean visual magnitude V = 13.22, the amplitude in V being nearly one magnitude. The origin of the heliocentric epochs of light maxima is taken at HJD 2443689.640.A metal abundance [Fe/H] = -1.6 relative to the sun is indicated from the ultraviolet excess parameter 8 ( U -B) -0.04.Thus, UW Gru which is located about 2.9 kpc away from the sun, 2.3 kpc below the galactic plane, definitely shows the typical features of a normal halo RR Lyrae star.

Abstract. We present a catalogue of positions and photographic R magnitudes at observed maximum and minimum brightness for 1061 variable stars newly detected in the direction of the Bright Cloud B in Sagittarius. The limiting R magnitude of the survey is about 18. Most of these stars are long period variables. Taking into account the previously published lists (Terzan et al. 1982(Terzan et al. , 1988(Terzan et al. , 1991, the total number of new variable objects discovered in the surveyed 100 square degree field amounts to 4430.

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After two years of research and development under ESQ suppon, LAM and Thales SESO present the results of their experiment for the fast and accurate polishing under stress of ELT 1.5 meter segments as well as the industrialisation approach for mass production. Based on stress polishing, this manufacturing method requires the conception of a warping harness able to generate extremely accurate bending of the optical s urface of the segments during the polishing. The conception of the warping harness is based on finite element analysis and allowed a fine tuning of each geometrical parameter of the system in order to fit an error budget of 25nm RMS over 300µm of bending peak to valley. The optimisation approach uses the simulated influence functions to extract the system eigenmodes and characterise the performance. The same approach is used for the full characterisation of the system itself. The warping harness has been manufactured, integrated and assembled with the Zerodur 1.5 meter segment on the IAM 2 .5meter POLARIS polishing facility. The experiment consists in a cross check of optical and mechanical measurements of the mirrors bending in order to develop a blind process, ie to bypass the optical measurement during the final industrial process. This article describes the optical and mechanical measurements, the influence functions and eigenmodes of the system and the full performance characterisation of the warping harness.