Context. Free-floating substellar candidates with estimated theoretical masses of as low as ∼5 Jupiter masses have been found in the ∼3 Myr old σ Orionis open cluster. As the overlap with the planetary mass domain increases, the question of how these objects form becomes important. The determination of their number density and whether a mass cut-off limit exists is crucial to understanding their formation. Aims. We propose to search for objects of yet lower masses in the cluster and determine the shape of the mass function at low mass. Methods. Using new-and (re-analysed) published IZJHK s [3.6]−[8.0]-band data of an area of 840 arcmin 2 , we performed a search for LT-type cluster member candidates in the magnitude range J = 19.5-21.5 mag, based on their expected magnitudes and colours. Results. Besides recovering the T type object S Ori 70 and two other known objects, we find three new cluster member candidates, S Ori 72-74, with J ≈ 21 mag and within 12 arcmin of the cluster centre. They have theoretical masses of 4 +3 −2 M Jup and are among the least massive free-floating objects detected by direct imaging outside the Solar System. The photometry in archival Spitzer [3.6]-[5.8]-band images infers that S Ori 72 is an L/T transition candidate and S Ori 73 a T-type candidate, following the expected cluster sequence in the mid-infrared. Finally, the L-type candidate S Ori 74 with lower quality photometry is located at 11.8 arcsec (∼4250 AU) of a stellar member of σ Orionis and could be a companion. After contaminant correction in the area complete to J = 21.1 mag, we estimate that there remain between zero and two cluster members in the mass interval 6-4 M Jup . Conclusions. We present S Ori 73, a new candidate T type and candidate σ Orionis member of a few Jupiter masses. Our result suggests a possible turnover in the substellar mass spectrum below ∼6 Jupiter masses, which could be investigated further by wider and deeper photometric surveys.

We present the discovery of a companion near the deuterium-burning mass limit located at a very wide distance, at an angular separation of (projected distance of ∼ 670 AU) from UScoCTIO 108, a brown dwarf 4.6 ‫ע‬ 0.1 of the very young Upper Scorpius association. Optical and near-infrared photometry and spectroscopy confirm the cool nature of both objects, with spectral types of M7 and M9.5, respectively, and that they are bona fide members of the association, showing low gravity and features of youth. Their masses, estimated from the comparison of their bolometric luminosities and theoretical models for the age range of the association, are and , respectively. The existence of this object around a brown dwarf at this wide orbit suggests ϩ2 60 ‫ע‬ 20 14 MϪ8 J up that the companion is unlikely to have formed in a disk based on current planet formation models. Because this system is rather weakly bound, they probably did not form through dynamical ejection of stellar embryos.

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We have studied the spatial clustering of high redshift (z > 1) extremely red objects (EROs) as a function of photometric redshift in the GOODS Southern Field using public data. A remarkable overdensity of extremely red galaxies (I−Ks > 4) is found at an average photometric redshift zphot= 1.10. Nine objects (six are EROs) within 50 arcsec of the brightest infrared galaxy in this overdensity present spectroscopic redshifts in the range 1.094 < zspec < 1.101 with a line‐of‐sight velocity dispersion of σv= 433+152−74 km s−1 typical of an Abell richness class R= 0 cluster. Other potential members of this cluster, designated as GCL J0332.2−2752, have been identified using photometric redshifts and the galaxy density profile studied as a function of radius. The mass of the cluster is preliminary estimated at Mcl∼ 5–7 × 1013 M⊙. Using available Chandra data, we limit the rest‐frame X‐ray luminosity of the cluster to less than LX= 7.3 × 1042 erg s−1 (0.5–2.0 keV). This low‐mass, low LX cluster at z > 1 shows the potential of EROs to trace clusters of galaxies at high redshift.

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AOLI (Adaptive Optics Lucky Imager) is a state-of-art instrument that combines adaptive optics (AO) and lucky imaging (LI) with the objective of obtaining diffraction limited images in visible wavelength at mid-and big-size ground-based telescopes.The key innovation of AOLI is the development and use of the new TP3-WFS (Two Pupil Plane Positions Wavefront Sensor). The TP3-WFS, working in visible band, represents an advance over classical wavefront sensors such as the Shack-Hartmann WFS (SH-WFS) because it can theoretically use fainter natural reference stars, which would ultimately provide better sky coverages to AO instruments using this newer sensor. This paper describes the software, algorithms and procedures that enabled AOLI to become the first astronomical instrument performing real-time adaptive optics corrections in a telescope with this new type of WFS, including the first control-related results at the William Herschel Telescope (WHT).

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Abstract-The authors propose an extension of Berenger's perfectly matched layer (PML) absorbing boundary conditions (ABC's) to achieve a perfect matching of waves propagating in anisotropic media. Although the procedure to obtain the matching conditions is valid for any kind of anisotropic material, it has been validated with a lossless two-dimensional uniaxial medium, in which the optical axis is not contained in its plane section. The finite difference time domain method, with an alternative scheme for anisotropic media, is used to simulate the problem and to obtain the numerical reflection coefficient.Index Terms-Absorbing boundary conditions, anisotropic media, FDTD methods, perfect matching layers.