Johann Kolb

A deep look into the cores of young clusters - I.

Context. Nearby young clusters are privileged places to study the star formation history. Over the last decade, the σ-Orionis cluster has been a prime location for the study of young very low mass stars, substellar and isolated planetary mass objects and the determination of the initial mass function. Aims. To extend previous studies of this association to its core, we searched for ultracool members and new multiple systems within the 1. � 5 × 1. 5 central region of the cluster. Methods. We obtained deep multi-conjugate adaptive optics (MCAO) images of the core of the σ-Orionis cluster with the prototype MCAO facility MAD at the VLT using the H and Ks filters. These images allow us to detect companions fainter by ΔH ≈ 5 mag as close as 0. �� 2 on a typical source with H = 14.5 mag. These images were complemented by archival SofI K s-band images and Spitzer IRAC and MIPS mid-infrared images Results. We report the detection of 2 new visual multiple systems, one being a candidate binary proplyd and the other one a low mass companion to the massive star σ Ori E. Of the 36 sources detected in the images, 25 have a H-band luminosity lower than the expected planetary mass limit for members, and H − Ks color consistent with the latest theoretical isochrones. Nine objects have additional Spitzer photometry and spectral energy distribution consistent with them being cluster members. One of them has a spectral energy distribution from H to 3.6 μm consistent with that of a 5.5 MJup cluster member. Complementary NTT/SofI and Spitzer photometry allow us to confirm the nature and membership of two L-dwarf planetary mass candidates.

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Context. Multi-conjugate adaptive optics (MCAO) combine the advantages of both standard adaptive optics, which provide high contrast and high spatial resolution, and of wide field imaging (≈1 � ). Up to recently, MCAO for astronomy was limited to laboratory experiments. In this paper, we present the first scientific results obtained with the first MCAO instrument. Aims. We present a new study of the Trapezium cluster using deep MCAO images with a field of view of 1 � × 1 � obtained at the VLT. Methods. We used deep J, H ,a ndKs images recently obtained with the prototype MCAO facility MAD at the VLT to search for new members and new multiple systems in the Trapezium cluster. On bright targets (Ks ≈ 9 mag), these images allow us to reach ∆Ks ≈ 6 mag as close as 0 . �� 4.

-Orionis

The European Southern Observatory together with external research Institutes is building a Multi-Conjugate Adaptive Optics Demonstrator (MAD) to perform wide field of view adaptive optics correction. The aim of MAD is to demonstrate on the sky the feasibility of the MCAO technique and to evaluate all the critical aspects in building such kind of instrument in the framework of both the 2nd generation VLT instrumentation and the 100-m Overwhelmingly Large Telescope (OWL). The MAD module will be installed at one of the VLT unit telescope in Paranal to perform on-sky observations. MAD is based on a two deformable mirrors correction system and on two multi-reference wavefront sensors capable to observe simultaneously some pre-selected configurations of Natural Guide Stars. MAD is expected to correct up to 2 arcmin field of view in K band. MAD has just started the integration phase which will be followed up by a long period of testing. In this paper we present the final design of MAD with a brief report about the status of the integration.

Multi-Conjugate Adaptive Optics images of the Trapezium Cluster ⋆

Several designs of future Adaptive Optics (AO) systems propose to use a large Deformable Mirror (DM), regarding the size as well as the number of actuators. Most of the time, there is no focal plane upstream the DM. Therefore, the classical way of calibrating the interaction matrix on an artificial source cannot be applied. Furthermore, the requirements in terms of calibration error budget are tight and the high order modes of such DMs are stiff and hence they achieve only a small stroke. This is why novel ways to determine the system Interaction Matrix (IM) have to be investigated. Several paths have been studied. One solution would be to simulate a synthetic IM. However, calibration on sky is also an option. Different techniques were simulated, tested and optimized on real AO systems. The results are presented in this paper.

MAD status report

Context. BL Lac objects are low-power active nuclei exhibiting a variety of peculiar properties caused by the presence of a relativistic jet and orientation effects. Aims. We present adaptive optics near-IR images at high spatial resolution of the nearby BL Lac object PKS 0521-365, which is known to display a prominent jet both at radio and optical frequencies. Methods. The observations were obtained in Ks-band using the ESO multi-conjugated adaptive optics demonstrator at the Very Large Telescope. This allowed us to obtain images with 0.1 arcsec effective resolution. We performed a detailed analysis of the jet and its related features from the near-IR images, and combined them with images previously obtained with HST in the R band and by a re-analysis of VLA radio maps. Results. We find a remarkable similarity in the structure of the jet at radio, near-IR, and optical wavelengths. The broad–band emission of the jet knots is dominated by synchrotron radiation, while the nucleus also exhibits a significant inverse Compton component. We discovered the near-IR counterpart of the radio hotspot and found that the near-IR flux is consistent with being a synchrotron emission from radio to X-ray wavelengths. The bright red object (red-tip), detached but well aligned with the jet, is well resolved in the near-IR and has a linear light profile. Since it has no radio counterpart, we propose that it is a background galaxy not associated with the jet. Conclusions. The new adaptive optics near-IR images and previous observations at other frequencies allow us to study the complex environment around the remarkable BL Lac object PKS 0521-365. These data exemplify the capabilities of multi conjugate adaptive optics observations of extragalactic extended sources.

Large DM AO systems: synthetic IM or calibration on sky?

Aims. We present a study aimed at deriving constraints on star formation at intermediate ages from the evolved stellar populations in the dwarf irregular galaxy UKS 2323-326. These observations were also intended to demonstrate the scientific capabilities of the multi-conjugated adaptive optics demonstrator (MAD) implemented at the ESO Very Large Telescope as a test-bench of adaptive optics (AO) techniques. Methods. We perform accurate, deep photometry of the field using J and Ks band AO images of the central region of the galaxy. Results. The near-infrared (IR) colour-magnitude diagrams clearly show the sequences of asymptotic giant branch (AGB) stars, red supergiants, and red giant branch (RGB) stars down to ∼1 mag below the RGB tip. Optical-near-IR diagrams, obtained by combining our data with Hubble Space Telescope observations, provide the best separation of stars in the various evolutionary stages. The counts of AGB stars brighter than the RGB tip allow us to estimate the star formation at intermediate ages. Assuming a Salpeter initial mass

The jet of the BL Lacertae object PKS 0521-365 in the near-IR: MAD adaptive optics observations

The Multi-Conjugate Adaptive Optics Demonstrator (MAD) built by ESO with the contribution of two external consortia is a powerful test bench for proving the feasibility of Ground Layer (GLAO) and Multi-Conjugate Adaptive Optics (MCAO) techniques both in the laboratory and on the sky. The MAD module will be installed at one of the VLT unit telescope in Paranal observatory to perform on-sky observations. MAD is based on a two deformable mirrors correction system and on two multi-reference wavefront sensors (Star Oriented and Layer Oriented) capable to observe simultaneously some pre-selected configurations of Natural Guide Stars. MAD is expected to correct up to 2 arcmin field of view in K band. MAD is completing the test phase in the Star Oriented mode based on Shack-Hartmann wavefront sensing. The GLAO and MCAO loops have been successfully closed on simulated atmosphere after a long phase of careful system characterization and calibration. In this paper we present the results obtained in laboratory for GLAO and MCAO corrections testing with bright guide star flux in Star Oriented mode paying also attention to the aspects involving the calibration of such a system. A short overview of the MAD system is also given.

Resolving stellar populations outside the Local Group : MAD observations of UKS 2323-326

The Multi-Atmospheric Phase screens and Stars (MAPS) instrument is a powerful tool that has been developed in the framework of the ESO Multi-conjugate Adaptive optics Demonstrator project (MAD). It allows emulating a 3D evolving Paranal-like atmosphere as well as up to 12 sources in a 2 arc minutes field of view, as seen at a Nasmyth focus of one of the VLT. It will be used to perform advanced laboratory tests on MAD before its shipment to Chile. In this paper we present the opto-mechanical design of MAPS. This one simulates the characteristics of the VLT focus and achieves a high Strehl Ratio over the whole Field of View in the visible as well as in the infrared. A curved entrance plate crowded with fibers emulates various stars configurations including real sky asterisms. In order to simulate the atmosphere, three rotating Phase Screens are placed in the beam and conjugated with different altitudes. Those are glass plates dig in their surface in a way that the beam passing through is distorted as it would be by an atmospheric turbulent layer. In this poster we also present the process of research that lead to the choice of a reliable technique to imprint the aberrations into the screens, their properties and expected performance.

MAD star oriented: laboratory results for ground layer and multi-conjugate adaptive optics

The detector is a critical component of any Adaptive Optics WaveFront Sensing (AO WFS) system. The required performance combination of fast frame rate, high quantum efficiency, low read noise and dark signal, number and size (24-50 μm) of pixels pushes detector technology to the edge such that in many cases custom detector developments are required. This paper examines the roadmap of optical and infrared detectors by reviewing; detectors that are currently available and/or are in use in current instruments, detectors that are under development and will be used in future instruments on existing telescopes, and the requirements and status of new detectors whose development are critical for the success of the next generation of extremely large telescopes (E-ELT, GMT, and TMT). In addition, the paper will report on the AO WFS detector development and testing programs currently under way at ESO.

MAPS: a turbulence simulator for MCAO

The Multiconjugate Adaptive optics Demonstrator (MAD) had successfully demonstrated on sky both Star Oriented (SO) and Layer Oriented (LO) multiconjugate adaptive optics techniques. While SO has been realized using 3 Shack-Hartmann wavefront sensors (WFS), we designed a multi-pyramid WFS for the LO. The MAD bench accommodates both WFSs and a selecting mirror allows choosing which sensor to use. In the LO approach up to 8 pyramids can be placed on as many reference stars and their light is co-added optically on two different CCDs conjugated at ground and to an high layer. In this paper we discuss LO commissioning phase and on sky operations.