Second generation instrumentation for the VLTI: The french VLTI connection

We describe the current French ideas for the instrumentation of the second generation of the VLTI. Instruments concepts addressed include: integrated optics beam combiner, extension of MIDI to a four beam facility, extension of AMBER to the visible and a densified pupil direct imaging beam combiner. This revised version was published online in July 2006 with corrections to the Cover Date.     

Improvements on the optical differentiation wavefront sensor

We describe a novel concept for high-resolution wavefront sensing based on the optical differentiation wavefront sensor (OD). It keeps the advantages of high resolution, adjustable dynamic range, ability to work with polychromatic sources and, in addition, it achieves good performance in wavefront reconstruction when the field is perturbed by scintillation. Moreover, this new concept can be used as multi-object wavefront sensor in multiconjugate adaptive optics systems. It is able to provide high resolution and high sampling operation, which is of great interest for the projected extreme adaptive optics systems for large telescopes.     

Prototyping a global soft X‐ray imaging instrument for heliophysics,planetary science,and astrophysics science

We describe current progress in the development of a prototype wide field‐of‐view soft X‐ray imager that employs Lobster‐eye optics and targets heliophysics, planetary, and astrophysics science. The prototype will provide proof‐of‐concept for a future flight instrument capable of imaging the entire dayside magnetosheath from outside the magnetosphere. Such an instrument was proposed for the ESA AXIOM mission (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Three Reflection Telescopes for Wide Field Space Astronomy. First Results from a 30 cm Prototype and Prospects

We present the basic concepts of the two-mirror, three-reflection optical system (2MTRT), and discuss the important benefits of such a system for space projects: wide ( 2^°) correctedand unvignetted FOV, without the use of refractive optics for thefield correction, planarity of the focal surface for an optimizedinstallation of wide area detectors, easy telescope adjustement, small volume and little mass.We also report the results of optical tests made with a 30 cm prototype,equipped with a 2k × 2k CCD camera, and give examples of scientific programmes which can be performed from space and in hostile terrestrial sites such as the Antarctic Plateau.     

Progress Toward Light Weight High Angular Resolution Multilayer Coated Optics

We have been working on 3 separate projects that together will give us the ability to make 1 arc second, light weightWolter I optics that work above 40 keV. The three separate tasks are: (a) plasma spraying of metal-coated micro-balloons; (b) coating of the inside of Wolter I mirrors, (c) actuator designs for improving figure quality.We give a progress report on our work on all three areas.     

The GREGOR adaptive optics system

The new 1.5‐m German solar telescope GREGOR at the Observatorio del Teide, Tenerife, is equipped with an integrated adaptive optics system. Although partly still in the commissioning phase, the system is already being used used for most science observations. It is designed to provide diffraction‐limited observations in the visible‐light regime for seeing better than 1.2″. We describe the AO system including the optical design, software, wavefront reconstruction, and performance (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

High-precision CTE measurement of aluminum-alloys for cryogenic astronomical instrumentation

We are completing the construction of GIANO, a high resolution near-infrared cryogenic spectrograph for the Telescopio Nazionale Galileo (TNG). Most of the optics are made of aluminium and operate at cryogenic temperature. We evaluated the optical degradation due to mis-matches between the thermal expansion coefficients of the different aluminium parts of the instrument. We performed accurate measurements of the relative thermal expansion coefficients (CTE) of Al-6061 and Al-6082 over the 300–77 K temperatures range. We find that the two alloys have identical thermal expansion coefficient within a maximum (3σ) uncertainty of Δα/α?<?0.28%. Our results show that it is possible to overcome the problem of the alignment of a cryogenic instrument, manufacturing the curved optics, the optics’ holders and the optical bench with different metallic alloys with small CTE mismatch (Al-6061 and Al-6082). This conclusion has also been confirmed by the results of the optical tests with the instrument cooled in the laboratory, showing no significant image quality degradation.     

Light scattering by Gaussian random particles

We introduce multivariate lognormal statistics to describe the shapes of small particles, and compute scattering phase matrices in the ray optics approximation. The results help us understand light scattering by solar system dust particles, and thereby constrain the physical properties of, for example, asteroid regoliths and cometary comae. The present stochastic geometry could turn useful in modeling the shapes of asteroids.     

Light scattering by Gaussian random particles

We introduce multivariate lognormal statistics to describe the shapes of small particles, and compute scattering phase matrices in the ray optics approximation. The results help us understand light scattering by solar system dust particles, and thereby constrain the physical properties of, for example, asteroid regoliths and cometary comae. The present stochastic geometry could turn useful in modeling the shapes of asteroids.     

Doing Research on Eclipsing Binary Stars with Small Telescopes and PC computers

Astronomical research with a small telescope (20 cm – 40 cm) has always been a challenging problem. The invention of CCD cameras and personal computers has now put this question to past as small telescopes can do good and practicle science. This paper describes the use of small telescope in the study of eclipsing binary stars. Binary stars play an important role as astrophysical laboratories in our quest to understand the evolution and structure of stars. The most useful aspects of research with a small telescope in binary star research is; 1) as a viable teaching laboratory for begining students 2) to teach and learn the fundamental observational techniques that are common to many types of astronomical research areas 3) as a starting point to initiate research programs in observational astronomy, optics, instrumentation, computational astrophysics and 4) as a foundation to develop an infrastructure and technical know how for larger telescope facility. This revised version was published online in July 2006 with corrections to the Cover Date.     

SKA Cost Model for Wide Field-of-View Options

We describe a SKA hardware component model that includes various concepts for achieving a wide field-of-view (FoV) as desired for survey speed. Costs for each of the components in the model are derived and in some cases optimum parameters are estimated. The model identifies components of major cost and allows comparison of the relative costs of the wide FoV concepts.     

An instrument for commissioning the active and adaptive optics of modern telescopes: the Infrared Test Camera for the Large Binocular Telescope

We describe the design, integration, and operation of the infrared test cameras for the commissioning of the Large Binocular Telescope. The design and construction phase lasted slightly more than one year from February 2007 to April 2008 and was the result of a joint collaboration among INAF Osservatorio Astronomico di Bologna, Università di Bologna Dipartimento di Astronomia (Italy) and the Max-Planck-Institut für Astronomie (Heidelberg, Germany). Thereafter, the camera was delivered to the LBT Observatory (USA) for commissioning of the telescope active optics and, more recently, for commissioning of the first light adaptive optics.     

Adaptive Optics on a 3.6-Meter Telescope. The ADONIS System.

ADONIS is an adaptive optics (AO) user friendly instrument offered to the European astronomical community on the ESO 3.6-m telescope at La Silla. It is an upgraded version of COME-ON-PLUS, the VLT AO prototype, which already produced significative astrophysical results in a wide range of fields, from planetology to extragalactic astrophysics. ADONIS is now allowing the astronomer to use adaptive optics as a common user instrument thanks to the implementation of an open artificial intelligence software that handles the large number of parameters needed to optimise the AO correction. We will describe the ADONIS system, including the two dedicated infrared cameras, summarize its performances and discuss the observing procedures.     

Hard X-ray imaging with microchannel plate optics

We investigate, by ray-trace simulation, two hard X-ray telescopes based on microchannel plate (MCP) optics. The first is the, by now well known, lobster-eye geometry, while the second is a novel design. The second design uses a pair of MCPs with square channels packed in a radial fashion and represents a conical approximation to the Wolter type I configuration. We show that such telescopes can provide X-ray imaging at energies up to 100 keV. Effective area may be scaled arbitrarily by co-aligning many MCP optics. As an example, we calculate that 50 parallel Wolter I units each of 60 mm diameter and 5 m focal length yield a sensitivity of 1 milli Crab at 45 keV in a 105 second integration.     

Keck adaptive optics images of Jupiter’s north polar cap and Northern Red Oval

We present observations at near-infrared wavelengths (1-5 μm) of Jupiter’s north polar region and Northern Red Oval (NN-LRS-1). The observations were taken with the near-infrared camera NIRC2 coupled to the adaptive optics system on the 10-m W.M. Keck Telescope on UT 21 August 2010. At 5-μm Jupiter’s disk reveals considerable structure, including small bright rings which appear to surround all small vortices. It is striking, though, that no such ring is seen around the Northern Red Oval. In de Pater et al. [2010a. Icarus 210, 742-762], we showed that such rings also exist around all small vortices in Jupiter’s southern hemisphere, and are absent around the Great Red Spot and Red Oval BA. We show here that the vertical structure and extent of the Northern Red Oval is very similar to that of Jupiter’s Red Oval BA. These new observations of the Northern Red Oval, therefore, support the idea of a dichotomy between small and large anticyclones, in which ovals larger than about two Rossby deformation radii do not have 5-μm bright rings. In de Pater et al. [2010a. Icarus 210, 742-762], we explained this difference in terms of the secondary circulations within the vortices. We further compare the brightness distribution of our new 5-μm images with previously published radio observations of Jupiter, highlighting the depletion of NH₃ gas over areas that are bright at 5 μm.     

An Explanation of the Differences Between the Sunspot Area Scales of the Royal Greenwich and Mt. Wilson Observatories,and the SOON Program

Several studies have shown that the sunspot areas recorded by the Royal Greenwich Observatory (RGO) between 1874?–?1976 are about 40?–?50 % larger than those measured by the NOAA/USAF Solar Observing Optical Network (SOON) since 1966. We show here that while the two measurement sets provide consistent total areas for large spots, the impossibility of recording small spots as anything except dots in the SOON drawings leads to an underestimate of small spot areas. These are more accurately recorded by the RGO and other programs that use photographic or CCD images. The large number of such small spots is often overlooked. A similar explanation holds for the RGO umbral areas, which amount to 40 % more than those measured from Mt. Wilson data between 1923 and 1982. The neglected small spots have a much lower photometric contrast. Our explanation suggests, therefore, that the adjustment to spot irradiance blocking at the 1976 transition from RGO to SOON areas is smaller than the almost 50 % correction advocated by some recent, purely statistical, studies.     

Magnetic polarimetric refraction in the solar corona

We present expressions which describe the angular displacement of radio sources due to refraction in a magnetized plasma. The main objective of the present paper is to take into account the combined effect of gradients of the electron density and the magnetic field. We use the geometrical optics approximation for the determination of the angular broadening of the radiation. The expressions obtained are applied to the case of the solar corona.     

Characterization of the mesospheric sodium layer at La Palma

We present the results of a mesospheric sodium monitoring programme at La Palma carried out through five campaigns of one week each, from 1999 September to 2000 August. The yearly averaged parameters of the layer (the sodium column density and the width) are given. We show that the short time-scale dynamics of the layer are governed by the sporadic layers with an average frequency of one event per night. The influence of the short time-scale dynamics of the layer on an adaptive optics system working on the William Herschel Telescope is quantified. It appears that it is a small effect in terms of defocus error. Finally, we present data obtained during the Perseid meteor shower and show that the dynamics of the sodium layer undergoes a transition with the meteoric activity.     

ALFA: Adaptive Optics for the Calar Alto Observatory Optics, Control Systems, and Performance

The adaptive optics system ALFA differs in some aspects from systems like ADONIS and PUEO which have delivered scientific results since years. Interchangeable lenslet arrays with different numbers of subapertures and a deformable mirror with many more actuators than the number of corrected modesresult in some peculiarities in the calibration of the system and the reconstruction of incident wavefronts.We describe the design of ALFA's optics and its modal control architecture with a focus on a comparative study of the performance of different mode sets used to correct the wavefront aberrations. An outlook on our plans to improve and simplify the use of ALFA is given.The last section is dedicated to issues related to observing with ALFA in its present state. Expected Strehl ratios for different seeing conditions and guide star magnitudes are summarized in a table. AO observations in general, direct imaging and doing spectroscopywith ALFA in particular are discussed.     

Pseudo-infinite guide stars for multi-conjugated adaptive optics on extremely large telescopes

We introduce a novel concept to sense the wavefront for adaptive optics purposes in astronomy using a conventional laser beacon. The concept we describe involves treating the light scattered in the mesospheric sodium layer as if it comes from multiple rings located at infinity. Such a concept resembles an inverse Bessel beam and is particularly suitable for multi-conjugated adaptive optics on extremely large telescopes. In fact, as the sensing process uses light apparently coming from infinity, some problems linked to the finite distance and vertical extent of the guide source are solved. Since such a technique is able to sense a wavefront solely in the radial direction, we propose furthermore a novel wavefront sensor by combining the inverse Bessel beam approach with the recently introduced z -invariant technique for a pseudo-infinite guide star sensor.