Focal Instruments Research Articles

THE RISE OF ULTRAVIOLET ASTRONOMY IN FRANCE

France was one of the few countries able to launch rockets soon after the end of WWII. Some of these rockets were used to observe the Sun and other astronomical targets in the ultraviolet in the early 1960s. This program continued with the placement of French UV cameras and spectrographs in the French satellite D2B-Aura (1975), in two Soviet satellites and in NASA's Skylab (1973) and Spacelab (1983 and 1985). In parallel, a stratospheric balloon program was initiated around 1978, which has been considerably more successful than the rocket and satellite programs. We describe these activities and their scientific results, which culminated in an important French participation in the focal instrumentation of the Hubble Space Telescope and of several NASA and ESA ultraviolet satellites.

High-contrast and resolution near-infrared photometry of the core of R136

ABSTRACT We present the sharpest and deepest near-infrared photometric analysis of the core of R136, a newly formed massive star cluster at the centre of the 30 Doradus star-forming region in the Large Magellanic Cloud. We used the extreme adaptive optics of the SPHERE focal instrument implemented on the ESO Very Large Telescope and operated in its IRDIS imaging mode for the second time with longer exposure time in the H and K filters. Our aim was to (i) increase the number of resolved sources in the core of R136, and (ii) to compare with the first epoch to classify the properties of the detected common sources between the two epochs. Within the field of view (FOV) of 10.8″ × 12.1″ ($2.7\,\text {pc}\times 3.0\, \text {pc}$), we detected 1499 sources in both H and K filters, for which 76 per cent of these sources have visual companions closer than 0.2″. The larger number of detected sources enabled us to better sample the mass function (MF). The MF slopes are estimated at ages of 1, 1.5, and 2 Myr, at different radii, and for different mass ranges. The MF slopes for the mass range of 10–300 M⊙ are about 0.3 dex steeper than the mass range of 3–300 M⊙, for the whole FOV and different radii. Comparing the JHK colours of 790 sources common in between the two epochs, 67 per cent of detected sources in the outer region (r > 3″) are not consistent with evolutionary models at 1–2 Myr and with extinctions similar to the average cluster value, suggesting an origin from ongoing star formation within 30 Doradus, unrelated to R136.

POLITICAL PARTIES AND NATIONAL INTEGRATION IN NIGERIA: A HISTORICAL PERSPECTIVE

In a democratic environment, Political Parties are the fulcrum and focal instrument because it set the foundation or the platform for representation in government and politics of a people. As an institution that continuously seeks the control of state power and authority it then behoove on it to set the agenda of integration so as to synergize the strength of bonding for national achievement. However, this can only be achieved through its policy templates, true process of democratization and a more nationalistic outlook instead of sectionalism amidst others. Nigeria, as a country have been persistently challenged with the problem of achieving a common front due to the myriad of factors that continuously bifurcate every of its fiber or fabrics. Hence, this paper examines the role of political parties in achieving National integration in Nigeria. After using the primary and secondary sources of data collection analysis it was obvi-ous that political parties have continuously failed in integrating the society due to a strong hold on ethnic divides, corruption, unfulfilled promises, thuggery among other negative portraits. Thus, the paper recommends that political parties should reflect a national outlook instead of been primordial, therefore the independent national elec-toral commission should not register parties with parochial ideology more so, citizens should be encourage to massively participate in politics so as to enclose the possibility of election rigging.

From Inauguration to Commercialisation: Incremental yet Contested Transitions Redefining the National Interests of International Degree Programmes in Finland

ABSTRACT International degree programmes (IDPs) act as focal instruments for the internationalization of higher education in many non-English–speaking countries serving a variety of national objectives, with the commercial objective becoming increasingly common. This study analyses how IDPs have developed in one Nordic country, Finland, from a marginal activity into programmes that underpin commercially oriented definition of internationalization. The data consists of key policy texts and administrative documents analysed to trace policy changes. The findings suggest that IDPs have developed from the internationalisers of the universities and development aid to recruitment channels for bringing skilled labour to Finland and promoting education export. Having global similarities in their development, policy changes towards commercial understandings of IDPs has been contested, particularly regarding funding, which relates to equality principles in the Finnish higher education system. These shifts have had repercussions for the idea of IDPs, universities and students.

九谱段焦面配准测试仪的研制

九谱段焦面配准测试仪的研制

Assessment of Marketing Skill Application in Tourism Places in Srikakulam District, Andhra Pradesh

The importance of marketing skill to Tourism industry is increasingly seen as a viable development strategy to promote for sustainable economy in an effective way to counter declining tourism incomes especially in the developing countries. The efforts associated with different strategically applications suited to the industry in the area of marketing with an emphasis on skill assessment are found to be the need of the hour now. The aim of this research study is to explore the essence of marketing skills and its applicability in tourism places in Srikakulam District of Andhra Pradesh. The design of the study is descriptive type in association of both applications of qualitative and quantitative approaches. Field surveys, focus group discussions, interviews, questionnaires’ distribution and direct observations were the focal instruments in data gathering. Real and practical representatives and key informants were confronted from tourism office, government leaders, tourism businesses and tourists through both probability and non-probability sampling techniques to understand the underlying scenarios. Qualitative approaches were used to analysis predominantly with the variables that are subject to descriptions of phenomena and narrations, whereas quantitative analysis was used for the quantifications of major themes and phenomena that consist quantifiable variables expressed in numerical figures and magnitudes using Statistical Package for Social Sciences (SPSS) 21 version software.

Uncrowding R 136 from VLT/SPHERE extreme adaptive optics

This paper presents the sharpest near-IR images of the massive cluster R 136 to date, based on the extreme adaptive optics of the SPHERE focal instrument implemented on the ESO Very Large Telescope and operated in its IRDIS imaging mode.The crowded stellar population in the core of the R 136 starburst compact cluster remains still to be characterized in terms of individual luminosities, age, mass and multiplicity. SPHERE/VLT and its high contrast imaging possibilities open new windows to make progress on these questions.Stacking-up a few hundreds of short exposures in J and Ks spectral bands over a field of view (FoV) of 10.9″ × 12.3″ centered on the R 136a1 stellar component, enabled us to carry a refined photometric analysis of the core of R 136. We detected 1110 and 1059 sources in J and Ks images respectively with 818 common sources. Thanks to better angular resolution and dynamic range, we found that more than 62.6% (16.5%) of the stars, detected both in J and Ks data, have neighbours closer than 0.2′′ (0.1′′). The closest stars are resolved down to the full width at half maximum (FWHM) of the point spread function (PSF) measured by Starfinder. Among resolved and/or detected sources R 136a1 and R 136c have optical companions and R 136a3 is resolved as two stars (PSF fitting) separated by 59 ± 2 mas. This new companion of R 136a3 presents a correlation coefficient of 86% in J and 75% in Ks. The new set of detected sources were used to re-assess the age and extinction of R 136 based on 54 spectroscopically stars that have been recently studied with HST slit-spectroscopy (Crowther et al. 2016, MNRAS, 458, 624) of the core of this cluster. Over 90% of these 54 sources identified visual companions (closer than 0.2′′). We found the most probable age and extinction for these sources are 1.8+1.2-0.8 Myr, AJ = (0.45 ± 0.5) mag and AK = (0.2 ± 0.5) mag within the photometric and spectroscopic error-bars. Additionally, using PARSEC evolutionary isochrones and tracks, we estimated the stellar mass range for each detected source (common in J and K data) and plotted the generalized histogram of mass (MF with error-bars). Using SPHERE data, we have gone one step further and partially resolved and studied the initial mass function covering mass range of (3–300) M⊙ at the age of 1 and 1.5 Myr. The density in the core of R 136 (0.1–1.4 pc) is estimated and extrapolated in 3D and larger radii (up to 6 pc). We show that the stars in the core are still unresolved due to crowding, and the results we obtained are upper limits. Higher angular resolution is mandatory to overcome these difficulties.

Sanctity of the Body and the Relational Paradigm.

The individual is in constant interaction with others from birth onwards. The primary experience evolves from the innate need for bodily touch and connection, which form the foundation for the psychobiological structure of the individual. The body's anatomy is made to yearn for another, for building a home with the body of another. This makes the body the focal instrument, which is discernible already in the mother-child relationship, as well as later in male-female or husband-wife relationships. The body thus provides the most sacred space, and deep within it carries a natural yearning for another, for having a relationship with another. Relationships are the means through which the body can come to full realization.

A systematic review of validity procedures used in neuropsychological batteries.

study presents a systematic review of validity evidence for neuropsychological batteries. Studies published in international databases between 2005 and 2012 were examined. Considering the specificity of neuropsychological batteries, the aim of the study was to review the statistical analyses and procedures that have been used to validate these instruments. A total of 1,218 abstracts were read, of which 147 involved studies of neuropsychological batteries or tests that evaluated at least three cognitive processes. The full text of each article was analyzed according to publication year, focal instrument of the study, sample type, sample age range, characterization of the participants, and procedures and analyses used to provide evidence of validity. The results showed that the studies primarily analyzed patterns of convergence and divergence by correlating the instruments with other tests. Measures of reliability, such as internal consistency and test-retest reliability, were also frequently employed. To provide evidence of relationships between test scores and external criteria, the most common procedures were evaluations of sensitivity and specificity, and comparisons were made between contrasting groups. The statistical analyses frequently used were Receiver Operating Characteristic analysis, Pearson correlation, and Cronbach's alpha. We discuss the necessity of incorporating both classic and modern psychometric procedures and presenting a broader scope of validity evidence, which would represent progress in this field. Finally, we hope our findings will help researchers better plan the validation process for new neuropsychological instruments and batteries. Keywords: neuropsychological assessment, validity, reliability, systematic review.

IRDIS, the dual-band imager camera of SPHERE: testing the performances in laboratory

AbstractNext year the second generation instrument SPHERE will begin science operations at the Very Large Telecope (ESO). This instrument will be dedicated to the search for exoplanets through the direct imaging techniques, with the new generation extreme adaptive optics. In this poster, we present the performances of one of the focal instruments, the Infra-Red Dual-beam Imaging and Spectroscopy (IRDIS). All the results have been obtained with tests in laboratory, simulating the observing conditions in Paranal. We tested several configurations using the sub-system Integral Field Spectrograph (IFS) in parallel and simulating long coronographic exposures on a star, calibrating instrumental ghosts, checking the performance of the adaptive optics system and reducing data with the consortium pipeline. The contrast one can reach with IRDIS is of the order of 10−6 at 0.5 arcsec separation from the central star.

The wind of the M-type AGB star RT Virginis probed by VLTI/MIDI

We study the circumstellar environment of the M-type AGB star RT Vir using mid-infrared high spatial resolution observations from the ESO-VLTI focal instrument MIDI. The aim of this study is to provide observational constraints on theoretical prediction that the winds of M-type AGB objects can be driven by photon scattering on iron-free silicate grains located in the close environment (about 2 to 3 stellar radii) of the star. We interpreted spectro-interferometric data, first using wavelength-dependent geometric models. We then used a self-consistent dynamic model atmosphere containing a time-dependent description of grain growth for pure forsterite dust particles to reproduce the photometric, spectrometric, and interferometric measurements of RT Vir. Since the hydrodynamic computation needs stellar parameters as input, a considerable effort was first made to determine these parameters. MIDI differential phases reveal the presence of an asymmetry in the stellar vicinity. Results from the geometrical modeling give us clues to the presence of aluminum and silicate dust in the close circumstellar environment (< ~5 stellar radii). Comparison between spectro-interferometric data and a self-consistent dust-driven wind model reveals that silicate dust has to be present in the region between 2 to 3 stellar radii to reproduce the 59 and 63 m baseline visibility measurements around 9.8 micron. This gives additional observational evidence in favor of winds driven by photon scattering on iron-free silicate grains located in the close vicinity of an M-type star. However, other sources of opacity are clearly missing to reproduce the 10-13 micron visibility measurements for all baselines. This study is a first attempt to understand the wind mechanism of M-type AGB stars by comparing photometric, spectrometric, and interferometric measurements with state-of-the-art, self-consistent dust-driven wind models. The agreement of the dynamic model atmosphere with interferometric measurements in the 8-10 micron spectral region gives additional observational evidence that the winds of M-type stars can be driven by photon scattering on iron-free silicate grains. Finally, a larger statistical study and progress in advanced self-consistent 3D modeling are still required to solve the remaining problems.

Beyond the diffraction limit of optical/IR interferometers

Context. Spectrally resolved long-baseline optical/IR interferometry of rotating stars opens perspectives to investigate their fundamental parameters and the physical mechanisms that govern their interior, photosphere, and circumstellar envelope structures.Aims. Based on the signatures of stellar rotation on observed interferometric wavelength-differential phases, we aim to measure angular diameters, rotation velocities, and orientation of stellar rotation axes.Methods. We used the AMBER focal instrument at ESO-VLTI in its high-spectral resolution mode to record interferometric data on the fast rotator Achernar. Differential phases centered on the hydrogen Br γ line (K band) were obtained during four almost consecutive nights with a continuous Earth-rotation synthesis during ~5 h/night, corresponding to ~60° position angle coverage per baseline. These observations were interpreted with our numerical code dedicated to long-baseline interferometry of rotating stars.Results. By fitting our model to Achernar’s differential phases from AMBER, we could measure its equatorial radius R eq = 11.6 ± 0.3 R ⊙ , equatorial rotation velocity V eq = 298 ± 9 km s-1 , rotation axis inclination angle i = 101.5 ± 5.2°, and rotation axis position angle (from North to East) PArot = 34.9 ± 1.6°. From these parameters and the stellar distance, the equatorial angular diameter ⌀eq of Achernar is found to be 2.45 ± 0.09 mas, which is compatible with previous values derived from the commonly used visibility amplitude. In particular, ⌀eq and PArot measured in this work with VLTI/AMBER are compatible with the values previously obtained with VLTI/VINCI.Conclusions. The present paper, based on real data, demonstrates the super-resolution potential of differential interferometry for measuring sizes, rotation velocities, and orientation of rotating stars in cases where visibility amplitudes are unavailable and/or when the star is partially or poorly resolved. In particular, we showed that differential phases allow the measurement of sizes up to ~4 times smaller than the diffraction-limited angular resolution of the interferometer.

First high dynamic range and high resolution images of the sky obtained with a diffractive Fresnel array telescope

This paper presents high contrast images of sky sources, obtained from the ground with a novel optical concept: Fresnel arrays. We demonstrate the efficiency of a small 20 cm prototype Fresnel array for making images with high brightness ratios, achieving contrasts up to 4 × 105 on sky sources such as Mars and its satellites, and the Sirius A–B couple. These validation results are promising for future applications in space, for example the 4 m array we have proposed to ESA in the frame of the “Call for a Medium-size mission opportunity for a launch in 2022”. Fresnel imagers are the subject of a topical issue of Experimental Astronomy published in 2011, but only preliminary results were presented at the time. Making images of astronomical bodies requires an optical component to focus light. This component is usually a mirror or a lens, the quality of which is critical for sharp and high contrast images. However, reflection on a mirror and refraction through a lens are not the only ways to focus light: an alternative is provided by diffraction through binary masks (opaque foils with multiple precisely etched sub-apertures). Our Fresnel arrays are such diffractive focusers, they offer weight, price and size advantages over traditional optics in space-based astronomical instruments. This novel approach requires only void apertures of special shapes in an opaque material to form sharp images, thus avoiding the wavefront distortion, diffusion and spectral absorption associated with traditional optical media. In our setup, lenses and/or mirrors are involved only downstream (at small sizes) for focal instrumentation and chromatic correction. Fresnel arrays produce high contrast images, the resolution of which reaches the theoretical limit of diffraction. Unlike mirrors, they do not require high precision polishing or positioning, and can be used in a large domain of wavelengths from far IR to far UV, enabling the study of many science cases in astrophysics from exoplanet surfaces and atmospheres to galaxy evolution.

Planckpre-launch status: The HFI instrument, from specification to actual performance

Context. The High Frequency Instrument (HFI) is one of the two focal instruments of the Planck mission. It will observe the whole sky in six bands in the 100 GHz-1 THz range. Aims: The HFI instrument is designed to measure the cosmic microwave background (CMB) with a sensitivity limited only by fundamental sources: the photon noise of the CMB itself and the residuals left after the removal of foregrounds. The two high frequency bands will provide full maps of the submillimetre sky, featuring mainly extended and point source foregrounds. Systematic effects must be kept at negligible levels or accurately monitored so that the signal can be corrected. This paper describes the HFI design and its characteristics deduced from ground tests and calibration. Methods: The HFI instrumental concept and architecture are feasible only by pushing new techniques to their extreme capabilities, mainly: (i) bolometers working at 100 mK and absorbing the radiation in grids; (ii) a dilution cooler providing 100 mK in microgravity conditions; (iii) a new type of AC biased readout electronics and (iv) optical channels using devices inspired from radio and infrared techniques. Results: The Planck-HFI instrument performance exceeds requirements for sensitivity and control of systematic effects. During ground-based calibration and tests, it was measured at instrument and system levels to be close to or better than the goal specification.

Mykerinos: Preparing Long Baseline Interferometry at Dome C

Site studies have proved Dome C to be an excellent site for optical interferometry, maybe the only possible site on Earth for the deployement of a large post-VLTI interferometric facility, like KEOPS. Indeed, recent studies have shown the possiblity of interferometric observations of faint objects, high sensitivity and high precision observations, direct imaging and nulling interferometry. However the achievement of this ambitious project assumes the pavement of a roadmap, including different steps. The first one should be a demonstrator, called Mykerinos. Mykerinos is a diluted aperture interferometer composed of at least two light collecting units with a baseline between 40 to 100 m (or more) consisting of 50 cm diameter telescopes. The telescope design is directly derived from our Laboratory's experience in the ASTEP experiment. Mykerinos will be equipped with a dual field focal instrument which is a pre-requisite for its site testing, as well as for its science demonstration purposes.

Fresnel Interferometric Imager: ground-based prototype

The Fresnel Interferometric Imager is a space-based astronomical telescope project yielding milli-arcsecond angular resolution and high contrast images with loose manufacturing constraints. This optical concept involves diffractive focusing and formation flying: a first "primary optics" space module holds a large binary Fresnel array, and a second "focal module" holds optical elements and focal instruments that allow for chromatic dispersion correction. We have designed a reduced-size Fresnel Interferometric Imager prototype and made optical tests in our laboratory in order to validate the concept for future space missions. The primary module of this prototype consists of a square, 8 cm side, 23 m focal length Fresnel array. The focal module is composed of a diaphragmed small telescope used as "field lens," a small cophased diverging Fresnel zone lens that cancels the dispersion, and a detector. An additional module collimates the artificial targets of various shapes, sizes, and dynamic ranges to be imaged. We describe the experimental setup, different designs of the primary Fresnel array, and the cophased Fresnel zone lens that achieves rigorous chromatic correction. We give quantitative measurements of the diffraction limited performances and dynamic range on double sources. The tests have been performed in the visible domain, lambda = 400-700 nm. In addition, we present computer simulations of the prototype optics based on Fresnel propagation that corroborate the optical tests. This numerical tool has been used to simulate the large aperture Fresnel arrays that could be sent to space with diameters of 3 to 30 m, foreseen to operate from Lyman alpha (121 nm) to mid IR (25 microm).

The fresnel interferometric imager

The Fresnel Interferometric Imager has been proposed to the European Space Agency (ESA) Cosmic Vision plan as a class L mission. This mission addresses several themes of the CV Plan: Exoplanet study, Matter in extreme conditions, and The Universe taking shape. This paper is an abridged version of the original ESA proposal. We have removed most of the technical and financial issues, to concentrate on the instrumental design and astrophysical missions. The instrument proposed is an ultra-lightweight telescope, featuring a novel optical concept based on diffraction focussing. It yields high dynamic range images, while releasing constraints on positioning and manufacturing of the main optical elements. This concept should open the way to very large apertures in space. In this two spacecraft formation-flying instrument, one spacecraft holds the focussing element: the Fresnel interferometric array; the other spacecraft holds the field optics, focal instrumentation, and detectors. The Fresnel array proposed here is a 3.6 ×3.6 m square opaque foil punched with 105 to 106 void “subapertures”. Focusing is achieved with no other optical element: the shape and positioning of the subapertures (holes in the foil) is responsible for beam combining by diffraction, and 5% to 10% of the total incident light ends up into a sharp focus. The consequence of this high number of subapertures is high dynamic range images. In addition, as it uses only a combination of vacuum and opaque material, this focussing method is potentially efficient over a very broad wavelength domain. The focal length of such diffractive focussing devices is wavelength dependent. However, this can be corrected. We have tested optically the efficiency of the chromatism correction on artificial sources (500 < λ < 750 nm): the images are diffraction limited, and the dynamic range measured on an artificial double source reaches 6.2 10 − 6. We have also validated numerical simulation algorithms for larger Fresnel interferometric arrays. These simulations yield a dynamic range (rejection factor) close to 10 − 8 for arrays such as the 3.6 m one we propose. A dynamic range of 10 − 8 allows detection of objects at contrasts as high as than 10 − 9 in most of the field. The astrophysical applications cover many objects in the IR, visible an UV domains. Examples are presented, taking advantage of the high angular resolution and dynamic range capabilities of this concept.

The Fresnel interferometric imager

The Fresnel interferometric imager is a new kind of high angular resolution space instrument for the UV domain, and the related astrophysical targets. This optical concept is meant to allow larger and lighter apertures in space than solid state optics. It yields high dynamic range images and same resolution as that of a solid aperture of the same size. The long focal lengths of the Fresnel imager (a few kilometers) require operation by two-vessel formation flying in space. The first vessel holds a large and thin opaque foil punched with thousands of holes: the interferometric array, the second vessel holds the focal instrumentation. This Fresnel imager has been designed for mapping high contrast stellar environments: dust disks, close companions and (we hope) exoplanets. Compact objects such as large stellar photospheres may be imaged with array sizes of a few meters in the UV. Larger and more complex fields can also be imaged, although with a lesser dynamic range, such as small fields on galactic clouds or extragalactic fields, or in an other domain: small solar system bodies. We present the first images obtained on artificial sources with an 8 cm laboratory testbed array having 26680 apertures, the measured dynamic range of these images and their diffraction limited angular resolution. A 3 m class probatory space mission will be studied and follow a validation path, It has been submitted as a proposal to the ESA Cosmic Vision program.

On-sky observations with an achromatic hybrid phase knife coronagraph in the visible

Context. The four-quadrant phase mask stellar coronagraph, introduced by D. Rouan et al., is capable of achieving very high dynamical range imaging and was studied in the context of the direct detection of extra-solar planets. Achromatic four-quadrant phase mask is currently being developed for broadband IR applications.Aims. We report on laboratory and on-sky tests of a prototype coronagraph in the visible. This prototype, the achromatic hybrid phase knife coronagraph , was derived from the four-quadrant phase mask principle.Methods. The instrumental setup implementing the coronagraph itself was designed to record the pre- and post-coronagraphic images simultaneously so that an efficient real-time image selection procedure can be performed. We describe the coronagraph and the associated tools that enable robust and repeatable observations. We present an algorithm of image selection that has been tested against the real on-sky data of the binary star HD 80081 (* 38 Lyn).Results. Although the observing conditions were poor, the efficiency of the proposed method is proven. From this experiment, we derive procedures that can apply to future focal instruments associating adaptive optics and coronagraphy, targeting high dynamic range imaging in astronomy, such as detecting extra-solar planets.

Differential Interferometry with the AMBER/VLTI instrument: Description, performances and illustration

AMBER is the near I.R. focal instrument of the VLTI. It recombines 3 beams simultaneously and has spectral resolution capability allowing simultaneous spectrum, visibilities, differential visibilities, closure phase and differential phases measurements on the observed sources. We present here the general formalism used on AMBER in order to compute differential phases and differential visibilities, in complement to the article of Tatulli et al. (2006). We show that these differential observables have precisions close to the fundamental noises and we present an illustration of model-fitting using them on the binary star γ 2 Velorum where we made a precise measurment of the astrometry of the 2 components (3.65 ± 0.1 mas).