arXiv subjects

B. Neichel

Publications and source records attributed to B. Neichel.

At least 37 records · Page 2Linked to original sources

arXiv2018

Overview of the European Extremely Large Telescope and its instrument suite

The European Extremely Large Telescope will see first lights by the end of 2024. With a diameter of almost 40 meters, it will be the biggest optical telescope ever built from the ground. The ELT will open a brand new window in a sensitivity / spatial angular resolution parameter space. To take the full benefit of the scientific potential of this giant, all the instruments will be equipped with Adaptive Optics (AO), providing the sharpest images. This paper provides a quick overview of the AO capabilities of the future instruments to be deployed at the ELT, highlight some of the expected performance and describe a couple of technical challenges that are still to tackle for an optimal scientific use. This paper has been presented at the "Societe Francaise d'Astronomie et Astrophysique" symposium in Bordeaux 2018, it is then naturally biased toward the French contribution for the ELT.

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arXiv2018

Focal plane $C_n^2(h)$ profiling based on single conjugate adaptive optics compensated images

Knowledge of the atmospheric turbulence in the telescope line-of-sight is crucial for wide-field observations assisted by adaptive optics (AO), for which the Point Spread Function (PSF) becomes strongly elongated due to the anisoplanatism effect. This one must be modelled accurately to extrapolate the PSF anywhere across the Field of view (FOV) and improve the science exploitation. However, anisoplanatism is a function of the Cn2(h) profile, that is not directly accessible from single conjugate AO telemetry. One may rely on external profilers, but recent studies have highlighted more than 10% of discrepancies with AO internal measurements, while we aim better than 1% of accuracy for PSF modelling. To tackle this existing limitation, we present the Focal plane profiling (FPP), as a $C_n^2(h)$ profiling method that relies on post-AO focal plane images. We demonstrate such an approach complies with a 1%-level of accuracy on the $C_n^2(h)$ estimation and establish how this accuracy varies regarding the calibration stars magnitudes and positions in the field. We highlight that photometry and astrometry errors due to PSF mis-modelling reaches respectively 1% and 50μas using FPP on a Keck baseline, with a preliminary calibration using a star of magnitude H=14 at 20". We also validate this concept using Canadas NRC-Herzberg HENOS testbed images in comparing FPP retrieval with alternative $C_n^2(h)$ measurements on HeNOS. The FPP approach allows to profile the $C_n^2(h)$ using the SCAO systems and improve significantly the PSF characterisation. Such a methodology is also ELT-size compliant and will be extrapolated to tomographic systems in a near future.

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arXiv2018

The adaptive optics modes for HARMONI: from Classical to Laser Assisted Tomographic AO

HARMONI is a visible and NIR integral field spectrograph, providing the E-ELT's core spectroscopic capability at first light. HARMONI will work at the diffraction limit of the E-ELT, thanks to a Classical and a Laser Tomographic AO system. In this paper, we present the system choices that have been made for these SCAO and LTAO modules. In particular, we describe the strategy developed for the different Wave-Front Sensors: pyramid for SCAO, the LGSWFS concept, the NGSWFS path, and the truth sensor capabilities. We present first potential implementations. And we asses the first system performance.

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arXiv2018

Off-axis point spread function characterisation in laser-guide star adaptive optics systems

Adaptive optics (AO) restore the angular resolution of ground-based telescopes, but at the cost of delivering a time- and space-varying point spread function (PSF) with a complex shape. PSF knowledge is crucial for breaking existing limits on the measured accuracy of photometry and astrometry in science observations. In this paper, we concentrate our analyses on anisoplanatism signature only onto PSF: for large-field observations (20") with single- conjugated AO, PSFs are strongly elongated due to anisoplanatism that manifests itself as three different terms for Laser-guide star (LGS) systems: angular, focal and tilt. We propose a generalized model that relies on a point-wise decomposition of the phase and encompasses the non-stationarity of LGS systems. We demonstrate it is more accurate and less computationally demanding than existing models: it agrees with end-to-end physical-optics simulations to within 0.1% of PSF measurables, such as Strehl-ratio, FWHM and fraction of variance unexplained.Secondly, we study off-axis PSF modelling is with respect to $C_n^2(h)$ profile (heights and fractional weights). For 10m class telescope, PSF morphology is estimated at 1% level as long as we model the atmosphere with at least 7 layers whose heights and weights are known respectively with 200m and 10% precision. As a verification test we used the Canada's NRC-Herzberg HeNOS testbed data, featuring four lasers. We highlight capability of retrieving off-axis PSF characteristics within 10% of fraction of variance unexplained, which complies with the expected range from the sensitivity analysis. Our new off-axis PSF modelling method lays the ground-work for testing on-sky in the near future.

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arXiv2018

Towards an automatic wind speed and direction profiler for Wide Field AO systems

Wide Field Adaptive Optics (WFAO) systems are among the most sophisticated AO systems available today on large telescopes. The knowledge of the vertical spatio-temporal distribution of the wind speed (WS) and direction (WD) are fundamental to optimize the performance of such systems. Previous studies already proved that the Gemini Multi-Conjugated AO system (GeMS) is able to retrieve measurements of the WS and WD stratification using the SLODAR technique and to store measurements in the telemetry data. In order to assess the reliability of these estimates and of the SLODAR technique applied to such a kind of complex AO systems, in this study we compared WS and WD retrieved from GeMS with those obtained with the atmospherical model Meso-Nh on a rich statistical sample of nights. It has been previously proved that, the latter technique, provided an excellent agreement with a large sample of radiosoundings both, in statistical terms and on individual flights. It can be considered, therefore, as an independent reference. The excellent agreement between GeMS measurements and the model that we find in this study, proves the robustness of the SLODAR approach. To by-pass the complex procedures necessary to achieve automatic measurements of the wind with GeMS, we propose a simple automatic method to monitor nightly WS and WD using the Meso-Nh model estimates. Such a method can be applied to whatever present or new generation facilities supported by WFAO systems. The interest of this study is, therefore, well beyond the optimization of GeMS performance.

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arXiv2017

Optimal correction of distortion for High Angular Resolution images. Application to GeMS data

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 based-telescope, 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 high-precision 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.

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arXiv2016

PSF reconstruction validated using on-sky CANARY data in MOAO mode

In preparation of future Multi-Object Spectrographs (MOS) whose one of the major role is to provide an extensive statistical studies of high redshifted galaxies surveyed, the demonstrator Canary has been designed to tackle technical challenges related to open-loop Adaptive-Optics (AO) control with jointed Natural Guide Star (NGS) and Laser Guide Star (LGS) tomography. We have developed a Point Spread Function (PSF)-Reconstruction algorithm dedicated to MOAO systems using system telemetry to estimate the PSF potentially anywhere in the observed field, a prerequisite to post- process AO-corrected observations in Integral Field Spectroscopy (IFS). In this paper we show how to handle off-axis data to estimate the PSF using atmospheric tomography and compare it to a classical approach that uses on-axis residual phase from a truth sensor observing a natural bright source. We have reconstructed over 450 on-sky Canary PSFs and we get bias/1-$σ$ standard-deviation (std) of 1.3/4.8 on the H-band Strehl ratio (SR) with 92.3% of correlation between reconstructed and sky SR. On the Full Width at Half Maximum (FWHM), we get respectively 2.94 mas, 19.9 mas and 88.3% for the bias, std and correlation. The reference method achieves 0.4/3.5/95% on the SR and 2.71 mas/14.9 mas/92.5% on the FWHM for the bias/std/correlation.

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arXiv2016

William Herschel Telescope site characterization using the MOAO pathfinder CANARY on-sky data

Canary is the Multi-Object Adaptive Optics (MOAO) pathfinder for the future MOAO-assisted Integral-Field Units (IFU) proposed for Extremely Large Telescopes (ELT). The MOAO concept relies on tomographically reconstructing the turbulence using multiple measurements along different lines of sight. Tomography requires the knowledge of the statistical turbulence parameters, commonly recovered from the system telemetry using a dedicated profiling technique. For demonstration purposes with the MOAO pathfinder Canary , this identification is performed thanks to the Learn & Apply (L&A) algorithm, that consists in model- fitting the covariance matrix of WFS measurements dependent on relevant parameters: $C_n^2(h)$ profile, outer scale profile and system mis-registration. We explore an upgrade of this algorithm, the Learn 3 Steps (L3S) approach, that allows one to dissociate the identification of the altitude layers from the ground in order to mitigate the lack of convergence of the required empirical covariance matrices therefore reducing the required length of data time-series for reaching a given accuracy. For nominal observation conditions, the L3S can reach the same level of tomographic error in using five times less data frames than the L&A approach. The L3S technique has been applied over a large amount of Canary data to characterize the turbu- lence above the William Herschel Telescope (WHT). These data have been acquired the 13th, 15th, 16th, 17th and 18th September 2013 and we find 0.67"/8.9m/3.07m/s of total seeing/outer scale/wind-speed, with 0.552"/9.2m/2.89m/s below 1.5 km and 0.263"/10.3m/5.22m/s between 1.5 and 20 km. We have also de- termined the high altitude layers above 20 km, missed by the tomographic reconstruction on Canary , have a median seeing of 0.187" and have occurred 16% of observation time.

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arXiv2016

Towards an automatic system for monitoring of CN2 and wind speed profiles with GeMS

Wide Field Adaptive Optics (WFAO) systems represent the more sophisticated AO systems available today at large telescopes. A critical aspect for these WFAO systems in order to deliver an optimised performance is the knowledge of the vertical spatiotemporal distribution of the CN2 and the wind speed. Previous studies (Cortes et al., 2012) already proved the ability of GeMS (the Gemini Multi-Conjugated AO system) in retrieving CN2 and wind vertical stratification using the telemetry data. To assess the reliability of the GeMS wind speed estimates a preliminary study (Neichel et al., 2014) compared wind speed retrieved from GeMS with that obtained with the atmospherical model Meso-Nh on a small sample of nights providing promising results. The latter technique is very reliable for the wind speed vertical stratification. The model outputs gave, indeed, an excellent agreement with a large sample of radiosoundings (~ 50) both in statistical terms and on individual flights (Masciadri et al., 2013). Such a tool can therefore be used as a valuable reference in this exercise of cross calibrating GeMS on-sky wind estimates with model predictions. In this contribution we achieved a two-fold results: (1) we extended analysis on a much richer statistical sample (~ 43 nights), we confirmed the preliminary results and we found an even better correlation between GeMS observations and the atmospherical model with basically no cases of not-negligible uncertainties; (2) we evaluate the possibility to use, as an input for GeMS, the Meso-Nh estimates of the wind speed stratification in an operational configuration. Under this configuration these estimates can be provided many hours in advanced with respect to the observations and with a very high temporal frequency (order of 2 minutes or less).

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arXiv2016

Correction of distortion for optimal image stacking in Wide Field Adaptive Optics: Application to GeMS data

The advent of Wide Field Adaptive Optics (WFAO) systems marks the beginning of a new era in high spatial resolution imaging. The newly commissioned Gemini South Multi-Conjugate Adaptive Optics System (GeMS) combined with the infrared camera Gemini South Adaptive Optics Imager (GSAOI), delivers quasi diffraction-limited images over a field of 2 arc-minutes across. However, despite this excellent performance, some variable residues still limit the quality of the analyses. In particular, distortions severely affect GSAOI and become a critical issue for high-precision astrometry and photometry. In this paper, we investigate an optimal way to correct for the distortion following an inverse problem approach. Formalism as well as applications on GeMS data are presented.

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arXiv2016

Deep GeMS/GSAOI near-infrared observations of N159W in the Large Magellanic Cloud

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 JHKs-band images obtained with the GeMS/GSAOI instrument on the Gemini South telescope. The typical angular resolution of the images is of 100 mas, with a limiting magnitude in H of 22 mag (90 percent 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 + or - 1 Myr for the central cluster, with its IMF described by a power-law with an index of gamma = - 1.05 + or - 0.2 , and with a total estimated mass of 1300 solar mass. 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.

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arXiv2015

GeMs/GSAOI observations of La Serena 94: an old and far open cluster inside the solar circle

Physical properties were derived for the candidate open cluster La Serena 94, recently unveiled by the VVV collaboration. Thanks to the exquisite angular resolution provided by GeMS/GSAOI, we could characterize this system in detail, for the first time, with deep photometry in JHK$_{s}$ - bands. Decontaminated JHK$_{s}$ diagrams reach about 5 mag below the cluster turnoff in H. The locus of red clump giants in the colour - colour diagram, together with an extinction law, was used to obtain an average extinction of $A_V =14.18 \pm 0.71$. The same stars were considered as standard - candles to derive the cluster distance, $8.5 \pm 1.0$ kpc. Isochrones were matched to the cluster colour - magnitude diagrams to determine its age, $\log{t(yr)}=9.12\pm 0.06$, and metallicity, $Z=0.02\pm0.01$. A core radius of $r_{c}=0.51\pm 0.04$ pc was found by fitting King models to the radial density profile. By adding up the visible stellar mass to an extrapolated mass function, the cluster mass was estimated as $M=(2.65\pm0.57) \times 10^3$ M$_{\odot}$, consistent with an integrated magnitude of $M_{K}=-5.82\pm0.16$ and a tidal radius of $r_{t}=17.2\pm2.1$ pc. The overall characteristics of La Serena 94 confirm that it is an old open cluster located in the Crux spiral arm towards the fourth Galactic quadrant and distant $7.30\pm 0.49$ kpc from the Galactic centre. The cluster distorted structure, mass segregation and age indicate that it is a dynamically evolved stellar system.

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arXiv2015

Variation around a Pyramid theme: optical recombination and optimal use of photons

We propose a new type of Wave Front Sensor (WFS) derived from the Pyramid WFS (PWFS). This new WFS, called the Flattened Pyramid-WFS (FPWFS), has a reduced Pyramid angle in order to optically overlap the four pupil images into an unique intensity. This map is then used to derive the phase information. In this letter this new WFS is compared to three existing WFSs, namely the PWFS, the Modulated PWFS (MPWFS) and the Zernike WFS (ZWFS) following tests about sensitivity, linearity range and low photon flux behavior. The FPWFS turns out to be more linear than a modulated pyramid for the high-spatial order aberrations but it provides an improved sensitivity compared to the non-modulated pyramid. The noise propagation may even be as low as the ZWFS for some given radial orders. Furthermore, the pixel arrangement being more efficient than for the PWFS, the FPWFS seems particularly well suited for high-contrast applications.

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arXiv2015

Deep near-infrared adaptive optics observations of a young embedded cluster at the edge of the RCW 41 HII region

We investigate the star formation activity in a young star forming cluster embedded at the edge of the RCW 41 HII region. As a complementary goal, we aim at demonstrating the gain provided by Wide-Field Adaptive Optics instruments to study young clusters. We used deep, JHKs 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 an AO instrument, delivering 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 JHKs catalog is used to build color-color diagrams, and select Young Stellar Objects (YSOs) candidates. We detect the presence of 80 Young Stellar Object (YSO) candidates. Those YSOs are used to infer the cluster age, which is found to be in the range 1 to 5 Myr. 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 evidence a potential age gradient across the field, suggesting 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 Msun). The logarithmic mass function rises to peak at 0.3 Msun, before turning over and declining into the brown dwarf regime. The total cluster mass derived is estimated to be 78 +/- 18 Msun, while the ratio of brown dwarfs to star derived is 18 p/- 5 %. When comparing 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.

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arXiv2015

Star formation in the filament of S254-S258 OB complex: a cluster in the process of making

Infrared Dark Clouds are ideal laboratories to study the initial processes of high-mass star and star cluster formation. We investigated star formation activity of an unexplored filamentary dark cloud (~5.7pc x 1.9pc), which itself is part of a large filament (~20pc) located in the S254-S258 OB complex at a distance of 2.5kpc. Using MIPS Spitzer 24 micron data, we uncover 49 sources with SNR greater than 5. We identified 45 sources as candidate YSOs of Class I, Flat-spectrum & Class II nature. Additional 17 candidate YSOs (9 Class I & 8 Class II) are also identified using JHK and WISE photometry. We find that the protostar to Class II sources ratio (~2) and the protostar fraction (~70%) of the region are high. When the protostar fraction compared to other young clusters, it suggests that the star formation in the dark cloud was possibly started only 1 Myr ago. Combining the NIR photometry of the YSO candidates with the theoretical evolutionary models, we infer that most of the candidate YSOs formed in the dark cloud are low-mass (<2 Msolar) in nature. We examine the spatial distribution of the YSOs and find that majority of them are linearly aligned along the highest column density line (N(H2) ~1 x 10^22 cm^-2) of the dark cloud along its long axis at mean nearest neighbor separation of ~0.2pc. Using observed properties of the YSOs, physical conditions of the cloud and a simple cylindrical model, we explore the possible star formation process of this filamentary dark cloud and suggest that gravitational fragmentation within the filament should have played a dominant role in the formation of the YSOs. From the total mass of the YSOs, gaseous mass associated with the dark cloud, and surrounding environment, we infer that the region is presently forming stars at an efficiency ~3% and a rate ~30 Msolar Myr^-1, and may emerge to a richer cluster.

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arXiv2015

Validation Through Simulations of a Cn2 Profiler for the ESO/VLT Adaptive Optics Facility

The Adaptive Optics Facility (AOF) project envisages transforming one of the VLT units into an adaptive telescope and providing its ESO (European Southern Observatory) second generation instruments with turbulence corrected wavefronts. For MUSE and HAWK-I this correction will be achieved through the GALACSI and GRAAL AO modules working in conjunction with a 1170 actuators Deformable Secondary Mirror (DSM) and the new Laser Guide Star Facility (4LGSF). Multiple wavefront sensors will enable GLAO and LTAO capabilities, whose performance can greatly benefit from a knowledge about the stratification of the turbulence in the atmosphere. This work, totally based on end-to-end simulations, describes the validation tests conducted on a Cn2 profiler adapted for the AOF specifications. Because an absolute profile calibration is strongly dependent on a reliable knowledge of turbulence parameters r0 and L0, the tests presented here refer only to normalized output profiles. Uncertainties in the input parameters inherent to the code are tested as well as the profiler response to different turbulence distributions. It adopts a correction for the unseen turbulence, critical for the GRAAL mode, and highlights the effects of masking out parts of the corrected wavefront on the results. Simulations of data with typical turbulence profiles from Paranal were input to the profiler, showing that it is possible to identify reliably the input features for all the AOF modes.

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arXiv2013

Haffner 16: A Young Moving Group in the Making

The photometric properties of main sequence (MS) and pre-main sequence (PMS) stars in the young cluster Haffner 16 are examined using images recorded with the Gemini South Adaptive Optics Imager (GSAOI) and corrected for atmospheric blurring by the Gemini Multi-Conjugate Adapative Optics System (GeMS). A rich population of PMS stars is identified, and comparisons with isochrones suggest an age < 10 Myr assuming a distance modulus of 13.5 (D = 5 kpc). When compared with the solar neighborhood, Haffner 16 is roughly a factor of two deficient in objects with sub-solar masses. PMS objects in the cluster are also more uniformly distributed on the sky than bright MS stars. It is suggested that Haffner 16 is dynamically evolved, and that it is shedding protostars with sub-solar masses. Young low mass clusters like Haffner 16 are one possible source of PMS stars in the field. The cluster will probably evolve on time scales of ~ 100 - 1000 Myr into a diffuse moving group with a mass function that is very different from that which prevailed early in its life.

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arXiv2009

The Physics and Mass Assembly of distant galaxies with the E-ELT

One of the main science goal of the future European Extremely Large Telescope will be to understand the mass assembly process in galaxies as a function of cosmic time. To this aim, a multi-object, AO-assisted integral field spectrograph will be required to map the physical and chemical properties of very distant galaxies. In this paper, we examine the ability of such an instrument to obtain spatially resolved spectroscopy of a large sample of massive (0.1 5) redshift bin. We find that a survey of Ngal galaxies that fulfil the range of science goals can be achieved with a ~90 nights program on the E-ELT, provided a multiplex capability M Ngal/8.

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