Very accurate cryogenic mechanisms for CRIRES+

After 5 years of operation on the VLT, a large upgrade of CRIRES (the ESO Cryogenic InfraRed Echelle Spectrograph) was decided mainly in order to increase the efficiency. Using a cross dispersion design allows better wavelength coverage per exposure. This means a complete re-design of the cryogenic pre-optic which were including a predispersion stage with a large prism as dispersive element. The new design requires a move of the entrance slit and associated decker toward the first intermediate focal plane right behind the window. Implement 2 functions with high positioning accuracy in a pre-defined and limited space was a real challenge. The design and the test results recorded in the ESO Cryogenic Test Facility are reported in this paper. The second critical function is the grating wheel which positions the 6 cross disperser gratings into the beam. The paper describes the design of the mechanism which includes a detente system in order to guaranty the 5 arc sec positioning reproducibility requested. The design includes also feedback system, based on switches, in order to ensure that the right grating is in position before starting a long exposure. The paper reports on the tests carried out at cryogenic temperature at the sub-system level. It also includes early performances recorded in the instrument along the first phases of the system test

The "+" for CRIRES: enabling better science at infrared wavelength and high spectral resolution at the ESO VLT

The adaptive optics (AO) assisted CRIRES instrument is an IR (0.92 - 5.2 μm) high-resolution spectrograph was in operation from 2006 to 2014 at the Very Large Telescope (VLT) observatory. CRIRES was a unique instrument, accessing a parameter space (wavelength range and spectral resolution) up to now largely uncharted. It consisted of a single-order spectrograph providing long-slit (40 arcsecond) spectroscopy with a resolving power up to R=100 000. However the setup was limited to a narrow, single-shot, spectral range of about 1/70 of the central wavelength, resulting in low observing efficiency for many scientific programmes requiring a broad spectral coverage. The CRIRES upgrade project, CRIRES+, transforms this VLT instrument into a cross-dispersed spectrograph to increase the simultaneously covered wavelength range by a factor of ten. A new and larger detector focal plane array of three Hawaii 2RG detectors with 5.3 μm cut-off wavelength will replace the existing detectors. For advanced wavelength calibration, custom-made absorption gas cells and an etalon system will be added. A spectro-polarimetric unit will allow the recording of circular and linear polarized spectra. This upgrade will be supported by dedicated data reduction software allowing the community to take full advantage of the new capabilities offered by CRIRES+. CRIRES+ has now entered its assembly and integration phase and will return with all new capabilities by the beginning of 2018 to the Very Large Telescope in Chile. This article will provide the reader with an update of the current status of the instrument as well as the remaining steps until final installation at the Paranal Observatory

A unique infrared spectropolarimetric unit for CRIRES+

High-resolution infrared spectropolarimetry has many science applications in astrophysics. One of them is measuring weak magnetic fields using the Zeeman effect. Infrared domain is particularly advantageous as Zeeman splitting of spectral lines is proportional to the square of the wavelength while the intrinsic width of the line cores increases only linearly. Important science cases include detection and monitoring of global magnetic fields on solar-type stars, study of the magnetic field evolution from stellar formation to the final stages of the stellar life with massive stellar winds, and the dynamo mechanism operation across the boundary between fully- and partially-convective stars. CRIRES+ (the CRIRES upgrade project) includes a novel spectropolarimetric unit (SPU) based on polar- ization gratings. The novel design allows to perform beam-splitting very early in the optical path, directly after the tertiary mirror of the telescope (the ESO Very Large Telescope, VLT), minimizing instrumental polariza- tion. The new SPU performs polarization beam-splitting in the near-infrared while keeping the telescope beam mostly unchanged in the optical domain, making it compatible with the adaptive optics system of the CRIRES+ instrument. The SPU consists of four beam-splitters optimized for measuring circular and linear polarization of spectral lines in YJ and HK bands. The SPU can perform beam switching allowing to correct for throughput in each beam and for variations in detector pixel sensitivity. Other new features of CRIRES+, such as substantially increased wavelength coverage, stability and advanced data reduction pipeline will further enhance the sensitivity of the polarimetric mode. The combination of the SPU, CRIRES+ and the VLT is a unique facility for making major progress in understanding stellar activity. In this article we present the design of the SPU, laboratory measurements of individual components and of the whole unit as well as the performance prediction for the operation at the VLT

Characterizing the cross dispersion reflection gratings of CRIRES+

The CRIRES+ project attempts to upgrade the CRIRES instrument into a cross dispersed Echelle spectrograph with a simultaneous recording of 8-10 diffraction orders. In order to transform the CRIRES spectrograph into a cross-dispersing instrument, a set of six reflection gratings, each one optimized for one of the wavelength bands CRIRES+ will operate in (YJHKLM), will be used as cross dispersion elements in CRIRES+. Due to the upgrade nature of the project, the choice of gratings depends on the fixed geometry of the instrument. Thus, custom made gratings would be required to achieve the ambitious design goals. Custom made gratings have the disadvantage, though, that they come at an extraordinary price and with lead times of more than 12 months. To mitigate this, a set of off-the-shelf gratings was obtained which had grating parameters very close to the ones being identified as optimal. To ensure that the rigorous specifications for CRIRES+ will be fulfilled, the CRIRES+ team started a collaboration with the Physikalisch-Technische Bundesanstalt Berlin (PTB) to characterize gratings underconditions similar to the operating conditions in CRIRES+ (angle of incidence, wavelength range). The respective test setup was designed in collaboration between PTB and the CRIRES+ consortium. The PTB provided optical radiation sources and calibrated detectors for each wavelength range. With this setup, it is possible to measure the absolute efficiency of the gratings both wavelength dependent and polarization state dependent in a wavelength range from 0.9 μm to 6 μm

Full system test and early preliminary acceptance Europe results for CRIRES+

CRIRES+ is the new high-resolution NIR echelle spectrograph intended to be operated at the platform B of VLT Unit telescope UT3. It will cover from Y to M bands (0.95-5.3um) with a spectral resolution of R = 50000 or R=100000. The main scientific goals are the search of super-Earths in the habitable zone of low-mass stars, the characterisation of transiting planets atmosphere and the study of the origin and evolution of stellar magnetic fields. Based on the heritage of the old adaptive optics (AO) assisted VLT instrument CRIRES, the new spectrograph will present improved optical layout, a new detector system and a new calibration unit providing optimal performances in terms of simultaneous wavelength coverage and radial velocity accuracy (a few m/s). The total observing efficiency will be enhanced by a factor of 10 with respect to CRIRES. An innovative spectro-polarimetry mode will be also offered and a new metrology system will ensure very high system stability and repeatability. Fiinally, the CRIRES+ project will also provide the community with a new data reduction software (DRS) package. CRIRES+ is currently at the initial phase of its Preliminary Acceptance in Europe (PAE) and it will be commissioned early in 2019 at VLT. This work outlines the main results obtained during the initial phase of the full system test at ESO HQ Garching

CFHT's FlyEyes: Assessing On-sky Performance of the New MIT/LL CCID-35 CCD Curvature Wavefront Sensor

International audienceDue to strict requirements of a very short integration time and very low readout noise, Avalanche Photodiodes (APDs) are the only detectors that have been used for curvature wavefront sensors in astronomy thus far. In 1999, Beletic et al. [1] presented a new CCD design that achieves the same performance as APDs, but with higher reliability and lower cost. In addition, this CCD has a higher quantum efficiency than APD modules and a larger dynamic range, eliminating the need for neutral density filters when viewing bright objects. In close collaboration with ESO and IfA, MIT Lincoln Laboratory designed and fabricated the device, the CCID-35. R. Dorn [2] tested the CCD in the laboratory at ESO extensively and proved that it achieves the predicted performance. CFHT is currently implementing this CCD on the PUEO Adaptive Optics system, to assess its performance on the sky for the first time, and for a direct comparison with the current 19 APD detector system. In this overview we present the current implementation scheme and discuss the upgrade we foresee for PUEO NUI, a 104 element high-order curvature AO system envisaged to replace the current AO system at CFHT [3,4]

FlyEyes: a dual CCD detector system for CFHT PUEO NUI's wavefront sensor

International audienceUntil now, only avalanche photodiodes (APD) have been used as the detectors in curvature wavefront sensors in astronomy. This is due to the strict requirements of very short integration time and very low readout noise. In 1999, Beletic et al. invented a new CCD design which should achieve the same performance as APDs but with higher reliability and lower cost. In addition, this CCD has higher quantum efficiency than APD modules and larger dynamic range, eliminating the need for neutral density filters on bright objects. The CCD was designed and fabricated by MIT Lincoln Laboratory in collaboration with ESO and IfA. R. Dorn extensively tested the CCD in laboratory at ESO and proved that it achieves the predicted performance. CFHT is currently implementing this CCD on PUEO, CFHT"s Adaptive Optics system, to assess its performance for the first time in real conditions on the sky for a direct comparison with the current 19 APD detector system. In this article we present the current implementation scheme and discuss the upgrade we foresee for PUEO NUI, a 104-element high-order curvature AO system envisaged to replace the current AO system at Canada-France-Hawaii Telescope

FlyEyes: integrating CCID-35 into PUEO AO system at CFHT

International audienc

FlyEyes: A CCD-based Wavefront Sensor for PUEO, the CFHT Curvature AO System

International audienceAdaptive optics wavefront sensing imposes stringent requirements on detectors, due to the simultaneous need for extremely low read noise and high frame rates. Curvature wavefront sensing measurements are based on the normalized intensity of the signal in a given subaperture, and avalance photodiodes (APDs) have traditionally been used as detectors in curvature systems such as the Canada-France-Hawaii Telescope (CFHT) adaptive optics (AO) bonnette, called PUEO after the endemic Hawaiian owl. Passively quenched APDs are robust but have low QE (~40%), while actively quenched APDs can have much higher QE, but have been known to fail. Furthermore, curvature systems with large numbers of subapertures are now in operation, and the cost of individual APDs may become prohibitive for such systems. Thus, a CCD-based alternative appears very attractive, and development of a specific chip was initiated at ESO 10 years ago. In this article, we report on the performance of the FlyEyes camera, a project that was conceived to compare the performance of the backside-illuminated custom-designed CCD detector with an array of APDs, used in an operational and well-characterized curvature wavefront AO system. The on-sky performance is demonstrated to be unaffected on bright guide stars (i.e., negligible latency), and although the faint end suffers from the 2.5 e- read noise, the performance can be regained by lowering the frame rate on the wavefront sensor. In this article, we report on results that show that the CCD can be used to replace an array of expensive APDs. This would enable a cost-effective upgrade of PUEO to a higher-order system, as has been proposed at various occasions