José V. Gigante

OSIRIS tunable imager and spectrograph for the GTC. Instrument status

OSIRIS (Optical System for Imaging and low Resolution Integrated Spectroscopy) is the optical Day One instrument for the 10.4m Spanish telescope GTC to be installed in the Observatorio del Roque de Los Muchachos (La Palma, Spain). This instrument, operational in mid-2004, covers from 360 up to 1000 nm. OSIRIS observing modes include direct imaging with tunable and conventional filters, long slit and multiple object spectroscopy and fast spectrophotometry. The OSIRIS wide field of view, high efficiency and the new observing modes (tunable imaging and fast spectrophotometry) for 8-10m class telescopes will provide GTC with a powerful tool for their scientific exploitation. The present paper provides an updated overview of the instrument development, of some of the scientific projects that will be tackled with OSIRIS and of the general requirements driving the optical and mechanical design.

FPGA adaptive optics system test bench

FPGA (Field Programmable Gate Array) technology has become a very powerful tool available to the electronic designer, specially after the spreading of high quality synthesis and simulation software packages at very affordable prices. They also offer high physical integration levels and high speed, and eases the implementation of parallelism to obtain superb features. Adaptive optics for the next generation telescopes (50-100 m diameter) -or improved versions for existing ones- requires a huge amount of processing power that goes beyond the practical limits of todays processor capability, and perhaps tomorrows, so FPGAs may become a viable approach. In order to evaluate the feasibility of such a system, a laboratory adaptive optical test bench has been developed, using only FPGAs in its closed loop processing chain. A Shack-Hartmann wavefront sensor has been implemented using a 955-image per second DALSA CA-D6 camera, and a 37-channel OKO mirror has been used for wavefront correcting. Results are presented and extrapolation of the behavior for large and extremely large telescopes is discussed.

Adaptive Optics Real-Time Control Using FPGA

Adaptive optics is a very promising field in earth-based astronomy, and has become a must in the development of large (10 m) and giant (50-100 m) telescopes. Real time compensation of the atmospheric turbulence requires a huge amount of processing power that goes beyond the practical limits of todays processor capability, and perhaps tomorrows. FPGAs may become a viable approach when exploiting their natural parallel arrangement and their continuously improving speed, after their size has grown up to the point of accepting a whole system to be embedded in just one unit. In order to evaluate the feasibility of such a system, a laboratory adaptive optical test bench has been developed, needing only one VTRTEX-4 FPGA to implement the whole closed loop processing chain, computing 39 actuations from a 8times8 microlenses array at 1000 images per second.

OSIRIS tunable imager and spectrograph for the GTC: from design to commissioning

OSIRIS (Optical System for Imaging and low Resolution Integrated Spectroscopy) was the optical Day One instrument for the 10.4m Spanish telescope GTC. It is installed at the Observatorio del Roque de Los Muchachos (La Palma, Spain). This instrument has been operational since March-2009 and covers from 360 to 1000 nm. OSIRIS observing modes include direct imaging with tunable and conventional filters, long slit and low resolution spectroscopy. OSIRIS wide field of view and high efficiency provide a powerful tool for the scientific exploitation of GTC. OSIRIS was developed by a Consortium formed by the Instituto de Astrofísica de Canarias (IAC) and the Instituto de Astronomía de la Universidad Nacional Autónoma de México (IA-UNAM). The latter was in charge of the optical design, the manufacture of the camera and collaboration in the assembly, integration and verification process. The IAC was responsible for the remaining design of the instrument and it was the project leader. The present paper considers the development of the instrument from its design to its present situation in which is in used by the scientific community.

EMIR and OSIRIS instruments: common data acquisition software architecture

OSIRIS (Optical System for Imaging and low/intermediate-Resolution Integrated Spectroscopy) and EMIR (InfraRed MultiObject Spectrograph) are instruments designed to obtain images and low resolution spectra of astronomical objects in the optical and infrared domains. They will be installed on Day One and Day Two, respectively, in the Nasmyth focus of the 10-meter Spanish GTC Telescope. This paper describes the architecture of the Data Acquisition System (DAS), emphasizing the functional and quality attributes. The DAS is a component oriented, concurrent, distributed and real time system which coordinates several activities: acquisition of images coming from the detectors controller, tagging, and data communication with the required telescope system resources. This architecture will minimize efforts in the development of future DAS. Common aspects, such as the data process flow, concurrency, asynchronous/synchronous communication, memory management, and exception handling, among others, are managed by the proposed architecture. This system also allows a straightforward inclusion of variable parts, such as dedicated hardware and different acquisition modes. The DAS has been developed using an object oriented approach and uses the Adaptive Communication Environment (ACE) to be operating system independent.

HARMONI pre-optics design at PDR

HARMONI is a visible and near-infrared (0.5 to 2.45 μm) integral field spectrograph, providing the E-ELTs core spectroscopic capability, over a range of resolving powers from R (λ/Δλ) ~ 3500 to ~18000. The instrument provides simultaneous spectra of ∼32000 spaxels arranged in a sqrt(2):1 aspect ratio contiguous field. The pre-optics take light entering the science cryostat (from the telescope or calibration system), reformatting and conditioning to be suitable for input for the rest of the instrument. This involves many functions, mainly relaying the light from the telescope focal plane to the integral field unit (IFU) focal plane via a set of interchangeable scale changing optics. The pre-optics also provides components including a focal plane mask wheel, cold pupil masks, spectral order sorting filters, a fast shutter, and a pupil imaging capability to check telescope/instrument pupil alignment. In this paper, we present the optical design of the HARMONI pre-optics at Preliminary Design Review and, in particular, we detail the differences with the previous design and the difficulties salved to the Preliminary Design Review.

Conceptual design of a cryogenic pupil mechanism with continuous complex movements for HARMONI

In order to improve the signal-to-noise ratio of HARMONI (E-ELT first light visible and near-infrared integral field VIR spectrometer), a pupil mask has been identified to be included at the fore-optics to limit the background radiation coming into the spectrographs. This mask should rotate synchronously with the telescope pupil during observations, taking into account the combined effects of the telescope tracking and the de-rotation of the FOV. The implementation of the pupil mask functionality will require complex movements with high precision at cryogenic temperatures which implies an important technological challenge. This paper details a set of experiments completed to gain knowledge and experience in order to accomplish the design and control of cryogenic mechanisms reaching this type of pupil motion. The conceptual design of the whole mechanism started from the feedback acquired from those experiments is also described in the following sections.

HARMONI instrument control electronics

HARMONI is an integral field spectrograph working at visible and near-infrared wavelengths over a range of spatial scales from ground layer corrected to fully diffraction-limited. The instrument has been chosen to be part of the first-light complement at the European Extremely Large Telescope (E-ELT). This paper describes the instrument control electronics to be developed at IAC. The large size of the HARMONI instrument, its cryogenic operation, and the fact that it must operate with enhanced reliability is a challenge from the point of view of the control electronics design. The present paper describes a design proposal based on the current instrument requirements and intended to be fully compliant with the ESO E-ELT standards, as well as with the European EMC and safety standards. The modularity of the design and the use of COTS standard hardware will benefit the project in several aspects, as reduced costs, shorter schedule by the use of commercially available components, and improved quality by the use of well proven solutions.

Enhancements over the electronic control for OSIRIS-Gtc Fabry-Perot tunable filters

OSIRIS (Optical System for Imaging and low Resolution Integrated Spectroscopy) is the optical Day One instrument for the 10.4m Spanish telescope GTC (Gran Telescopio Canarias). The instrument spectral range covers from 365 up to 1000 nm. One of the most important elements of OSIRIS is its two commercial ICOS ET100 wide field Fabry-Perot tunable filters, that will provide a powerful tool to analyse faint emission line objects. Currently, the unique controller available for such device is the so called CS100. Due to the necessity of improvement and addition of some specifications of such controller, a first prototype electronic module has been made and tested successfully. Now, it has developed the final product: a compact mini-module integrated in the CS100 controller, offering a 16-bit resolution over the full range cavity spacing; be able to synchronize cavity changes with an external trigger; full remote control over the front panel of the device and capability to monitor all their signals. It also offers the possibility to load a preprogrammed table sequence of cavity spacing changes, programmable security limits of dynamic range and slew rate applied; and it has high stability over time too. The electronic control is based on an embedded microcontroller into a FPGA.

Are 16 bits really needed in CCDs and infrared detectors for astronomy

One of the problems found in the design of the electronics for astronomical instruments is the difficulty to find precise digitizers (16 bits) at high speed. In fact, most of the chips which claim to have 16-bit actually have a lower ENOB (Effective Number Of Bits), normally around 14, when considering their noise effects. In this paper, a technique based in auto-adjustable gain amplifiers is proposed as a way to relax the A/D requirements for astronomical CCDs and infrared detectors. The amplifiers will automatically toggle between 2 different gains depending on the pixel value. The technique is based on the fact that, due to the shot (photon) noise of the detectors, the maximum signal to noise ratio achievable in most of these devices is relatively low, allowing the use of A/D converters with an ENOB of only 14 (or even 12) bits when combined with auto-adjustable gain amplifiers. It will be shown that the lower resolution of the A/D converters will not affect the accuracy of the science data, even when many images are averaged out to compensate the effects of the shot noise. Furthermore, given that many real A/D converters do not reach an ENOB of 16, for low level signals the accuracy can be even slightly improved with the technique described in this paper. On the other hand, this relaxing of the A/D requirements can allow the use of off-the-shelf boards for the acquisition systems.