Francisco Cobos

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.

VIRUS: a massively replicated IFU spectrograph for HET

We investigate the role of industrial replication in the construction of the next generation of spectrographs for large telescopes. In this paradigm, a simple base spectrograph unit is replicated to provide multiplex advantage, while the engineering costs are amortized over many copies. We argue that this is a cost-effective approach when compared to traditional spectrograph design, where each instrument is essentially a one-off prototype with heavy expenditure on engineering effort. As an example of massive replication, we present the design of, and the science drivers for, the Visible IFU Replicable Ultra-cheap Spectrograph (VIRUS). This instrument is made up of 132 individually small and simple spectrographs, each fed by a fiber integral field unit. The total VIRUS-132 instrument covers ~29 sq. arcminutes per observation, providing integral field spectroscopy from 340 to 570 nm, simultaneously, of 32,604 spatial elements, each 1 sq. arcsecond on the sky. VIRUS-132 will be mounted on the 9.2 m Hobby-Eberly Telescope and fed by a new wide-field corrector with a science field in excess of 16.5 arcminutes diameter. VIRUS represents a new approach to spectrograph design, offering the science multiplex advantage of huge sky coverage for an integral field spectrograph, coupled with the engineering multiplex advantage of >102 spectrographs making up a whole.

Design of an f/1 Camera for the HET Low-Resolution Spectrograph IR Extension *

We present the optical design of the f/1 camera for the Hobby-Eberly Telescope Low Resolution Spectrograph Infrared Extension (LRS-J). This instrument extends the coverage of the LRS to 1300 nm by adding a fast cryogenic camera and volume holographic grisms (VPHG) to the LRS. This approach enables new science without the expense of building a complete new instrument. The camera is a catadioptric Maksutov type design, based on that of the optical LRS, that uses a HAWAII-1 1024x1024 detector. The design succeeds in imaging virtually all the light into one pixel over the HET field of view (FOV) and the wavelength range 900-1300 nm. We discuss the challenges of designing and manufacturing a fast camera for cryogenic use, and give details of the tolerance analysis.

Dual infrared camera for near and mid infrared observations

We present the dual IR camera CID for the 2.12 m telescope of the Observatorio Astronomico Nacional de Mexico, IA-UNAM. The system consists of two separate cameras/spectrographs that operate in different regions of the IR spectrum. In the near IR, CID comprises a direct imaging camera with wide band filters, a CVF, and a low resolution spectrograph employing an InSb 256 x 256 detector. In the mid IR, CID uses a BIB 128 x 128 detector for direct imaging in 10 and 20 microns. Optics and mechanics of CID were developed at IR-Labs (Tucson). The electronics was developed by R. Leach (S. Diego). General design, construction of auxiliary optics (oscillating secondary mirror), necessary modifications and optimization of the electronics, and acquisition software were carried out at OAN/ UNAM. The compact design of the instruments allow them to share a single dewar and the cryogenics system.

OSIRIS optical design

The Optical System for Imaging and low Resolution Integrated Spectroscopy (OSIRIS) is a first generation instrument for the 10.4-m Gran Telescopio Canarias (GTC) that will be operational in mid-2004. On such a large telescope, OSIRIS is the first instrument to use tunable filters, combined with charge shuffling capabilities, covering the wavelength range (365 - 1000 nm). To be installed first at a Nasmyth platform, OSIRIS is also compact enough to fit in the Cassegrain focus envelope. This paper discusses the OSIRIS optical design process based on the classical collimator plus camera focal reducer configuration concept. To provide a wide mode and resolution versatility, several combinations of grisms, color, order sorter, interference and tunable filters are attainable in the collimated beam, near the pupil. The OSIRIS geometry, specifications, features, and performance are briefly discussed. Subsection (#5) is centered on the pupil size to calculate angular magnification and collimator FOV. These values are compared with those taken from similar instruments for 6.5-m to 10-m telescopes. This contribution is meant to share our experience on the optical design issue with colleagues not necessarily familiarized with astronomical instrumentation design. A previous approach on the OSIRIS optical design and two more general descriptions are available.

Site acceptance of the commissioning instrument for the Gran Telescopio Canarias

In March 2004, the Commissioning Instrument (CI) for the GTC was accepted in the site of The Gran Telescopio Canarias (GTC) located in La Palma Island, Spain. During the GTC integration phase, the CI will be a diagnostic tool for performance verification. The CI features four operation modes-imaging, pupil imaging, Curvature Wave-front sensing (WFS), and high resolution Shack-Hartmann WFS. The imaging mode permits to qualify the GTC image quality. The Pupil Mode permits estimate the GTC stray light. The segments figure, alignment and cophasing verifications are made with both WFS modes. In this work we describe the Commissioning Instrument and show some tests results obtained during the site acceptance process at the GTC site.

The commissioning instrument for the Gran Telescopio Canarias: made in Mexico

In March 2004 was accepted in the site of Gran Telescopio Canarias (GTC) in La Palma Island, Spain, the Commissioning Instrument (CI) for the GTC. During the GTC integration phase, the CI will be a diagnostic tool for performance verification. The CI features four operation modes-imaging, pupil imaging, Curvature Wave-front sensing (WFS), and high resolution Shack-Hartmann WFS. This instrument was built by the Instituto de Astronomia UNAM in Mexico City and the Centro de Ingenieria y Desarrollo Industrial (CIDESI) in Queretaro, Qro under a GRANTECAN contract after an international public bid. Some optical components were built by Centro de Investigaciones en Optica (CIO) in Leon Gto and the biggest mechanical parts were manufactured by Vatech in Morelia Mich. In this paper we made a general description of the CI and we relate how this instrument, build under international standards, was entirely made in Mexico.

OSIRIS camera barrel optomechanical design

A Camera Barrel, located in the OSIRIS imager/spectrograph for the Gran Telescopio Canarias (GTC), is described in this article. The barrel design has been developed by the Institute for Astronomy of the University of Mexico (IA-UNAM), in collaboration with the Institute for Astrophysics of Canarias (IAC), Spain. The barrel is being manufactured by the Engineering Center for Industrial Development (CIDESI) at Queretaro, Mexico. The Camera Barrel includes a set of eight lenses (three doublets and two singlets), with their respective supports and cells, as well as two subsystems: the Focusing Unit, which is a mechanism that modifies the first doublet relative position; and the Passive Displacement Unit (PDU), which uses the third doublet as thermal compensator to maintain the camera focal length and image quality when the ambient temperature changes. This article includes a brief description of the scientific instrument; describes the design criteria related with performance justification; and summarizes the specifications related with misalignment errors and generated stresses. The Camera Barrel components are described and analytical calculations, FEA simulations and error budgets are also included.

Commissioning instrument for the Gran Telescopio Canarias

During the GTC integration phase, the Commissioning Instrument (CI) will be a diagnostic tool for performance verification. The CI features four operation modes-imaging, pupil imaging, Curvature WFS, and high resolution Shack-Hartmann WFS. After the GTC Commissioning we also plan to install a Pyramid WFS. This instrument can therefore serve as a test bench for comparing co-phasing methods for ELTs on a real segmented telescope. In this paper we made a general instrument overview.

Optical characteristics of the UNAM 2-m Ritchey-Chretien telescope.

Measurements made on the components and on two assembled systems of a 2-m Ritchey-Chretien telescope have been used to determine the actual characteristics of the telescope. Sufficient precision has been obtained so that other focal ratio systems can be designed.