CFHT Observatory Manual

Section 5 - INSTRUMENTS

TABLE OF CONTENTS
Currently available instruments are listed and are briefly described in this manual. More complete operational manuals are available in Instrument Manuals.

Present CFHT instruments cover the following uses:
Also, CFHT astronomers are involved in future Instrumentation Projects:

The summit data acquisition and instrument control system, the Hale Pohaku data reduction system, and the Waimea observing, permanent record/software development/data reduction facilities function in a fully integrated way via:




At the summit there are several HP workstations, LINUX workstations, and Xterminals.  Another set of terminals are at Hale Pohaku, and several terminals are at the Waimea Headquarters. There are also Sun Sparcstations at the summit, another at Hale Pohaku, and several in Waimea.  A fiber link exists between the summit and Hale Pohaku.

The arrangement of having the display in a different machine of the one actually taking the data or controlling the instrument, permits us to run the observing environment from any machine with a suitable display in the network. However, only one login session for a particular instrument is permitted to avoid any interference with the present observer's run. Other logins for different instruments are available to permit development, debugging and preparations prior to the scheduled observing run.

Currently, all our controllers are purchased from Bob Leach at San Diego State University. These consist of a set of boards providing the analog and the digital functions, and are based around the Motorola 56000 Digital Signal Processor (DSP).

MegaCam uses a controller designed at the C.E.A. in France by Jean de Kat, which is based on Analog Devices' "sharc'' DSP.  This new controller handles the higher readout speeds of MegaCam. The guide CCDs for MegaCam use the San Diego State controller.

A controller for WIRCAM (under development) has not yet been determined.

All controllers currently use fiber optic links to send pixel data down to the 4th floor computer room.

The HP machines, and PC Linux workstations, are used for data acquisition and instrument control running under the Unix operating system. The vast majority of the programs are written in the C programming language and use the X-window standard. Details of the Pegasus system can be found in the Pegasus User's Manual.
 
The user interface environment is built on top of the X-window system and consist of a "Session Manager" and "Feed Back" windows. The main interactions mode is "point and click". When the user sees a desired command, mode, action, etc. the mouse is moved over the appropriately labeled gadget and the left mouse button is pressed. Windows come and go automatically, as do status icons. No window knowledge is required of the user.
 
At login the Session Manager and the Feed Back windows appear automatically. The Session Manager window contains a set of buttons which has been tuned to the particular instrument configuration. When an item has been selected (click) a "forms" window will appear.
 
Forms are the main way to communicate with a program. They, for instance, allow writing parameters in text input fields (such as the integration time for a CCD exposure) and deciding actions through checked boxes (e.g., click the ACCEPT push button will to begin a CCD exposure). For actions that take a long time (CCD integration, filter wheel movement, etc.) a visual icon will appear on the screen to identify the state of that resource or program. These icons go away when the action is completed.

The "feedback" window contains a stream of output messages from the action taking place, each action being a separate program which starts up, does its work, and then dies. This allows writing UNIX or IRAF scripts to manage sophisticated observing situations. It is also possible to use normal UNIX command interpreters to run any of our programs providing terminal access as well as our normal windowed environment.



The new prime focus upper end (PFUE) has been designed at CFHT with the help of INSU-Division Technique: a  new base ring, a new set of spiders, and a prime focus base which will receive all the other components of MegaPrime. The PFUE has been built on the West Coast of the USA by L&F Ind.

In addition to its basic structure, the PFUE provides a temperature controlled environment for MegaCam and its readout electronics. A temperature controlled enclosure for the electronics of MegaPrime is installed on the telescope "caisson central" .


The parabolic main mirror of the telescope alone does not produce a good image of the whole field of view, and so a WideField Corrector (WFC) is installed in front of the camera.

The WFC has been designed at HIA (Victoria, Canada). The lenses have been fabricated by SAGEM/REOSC, which also built the mechanical structure of the WFC and coated the lenses.

A succession of lenses and baffling rings ultimately extends to the mosaic of MegaCam.


To accommodate the changes in focal length of the telescope with temperature, and the focus position changes induced by the various filters, the camera must be able to move along the optical axis of the telescope. The focus stage assembly (FSA) accommodates this motion, supporting the camera and its shutter on a motorized stage bolted on top of the upper end platform. In order to follow the apparent motion of the sky due to the Earth's rotation, two small cameras fix on stars outside of the field of view, providing automatic guidance of the telescope and measurements of the focal changes.


At the heart of MegaPrime is MegaCam, a unique camera built by the "Département d'Astrophysique, de Physique des Particules, de Physique Nucléaire et de l'Instrumentation Associée" at the French "Commissariat à l'Energie Atomique" (CEA). In addition to a cryostat housing the mosaic, and its cryogenics system to maintain it cold, CEA built the camera shutter, the filter jukebox and the electronics to acquire the image and send it to a computer through fiber optics cables.


The Adaptive Optics Bonnette (AOB), also called PUEO after the sharp vision Hawaiian owl, was developed for the Canada-France-Hawaii Telescope, based on F.Roddier's curvature concept. The ``bonnette'' (adaptor) is a facility instrument mounted at the f/8 Cassegrain focus of the CFH 3.6 m telescope on top of Mauna Kea (Hawaii). The instrument is the result of a collaborative effort between several institutes : The CFHT (managing the project and designing the general user interface); The Dominion Astrophysical Observatory (Canada) who designed and fabricated the opto-mechanical bench, the curvature wavefront sensor and its electronics; the  company Cilas (France) who provided the deformable curvature mirror and the Real Time Computer and software, including a high level maintenance interface; the Observatoire de Paris-Meudon (France) who manufactured the separate tip-tilt mirror and was in charge with the final integration, testing and calibration of the instrument. The UH adaptive optics team provided guidance throughout the project. The system was commissioned at CFHT during three runs in the first semester 1996.

KIR is a high resolution 1024 x 1024 near-infrared camera based on the Rockwell Science Center HAWAII (HgCdTe Astronomical Wide Area Infrared Imaging) focal plane array. This array is sensitive to radiation from 0.7 to 2.5 microns. KIR has been designed to be used at the F/20 output focus of PUEO, the CFHT Adaptive Optics Bonnette (AOB). It consists in an LN2 cryostat which harbors the detector, the fixed 0.67:1.0 transfer optics, an F/20 cold stop and a filter wheel. The standard I, J, H, K and K' broad-band filters are available, as well as several narrow-band filters. A preamplifier and a shutter are mounted externally to the dewar. The system is driven by an SDSU/Leach CCD controller which is the controller commonly used at CFHT for all visible and infrared detectors. The system provides the observers with a user interface , called DetI, incorporated into the CFHT/Pegasus observing environment, through which they will configure the camera, control the data acquisition, monitor the data storage and do some pre-processing.

The Dewar has been constructed by the Universite de Montreal, part of the array DSP code by the Observatoire Midi-Pyrenees. The acquisition system and software were under the responsability of CFHT. The final integration of the science grade detector has been carried out at CFHT. The first light has been obtained during the first technical run in September 1997 and the final acceptance as well as the first astronomical observations were carried out in December 1997 and January 1998.

GriF is an upgrade to KIR that allows integral field spectroscopy in the K band, with a spatial resolution at the diffraction limit of the telescope (~0.12") using PUEO, the CFHT adaptive optics bonnette . It consists of a (warm) Fabry Perot interferometer, coupled with a grism in the KIR filter wheel, that disperses the Fabry Perot orders. A rectangular field selector in the focal plane (~6" x 36" on the sky) prevents the orders from overlapping spatially on the detector.

The Fabry Perot Perot mode will be available for 2004A, although narrow band filters will need to be used for order sorting . The focal plane wheel, which normally allows for coronography, long slit spectroscopy and the cross dispersed mode is undergoing major redesign and will not be available for 2004A.


CFHT-IR is a general purpose 1024 x 1024 near-infrared camera for direct imaging at the F/8 Cassegrain focus (0.2" pixels, 3.5' FOV). It has also been in the past the infrared detector for multi-object spectroscopy with OSIS. CFHT-IR has been developed as a collaborative effort between Université de Montréal and CFHT. Commissioning took place in November 2000 and CFHT-IR has been regularly used for science since then.


At a meeting in 1986, the CFHT users' community identified a low spectral resolution multi-object spectrograph as one of the highest priorities for new instrumentation at CFHT. Although the original intermediate dispersion spectrographs constructed for the CFHT had high throughput and were of excellent optical and mechanical quality, they were designed for single slit observations with image intensifiers or electronographic cameras as detectors. The desire to observe many faint objects simultaneously and also the realization that the image quality at CFHT is routinely better than one arcsecond led to the design of the MOS/SIS spectrograph, a dual Multi-Object and Subarcsecond Imaging Spectrograph. It is composed, in fact, of two distinct spectrographs sharing a common interface with the telescope after the Cassegrain bonnette: one is optimized for multi-object observations over a large field (MOS), the other (SIS) for high spatial resolution observations incorporating rapid tip/tilt image stabilization similar to that very successfully used in the CFHT/DAO high resolution camera HRCam (McClure et al. 1989). Two movable 45 degree mirrors permit a feed to either MOS or SIS. The MOS/SIS spectrograph was jointly designed and built by teams from the Dominion Astrophysical Observatory (DAO) in Victoria, theObservatoire de Paris-Meudon (OPM), the Observatoire de Marseille andCFHT. Work began on the designs in May 1988 and resulted in an instrument which saw its first light in July 1992. For several years from that time, MOS/SIS was the most popular instrument at CFHT. With the advent of wide-field imaging and regular AOB observations, it has taken a smaller, but still quite significant role in the observering schedule. MOS/OSIS have accounted for 25 - 30 night per semester over the past few semesters (Sept 2001).

MOS is primarily designed for multi-aperture spectroscopy over a 10´ x 10´ field, just covered with a 2048 x 2048 15 µm pixel CCD. This gives images with a correct spatial sampling of 0.8". This is considered the best compromise between field size and spatial resolution. The designed wavelength range is from 365 to 1000 nm, and typical efficiencies are approximately 80% for imagery and 60% for spectroscopy.


MOS/OSIS


Fabry-Perot spectroscopy offers moderate resolution (~5000 to 10000) 2-D spectroscopy for the observation of various astronomical sources. The field of view varies between 1 and 10 arcmin depending on the intrumental configuration, and the spectral resolution depends essentially on the Fabry-Perot etalon inserted in the instrument. The spectral PSF is oversampled so that there is no lost of resolution resulting from a coarser sampling (except maybe at the edge of the field with a large gap etalon).

Fabry-Perot spectroscopy has been used particularly on extended objects like galaxies and nebulae. It is particularly efficient for emission lines, to obtain velocity or velocity dispersion fields.


The CFHT coudé spectrograph, commonly referred to as Gecko, provides spectroscopists with a spectral resolving power R up to 120,000 from the atmospheric cutoff near 3000Å to 1µm for CCD's with up to 4400 13.5µm pixels. Unlike most echelle spectrographs, Gecko has been optimized for use with a single spectral order (between 5 and 18) from the 316 groove/mm echellette mosaic. Order sorting is achieved with interference filters or by one of three variable grisms. An image slicer is used to optimize the throughput of the instrument. To minimize traffic into and out of the inner coudé room, the entire spectrograph can be operated remotely from the control room.

Since July 2000, CAFE, the CAssegrain Fiber Environment, replaces the red coudé mirror train with optical fibers. CAFE consists of an optical bench mounted to a port on the Cassegrain Bonnette, two fiber optic cables and a Bowen-Wallraven slicer for injecting the beam into the Gecko Spectrograph.

A "fiber agitator" (which agitates the optical fiber with an amplitude of 1 mm and a frequency of 30 Hz) has been installed to prevent modal noise and the S/N degradation associated with it. Flat field correction seems to be better than with the coudé mirror train.


The CAFE is an instrument that replaces the old coude mirror train with a fiber optic. The project consists of 3 pieces:

1) An optical bench mounted to a port on the Cassegrain Bonnette which contains a holder for the fiber, feed optics for the fiber, flat field and spectral (ThAr) calibration lamps, feed optics for the calibration lamps, and a mechanism to select between telescope feed and calibration feed. The light from the telescope is fed into this optical bench using the Cassegrain Bonnette central mirror. The electronics for the optical bench is controlled from a crate mounted on the Cassegrain environment.

2) Two fiber optic cables (one for spare) with microlenses on either end to shape the beam. The fibers are ~28 m long.

3) Optics for injecting the beam into the Gecko Spectrograph. This is a Bowen-Wallraven slicer to which the fiber cable is attached. The beam is injected into the spectrograph at f/20 as is was the case with the coude train.

The CAFE was built for CFHT by Jacques Baudrand, Rene Vitry, and Michel Lesserter at the Observatoire de Paris-Meudon.

CAFE was first delivered to CFHT at the end of September 1999 and a preliminary acceptance test was held at CFHT with Jacques Baudrand and Rene Vitry of OPM during the last two weeks of October.  The tests went well with much progress being made on the controller software in the two weeks Jacques and Rene were here. Optically and mechanically, CAFE was shown to be very stable and reliable.

CAFE returned to CFHT in mid-2000 and was used for the first time for science in July 2000. CAFE is now a commissioned instrument at CFHT and is the primary feed for Gecko.

The CFHT filter list is available in a companion document (CFHT Filters).


The MOS/OSIS grism information is provided in two tables, one for MOS/OSIS visible, the other one for OSIS-IR.


At the beginning of 1998, an upgraded version of the Gumball calibration unit was commissioned at CFHT. Not only optomechanics and electronics components were modified or changed but a new Pegasus interface was also implemented. For an observer, the major changes include the possibility to define different exposure times for each lamp for the same calibration frame, pre-defined setups for diverse intrumental configurations to optimize the utilisation of the Gumball, and the availability of two Fabry-Perot interferometers providing regularly spaced calibration lines over large spectral ranges.  See the Gumball Web Page for more information.


LAMA (LAzer MAchine) - This is a Micro-Control YAG laser driller, which has been installed by CFHT in 1990, with the help of the Observatoire de Marseille. Maximum size of the drilling section is 150x150mm.

Currently for the MOS/SIS, we are using 75 microns thick, black anodized, commercial aluminum wafers. The practical limit for the minimum width of the slits is 0.25 arc sec. at f/8. Residual r.m.s. drilling errors on the slit edges are about 2 microns.

With recent refinements of the system, especially the adoption of a travelling salesman algorithm to speed up transfer time of the x-y stage from one slit position to another, drilling time, including data transfer to the LAMA controller, is typically 20 minutes for 150 slitlets (say 1.5 arc sec. x 12 arc sec. each). To this value, one must add ~10-15 minutes for various overheads, quite independent of the number of slits.

Note that these values are quite comparable to typical integration time (except for very faint objects), and the observers are strongly encouraged to plan their observing sequences as well as possible. In particular, during long MOS/SIS multi- slit runs, it makes sense that each observer makes a couple of images for his/her successor, so that a run can start with a few masks already quietly made during the day.


Detectors






Version 1.0 January, 2003