The SAC Report

The Scientific Advisory Council of CFHT held its 45th meeting on May 19th to 21st at the Hotel Clarendon in Quebec City, Canada. The SAC members from Canada are Michael DeROBERTIS, David HANES, Gilles JONCAS and Harvey RICHER (chairperson). The function of the SAC is to advise CFHT on scientific matters.

INSTRUMENTATION AND DETECTORS

CCDs: The problem of the CFHT dewars remaining cold for less than a night has been solved by a remotely operated LN_2 filling system and by contracting with G. Luppino of IfA for several new dewars capable of remaining cold for significantly longer than a winter observing night. The SAC was informed that Loral4, the thinned CCD recently obtained by CFHT, was likely made inoperable by an electrical surge during the testing phase. Although efforts will be made to repair the chip, the prognosis is poor.
MOS: The MOS/ARGUS configuration within MOS was built at the Paris-Meudon Observatory, and is now proposed by its builders as an additional observing mode of MOS. This configuration uses a 655-fiber bundle at the f/8 focus to feed the MOS, and allows for 2D spectroscopy at MOS. The optical and mechanical layout of this instrument results in a simple by-pass of the MOS mirror and mask, so that its installation requires only minor staff intervention. The SAC recommended to CFHT that this ARGUS mode be supported as a CFHT instrument.
SIS: The SIS guiding system has been upgraded and it is now possible to fast guide using stars fainter than R = 18. With the current Loral3 CCD the scale with SIS is 0.0867"/pixel, the field of view is 3' x 3' and the spectral range over which SIS can be used is 0.36 to 1 micron. There are plans, through a French- Canadian collaboration, to extend the range of sensitivity of SIS out into the infrared, that is through the J, H and possibly K' bands.
Fourier Transform Spectrometer: The InGaAs photodiodes recently obtained by CFHT exhibited a lack of sensitivity when used on the sky with the FTS. New photodiodes with higher gain preamplifiers have been obtained and will be tested before the end of the 94I semester.
Herzberg Spectrograph: The Herzberg Spectrograph was used successfully for near UV observations of several nuclei of comet Shoemaker-Levy. However, one and a half nights of engineering time were required to fully test and verify the operation of the spectrograph which had not previously been used for 20 months. Given the unique capabilities of the instrument (UV capability, moderate resolution, high throughput) and its excellent recent performance, the SAC concluded that it would be premature to decommission it at this time.
Computers and Software: The archive project with the CADC is continuing and apparently working well. Usage of the World Wide Web network access to the CFHT homepages by mosaic has increased enormously. Several users' manuals are being converted to this format and will thus provide up-to-date access to the status of CFHT instruments for observers at the time of writing proposals for telescope time and prior to their arrival in Hawaii for observing.

Report on the Adaptive Optics Meeting

The SAC, together with CFHT, organized a meeting on the science that can be done with the Adaptive Optics bonnette (called PUEO). This meeting was held just prior to the SAC meeting. Below are some key points from this workshop.

The Workshop ``Science with PUEO'' was highlighted by the presentation of a number of leading programs that are likely to be performed with CFHT's AO Bonnette which should provide spatial resolution of the order of 0.1-0.2" FWHM at visible and near-IR wavelengths starting early in 1996. Those fields which will benefit most from PUEO appear to be solar-system studies, the investigation of circumstellar matter around young and evolved stars, rich stellar systems such as globular clusters, extragalactic astronomy including galactic cores and nuclei, AGN's, and, to a lesser extent due to the faintness of the objects involved and the lack of suitably bright reference stars, the study of distant galaxies.

While the presently planned instrumentation (imaging in the visible and near-IR, low-resolution integral field spectroscopy in the visible with OASIS) seems to cover the most urgent needs to take advantage of the high spatial resolution of PUEO and perform the most interesting programs, a real demand was expressed during the workshop for the development of a low-resolution near infrared spectrograph as well as for more exotic instrumentation such as a polarimeter and a coronograph, and for a fiber link between the AOB and the f/4 Coude.

This workshop also offered an opportunity to discuss remaining issues and concerns related to Adaptive Optics at CFHT. One of the major concerns regarding PUEO instrumentation expressed during the workshop is the pixel size of Red-Eye behind the AOB which, as presently planned (0.082 arcsec/pix), does not provide an adequate sampling of the diffraction-limited PSF. Other key issues raised during the workshop included the possibility of achieving good photometric and astrometric accuracy with the AOB. The possible need for dedicated CFHT staff to run the AOB, at least in the early phases of operation, was also mentioned. Finally, it was widely acknowledged that the use of an artificial laser star for wavefront sensing would make the AOB even more attractive by giving access to a much larger fraction of the sky and, therefore, enabling demanding programs, especially those of cosmological interest, to be undertaken.

The proceedings from the workshop are available and can be obtained by contacting Robin Arsenault at CFHT. arsenault@cfht.hawaii.edu Gemini North Fiber Link to CFHT There are no current plans for the Gemini telescope on Mauna Kea -- Gemini North -- to be equipped with a high resolution spectrograph. Because high quality, high dispersion spectroscopy is a particularly powerful tool for studying stellar abundances, for example, the Gemini SAC has expressed an interest in fiber feeding the f/4 CFHT coude spectrograph (aka Gecko) from Gemini North. While the distance between the neighbouring telescopes is about 100 meters, the total length of fiber required would be closer to 250 meters if the cable were buried underground. Currently, a fiber of this length appears impractical because of excessive light loss, but with expected improvements in fiber technology in the near future, this option may prove feasible.A study is now underway to investigate fiber feeding the coude spectrograph from the f/8 focus at the CFHT using a 40 meter fiber. Thus far, the study appears to be successful, making the Gemini-CFHT proposal more encouraging.

There are two important aspects of concern to the SAC from this venture apart from its ultimate technical feasibility: The first is the nature of the fiber feed which will have to be built at the CFHT. Presumably its design will involve both the CFHT and Gemini and its cost will be borne by Gemini. The second is the compensation the CFHT corporation would require for use of Gecko by Gemini. This proposal has strong scientific appeal and the SAC considered it important that the CFHT and Gemini continue to discussboth of these concerns, as well as investigating the technical feasibility. The SAC felt that a trading of nights would be of greatest interest to our communities.

MEGACAM

Yannick Mellier presented to SAC a new project for building a wide field CCD camera for the prime focus of CFHT (MEGACAM). The camera is a mosaic of 8x8 2Kx2K thinned CCDs, with 15 micron pixels (0.205 arcsec/pixel) which would cover a total field of view of 55 arc minutes. Eventually, the builders propose to build another camera for the infrared which would consist of 3x3 1Kx1K IR detectors mounted at the prime focus. These camera would be particularly well suited for CFHT which has the best wide field image quality in the world, from U to K'.
The scientists and the institutes involved in the MEGACAM project are L. Vigroux from the Commisariat a l'Energie Atomique (Saclay, France), D. Crampton from the DAO, Y. Mellier from the Observatoire Midi-Pyrenees (Toulouse, France) and Nick Kaiser from CITA. The main scientific goals are the observation of large scale mass concentrations from weak gravitational shear, the evolution of distant galaxies from wide field deep multiband photometry, and the detection of supernovae. A large number of other scientific programmes could also benefit from the use of MEGACAM.
SAC was very enthusiastic over the scientific goals of the MEGACAM project and recognizesthat the project must be discussed in detail at the next CFHT users meeting in May 1995. Regarding the future of the CFH telescope in the era of 8 meter instruments, SAC is interested in identifying new projects which will make CFHT competitive. SAC believes that the MEGACAM project has the potential of being such a project.

Electronic Submission of CFHT Proposals
The Director proposed that observing time requests be submitted by electronic mail only beginning next semester (95I). His arguments were that (1) much preparation time will be saved at the agencies, (2) it will be an economy of paper and postal costs if the CADC is used as a mail exploder, (3) it will increase reliability, and (4) a template of the request form is already available via ftp. The main problem that SAC forsees is the transmission of the figures that accompany many of the proposals. Taking into account the possibility of numerous unforeseen glitches, SAC felt that a test period should be implemented before adopting such a procedure. This test will be done on the proposals submitted for time for semester 95II. Further, it was also noted that both ESO and NRAO give their applicants the choice of using either paper or electronic mail. Therefore, SAC decided that proposers should always have the option of submitting proposals in paper form.

Archiving of CFHT Data
The CADC has developed an efficient procedure whereby all astronomical frames acquired at the CFHT are promptly and securely archived in a database which will prove to be scientifically useful, rather than merely a backup repository. The FITS headers of all frames taken at the telescope with CFHT-supported instruments are electronically transmitted to the CADC within a matter of hours and added to the archive; the frames themselves follow on optical disk when a sufficient number have accumulated. Procedures are in place to permit rudimentary pre-processing and calibration, and to provide cross-referencing by object name or position and other descriptors.
Access to data frames will be restricted within the proprietory period, but thereafter browse facilities will permit general access to any images in the archive; compressed versions of the images will be obtainable over the network for quick inspection. In the long term the archive will prove a valuable astronomical resource, especially given that the CADC provides a gateway to other similar archives (such as HST) wordwide. Further developments will be reported to the community at the 1995 CFHT Users' Meeting.

Immediate and Long Term Strategy for CFHT
CFHT prepared a document for SAC to aid in the continuing discussion between the SAC and the Executive about the possible long term strategies that could be adopted for CFHT. These issues are reviewed below and some ideas concerning the long term strategies are discussed. There are some obvious differences in the context within which the three member countries of CFHT operate and which have to be kept in mind. (i) UH develops instruments which are tested on smaller telescopes and then used on larger telescopes, so UH will certainly want to maintain the ability to use visitor instruments on CFHT. (ii) Canadians want to have reliable and optimized instruments on CFHT rather than prototypes. (iii) The French community has many laboratories involved in instrumental development and has for many years proposed more visitor instruments than Canadian teams.
In terms of current and soon to be available instrumentation CFHT has available to the user community the following. (i) MOS-SIS stands out above the other instruments as the most competitive, until the 8 meter class telescopes begin to operate similar instruments. A non-thermal IR extension of its use (OSIS) will provide a truly unique capability. (ii) The cassegrain adaptive optics bonnette, complemented by an integral field spectrograph (OASIS), will make use of the exceptional quality of seeing at CFHT. The use will be limited to narrow fields limited by the isoplanatism, but it will be highly competive for the near term. CFHT will have to decide if it will also operate a laser artificial guide star for adaptive optics. (iii) The wide field corrector available at the prime focus allows for the development of very large field imagery with a mosaic of CCDs and possibly large, non- thermal IR arrays. This is considered as an important niche to be occupied by CFHT. Presently FOCAM andHRCAM use this prime focus, MOCAM and possibly MEGACAM will give CFHT mosaic CCD cameras. HRCAM will be decommissioned as soon as SIS guiding for the tip tilt mirror with APDs sensors is proven more efficient, which is almost assured now. (iv) The Gecko (coude f/4) spectrograph will have tough competition from similar instruments on larger telescopes. It will have to be feed by fibers from the cassegrain (and possibly from the prime focus) as soon as possible to make the set up easier and to complement the block scheduling of cassegrain and prime focus instruments by "bright time" usage of the coude spectrographs. On the longer term, it has a unique advantage of high spectral dispersion and its competitiveness could be significantly increased by a fiber feed from Gemini North. (v) The Fourier Transform Spectrometer, complemented by IR and CCD imaging modes can give unique results, but will not be competive with cooled grating spectrographs on other telescopes. (vi) UV instruments, namely, the Herzberg spectrograph and the coude spectrographs are unique and will have only a limited number of competing instruments on larger telescope in the foreseeable future. But the Herzberg and the coude spectrographs are not presently under high demand. Is it necessary to support them in order to maintain a niche for the future?
Into the next century we cannot imagine a solution for CFHT without significant investment: on the mid-term it will be necessary to specialize the telescope and to develop an instrumentation plan which will reduce the manpower needed to operate it. On the longer term the site CFHT has on Mauna Kea might be better used by a larger telescope. Each of these topics (new instrumentation plan, implantation of an 8m or larger class telescope on the site currently occupied by CFHT) may well need new partners and a modified international agreement to permit CFHT to evolve.

Site for 1995 Users Meeting
The CFHT users meeting will be held on May 15--16 1995 in France. The preferred location is Lyons, but if this proves to be impractical, the meeting will be held in Toulouse. All users of the telescope should consider attending this meeting. It is likely that many issues related to the long term status of CFHT will be discussed and decided upon at this time.
Harvey Richer

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