CFHT, Instruments, Spectroscopy, Fabry-Perot, Future Prospects.

Canada-France-Hawaii Telescope

User's Manual for the Scanning Fabry-Perot Spectrograph with the MOS/SIS Focal Reducers

R. Arsenault, P. Martin
Version 3.2
December, 1998

4 Future Prospects

All systems and instruments at CFHT are in constant evolution. Astronomical instruments are prototypes, and therefore often requires modifications to overseen weaknesses and improvements to better answer the needs of visiting astronomers. Also, aging instruments or aspects of an instrument might become obsolete with time and require a complete refurbishing. These facts stress the need for visiting astronomers to get re-acquainted with instruments and systems when they come back to CFHT. Taking for granted that an instrument already used will perform similarly as during the last run might be a dangerous assumption. Consult your support astronomer. This also means that we welcome any criticisms or comments visiting observers might have on all aspects having an impact on an observing run.

4.1 SIS Upgrade to OSIS: OSIS/FP

The SIS spectrograph has been upgraded during the first part of 1996. The upgrade included a change of optics and detector mount. These changes nos allows an instrument spectral coverage from 0.4 to 2.5 micron. Depending on the wavelength domain chosen, a CCD or one of the Redeye camera can be used. The University of Montreal is building an 1Kx1K IR camera specifically for OSIS. Consult with the detector group for update. The sampling with the new OSIS optics is slightly coarser than with the original optics; f/8 instead of f/10. Therefore, Fabry-Perot work requiring high spatial sampling (0.1" per 15 micron pixel) will still be possible plus the possibility of doing Fabry-Perot work in the near, non-thermal infrared (1 to 1.8 micron). There is no changes on the fast-guiding tip-tilt capability offered by OSIS. The entrance focal plane and the field of view is slightly larger, 200 arcsec on the side. This implied the fabrication of new masks holders, which are used as filter holders for SIS/FP. However, again, only 2 inch filters will be accomodated.

The following illustrations provide some more information about OSIS. This link provides a quick comparison between the characteristics of SIS and OSIS. This plot shows a comparison between SIS and OSIS focus change with wavelength. Click here for a brief status report of the OSIS project.


The CFHT Adaptive Optics Bonnette, PUEO, has been commissioned at CFHT during the first half of 1996. In June 1997, the new Integral Field Spectrograph OASIS has undergone a first engineering run at the telescope. Since then, OASIS has been used succesfully on the sky for many runs in 1998. OASIS is a complex multi-modes instrument, its main modes being imagery and TIGER-type spectroscopy. However, other modes could be implemented: ARGUS-type integral field spectroscopy, long-slit spectroscopy, Fabry-Perot mode and PYTHEAS mode. Check out the OASIS Web Page for more information regarding OASIS. Since the main mode of OASIS is a TIGER integral-field spectrograph, you might want to consult also the OASIS Instrument Overview page.

The Pegasus User's Interface (UI) has been tested also and concentrates on the TIGER mode of OASIS. The UI has a slightly different look. Due to the complexity of the instrument and to the multiple wheels (enlargers, apertures, filters, grisms, etc.), a usual type of instrument control would likely lead to mistakes. Therefore, the Pegasus front offers a more sophisticated approach asking the observer to define the instrument characteristics required by the observing program: wavelength range, dispersion, resolution, spatial sampling etc. Pegasus will control the various electro-mechanisms that achieves these specifications. At the time of this writing (December 1998) only the TIGER and imagery modes are offered.

A Fabry-Perot mode could eventually become available in OASIS. Installation as for MOS or OSIS -FP requires the removal of the grisms box to accomodate the FP module. It is still not clear whether there will be a strong demand for this type of instrument at such high spatial resolution. However, there are reasons to believe that if the basic structure of the studied medium is clumpy, high spatial resolution will reveal these brighter, clumps.

The PYTHEAS mode is more complex. It is a TIGER integral field spectrograph with a FP inserted before the micro-lens array. The gain is that the resolution of the spectrograph is boosted by the FP, but many channels must be observed to reconstruct a continuous spectra. The data reduction of this mode is somewhat complicated but programs have been developed to this purpose (not residing at CFHT). At this moment, however, it is doubtful that this mode will be implemented on OASIS.


There has been plans in the community to retro-fit MOS/FP (and/or OSIS/FP) in a MORGANE configuration. MORGANE is a set-up using a Fabry-Perot mode working very much like MOS/FP, ie. that a scan of several channels with different FP settings must be performed, but allows a much larger spectral domain to be accessible. A large slit is used at the entrance focal plane (the width must not exceed the Jacquinot criteria) to limit the field, and a grism behind the FP in the collimated beam separates the interference orders. As said previously, this mode allows a very large spectral domain to be accessible, at the spectral resolution offered by the FP etalon. It is particularly well suited for the observation of absorption lines.

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