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The WYFFOS long camera will be commissioned at the end of July 2004. Subject to successful commissioning it will be offered with the 2xEEV mosaic detector with AF2 and the visitor instrument INTEGRAL in 2004B, on a shared risks basis.
If the long camera is not successfully commissioned, the existing short camera will be offered with the Tek6 detector.
For the time being, we do not have precise figures for the spectral coverage and sensitivity with the Long Camera, as we do not know the performance of the new optics. However, when writing a proposal, it can be safely assumed that the spectral coverage will be similar to the present (short) camera, say within 10% of the present value, and that sensitivity will be at least as good all over the spectral range, being likely slightly better at wavelengths below 6000 angstrom and with a larger gain below 4500 angstrom. Spectral resolution will be similar, but with a better pixel sampling.
Because of the gap between CCDs in the EEV12 mosaic, no spectral range will be lost, but just very few fibres.
For further questions, contact Romano Corradi at rcorradi@ing.iac.es

Science fibres

The Small Fibre module contain 150 fibres with 1.6 arcsec diameter (90 micron), which run without connectors from AF2 to WYFFOS. The fibres are high-content OH fused silica made by Polymicro. Compared to the Large Fibre module, small fibres have the following main two advantages:

The Small Fibres are imaged onto less than 2 pixels (FWHM) on the TEK6 detector in the spatial and spectral directions. The full spatial image of the fibres is therefore sampled by less than 3 pixels. There may be a slight gain in S/N of the extracted spectrum with respect to the Large Fibre case, as less pixels have to be extracted when sampling the wings of the spatial profile. For Small Fibres, the fibre distance in the WYFFOS entrance slit is 1mm, which transforms onto a peak-to-peak aperture distance of 6-7 pixels on the detector.
Although the nominal spectral resolving power has increased as the ratio of Large to Small fibre diameters, the actual resolution is limited by the CCD pixels, because of the undersampling along the spectral direction. We expect the highest resolution to be around R~7500 in echelle mode.

The 1.6 arcsec fibres were chosen as a compromise between minimum sky contribution and maximal source contribution. As the positioning and (automated) guiding errors may add to 0.5 arcsec, there will be no room anymore for astrometrical errors. Field setups that suffer from inaccurate astrometry or an insufficient number of fiducial stars may suffer light losses of more than 50% at the fibre entrance. We caution observers for this effect, as bad astrometry may cancel all the gains that the new Small Fibre Module is offering.

Fiducial bundles

	50	100	200	300	400	500	1000
10 arcmin radius	5/5	10/12	17/19	26/32	31/43	32/49	38/98
20 arcmin radius	14/16	29/37	51/75	60/112	71/150	75/187	84/374
30 arcmin radius	30/34	53/72	82/154	93/237	99/323	99/405	101/810

Dispersion

The WYFFOS echelle grating is operated with order sorting ( PS format ) filters. Click for filter scans ( PS format ).

As mentioned above, the distribution of relative throughput is much more homogeneous than for the Large Fibres. In the figure, the relative throughput is plotted as a function of the fibre number. Most fibres lie in the region within 15% from the median throughput; the few ones with lower throughput are under examination and a higher sensitivity might be restored for the forthcoming runs.

On July 31st, 2001, the absolute throughput of the Small fibres was measured using grating R600B, under variable seeing conditions of 1-1.3 arcsec. The following Table reports the magnitude of a star giving 1 electron/sec/Angstrom when observed at zenith (1 airmass). Numbers are scaled to the "median" fibre (i.e. to the median relative throughput).

Lambda (Å)	4500	5000	5500	6000	6500
mag (1 e-/sec/Å)	16.5	16.7	16.8	16.7	16.6

Estimates for other gratings can be obtained by scaling the above figures according to the relative efficiency of the ISIS gratings.

The numbers above are similar to those measured in the past for the best Large Fibres. Note, however, that the actual throughput of the Small Fibres is strongly sensitive to the seeing conditions.

No direct throughput measurements are available yet for the WYFFOS echelle mode with the Small Fibres, but again they are expected to be similar to the figures ( PS format ) measured in the past for the Large Fibres.

Detector

Last updated December 2002 Romano Corradi (Instrument specialist) rcorradi@ing.iac.es