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UPGRADES AND FUTURE PLANS

We are presently designing and constructing a second module of 150 smaller - 1.5 arcsec diameter- fibres, to be commissioned during Semester 1997B. The principal scientific advantage to be gained by building a new small diameter fibre module for the WYFFOS/Autofib-2 system is to cut down the sky background transmitted by the fibre, thus enabling spectra of much fainter objects to be obtained successfully. Cutting down the fibre diameter by a factor 2 would result in a decrease in the sky background by a factor 4 and a corresponding gain in the magnitude limit (for sky-limited observations) of 0.75 mag. The 1.5 arcsec fibres will also be better matched to the present TEK chip, and will project to 1.8 TEK pixels; this will improve the velocity resolution. Another advantage of the small fibre module is that it will not have the connectors used with the present 2.7 arcsec fibres, which will improve the throughput and reduce variations in fibre transmission. Though the final decision has not yet been made, it is likely that the 1.5 arcsec fibres will also be high-OH silica fibres, which offer good response in the blue part of the spectrum (from 3500 Angstrom on). As can be seen from this plot, these fibres have at least 50% transmission from 3500 to 8700 Angstrom, and thus features extending from OII 3727 to the Ca triplet at 8550 Angstrom are all obtainable.

In November 1996 we plan to commission a so-called `echelle' grating for use in reflection mode. This is actually a 632 lines/mm grating blazed near 57 deg. 5 orders are accessible covering the wavelength range 3500 - 9500 angstroms, giving a range in dispersion of 23.73 A/mm in order 3 to 10.17 A/mm in order 7.

Order-sorting filters will be purchased for this grating, to allow observations of each of these 5 orders.

Order Wavelength Disp. Disp. Free Spectral CCD coverage

(A) @ blaze A/mm A/pix Range (A) (A)

3 8830 23.73 0.57 2940 580

4 6623 17.80 0.43 1650 435

5 5298 14.24 0.34 1060 350

6 4415 11.87 0.28 740 290

7 3784 10.17 0.24 540 245

Table 1: Echelle Grating Parameters

**Table 1:** Echelle Grating Parameters
Order	Wavelength	Disp.	Disp.	Free Spectral	CCD coverage
	(A) @ blaze	A/mm	A/pix	Range (A)	(A)
3	8830	23.73	0.57	2940	580
4	6623	17.80	0.43	1650	435
5	5298	14.24	0.34	1060	350
6	4415	11.87	0.28	740	290
7	3784	10.17	0.24	540	245

We would like to upgrade the present TEK 1024 x 1024 CCD to a thin Loral 2048 x 2048 device. The Loral devices have excellent quantum efficiency, and are much better than TEKs from 3500-4000 Angstrom. The pixel size is also smaller (15 micron as compared to 24 micron with TEK), however tests at RGO show that the effective pixel size is larger than this due to charge diffusion in the silicon; thus the Loral resolution will be similar to that of the TEK in practice. The Loral chips are also slightly larger in physical size, and this should allow all of the 126 x 2.7 arcsec fibres to be imaged onto the CCD. RGO is currently testing some Loral devices, and have commissioned one Loral chip on the WHT. We are awaiting more working devices, and we don't know when the upgrade will happen ... you can learn more about the Loral devices from the RGO CCD group's Loral page here