TECHNICAL FEASIBILITY OF SWIFT

The guiding design principle of SWIFT is that it is an integrated telescope+spectrograph optimized for wide-field, extremely efficient, and highly multiplexed slitlet spectroscopy. To achieve this goal, the spectrograph and telescope optics are designed together as a system. The primary design objective is to preserve as wide a field of view as possible on as large an aperture as possible without compromising the capability for highly efficient beam-fed spectroscopy. In this section, we outline one possible realization of SWIFT which minimizes risk and can be built at the present time. Although the current design demonstrates the technological feasibility of the concept as an `existence theorem', in practice there are various technological paths we intend to investigate in order to maximize the scientific effectiveness of this facility and enable us to determine the relevant technological paths to future instrumentation on the next generation of large-aperture telescopes.

**Figure 13:** SWIFT occupies a unique region of parameter space when compared with existing and planned multi-object spectrographs. Fiber systems are shown in blue, beam-fed systems in red. The size of the labels is proportional to the limiting magnitude. SWIFT can target 2000-10000 sources at a time.

**Table 5:** Baseline Concept for SWIFT
Fore-optic	>8-m diameter effective aperture
Field of view	1.5^o diameter
Wavelength range	0.36 -- 1.7 micron
Spectral resolution	500, 5000, 25000
Image quality	<0.25 arcsec¹
Slitlet density	2000--10000
Total system throughput	50% optical; 40% near-IR
Detectors	CCD Mosaics
	InSb Mosaics

¹ 80% encircled energy diameters for `white' light (0.36--1.7m ) over the entire field.

**Table 6:** Existing & Planned Spectrographs on Large Aperture Telescopes
Telescope	Aperture	Spectrograph		FOV		Comments
WIYN	3.5	Hydra	0.05	60' dia.	100	fiber
Mayall	3.8	SamSpec	0.45			slit
Blanco	3.9	Hydra-CT	0.05	40' dia	138	fiber
AAT	3.9	2DF	0.05		400	fiber
Magellan	6.5	IMACS	0.3?		600	slit
MMT	6.5	Hectospec	0.24³	60' dia	300	fiber
MMT	6.5	Binospec	0.40		<150	slit
3DT 8.4m	6.9		0.1?	180' dia.	<500	fiber
Gemini	8.1	GMOS	0.40		<600	slit
VLT	8.2	VIRMOS	0.3?		150-750	slit
Subaru	8.3	FOCAS				slit?
HET	9.2	LRS	0.40	4' dia.	13	slit
Keck	10	LRIS	0.35		20	slit
Keck	10	DEIMOS	0.35		80	slit
GTC	10	ODIN	0.05?	12' dia	60	fiber
GTC	10	OSIRIS	?	8' dia	15	slit
GTC	10	EMIR	?	6' dia	10	fiber or slit?
SWIFT	8.4		0.45	90' dia.	2000-10000	slit

¹ Optical throughput of spectrograph and telescope.

² Maximum number of objects which can be simultaneously observed.

³ Sky subtraction with fibers sets a limit of mag on faint-object spectroscopy.