1. Overview Instrument Role Science Niches Consortium science
Kenneth Nordsieck
University of Wisconsin
Instrument Role
Science Niches
Consortium science
Design Concept
Performance
Risks
Oct 17, 2001
SALT PFIS PDR - Overview

2. Prime Focus Spectrograph
Major instrument on the prime focus platform
Straight-through focus position
8 arcmin diameter field of View
Good response down to 320 nm
Oct 17, 2001
SALT PFIS PDR - Overview

3. SALT PFIS PDR - Overview
Instrument Role
Provisional name: IMPALAS
(Imaging Prime focus ArticuLAting Spectrograph)
Common collimator with multi-object slitmasks
(> 100 objects over 8 arcmin field)
Visible beam nm (first light)
Simultaneous NIR beam nm (growth path)
Science niches:
UV Spectroscopy ( nm).
Rare on large telescopes
Dark sky; Good use of natural seeing large telescope
Stellar, nebular lines; VUV features at low redshift
Exploit SALT UV sensitivity and access to prime focus
Oct 17, 2001
SALT PFIS PDR - Overview

4. SALT PFIS PDR - Overview
Niches - cont
Very high throughput, medium resolution spectroscopy
Overcome sky background
Galaxy stellar envelope kinematics
Exploit VPH grating technology
Fabry-Perot imaging spectroscopy
Double etalon: unique on large telescope
Efficient use of access to focal plane
High Time resolution spectroscopy
Rare on large telescopes
Stellar astrophysics 0.1 sec – 100 sec
Exploit CCD technology
Spectropolarimetry.
Rare on large telescopes. Photon starved technique
Unique cross modes:
medium resolution spectropolarimetry (Doppler tomography)
Fabry-Perot imaging spectropolarimetry of scattered lines
Oct 17, 2001
SALT PFIS PDR - Overview

5. Consortium Questionnaire
Consortium roughly equally split between stellar and galactic/ cosmology programs
Grating Spectroscopy (26 responses)
Combination of wavelength and resolution
Resolutions down to 500
Lower resolutions require good UV/ blue response
Higher resolutions especially in red
Slitmask configurations
Long slit and slitmask programs evenly split
Field of view
Evenly split between narrower fields (< 4 arcmin) and largest possible fields (8 arcmin)
Oct 17, 2001
SALT PFIS PDR - Overview

6. Consortium Questionnaire
Time resolution (out of 26)
> 10 Hz [ 3 ] (Requires high-speed readout)
Hz [ 6 ] (Requires high-speed readout)
Several/ minute [ 13 ]
one per night/none [ 18 ]
Fabry-Perot Spectroscopy (17 responses)
Combination of wavelength and resolution
Few low resolution (single etalon) programs
Wavelengths 400 – 900 nm
Ha region important at higher resolutions
Equal split absorption/ emission lines
Equal split within and beyond F-P “bullseye”
Oct 17, 2001
SALT PFIS PDR - Overview

7. Consortium Questionnaire
Spectropolarimetry (10 Responses)
Combination of wavelength and resolution
UV/ blue response important at low resolution
Ha programs at highest (reduced slit) resolution
Linear spectropolarimetry - all
Circular spectropolarimetry – 30%
Most important: polarimetric precision, efficiency
NIR Upgrade Path
38% would use it some; 54% would use it a lot
76% of NIR users would use simultaneous IR/ Visible
Oct 17, 2001
SALT PFIS PDR - Overview

8. SALT PFIS PDR - Overview
IMPALAS Layout
Oct 17, 2001
SALT PFIS PDR - Overview

9. SALT PFIS PDR - Overview
Structure
Oct 17, 2001
SALT PFIS PDR - Overview

10. Grating Resolution-Wavelength
5 VPH gratings + 1 conventional
R = 500 – 6500 (0.9” slit)
320 – 900 nm
Oct 17, 2001
SALT PFIS PDR - Overview

11. SALT PFIS PDR - Overview
Sensitivity
VPH mode: low res = 780 l/mm; med res R = 4000
Competitive over entire wavelength range; superior in UV-blue
Oct 17, 2001
SALT PFIS PDR - Overview

12. SALT PFIS PDR - Overview
Risks
In the Concept Proposal, these risks were identified (technical, cost, and schedule risk)
Optics complexity (technical, cost, schedule)
NaCl elements (technical)
Structure – flexure, weight, articulation, mechanisms (technical, cost, schedule)
All addressed in detail in the package
Oct 17, 2001
SALT PFIS PDR - Overview