1. IMPALAS Fabry-Perot System
Full two-dimensional spectroscopic imaging
8’ (diameter) field of view
seeing-limited spatial resolution
Three spectral resolution modes
500 –
25 km/s 5 km/s 1 km/s
Wavelength range: 430 – 860 nm (continuous)

2. Sensitivity Resolution Absorption V=20 500nm R=20 600nm Emission
1 R Hα
500
12 s
19 s
3663 s
1000
24 s
38 s
2090 s
2500
74 s
118 s
1494 s
12500
370 s
589 s
966 s
Exposure times for a single S/N = 10 per sample image
Samples: Absorption 3x3 bp(0.78”) Emission 4x4 bp (1.0”)
9 – 15 exposures required for a typical datacube

3. Etalons and Filters Dual etalon system
R= : low resolution etalon + filter
R=2500: low + mid-resolution etalons + filter
R=12500: low + high-resolution etalons + filter
Etalon finesse 30 (FWHM / Order Separation)
– peak transmission ~ 80%
~ 30 filters required

4. Spectral Range Users desire 350 – 900 nm range
Etalon coatings provide ~ 1 octave range
Science drivers
kinematics
emission: Hα (656.3 nm) or [OIII] (500.7 nm)
absorption: Hα, Ca (854.2 nm), Mg (518.3 nm)
nebular line analysis
[OIII] ( )/436.3, [NII] ( )/575.5
[SII] 671.6/673.1
H Balmer ratios: , 434.0

5. Cosmology Source Wavelength Strength Z range Hα 656.3 1.00 0.00 – 0.31
[OIII]
500/7
0.56
0.00 – 0.72
405.9
0.18
0.00 – 0.73 Hβ
486.1
0.24
0.00 – 0.77
[OII]
372.7
0.40
0.15 – 1.31
NeIV
242.3
0.12
0.78 – 2.55
CIII]
190.8
0.17
1.25 – 3.51
CIV
154.9
0.47
1.78 – 4.55 Lα
121.6
1.00(?)
2.54 – 6.07

6. Choose 430 – 860 nm spectral range
satisfies largest number of users
supports almost all imaging science programs
Future upgrade
either: add blue etalon
or: strip & recoat existing etalon (60% cost)
in both cases: add blue filters