Transcript Document

Robert Stobie
Prime Focus Imaging
Spectrograph
• Science Rationale
• Modes
–
–
–
–
Fabry-Perot Spectral Imaging
Grating Spectroscopy; VPH Gratings, MOS
Spectropolarimetry
Mode table
• Status
Oct 26, 2007
SALT Workshop UKZN
1
What science should RSS do?
• SALT features
–
–
–
–
–
very large aperture
good field of view (8 arcmin)
excellent ultraviolet throughput
queue scheduling
modest imaging
• RSS: emphasize unique observing modes that do not
require excellent imaging
– UV spectroscopy down to 3200 Ǻ (rare on large telescopes)
– higher resolution: high-throughput grating 3200 - 9000 Ǻ; FabryPerot 4300 - 9000 Ǻ (Visible Beam); later - 1.7 μm (NIR)
– polarimetry (circular and linear) (very rare)
– high-speed detector mode (very rare)
Oct 26, 2007
SALT Workshop UKZN
2
Optics
NIR Beam (future)
Fold/ Dichroic
Articulation
Axis
Fold
Visible Camera
Collimator
Focal plane
• All-refractive UV optics for high throughput
• At prime focus for UV and full-field access
• NIR upgrade path: simultaneous 3200 Ǻ – 1.7 μ
Oct 26, 2007
SALT Workshop UKZN
3
Mechanisms
Polarizing
Beamsplitter
(slide)
6-Grating Magazine
40-Slitmask
Magazine
2 Fabry-Perot
Etalons (slides)
3 CCD
Mosaic
Detector
Shutter
Camera Articulation
0 - 100°
Oct 26, 2007
20-Filter
Magazine
SALT Workshop UKZN
2 Polarimeter Waveplates
(slides)
4
RSS on SALT
Detector
Camera
Articulation
Rail
Etalons
Collimator
Oct 26, 2007
SALT Workshop UKZN
5
Imaging/ FabryPerot Spectroscopy
Fabry-Perot etalons
(scans wavelength)
Filters
Perseus A in
Hydrogen Light
Perseus
Cluster of
Galaxies
Oct 26, 2007
SALT Workshop UKZN
6
Multi-Object Grating Spectroscopy
Filters
"VPH" Grating
disperses
wavelengths
Up to 40 Spectra
Hubble
Deep
Field
(South)
Slitmasks
selects objects
Oct 26, 2007
SALT Workshop UKZN
7
Spectropolarimetry Submode
Beamsplitter
splits 2
polarizations
Hubble Deep
Field (South)
Polarization
of 20 Spectra
Also works in
Imaging/
Fabry-Perot
Modes
Oct 26, 2007
SALT Workshop UKZN
Waveplate
rotates
polarization
8
High Efficiency with Volume Phase
Holographic Gratings
Resolution vs wavelength for 1.2 arcsec slit
6000
2300 l/mm
3000 l/mm
1800 l/mm
Constant
Efficiency
Contours
50°
50°
50°
4000
40°
40°
40°
35°
R
= λ/Δλ
30°
30°
30°
25°
2000
1300 l/mm
15°
900 l/mm
[OII]
300
Oct 26, 2007
400
Hβ [OIII]
500
CaII
Hα [SII]
700
600
Wavelength (nm)
SALT Workshop UKZN
800
900
9
How VPH Gratings Work
VPH Gratings. From Barden, et al, 2000, PASP
Astronomical Gratings
{
7
1
{
{
0
3
{
• Created by exposing holograph material (“DiChromated Gelatin") to
interference pattern from laser
• Index of refraction of DCG is modulated in space
• Large; inexpensive; custom design; efficient at high groove density
Oct 26, 2007
SALT Workshop UKZN
10
One RSS VPH
1300 gr/ mm VPH
Oct 26, 2007
SALT Workshop UKZN
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Multi-Object Spectroscopy with custom
masks
at focus of telescope:
• Laser-cut slit masks
• Standard set of longslits
• Unique mask cut for each
individual MOS observation
• Slit mask magazine will hold 10
longslits, 30 MOS masks
• Reload once/ week
Oct 26, 2007
Giant
Elliptical
"Longslit" mask
Galaxy
NGC1399 to get spectrum
along one
position angle
SALT Workshop UKZN
Mask with slits
cut in it to let
through selected
nebulae in galaxy
12
MOS Test Field
Courtesy: Petri Vaisanen
Oct 26, 2007
SALT Workshop UKZN
13
MOS Test Run Spectra
4080 A
7180 A
Position
Reference
Stars
HII
and
PNe
NGC6822 – Oct 20
Oct 26, 2007
SALT Workshop UKZN
14
17 PFIS Modes
Optics configuration
Detector Configuration
Config
Pol
Slit
Normal
Hi Spd
Imaging
No
No
X
x
L,C,S
No
x
Multislit
X
No
x
Longslit
Longslit
X
X
X
Multislit
X
No
No
X
L,C,S
No
x
VPH
Spectroscopy
No
Multislit
L,C,S
FabryPerot
Tried: 6
Oct 26, 2007
Shuffle
Drift
x
x
x
X
Team Commissioned: 9
SALT Workshop UKZN
x
X
x
x
User Commissioned: 8
15
Status
• On telescope Nov 2005 - Oct 2006
• Off telescope Nov 2006 - present
– improving UV throughput, ghosts
– Measured throughput to be 75 100% of design, sensitivity
comparable or better than design
throughput of other large
telescope spectrographs
e/sec nm for AB=20
– longslit mode, polarimetry
commissioning
– other mode tests
– on-sky throughput tests
25
20
15
10
5
0
3000
4000
5000
6000
7000
8000
9000
Wavelength (Ang)
• Back on telescope for further
commissioning April 2008
Oct 26, 2007
SALT Workshop UKZN
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