Oct 26, 2007SALT Workshop UKZN1 Robert Stobie Prime Focus Imaging Spectrograph Science Rationale...
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![Page 1: Oct 26, 2007SALT Workshop UKZN1 Robert Stobie Prime Focus Imaging Spectrograph Science Rationale Modes –Fabry-Perot Spectral Imaging –Grating Spectroscopy;](https://reader035.fdocuments.us/reader035/viewer/2022062423/56649f4a5503460f94c6be62/html5/thumbnails/1.jpg)
Oct 26, 2007 SALT Workshop UKZN 1
Robert StobiePrime Focus Imaging
Spectrograph
• Science Rationale• Modes
– Fabry-Perot Spectral Imaging
– Grating Spectroscopy; VPH Gratings, MOS
– Spectropolarimetry
– Mode table
• Status
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Oct 26, 2007 SALT Workshop UKZN 2
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; Fabry-Perot 4300 - 9000 Ǻ (Visible Beam); later - 1.7 μm (NIR)
– polarimetry (circular and linear) (very rare)
– high-speed detector mode (very rare)
![Page 3: Oct 26, 2007SALT Workshop UKZN1 Robert Stobie Prime Focus Imaging Spectrograph Science Rationale Modes –Fabry-Perot Spectral Imaging –Grating Spectroscopy;](https://reader035.fdocuments.us/reader035/viewer/2022062423/56649f4a5503460f94c6be62/html5/thumbnails/3.jpg)
Oct 26, 2007 SALT Workshop UKZN 3
Optics
• 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
C o llim a to rVis ib le C am era
N IR B eam (fu tu re )
F o ca l p lan e
A rticu la tio nA x is
F o ld / D ich ro icF o ld
![Page 4: Oct 26, 2007SALT Workshop UKZN1 Robert Stobie Prime Focus Imaging Spectrograph Science Rationale Modes –Fabry-Perot Spectral Imaging –Grating Spectroscopy;](https://reader035.fdocuments.us/reader035/viewer/2022062423/56649f4a5503460f94c6be62/html5/thumbnails/4.jpg)
Oct 26, 2007 SALT Workshop UKZN 4
Mechanisms
2 Fabry-Perot Etalons (slides)
Polarizing Beamsplitter
(slide)
2 Polarimeter Waveplates (slides)
6-Grating Magazine
40-Slitmask Magazine
Camera Articulation 0 - 100°
Shutter
20-Filter Magazine
3 CCD Mosaic
Detector
![Page 5: Oct 26, 2007SALT Workshop UKZN1 Robert Stobie Prime Focus Imaging Spectrograph Science Rationale Modes –Fabry-Perot Spectral Imaging –Grating Spectroscopy;](https://reader035.fdocuments.us/reader035/viewer/2022062423/56649f4a5503460f94c6be62/html5/thumbnails/5.jpg)
Oct 26, 2007 SALT Workshop UKZN 5
RSS on SALT
Articulation Rail
Camera
Detector
Etalons
Collimator
![Page 6: Oct 26, 2007SALT Workshop UKZN1 Robert Stobie Prime Focus Imaging Spectrograph Science Rationale Modes –Fabry-Perot Spectral Imaging –Grating Spectroscopy;](https://reader035.fdocuments.us/reader035/viewer/2022062423/56649f4a5503460f94c6be62/html5/thumbnails/6.jpg)
Oct 26, 2007 SALT Workshop UKZN 6
Perseus Cluster of Galaxies
Perseus A in Hydrogen Light
Imaging/ Fabry-Perot Spectroscopy
Filters
Fabry-Perot etalons(scans wavelength) M
any
wavele
ngths
![Page 7: Oct 26, 2007SALT Workshop UKZN1 Robert Stobie Prime Focus Imaging Spectrograph Science Rationale Modes –Fabry-Perot Spectral Imaging –Grating Spectroscopy;](https://reader035.fdocuments.us/reader035/viewer/2022062423/56649f4a5503460f94c6be62/html5/thumbnails/7.jpg)
Oct 26, 2007 SALT Workshop UKZN 7
Hubble Deep Field
(South)
Up to 40 Spectra
Slitmasksselects objects
Filters
"VPH" Grating disperses wavelengths
Multi-Object Grating Spectroscopy
![Page 8: Oct 26, 2007SALT Workshop UKZN1 Robert Stobie Prime Focus Imaging Spectrograph Science Rationale Modes –Fabry-Perot Spectral Imaging –Grating Spectroscopy;](https://reader035.fdocuments.us/reader035/viewer/2022062423/56649f4a5503460f94c6be62/html5/thumbnails/8.jpg)
Oct 26, 2007 SALT Workshop UKZN 8
Hubble Deep Field (South)
Waveplate rotates polarization
Beamsplitter splits 2 polarizations
Polarization of 20 Spectra
Spectropolarimetry Submode
Also works in Imaging/ Fabry-Perot Modes
![Page 9: Oct 26, 2007SALT Workshop UKZN1 Robert Stobie Prime Focus Imaging Spectrograph Science Rationale Modes –Fabry-Perot Spectral Imaging –Grating Spectroscopy;](https://reader035.fdocuments.us/reader035/viewer/2022062423/56649f4a5503460f94c6be62/html5/thumbnails/9.jpg)
Oct 26, 2007 SALT Workshop UKZN 9
High Efficiency with Volume Phase Holographic Gratings
R
6 0 0 0
4 0 0 0
2 0 0 0
3 0 0 4 0 0 5 0 0 6 0 0 7 0 0 8 0 0 9 0 0W av e len g th (n m )
[O II] H β [O III] H α [S II] C a II
3 0 0 0 l/m m2 3 0 0 l/m m
1 8 0 0 l/m m
1 3 0 0 l/m m
9 0 0 l/m m
1 5 °
3 0 ° 3 0 ° 3 0 °2 5 °
4 0 ° 4 0 °4 0 °
3 5 °
5 0 ° 5 0 ° 5 0 °
= λ/Δλ
Resolution vs wavelength for 1.2 arcsec slit
Constant Efficiency Contours
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Oct 26, 2007 SALT Workshop UKZN 10
How VPH Gratings Work
• 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
{ 17 {
{ 30 {
VPH G ratings. F rom Barden, e t a l, 2000, PASP
Astronom ical G ratings
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Oct 26, 2007 SALT Workshop UKZN 11
One RSS VPH
1300 gr/ mm VPH
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Oct 26, 2007 SALT Workshop UKZN 12
Multi-Object Spectroscopy with custom masks
• 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
Giant Elliptical Galaxy NGC1399
at focus of telescope:
Mask with slits cut in it to let through selected nebulae in galaxy
"Longslit" mask to get spectrum along one position angle
![Page 13: Oct 26, 2007SALT Workshop UKZN1 Robert Stobie Prime Focus Imaging Spectrograph Science Rationale Modes –Fabry-Perot Spectral Imaging –Grating Spectroscopy;](https://reader035.fdocuments.us/reader035/viewer/2022062423/56649f4a5503460f94c6be62/html5/thumbnails/13.jpg)
Oct 26, 2007 SALT Workshop UKZN 13
MOS Test Field
Courtesy: Petri Vaisanen
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Oct 26, 2007 SALT Workshop UKZN 14
NGC6822 – Oct 20
4080 A 7180 A
MOS Test Run Spectra
Position Reference Stars
HII and PNe
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Oct 26, 2007 SALT Workshop UKZN 15
17 PFIS ModesOptics configuration Detector Configuration
Config Pol Slit Normal Hi Spd Shuffle Drift
Imaging No No X x x
L,C,S No x
Multislit X x
VPH Spectro- scopy
No No x x
Longslit X X x
Multislit X X
L,C,S Longslit X x
Multislit X
Fabry- Perot
No No X x
L,C,S No xTried: 6 Team Commissioned: 9 User Commissioned: 8
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Oct 26, 2007 SALT Workshop UKZN 16
0
5
10
15
20
25
3000 4000 5000 6000 7000 8000 9000
Wavelength (Ang)
e/se
c n
m f
or
AB
=20
0
5
10
15
20
25
3000 4000 5000 6000 7000 8000 9000
Wavelength (Ang)
e/se
c n
m f
or
AB
=20
Status
• On telescope Nov 2005 - Oct 2006– longslit mode, polarimetry
commissioning
– other mode tests
– on-sky throughput tests
• 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
• Back on telescope for further commissioning April 2008