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Дата изменения: Fri Mar 26 04:33:49 1999
Дата индексирования: Sun Apr 10 06:20:33 2016
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sgs summary

SDSS Spectrograph Guide Sensor

Patrick Waddell


Table of contents: 

 


Guider functions:

 

 

System requirements:

 

 

Design overview:

Camera parameters:

Image scale:

60.6 µm/arcsec

Assumed sky background:

4.1 e- s-1(arcsec2)-1 [ 21.7 Mv/arcsec2, Solar]

Sensor optical bandwidth:

450-650 nm (thick CCD + 2 mm BG-38)

Sensor detector parameters (binned 2x2):

Detector type:

Kodak CCD, Thick (frontside illum.)

Readnoise:

13 e- rms pixel-1

Dark current:

2.8 e- pixel-1 s-1

Array geometry:

384 x 256 (768 x 512 - engineering mode)

Pixel size:

18 µm sq (9 µm sq - engineering mode)

Pixel sampling:

0.30 arcsec/pixel

 

Fiber bundles parameters:

IGN-05/10

IGN-08/30

Diameter of fiber bundle (mm):

0.45

0.75

Distance between neighboring cores ( µm):

4 - 5

3 - 4

Number of cores:

~ 10,000

~ 30,000

Net throughput efficiency (%)

~25

~25

Numerical aperture:

0.35

0.35

Core material:

GeO2 +silica

GeO2 +silica

Cladding material:

F + silica

silica

2-Axis Calibrated Accuracy:

Accuracy with which each measured guide star centroid ties the focal plane reference (plug plate) to the astrometric reference frame

Error Source

mm RMS

Milliarcsec RMS

Guide star astrometry

TBD (6 mm)

(100)

Accuracy of FOV distortion calibration

TBD (10)

(165)

Plate deformation

5

83

Hole drilling

9

149

Ferrule/hole concentricity

8

132

Fiber bundle/ferrule concentricity

7

116

Calibrated fiber position (output end)

TBD (2 mm)

(33)

Camera/fiber flexure effects (over 60 min)

TBD (2 mm)

(33)

Centroid calculation and detector flaws

TBD (6 mm)

(100)

Total

TBD (20)

(331)

 

Guide Sensor Performance: (2-Axis, RMS) (using any fiber cartridge)

 

(per sensor star)

•Calibrated Accuracy:

TBD (0.331 arcsec)

•Sensor Noise (per 15 seconds):

TBD (0.06 arcsec)

 

(sensor ensemble)

•Calibrated Accuracy:

TBD (0.110 arcsec) (7 µm)

•Sensor Noise (per 15 seconds):

TBD (0.02 arcsec)

 

 

 

Transverse Position Error Budget for science fibers:

Error Source

µm RMS

Milliarcsec RMS

Science object astrometry

TBD (6 µm)

(100)

Accuracy of FOV distortion calibration

TBD (10)

(165)

Plate deformation

5

83

Hole drilling

9

149

Ferrule/hole concentricity

8

132

Fiber bundle/ferrule concentricity

7

116

Temperature gradients

5

83

Guide sensor

TBD (7)

(110)

Total

TBD (21)

(340)

Max desired (10% of core dia.)

18

297

 

 

 

Guide Sensor Sky Coverage/ Star Availability:

 

However, to meet g'-r' criteria (blue objects), throw out ~ 2/3

 

Assume other criteria, close neighbors, etc., eliminate another factor of 0.5

 

We have a density of 7 stars, for each of 10 evenly distributed samples -->
yielding 99.5% probability of finding a star in each sample area -->
We should have a sufficient number of available guide stars.
 

 

 

Guide Star Selection Criteria:

 

 

 

Sky Selection Criteria:

 

 

 

Photographs:

 

Figures:

 

Guider Block Diagram

 

 

Guide harness in slit head (front view of slit)

 

 

 

Guide harness in slit head (side view)

 

 

 

Guide camera on spectrograph

(Top and Side views / reimaging optics not shown)

 

 

 

Guider harness

 

 

Guide fiber organization and reach at plug plate

 

 

Guider S/N performance as a function of star temperature (Mv=15.5)

Guide Fiber Bundle Transmission