STIS Instrument Design
STIS has three large-format (1024 x 1024 pixel) detectors:CCD: Scientific Image Technologies (SITe) CCD with ~0.05 arcsecond square pixels, covering a nominal 52 x 52 arcsecond square field of view (FOV), operating from ~2000 to 10,300 Å.
NUV-MAMA: Cs2Te Multi-Anode Microchannel Array (MAMA) detector with ~0.024 arcsecond square pixels, and a nominal 25 x 25 arcsecond square field of view (FOV), operating in the near ultraviolet from 1600 to 3100 Å.
FUV-MAMA: Solar-blind CsI MAMA with ~0.024 arcsec-pixels, and a nominal 25 x 25 arcsecond square FOV, operating in the far ultraviolet from 1150 to 1700 Å.
|Architecture||Thinned, backside illuminated|
|Wavelength range||2000-11,000 Å|
|Pixel format||1024 x 1024 illuminated pixels|
|Field of view||52 x 52 arcseconds|
|Pixel size||21 x 21 Ám|
|Pixel plate scale||0.05071 arcseconds|
|Quantum efficiency||~ 20% @ 3000 Å
~ 67% @ 6000 Å
~ 29% @ 9000 Å
|Dark count at -83° C||0.003 e- sec-1 pix-1|
|Read noise||4.4-5.3 e- rms at GAIN=1*
7.3-7.8 e- rms at GAIN=4
|Full well||144,000 e- over the inner portion of the detector
120,000 e- over the outer portion of the detector
|Saturation limit|| 33,000 e- at GAIN=1
144,000 e- at GAIN=4
* When STIS began operating with "Side 2" electronics in July 2001,
CCD read noise increased from 4.4 to 5.3 e- for GAIN=1, and from 7.3
to 7.75 e- for GAIN=4. ETC calculations use the most recent estimates
of the read noise.
** See also ISR 98-31: STIS CCD Performance Monitor
The STIS/CCD is a low-noise device capable of high sensitivity in the visible and the near UV. It is a thinned, backside-illuminated device manufactured by Scientific Imaging Technologies (SITe). In order to provide a near-UV imaging performance, the CCD was backside-treated and coated with a wide-band anti-reflectance coating. The process produces acceptable near-UV quantum efficiency (QE) without compromising the high QE of the visible bandpass.
The CCD has only one operating mode, ACCUM, for imaging and spectroscopy. Electrons which accumulate in the CCD wells are read out and converted to data numbers by the analog-to-digital converter. The conversion factor can be selected by the CCDGAIN parameter. While the default is CCDGAIN=1, a CCDGAIN=4 value can be chosen if CCD saturation is a concern. Scientific data are obtained on 1024 x 1024 pixels for a full readout. The CCD supports both on-chip binning and the use of sub-arrays.
Additional CCD Information:
- Scaling Side-2 CCD Dark Frames with Temperature
- CCD Bias Subtraction and Amplifier Non-Linearity
- Detector Backgrounds
- CCD Subarrays
- CCD Shutter Effects
- Cosmic Rays
- CCD Optical Performance
- Fringing due to the Order Sorter Filters
- Fringing Amplitude in Percent as a Function of Wavelength
- ISR 98-19: STIS Near-IR Fringing. II. Basics ...
- ISR 98-29: STIS Near-IR Fringing. III.
- Residual fringe amplitude after flat-fielding
- Comparison of De-fringing Capabilities of Flats
Change to Side 2 operations
- ISR 2001-05: Read Noise During Side-2 Operations
- ISR 2001-03: Temperature Dependence of the Dark Rate...
- ISR 98-06: STIS CCD Anneals
- CL Script for Creating Daily Dark Files
- Monthly Hot Pixel Anneal Monitor
Charge Transfer Efficiency
UV Light and the STIS CCD
|Characteristic||FUV-MAMA Performance||NUV-MAMA Performance|
|Wavelength range||1150-1700 ┼||1600-3100 ┼|
|Pixel format||1024 x 1024||1024 x 1024|
|Pixel size||25 x 25 Ám||25 x 25 Ám|
|Image mode pixel plate scale||0.0245 x 0.0247 arcseconds (clear)
0.0246 x 0.0247 arcseconds (filtered)
|0.0245 x 0.0248 arcseconds|
|Field of view||25.1 x 25.3 arcseconds||25.1 x 25.4 arcseconds|
|Quantum efficiency||25% @ 1216 ┼||10% @ 2537 ┼|
|Dark count||5 x 10-6 to 1 x 10-5 counts sec-1 pix-1||8 x 10-4 to 1.7 x 10-3 counts sec-1 pix-1|
|Global count-rate linearity limit 1||285,000 counts sec-1||285,000 counts sec-1|
|Local count-rate linearity limita||~220 counts sec-1 pix-1||~340 counts sec-1 pix-1|
The STIS MAMA detectors are photon-counting devices which process events serially. In MAMA ACCUM mode, photons are accumulated into a 2048 x 2048 array in the STIS data buffer memory as they are received. In TIME-TAG mode, the MAMA produces an event stream of data points with a time resolution of 125 microseconds.
MAMA Bright Object Protection
The MAMAs are subject to catastrophic damage at high global and local count rates and cannot be used to observe sources which exceed the defined safety limits. Observers will have to adjust their observing strategies if a target exceeds these limits. The STIS Imaging and Spectroscopic Exposure Time Calculators issue a warning if an applicable limit is exceeded.
Additional MAMA information:
- Saturation Overflowing the 16 Bit Buffer
- MAMA Non-linearity
- On-board Doppler Compensation
- MAMA ACCUM and TIME-TAG Modes
- TIME-TAG Event Processing
- Spectral Mode Offsetting
- Out-of-Band Spectral Response of Clear Imaging Modes
MAMA Dark Current
- FUV-MAMA and NUV-MAMA Dark Current
- FUV-MAMA Dark Current Glow Image Files
- NUV-MAMA Dark Current vs Temperature
- ISR 99-02: Scientific Requirements for Thermal Control
MAMA Bright Object Protection