STIS Instrument Design

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.

CCD

Characteristic	CCD Performance
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 µm
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:

IR Fringing

Change to Side 2 operations

Hot Pixels

Charge Transfer Efficiency

UV Light and the STIS CCD

Spectroscopic CCD Obs at wavelengths > 2500 Å

MAMA

Characteristic	FUV-MAMA Performance	NUV-MAMA Performance
Photocathode	CsI	Cs₂Te
Wavelength range	1150-1700 Å	1600-3100 Å
Pixel format	1024 x 1024	1024 x 1024
Pixel size	25 x 25 µm	25 x 25 µm
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 Å	10% @ 2537 Å
Dark count	5 x 10^-6 to 1 x 10^-5counts 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 limit^a	~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: