Cosmic Origins Spectrograph Instrument Handbook for Cycle 17

3.5 COS Quick Reference Guide

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Table 3.4: COS Instrument Characteristics

Property	FUV channel	NUV channel
Entrance aperture	2.5 arcsec round	2.5 arcsec round
Detector plate scale (cross dispersion)	22 mas per pixel 158 mas per resel	26 mas per pixel 77 mas per resel

Table 3.5: COS Detector Characteristics

Table 2:

		FUV XDL	NUV MAMA
Photocathode		CsI (opaque)	Cs2Te (semi-transparent)
Window		None	MgF2 (re-entrant)
Wavelength range		1150 - 2050 Å	1700 - 3200 Å
Active area		85 × 10 mm (two)	25.6 × 25.6 mm
Pixel format (full detector)		16384 × 1024 (two)	1024 × 1024
Pixel size		6 × 24 µm	25 × 25 µm
Spectral resolution element size (= "resel")		7 × 10 pix	3 × 3 pix
Quantum efficiency		~26% at 1335 Å ~12% at 1560 Å	~10% at 2200 Å ~8% at 2800 Å
Dark count rate		~0.5 cnt s-1 cm-2 ~7.2x10-7 cnt s-1 pix-1 ~4.3x10-5 cnt s-1 resel-1	~34 cnt s-1 cm-2 ~2.1x10-4 cnt s-1 pix-1 ~1.9x10-3 cnt s-1 resel-1
Detector global count rate limit	TIME-TAG mode	~21,000 cnt s-1	~21,000 cnt s-1
	ACCUM mode	~60,000 cnt s-1 per segment	~170,000 cnt s-1
Local count rate limit		~100 cnt s-1 resel-1 ~1.67 cnt s-1 pix-1	~1800 cnt s-1 resel-1 ~200 cnt s-1 pix-1
Dead-time constant		7.4 µsec	negligible

Table 3.6: COS Calibration Accuracies

Table 3.7:
 

Property	FUV channel	NUV channel
Wavelength zero point: M gratings	15 km s-1	15 km s-1
Wavelength zero point: L gratings	150 km s-1	175 km s-1
Wavelength scale	5 km s-1	5 km s-1
Absolute photometry	5%	5%
Relative photometry (same object at a different time)	2%	2%
Flat field random noise
Flat field systematic effects	30:1	100:1

Table 3.8: Useful Figures and Tables

Table 3.9:
 

Topic	Sources
Usage planning	Table 3.1 COS Spectroscopic Modes
	Table 3.8 Useful Figures and Tables
	Table 5.3 Wavelength ranges for FUV gratings
	Table 5.4 Wavelength ranges for NUV gratings
	Table 10.2: "Background contributions from the Moon and Earth." on page 124
	Table 10.3: "Extinction in magnitude as a function of wavelength, using Seaton's 1979 Galactic model." on page 128
	Table 10.2: "Earthshine and zodiacal light in the COS PSA." on page 128
	Table 10.4: "Strengths of important ultraviolet airglow lines" on page 130
Aperture parameters and PSFs	Figure 3.2: COS aperture location
	Figure 7.1 on page 87: COS PSF for 1450 Å
	Figure 7.2 on page 89: COS PSF for 2550 Å
	Figure 6.1 on page 80: COS two-dimensional PSF
Sensitivity and throughput	Figure 3.4: far-UV sensitivity curves
	Figure 3.5: near-UV sensitivity curves
	Figure 4.1: COS throughputs in comparison to STIS
Acquisitions	Figure 7.1 on page 92: exposure times for ACQ/IMAGE
	Figure 7.1 on page 96: spiral search pattern
	Figure 7.2 on page 96: exposures times for FUV dispersed light
Detector characteristics	Figure 4.3: schematic layout of XDL
	Figure 4.3: schematic layout of MAMA
	Table 8.1: "COS Count Rate Limits" on page 104
	Table 8.2: "Local and global flux limits for COS" on page 105
	Table 10.1: "Detector background count rates for COS" on page 123
Overheads and observing parameters	Table 5.1 TAGFLASH intervals
	Table 5.2 Times of TAGFLASH lamp exposures.
	Table 9.1: "Generic Observatory Overhead Times" on page 112
	Table 9.3: "Overhead Times for Motions Between OSM1 Spectral Elements" on page 113
	Table 9.5: "Overhead Times for Motions Between OSM2 Spectral Elements" on page 113
	Table 9.7: "Science Exposure Overhead Times" on page 115
Celestial backgrounds	Figure 10.1 on page 123: sky backgrounds vs. wavelength
	Figure 10.2 on page 124: background from the Sun and Moon
	Figure 10.3 on page 128: extinction