Cosmic Origins Spectrograph Instrument Handbook for Cycle 17

3.5 COS Quick Reference Guide

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Table 3.1: COS Instrument Characteristics

Property	FUV channel	NUV channel
Entrance aperture	2.5 arcsec round: clear (PSA) or attenuated (BOA)
Detector plate scale (cross dispersion)	22.6 mas per pixel 136 mas per resel	23.6 mas per pixel 70.5 mas per resel

Table 3.2: COS Detector Characteristics

		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
Image size recorded per spectrum		16384 × 128 (two, ACCUM) 16384 × 1024 (two, TIME-TAG)	1024 × 1024
Pixel size		6 × 24 µm	25 × 25 µm
Spectral resolution element size (= "resel")		6 × 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	~60 cnt s-1 cm-2 ~3.7x10-4 cnt s-1 pix-1 ~3.3x10-3 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
Screening limits for bright objects		see Section 11.5.2
Dead-time constant		7.4 µsec	280 nsec

Table 3.3: COS Predicted Calibration Accuracies

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	15 km s-1	15 km s-1
Absolute photometry	5%	5%
Relative photometry (same object at a different time)	2%	2%
Flat field quality measured	62:1	100:1
Flat field quality goal	100:1	100:1

Table 3.4: Useful Figures and Tables

Topic	Source	Content
Usage planning	Table 5.1	Summary of COS spectroscopic modes
	Table 5.3	FUV grating wavelength ranges
	Table 5.4	NUV grating wavelength ranges
	Table 10.2	Earthshine and zodiacal light fluxes
	Table 10.3	Strengths of airglow lines
Aperture parameters and PSFs	Figure 3.1	HST focal plane and COS aperture
	Figure 3.4	BOA transmission
	Figure 13.5	Modeled HST PSF at COS PSA for 1450 Å
	Figure 13.6	Modeled HST PSF at COS PSA for 2550 Å
	Figure 13.7	Cross-section of the HST PSF at COS PSA at 2550 Å
	Figure 6.2	Two-dimensional NUV imaging COS PSF
	Figure 7.1	Relative transmission of the PSA
Sensitivity and throughput	Figure 5.2	FUV sensitivity curves
	Figure 5.3	NUV sensitivity curves for M gratings
	Figure 5.4	Sensitivity curve for G230L
Acquisitions	Figure 7.3	ACQ/IMAGE exposure times
	Figure 7.4	Cross section of image using MIRRORB
	Figure 7.5	Cross section of image using MIRRORB + BOA
	Figure 7.8	Spiral search pattern for 3 × 3
	Figure 7.9	Acquisition exposure times for FUV dispersed light
Detector characteristics	Figure 4.1	FUV XDL detector schematic layout
	Figure 4.4	NUV MAMA detector schematic layout
	Table 11.1	COS detector count rate limits
	Table 11.2	Local and global flux limits
	Table 10.1	Detector dark count rates
Overheads and observing parameters	Table 13.4	TAGFLASH exposure intervals
	Table 13.5	TAGFLASH exposure durations
	Table 9.1	Generic observatory overhead times
	Table 9.2	Overhead times for OSM1 movements
	Table 9.3	Overhead times for OSM2 movements
	Table 9.4	Science exposure overhead times
Celestial backgrounds	Figure 10.1	Sky background versus wavelength
	Figure 10.2	Moon and Earth background levels
	Figure 10.3	Galactic extinction model
Data quality	Figure 5.1	Scattered light in the FUV
	Figure 5.5	FUV flat-field example
	Figure 5.6	NUV flat-field example
	Figure 7.2	Resolving power vs. position in aperture