COS Tables

Detector Count Rate Restrictions

The ETC uses the current count rate screening restrictions, which are taken from Section 10.1 of the COS Instrument Handbook. If the observation will exceed any of the count rate restrictions, a warning message will be given in the output page. The count rate restrictions for the detectors are as follows:

COS Count Rate Screening Limits

Detector	Source type [1]	Type_of_limit	Limiting count rate [2]
FUV	Predictable	Global	15,000 per segment
FUV	Predictable	Local	0.666 per pixel or 40 per resel [4]
FUV	Irregular	Global	6,000 per segment
FUV	Irregular	Local	0.666 per pixel or 40 per resel [3], [4]
NUV	Predictable	Global	30,000 per stripe
NUV	Predictable	Local	70 per pixel
NUV	Irregular	Global	12,000 per stripe
NUV	Irregular	Local	70 per pixel
NUV	Predictable (Imaging)	Global	170,000 (over entire detector)
NUV	Predictable (Imaging)	Local	50 per pixel
NUV	Irregular (Imaging)	Global	68,000 (over entire detector)
NUV	Irregular (Imaging)	Local	50 per pixel

[1]	“Predictable” means the brightness of the source can be reliably predicted for the time of observation to within 0.5 magnitude.

[2]	Entries are counts per second.

[3]	The FUV spectral resolution is 6 pixels, the NUV is 3 pixels.

[4]	(1, 2) Except for central wavelengths 1055 and 1096, for which the value is 0.2 per pixel.

Detector Dark Background

The following table lists the dark count rate and read noise characteristics of the COS detectors as measured in ground tests.

Detector background count rates (per second) for COS

Detector	Mode	Dark Rate	Read Noise
		counts s-1 pixel-1	counts pixel-1
FUVB	target ACQ	7.88 x 10-6	0
FUVA	target ACQ	7.10 x 10-6	0
FUVB	spectroscopic	4.93 x 10-6	0
FUVA	spectroscopic	3.83 x 10-6	0
NUV	-	1.25 x 10-3	0