COS Tables

Detector Count Rate Restrictions

The ETC uses the current count rate screening restrictions, which are taken from Section 11.5 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
FUV	Irregular	Global	6,000 per segment
FUV	Irregular	Local	0.666 per pixel or 40 per resel [3]
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	Imaging	Global	170,000 (over entire detector)
NUV	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.

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:	FUV_XDL	NUV_MAMA
Dark rate (counts sec-1)	5.35 x 10-6 per pixel (target acquisition mode)	9.92 x 10-4 per pixel
	4.37 x 10-6 per pixel (spectroscopic mode)
Read noise	0	0