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 \cdot s-1 \cdot pixel-1 counts \cdot 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