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:
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. |
The following table lists the dark count rate and read noise characteristics of the COS detectors as measured in ground tests.
Detector | Mode | Dark Rate | Read Noise |
---|---|---|---|
counts ![]() ![]() |
counts ![]() |
||
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 |