XSHOOTER: Dark
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HC PLOTS |
UVB median dark and rms: |
![](/observing/dfo/quality/ALL/img/sq1.png) |
VIS |
![](/observing/dfo/quality/ALL/img/sq1.png) |
AGC |
![](/observing/dfo/quality/ALL/img/sq1.png) |
NIR remnance: |
![](/observing/dfo/quality/ALL/img/sq1.png) |
NIR parameters for DIT=1sec |
![](/observing/dfo/quality/ALL/img/sq1.png) |
NIR parameters for DIT=5sec |
![](/observing/dfo/quality/ALL/img/sq1.png) |
NIR parameters for DIT=300sec |
![](/observing/dfo/quality/ALL/img/sq1.png) |
NIR parameters for DIT=600sec |
![](/observing/dfo/quality/ALL/img/sq1.png) |
NIR parameters for DIT=900sec |
![](/observing/dfo/quality/ALL/img/sq1.png) |
QC1 database (advanced users):
browse |
plot
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UVB and VIS-arm dark calibrations are acquired as a set of three
shutter-closed frames, each one 3600sec (=1h) exposure time. NIR-arm dark
calibrations are acquired as a set of three frames coherent in exposure time.
Set of frames with low exposure (e.g. DIT=5sec, 10 ...) use three
subintegrations (NDIT=3) averaged on the chip, while set of frames with longer
exposure times (e.g. DIT=900sec) use NDIT=1.
UVB and VIS dark calibrations are technical calibrations. They are not used to
calibrate the science. Their purpose is to monitor the intrinsic dark current
of the detector, and radiation not shielded by the detector enclosure, which
can be a cosmics and dark level. The same holds for the dark current of the
AGC detector
The NIR-arm dark frames are used to calibrate
science and standard star observations acquired in STARE mode. Long DIT
NIR-arm dark frames rarely suffer from persistence, either induced by a bright
arc-lamp exposure or saturation in the K-band. Those dark calibrations are
rejected as it is assumed that the persistence is a short period effect.
Dark level
QC1_parameters
FITS key |
QC1 database: table, name |
definition |
class* |
HC_plot** |
more docu |
QC.MDARKMED | xshooter_dark..median_dark | median value of master dark | HC | | [docuSys coming] |
*Class: KPI - instrument performance; HC - instrument health; CAL - calibration quality; ENG - engineering parameter
**There might be more than one. |
Trending
For the UVB
and VIS
arm the dark level is monitored for both read out modes
in 1x1 binning. In the long term, the low-gain setup is
stable with a larger scatter, while the high-gain setup
shows a minor trend. Data from early operations might
be biased from from slightly different algorithms used
in the early versions in the pipeline.
For the NIR-arm the dark level starts after each
detector intervention (warm-up and cool-down
of the detector cryostat) at a low value,
symptomatically increasing in the long term to
a value of about 20 ADU (for DIT=600sec). The
NIR-arm dark level is monitored for several DIT
values.
The dark of the AGC is not stable.
Scoring&thresholds Dark level
The value is scored. Thresholds are set to operational meaningful values.
History
Date |
event |
2011-07-07 | NIR intervention, as usual for NIR-arm interventions, dark level starts at a low value and increases over months to the pre-intervention value. |
2012-07-01 | UVB change of dark level for the high gain setup |
2017-02-09 | the UVB-arm shutter was replaced |
2017-05-05 | The dome lights were on. In the UVB arm the registered dark level was 0.018 ADU/sec, while it is normally (dome light off) three times lower at 0.0005 ADU/sec. In the VIS arm 0.01 ADU/sec were measured while it is usually 0.001 ADU/sec |
2018-01-01 | The AGC-arm dark frames are from now on acquired for four DIT only: 10sec, 50sec, 150sec and 300sec. |
2018-11-01 | The NIR-arm DIT=5sec setup is acquired with NDIT=1, while before is was acquired with NDIT=3. All monitored QC parameters show a slightly different mean level. |
Algorithm Dark level
A median stacking method is used to generate a master dark
product. The median dark level is the median of the master dark frame.
Rms
QC1_parameters
FITS key |
QC1 database: table, name |
definition |
class* |
HC_plot** |
more docu |
QC.MDARKRMS | xshooter_dark..sigma_dark | RMS value of master dark | CAL | | [docuSys coming] |
*Class: KPI - instrument performance; HC - instrument health; CAL - calibration quality; ENG - engineering parameter
**There might be more than one. |
Trending
For the
UVB and
VIS arm the dark rms is monitored for both
read out modes in 1x1 binning.
The dark rms (the root mean square over all pixel of the master dark) is not monitored for ther NIR-arm and the AGC-arm.
Scoring&thresholds Rms
The rms is not scored.
History
Date |
event |
2010-06-01 | new pipeline version (1.0.0); dark_rms calculated correctly now; results from older versions erased from QC1 database |
2010-09-19 | - 2010-10-07 typo in pipeline; computation of dark_rms changed , values removed from QC1 database |
2011-07-07 | NIR intervention |
Algorithm Rms
The RMS is the robust root mean square over all pixel of the master dark product.
Remnance
QC1_parameters
FITS key |
QC1 database: table, name |
definition |
class* |
HC_plot** |
more docu |
QC.MDARK.CONTAM | xshooter_dark..remnance | count difference between region within the redmost echelle order and outside | HC | | [docuSys coming] |
*Class: KPI - instrument performance; HC - instrument health; CAL - calibration quality; ENG - engineering parameter
**There might be more than one. |
Trending
The QC parameter is for the NIR-arm only.
Scoring&thresholds Remnance
The threshold is 5.5: if this value is above 5 there
is a good chance to see remnants from previous high
level exposures.
History
Date |
event |
| NIR darks taken shortly after high flux observations (e.g. flat fields or flux standard stars in twilight) may show remnance in the top orders (raw data) or at right edge (processed data). Below in Fig.A you find an example of a 120s DARK, taken 30 minutes after a bright observations. The cuts are at 23 and 45 counts. |
2010-12-05 | the VIS CCD got a new cryostat. |
2014-01-01 | monitoring of the AGC bias level has started |
![](/observing/dfo/quality/XSHOOTER/qc/problems/DARK_120s_23_45.png) |
Figure A, NIR-arm remnance in the K-band Echelle orders.
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Algorithm Remnance
Remnance gives the difference in flux between the
red-most order and the area to its right.
Readout noise
QC1_parameters
FITS key |
QC1 database: table, name |
definition |
class* |
HC_plot** |
more docu |
QC.RON | xshooter_dark..ron | read out noise | HC | | [docuSys coming] |
*Class: KPI - instrument performance; HC - instrument health; CAL - calibration quality; ENG - engineering parameter
**There might be more than one. |
Trending
The
NIR-arm read-out noise is monitored for several DIT
values. For UVB and VIS, ron is extracted from
Bias frames.
Scoring&thresholds Readout noise
The scoring thresholds are based on statistical grounds.
History
No Remarks.
Algorithm Readout noise
Two NIR-arm raw dark frames are subtracted. The rms of the difference frame within the standard region is the read-out noise.
Cosmics
QC1_parameters
FITS key |
QC1 database: table, name |
definition |
class* |
HC_plot** |
more docu |
QC.CRRATE | xshooter_dark..cosmic_rate | average number of cosmic rays per cm^2 and second | HC | | [docuSys coming] |
*Class: KPI - instrument performance; HC - instrument health; CAL - calibration quality; ENG - engineering parameter
**There might be more than one. |
Trending
The
NIR-arm cosmic rate is monitored for several DIT
values. The cosmic rate for the UVB and VIS-arm is
registered in the QC1 DB, but not monitored.
Scoring&thresholds Cosmics
The scoring thresholds are based on statistical grounds.
History
Date |
event |
2010-02-01 | The new pipeline version; cosmic_rate calculated slightly differently |
2010-09-19 | from 2010-09-19 to 2010-10-07 typo in pipeline; computation of cosmic_rate affected, values removed from QC1 database |
Algorithm Cosmics
The number of detected cosmic ray hits per surface unit (cm2) and per second.
Fixed-pattern noise
QC1_parameters
FITS key |
QC1 database: table, name |
definition |
class* |
HC_plot** |
more docu |
QC.NORMFPN | xshooter_dark..fp_norm | fixed pattern amplitude normalized by exposure time | HC | | [docuSys coming] |
*Class: KPI - instrument performance; HC - instrument health; CAL - calibration quality; ENG - engineering parameter
**There might be more than one. |
Trending
The
NIR-arm relative fixed pattern noise is monitored for several DIT
values. The fixed pattern noise for the UVB and VIS arm is
stored in the QC1 DB, but is not monitored.
Scoring&thresholds Fixed-pattern noise
The scoring thresholds are based on statistical grounds.
History
Date |
event |
2012-02-10 | new pipeline version with different algorithm, and new fp_norm values. |
2013-05-01 | new pipeline version with different algorithm, and new fp_norm values. |
Algorithm Fixed-pattern noise
Fixed pattern noise, scaled to exposure time of 1sec.
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