MUSE: System efficiency
The MUSE instrument throughput is estimated in two ways: from the
daily technical calibrations comparing number of photons detected on
the channels (each slice) with the amount generated by photodiodes
located in front of the instrument, and from the spectrophotometric
observations of standard stars.
Throughput
Throughput data are technical calibrations taken daily in two
instrument setups: INS.MODE=WFM-NOAO-E, INS.OPTI1.NAME=Clear,
DET.READ.CURNMAE=SCI1.0, and INS.MODE=WFM-NOAO-N, INS.OPTI1.NAME=Blue,
DET.READ.CURNMAE=SCI1.0. Their purpose is to monitor MUSE throughput
by comparing amount of photons generated by photodiode 2 and 1, located
in front of the instrument (calibration unit), with amount detected on
the channels (each slice).
QC1_parameters
FITS key |
QC1 database: table, name |
definition |
class* |
HC_plot** |
more docu |
QC.AMPL.THRU1 | muse_throughput..thru1 | [%] Channel throughput compared to photodiode 1 | HC | | [docuSys coming] |
QC.AMPL.THRU2 | muse_throughput..thru2 | [%] Channel throughput compared to photodiode 2 | HC | | [docuSys coming] |
QC.AMPL.THRU2ERR | muse_throughput..thru2err | [%] Estimated error of throughput compared to photodiode 2 | HC | | [docuSys coming] |
*Class: KPI - instrument performance; HC - instrument health; CAL - calibration quality; ENG - engineering parameter
**There might be more than one. |
Trending
We monitor the throughput averaged across all the
24 chanels (IFUs) compared to the "photodiode 1" and
to the "photodiode 2" (in percent). We also trend
estimated error of throughput compared to "photodiode
2" (in percent). The values of the parameters do not
directly correspond to absolute measure of
instrument's throughput. This is a relative
measurement.
Scoring&thresholds Throughput
The tight lower threshold is set empirically to
detect decrease of the throughput but also, possible
photodiode failures.
History
Date |
event |
July 2014 | Throughput calibrations are taken regularly |
2015-03-31 | CHAN01 detector vessel exchanged, DET.CHIP.ID changed from psyche to egeria |
Algorithm Throughput
Several separate amplifier images (flat-fields with special FITS
headers containing pico amplifier measurements) are combined into one
master image file. To compute the throughput the image is converted
into a pixel table, the flux is then integrated over the given filter
band, and the ratio of the expected flux (FITS header INS.AMPL2.CURR)
to measured flux is taken, in the same units. The resulting ratio is
the instrument efficiency (throughput).
STD Throughput
We also monitor throughput of the instrument measured from
observations of the spectrophotometric standard stars.
QC1_parameters
FITS key |
QC1 database: table, name |
definition |
class* |
HC_plot** |
more docu |
QC.STANDARD.THRU5000 | muse_std..std_thru5000 | Throughput computed at 5000 &/- 100 A | HC | | [docuSys coming] |
QC.STANDARD.THRU7000 | muse_std..std_thru7000 | Throughput computed at 7000 &/- 100 A | HC | | [docuSys coming] |
QC.STANDARD.THRU8000 | muse_std..std_thru8000 | Throughput computed at 8000 &/- 100 A | HC | | [docuSys coming] |
QC.STANDARD.THRU9000 | muse_std..std_thru9000 | Throughput computed at 9000 &/- 100 A | HC | | [docuSys coming] |
*Class: KPI - instrument performance; HC - instrument health; CAL - calibration quality; ENG - engineering parameter
**There might be more than one. |
Trending
The throughput of the instrument measured from observations of the
spectrophotometric standard stars is monitored. The thoughput is
estimated in different wavelength bands +/- 100 A wide centered at:
5000 A, 7000 A, 8000 A and 9000 A. The 6000 A band is not used as it
is affected by the presence of Na Notch filters in the AO mode. Only
data points determined from calibrations taken in the read out mode
(DET.READ.CURNAME) SCI1.0 are selected.
Scoring&thresholds STD Throughput
No scoring
History
Date |
event |
2017-05-09 | Pipeline updated, the std_thru parameters started being calculated |
2017-09-05 | M1 re-coated; std_throughput increased |
Algorithm STD Throughput
The thoughput is estimated in different wavelength bands +/- 100 A
wide centered at: 5000 A, 7000 A, 8000 A and 9000 A. The observed
counts are integrated over the filter function, then multiplied with
hc/lambda/area (where area is the effective VLT area) to get observed
fluxes (f_obs). The reference fluxes are integrated over the filter
function (fref) and then the zeropoint is computed as zp = -2.5
log10(fobs/fref). The throughput is calculated using formula 10^(-0.4 zp).
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