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ISAAC Quality Control:
Flux standard star

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Trending & QC1
   Flux Std
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wavelength parameters | intensity | spectrum PSF | flux calibration
not implemented
flux calibration
QC1 database (advanced users): browse | plot
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   Click on HISTORY to see the historical evolution of the trending.

Since 2006 the ISAAC calibration plan includes the observation of bright flux standard stars. The standards are taken with setup SW-arm, LR-grating and mask_L2 meaning slit less spectroscopy. The observations are done usually 6 times a year in all four wavelength filters/wavelength bands: SZ,J, SH, and SK. Only eight stars have been selected out of the operational catalog of telluric standards for this calibration.The flux standard star observations are processed by the pipeline. In a first part the two raw spectra are co-added and extracted in the same manner as for science spectroscopy or telluric standard stars. As there are no sky emission lines in slit less spectroscopy day time arc-lamp calibrations are used for the wavelength calibration. Generally if the flux standard is used to calibrate science spectra it is advised to flat field the flux standard with the same flat as the science spectrum in order to cancel out the lamp spectrum and other low order features. Within the QC process the flux standards are not used to calibrate science spectra; the flux standard spectra are not flat fielded. The high order fixed pattern noise (= pixel to pixel gain variations) is not reduced but the spectra are clean from lamp features. In as second part the spectra are compared with stellar spectra for spectrophotometric calibrations.

The final pipeline product table consisting of three columns: for wavelength, source spectrum and residual sky spectrum as the product spectra of science spectra and telluric standard stars. In addition the product table for flux standards contains two more columns, one for the efficiency as function of wavelength and one for the conversion (from ADU in erg/cm/cm/sec/Ang) as a function of wavelength.

The conversion as monitored as part of the QC process is a pure technical calibration and is not suitable to be used directly to calibrate science spectra delivered by the pipeline, as the science spectra are flat fielded but the flux standards not.

Star RA DEC J H K Type
HD 216009 22:49:51.0 -44:25:26 7.96 7.97 7.91 A0V
Hip 093004 18:56:47.2 -14:01:41 7.52 7.57 7.50 B9V
Hip 077677 15:51:29.8 -30:35:14 7.39 7.39 7.34 B9V
Hip 065688 13:28:04.9 -33:16:34 8.42 8.47 8.45 B8V
Hip 049042 10:00:22.4 -17:49:47 8.71 8.76 8.75 B9V
Hip 029201 06:09:33.6 -05:04:00 7.80 7.75 7.67 B0V
Hip 015188 03:15:45.9 -16:49:43 8.23 8.31 8.35 B3V
Hip 000328 00:04:11.9 -30:08:05 7.20 7.28 7.25 B8V

Table of the 8 monthly taken ISAAC flux calibration standard stars.

top wavelength calibration parameters

QC1 parameters

parameter QC1 database: table, name procedure
wavelength calibration method isaac_flux, qc_wl_method - the wavelength calibration method finally used (arc lines, sky lines or physical model). arc lines is the operational default.
central wavelength isaac_flux, qc_wlen - the central wavelength in micron, derived from the dispersion solution
dispersion solution isaac_flux, qc_dispco1, qc_dospco2, qc_dispco3, qc_dispco4 - the wavelength calibration polynomial coefficients
fit quality isaac_flux, qc_xcorr - the wavelength calibration correlation coefficient
arc line results isaac_flux, arc_... - the wavelength calibration results from the associated arc line calibration product
grating offset isaac_flux, qc_SA_offset - grating offset between associated arc product and flux standard star ( = ( qc_wlen(telluric) minus qc_wlen(arc) ) in pixel


top intensity parameters

QC1 parameters

parameter QC1 database: table, name procedure
average intensity isaac_flux, qc_ew_a - spectrum average intensity in ADU
weighted average intensity isaac_flux, qc_ew_i - spectrum integral average intensity in ADU
total intensity isaac_flux, qc_intens - integrated spectrum in ADU


top point spread function

QC1 parameters

parameter QC1 database: table, name procedure
Gauss-fit parameters isaac_flux, qc_psf_g - fit the product PSF at x=400 by Gaussian, return sigma (not FWHM)
Gauss-fit parameters isaac_flux, qc_psf_cg - fit the median collapsed product PSF by Gaussian, return sigma (not FWHM)
Moffat parameters isaac_flux, qc_psf_m_R - fit the product PSF at x=400 by Moffat function, return R (~width)
Moffat parameters isaac_flux, qc_psf_m_beta - fit the product PSF at x=400 by Moffat function , return beta (~wing)
Moffat parameters isaac_flux, qc_psf_cm_R - fit the median collapsed product PSF by a Moffat function, return R (~width)
Moffat parameters isaac_flux, qc_psf_cm_beta - fit the median collapsed product PSF by a Moffat function, return beta (~wing)


Not implemented

top flux calibration parameters

We plot the efficiency as a function of wavelength. The efficiency (measured flux in units of real flux) is fit by a linear function (SZ,SH, SK), but for the J band by a quadratic function. The wavelength intervals for the fit are:

QC1 parameters

parameter QC1 database: table, name procedure
conversion factor isaac_flux, qc_cf - conversion factor at central wavelength
efficiency isaac_flux, qc_ew_i - efficiency at central wavelength
spectral slope isaac_flux, qc_hr - fit the efficiency within a narrow 'clean' wavelength range by a low order function to get the spectral slope.