SPECTROSCOPY
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RELATIVE FLUX CALIBRATION
Correcting spectra for instrument and atmosphere using reference spectra from the MILES database
A series of exercises exploring the precision of relative flux calibration of low resolution spectra using slitless and slit spectrographs.
See this document for information and useful tips on how to
calibrate spectra in (relative) flux
Updated 2020-09-25 (clarification
of terminology) 2020-10-07 (link
to absolute flux calibration) 2022-12-22 (link to info on slitless flat
faults)
IMPORTANT NOTE!
The MILES spectra as published are corrected for interstellar extinction. Since this changes the shape of the spectum continuum, this correction must be removed before comparing with the measured spectrum. This has been done for the spectra in the ISIS database and are also available from Paolo Berardi's spreadhseet below
To help choose suitable reference stars for low resolution spectroscopy, members of the ARAS group have developed the following tools
Paolo
Berardi has a link to the non interstellar corrected, professionally measured
MILES star spectra and a spreadsheet to select them
http://www.spectro-aras.com/forum/viewtopic.php?f=8&t=941&start=10
Francois
Teyssier has produced a spreadsheet "Reference Star Finder" downloadable from
this page which includes MILES and other bright A/B stars with low
extinction
http://www.astronomie-amateur.fr/ProjetsSpectro0.html
(Click to download pdf)
This document demonstrates how an instrument response derived from a measurement of an A class star from the MILES database of reference star spectra can be used to correct Star Analyser spectra of any target regardless of spectral class.
(Click to download pdf)
This document describes a similar exercise using the ALPY 600 slit spectrograph. Note how changes in focus of this achromatic setup affected the instrument response due to selective sampling by wavelength at the slit.
(Click to download pdf)
This document describes a further exercise exploring the precision of relative flux calibration using the ALPY 600 slit spectrograph. It was carried out as part of a BAA spectroscopy initiative. Good repeatability and errors in relative flux of the order of 2% or better were obtained in the range 4000-7300A.
See these discussions on the ARAS forum for more details of how the Miles database can be used as a source of reference stars for calibration of low resolution spectra.
http://www.spectro-aras.com/forum/viewtopic.php?f=6&t=207 (Thread in French initially, changing to English)
http://www.spectro-aras.com/forum/viewtopic.php?f=6&t=207&start=30#p2162 (Direct link to post describing spreadsheet developed to select Miles spectra)
Note that the Miles and many other reference spectra are now also built into the ISIS data reduction software package