› Forums › Spectroscopy › Need help with instrumental response for low-res spectroscopy › Reply To: Need help with instrumental response for low-res spectroscopy
Hi Magnus,
I am not saying that this is necessarily the problem here but with the technique generally used by amateurs for flux calibration using reference stars nearby in the sky to the target it is important to do some investigations into the stars used as a reference. This is different to photometry where others (eg AAVSO/BAAVSS) have done the hard work and prepared nice sets of reference stars, checking that they are non variable and accurately measuring their brightness. As spectrcoscopists we are not so fortunate so we work with what we can find . A rule of thumb for example is to use main sequence stars as giants are more likely to be variable. Also look to see how they are described in SIMBAD and if they appear as variables in AAVSO VSX.
HD207673 raised a number of red flags for me. SIMBAD defines it as A2ib a hypergiant star so likely to be variable. Its MILES spectrum does not look like it should for the given spectral classification possibly due to reddening, even though the data in the spreadsheet suggests E(B-V) =0. This is likely to be wrong as the SIMBAD data suggests E(B-V) = 0.4 which would confirm some reddening. Perhaps the MILES spectrum is ok, perhaps not.
Professionals take a different approach, using a small set of reliable standards which might be far from the target at a different air mass and correcting for the atmospheric extinction separately. Christian Buil advocates this method for his StarEx/SpecInti project and it might work for you. If it does it is perhaps a better method but it does not work for me as my atmospheric conditions are not stable enough and my telescope has achromatic lenses (a focal reducer) so the instrument response is not constant but highly dependent on the focus on the night.
If you were getting good results with your previous camera but not now and suspect this is a new problem perhaps the best thing to do is to try to reproduce some of your previous measurements using the same stars. This would then narrow the area down that you need to investigate.
Cheers
Robin