slant correction in ISIS and influence on calibration
Posted: Tue Jun 12, 2018 8:28 am
Hello all,
I'm working with a L200 spectrograph with 1800 l/mm grating with a TRIUS SX814 CCD-camera on a C11 telescope and use ISIS 5.9.2 software for datareduction. For an observing session i take first a calibrationspectrum, then some spectra images of the same star and at the end again a calibrationspectrum.
I follow the tutorial of ISIS to calibrate the Ne-spectrum obtained by the internal Ne-calibrationlamp of the L200. so far so good.
I select also the 'slant' on the same calibrationline as selected as referencepoint in the spectrum of the Ne-lamp for ISIS, in my case the 6506.528 Ang. line.
After that i do the complete calibration on the spectrum of the Be-star.
Then i check my calibrated spectrum of the star on the H2O-lines as provided in ISIS.
What I notice now is that I can not let the H2O lines coincide with my spectrum over the entire spectrum. In one way or another, there is a shift that is not linear. (see screenshot of VSpec - check the error on the left side is positiv, on the right end negativ). The first thing that comes to mind is that the calibration is wrong, so next step:
I took care of the complete calibration procedure and also carried out this calibration manually in ISIS.
Upon closer inspection of my calibration spectrum, I notice that the slant is different for each Ne-line (see screenshot in appendix). I can obtain a further slant here when choosing a Ne-line that nevertheless has an influence on the final result.
I thought it was a problem with the L200, but when I download the ISIS turorial file and see the calibration spectrum there, I also notice a similar variation in the slant for each calibration line.
I was thinking that this could be a possible cause of the problem of the variation in the H2O lines of the Be-star calibrated spectrum.
I do not know if there is a correction for this problem in ISIS, in any case I did not find it immediately. can a function be provided in ISIS that corrects the variation in slant over the entire calibration image (for example by measuring the slant for each calibration line or at 3 points)? Or maybe i'm wrong and this slant variation has no influence on the calibration ?
Or possibly I do not apply the calibration procedure correctly or i'm overlooked something in ISIS or another problem?
Has someone the same problem and how can this be resolved or deal with this ?
thanking in advance,
Erik
I'm working with a L200 spectrograph with 1800 l/mm grating with a TRIUS SX814 CCD-camera on a C11 telescope and use ISIS 5.9.2 software for datareduction. For an observing session i take first a calibrationspectrum, then some spectra images of the same star and at the end again a calibrationspectrum.
I follow the tutorial of ISIS to calibrate the Ne-spectrum obtained by the internal Ne-calibrationlamp of the L200. so far so good.
I select also the 'slant' on the same calibrationline as selected as referencepoint in the spectrum of the Ne-lamp for ISIS, in my case the 6506.528 Ang. line.
After that i do the complete calibration on the spectrum of the Be-star.
Then i check my calibrated spectrum of the star on the H2O-lines as provided in ISIS.
What I notice now is that I can not let the H2O lines coincide with my spectrum over the entire spectrum. In one way or another, there is a shift that is not linear. (see screenshot of VSpec - check the error on the left side is positiv, on the right end negativ). The first thing that comes to mind is that the calibration is wrong, so next step:
I took care of the complete calibration procedure and also carried out this calibration manually in ISIS.
Upon closer inspection of my calibration spectrum, I notice that the slant is different for each Ne-line (see screenshot in appendix). I can obtain a further slant here when choosing a Ne-line that nevertheless has an influence on the final result.
I thought it was a problem with the L200, but when I download the ISIS turorial file and see the calibration spectrum there, I also notice a similar variation in the slant for each calibration line.
I was thinking that this could be a possible cause of the problem of the variation in the H2O lines of the Be-star calibrated spectrum.
I do not know if there is a correction for this problem in ISIS, in any case I did not find it immediately. can a function be provided in ISIS that corrects the variation in slant over the entire calibration image (for example by measuring the slant for each calibration line or at 3 points)? Or maybe i'm wrong and this slant variation has no influence on the calibration ?
Or possibly I do not apply the calibration procedure correctly or i'm overlooked something in ISIS or another problem?
Has someone the same problem and how can this be resolved or deal with this ?
thanking in advance,
Erik