spectro-aras.com

Hello
Some days my spectra show a deviation of the continuum linewhich I can'texplain,the other day everything seems o.k.I looks like interference from outside??The circumstances in my observatory do'nt change:two desktops one lcd monitor and one led screen, LCD TV with DVB-T antenna.My observatory is located at 50 m away from one railroad rack and 500m from another railroad.Could it be the ccd camera ST7XME.
Clear skies
Valère Van Ruymbeke

The optical interference is highly improbable. Problem during processing are more probable.
Could you precise the processing procedure (software, method, option, ... cosmic rays detection for example...) ?

Christian B

Hallo Christian,
Processing is with Audela. Pipeline :Instrumental response.I never succeeded to process with ISIS,maybe because SGS spectra are red at left and blue at right.Which program should I use to inverse all raw spectra at once,so I can try ISIS.
Regards
Valère

Hello Valere,

you may use ISIS, in V4.1.2 you can do it under Tools - Image processing 1 - image permutation for all spectra in a series.
For all files in a directory you can use a script in Audela, described in the eshel user manual (chapter 8):
http://thizy.free.fr/shelyak/eshel/DC00 ... 0Guide.pdf

Martin

Hello Christian, Martin
Appreciate your help!
I reprocessed spectrum ABAUR spectrum ,now it looks allright,maybe I forgot to check the "remove cosmic rays box in Spcaudace"Default = no.There are other raw spectra with show bright white spots which I can not eliminate after carefully recalibrating f.i this spectrum of delsco.
regards

Valère,

there is definitively something wrong with your processing. Could you post how a raw spectrum looks like? Have you tried processing with ISIS to see the difference?

Cordialement,
Olivier

Hello Olivier,
90% of my Delsco spectra are normal.I didn't yet try Isis because on earlier occasions it didn't work ,maybe because Sgs spectra are red left I have to inverse them and must learn Isis
kind regards
Valère.

Hello Valere,

I had a quick look at your spectra. They look allright. A quick analysis in ISIS (without specrtral calibration) showed no modulation of your baseline as in your spectrum. So my guess it has to do with the processing. Some time ago I had a similar problem with some echelle spectra in Audela: I attributed it to a very narrow width of the spectrum (about two pixels), which the algorithm for calculating the spectral intensity was not doing correctly. What you see is a modulation when jumping from ond CCD row to the next. In your spectrum the width is also quite narrow, so I could imagine it is a similar error. Maybe you had a better guiding for this spectrum,so the effect shows only here, but this is only speculation.
My recommendation: learn and use ISIS, I never had this problem there (although I am not using 2x2 binning in the camera anymore). Try without and with optimal binning and see if there is a difference.

Regards,

Martin

Hi Martin
The binning used is 1x(4 vertical binning ), maybe this is important.
regards
Valère

I am suspicious of optimal binning routines unless I know exactly how they work. I have not had this particular problem but I know for example that Vspec optimum binning can distort the shape of the continuum if the spectrum is not exactly level or there is a change in the height of the spectrum across the field (eg because of varying focus)

Robin