Interference ?,

[Valere Van Ruymbeke]

abaur--profil-1c.png (19.38 KiB) Viewed 9963 times

abaur--profil-1b.png (21.89 KiB) Viewed 9963 times

abaur--profil-1c.png (19.38 KiB) Viewed 9963 times

abaur--profil-1b.png (21.89 KiB) Viewed 9963 times

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

[Christian Buil]

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

[Valere Van Ruymbeke]

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

[Martin Dubs]

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

[Valere Van Ruymbeke]

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

[Olivier Thizy]

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

[Valere Van Ruymbeke]

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.

[Martin Dubs]

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:

modulation in binned echelle spectrum with Audela eshel

binning echelle.jpg (41.8 KiB) Viewed 9910 times

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

[Valere Van Ruymbeke]

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

[Robin Leadbeater]

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