How to measure intensity of emission lines in low resolutio?

[Sam Anderegg]

I am coaching a high school student in his first science project making spectroscopic observations of Planetary Nebulae (PN). In our school observatory he is using our 36cm RC telescope and the low resolution Alpy (R=600) spectrograph including the calibration and guiding modules. The imaging CCD is an Atik 314.

After many weeks of bad weather during Spring in Switzerland, we have now recorded several spectra of three PN. NGC6543 (famous Cat's Eye), NGC6210 and the much fainter NGC7026. The student then used Demetra SW for processing the spectra that all worked well with plausible results. We also took reference spectra of nearby MILES stars.

Example: NGC6543, 9 x 300sec, no binning, CCD cooled to zero degrees.

NGC6543 (9x300sec, no binning)

The next task of the student is trying to estimate the intensities of selected emission lines and then calculate ratios of pair of lines in order to estimate the temperature and density of the electron gas in the PN. Basically he is following the work of Olivier and Francois in their Astrosurf letter from 2015 (starting on page 34).

Question:

It is obviously a challenge to estimate these intensities in low resolution spectra. What is your advice? Should he simply measure the peak intensity and use these values to calulation the ratios?

Example: blended lines of H-gamma and [OIII] compared in Alpy compared with high-res spectra

Emission lines in NGC7026 near A4350

[Francois Teyssier]

Hi Sam,

Could you send me the spectrum (fits).
I'll look at it and say you.
François

francoismathieu.teyssier at gmail.com

[Sam Anderegg]

Merci François, pour nous aider.

You can download the three output FITS spectra files from data reduction in Demetra from here. The student also applied a response curve correction using nearby Miles stars.
https://drive.google.com/drive/folders/ ... share_link

screenshot.png (42.35 KiB) Viewed 2192 times

Cheers
--Sam