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Emission Lines in Deneb

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Emission Lines in Deneb

I captured a spectrum of Deneb on 10-1-14 and it shows some nice Hydrogen-beta and Sodium emission lines. Other spectra the same night show these lines as absorption lines. Anyone want to try and expain the source of the transient emission lines?



I do not have an explanation.

I do not have an explanation.  But at the same time it does not surprise me.  Nearly all hot stars have a tendency to exhibit the Be phenomenon from time to time.  Honestly, while there are theories and it is probably related to the stellar wind and stellar activity, the Be phenomenon still perplexes us.

A literature search may turn something up.  I encourage you to do that.

One observation can be dismissed as a fluke, so I would encourage you to keep checking in on Deneb to see if it reappears.  With more data, there is a better chance of figuring out a pattern if one exists. 

This is one area where availability of spectroscopy for small telescopes has the potential to help discover new things.  Imagine, if you had just been watching the stars brightness this would have been barely measurable.  But spectroscopy potentially reveals a lot more about the variability of stars.




PJOC's picture
Hi Robert, I'm not 100% sure

Hi Robert,

I'm not 100% sure that those are H beta and Na.  The spectral shape doesn't look right - an A2 star should peak around 4000 while yours peaks at 5300.  Plus, the absorption lines that are there seem not to match the rest of the Balmer lines.  An A2 spectrum should show prominent lines at 4340 and 4101, and yours doesn't have any lines there at all.

Deneb's in a crowded field.  I suspect that what has happened is that you've picked up a couple of field stars, the sero order image of which are overlaid on your Deneb spectrum.  Then you've calibrated on these "emission lines", which has thrown your dispersion calculations right off. 

Are you using a DSLR? Can you post your raw spectrum image? Also the earlier spectrum that showed absoption not emisison?



Great input


Yes, your question regarding zero order field stars is good one, I will check the spectrum again and post the raw data later today. There were a series of 45 images and I have only analyzed about 4 so far. I did have this exact issuew on a previous image that was about 6500A, but I was able to adjsut the capture window to eliminate it.

 I believe I did the calibration on an earlier image and then did a single point calibration on the star using my previous calibration data. However, something to check.

I did notice that the shape of the spectrum is highly influenced by the iso and exposure length. At longer exposures and/or higher iso's I believe the CCD starts to become saturated and there are some weird humps that start to appear. I am using Backyard EOS as my capture software and it limits me to a minimum of 1sec exposure times, but even this may be too long with iso200. I will give it another try at sub 1 sec second exposre length to see if the shape changes at all. I also should check my calibration curve to ensure it is good.

Thanks for your input.


What processing steps did you

What processing steps did you passed to correct the observed spectrum for instrumental response? Did you used a star with known energy distribution? Or did you just summed stellar signal from different pixel rows/columns? At the moment your result seems to be bit too wavy for an A-type supergiant star.

Look for example Deneb in Elodie archive:

The spectrum there is kind of "fluxed" or in pseudo-energetic units, and it is pretty smooth. As one could expect from such star.

Not reproducible.

Well, I could not reproduce my results, so obviously something went wrong with the processing. Perhaps some field stars as suggested.

Attached is another attempt. This looks much more like it should.

Thanks for the feedback, my learning curve is still pretty steep.



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