Psi Persei, emission lines in Fe II ?

[John Coffin]

I’ve captured my first spectrum of a Be star using my Alpy, Equinox Pro 80 and Canon 450D (full spectrum mod). Psi Persei appears to have emission lines in Fe II. Are these artefacts? What would cause them? I can’t find anything about this on the web. 

Attachments:

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   merak_psi-persei.png
   

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   psipersei_-20180215_945_John-Coffin.png
   

[Alun Halsey]

Hi John,

     Nice spectra,I managed to find this thread on Cloudy nights and it seems the emission lines are not artifacts but are indeed real. 

     https://www.cloudynights.com/topic/592631-psi-persei-and-phi-persei-spectroscopy/

    Regards

        Alun

[David Swan]

Tony Rodda has posted his spec of the star. He sees the Fe emission too. Click spec database on the right, type psi per into the box and click fetch spectra. David

[David Swan]

I am no expert, but according to the Spectral Atlas for Amateur Astronomers (Walker), you see Fe I/II emission lines in Be stars of classifications e3, e3+ and e4 – maybe weak in e2 class (psi Persei).

[John Coffin]

Thanks. I should have looked at Walker’s atlas. I have the PDF version. 

[John Coffin]

Why are there emission lines for Fe but not C, N, and O which must be present in the star before iron can be formed? If the iron is dredged up from the star’s core wouldn’t C, N and O be dredged up too? The ionisation potential for Fe is similar to the other metals. Surely it can’t be just centrifugal force that brings the Fe to the surface and into the circum-stellar disc in preference to the lighter elements? 

[Dr Andrew Smith]

There are a vast number of Fe II lines ( https://arxiv.org/pdf/1210.4773.pdf ) and in it’s other ionisation states  so Fe is strongly influenced by radiation pressure compared to C, N or O which have fewer lines.

Regards Andrew

[Hugh Allen]

Hi John,

Nice spectra. It’s interesting to see a DSLR being used with the Alpy. I think it’s important to remember that the expression of spectral lines is strongly determined by the environment. Absence of lines doesn’t necessarily imply absence of the chemical element. And conversely, presence of strong lines doesn’t necessarily mean a high concentration of the element. The iron in the disc around psi Per won’t I don’t think have been dredged up from the core, it will have been present in the nebula in which the star was originally formed. The Sun shows strong iron absorption lines, and exceedingly strong calcium lines, much stronger than the hydrogen absorption lines even though hydrogen atoms vastly outnumber calcium and iron in the Sun’s composition

Cheers

Hugh

[John Coffin]

Thanks, that makes sense. The DSLR will probably need changing for a CCD when I tackle fainter targets and funds become available. John. 

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