20 February 2018 at 7:18 pm #573968
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:20 February 2018 at 8:02 pm #579148Alun HalseyParticipant
Nice spectra,I managed to find this thread on Cloudy nights and it seems the emission lines are not artifacts but are indeed real.
Alun20 February 2018 at 8:10 pm #579150David SwanParticipant
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. David20 February 2018 at 8:23 pm #579149David SwanParticipant
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).21 February 2018 at 7:34 am #579156
Thanks. I should have looked at Walker’s atlas. I have the PDF version.21 February 2018 at 8:06 pm #579166
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?21 February 2018 at 10:35 pm #579167Dr Andrew SmithParticipant
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 Andrew21 February 2018 at 11:29 pm #579169Hugh AllenParticipant
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
Hugh22 February 2018 at 12:01 am #579170
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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