by Anthony Barreiro » Fri Aug 23, 2013 6:28 pm
Ann wrote:I love this picture, and I have already written a rather long comment on what can be learnt from these spectra. I'm going to paste my previous comment here:
...
8) We can see that there appear to be bright emission lines right next to the dark absorption lines. Nova Delphini therefore appears to have a P Cygni spectrum, where dark absorption lines are bordered (on the red side) by bright emission lines. This feature means that we are looking at ejecta coming our way, or, in other words, we are looking at fragments from an explosion.
So the picture is indeed highly informative!
Ann
It is a beautiful and informative spectrum! You can really see the Hydrogen alpha, beta, and gamma absorption lines in Nova Delphini 2013's spectrum, and the emission lines at slightly longer wavelengths.
Why are the absorption lines blueshifted relative to the emission lines? I'm trying to picture the sequence of events, but my mental house of cards collapses before reaching a stable equilibrium. Hydrogen from a companion star falls onto a white dwarf, eventually triggering a thermonuclear explosion which we see as a nova. The explosion blows hydrogen out into space. The hydrogen in the cloud around the white dwarf is absorbing and emitting photons at the Balmer wavelengths, thus we see the Hydrogen alpha, etc. emission lines. The hydrogen in the gas that is directly between us and the still glowing nova absorbs photons at the Balmer wavelengths and re-emits them in random directions, causing the absorption lines. The gas that is directly between us and the white dwarf is traveling toward us faster than any of the other gas, so the absorption lines appear slightly blue-shifted.
After trying three or four times, I think I've figured it out. Is this right?
[quote="Ann"]I love this picture, and I have already written a rather long comment on what can be learnt from these spectra. I'm going to paste my previous comment here:
[quote]...
8) We can see that there appear to be bright emission lines right next to the dark absorption lines. Nova Delphini therefore appears to have a P Cygni spectrum, where dark absorption lines are bordered (on the red side) by bright emission lines. This feature means that we are looking at ejecta coming our way, or, in other words, we are looking at fragments from an explosion.
So the picture is indeed highly informative! :D
Ann[/quote][/quote]
It is a beautiful and informative spectrum! You can really see the Hydrogen alpha, beta, and gamma absorption lines in Nova Delphini 2013's spectrum, and the emission lines at slightly longer wavelengths.
Why are the absorption lines blueshifted relative to the emission lines? I'm trying to picture the sequence of events, but my mental house of cards collapses before reaching a stable equilibrium. Hydrogen from a companion star falls onto a white dwarf, eventually triggering a thermonuclear explosion which we see as a nova. The explosion blows hydrogen out into space. The hydrogen in the cloud around the white dwarf is absorbing and emitting photons at the Balmer wavelengths, thus we see the Hydrogen alpha, etc. emission lines. The hydrogen in the gas that is directly between us and the still glowing nova absorbs photons at the Balmer wavelengths and re-emits them in random directions, causing the absorption lines. The gas that is directly between us and the white dwarf is traveling toward us faster than any of the other gas, so the absorption lines appear slightly blue-shifted.
After trying three or four times, I think I've figured it out. Is this right?