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P Cygni H-alpha


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About this observation
Andy Wilson
Time of observation
02/10/2016 - 20:40
P Cygni
Observing location
Yatton, Somerset
Altair Astro RC 250
Lhires III spectrograph 2400 l/mm
Astro-Physics AP1200
180 seconds

P Cygni is a blue hypergiant. One of the brightest stars in our galaxy it is more than half a million times as luminous as our Sun.
It also lends its name to an important feature of astronomical spectroscopy, the P Cygni profile. This is a line profile that contains both an emission and absorption component. The emission comes from the bulk of the gas, while the absorption component is blue shifted. This blue shifted absorption is telling us about the motion of gas that is coming towards us along our line of sight.
This spectrum from last night is of P Cygni's H alpha profile, clearly showing both the absorption and emission features. In the case of P Cygni this is due to a powerful wind being thrown off by the star. I measured the wind speed at 150-250 km/s from the two edges of the absorption profile in my spectrum.

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