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Re: APOD: Messier 2 (2019 Apr 04)
Posted: Sun Apr 07, 2019 11:55 am
by Ann
Nitpicker wrote: ↑Sun Apr 07, 2019 11:28 am
Ann wrote: ↑Sun Apr 07, 2019 11:14 am
Nitpicker wrote: ↑Sun Apr 07, 2019 11:07 am
But, Ann, do the narrow bands of ionisation wavelengths relate to temperature in the same way as starlight? I think they rather relate to the elements being ionised.
They relate to the degree of ionization of the nebula, which in turn is dependent on the temperature of (or distance from) the ionizing source.
Ann
No, the narrow bands relate to the specific elements in the nebula, that are being ionised by photons from nearby stars. Each different ionised element emits a different, narrow band of wavelengths. The strength of the signal of each narrow band, relates to the degree of ionisation, which would depend on the photon flux and the density of the corresponding element in the nebula.
True, but you need more energy to ionize an OIII nebula than an SII one.
Ann
Re: APOD: Messier 2 (2019 Apr 04)
Posted: Mon Apr 08, 2019 12:24 am
by Nitpicker
Ann wrote: ↑Sun Apr 07, 2019 11:55 am
Nitpicker wrote: ↑Sun Apr 07, 2019 11:28 am
Ann wrote: ↑Sun Apr 07, 2019 11:14 am
They relate to the degree of ionization of the nebula, which in turn is dependent on the temperature of (or distance from) the ionizing source.
Ann
No, the narrow bands relate to the specific elements in the nebula, that are being ionised by photons from nearby stars. Each different ionised element emits a different, narrow band of wavelengths. The strength of the signal of each narrow band, relates to the degree of ionisation, which would depend on the photon flux and the density of the corresponding element in the nebula.
True, but you need more energy to ionize an OIII nebula than an SII one.
Ann
It is true that photons require more energy by a factor of 3 to 3.5 to create OIII (35.1 eV), than either Ha (13.6 eV) or SII (10.4 eV). Since photon energy is solely dependent on photon wavelength, with smaller wavelength (bluer) photons having more energy, I do see your point. It would appear that all the photons required to create these ions, need to be well into the UV spectrum, but maybe that is neither here nor there.
It really boils down to an argument between RGB=SHO (aka Hubble palette) and RGB=HOS (aka CHFT palette). I imagine the choice of one or the other will often consider factors other than wavelength/tempertaure/energy.