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Why is it H beta but O III?

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#1 Lee D

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Posted 06 December 2021 - 02:34 AM

If an H beta filter is for an emission line of singly ionized hydrogen, why isn't a filter for an emission line of doubly ionized oxygen called an O gamma filter?

 

Or why not H II and O III?



#2 ziggeman

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Posted 06 December 2021 - 03:02 AM

Water and Oxygen filter?



#3 Mark9473

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Posted 06 December 2021 - 03:47 AM

I believe the H in H beta is not an ionised state but an excited state, as opposed to O III which is O2+.


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#4 rob1986

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Posted 06 December 2021 - 04:20 AM

they're both excited states. But, hydrogen results from extra excited state. I suppose you could also break up the various OIII lines into alpha, beta, gama, etc(OIII  being a substance, the common OIII line referring to two specific spectra lines)

but as I understand the hydrogen lines result from different spectral lines (from different excited states, per quantum mechanics) present from the same substance.



#5 Tony Flanders

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Posted 06 December 2021 - 05:12 AM

If an H beta filter is for an emission line of singly ionized hydrogen

As Rick Fienberg liked to point out to us Sky & Telescope editors when he was editor-in-chief, the H Beta line does not come from ionized hydrogen. Ionized hydrogen atoms (also called protons) have no electrons, and therefore cannot emit this kind of radiation at all.

 

The H-Alpha and H-Beta lines of hydrogen are emitted by neutral hydrogen  -- one electron orbiting a proton -- when it drops from a highly excited state to a less excited state. They could also be called H-I lines, the -I suffix denoting an electrically neutral atom. H-II is a proton, and H-III (doubly ionized hydrogen) cannot exist, since you can't remove two electrons from an atom that has only one.

 

Likewise, as rob1986 says, the O-III lines are emitted by excited states of doubly ionized oxygen. As far as I know neutral oxygen has no emission lines within the visual spectrum.


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#6 rob1986

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Posted 06 December 2021 - 05:32 AM

As Rick Fienberg liked to point out to us Sky & Telescope editors when he was editor-in-chief, the H Beta line does not come from ionized hydrogen. Ionized hydrogen atoms (also called protons) have no electrons, and therefore cannot emit this kind of radiation at all.

 

The H-Alpha and H-Beta lines of hydrogen are emitted by neutral hydrogen  -- one electron orbiting a proton -- when it drops from a highly excited state to a less excited state. They could also be called H-I lines, the -I suffix denoting an electrically neutral atom. H-II is a proton, and H-III (doubly ionized hydrogen) cannot exist, since you can't remove two electrons from an atom that has only one.

 

Likewise, as rob1986 says, the O-III lines are emitted by excited states of doubly ionized oxygen. As far as I know neutral oxygen has no emission lines within the visual spectrum.

i think it does, but they're really dim and not meaningful.



#7 SchoolMaster

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Posted 06 December 2021 - 05:55 AM

Hydrogen has a super-power, you cannot take away i its electron to get H+  That's a naked proton.  You can force another electron on it for H-

 

Electrons are best represented in this circumstance as waves, and can have only very specific energies.

 

H alpha is produced when hydrogen's electron drops from level 3 down to level 2.

 

This diagram shows the energies/wavelengths for various energy transitions in the Lyman and Balmer series.

 

Balmer-Series-and-Hydrogen-Alpha.png

 

 

The Balmer series is more or less visible, and H Alpha is the first, Beta the second.

 

Oxygen has a lot more electrons, with two of them easy to strip off, so there are three possible Oxygen species to deal with, where there is only 1 for Hydrogen.

 

O I  Neutral (H I neutral, but the only state)

O II one electron removed (H II = hydrogen plasma)

O III two electrons removed.

 

Here are possible transitions and their energies for O III

 

-Oiii-lines.png

 

EDIT:  There's a fair bit of nuance to the simple statements I have made.  Where there's a lot of matter about, a naked proton is going to take someone else's electron.  In space, the energies can be tremendous and the matter density is very low, even in many molecular clouds, so with enough energy, hydrogen molecules are broken into hydrogen atoms, and with more energy, the electron can be stripped away, and the resulting proton is ready to interact with any matter or passing electrons.  A cloud of free protons and electrons, even low density clouds, are plasmas.  The temperature (average energy of particles) is high, but the energy density is low.  Space in the solar system is both hot and cold at the same time.  The particles are hot because the solar wind has a high energy, but a cubic meter of space is cold because the total energy of the volume is low,   Being hit by a bowling ball at 20mph is much more painful than being hit by a grain of sand at 200mph.

 

I'm just a chemist.  There must be astrophysicists here who can explain things better.


Edited by SchoolMaster, 06 December 2021 - 12:25 PM.

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#8 Voyager 3

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Posted 06 December 2021 - 08:13 AM

As Rick Fienberg liked to point out to us Sky & Telescope editors when he was editor-in-chief, the H Beta line does not come from ionized hydrogen. Ionized hydrogen atoms (also called protons) have no electrons, and therefore cannot emit this kind of radiation at all.

 

The H-Alpha and H-Beta lines of hydrogen are emitted by neutral hydrogen  -- one electron orbiting a proton -- when it drops from a highly excited state to a less excited state. They could also be called H-I lines, the -I suffix denoting an electrically neutral atom. H-II is a proton, and H-III (doubly ionized hydrogen) cannot exist, since you can't remove two electrons from an atom that has only one.

 

Likewise, as rob1986 says, the O-III lines are emitted by excited states of doubly ionized oxygen. As far as I know neutral oxygen has no emission lines within the visual spectrum.

If H-II has no electron , then how does the H-II regions glow ? What's happening in H-II regions ? Is it the free electrons that glow like in a plasma state ? 



#9 SchoolMaster

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Posted 06 December 2021 - 08:23 AM

If H-II has no electron , then how does the H-II regions glow ? What's happening in H-II regions ? Is it the free electrons that glow like in a plasma state ? 

HI is molecular (H2 molecules)

HII is more atomic, single H atoms and is energetic enough to form a plasma where the free protons are imbedded in a sea of electrons.



#10 spereira

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Posted 06 December 2021 - 09:42 AM

Moving to Eyepieces.

 

smp


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#11 sixela

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Posted 06 December 2021 - 12:05 PM

Has nothing to do with either eyepieces nor filters, but with astrophysics and nomenclature.


Edited by sixela, 06 December 2021 - 12:05 PM.

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#12 JuergenB

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Posted 06 December 2021 - 01:15 PM

If H-II has no electron , then how does the H-II regions glow ? What's happening in H-II regions ? Is it the free electrons that glow like in a plasma state ? 

Your question is very valid. The answer is that a small fraction of the total ions and electrons in a HII region will recombine and thus emit radiation before they undergo ionization again. To give an example from literature: The fraction of neutral hydrogen is only about 4 x 10-4, calculated for a distance of 5 pc from a typical spectral class O star (T = 40,000 K). Not much, but sufficient to emit the light that we can observe.


Edited by JuergenB, 06 December 2021 - 01:16 PM.


#13 MrJones

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Posted 06 December 2021 - 03:29 PM

If an H beta filter is for an emission line of singly ionized hydrogen, why isn't a filter for an emission line of doubly ionized oxygen called an O gamma filter?

 

Or why not H II and O III?

The simplest explanation is that it is historical for H-alpha and H-beta as the transitions are from the Balmer series although the greek alpha, beta ... naming came from Lyman.

 

Oxygen is much more complicated and there is no such straightforward abbreviated nomenclature. There is actually a 3rd forbidden O-III optical transition. 1D2→ 3P2 (501 nm), 1D2→ 3P1 (496 nm) and 1S0→ 1D2 (436 nm)

 

The 436nm transition is also observed by researchers but can be difficult to distinguish as it is close to H-gamma (434nm) and others.



#14 j.gardavsky

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Posted 06 December 2021 - 03:30 PM

Per convention in the astronomy:

The ionized hydrogen HII region is a region of interstellar atomic hydrogen that is ionized, full stop.

Read: https://en.wikipedia...iki/H_II_region

Typically, the ionization of hydrogen clouds is due to the UV radiation of the hot OB stars.

 

The OIII doublet is due to the collisional ionization of oxygen, like in the SNR, Wolf-Rayet nebulae, planetary nebulae, and in the high kinetic energy star birth regions.

Read: https://en.wikipedia..._ionized_oxygen

 

Best,

JG


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#15 lylver

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Posted 06 December 2021 - 03:45 PM

Hydrogen rays are the basis. Oxygen and Nitrogen are the start of life.

Optic maker took H-alpha and H-beta because it is useful for mesurement (widely separate ray)

Comets have also Na ray C ray, NH composite, Oxygen I etc etc

Orion-M42.jpg

Nebulium.JPG

Attached Files



#16 faackanders2

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Posted 06 December 2021 - 10:22 PM

If an H beta filter is for an emission line of singly ionized hydrogen, why isn't a filter for an emission line of doubly ionized oxygen called an O gamma filter?

 

Or why not H II and O III?

Hydrogen Alpha is the Balmer seies when one excited electron falls from the 3rd shell to the second and its' photon are seen as red light.

Hydrogen Beta is the Balmer seies when one excited electron falls from the 4th shell to the second and its' photon are seen as different light blue light.

 

https://www.thoughtc...r-series-604381

 

http://eilat.sci.bro... hws/hw2d_c.htm

 

https://en.wikipedia...transitions.svg

 

Oxygen III is doubly inionized oxygen (initially though may be new element Nebulium)

 

https://en.wikipedia..._ionized_oxygen



#17 sixela

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Posted 07 December 2021 - 03:15 PM

Optic maker took H-alpha and H-beta because it is useful for mesurement (widely separate ray)

Let's not make it more complicated than it is.

 

Roman numerals refer to ionisation states of atoms. See https://en.wikipedia...scopic_notation . "OI" is neutral oxygen, "OII" is singularly ionised oxygen, "OIII" is doubly ionised hydrogen.

 

Obviously only HI can generate radiation with emission ray spectra when an electron drops to a lower energy state; HII does not have an electron at all (though it can indeed sometimes swim in a sea of them that it can capture to become HI again).

 

HII regions (which are regions that have ionized hydrogen, hence the name) still emit radiation, but through the capture of an electron by HII (which then becomes HI) and its drop to another energy state before the atom can be ionised again. Not to mention that these regions also have other atoms that can also get ionised.

 

Greek letters correspond to emission rays that occur for a particular (possibly ionised state of) an atom. Sure, we could have assigned different greek letters to the different [OIII] emission rays, but no one bothered, we just call the lot "OIII" in general.

Those of HI were assigned letters. Since it's clear which ionisation state of H they refer to (there's only one relevant one), no one bothered to call them HI-alpha, HI-beta, etc.


Edited by sixela, 08 December 2021 - 07:28 AM.

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#18 happylimpet

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Posted 07 December 2021 - 03:24 PM

Moving to Eyepieces.

 

smp

Eyepieces?! What? This is astrophysics.


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#19 David Knisely

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Posted 07 December 2021 - 10:34 PM

I suppose we can get a bit technical here.  The two prominent Oxygen lines in emission nebulae are the 4958.9 angstrom and 5006.9 angstrom lines and are probably more commonly designated in spectroscopy as [O III], with the [  ] brackets meaning that these are the results of "forbidden" electron transitions (i.e., those not commonly found in laboratory emission spectra).  Once excited, you kind of have to sort of "leave the Oxygen ion alone" for a while until the electron finally drops down to a lower energy level and emits an O III line, which usually requires conditions of low density, like that in a nebula.  We just commonly call it OIII in amateur astronomy for short.  It is fortunate for us that we have those lines, as they sit near the peak of the eye's sensitivity curve.  Clear skies to you.  


Edited by David Knisely, 07 December 2021 - 10:35 PM.

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#20 Lee D

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Posted 07 December 2021 - 11:23 PM

Thanks everyone for the educational posts. David's post brings things back to the start, since it was while transcribing his notes on best filters for certain objects into a personal observing list that the original question occurred to me. 

 

Clear skies.



#21 rob1986

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Posted 11 December 2021 - 03:55 PM

Let's not make it more complicated than it is.

 

Roman numerals refer to ionisation states of atoms. See https://en.wikipedia...scopic_notation . "OI" is neutral oxygen, "OII" is singularly ionised oxygen, "OIII" is doubly ionised hydrogen.

 

Obviously only HI can generate radiation with emission ray spectra when an electron drops to a lower energy state; HII does not have an electron at all (though it can indeed sometimes swim in a sea of them that it can capture to become HI again).

 

HII regions (which are regions that have ionized hydrogen, hence the name) still emit radiation, but through the capture of an electron by HII (which then becomes HI) and its drop to another energy state before the atom can be ionised again. Not to mention that these regions also have other atoms that can also get ionised.

 

Greek letters correspond to emission rays that occur for a particular (possibly ionised state of) an atom. Sure, we could have assigned different greek letters to the different [OIII] emission rays, but no one bothered, we just call the lot "OIII" in general.

Those of HI were assigned letters. Since it's clear which ionisation state of H they refer to (there's only one relevant one), no one bothered to call them HI-alpha, HI-beta, etc.

don't forget hydrogen's importance as it was used to investigate the orbital shapes.

 

the simplicity made it easy to control the reaction. "other atoms orbitals don't really look like this, but its close enough".

 

that makes naming each and every transition separately very important for streamlining discussion of the subject.




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