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@REPLYADDR Martin Brown
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@REPLYTO 2:5075/128 Martin Brown
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On 15/09/2023 14:33, Chris L Peterson wrote:
> On Fri, 15 Sep 2023 14:06:32 +0100, Martin Brown
> <```newspam```@nonad.co.uk> wrote:
>
>> On 15/09/2023 13:43, Will Peters wrote:
>>> Seems suspect that the "plasma arc" near M31 oddly has not been noticed
>>> until recently. The write up mentions that "scientists are now
>>> investigating" so it must really exist. Hard to believe that with as
>>> many images of M31 of varying exposures and filtration that something
>>> like that would be missed.
>>
>> I`m inclined to agree. I`m also a bit puzzled why it hasn`t shown up on
>> various 21cm hydrogen line observations. It isn`t like M31 hasn`t been
>> observed in all wavebands and lots of times.
>>
>> However, their image frame is larger and deeper than most.
>
> It`s an [O III] emission region, with no H-alpha and apparently no
> neutral H (so no radio emission).
It is quite a peculiar cloud of plasma then. Normally you would expect
at least some neutral hydrogen in it simply because it is so common.
My guess would then be that it is something by way of a local planetary
nebula of lost CNO from some former large star that happens to be in the
same line of sight as M31 as opposed to a huge cloud near the galaxy.
> Quite a few interesting objects and regions have been discovered in
> recent years by amateur imagers, using widefield instruments that are
> largely absent in professional observatories outside of a few survey
> instruments... and they are usually not using narrowband or long
> exposure times.
Indeed - amateur capabilities have closed the gap a long way on
professional equipment in terms of basic imaging from dark skies.
Narrow band filters for deep sky have changed the game a lot.
Likewise for spotting things hitting the gas giants and supernovae.
--
Martin Brown
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