Sunday, April 19, 2015

M82 and M81 with Holmberg IX and PGC 28731

This was a frustrating image to acquire and process.   Learned a lot of things, but the most painful lesson that I learned is that the neighborhood produces enough light pollution that processing the IFN (flux nebulosity) is intensely challenging.   The light pollution is not really evident in shorter 5 minute subexposures.  But it quickly raises its head when processing faint detail in longer exposures.   I suspect I need to gather 40+ hours of data to get much flux nebulosity in the north.   That means probably 8-10 nights of data.    Which in turn probably means it has to be done over 2-3 months.    The alternative, which is more appealing is to find a dark site where I can spend 4-5 nights.



Exposure details:
Dates: Feb 12,13,14,15,16 and 17.  
Exposures: 65 x 10 min exposures, 80 x 2 min exposures, 10 x 20 min H-alpha exposures.
50 Bias frames, 50 Flats, 60 Dark flats, 90 dark frames (for 10 min exposures only). 
ISO:  1600
Scope:  Takahashi TSA102S w/Televue .8x focal reducer/flattener.  
Camera:  Modded T3i with Astrodon UV/IR filter.
Mount:  Used AP1200.  
Misc:   Guided w/Orion 50mm guidescope and QHY5II-L autoguider, BackyardEOS, PHD2, Photoshop CC

I had a lot more flux nebulosity, but in an effort to combat light pollution gradients, a lot of
that flux got destroyed.   >sigh<

On a more positive note, I'm glad that I got some granularity in Holmberg IX which is right below M81.   And I'm glad to see I've got some detail in PGC 28731 (lower right) -- mainly that it is oval in shape and has a brightening core.  It's actually pretty large as far as PGC galaxies go.

You may note that I have 10 x 20 minute H-Alpha subs which were taken with an Astronomik 12nm H-alpha filter clipped into the Canon.   The H-alpha information allowed me to get that exploding red in M82.   And it's also responsible for the "measles" in the arms of M81.

Finally, the composition is about a 50% crop of the original.

Probably have over 80 frustrating hours of processing time in this image.  
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3 comments:

  1. Charles Nathaniel ErwinApril 19, 2015 at 8:52 PM

    I was certainly impressed with M82 and visually I'd lever gotten the sense of its nature until seeing this. How hard is it to use a clip filter like the Astronomik? Can you easily do it in the field between shots?

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  2. Literature and Movie BlogApril 19, 2015 at 9:46 PM

    There's something really violent happening in M82. If Drake's equation for advanced civilizations is even vaguely accurate, there's probably nothing going in that galaxy due to tremendous cosmic ray and x-ray radiation.

    As for the Astronomik clip-in filter, it is easy to clip in and remove. Though you sometimes need a small flat-head to make the clip budge as it's a metal (filter) on metal (camera innards) contact. For the sake of safety (and out of laziness),
    I'd plan to keep the H-alpha filter in the camera for the full night. You may want to collect H-alpha data on a second subject.

    Though I collected 10x20 min subframes in H-alpha, upon looking at the data, I realized I should have collected 30-45 minute subframes. The signal is SO WEAK through a H-alpha filter that you don't see much unless you're photographing a very powerful emitter of H-alpha like M82. The frame looks like a very underexposed piece of film.

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  3. Literature and Movie BlogApril 19, 2015 at 10:54 PM

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