Dramatic M82 in Ha + Near Infrared

[Menno555]

Clouds, clouds, clouds ... oh and clouds
So I was going through my data from last year to see for some re-processing.

In April this year I did (for me) extensive sessions of M82. I did capture in broadband but also in Ha (Optolong L-eNhance filter) and in Near Infrared (Baader IR-Pass 685nm filter). But I never did combine only these 2. This is the rather dramatic result of that

I did not use any calibration files for stacking which resulted in rather noise free stacks. Because of that I could also set it to 200% scale in Photoshop.
Stacked Ha and IR separate and tried some different processing steps in Photoshop (lots of playing around ) and in the end this one came out best. I did try to keep more of the starburst arms but the features in/on the main "body" are way more interesting. It really is a balance between the Ha and IR data.
The HaRGB version from May is here: viewtopic.php?f=16&t=4104

The 2400px version can be seen here: https://i.ibb.co/whrdLLw/M82-Ha-IR.jpg

Bortle 6/7
Meade LX200 8" f/10 ACF OTA
Ioptron CEM25EC mount (no guiding)
Optolong L-eNhance filter
Baader IR-Pass 685nm filter
Zwo ASI071MC Pro camera

Captured with SharpCap Pro @ -10 Celsius / White balance R50 B50
Baader IR-Pass filter
10 x 600 sec / Gain 90 / Offset 4
Optolong L-eNhance filter
54 x 600 sec / Gain 90/ Offset 4

M82-Ha+IRsm.jpg (492.3 KiB) Viewed 1592 times

[timh]

Intriguing. Your post puzzled me at first Menno because I couldn't work out why the IR signal has apparently come out white rather than red using an OSC camera. Then I looked it up and found that it is because that at 800-850 nm the blue and green pixels of the Bayer matrix on these ZWO cameras respond about equally as the red and so the net result is about white --i.e. so in the near IR the OSC starts responding more or less as a mono camera (but at lower efficiency).

Another interesting experiment and idea brought to the table. To me, near IR seems to be an interesting option to to try that must offer significant deliverance from light pollution. But overall perhaps a bit confusing to interpret any image that mixes near IR captures with L-enhance filtered visible light using an OSC ? Anyway the image looks good
Tim

[Menno555]

Thanks Tim!

And yes, there is almost no color in the near IR-capture other then some color noise of the background.
And indeed all pixels are used: I assumed it would give the same result as with a multiband Ha/OII where the Red channel has the most amount of data and the least amount of noise in it. With this IR filter though that was not the case: R,G and B had roughly the same amount of data and noise in them.
This also showed in the exposure time. The filter is very dark to look through so I (again) assumed the times would be long or the captures low on data. But to my surprise this was not the case. Plate solving was no problem at all with only 2 seconds and the captures themselves were fine
Because of all of this, I am going to get a "real" IR Pass filter. Not in the 800nm range cause my camera is not sensitive enough for that but a 742nm version which is very close to a 60% relative sensitivity peak of the camera.

And indeed, mixing it can be confusing. It really only makes sense to use for experimenting or when an object also has some IR data. And in the case of M82 it gives more of the core shining through the dust plus a star that is normally not shown in broad- and narrowband. See https://i.ibb.co/swcRs3K/M82-IR.jpg where I marked that star. That image is the IR capture in B/W.

And talking about IR-Pass filters: they are great to use for collimating They let through a lot of signal but more importantly, the effects caused by seeing are reduced a lot. I used that filter and for the first time I got to see the airy disks in their full glory. I also could get way closer into focus with the discs still showing.

Menno