Messier 81, NGC3031, Bode's Nebula and Holmberg IX (unresolved)

[windjammer]

Its a while since I've posted, here is my effort at M81 - an RGHb mixed broad and narrow band image with excess Ha emission.  Pics are a close in crop, the full FoV, and an annotated FoV.

Holmberg IX, a satellite dwarf galaxy of M81 is just seen centre left as a vague blur, stars unresolved.  Checking out the master lights, the G channel sort of shows some star points in the right position, but nothing made it into PI's Starnet star mask.  More exposures might well have got Holmberg IX over the line, but the weather did not cooperate in March and April.  Does it ever?

The most distant galaxy catalogued is NGC28505, centre right of M81, coming in at 148Mpc (480 Mlyrs).  It even has some colour.  I've included info on the catalogued galaxies further down this post and links to the NED database where entries exist for those interested (OK, nerdy but fun).

As usual, mixed feelings about the image.  I have been thrashing it for weeks and conclude 12 hours of data with a 6inch achro is not really enough.  The whirling dervish look of M81, fizzing across the cosmos with hair on fire works quite well.  Some of the galaxy detail is a bit overcooked, but I like the excess Ha emission overlay, and the stars aren't bad, though a bit more colour in them would be nice.  The double star pair TYC4383-1127 and -2044 just below and left of M81came out well without splurging (technical term) together.

Exposure and processing details at the end.

Simon
----

Close in crop:

 

Full frame:

 

Annotated image:

 

----
Galaxy object info:

PGC HYPERLEDA I catalog of galaxies (Paturel+, 2003) (983,261 galaxies)                    
Name        RA(deg)    Dec(deg)    Mpc    Mlrs    
PGC2728721    147.68    69.23            
PGC2730379    148.07    69.44            
PGC28505    148.29    69.00    148    482.48    
PGC28529    148.45    68.97    3.685    12.01    
PGC28630    148.89    69.07    3.675    11.98    
PGC28757    149.38    69.05    4.408    14.37    Holmberg IX
PGC2724146    149.48    68.82            
PGC2726822    149.63    69.03            
PGC28848    149.80    69.26    19.16    62.46    
PGC28630    148.89    69.07    3.675    11.98    M81, NGC3031

https://ned.ipac.caltech.edu/byname?objname=PGC28505&hconst=67.8&omegam=0.308&omegav=0.692&wmap=4&corr_z=1
https://ned.ipac.caltech.edu/byname?objname=PGC28529&hconst=67.8&omegam=0.308&omegav=0.692&wmap=4&corr_z=1
https://ned.ipac.caltech.edu/byname?objname=PGC28630&hconst=67.8&omegam=0.308&omegav=0.692&wmap=4&corr_z=1
https://ned.ipac.caltech.edu/byname?objname=PGC28757&hconst=67.8&omegam=0.308&omegav=0.692&wmap=4&corr_z=1

https://ned.ipac.caltech.edu/byname?objname=PGC28848&hconst=67.8&omegam=0.308&omegav=0.692&wmap=4&corr_z=1
https://ned.ipac.caltech.edu/byname?objname=PGC28630&hconst=67.8&omegam=0.308&omegav=0.692&wmap=4&corr_z=1

---
Data taken in Astronomik broadband and narrowband filters: R, G, Hb (486nm) and Ha (656nm). Ha-RGHb total exposure time 12.3 hrs.  

R 1x1 bin - 24x 120s= 0.8hrs, 3-4 March 2024, seeing 1.3", scope West side, prime focus
R 1x1 bin - 60x 120s= 2.0hrs, 3-4 March 2024, seeing 1.3", scope East side, prime focus
G 1x1 bin - 30x 120s = 1.0hrs, 30-31 March 2024, seeing 1.4", scope West side, prime focus
G 1x1 bin - 82x 120s = 2.7hrs, 30-31 March 2024, seeing 1.4", scope East side, prime focus
Hb 1x1 bin - 12x 600s = 2.0hrs. 9-10 April 2024, seeing 2.0", scope East side, prime focus
Ha 1x1 bin - 23x 600s = 3.8hrs, 14-15 April 2024, seeing 1.6", scope East side, prime focus

----
Master Lights:
FWHM (pxl)    pre BXT        post BXT
R        3.06        1.77
G        2.48        1.65
Hb        3.93        2.23
Ha        3.66        1.49

-----
Plate solver:
Resolution ..............1.248 arcsec/px
Focal distance ....... 750.39 mm
Pixel size ............... 4.54 um
Field of view .......... 55' 37.0" x 43' 39.4"
Image center ......... RA:  9 55 32.466  Dec: +69 03 32.93
Image bounds:
   top-left .............. RA: 10 01 11.387  Dec: +69 22 03.61
   top-right ............ RA:  9 50 42.343  Dec: +69 27 48.91
   bottom-left ........ RA: 10 00 11.617  Dec: +68 38 46.40
   bottom-right ...... RA:  9 50 02.906  Dec: +68 44 20.05  

-----
Rig:
Imaging scope: SW Startravel 150mm F5 Refractor, Baader Diamond Track, (2.5x Celestron Luminos 2inch imaging barlow), Atik 460EX mono

Guide scope: SW Evostar 90mm F10, with guiding XY stage, ZWO 120MM camera

Guiding: 2 stage PHD: high frequency guide scope (mount tracking) and low frequency OAG image train guiding (guidescope flex)

Mount: Home made German Equatorial pillow block mount, permanently rooftop mounted.  Spring loaded DEC axis gearing.

Other gadgets: ST4 based anti vibration shutter, ST4 based PEC

-----
Processing Lights:

PixInsight: Lights, Darks, Flats, Biases: master dark/dark library-> masterbias-> superbias-> calibrated flats-> master flat-> calibrated lights-> cosmetic correction-> aligned lights-> master light

PixInsight: Master lights-> crop-> Gradient Correction-> BXT-> linfit-> final master lights

PixInsight: final master lights-> RGB Channel Combination (RGHb)-> StarNet2 starless-> export starless fits32 RGHb master, export star mask tiff16.

Affinity Photo 32 bit image processing: import starless fits32-> reject default stretch-> curves-> Topaz Denoise(ST0,81)-> curves-> Tpzdn(LL0,84)-> curves (B layer)->Tpzdn(LL3,0)-> curves-> levels (B layer)-> vibrance/saturation/selective colour-> export RGHb tiff16

PixInsight: import RGHb tiff16-> gradient correction-> export RGHb tiff16

Affinity Photo: import RGHb tiff16-> paste in star mask layer, blend mode 'screen' -> paste in Ha mask layer, blend mode 'screen'

-----
Processing Star Mask:

Affinity Photo: import star mask tiff16-> curves-> invert selection of brightest stars-> curves(invert selection)-> add to invert selection of brightest stars-> curves(invert selection)-> manual white balance-> vibrance/saturation-> brightness /contrast-> paste Star Mask layer on top of starless final (blend mode 'screen')

-----
Processing Ha Mask - continuum subtraction:

PixInsight: import R and Ha master lights-> pixel maths: create H2 = (k*Ha-R)/(k-1) for a range of k values, 2.0 a good starting point.  Select a k which picks out excess emission without too much background-> k=1.5 in this case->

-> pixel maths: create H3 = H2 - K*med(H2) for a range of K values, 1.0 a good starting point.  med(H2) function is the median value of the H2 pixel intensity distribution.  Select a K which removes any surplus continuum emission in H2 as far as possible-> K = 1.02 in this case-> export H3 fits32 as Ha mask

Affinity Photo: import fits32 Ha mask-> accept default stretch-> select target area-> curves (stretch)-> invert selection-> curves (suppress)-> curves (cosmetic suppress)-> convert to RGB16-> levels(suppress G,B channels) -> gausian blur (1.0 pixel)-> paste Ha Mask layer on top of image final (blend mode 'screen')

-----