Early spring galaxies. Adding luminance to OSC images

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timh
Posts: 515
Joined: Mon Aug 26, 2019 5:50 pm

Early spring galaxies. Adding luminance to OSC images

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Post by timh »

I had some rgb OSC frames of NGC2903 in Leo and of NGC3344 (the sliced onion galaxy) in Leo minor but not enough for a really good image - they both needed to be a bit sharper. Bortle 6 skies are inherently somewhat hopeless for seeing faint outer detail in galaxies but it is possible to try to image for more detail at the brighter core. So rather than just collect more RGB frames with the OSC I opted to collect luminance using a mono camera based on the notion that replacing this into the luminance channel of the OSC RGB might counteract any slight blurring associated with debayering and resolve more core detail.

It sort of worked - the images with the added mono luminance did appear sharper and more detailed - although the seeing was not that great on the particular nights for mono imaging meaning that even after selecting out only the best frames the FWHM of the mono luminance integration was estimated as 2.85 (PI subframe selector) as compared to about 3.1 or better for the earlier taken RGB integrations.

SW200PDS Newtonian (f = 1000mm, F5.0) Baader MkIII coma corrector, CEM70 Ioptron mount, Baader steeltrack focuser, Pegasus Cube2 focus controller, PHD2 guiding using an ASI 120 mm guide camera and 80 mm SW startravel refractor at f = 400 mm.

ZWO AS1294 MC OSC camera, 4.63 um pixels, 14 bit ADU for RGB captures or ZWO ASI294MM mono camera, 2.315 um , 12 bit ADU for LUM , both cameras cooled to -10 C. Filter was a ZWO IR/UV cut filter. Also a 7nm Optolong HA filter for NGC2903 only. All frames taken under moonless Bortle 6 skies. All frames pre-selected for quality using the FWHM and brightness filter within Sharpcap, darks and grayscale master flats (no bias) prepared using Sharpcap. Preprocessing and processing in PixInsight.

1) NGC2903. 137x70s plus 140 x40s RGB frames, gain124 plus 103 x 40s mono LUM frames (here the mono and RGB luminances were combined and rescaled together since the RGB frames were almost as sharp anyway) and also 15 x 3 min of gain 151 frames using an HA filter. A small fraction of the HA - red difference signal was added into the red channel.

2) NGC3344. 156 x 70s RGB images plus 205 x 40s mono LUM images (here the RGB luminance was completely replaced with mono luminance)

NGC2903 seems to be the equal of many of the Messier galaxies - rather reminiscent of M106 with a similar shape and dusty core region - although unlike M106 NGC2903 is not thought to have an active core. The core region is a starburst region and to show this better an image was also taken in HA and part of that fed back into the red channel. The irregular dwarf galaxy faintly visible to the left is thought to be a companion.

NGC3344 is really quite a photogenic object. It is a fairly small galaxy about 25 M ly away and one that appears to have been little studied.

Tim
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NGC2903_newt_baader_137x70s_140421_140x40s_3001_060222_RGB_CROP_DBE_ABE_PCC_strmsk2_MLT_plusHA_tran_REGto103x40sMONOLUM46Mb_plusRGBlum_LRGB_scnr_curves_MLT_affinity_PX_big.jpg
NGC2903_newt_baader_137x70s_140421_140x40s_3001_060222_RGB_CROP_DBE_ABE_PCC_strmsk2_MLT_plusHA_tran_REGto103x40sMONOLUM46Mb_plusRGBlum_LRGB_scnr_curves_MLT_affinity_PX_big.jpg (935.03 KiB) Viewed 1313 times
NGC3344_Newt_Baader_3hRGB_DBE_DEBe_ABE_PCC_MLT_TRAN_LUMfrom205xmono46Mbframes_curves_MLT_affinity_PX_big.jpg
NGC3344_Newt_Baader_3hRGB_DBE_DEBe_ABE_PCC_MLT_TRAN_LUMfrom205xmono46Mbframes_curves_MLT_affinity_PX_big.jpg (997.57 KiB) Viewed 1313 times
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