Newtonian HOO of IC1795 fish-head nebula with RGB stars

[timh]

Rather out of season but I had problems processing this back in January when the last of the data were obtained. With no mount and dark skies still about 3 weeks away now seemed an ideal time to work on old data.

IC1795 - an appendage of the heart nebula - seems to be an HII region on a scale well suited to long focus (image-scale here about 0.95 arcsec pixel). Most interpretations and images on-line seem to be SHO and predominantly show blue (OIII) at the core fringed with browns, reds and oranges (SII admixed with HII). I did also obtain SII as well as OIII and HII data but, relatively, it seemed too weak too include and would have only added noise. There may be something of Aesop's fable of the fox with no tail in me saying that in some ways I prefer this HOO image comprising only 2h each of OIII and of HA (plus 1.2h RGB for the stars). In terms of signal intensity the HA is in fact by far predominant and so it seems more naturalistic to have the nebula show as mainly red with just touches of blue/ green localizing the OIII. The image was processed in PixInsight using Starnet to create a separate mask of the RGB stars and starless OIII and HA images. These latter two were combined using PixMath into an HOO image with some (15%) of the HA also adding into the blue channel to model the anticipated contribution of H beta transitions. The RGB stars and starless images were processed and stretched independently using MLT noise reduction, star reduction and curves before being recombined back into the final image.

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 camera for RGB (UHC) captures or ZWO ASI294MM mono camera for HA and OIII , both 4.63 uM pixels cooled to -10C

ZWO IR/UV cut filter, Astronomik UHC filter , Astronomik 6.0 nm OIII filter, Optolong HA 7 nm filter

56 x 70s RGB (UHC) frames at gain 124 and 39 x 3min gain 151 OIII under moonless Bortle 6 skies. 61 x 2 min gain 151 HA frames captured with the moon risen but low in the sky. All frames (0.95 AS/ pixel) pre-selected for quality using the FWHM and brightness filter within Sharpcap, darks and grayscale master flats (no bias) prepared using Sharpcap. 2.0 h HA and O3 images taken using a mono camera were combined into a starless narrowband OOHa image. To improve detail the dominant HA image was used as luminance for the combined NB starless image.

Tim

[turfpit]

Tim

A really good image coupled with an excellent detailed write-up.

Dave

[timh]

Thanks Dave - appreciated. There are just so many variations in how data can be processed, choices about what to emphasise and what sort of image you can therefore end up with that it does seem important to try and be explicit as far as possible. Tim

[Menno555]

Nice capture and text Tim.
Indeed these kind of object are excellent for the slow scopes. Waiting here for them to get in a good position again.

Menno