NGC6781: Stars with mass similar to that of our Sun throw off their outer gasses after fusion has stopped in their core. One of the most famous, and easily found, of these "planetary nebulae" is the Ring Nebula, M57; from photos online, I expected this object to bear a strong resemblance to M57. But, after processing the data, I now feel that NGC6781 is strikingly similar to the Helix Nebula, except being smaller and farther away.

The bluish star at the center of the nebula is the old core of the original star, now evolving into a white dwarf. Nebulae of this type are called "planetary nebulae," because in older smaller scopes, they looked like small, blurry planets. It is about 3000 light years from Earth, visually in the constellation Aquila. At that distance, it has a diameter of about 2 light years.

Technical Information:

(HaL)(HaR)(OIIIG)(OIIIB): 720:690:510:210:180:240 (42.5 hours of exposures; L, R and G individual images were all 15-minute exposures; B images were 20 minutes each, and Ha and OIII were 30-minute individual exposures). All images were unbinned. The luminance layer is a blend of the L-filtered images and the Ha-filtered images; the red channel is a blend of the R-filtered images and Ha-filtered images; the green channel is a blend of the OIII images and G images, and the blue channel is a blend of the OIII images and B images.

Equipment: RC Optical Systems 14.5 inch Ritchey-Chrétien carbon fiber truss telescope, with ion-milled optics and RCOS field flattener, at about f/9, and an SBIG STX-16803 monochrome camera with internal filter wheel (SBIG filter set), guided by an SBIG AO-X, all riding on a Bisque Paramount ME German Equatorial Mount.

Image Acquisition/Camera Control: Maxim DL, controlled with ACP Expert/Scheduler, working in concert with TheSky X Professional Edition.

Processing: All images calibrated (darks, bias and sky flats), aligned, combined and cropped in Pixinsight. RGB Color combine in Pixinsight. Ha and OIII data blended in Pixinsight. Some finish work (background neutralization, color calibration, HDR Mulitscale Transform and Multiscale Linear Transform of luminance data, and noise reduction) done in Pixinsight; LRGB combination and some further finish work was done in Photoshop CC.

Location: Data acquired remotely with my equipment hosted by Sierra Remote Observatories, Auberry, California, USA.

Date: Images taken on many nights in September and October, 2021. Image posted November 1, 2021.

Date: Image scale of full-resolution image: 0.56 arcseconds per pixel.

Seeing: Generally very good, with individual calibrated luminance frames varying from 1.7 to 2.4 arcsecond FWHM.

CCD Chip temperature: -25C

Copyright 2021 Mark de Regt

Hit Counter