HDW 3
Astrobin Image Of The Day 23 December 2019
British Astronomical Association Image Of The Week 28 December 2019
Published in Astronomy Now Magazine February 2020
Amateur Astronomy Picture Of The Day 22 May 2020 https://www.aapod2.com/blog/hartl-dengel-weinberger-3-hdw-3

Hartl-Dengel-Weinberger 3 (HDW 3) is an extremely faint ancient planetary nebula in the constellation Perseus. It is so faint that it is very rarely imaged.
The progenitor star is the small blue star at the 5 o-clock position just below the large yellow star in HDW 3. The progenitor is not, as one would expect, in the centre of the nebula. This is because it is moving rapidly in a north-westerly direction. It is moving through a dense area of interstellar medium (ISM). This ISM is slowing down HDW 3, creating a shock front and the unusual "braided" appearance. As the star isn't slowed by the ISM it has continued to move and is thus no longer at the centre of HDW 3 and is slowly overtaking HDW 3. This causes the shock front to be brighter as it's getting more ultraviolet radiation, whereas the opposite side of HDW 3 is getting less UV radiation and has become invisible. This movement of the star causes differential excitation of the shell. OIII emission, which requires higher energy of the ionizing radiation than HII emission, only happens close to the star.



TARGET
Nomenclature:  HDW 3, Hartl-Dengel-Weinberger 3, PK149-09.1, PNG149.4-09.2
Right Ascension: 03:27:15.44
Declination: +45:24:20.5
Size: 12 arc min
Discovery: H Hartl, J Dengel, R Weinberger in 1983

EQUIPMENT USED
Twin APM TMB LZOS 152 refractors
10Micron GM2000 HPS mount
Twin QSI6120 CCD cameras
Astrodon filters
IMAGE CAPTURE
5nm H-Alpha: 76x1800 bin 2x2
3nm OIII: 51x1800 bin 2x2
Luminance: 39x300 bin 1x1
Red: 20x300 bin 1x1
Green: 20x300 bin 1x1
Blue: 17x300 bin 1x1
Total integration: 71.5 hours
Pixel scale: 0.534 arcsec/pixel
Field radius: 0.359 degrees
Capture dates: 15 November - 8 December 2019
Capture location:  Fregenal de la Sierra, Spain
IMAGE PROCESSING
Pre-processing: CCDStack2
Post-processing: Photoshop CS2