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Hartl-Dengel-Weinberger 3 (HDW 3)

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About this observation
Observer
Peter Goodhew
Time of observation
08/12/2019 - 17:55
Object
Hartl-Dengel-Weinberger 3 (HDW 3)
Observing location
Fregenal de la Sierra, Spain
Equipment
APM TMB 152 LZOS refractor
QSI6120wsg8 camera
Exposure
HaOIIILRGB 71.5 hours total integration
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In another of his "long exposure of faint stuff" series, Peter has produced this stunning image of Hartl-Dengel-Weinberger 3 (HDW 3, PK149-09.1, PNG149.4-09.2) which is an extremely faint ancient planetary nebula in the constellation of Perseus. the object 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, which is because it is moving rapidly in a north-westerly direction 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 receiving 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.

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