StDr 4 - a new discovery
When we discovered this unusual and interesting nebula with internal apparent bow shock not far from the Elephant Trunk Nebula / IC 1396 in 2019, we initially believed it to be a planetary nebula.
However the absence of a central white dwarf in such a bright object was unusual, even if the bubble-like structure suggested a planetary nebula.
A spectrum made by Pascal le Dû revealed the surprise - an SII signal suggesting shocked gas. What this object is is not yet clear, but another piece of the puzzle is a very clear and strong radio signal identified in the NVSS survey.
The dark radiant bok-globule structures at the top of the image were formed when the bright and hot blue stars in the centre of nearby IC 1396 blew dust and gas outwards with their strong stellar winds.
However the absence of a central white dwarf in such a bright object was unusual, even if the bubble-like structure suggested a planetary nebula.
A spectrum made by Pascal le Dû revealed the surprise - an SII signal suggesting shocked gas. What this object is is not yet clear, but another piece of the puzzle is a very clear and strong radio signal identified in the NVSS survey.
The dark radiant bok-globule structures at the top of the image were formed when the bright and hot blue stars in the centre of nearby IC 1396 blew dust and gas outwards with their strong stellar winds.
TARGET
Nomenclature: StDr 4
Right Ascension: 21:41:30.10
Declination: +55:47:52
Discovery: Xavier Strottner and Marcel Drechsler
Size: 3x2.3 arc minutes
EQUIPMENT USED
Twin APM TMB LZOS 152 refractors, Celestron C14 EdgeHD
10Micron GM2000 HPS mount, iOptron CEM120
Twin QSI6120 CCD cameras, ZWO ASI1600MM Pro
Astrodon and Chroma filters
IMAGE CAPTURE
Blue: 31x300" bin 1x1
Green: 31x300" bin 1x1
Red: 27x300" bin 1x1
Ha: 25x900" bin 1x1, 2x600" bin 1x1
OIII: 116x600" bin 1x1
SII: 70x900" bin 1x1, 41x600" bin 1x1
Total Integration: 57 hours 40 minutes
Pixel scale: 0.531 arcsec/pixel
Field radius: 0.377 degrees
Capture dates: 25 November - 17 December 2022
Capture location: Fregenal de la Sierra, Spain
IMAGE PROCESSING:
CCDStack 2, PixInsight and Photoshop
CCDStack 2, PixInsight and Photoshop
The object was decisively revealed by the unusually strong SII signal that is caused by gases being shocked very strongly:
In this excerpt from the IPHAS H-alpha Survey, it can be seen that the internal structure is not a bubble, but rather a bow shock:
Spectroscopically observed by a French amateur group at Kermerrien Observatory (Porspoder, France) on 12/03/2019 by P. Le Dû. [NII]>H-alpha, strong [SII], H-beta in blue only:
The NRAO VLA Sky Survey (NVSS) is a 1.4 GHz continuum survey covering the entire sky north of -40 deg declination:
