South-West of the Large Magellanic Cloud (LMC) there lies a relatively rarely imaged area of the LMC 8 supergiant shell [1-4] containing a remarkable collection of superbubbles, HII regions and long-stretched star associations. The diameter of the shell is estimated to be of about 2.8 kly [1, 2]. The walls of the shell are better illuminated by the OB star associations on the Northern and Eastern sides (lower part of the image), so the shell may appear as opened on the Northeastern side [1, 2] (upper part of the image) even though some faint diffuse structures are revealed in the image on that side of the shell as well.
Fig. 1 (revision P) shows the manually annotated version of the image indicating all major HII regions, star associations, star clusters and supernova remnants (SNRs) that are identifiable in it. The most prominent feature of the interior of this supershell is the remarkably large and luminous superbubble (SB) DEM L 50 [5-9] visible in the upper right corner of the image. The SB DEM L 50 has a distorted elliptical shape with major axis length of about 400 ly (at the distance to LMC taken as 158 kly) which is filled with multiple layers of shock fronts from older SNRs and two yonder SNRs PMN J0459-7009 [10] and SNR J045949-700835 [11] embedded in the outer wall. Fig. 2 (revisions Q and D) shows the cropped annotated version of the image showing SB DEM L 50 and its surroundings.
Fig. 1. Manually annotated version of the image shown at 100% of original resolution. Note that the LHA 120-N 186 has 5 components (A-E): the main one (which is DEM L 50 [5-9[), the smaller one - LHA 120-N 186B on the right from the main one in the image, plus 3 more (C, D, E) that are sitting inside of the main component.
Fig. 2. Manually annotated cropped version of the image showing the area containing SB DEM L 50 [5-9] shown at 100% of original resolution. Note that the LHA 120-N 186 has 5 components (A-E): the main one (which is DEM L 50 [5-9[), the smaller one - LHA 120-N 186B on the right from the main one in the image, plus 3 more (C, D, E) that are sitting inside of the main component.The central part of the image contains the following two structures shown in the Fig. 3 (also in revisions E and F):
- DEM L 55 HII region [12] with a peculiar double wall with embedded radial filaments on the Northern side.
- A cascade of open clusters KMHK 492 [13], NGC 1823 [14], NGC 1813 [15], KMHK 468 [16] embedded into LH18 OB star association [17].
Fig. 3. Manually annotated cropped version of the image showing the area containing DEM L 55 HII region [12] and LH18 OB star association [17] - shown at 100% of original resolution.Fig. 4 (revisions G and H) shows the cropped version of the lower left part of the image containing:
- OB star associations LH24 [18] and LH26 [19] and a more compact one - NGC 1873 [20] sitting inside the LH24. The LH26 association is situated close to the wall of the LHC 8 supershell and thus creates a rather impressive display of a veil of diffuse structures with threads of neutral gas clouds within.
- NGC 1833 emission nebula [21] showing a rather complex internal structure with an outer wall and a spiral structure comprised of multiple ionization fronts in the middle.
- Bipolar shaped LHA 120-N 191 object consisting of a compact HII region on one side and a more diffuse emission nebula on the other side [22, 23].
Fig. 4. Manually annotated cropped version of the image showing the area containing OB star associations LH24 [18], LH26 [19], and NGC 1873 [20] as well as NGC 1833 emission nebula [21] - shown at 100% of original resolution.Yet, perhaps the most intriguing feature in this scene is a peculiar elliptical shape asterism found next to NGC 1873 as shown in Fig. 5 (revisions J, K, L) at 200% of the original resolution. It appears as a double wall “negative space” structure outlined by two or more star streams bending around the long-period variable candidate star SP77 40-9 [24] that is about 67 kly away based on Gaia DR3 parallax measurements [25, 26]. The angular size of these elliptical outlines are 1.2 arc.min x 1.3 arc.min and 1.5 arc.min x 1.7 arc.min which corresponds to 55 - 78 ly at the distance to the LMC or just 13 - 19 ly at the distance to a few stars in those shells for which parallax data available in Gaia DR3 [25, 26]. Additional astrometric / spectroscopic data is needed to determine the scale of this structure and whether there is a physical connection between its components. The asterism is labeled in Fig. 5 as “LMC SH8 X1” for future reference.
Fig. 5. (a) Manually annotated cropped version of the image showing the area containing OB star association NGC 1873 [20], NGC 1833 emission nebula [21] and the peculiar asterism labeled here as LMC SH8 X1 - shown at 200% of original resolution. (b) Same area of the original image shown at 200% of original resolution without annotations.Data and initial calibration/integration: Alexandr Zaytsev
https://www.astrobin.com/users/m57ring/ASA-N D=0.5m, f/3.8 on German equatorial mount, FLI ProLine 16803 (Telescope #3 system of ChileScope observatory, Río Hurtado Valley, Chile).
14x Ha + 11x OIII + 11x SII guided 1200 sec exposures (12h of combined integral) collected over 4 imaging sessions carried out on Aug 30, 31, 2024 and Sep 1, 2, 2024 using Chilescope Telescope #3 system.
Image Processing: Mark Hanson
https://www.hansonastronomy.comEnjoy, Mark and Alex
[1]
https://iopscience.iop.org/article/10.1086/523897[2]
https://iopscience.iop.org/article/10.1086/523897/pdf[3]
https://astrodrudis.com/large-magellanic-cloud-nebulous-systems/[4]
https://astrodrudis.com/wp-content/uploads/2017/11/lmc-masterannotated-thingreencircles-v7ff-cr-b.jpg[5]
https://simbad.cds.unistra.fr/simbad/sim-id?Ident=DEM+L+50&NbIdent=1&Radius=2&Radius.unit=arcmin&submit=submit+id[6]
https://arxiv.org/abs/2310.01531[7]
https://arxiv.org/pdf/2310.01531[8]
https://www.nasa.gov/universe/superbubble-dem-l50/[9]
https://chandra.harvard.edu/photo/2013/deml50/more.html[10]
https://simbad.cds.unistra.fr/simbad/sim-id?Ident=PMN+J0459-7009+&NbIdent=1&Radius=2&Radius.unit=arcmin&submit=submit+id[11]
https://simbad.cds.unistra.fr/simbad/sim-id?Ident=SNR+J045949-700835&NbIdent=1&Radius=2&Radius.unit=arcmin&submit=submit+id[12]
https://simbad.cds.unistra.fr/simbad/sim-id?Ident=DEM+L+55&NbIdent=1&Radius=2&Radius.unit=arcmin&submit=submit+id[13]
https://simbad.cds.unistra.fr/simbad/sim-id?Ident=KMHK+492&NbIdent=1&Radius=2&Radius.unit=arcmin&submit=submit+id[14]
https://simbad.cds.unistra.fr/simbad/sim-id?Ident=ngc+1823&NbIdent=1&Radius=2&Radius.unit=arcmin&submit=submit+id[15]
https://simbad.cds.unistra.fr/simbad/sim-id?Ident=ngc+1813&NbIdent=1&Radius=2&Radius.unit=arcmin&submit=submit+id[16]
https://simbad.cds.unistra.fr/simbad/sim-id?Ident=KMHK+468&NbIdent=1&Radius=2&Radius.unit=arcmin&submit=submit+id[17]
https://simbad.cds.unistra.fr/simbad/sim-id?Ident=LH18&NbIdent=1&Radius=2&Radius.unit=arcmin&submit=submit+id[18]
https://simbad.cds.unistra.fr/simbad/sim-id?Ident=LH+24&NbIdent=1&Radius=2&Radius.unit=arcmin&submit=submit+id[19]
https://simbad.cds.unistra.fr/simbad/sim-id?Ident=LH+26&NbIdent=1&Radius=2&Radius.unit=arcmin&submit=submit+id[20]
https://simbad.cds.unistra.fr/simbad/sim-id?Ident=ngc+1873&NbIdent=1&Radius=2&Radius.unit=arcmin&submit=submit+id[21]
https://simbad.cds.unistra.fr/simbad/sim-id?Ident=ngc+1833&NbIdent=1&Radius=2&Radius.unit=arcmin&submit=submit+id[22]
https://www.aanda.org/articles/aa/abs/2012/09/aa19706-12/aa19706-12.html[23]
https://www.aanda.org/articles/aa/pdf/2012/09/aa19706-12.pdf[24]
https://simbad.cds.unistra.fr/simbad/sim-id?Ident=SP77+40-9&NbIdent=1&Radius=2&Radius.unit=arcmin&submit=submit+id[25]
https://www.aanda.org/articles/aa/abs/2023/06/aa43940-22/aa43940-22.html[26]
https://www.aanda.org/articles/aa/pdf/2023/06/aa43940-22.pdf
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