RCW 75 (Gum 48a) HII region in Centaurus in HOS colors by Zaytsev and Hanson

Central part of RCW 75 (also known as Gum 48a) HII region [1, 2] featuring HD 115669 star, elephant trunk nebula, and a “very young" (4-6 Myr of age) Stock 16 open cluster [3-5] (part of Cen OB1 star association) located at the distance of 1.64 kpc [6, 7] and serving as primary ionization source for this region. The area also contains reflection nebulae VdBH 60a placed at an estimated distance of 1.9 kpc [8] and VdBH 60b both located at the “tip” of the elephant trunk nebula, as well as VdBH 60d and VdBH 60c reflection nebulae in the upper left corner.The angular size of the FOV in this image is 18’17” (side of the square) which for the distance of 1.9 kpc corresponds to the linear size of about 33 ly.

Both earlier [3] and later [4, 5] studies conclude that the Stock 16 cluster has formed on the outer edge of the elephant trunk nebula which used to be larger prior to formation of the cluster. It is further derived [3] that that original (larger) elephant trunk nebula suffered an implosion triggered by the intense radiation from preceding generation of the OB stars from a cluster that is now dispersed over the larger area of the HII region, thus resulting in creation of the currently observable scene. It is also concluded that RCW 75 remains an active star formation region and that the site of next generation of stars “should lie in the dense dust clouds located along the ionization-bound edge of the complex” [3] pointing to the central stars of the four VdBH 60a-d reflection nebulae as possible newly formed objects.

Description Continued below image.

The image shows the unprecedented level of details in both dark nebulae in the middle and also in the “veil” preceding the ionization-bound edge of RCW 75 complex on the right of the trunk nebula, revealing many ghostly features there. A considerable amount of details is revealed in the part of the nebula complex on the left of the trunk nebula as well.

ASA Ritchey-Chretien RC-1000: D=1m, f/6.8 on alt-azimuthal direct drive fork mount, FLI ProLine 16803 with secondary mirror based motorized focusing and automatic de-rotation (Telescope #1 system of ChileScope observatory, Río Hurtado Valley, Chile).

Data and initial calibration/integration: Alexandr Zaytsev https://www.astrobin.com/users/m57ring/ 9x Ha + 9x OIII + 9x SII guided 1200 sec exposures (9h of combined integral) collected over 6 imaging sessions carried out on Jul 8, 12, 14, 15, 16, 22 of 2023 using Chilescope Telescope #1 system.

Image Processing: Mark Hanson www.hansonastronomy.com   

Enjoy, Mark and Alex

[1] http://galaxymap.org/cat/view/rcw/75 

[2] https://arxiv.org/abs/1712.01474  

[3] https://articles.adsabs.harvard.edu/pdf/1985ApJ...292..148T 

[4] https://www.aanda.org/articles/aa/abs/2005/05/aa1089/aa1089.html 

[5] https://www.aanda.org/articles/aa/abs/2005/21/aa1089-04e/aa1089-04e.html 

[6] https://arxiv.org/abs/1102.2503 

[7] https://ui.adsabs.harvard.edu/abs/2004AN....325..740K/abstract 

[8] https://arxiv.org/abs/astro-ph/0301221 

Enjoy, Mark and Alex