ShaRA team, for its 8th project, landed to the Dolphin nebula, alias SH2-308. As usual we used a remote telescope located in Rio Hurtado sharing the renting costs. This is the final superstak, obtained combining 12 different images from 12 different authors using this formula in PixelMath:
ShaRA#8.1 = Bertocco x 0.06 + Curzi x 0.08 + DiFusco x 0.18 + Linsalata x 0.11 + Lioce x 0.07 + Maffioli x 0.11 + Michieletto x 0.02 + Ravagnin x 0.1 + Vergani x 0.04 + Iorio x 0.14 + Ligustri x 0.06 + Trabuio x 0.03
During the processing, we studied a little bit this nebula and we faced some unknown objeccts. Here below the results:
EZ Canis Majoris is one of the brightest known stars of its kind. Its outer shell of hydrogen gas was ejected into interstellar space and depleted, revealing inner layers of heavier elements rich in ionized helium and nitrogen produced by the CNO cycle (hence the classification of WR stars as WN-type, based on the intensity of the NIII lines at 463.4-464.1 nm and 531. 4 nm, NIV at 347.9-348.4 nm and 405.8 nm, and NV at 460.3 nm, 461.9 nm, and 493.3-494.4 nm) that burn at very high temperatures. Below is the spectrum imaged by Alessandro Ravagnin with his C11HD and the StarAnalyzer200 + ASI2600MM, the same night of imaging done with the T2 telescope in Chile.



The intense radiation emitted forms intense stellar winds (even exceeding 2000Km/s) that shape the surrounding gas into a vast bubble of ionized hydrogen and oxygen. Ionized Oxygen at 500nm (forbidden line identified with [OIII] originated by “collisional” effect) is what we see in the cyan-colored region of the spectrum and which in nebular bubbles such as the one around WR6 (type II) has temperature above 10,000K and originates by shock due to the expansion of hydrogen ejected from the central star into a medium with density low enough to allow slow cooling. In fact, a discrete “displacement” between the H-alpha emission (which follows) and the [OIII] emission (which precedes) can be seen in the SH2-308 nebula. In the literature, the difference in the relative positions/dimensions of the respective H-alpha and [OIII] shells go to define the type of WR Ring nebula (SH2-308 is indeed a Type II) and are dependent on the density of the interstellar medium, in which the bubble of hydrogen ejected by the progenistral star is expanding. We tried to hestimate the displacement between H-alpha and [OIII] bubbles, using the following portion of the image: 2% of the diameter of the Nebula (a portion of light-year).



The central star also is slightly offset from the center of the shell and is close to the part of the nebula with higher intensity, along the direction of displacement. One can also see a less than perfect sphericity of the shell [OIII] with a spike ("hernia" in the literature) probably due to an area wih lower-dense interstellar medium (the Dolphin’s beak).



Widening the view, farther away from the main Shell (the Dolphin’s head) one can see other nebulosity that also appears to be circular in shape and also centered on WR6.


The two main “complexes” of this structure are classified as SH2-303, SH2-304 and appear to be precisely close relatives of SH2-308 and WR6, much richer in ionized hydrogen than third oxygen. Here is a portion of the shot taken with the 135mm Samyang in Namibia in mid-March.

Going instead to focus the view, it is possible to spot other objects in the field framed by T2.The main one (pointed out by Andrea Iorio) is the planetary nebula classified as PN G234.9-09.7, whose central star is a very faint magnitude 19 star classified as Gaia EDR3 2922355602864621568 (ar: 103.9998 – dec: -23.9471) and 2.9kpc, or 9,500 light-years away.
The apparent angular size of this nebula is less than one-tenth that of Dolphin, or 2.6’x2.6′.Also in the field, two other small cyan-colored “speckles” were identified (by Gianpaolo Michieletto), afferent to as many nebulae. Searches on the net yielded no results. We scoured the DB HASH (Hong Kong/AAO/Strasbourg H-alpha planetary nebula database) but nothing. Unknown and uncatalogued spots. We checked the veracity of the spots by searching for ultra-deep photographs in the Astrobin DB, and indeed there was confirmation: they are not due to noise.What did we pick up then? They look like two planetaries or two more WR shell OIIIs, but without a spectroscopic investigation nothing can be said.



Certainly, looking at the size, the two nebulae are much more distant than both SH2-308 and the smaller circular planetary; taking Gaia maps, we can assume that we are in the outer arm of our Milky Way.Let’s see if any astronomers support us in this compelling quest.




More info here: https://astrotrex.wordpress.com/2024/03/22/shara8-1-the-dolphin/