With total integration time of over 32 hours on six different nights , this is my longest exposed image up to now. The Canon EF 200mm was operated at f2.8 for the [OIII] channel and at f2.8 and f4 (with aperture stopper) for Ha.

Outters 4 is undoubtably the faintest object I have imaged so far. It is almost invisible on individual 15 min [OIII] frames. Even after stacking 67x900 sec [OIII] frames it required heavy, mask-supported stretching and denoising. Processing with different methods in Pixinsight using Tonemaps and NBRGB script. Star colors from RGB. Final touch in PS.

[OIII] stack (16,75 h)

STF stretched, otherwise unprocessed





Ha stack (14,6 h)

STF stretched, otherwise unprocessed



Annotated image



Size and location compared to adjacent IC 1396 (elefant trunk)





Object description:

Ha- emission nebula Sharpless 129 in Cepheus is close to the brighter and more popular IC 1396. Sh2-129 is also called the "Flying Bat" nebula due to the form of the nebulosity which is the red part of the object.

The turquoise colored nebula inside Sh2-129 is known as Outters 4 and is nicknamed the "Giant Squid" for the obvious form. It is also extremely faint and only appears on [OIII] filtered images.

Despite spanning over 1 degree on the sky, Ou4 was only recently discovered by the French amateur astronomer Nicolas Outters while imaging the Sh 2-129 nebula in June 2011. First suspected to be a Planetary Nebula, Corradi et al. (2014) concluded that Ou4 is a bipolar outflow launched some 90,000 yr ago from the massive triple star system HR 8119 located inside the Sh 2-129 Hii region. HR 8119 is also responsible for ionizing the red emission nebula Sh2-129, located at the distance of 2300 light years.

Ou4 is mainly composed of two collimated lobes with arc-shaped tips of enhanced [O iii] emission resembling bow-shocks observed in stellar outflows and few bubbles and complex filamentary arcs. The gas in the lobes is ionized by shocks generated by colliding with the surrounding ambient gas of the Hii region. The bipolar lobes measure 47×8 light years.

References:

Romano Corradi, Nicolas Grosso, Agnes Acker, Robert Greimel, Patrick Guillout, “Gas physical conditions and kinematics of the giant outflow Ou4”, Astronomy & Astrophysics, 570, A105, (2014).

http://www.aanda.org/articles/aa/abs/2014/10/aa22718-13/aa22718-13.html

https://hal.archives-ouvertes.fr/hal-01022286

Acker, A., Boffin, H. M. J., Outters, N., et al., “Discovery of new faint northern galactic Planetary Nebulae”, Rev. Mexicana Astron. Astrofis., 48, 223, (2012)

http://www.astroscu.unam.mx/rmaa/RMxAA..48-2/PDF/RMxAA..48-2_aacker.pdf