Ou4, commonly known as the Squid Nebula, is a large and extremely faint emission nebula located within the constellation Cepheus, embedded in the broader region of Sh2-129. Its exact distance remains uncertain, but it is believed to be associated with nearby ionizing sources within a few thousand light-years. The nebula is dominated by strong OIII emission, with comparatively weaker H-alpha contribution, making it particularly challenging to detect and image.
The morphology of Ou4 is characterized by a bipolar, jet-like structure extending across several degrees of sky, with a central constriction and expanding lobes on either side. These features suggest a high-energy outflow, possibly driven by stellar winds or a collimated jet from an evolved stellar system. The surrounding hydrogen-rich environment of Sh2-129 provides contrast to the oxygen-dominated structure, helping to delineate the boundaries of the outflow.
This image was created using narrowband H-alpha and OIII data mapped to an HOO palette, along with broadband RGB stars acquired from Arnold, CA. The data were collected with a total integration time of 48.5 hours . The processing emphasizes the strong OIII signal that defines the nebula’s structure while preserving the surrounding hydrogen emission and natural star color, enabling clear separation between the Squid Nebula and the ambient interstellar medium.