Sh2-129 / Ou4
Sh2-129 and Ou4 – the Squid within the Flying Bat’s wings
A red arc stretches across the star field in Cepheus: Sh2-129, the Flying Bat Nebula. This time, its glowing wings are not the only attraction. Within them, Ou4, the Squid Nebula, emerges as a turquoise, two-lobed structure. The left outline is ragged and partly crossed by red nebulosity; on the right, an elongated shell with a rounded end is easy to follow. The new processing separates the two shapes clearly while keeping the faint Squid within its wide surroundings.
Why red and turquoise? This HOO rendering assigns the hydrogen Hα channel to red and the oxygen-weighted channel to green and blue. Hα at about 656.3 nm is emitted when excited hydrogen drops to a lower energy state; the prominent [O III] line at 500.7 nm comes from doubly ionized oxygen. With a colour camera and a dual-band filter, these channels are not perfectly separate spectroscopic measurements. The palette reveals structure, but does not directly reproduce natural star colours, temperature or elemental abundance.
The elusive Squid comes into view. Nicolas Outters discovered Ou4 in 2011 in deep [O III] images. Here, too, its shape depends on the contrast between oxygen-weighted turquoise and Sh2-129’s strong hydrogen red. Both lobes can now be followed across the central field as one connected form: delicate bright rims, translucent interiors and a narrower connection in the middle. Not every faint filament is equally distinct, but the characteristic Squid silhouette is now much more than a hinted patch of light.
What drives Ou4? Corradi and colleagues interpret its measured gas motions and line ratios as a shock-excited outflow. An association with the central multiple star HR 8119 / HD 202214 and Sh2-129 is plausible, but does not settle Ou4's nature. If they share a distance of about 2,300 light-years, the Squid would be nearly 50 light-years long. This size is conditional, not a distance measured directly from this photograph.
Two edges, two different stories. At upper left sits vdB 140 around HD 203025; near the right edge a turquoise glow surrounds HD 203232. SIMBAD lists the latter as a K2 star: treating blue as proof of a hot star or an oxygen nebula would be misleading here. The four crops separate the central field, vdB 140, the right-hand stellar surroundings and the entire Bat. In this orientation, north is right and east is up.
Where in the sky
The rectangle is this image's real field of view, with its measured rotation — not a symbol. Constellation figures and star positions come from SIMBAD.
7 entries sit within 30° of each other here — click a field to jump to it.
Crops
Ou4 · Squid
Ou4 – the Squid comes into view
1.56° × 0.85°·21h 12m 21.91s +60° 00′ 50.6″
This crop focuses on the now clearly recognizable two-lobed form of Ou4. On the left, ragged turquoise rims lie across and between red structures; on the right, an elongated shell ends in a rounded tip. Bright edges and the narrower middle reveal the connection between both sides. The central field contains HR 8119 / HD 202214, the multiple-star system discussed as a possible driver. The overlay circle helps locate the nebula; it does not trace its outline.
vdB 140
vdB 140 – starlight and dust
45.2′ × 38.0′·21h 18m 04.17s +58° 37′ 04.0″
The compact nebulous patch at the left of the full image is vdB 140, around HD 203025. The illuminating star is catalogued as an early B-type star. Reflection nebulae scatter starlight from dust, so their appearance differs fundamentally from a pure emission-line image. The turquoise and red in this dual-band/HOO rendering are not natural RGB colours. The marker uses the star's catalogued position; the ring is only a guide.
HD 203232
HD 203232 – a star at the edge
43.0′ × 46.5′·21h 18m 08.42s +61° 26′ 40.7″
The conspicuous turquoise glow at the right edge surrounds the projected position of HD 203232. SIMBAD lists it as a spectroscopic binary with spectral type K2. Its colour in this HOO processing therefore cannot be read directly as stellar temperature. This finished image alone cannot separate the contributions of scattered light, filter halos and diffuse surroundings. The crop is deliberately identified by the star rather than by an unverified nebular name.
Sh2-129
The wings of the Flying Bat
2.43° × 2.15°·21h 11m 30.37s +60° 06′ 52.8″
This larger crop shows the shape behind Sh2-129's nickname: a bright curved leading edge and long red flanks. The left rim appears narrow and filamentary, the upper brightening broader; towards the bottom the structure fades into the darker field. This describes the visible distribution of Hα-weighted emission. The marked subregions are landmarks within Sh2-129, not additional catalogued nebulae.
Acquisition and processing
Acquisition. This new version combines 53 × 300 s = 15,900 s, or 4 h 25 min, from four nights between 5 and 11 September 2026. Slightly offset fields were grouped into the Sh2-129/Ou4 virtual panel. Equipment: ZWO ASI2600MC Air and William Optics RedCat 71 at 349 mm, Duo-Hα/O III filter, sensor near −10 °C. There are 32 lights at gain 0 and 21 at gain 100. All 53 were registered, locally normalized and included in the weighted integration. That provides about 2.8 times the exposure of the previous 95-minute version.
Calibration. Gain and flat groups were handled separately. Gain-0 lights used bias and flat calibration but no dark, because a matching gain-0 dark was unavailable. Gain-100 lights used bias, a master dark and flats assigned to the respective acquisition group. The missing gain-0 dark remains a limitation of this combined data set.
Processing and framing. The PiMagic Duo/HOO workflow treats hydrogen and oxygen separately and corrects gradients in the individual channels. Automatic cropping was disabled for this run; the complete 6,248 × 4,176-pixel master was retained through the layered Photoshop stage. The new rendition shown here then received its own final crop and dedicated colour and contrast adjustments. Turquoise and red form an HOO representation, not natural RGB colours or independent spectroscopic measurements.
Annotation alignment. The published AVIF measures 5,800 × 3,867 pixels and has its own astrometric solution: 7,834 stars, 0.96″ residual, approximately 2.218″/pixel and a 3.57° × 2.38° field. Existing sky coordinates for crops and object markers are projected onto this new image geometry. Circles remain locating aids, not measured nebular outlines.