Sh2-115 is an extended emission nebula located in the rich star fields of the northern constellation Cygnus, close to the border with Cepheus. It is catalogued as Sh2-115 in Stewart Sharpless' catalogue of H II regions, published in 1959. The nebula lies at an estimated distance of approximately 7,500 light-years from Earth and forms part of a much larger complex of ionised gas and interstellar dust associated with ongoing star formation in this region of the Milky Way.
The image also includes Sh2-116, also known as the planetary nebula Abell 71 (PK 85+04.1). Originally discovered by George Abell in 1955, it was later included by Stewart Sharpless in his catalogue of H II regions as Sh2-116, illustrating the difficulty of classifying this unusually large and faint object.
Surrounding these emission nebulae are several diffuse nebulae from the Lynds Bright Nebula catalogue, including LBN 357, LBN 358, LBN 362, LBN 367 and LBN 368. These faint clouds are composed of ionised gas mixed with dust and display subtle variations in brightness and colour depending on their excitation and illumination. Dark absorbing structures scattered across the field further reveal the complex distribution of interstellar dust within this part of the Galactic plane.Together, these objects illustrate the different evolutionary stages of the interstellar medium, from regions where massive stars ionise their natal clouds to the expanding shells produced by evolved stars. Their combination makes this a particularly rich field for wide-field astrophotography, allowing the relationships between the various nebulae to be appreciated far better than when each object is observed individually.
Image Acquisition
The narrowband data were collected using an Astrodon Hα filter together with Baader O III and S II filters. Individual sub-exposures were 1800 seconds for the narrowband images and 600 seconds for the RGB data.
The wide-field HOO and HSO images were processed at the TOA-150 native image scale of 1.69"/pixel. In addition, a cropped view centred on Sh2-116 was produced using 2× drizzle during integration, increasing the effective image scale to 0.845"/pixel in order to better reveal the fine structure of this faint planetary nebula.
The total integration time for the project amounts to 47 hours.
lImage Processing
The processing strategy for this image was based on removing the stars from the linear datasets using StarXTerminator, allowing the nebular structures and the stellar component to be processed independently.
The starless image, mapped using an HOO palette, was then processed in PixInsight. The main tools and processing steps were:
BlurXTerminator to improve the definition of the nebular structures.
NarrowbandNormalization to balance the Hα and O III channels according to my preferred colour rendition.
MultiscaleAdaptiveStretch (MAS) for delinearisation.
HDRMultiscaleTransform to enhance local contrast and manage the dynamic range.
LocalHistogramEqualization to improve fine detail and increase the perception of depth.
NoiseXTerminator for noise reduction.
CurvesTransformation for colour enhancement and final colour adjustment.
Once the nebular processing was completed, the RGB stars—acquired with the FSQ-106N and processed separately to preserve their natural colours—were seamlessly reinserted using the ScreenStars script developed by Mike Cranfield and Bill Blanshan.
This HOO image is the first result of the project. Two additional versions will be presented separately: an HSO rendition of the same wide-field image and a high-resolution, 2× drizzle close-up of Sh2-116 (Abell 71).
In this image, north is up.
Click on the image for the full resolution version, or visit the Gallery section for complete exposure details.
Image processing: Pixinsight.
Observatory automation and remote operation: Talon6.
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