sh2-187: Discover this fascinating area

Sh2-187 from my own „Sterntaucher“ observatory

In 2020 I imaged Sharpless 187 (Sh2‑187) in LHaRGB from my own observatory using a dual rig, with a longer focal length for the L and H‑alpha channels and a wider field for the RGB data.

My LHaRGB imaging strategy leverages the strengths of both narrowband and broadband techniques. The longer‑focal‑length system for L and H‑alpha provides high spatial resolution and sensitivity to faint emission, allowing the small‑scale structure of the H II region to be captured: bright knots, filaments, and ionization fronts around the embedded stars. The H‑alpha frames isolate the line emission from ionized hydrogen, boosting contrast against the background and revealing the geometry of the ionized shell and any asymmetric features caused by density variations in the surrounding cloud.

The luminance (L) channel, often taken through a broad filter, enhances overall signal‑to‑noise and sharpness, helping to bring out fine detail in both the nebula and the star field when combined with RGB. The wider‑field RGB system, in turn, records natural star colors and the diffuse glow of reflection and emission outside the core, mapping the larger molecular and dust environment that Sh2‑187 inhabits.

When these datasets are combined into an LHaRGB image, the result is both aesthetically striking and scientifically informative. The H‑alpha data accentuate the bright core and filaments, giving the nebula a crisp, textured appearance, while the RGB data supply realistic star colors and the subtle hues of reflection nebulosity and scattered light. Dark lanes cut across the field, emphasizing the clumpy, inhomogeneous nature of the molecular cloud. Small embedded stars and possible young stellar objects show up as point sources embedded in or adjacent to the emission, hinting at the ongoing formation of a cluster within Sh2‑187.

Sh2-187 is a small but very active star‑forming region in Cassiopeia, a mix of emission, reflection, and dark nebulae embedded in a larger molecular cloud complex.

Sh2-187 lies in Cassiopeia, about 1.5° north of the star δ Cassiopeiae (Ruchbah), in a rich Milky Way field. It is a relatively compact nebula, only a few arcminutes across, surrounded by much more extended dark and molecular material that fills the wider field.

Distance estimates place Sh2‑187 at around 1,440 parsecs, roughly 4,700 light‑years from Earth. At that distance, the visible emission region is only a few light‑years across, but it sits inside a neutral hydrogen shell and molecular cloud with a mass of about 7,600 solar masses.

Physically, Sh2‑187 is an H II region and star‑forming “stellar nursery” embedded in that larger cold cloud. The central bright patch is mainly hydrogen‑alpha emission excited by young, hot stars, while reflection components and dark dust lanes trace the surrounding dusty material.

Infrared and radio observations show multiple signs of ongoing star formation. At least two strong infrared sources have been identified within Sh2‑187, notably S 187 IRS and IRAS 01202+6133, which mark deeply embedded protostars or very young stars still enshrouded in dust. There is also a molecular jet detected, indicating high‑velocity outflows from a young object interacting with the surrounding gas.

Age estimates of around 100,000–200,000 years make Sh2‑187 a very young star‑forming region on galactic timescales. It sits on the edge of a larger neutral hydrogen structure, and the configuration suggests that earlier generations of massive stars may have compressed part of this cloud, triggering the current burst of star formation.

The bright emission is wrapped in a complex of dark nebulae catalogued in the Lynds Dark Nebula (LDN) list, including LDN 1317 and neighbouring clouds like LDN 1314 and 1316. These appear in your images as dark patches and filaments that partially obscure the background star field and frame the glow of Sh2‑187 itself.

The combination of glowing gas, reflection patches, heavy extinction and embedded infrared sources makes Sh2‑187 a good example of a small, embedded H II region just “switching on” inside a much larger cold molecular complex.

Data calibration and registration and the final processing was done with PixInsight. The RGB Data was upscaled to the luminance data. The result was as follows: