Messier 52, NGC 7635 and Sh2-157 - Bubble Nebula Region

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Location / Date

Zellerndorf, August 2017

Telescope / Mount / Guiding

ASA 10" Astrograph, ASA 3" Wynne Corrector
ASA DDM60, no Guiding

Camera / Exposure

Moravian G3-16200, Astrodon Gen2 Filter

4-panel mosaic:
L 4 x (25 x 5min), RGB 4 x (R 12 x 5min, G 12 x 5min, B 12 x 5min)
Hα 4 x (16 x 10min)

Total exposure time: 31h


PixInsight, Fitswork, Photoshop


NGC 7635, also called the Bubble Nebula, Sharpless 162, or Caldwell 11, is a H II emission nebula in the constellation Cassiopeia. It lies close to the direction of the open cluster Messier 52. The "bubble" is created by the stellar wind from a massive hot, 8.7 magnitude young central star, SAO 20575 (BD+60°2522). The nebula is near a giant molecular cloud which contains the expansion of the bubble nebula while itself being excited by the hot central star, causing it to glow.

NGC 7538 is a region of active star formation including several luminous near-IR and far-IR sources and is located in the constellation Cepheus. It is home to the biggest yet discovered protostar which is about 300 times the size of the Solar System. It is located in the Perseus Spiral Arm of the Milky Way and is probably part of the Cassiopeia OB2 complex.

Sh2-157 is aweak emission nebula but of remarkable extent visible in the constellation of Cassiopeia. It is located on the Perseus Arm, one of the main spiral arms of the Milky Way, and is directly connected with the great OB Cassiopeia OB2 association . The northern part of the cloud has a ring shape due to the action of the stellar wind of several giant stars, while the southern sector is excited by the radiant light of the spectral O-stars.
The nebula is associated with a large number of young stars, as it is typical of H II regions. Located in the northern part of the cloud is the open star cluster Mrk 50, including HD 219460, a supergigant class of Wolf-Rayet also cataloged as WR 157, which is a binary star whose mate is a brilliant giant of spectral class B1II with an orbital period of about two days. The evolutionary models of the region suggest that the star formation processes through this Perseus Arm region have first affected the region from which Cas OB2 originated and then extended to the formation of the NGC 7510 and finally Markarian (Mrk) 50, which is therefore the product of the last generation of stars in the region.
The nebula contains some very compact regions, among which the most conspicuous is Sh2-157A; this is a well-visible concentration in the Ha band , where the main source of gas ionization seems to be a star of class O8 or B0. The cloud is subdivided into two components: Component A, corresponding to the optically visible cloud, and Component B, which is in the dark region detectable in the photographs. The amount of ionized hydrogen present in Component A is considerably lower than the mass of the central star, which suggests that there is also a certain amount of neutral hydrogen present; Component B is composed of unlit powders. Its distance is comparable to that of the diffused nebula behind it, of which it is part. A second agglomerate, less brilliant, has been cataloged as Sh2-157B.

KjPn 8 is an unusually-shaped planetary nebula. Lopez et al.(Astrophysical Journal, 538:233-240, 2000) describes KjPn 8 as an "extreme polypolar planetary nebula with a large scale structure characterized by a giant biconical envelope".

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