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NGC 7822: A Star Cradle in Cepheus

NGC 7822 is a fascinating emission nebula located in the constellation Cepheus, about 3000 light-years from Earth ( 4.6)

This star-forming region is home to hot young stars whose powerful stellar winds and intense radiation sculpt the surrounding gaseous environment.


NGC 7822

Main features

NGC 7822 is part of a large nebular complex that also includes Cederblad 214 ( 5) . This region spans about 40 light-years (4) and includes several interesting substructures:

  • The Sharpless 171 emission region

  • The young star cluster Berkeley 59 (1, 7)

The newly formed stars within NGC 7822 have a significant impact on their surroundings. Their stellar winds and radiation ionize the surrounding gas, creating the beautiful luminous structures we observe.


Astrophysical characteristics

Chemical composition

The nebula is composed primarily of ionized hydrogen, but also contains ionized oxygen and sulfur, as revealed by narrow-band imaging (1, 2) . This composition is typical of active star-forming regions.


Ionization source

The ionization of the gas is mainly due to the intense ultraviolet radiation emitted by the young massive O and B type stars that formed within the nebula (4) . The star BD+66 1673, a binary system containing an extremely hot O5V type star (about 45,000 K), plays a major role in this ionization process.





Gas structures

The image reveals spectacular filamentary structures and pillars of dense gas ( 4,6) . These formations are the result of the interaction between radiation and stellar winds from massive stars with the surrounding gas. The denser areas are more resistant to erosion, creating these characteristic shapes.





Star formation process

NGC 7822 is an excellent laboratory for studying star formation:


Berkeley 59 star cluster

This young open cluster, visible in the upper left part of the image, contains several recently formed massive stars (1, 7) . Its study allows us to better understand the early phases of the evolution of star clusters.


Gas Pillars

The observed pillar-like structures are likely sites of active star formation (4, 6) . Compression of gas by stellar winds and radiation can trigger gravitational collapse of these structures, leading to the birth of new stars.


Stellar Feedback

The image perfectly illustrates the concept of stellar feedback: massive stars, once formed, strongly influence their environment, being able to both stimulate and inhibit the formation of new stars in different regions of the nebula (4) .





Imaging Challenges

Capturing NGC 7822 presents several challenges for astrophotographers:


Scope of field

The nebula is very large, requiring a wide field of view to capture it entirely (5) . A short focal length or focal reducer may be necessary. Here we have focused on a region of 1°19'.


Low surface brightness

NGC 7822 has low surface brightness, requiring long exposure times and optimal sky conditions (5). With a shot taken from my backyard in the middle of the city, light pollution means longer acquisition times.

This time, nearly 40 hours of data were accumulated.


Weather conditions

Autumn, an ideal time to photograph NGC 7822, can present difficult atmospheric conditions with high altitude haze or humidity (5) .


Technical details of the capture

Equipment

  • Telescope: Orion Newtonian 200/800 mm 8" f/4 Astrograph

  • Camera: QHYCCD QHY249M (CMOS)

  • Mount: Sky-Watcher EQ-6R Pro

  • Filters: Antlia H-alpha (4.5nm), Antlia OIII (4.5nm), Optolong SII (6.5nm)

  • Accessories: PrimaLuceLab Sesto Senso autofocuser, Baader Planetarium MPCC mkIII 2.00" coma corrector, QHYCCD CFW3 US filter wheel, ZWO Optical ZWO OAG off-axis corrector


Acquisition

  • Period: 6 nights from September 20 to October 2, 2024

  • Conditions: Seeing 3/5, Transparency 3/5, Bortle Scale 9

  • Total integration time: 39 hours 18 minutes


An image made with an integration time of only 20 hours provides a much lower amount of detail.






Image processing

Processing was performed with PixInsight 1.8 and Photoshop, using advanced techniques to maximize detail and contrast while controlling noise. The Foraxx technique (SII, H-alpha, OIII), was used to create the final image (9).


Image analysis

The final image reveals the complexity and beauty of NGC 7822. Filamentous structures of ionized gas are clearly visible, testifying to the dynamic interaction between young stars and their environment. The brightest regions likely correspond to areas of active star formation, where new stars are emerging from clouds of gas and dust.

The chosen color palette highlights the different chemical components of the nebula. The reddish tones mainly represent ionized hydrogen, while the bluish hues indicate the presence of ionized oxygen (1, 2) .


Implications for our understanding of galactic evolution

The study of NGC 7822 contributes to our broader understanding of galactic evolution:

  • It allows us to observe the processes that regulate star formation at the scale of giant molecular clouds.

  • It provides insight into the enrichment of the interstellar medium with heavy elements by massive stars.

  • It illustrates how HII regions shape the structure and dynamics of the galactic disk.


Conclusion

This image of NGC 7822, with its impressive integration time of 39 hours, remarkably captures the complexity and beauty of astrophysical processes in action. Each pixel in this image tells a piece of the cosmic story unfolding in this stellar nursery, reminding us of the dynamic and evolving nature of our universe. NGC 7822 remains a fascinating object for astronomers and astrophotographers, offering unique insights into the mechanisms of star formation and nebula evolution in our galaxy.


Sources

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