LL Pegasi
A binary carbon star hidden in a precise Archimedean spiral nebula.
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LL Pegasi, also cataloged as AFGL 3068, is a binary star system whose primary component is an extreme carbon star. The pair is enshrouded by a dust cloud ejected from the carbon star, making it invisible at visual wavelengths and detectable only in infrared light. The system is a Mira variable, exhibiting strong infrared brightness variations with a period of roughly 696 days.
Surrounding the star is a pinwheel-shaped nebula designated IRAS 23166+1655, which is believed to be a preplanetary nebula. This nebula is notable for its unusually precise Archimedean spiral shape, thought to result from the gravitational interaction between the carbon star and its stellar companion. While similar spiral structures have been observed in other binary systems, none display such a geometrically perfect form. The spacing between the spiral arms and their rate of expansion match the estimated 810-year orbital period of the binary pair, derived from their apparent angular separation.
Quick Facts
- Variable type
- Mira variable
- Period
- 696 days
- Orbital period (binary)
- 810 years
- Associated nebula
- IRAS 23166+1655
Facts from the source article.
Lore & Background
LL Pegasi is obscured at visual wavelengths but is strongly variable in brightness at infrared wavelengths. It is classified as a Mira variable and has a period of about 696 days.
The nebula displays an unusual Archimedean spiral shape. The shape is thought to be formed through the interaction between the stellar companion and the carbon star, as has been seen in other binary systems, although not with such a precise geometric form. The distance between the spiral arms and their rate of expansion is consistent with estimates of the pair's 810 year orbital period based on their apparent angular separation.
Reader's Guide
LL Pegasi is notable for its remarkably precise Archimedean spiral nebula, which is thought to be a preplanetary nebula. The spiral shape is interpreted as the result of interaction between the binary components—an extreme carbon star and its companion—producing a geometric form not seen with such exactness in other binary systems.
The nebula's structure provides a direct observational link to the orbital dynamics of the system: the spacing and expansion rate of the spiral arms match the estimated 810-year orbital period derived from the stars' angular separation. Because the system is hidden by its own dust cloud at visual wavelengths, it is studied primarily in infrared light, where its Mira-type variability with a 696-day period is observed. The system's significance lies in its demonstration of how binary interactions can shape circumstellar material into highly ordered patterns, offering a clear example of a process that may be common but is rarely seen with such clarity.
More in Emission, Dark and Reflection Nebulae
Sources
Compiled from Wikipedia and the sources listed below. Text from Wikipedia is available under CC BY-SA 4.0; this entry is adapted from it.
- Wikipedia: LL Pegasi (CC BY-SA 4.0).
- Word definitions: the Codexery glossary, each quoted from its Wikipedia article.
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