TT Cygni is a carbon star. It is 561 parsecs (1,830 ly) away in Cygnus. It has an apparent magnitude of 7.44. It is called a carbon star because it has a high ratio of carbon to oxygen in its surface layers. The carbon was produced by helium fusion, dredged up from inside the star. A shell of carbon monoxide, about half a light year across, was emitted 6,000 years before the star was as it appears from Earth now.
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TT Cygni Wikipedia(Text) CC BY-SA