TT Cygni is a carbon star located 561 parsecs (1,830 ly) away in the northern constellation of Cygnus. It is classified as a semiregular variable of subtype SRb that ranges in brightness from magnitude 7.26 down to 8.0 with a period of 118 days.[3] This object 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 by deep convection triggered by a flash from the helium shell.
In 1898 it was announced that Louisa Dennison Wells had discovered that the star, then known as BD +32°3522, is a variable star.[10] It was listed with its variable star designation, TT Cygni, in Annie Jump Cannon's 1907 work Second Catalog of Variable Stars.[11]
A thin spherical shell around the star, about half a light year across, was emitted 7,000 years ago.[12] It was first detected from its carbon monoxide emission and has a mass around four thousandths M☉, of which about a tenth is dust. The dust is thought to be mostly amorphous carbon.[8]
^McDonald, I.; Zijlstra, A. A.; Watson, R. A. (2017), "Fundamental parameters and infrared excesses of Tycho–Gaia stars", Monthly Notices of the Royal Astronomical Society, 471 (1): 770–791, arXiv:1706.02208, Bibcode:2017MNRAS.471..770M, doi:10.1093/mnras/stx1433.
^Olofsson, H.; et al. (January 2000), "A high-resolution study of episodic mass loss from the carbon star TT Cygni", Astronomy and Astrophysics, 353: 583–597, Bibcode:2000A&A...353..583O.
