The spectrum of Psi9 Aurigae matches a giant star with a stellar classification of B8 IIIe.[3] The 'e' suffix indicates this is a Be star that shows emission lines of hydrogen in its spectrum. This is caused by a circumstellar shell of hot gas. The emission undergoes variability on a time scale of sixteen years.[3]
^ abcGhosh, K. K. (September 1989), "Search for rapid spectral variability in Psi(9) Aurigae", Publications of the Astronomical Society of the Pacific, 101: 839–843, Bibcode:1989PASP..101..839G, doi:10.1086/132504.
^ abCrawford, D. L. (February 1963), "U, b, v, and Hβ Photometry for the Bright B8- and B9-TYPE Stars", Astrophysical Journal, 137: 530, Bibcode:1963ApJ...137..530C, doi:10.1086/147526.
^Wilson, Ralph Elmer (1953), "General Catalogue of Stellar Radial Velocities", Carnegie Institute Washington D.C. Publication, Washington: Carnegie Institution of Washington, Bibcode:1953GCRV..C......0W.