Solar corona
Solar coronal lines
An emission line in the spectrum of the solar corona caused by highly ionized metal ions; especially those of iron, such as the red and green lines at 6375 Å and 5303 Å [Fe X] and [Fe XIV], respectively. From their discovery in 1870 until 1939, it was believed that these forbidden lines would be due to an unknown element, called coronium. Ultraviolet and X-ray coronal lines are also detectable in stars.
Stellar coronal lines