The Spectra of Stars with Different Surface Temperatures.

The Spectra of Stars with Different Surface Temperatures.
The corresponding spectral types are indicated on the right side of each spectrum. (Note that stars of each spectral type have a range of
temperature.) The hydrogen Balmer lines are strongest in stars with surface temperatures of about 10,000 K (called A-type stars). Cooler
stars (G- and K-type stars) exhibit numerous atomic lines caused by various elements, indicating temperatures from 4000 to 6000 K. Several
of the broad, dark bands in the spectrum of the coolest stars (M-type stars) are caused by titanium oxide (TiO) molecules, which can exist
only if the temperature is below about 3700 K. Recall from Section 4-5 that the Roman numeral I after a chemical symbol means that the
absorption line is caused by a neutral atom; a numeral II means that the absorption is caused by atoms that have each lost one electron