In the context of the spectral sequence, briefly explain L dwarfs and T dwarfs

Question

What will be an ideal response?

Answer 1

The set of star types, called the spectral sequence, is important because it is a temperature sequence. The O stars are the hottest, and the temperature continues to decrease down to the M stars, the coolest. For further precision, astronomers divide each spectral class into 10 subclasses. For example, spectral class A consists of the subclasses A0, A1, A2, . . . A8, A9. Next come F0, F1, F2, and so on. These finer divisions define a star's temperature to a precision of about 5 percent.The study of spectral types is more than a century old, but astronomers continue to discover and define new types. The L dwarfs, found in 1998, are cooler and fainter than M stars. They are understood to be objects smaller than stars but larger than planets and are called brown dwarfs. The spectra of M stars contain bands produced by metal oxides such as titanium oxide (TiO), but L dwarf spectra contain bands produced by molecules such as iron hydride (FeH). The T dwarfs are an even cooler and fainter type of brown dwarf than L dwarfs. Their spectra show absorption by methane (CH4 ) and water vapor.