What key observational difference, related to chemical signatures, can help distinguish late $ ext{M}$-types from the hottest brown dwarfs?
Answer
The presence or absence of lithium
Since stars rapidly deplete lithium during hydrogen fusion, a positive lithium signature often indicates that an object is a brown dwarf that never achieved full stellar status.
Related Questions
What scientific classification describes the coolest true stars that sustain core hydrogen fusion?What is the typical surface temperature range for Red Dwarfs in Kelvin?Approximately what fraction of all hydrogen-fusing stars in the Milky Way are believed to be red dwarfs?What internal mechanism allows small red dwarfs (below $0.35 ext{ M}_ ext{sun}$) to consume nearly all their hydrogen fuel?How long are the smallest red dwarfs predicted to burn on the main sequence?What minimum mass ($ ext{M}_ ext{sun}$) is generally cited as the threshold for an object to be considered a main-sequence star capable of sustained hydrogen fusion?What are objects called that fall below the hydrogen fusion threshold and are often termed 'failed stars'?Which spectral class represents the coldest known substellar objects, sometimes reaching temperatures around $250 ext{ K}$?What is the official measured surface temperature of the coolest confirmed main sequence star, $2MASS ext{ J}0523-1403$?What is the spectral class of the coolest confirmed main sequence star, $2MASS ext{ J}0523-1403$?What key observational difference, related to chemical signatures, can help distinguish late $ ext{M}$-types from the hottest brown dwarfs?