Question

Provide a quantitative explanation to the following question: Why do the spectra of A-type stars show strong Hydrogen Balmer absorption lines, but M-stars have none?

Answer 1

The lines are the result of electrons in orbit around a nucleus changing energy levels.The hydrogen lines in the visible part of the spectrum (called Balmer lines) are strongest in stars with intermediate temperatures—not too hot and not too cold.so A type star shows strong Hydrogen Balmer absorption lines whereas M star has different temperature.

Spectral Class Approximate Temperature (K) Color Principal Features Neutral and ionized helium lines, weak hydrogen lines Neutral helium lines, strong hydrogen lines Strongest hydrogen lines, weak ionized calcium lines, weak ionized metal (e.g., iron Examples >30,000 10 Lacertae ue 10,000-30,000 Rigel, Spica white White 7500-10,000 Sirius, Vega magnesium) lines Yellow- white Strong hydrogen lines, strong ionized calcium lines, weak sodium lines, many ionized Canopus Procyon 6000-7500 metal lines Weaker hydrogen lines, strong ionized calcium lines, strong sodium lines, many lines of ionized and neutral metals Yellow 5200-6000 Sun, Capella Very weak hydrogen lines, strong ionized calcium lines, strong sodium lines, many lines of neutral metals Arcturus Aldebaran Orange 3700-5200 Betelgeuse Red 2400-3700 Strong lines of neutral metals and molecular bands of titanium oxide dominate Metal hydride lines, alkali metal lines (e.g., sodium, potassium, rubidium) Methane lines Antares Teide 1 Gliese 229B WISE Red Magenta 700-1300 Infraed < 700 1300-2400 Ammonia lines 1828+2650

lonized Neutral Hydrogen lonized helium helium Neutral Molecules (TiO) metals 7 metals Spectral Class 30,000 10,000750060005200 37002400 5200 30,000 10,000 7500 6000 3700 Approximate Temperature (K)