Stellar Classification

Harvard Classification Scheme from A to P class stars are based on

• Star's temperature

• Strength of Balmer lines

• Stellar Compositions

• Star's Energy

Balmer lines are strongest in which class stars?

• O5 class stars

• A2 class stars

• G2 class stars

• M5 class stars

What is the relation between the strength of Balmer lines and classification the classification of OBAFGKM

• The coolest star is Hydrogen poor has the strongest Balmer lines

• The hottest star is Hydrogen rich, hence the strongest Balmer lines

• Balmer lines is lower near the hottest star and steadily increases from O class to A class

• Balmer lines is strongest near the hottest star with highest Helium and Metal

Equivalent Width (EW) is useful to characterize the strength of absorption lines. EW is proportional to

• The distance of the star

• The intensity of the flux density

• The length of missing flux

• Wavelength of the stars measured

Boltzmann Excitation Equilibrium Equation states the

• Ratio of exited atoms to the other energy levels

• Ratio of exited ions to the other energy levels

• Energy of the atom in exited state

• Energy of the ion in exited state

Boltzmann Excitation Equilibrium Equation conclude that

• The strength of Balmer lines is proportional to the number of Hydrogen ion in exited state, n=2

• The strength of Balmer lines is proportional to the number of Hydrogen atom in exited state, n=2

• The strength of Balmer lines is proportional to the temperature of Hydrogen atom populated

• The strength of Balmer lines is proportional to the temperature of Hydrogen ions populated

Saha equation tells us that

• Strength of Balmer lines in higher temperature where the atoms is ionized

• ratio of the number of Hydrogen atom in higher state

  to the number of atom in lower state

• ratio of the number of ions in higher state

  to the number of ions in lower state

• Strength of Balmer lines at temperature 10000K where the Hydrogen atoms is completely ionized

This diagram displays the rise and fall of

all non-ground state transitions with temperature. From this diagram we can deduce that

• series of optical stellar spectra displays the

  systematic change in absorption line strengths

  with temperature.

• smooth variation along the spectral types indicates minor variations of the chemical composition of stars with temperature.

• ionization occurs over a small temperature range. The Hydrogen neutral at 7000 K - 10,000 K.

• equivalent width is the amount

  of wavelength the amount of

  spectrum that would be completely “black”.

Why were there not any hydrogen features in red and cooler stars?

• because it is late type and Hydrogen poor

• because it is early type and Helium rich

• because the Hydrogen atom is in ground state

• because the stars are runs out of Hydrogen

Why were very minimum hydrogen features in blue and hottest stars?

• because it is early type, hence Hydrogen poor

• because all the Hydrogen is almost ionized

• because it early type, hence Helium rich

• because the Hydrogen is in the ground state