Stellar Spectral Classes Flashcards
When is an atom excited?
when one or more of its electrons is in an energy level higher than the ground state.
How do electrons move up energy levels?
by absorbing a photon.
why are stars approximated as black bodies?
o they emit a continuous spectrum of electromagnetic radiation.
How do you get absorption lines?
when radiation from the star passes through a cooler gas in the star’s atmosphere
What happens when the absorption at a particular wavelength is more intense?
The more intense the absorption at a particular wavelength, the more radiation of that wavelength has been absorbed.
How are photons of particular wavelength absorbed?
by the electrons to excite them to higher energy levels
What happens when electrons de-excite them?
the same wavelength of light is emitted and radiated in all directions. This means the intensity of radiation with this wavelength reaching Earth is reduced.
Where are Hydrogen Balmer absorption lines found?
found in the spectra of O, B and A type stars.
What causes Hydrogen Balmer absorption lines?
caused by the excitation of hydrogen atoms, from the n = 2 state to higher/lower energy levels
What happens when the temperature of a star is too high? (3)
most hydrogen atoms-> excited to higher levels than n = 2
or electrons might be -> ionised,
hydrogen Balmer lines not present
What happens when the temperature of a star is too low?
hydrogen atoms- unlikely to become excited, may not be present at all
hydrogen balmer lines will not be present.
what is the intensity of hydrogen balmer lines dependent on?
temperature
How can stars be classified?
Stars can be classified into spectral classes based on the strength of absorption lines
Spectral class table
