Questions and Answers
What does stellar classification refer to in astronomy?
What percentage of all stars are included in the main sequence?
more than 90 percent
What are O class stars?
A main-sequence star of spectral type O and luminosity class V
What is a B class star?
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What characterizes an A type star?
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What is a G type star also known as?
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What is a brown dwarf?
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Define Wolf-Rayet stars.
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What is a subgiant star?
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What is the definition of a red giant?
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What is a blue supergiant?
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Which of the following is true about carbon stars?
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Study Notes
Stellar Classification
- Stellar classification categorizes stars based on their spectral characteristics.
- More than 90 percent of all stars are found on the main sequence, a prominent diagonal area on the H-R diagram.
Main Sequence Stars
- O-class stars: Hot, massive stars with high luminosity (spectral type O, luminosity class V).
- B-class stars: Hydrogen-burning stars of spectral type B (luminosity class V).
- A-type stars: Exhibits strong hydrogen absorption lines.
- F-type stars: Hydrogen-fusing stars of spectral type F (luminosity class V).
- G-type stars: Often known as yellow dwarfs, these stars are spectral type G.
- K-type stars: Known as K dwarfs or orange dwarfs, these are hydrogen-burning stars of spectral type K.
- M-type stars: Known as red dwarfs, they are the smallest and coolest stars on the main sequence.
Advanced Stellar Types
- Brown dwarfs: "Failed" stars lacking sufficient mass for nuclear fusion.
- Wolf-Rayet stars: Identified over 220, very hot (25,000 to 100,000 K), rapidly losing mass (over 10^-5 solar masses/year), with extreme wind speeds (800 to 3000+ km/s).
- OB stars: Hot, massive stars (spectral types O or early B) that form OB associations.
Subdwarf Classification
- Subdwarf (sd): Stars with luminosity class VI, exhibiting lower luminosity than regular main-sequence stars.
- Subdwarf O stars (sdO): Hot, low-mass stars.
- Subdwarf B stars (sdB): A specific kind of subdwarf star with spectral type B.
Stellar Evolution Stages
- Subgiants: Intermediate stars between main-sequence and giants with inert helium cores and hydrogen-fusing shells.
- Giants: Large, bright stars with exhausted hydrogen in their cores.
- Blue giants: Extremely hot, large, and bright stars.
- Yellow giants: Luminous giant stars of low or intermediate mass in later evolutionary phases.
- Red giants: Large, reddish stars at a late life stage.
Supergiants
- Bright giants: Highly evolved massive stars, classified as Luminosity Class II.
- Supergiants: Very large stars, brighter than giants, despite being relatively cool.
- Blue supergiants: Largest and hottest stars located at the upper-left end of the main sequence.
- Red supergiants: Massive stars during their expansion phase, becoming very bright.
- Yellow supergiants: Stars, typically of spectral type F or G, classified as supergiants.
Hypergiants
- Hypergiants: Extremely massive and luminous stars that lose mass rapidly due to their size.
- Yellow hypergiants: Massive stars with extended atmospheres and significant mass loss, possessing spectral classes from A to K.
Unique Stellar Types
- Carbon stars: Red giants with strong absorption lines of carbon.
- S-type stars: Cool giants with equal amounts of carbon and oxygen in their atmospheres.
- CN stars: Stars exhibiting unusually strong cyanogen bands in their spectra.
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Description
Test your knowledge of stellar classification and the characteristics of various types of stars. This quiz covers everything from O-class to M-type stars, including the main sequence and advanced stellar types. Understand how stars are categorized based on their spectral characteristics.
