Questions and Answers
What does 'early/late' refer to in stellar classification?
What is the main sequence in an H-R diagram?
A diagonal area that includes more than 90 percent of all stars.
O-type stars are the coolest stars.
False
What characterizes a B-type star?
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What do A-type stars exhibit?
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An F-type main-sequence star has surface temperatures between _____ K.
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What is a G-type main-sequence star also known as?
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A K-type star is also referred to as a _____ dwarf.
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M-type stars can be easily observed from Earth.
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What is a brown dwarf?
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Who discovered Wolf-Rayet stars?
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What are OB stars characterized by?
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Study Notes
Stellar Classification
- Stellar classification categorizes stars based on spectral characteristics and temperature of their photosphere.
- Spectra are generated by splitting a star's electromagnetic radiation, revealing a rainbow of colors with specific spectral lines indicating chemical elements.
- The spectral class of a star summarizes its ionization state, providing an objective measure of temperature.
Main Sequence
- The main sequence is a diagonal band on the Hertzsprung-Russell (H-R) diagram where over 90% of stars are located.
O-Type Stars
- O-type stars have the hottest surface temperatures.
- Their brief lifespan limits the potential for planet formation around them.
B-Type Stars
- B-type main-sequence stars are hydrogen-burning and possess 2 to 16 times the mass of the Sun.
- These stars exhibit surface temperatures between 10,000 and 30,000 K, characterized by a blue hue and prominent neutral helium lines, especially at the B2 subclass.
- Notable examples include Regulus and Algol A.
A-Type Stars
- A-type stars display strong hydrogen absorption lines in their spectra.
F-Type Stars
- F-type main-sequence stars possess 1.0 to 1.4 solar masses and surface temperatures between 6,000 and 7,600 K.
- They give off a yellow-white hue and are also referred to as yellow-white dwarfs.
- Famous examples include Procyon A and KIC 8462852.
G-Type Stars
- G-type main-sequence stars, commonly called yellow dwarfs, have masses of 0.9 to 1.1 times that of the Sun, with effective temperatures ranging from 5,300 to 6,000 K.
- G-type stars undergo hydrogen to helium fusion in their cores; the Sun is a notable example, fusing around 600 million tons of hydrogen every second.
K-Type Stars
- K-type stars, or K dwarfs, are intermediate in size between red M and yellow G stars, with masses between 0.5 and 0.8 solar masses.
- They have lower surface temperatures (3,900 to 5,200 K) and are of interest in extraterrestrial life studies, with Alpha Centauri B being a prominent example.
M-Type Stars
- M-type stars are the smallest and coolest main-sequence stars, known as red dwarfs.
- They are the most common stars in the Milky Way, but due to low luminosity, they are not visible to the naked eye.
- Prominent red dwarfs include Proxima Centauri, the closest star to the Sun.
Brown Dwarfs
- Brown dwarfs are considered "failed" stars, as they lack the mass needed to sustain nuclear fusion.
Wolf-Rayet Stars
- Wolf-Rayet stars were identified in 1867 and include over 220 known examples.
- They possess high temperatures ranging from 25,000 to 100,000 K and lose mass rapidly at over 10^-5 solar masses per year.
- Characterized by wind speeds exceeding 800 to 3,000 km/s, they typically start with masses under 20 solar masses and exhibit no dramatic variability.
OB Stars
- OB stars are hot, massive, early-type stars found in loosely organized groups known as OB associations.
- They have short lifespans, which influences their movement and association in star clusters.
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Description
Explore the intriguing world of stellar classification with these flashcards! Dive into how astronomers categorize stars based on their spectral characteristics. Each card will help you understand the significance of spectral lines and what they reveal about the universe.
