Stellar Spectral Classification Flashcards

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.