Module 5: Stellar Evolution and Classification

As the surface temperature of a star increases, the wavelength of maximum brightness

• decreases

• stays the same

• increases

• may change. More information is needed.

Answer explanation

•This is according to Wien’s Law, which says temperature and peak wavelength are inversely proportional

If you detect a star that has weak lines of hydrogen and helium in its spectrum, what is the most likely conclusion?

• The star formed primarily out of heavier elements

• The star's photosphere has a low temperature

• The star's photosphere has a high temperature

• The star's photosphere is unusually dense

Answer explanation

•O-F type stars have strong (A have the strongest) Hydrogen absorption lines. Cooler stars lack strong H absorption lines.

A star that is cool and very luminous must have

• a very large radius

• a very small radius

• a very small mass

• a very great distance

• a very low velocity

Answer explanation

•To be a cool star and still have a high luminosity means the star is large, like a red supergiant.

Stars that appear red but are not very luminous are located in what part of the H-R diagram?

• Upper left

• Lower left

• Upper right

• Lower right

• Near the Sun

Answer explanation

•These stars are the red dwarfs

After its main sequence phase, the Sun's luminosity will

• decrease

• stay approx. the same

• increase

• steadily fluctuate about its main sequence luminosity

Answer explanation

•The sun will move right (toward lower temperature) and up (toward higher luminosity) when it moves off of the main sequence and enters its giant phase.

A star leaves the main sequence when

• it has converted all of its hydrogen into helium throughout the star

• it has converted all of its hydrogen into helium in its core

• it has converted all of its helium into carbon in its core

• it begins to fuse hydrogen into helium in its core

Answer explanation

•This is the beginning of the transition to becoming a giant star

As low-mass stars evolve off the main sequence, they become more luminous because

• surface temp increase

• surface temp decrease

• sizes increase

• sizes decrease

• surface temp + sizes both increase

Answer explanation

•Although the temperature of a star decreases after is moves off of the main sequence, the large increase in radius while becoming a giant causes an increase in overall luminosity.

Which of the following is not a possible stellar remnant?

• Brown dwarf

• White dwarf

• Neutron star

• Black Hole

Massive stars have shorter lifetimes than low mass stars bc massive stars

• have low core temps, which means the average particle speeds are slower

• have less hydrogen in their cores to fuse into helium

• fuse hydrogen more rapidly in order to supply the energy needed to support their masses

• have lower luminosities, meaning they produce less energy

As a star like the Sun evolves into a red giant, its core..

• expands + cools

• contracts + heats

• turns into iron

• expands + heats

• turns into uranium