Astronomy and Star Formation Notes Winter 2025

STAR TYPES

• Solar Neighborhood: Examined stars within 21 light years of the Sun,

  • Types: A-stars, F/G stars, K/M stars, white dwarfs, brown dwarfs.

• Most luminous stars are observable even from great distances.

BINARY STARS

• Two types: visual binaries, spectroscopic binaries, eclipsing binaries.

• Characteristics are determined using Kepler's Third Law.

MASS-LUMINOSITY RELATIONSHIP

• Non-linear relationship between mass and luminosity (more massive stars = much more luminous).

STELLAR SIZES AND MEASUREMENTS

• Use light curves to measure stellar diameters; relate luminosities and temperatures.

• Hertzsprung-Russell Diagram: correlates stellar characteristics (spectral class vs luminosity).

  • 90% of stars are main sequence; demonstrates evolutionary stages.

INTERSTELLAR MEDIUM

• Extremely low density materials fill the space between stars, contributes significantly to overall mass.

  • Comprises mostly gas, particles, and dust; can glow due to heat from stars.

STAR FORMATION

• Begins in molecular clouds, collapses under gravity to form protostars and then into stars eventually.

  • Disks form around protostars; conservation of angular momentum is critical.

PLANET FORMATION

• Disks around protostars become regions for planet formation, influenced by core mass.

EXOPLANET DETECTION METHODS

• Radial Velocity Method: Detects wobbles of stars due to orbiting planets.

• Transit Method: Measures light dips when planets pass in front of stars; requires multiple transits.

• Direct Method: Challenges include distinguishing faint planets from bright stars.

THOUGHT QUESTION

• Exoplanets in eccentric orbits spend more time further away, as per Kepler's second law.