Variable Stars and Their Pulsations

Cepheid variable stars pulsate due to a delicate balance between the outward pressure from radiation and the inward pull of gravity. As the star expands, it cools and the radiation pressure decreases, causing it to contract. This contraction heats the star, increasing the radiation pressure and causing it to expand again, repeating the cycle.

The pulsation period of a Cepheid variable star is directly proportional to the square root of its average luminosity. This relationship, known as the Leavitt Law, is crucial for using Cepheids as distance indicators in astronomy.

RR Lyrae variable stars have pulsation periods ranging from about 0.2 to 1 day. They are typically old, low-mass stars that are in the horizontal branch of the Hertzsprung-Russell diagram.

Mira variable stars exhibit non-radial pulsations, where different parts of the star's surface pulsate with different amplitudes and phases. This results in the characteristic irregular light variations observed in these stars.

Delta Scuti variable stars pulsate due to convection in their outer layers. The convective motions generate acoustic waves that propagate through the star, causing it to pulsate.

White dwarf variable stars, also known as pulsating white dwarfs, have pulsation periods ranging from seconds to minutes. These pulsations are driven by various mechanisms, including convection, rotation, and magnetic fields.

Beta Cephei variable stars exhibit non-radial pulsations, with different parts of the star's surface pulsating with different amplitudes and phases. These pulsations are driven by instabilities in the star's radiative envelope.

BL Herculis variable stars pulsate due to magnetic field interactions in their stellar atmospheres. These interactions generate Alfvén waves that propagate through the star, causing it to pulsate.

SX Phoenicis variable stars exhibit radial pulsations, where the entire star expands and contracts in unison. These pulsations are driven by instabilities in the star's outer layers.

ZZ Ceti variable stars pulsate due to convection in their outer layers. The convective motions generate acoustic waves that propagate through the star, causing it to pulsate.

RV Tauri variable stars exhibit mixed-mode pulsations, where both radial and non-radial pulsation modes are present. These pulsations are driven by instabilities in the star's outer layers.

V1093 Herculis variable stars pulsate due to magnetic field interactions in their stellar atmospheres. These interactions generate Alfvén waves that propagate through the star, causing it to pulsate.

Pulsating subdwarf B stars have pulsation periods ranging from minutes to hours. These pulsations are driven by instabilities in the star's outer layers.