Introduction

The study of stellar spectra provides astronomers with crucial information about stars' physical properties. When we analyze the light from stars using spectroscopy, we can determine their temperature, chemical composition, motion, and density. This article explores how scientists extract this valuable information from stellar spectra.

Understanding Stellar Spectra

A stellar spectrum is created when starlight is spread out into its component wavelengths. While stars emit a continuous spectrum of radiation, their outer layers absorb specific wavelengths of light, creating dark lines called absorption lines. These absorption lines form a unique pattern that reveals important information about the star's properties.

Surface Temperature

The surface temperature of a star can be determined by analyzing the peak wavelength of its spectrum. This relationship is described by Wien's displacement law:

$\lambda_{max} = \frac{2.898 \times 10^{-3}}{T}$

where:

Stars with higher surface temperatures have shorter peak wavelengths, following an inverse relationship.

Chemical Composition

The absorption lines in a stellar spectrum act as a chemical fingerprint of the star's composition. These lines form when atoms in the star's outer layers absorb specific wavelengths of light, corresponding to electron transitions between energy levels. By comparing these absorption patterns with known spectral lines of elements measured on Earth, astronomers can identify the chemical elements present in the star's atmosphere.

Stellar Motion

Translational Motion

The Doppler effect allows astronomers to measure a star's motion relative to Earth:

Rotational Motion

A star's rotation affects its spectral lines:

The combined effect creates broadened absorption lines, with the amount of broadening indicating the star's rotational velocity.

Density

The width of absorption lines also provides information about stellar density. In denser stars, increased gas pressure leads to more frequent atomic collisions, affecting electron energy levels. These interactions cause variations in absorption wavelengths, resulting in broader spectral lines. Therefore, broader absorption lines generally indicate higher stellar density.