SPECTROSCOPY

To determine the way the Beta Persei system is organized, astronomers use a variety of methods. One of these is spectroscopy. It consists of splitting a beam of light into a spectrum of colors, or light with different wavelengths. It is used to detect what elements are present in an object.

The light emitted from an atom is a result from the movement of an electron from an excited to a ground state. In this process, the electron decreases its energy, relieving it as a photon. Because all elements have unique electron configurations, they have different spectra. They appear in spectrographs, the records of the spectrum, as lines at the corresponding wavelength.

In astronomy, spectroscopy is used to determine the composition of distant, light-emitting objects, such as stars. Furthermore, it can be used to measure the rate at which an object approaches to or retreats from Earth. If the object is coming closer, the spectral lines of the elements are shifted to lower wavelengths; this is the so called Blue Shift. If the object is moving away from the observer, the lines are shifted to longer wavelengths; this phenomenon is known as Red Shift. The blue and the red shifts result from the Doppler effect: if the source and observer are approaching, the observer will meet the waves emitted from the source more frequently (i.e. with a smaller wavelength) and vice versa.

In spectral analysis of binary stars, the Doppler shifts are different for the two stars, unless the plane of their orbit is parallel to the earth. This difference is variable and changes with the movement of the stars around each other. This is visible on spectrographs as multiplication of the lines of the elements: characteristic lines of one element can be present more than once. In the case when the system consists of two stars, two distinct spectra appear.

Some variable stars, such as Algol, cannot be observed as binary in any other way because the distance between the components is very small and they are very distant from Earth. This type of stars is called “spectroscopic binaries”.