RV Tauri variable

RV Tauri stars are pulsating yellow supergiants whose light variation is characterized by alternating shallow and deep minima at round maxima.

Light change

The period of the light variation of RV Tauri stars is measured by a deep minimum to the next deep minimum and between 30 and 150 days. The amplitude can be up to 4 may achieve. Using the light curve, a division is made in two sub-groups:

• RVb: the minima is a long-period light changes, often superimposed in the form of a wave, with a cycle length from 600 to 1500 days.

The intensity changes are semi- regular basis. A defined period is always present, but the shape of the light curve is subject to changes in each cycle.

Spectrum

The spectral ranges from F or G to K at a maximum or minimum at M in the change of the radial speed of 10 to 50 km / s. This is characteristic of pulsationsveränderliche stars. In the spectra of RV Tauri stars shock waves were detected in the supergiant atmospheres, leading to a discontinuous course of the radial velocities. The presence of Balmer lines in emission, which are typical of early stars, and the typical late star titanium oxide absorption bands in making a determination of temperature and luminosity difficult.

Development Status

RV Tauri stars are old and rare stars. They show an infrared excess, caused by a strong stellar wind on the Asymptotic Giant Branch ( AGB). Either they are after a helium flash in the short term from the Terms and Conditions on a blue loop during which they cross the instability strip, or transform itself after the end of the AGB phase of a red giant to a white dwarf. Both stages were astronomically short and therefore was trying to find period changes in RV Tauri stars, to measure the speed and direction of development. However, the observed period changes are consistent with random noise. The masses of the RV Tauri stars have been estimated to be about one solar mass.

Cause of light variation

The light change is either a consequence of a 2:1 orbital resonance. The first harmonic is only half as long as the fundamental, which spans the period between two deep minima. After the second hypothesis show RV Tauri stars low dimensional chaos.

Hypothetical binary nature

The superimposed light change the RVb sub-group could be the result of a coverage in a wide binary system. From the strong stellar wind of the RV Tauri star, the companion material is stored in a torus around and this dust disk periodically covered the RV Tauri star. It has been suggested that all RV Tauri stars are formed in binary systems.