Hertzsprung progression

from Wikipedia, the free encyclopedia

The Hertzsprung progression describes a hump in the light curve of classic Cepheids and is named after the author of the first scientific description of the phenomenon, Ejnar Hertzsprung .

In Population I cepheids with periods shorter than six days, no hump can be detected in the first approximation of the sinusoidal light curve. From a pulsation period of six days, the hump appears in the descending branch of the light curve. As the period increases, the hump moves in the direction of the maximum and its amplitude increases. With a period of about ten days, the Cepheide shows a double maximum, since the regular maximum and the hump almost coincide in time. For even longer periods, the hump appears in the rising branch of the light curve, with the amplitude gradually decreasing again. The disturbance of the light curve can also be detected in the course of the radial velocities from the spectral lines .

The cause of the Hertzsprung progression is considered to be a shock wave that is triggered in the zone of the pulsation-variable star in which the kappa mechanism works and runs into the star. It is reflected from the denser layers in the star's interior and causes the hump in the light curve when it penetrates the photosphere of the Cepheid. The Hertzsprung progression can be used to determine the mass of the Cepheid.

literature

  • Mine Takeuti (Editor), Dimitar D. Sasselov (Editor): Stellar Pulsation: Nonlinear Studies (=  Astrophysics and Space Science Library . Volume 257). Kluwer Academic; 1 edition, Dordrecht 2001, ISBN 0-7923-6818-5 .
  • John R. Percy: Understanding Variable Stars . Cambridge University Press, Cambridge 2007, ISBN 978-0-521-23253-1 .
  • C. Aerts (Author), J. Christensen-Dalsgaard (Author), DW Kurtz (Author): Asteroseismology (=  Astronomy and Astrophysics Library ). Springer Verlag, Berlin 2010, ISBN 978-1-4020-5178-4 .