Gamma Doradus star

from Wikipedia, the free encyclopedia

Gamma Doradus stars or also Gamma Doradus variables ( GCVS systematic abbreviation : GDOR ) are pulsation -variable stars that fluctuate in their luminosity due to non-radial pulsations on the surface . Such stars are typically young, on the main sequence, and have a spectral type between F0 and F2. Characteristic amplitudes of the brightness fluctuations are up to 0.1 magnitudes with periods between 0.4 and 3 days.

The prototype Gamma Doradus was identified as a variable star in 1963 and has long been considered a variable without reason . The assumption of non-radial vibrations as the cause of the light change is based on the exclusion of all other known mechanisms.

The absolute brightness of Gamma Doradus stars is between +3.1 and +1.9 mag, which corresponds to 5 to 15 times the luminosity of the sun. The effective temperature is in the range between 6950 and 7350 K , the radius between 1.43 and 2.36 solar radii and the mass between 1.51 and 1.84 solar masses. The radial velocities observed are low and lie between 1 and 4 km / s.

All Gamma Doradus variables lie on or slightly above the main sequence just outside or on the blue edge of the instability strip . With the narrow band of parameters, they are considered the most homogeneous group among the variable stars. In their position in the Hertzsprung-Russell diagram , the Gamma-Doradus variables and the Delta-Scuti stars partially overlap . Some stars could be classified as both Delta Scuti and Gamma Doradus stars ( hybrid pulsators ), as they show periods characteristic of Gamma Doradus stars on the order of days and short-period oscillations lasting from minutes to Hours typical of Delta Scuti stars.

The group of Gamma Doradus variables discovered is relatively small, and all known members belong to the young disc population . According to a theoretical work, Gamma Doradus stars can either be main sequence stars or just born stars that cross the Gamma Doradus instability strip . These two types differ in their mass and the depth of the outer convection layer . These differences should be reflected in the frequency spectrum so that an age can be determined with the help of asteroseismology .

Occurrence in star catalogs

The General Catalog of Variable Stars currently lists a little less than 100 stars with the abbreviation GDOR , which means that only about 0.2% of all stars in this catalog belong to the class of Gamma Doradus stars.

Examples

Individual evidence

  1. ↑ JR Percy: Understanding Variable Stars . Cambridge Univ. Press, Cambridge 2007, ISBN 978-0-521-23253-1 .
  2. ↑ LA Balona, K. Krisciunas, AWJ Cousins: gamma Doradus - Evidence for a New Class of Pulsating Star . In: Monthly Notices of the Royal Astronomical Society . tape 270 , 1994, pp. 905-913 .
  3. ↑ A. Tkachenko, H. Lehmann, B. Smalley, J. Debosscher, and C. Aerts: Spectrum Analysis of Bright Kepler γ Doradus Candidate Stars . In: Astrophysics. Solar and Stellar Astrophysics . 2012, arxiv : 1202.1116 .
  4. ↑ M.-P. Bouabid1, J. Montalban, A. Miglio, M.-A. Dupret, A. Grigahcene, and A. Noels: Theoretical seismic properties of pre-main sequence gamma Doradus pulsators . In: Astrophysics. Solar and Stellar Astrophysics . 2011, arxiv : 1103.4389 .
  5. ↑ Variability types General Catalog of Variable Stars, Sternberg Astronomical Institute, Moscow, Russia. Retrieved May 4, 2019 .