Fr.: bande de l'instabilité
A narrow, almost vertical, band on the right hand side of the → main sequence in the → H-R diagram occupied by many different types of → pulsating stars (→ RR Lyrae, → Cepheids, → W Virginis, → ZZ Ceti). Stars traverse this region at least once after they leave the main sequence. The narrow temperature range of the instability strip corresponds to the stellar → effective temperature that can sustain → partial ionization zones, capable of maintaining stellar oscillations. The blue (hot) edge of the instability strip pertains to stars with surface temperatures hotter than ~ 7500 K. Because these stars have partial ionization zones too close to their surface, the pulsation mechanism is not active. The red (cooler) edge of the instability strip is determined by stars with a temperature lower than ~ 5500 K. In these stars convection prevents the build-up of heat pressure necessary to drive pulsations.
ram pressure stripping
loxtâneš bâ fešâr-e qucvâr
Fr.: balayage par la pression dynamique
A process proposed to explain the observed absence of gas-rich galaxies in → galaxy clusters whereby a galaxy loses its gas when it falls into a cluster. There is a tremendous amount of hot (~ 107 K) and tenuous (~ 10-4 cm-3) gas (several 1013 → solar masses) in the → intracluster medium (ICM). Ram pressure stripping was first proposed by Gunn & Gott (1972) who noted that galaxies falling into clusters feel an ICM wind. If this wind can overcome the → gravitational attraction between the stellar and gas disks, then the gas disk will be blown away. The mapping of the gas content of spiral galaxies in the → Virgo cluster showed that the → neutral hydrogen (H I) disks of cluster spiral galaxies are disturbed and considerably reduced. Their molecular gas, more bound to the galaxy, is less perturbed, but still may be swept out in case of very strong ram pressure. These observational results indicate that the gas removal due to the rapid motion of the galaxy within the intracluster medium is responsible for the H I deficiency and the disturbed gas disks of the cluster spirals (e.g., J. A. Hester, 2006, ApJ 647:910).
1) navâr; 2a) loxtândan, loxt kardan, 2b) loxtidan, loxt šodan
Fr.: 1) bande; 2a) désabiller, décaper, démonter, 2b) se désabiller
1) M.E. probably from M.L.G. strippe "strap, thong,"
related to stripe.
1) Navâr "strip."
Fr.: balayage par effet de marées
The phenomenon whereby gas and stars are ripped out from a gravitationally → bound system, such as a galaxy or → globular cluster, by the action of → tidal forces from an external, more massive object. See also → ram pressure stripping.
Fr.: balayé par effet de marées