- published: 29 Sep 2015
- views: 131
The Instability strip is a nearly vertical region in the Hertzsprung–Russell diagram which is occupied by pulsating variable stars (including RR Lyrae variable, Cepheid variable, W Virginis variable, ZZ Ceti variable, RV Tauri variable, Delta Scuti variable, SX Phoenicis variable and rapidly oscillating Ap stars).
The instability strip intersects the main sequence in the region of A and F stars (1–2 solar mass) and extends upwards almost vertically (slightly inclined to the right) to the highest luminosities. The lower part of instability strip appears as the Hertzsprung gap on the Hertzsprung–Russell diagram.
Stars in the instability strip pulsate due to He III (doubly ionized helium). In normal A-F-G stars He is neutral in the stellar photosphere. Deeper below the photosphere, at about 25,000–30,000K, begins the He II layer (first He ionization). Second ionization (He III) starts at about 35,000–50,000K.
When the star contracts, the density and temperature of the He II layer increase. He II starts to transform to He III (second ionization). Opacity increases and the energy flux from the interior of the star is effectively absorbed. The temperature of the layer increases and it starts to expand. After expansion, density and temperature decrease and He III begins to recombine into He II. The outer layers contract and the cycle starts from the beginning.
Cepheid variable - Video Learning - WizScience.com
Instability Strip - 3MBS Interview
KT Tape: Ankle Stability
Cepheid variable
Massive Israeli Strike-back on Gaza Strip (Disturbing Video)
Sounds of Threat - "Mental Instability" SquidHat Records
Low-dimensional chaos in stellar pulsations - Video Learning - WizScience.com
Strip Of Wind | Tokyo Metropolitan Art Museum
06 ChronOS Strip
Las Vegas Strip Hotels
GETTING A GIRLFRIEND IN GTA 5 Ep.2 (Gta 5 Online Love Story)
Political Instability-The Main Cause of Under-development
BUILD UP TO WWIII ISRAEL POUNDS HAMAS (GAZA STRIP) 12/17/12
Hypergiant star Rho Cassiopeia tribute