Instability Strip

Instability Strip
A Hertzsprung-Russell diagram showing the location of the instability strip.

Instability Strip
A region in the Hertzsprung gap (q.v.) occupied by pulsating stars in a post-main-sequence stage of stellar evolution.

Instability Strip
The region of the H-R diagram in which stars are unstable to pulsation. A star passing through this strip becomes a variable star.
Intercrater Plain ...

INSTABILITY STRIP
A region of the Hertzsprung-Russell diagram wherein a large number of variable stars are to be found.
INTENSITY ...

Instability Strip - A region of the H-R diagram occupied by pulsating stars, including Cepheid variables and RR Lyrae stars
Intercrater Plain - Smooth portions of the surface of Mercury that lie between and around clusters of large craters ...

instability strip on H$-$R diagram
stellar pulsation, periods $1-90$ days
RR Lyrae (fainter, lower mass)
Cepheids (brighter, higher mass)
period$-$luminosity relation
distance estimates ...

The Instability Strip is located in the upper part of the H-R diagram, so the stars that tend to pass into it are either Red Giants or Supergiants.

(of the RR Lyrae instability strip) The curve on the H-R diagram that is traced out by the maximum temperature at which a stellar model is unstable against small-amplitude pulsations as the luminosity is varied.

These variables are located in a certain region of the HR diagram known as the "instability strip." This strip lies up above the main sequence near the red giant region.

instability strip
instantaneous bandwidth
Integral Sign Galaxy (UGC 3697)
interacting binary
Interamnia (minor planet 704)
interferometer
intergalactic absorption
intergalactic magnetic field
intergalactic medium (IGM) ...

The conditions necessary to cause pulsations are not found in main-sequence stars; they occur in evolved post"main-sequence stars as they pass through a region of the Hertzsprung"Russell diagram known as the instability strip (Figure 23.6).

A nearly vertical region of the HR diagram, known as the instability strip, is occupied by pulsating variable stars known as Cepheid variables. These stars vary in magnitude at regular intervals, giving them a pulsating appearance.

These are lower-luminosity stars, where the instability strip crosses the horizontal branch. They may appear on cluster H-R diagrams by omission in the "RR Lyrae gap", since variables are usually not plotted.

They lie in the instability strip of the Hertzsprung-Russell diagram and suffer instabilities that cause their size to periodically change. This change in size also changes the temperature of the star giving rise to their variability.

The reason the RR Lyrae stars are divided into these classes is due to their location within the Cepheid instability strip.

RR Lyraes fit on the Instability Strip on an HR diagram.
RV Tauri
RV Tauri variables are yellow supergiants, mostly G and K-class stars.

A5 and G0 spectral type and between +1 and -3 absolute magnitudes (i.e. between the top of main sequence and the giants in the horizontal branch). RR Lyrae stars can be found in the left of this gap. Hertzsprung gap is a subset of instability strip.

Also called ZZ Ceti stars, they lie on the extended instability strip and vary by a few tenths of a magnitude over periods of minutes. Temperatures range from 10,500 to 13,000 Kelvin.
DB: White dwarf variables with pure helium outer layers.

These stars pulsate because the hydrogen and helium ionization zones are close to the surface of the star. This more or less fixes the temperature of the variable star, and produces an instability strip in the H-R diagram.

They have a relatively narrow mass range, and when plotted by their luminosity versus their color (called a Hertzsprung-Russell diagram), they fall within a narrow band that is called the instability strip.

They may also have variable amplitudes resulting from the superposition of two simultaneous pulsation periods. Like their normal relatives, their variability results from being located in a region of the known as the instability strip.

See also: Star, Luminosity, Sun, Temperature, Time