Gamma Doradus variables are
variable stars
A variable star is a star whose brightness as seen from Earth (its apparent magnitude) changes with time. This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are classified as e ...
which display variations in
luminosity
Luminosity is an absolute measure of radiated electromagnetic power (light), the radiant power emitted by a light-emitting object over time. In astronomy, luminosity is the total amount of electromagnetic energy emitted per unit of time by a st ...
due to non-radial pulsations of their surface. The stars are typically young, early F or late A
type main sequence
In astronomy, the main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Her ...
stars, and typical brightness fluctuations are 0.1
magnitudes with periods on the
order of one day. This class of variable stars is relatively new, having been first characterized in the second half of the 1990s, and details on the underlying physical cause of the variations remains under investigation.
![GammaDorLightCurve](https://upload.wikimedia.org/wikipedia/commons/d/db/GammaDorLightCurve.png)
The star
9 Aurigae was first noticed to be variable in 1990. However, none of the currently-accepted explanations were adequate: it pulsated too slowly and was outside of the
Delta Scuti
Delta Scuti, Latinized from δ Scuti, is a variable star in the southern constellation Scutum. With an apparent visual magnitude that fluctuates around 4.72, it is the fifth-brightest star in this small and otherwise undistinguished con ...
instability strip
The unqualified term instability strip usually refers to a region of the Hertzsprung–Russell diagram largely occupied by several related classes of pulsating variable stars: Delta Scuti variables, SX Phoenicis variables, and rapidly oscillati ...
, and there was no evidence for any eclipsing material, although
Gamma Doradus
Gamma Doradus, Latinized from γ Doradus, is the third-brightest star in the southern constellation of Dorado. It is faintly visible to the naked eye with an apparent visual magnitude of approximately 4.25, and is a variable st ...
and
HD 96008 were noted to be similar.
These three stars, as well as
HD 224638, were soon hypothesized to belong to a new class of variable stars in which variability was produced by
g-mode pulsations rather than the
p-mode pulsations of Delta Scuti variables.
HD 224945 and
HD 164615 were noticed to be similar as well, while HD 96008 was ruled out on the basis of its more regular period.
Eclipses
An eclipse is an astronomical event that occurs when an astronomical object or spacecraft is temporarily obscured, by passing into the shadow of another body or by having another body pass between it and the viewer. This alignment of three ce ...
and
starspot
Starspots are stellar phenomena, so-named by analogy with sunspots.
Spots as small as sunspots have not been detected on other stars, as they would cause undetectably small fluctuations in brightness. The commonly observed starspots are in gene ...
s were soon ruled out as the cause of the Gamma Doradus' variability,
and the variability of 9 Aurigae was confirmed to be caused by g-mode pulsations a year later, thus confirming the stars as the prototypes of a new class of variable stars.
Over ten more candidates were quickly found,
and the discoverers dubbed the group the ''Gamma Doradus stars'', after the brightest member and the first member found to be variable.
List
References
{{Variable star topics