Gaia Focused Product Release (en)
Gaia Focused Product Release
Gaia Observations of Mira Long Period Variables
The Gaia Mission of the European Space Agency has observed thousands of pulsating cool giant stars. Gaia has repeatedly observed these variable stars for more than five years since launch in 2013.
Red giants are about ten to hundreds of times larger than the Sun, while their outer envelope is lower in temperature giving them a yellowish-orange hue. They have luminosities up to nearly three thousand times that of the Sun, with spectral types of K or M, and surface temperatures of 2700 to 3700 degrees Celcius. The outer layers of these large red stars continuously expand and contract over long periods of time, from about a hundred to 400 days.
The red giant star Mira is considered the prototype of the long period variables. The atmospheric pulsations cause the periodical brightness variability observed by Gaia. But Gaia also observes the spectrum from which the envelope expansion and contraction velocities are measured. The dark spectral lines move back and forth, changing their wavelength positions due to the Doppler effect. The spectral line shifts are proportional to the velocities with which the envelope contracts and expands in our line-of-sight to the red giant.
The Gaia Data Archive offers the largest sample of velocity and brightness curves of Mira variables observed to date.