Mira variables

Roche COBAS MIRA variable 125 30 2-95 37 AMW,P disposable cuvettes... 

The ejected material forms a cool molecular and dusty envelope which initially veils the star from optical observations as it goes through the stages of Mira variable followed by OH-infirared star or infrared carbon star later the star becomes hot enough to ionize part or all of the expanding gas-dust envelope forming a planetary nebula. 

The physical parameters of the CO absorption layer in red (super)giant stars are very similar to those of the stationary layer of Mira variable star X Cyg mentioned above(Hinkle,Hall,Ridgway,1982). Thus,the presence of a separated stationary CO layer may be not restricted to Mira variable stars, but rather it may be a basic characteristics of red giant and supergiant stars in general. 

Mira variables form an important subgroup of the red giant stars which are typical representatives of stars showing burnt material at their surfaces. Since the photospheres of Miras are not in hydrostatic equilibrium but are characterized by spherically very extended density stratifications, their properties and emitted spectra differ substantially from those of non-Miras, and any attempts to analyse Mira spectra by means of conventional techniques must fail. Non-hydrostatic models are needed for analysis work. 

Nguyan-Q-Rieu, S. Deguchi, H. Izumiura, N. Kaifu, M. Okiski, H. Suzuki, and N. Ukita 185 Photospheres of Mira Variables... 

Mira variables 80-1,000 days Pulsating red giants 1,000 known... 

Figure 5. Spectrophotometric and polarimetric observations of the S-type Mira variable R And on 1973 June 22 [28],...

Molecules are frequently observed in the outer envelopes of red supergiants with surface temperatures less than about 5000 K. These stars have strong stellar winds, of order 10 to 10 M yr with velocities typically less than 50 km s . A few hotter stars, such as 89 Herculis and HD 161796, have also been found to show CO emission these and related stars are proto-planetary nebula objects in the process of becoming white dwarf stars. For some very highly evolved dusty stars, strong far-IR emission, indicative of dust, is accompanied by maser emission. These are the so-called OH/IR stars, which are most frequently Mira variables. Some evolved stars also show SiO masers. A few stars, such as the extreme supergiant IRC -t-10216, are veritable chemical factories, displaying almost all of the molecular species observed in comets and in dense interstellar molecular clouds. 

Fig. 7.4 Cartoon representation of the location of SiO and H2O masers in the inner envelope of a Mira variable. The star is located in the lower left comer. The abscissae give from top to bottom the radial distance from the star in stellar radii, astronomical units, and miUiarcseconds if observed at the Galactic center distance. SiO masers arise from within a few steUar radii of the central star, while H2O masers from the vibrational ground state arise from regions somewhat further out in the envelope, where dust formation is occuring. Image credit Menten, K.M., MPIfR (Sub)miUimeter Astronomy Group...

Searches for 1612-MHz OH and 22 335-MHz H2O maser emission from symbiotic Mira variables were reported by Seaquist, Ivison, and Hall, 1995 [303]. Because only two cases were found a mechanism for the deficiency was proposed. A powerful wind from the hot companion sweeps much of the volume of the dusty Mira wind away from the hot companion, thus exposing the Mira to UV emission. The UV emission then photodissociates molecules responsible for all known masers. 

First,one important result of the infrared molecular spectroscopy is a discovery of stationary CO layer in Mira type variable star x Gyg, in which CO lines that stay stationary have been clearly separated from the photospheric CO lines that show cyclic Doppler-shifts by the large amplitude pulsation of the photosphere in time series spectra( Hinkle, Hall, Ridgway, 1982). It was suggested that the stationary CO layer may be located at several stellar radii above the stellar surface, since excitation temperature of the stationary CO layer of x Cyg was found to be 800K. 

M ira-type variable star (Mira Ceti variable) A star in the red giant or red supergiant category whose radiated energy varies regularly over a quite long period. Pulsation of the surface layers is thought to be the cause of the variation, which recurs every 2 to 30 months. The stars are named after their prototype, Mira Ceti. 

The presence of water in the atmosphere of cool stars was already predicted by Russell in 1934. His calculations showed that water should be the most abundant molecule besides the H2 molecule and atomic hydrogen for cool stars at about 2800 K. The first detection of water was made in the spectrum of the well known star Mira. This is a pulsating variable star, an expansion and contraction produces large change in temperature and radius and therefore strong variations in its luminosity are observed. Kuiper (1963) observed Mira in the wavelength range from 1400 nm to 1900 nm. 

---