Long-period variables - Stellar and expansion velocities

Astronomy and Astrophysics – Astrophysics

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Masers, Radial Velocity, Silicon Oxides, Stellar Envelopes, Variable Stars, Absorption Spectra, Ground State, Hydroxyl Emission, Spectral Line Width, Thermal Emission

Scientific paper

We have detected emission from the J = 2-1 transition in the ground-vibrational state of SiO in 10 long-period variable stars. The line profiles are best understood as the result of thermal emission from an expanding circumstellar envelope. These lines clearly define the stellar radial velocity with uncertainties of about 1 km/s. Where comparisons are possible, the stellar radial velocity always falls near the midpoint of the double-peaked OH maser emission, and displaced toward the blue from the optical absorption lines. The evidence is now convincing that optical absorption lines are redshifted from the stellar velocity in long-period variable stars. The circumstellar expansion velocities deduced from the SiO line widths are correlated with stellar period in much the same way as are the velocity separations of the two OH maser peaks. In one star, NML Cyg, there is evidence for a ground-vibrational state maser.

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