Journal of Physical Studies 12(1), Article 1301 [5 pages] (2008) DOI: https://doi.org/10.30970/jps.12.1301 RADIO SPECTROSCOPY OF LATE-TYPE VARIABLE STARS G. M. Rudnitskij Sternberg Astronomical Institute, Moscow State University 13 Universitetskij prospekt, Moscow, 119991, Russia gmr@sai.msu.ru

The results of the monitoring of a sample of late-type variable stars (Mira Ceti-type and semiregulars) are reported. Since 1980 a sample of 60 stars has been observed in the maser line of the H$_2$O molecule at a wavelength of 1.35 cm. The observations are performed on the RT-22 radio telescope of the Pushchino Radio Astronomy Observatory. Since 1994 optical spectra of some of these stars have also been monitored on the 1.25-meter telescope of the Crimean Laboratory of the Sternberg Astronomical Institute. Variations of the circumstellar H$_2$O masers correlate with the visual light curves with a time lag of 0.3-0.4$P$ ($P$ is the star's period). Flares of the H$α$ emission noted in R Leo, U Aur, R Cas, and R LMi were followed 1.5-2 years later by the corresponding flares of the H$_2$O masers. These phenomena can be interpreted as a consequence of propagation of a shock wave driven by stellar pulsation. However, radio continuum observations suggest that such shocks (if any) may be rather weak, with a velocity that does not exceed 15-20 km/s. Alternatively, the shock can be produced by the motion of a low-mass companion (a planet or a brown dwarf) in the inner layers of the circumstellar envelope. The effects of such a companion on the spectrum and light curve of the primary star are discussed. It is shown that a cone shock (similar to that produced in the Earth's atmosphere by the motion of a large meteoritic body) can produce sufficient Balmer line emission without significant accompanying radio continuum. The companion's motion may also account for a significant portion of the primary's light variations without invoking large-amplitude stellar pulsations, which so far have been accepted as the main mechanism of Mira-type variability in red giants.

PACS number(s): 33.20.Bx, 95.85.Bh, 97.20.Li, 97.30.-b, 97.60.-s, 97.10.Fy

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