Juan R. Pardo-Carrion
Main Results

11 years monitoring
of SiO maser sources


A long-term and short-spaced monitoring of 21 SiO maser sources, mostly evolved stars, has been carried out in two SiO maser lines at 43 GHz with the Observatorio Astron\'omico Nacional 13.7 meter telescope at the Centro Astronomico de Yebes (Guadalajara, Spain). The availability of optical light curves from the AAVSO for most of the objects during the whole period of the SiO monitoring, ground-based near-IR data for four sources overlapping with 3 to 5 observed SiO periods, and DIRBE near-IR data covering a significant portion of an SiO period in 10 sources, make this data set a unique reference for comparing optical, NIR and SiO variability in order to elucidate the physical mechanisms that pump SiO masers in evolved stars. A numerical time series analysis of the suitable SiO, optical and NIR light curves in regular variables has been performed to obtain precise values of the periods and phase lags between the different curves: There is evidence that in regular variable evolved stars the three types of emission have the same period and that the SiO maxima happen in phase with NIR maxima and with a phase lag typically between 0.05 and 0.20 with respect to optical maxima. Therefore, we conclude that in these objects the observational evidence presented in this work favors the radiative pumping of SiO masers against the collisional pumping.

You can get more information about this work by downloading paper 35 from my publications list.

Left: Optical and SiO v=1,2 J=1-0 light curves of Mira between mid 1984 and mid 1995. The v=2 curves have been shifted by 600 Jy (peak) and 2000 Jy km/s (area) for clarity. Right: Time evolution of the monitored SiO lines as a function of LSR velocity. The contours mark the following flux levels (in Jy): 20, 40, 60, 100, 200, 400, 600, 1000, and 2000 for both v=1 and v=2. Dates of optical maxima are indicated by vertical lines. The solid horizontal line in the right panels represents the velocity of the CO J=2-1 peak emission, the dashed horizontal lines are the velocities at which the CO emission is half of the peak, and the dotted horizontal lines represent the terminal velocities at which CO emission disappears. The small vertical ticks mark the dates of observations.

This figure is aimed at showing that the SiO maxima occur with some lag respect to the optical ones in the case of R Leo. This can be found in many other cases.