Astronomy and Astrophysics – Astronomy
Scientific paper
May 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999arep...43..311p&link_type=abstract
Astronomy Reports, Volume 43, Issue 5, May 1999, pp.311-324
Astronomy and Astrophysics
Astronomy
3
Scientific paper
Observations of the circumstellar maser emission of the M supergiant VX Sgr in the water-vapor line at 1.35 cm are presented. The observations were carried out from 1981-1998 (JD 2 444 655-2 450 966) on the 22-m radio telescope of the Pushchino Radio Astronomy Observatory of the Astro Space Center of the Lebedev Institute of Physics. Throughout the 17 years of the observations, there were two groups of emission features in the H2O-line profile, which originate in the two oppositely directed lobes of a bipolar outflow from the star. A redistribution of the integrated flux F_int between the two groups of features was noted: in 1981-1987, the group with negative velocities (V_LSR < V_*, where V_* is the stellar velocity) dominated; starting from 1993, F_int for the features with V_LSR > V_* slightly exceeded that for features with V_LSR < V_*. This redistribution of F_int in the H2O-line profile may be associated with a change in the dominant direction for the bipolar outflow due to restructuring of the overall dipolar magnetic field of VX Sgr. A model for the VX Sgr H2O maser source with a circumstellar disk and bipolar outflow in two cones with half-opening angle theta ~ 60deg is discussed. The axis of the bipolar outflow also forms an angle i ~ 60deg to the line of sight. The estimated bipolar-outflow expansion velocity V_0 in the H2O-maser region (R = (1.5-5) x 10^15 cm) is ~10 km/s. The variability of the H2O maser is correlated with the visual light curve of VX Sgr. However, the phase delay delta phi of the F_int(H2O) variations relative to the optical variations changed form 0 to ~1 stellar period (P = 732d) over the time covered by the maser observations. If the variability of the H2O-maser source is the result of periodic impacts of shock waves driven by stellar pulsations, the travel time for the shock from the photosphere to the inner boundary of the H2O maser shell may be as long as (10-15)P.
Pashchenko M. I.
Rudnitskii Georgii M.
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