Stellar Winds and Interstellar Medium
Masers & (Post-)AGB stars

Hamburger Sternwarte - Research

Water vapor masers in stars departing from the AGB

Engels D., 2002, A&A 388, 252
Engels D., 2002, preprint

The 22 GHz water vapor masers of four ``non-variable'' OH/IR stars considered to be young Proto-Planetary Nebulae (PPNs) were monitored for more than 10 years. In two of them, OH 15.7+0.8 and OH 17.7-2.0 having Mira-like line profiles, the maser flux decreased and the maser finally disappeared. The decrease of the maser brightness is spectacular for OH 17.7-2.0 in particular. The maser had a flux density of several hundred Jansky in the eighties and is now absent since 1990. The masers of OH 15.7+0.8 and OH 17.7-2.0 probably emerged in the ``dying AGB wind'' during the mass loss reduction process accompanying the departure from the AGB. The other two, OH 12.8-0.9 and OH 37.1-0.8, have double-peaked profiles with a considerably larger velocity spread than the OH masers in these sources. The velocities are incompatible with the spherical symmetric mass loss process on the AGB and give evidence for the presence of probably bipolar outflows with a projected velocity of ve~28 km/s during the very early PPN phase. The gross structure of their profiles was rather stable during the monitor period while individual maser lines appeared and disappeared. An increase of the velocity range was found in both sources implying that the outflow is accelerating.

OH 17.7-2.0

The H2O maser lightcurve
All spectra 1987 - 1999 (also in Postscript )

OH 15.7+0.8

All spectra 1990 - 1997 and 1999 (also in Postscript )

OH 12.8-0.9 and OH 37.1-0.8

All spectra 1987 - 1999 of OH 12.8-0.9
All spectra 1990 - 1999 of OH 37.1-0.8 (both also in Postscript )

You may download all spectra in CLASS-Format:

OH 17.7-2.0, OH 15.7+0.8, OH 12.8-0.9, OH 37.1-0.8

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