SiO masers in OH/IR stars, proto–planetary and planetary nebulae^*

¹ ESO/La Silla, Casilla 19001, Santiago 19, Chile
² Onsala Space Observatory, S–439 92 Onsala, Sweden
³ Australia Telescope National Facility, PO Box 76, Epping, NSW 2121, Australia
⁴ Stockholm Observatory, S–133 36 Saltsjöbaden, Sweden

Send offprint request to: L.–Å. Nyman (ESO address)

Received: 28 February 1996
Accepted: 5 May 1997

Abstract

We present a search for SiO masers towards a sample of 126 objects including OH/IR stars, proto–planetary and planetary nebulae. All objects are classified as oxygen–rich, and most of them are associated with OH or masers. SiO masers were found only in variable objects like the OH/IR stars and a few objects classified as proto–planetary nebulae, but with variable central stars that may be part of binary systems. In one object, OH 15.7+0.8, which appears to be varying irregularly and most likely recently left the AGB, an SiO maser was tentatively detected. Thus, we conclude that variability and SiO maser emission are closely linked, and that SiO masers disappear very soon after a star has reached the end of the AGB, when pulsation and mass loss cease.