Properties of OH/IR stars with IRAS LRS spectra

Abstract

Abstract. 1858 OH satellite line (1612 MHz) maser sources associated with the IRAS counterparts were assembled from the literature. Cross-correlation between collected OH/IR -IRAS sources and the recent catalogue of the IRAS LRS spectra (Kwok et al. 1997) allows us to subdivide 1024 of them (after excluding OH sources with uncertain IRAS associations) into 10 groups according to the Volk & Cohen (1989) classification scheme. We have found that sources with silicate emission form the largest group (about 57%), followed by the group with silicate absorption (only about 16%). For more sensitive individual OH maser surveys these numbers differentiate even more and the ratio between silicate emission and absorption sources reaches a value close to 6. Surprisingly, we found an association of OH maser emission with a small number of stars with carbon-rich atmospheres. The distribution of these subgroups of OH/IR stars in the IRAS colour-colour and the period-colour diagrams as well as histograms of some physical properties are presented. The galactic distribution of important parameters (periods, IRAS colours, expansion and stellar velocities) for different classes of OH/IR sources is analyzed from the point of view of the stars' evolutionary status. The correlations among the periods, colours, expansion and star velocities and the pumping efficiencies for selected subgroups of OH/IR stars are also investigated. These analyses allow us to demonstrate that a significant fraction of silicate emission group sources do not form an evolutionary sequence with the silicate absorption objects -as is suggested e.g. by the IRAS colour-colour diagram, but rather form a lower initial mass sequence, i.e. these sources will never develop sufficient mass loss to manifest silicate absorption.

MONITORING OBSERVATIONS OF H2O AND SiO MASERS TOWARD POST-AGB STARS

“…We adopted the stellar velocity of −22.2 km s −1 derived from the OH maser emission (Chen et al 2001). As a whole, the peak velocity variations according to the observational epochs are not substantial (∼ ±1.8 km s −1 ).…”

Infrared properties of planetary nebulae with [WR] central stars

“…• 3639 (see Chen et al 2001 and references therein). Thus there is evidence for O-rich material in many [WR] PN.…”

Search for radiative pumping lines of OH masers

“…to check the frequency of the detection of this line. A preliminary analysis of available ISO data around 34.6 µm for OH-IR objects from the Chen et al (2001) catalog has been presented by Szczerba et al (2003). Here we present an improved analysis of 178 ISO Short Wavelength Spectrometer (SWS -de Graauw et al 1996) spectra obtained towards 87 galactic OH-IR objects with the aim to search for the 34.6 µm OH absorption line.…”