| We present the results of a search for 1612 MHz OH circumstellar masers in a colour limited sample of cool IRAS sources. 41 previously unknown detections are reported. This work is the fourth part of the surveys of IRAS evolved stars. A comprehensive comparison between the results herein and those obtained previously, is developed. Special attention is given to the relationship between the satellite and main line data and, to the evolution of the circumstellar environment along the sequence of reddening colours. The maser profiles indicate an evolving envelope in which the main and satellite line masers are produced in regions with a similar velocity field. Indications for the detachment of a part of the cirumstellar envelope, or its splitting into two distinct envelopes where a peripheral deceleration might occur in the exterior parts of the outer envelope, are deduced from the profiles of the objects exhibiting both a main and satellite line maser, and further suggested by the detection rates. It is shown that, contrary to the expected, the envelope does not homogenize with reddening colours. With a roughly equal contribution, the large number of 35 and 53 m photons can easily invert the satellite line. Enough IR photons are available to simply pump the main line in many of the objects but for several others, an enhancing mechanism such as line overlap is required. The dumpiness of the circumstellar envelope for a large set of sources is measured. The results obtained have been used to clarify some of the points of the various evolutionary scenarios that have been proposed. |
Comments:
Spectral type was set to:
""S"", where only one peak was found.
""D"", where two peaks were found.
IRAS 17135-2748 renamed as
IRAS 17135-2748A
IRAS 17392-2722 removed
IRAS 17428-2438 (second object) renamed as
IRAS 17428-2438A
IRAS 18568+0550 (second object) renamed as
IRAS 18568+0550A
IRAS 22577+6609 renamed as
IRAS 22574+6609
Velocity resolution: 0.6 and 1.2 km/s
Upper limit for non-detections: 0.15 Jy (3σ)
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