Phase–Referencing Observations of Galactic Circumstellar Masers

Circumstellar masers

Circumstellar masers are unique tools for probing the envelopes around low mass dying stars using VLBI. In this contribution I briefly review the status of our knowledge on these emissions, especially focusing on the latest results obtained by means of VLBI observations. I also outline some of the new windows that will open for VLBI maser research thanks to the upcoming new instrumentation.

Astrometry of Circumstellar Masers

The circumstellar masers around evolved stars offer an interesting possibility to measure stellar parameters through VLBI astrometry. In this paper the application of this technique is discussed, including the accuracy and the uncertainties of the method. The different maser species (OH, H2O, SiO) have slightly different characteristics and applications. This paper does not concern astrometry o...

Single - dish monitoring of circumstellar water masers

We present an overview of the long-term H 2 O maser monitoring program of a sample of late-type stars, carried out with the Me-dicina 32-m and Effelsberg 100-m telescopes, and describe the results in some detail. The role the SRT could play in this program is outlined.

Methanol Masers as Tracers of Circumstellar Disks

VLBI Observations of Water Masers in the Circumstellar Envelope of IRC+60169

Water masers around an AGB star, IRC+60169, were observed at four epochs using the Japanese VLBI networks. The distribution of the maser features is limited in a thick-shell region, which has inner and outer expansion velocities of 7 km s and 14 km s at radii of 25 mas and 120 mas, respectively. The distribution of the red-shifted features exhibits a ring-like structure, the diameter of which i...