Authors: F. Colomer, V. Bujarrabal
Journal: Transactions of IAA RAS vol. 40
Pages: 68 - 77
Keywords: VLBI, astronomical masers
Microwave amplification by stimulated emission of radiation (maser) processes are common in the Universe. These can be found in star formation regions, in circumstellar envelopes (CSEs) around evolved stars (mainly around AGB and post- AGB stars), in our and other galaxies. Since the maser emission is bright and compact, high resolution VLBI observations are a basic tool to study their distribution and other characteristics, therefore providing useful information to derive physical conditions in the regions where they occur. The advent of recent technological developments and instruments make now possible to study cosmic masers not only in a more efficient way, but also opens new scenarios for modeling of the emission. In particular, observations of several maser lines simultaneously provide unique information to constrain pumping models.