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Using the characteristics of the KVN 4 band receiving system, we set up following scientific goals. (1) We aim at investigating spatial structures and dynamical effects from SiO to 22 GHz H2O maser regions (i. e., atmosphere to circumstellar envelope) according to stellar pulsation through simultaneous monitoring observations of KVN 4 bands using both KVN single dish and VLBI network. The SiO maser lines, due to their high excitation temperature and density, are suitable for investigating nearby regions of central star which are under accelerating and decelerating by the influence of a stellar pulsation. On the other hand, 22 GHz H2O maser traces the region above dust forming layer in which outflow velocities approach to a terminal velocity of mass-loss. Therefore, both masers are good probes for investigating the development of outflow motion and asymmetry from the atmosphere to the circumstellar envelope. Furthermore, we can investigate the shock propagation effect from SiO to H2O maser regions because both masers are affected by shock waves. These works will lead us to understand how the mass-loss process is connected to stellar pulsation.
(2) Mutual association and difference between SiO and H2O maser properties are also investigated based on combined studies of SiO and H2O masers for a basis. In the last analysis, SiO and H2O maser models coupled to hydrodynamical model of circumstellar envelope should be established.
(3) We trace correlation and difference of SiO maser properties including spatio-kinematic properties among SiO J = 1-0, J = 2-1, and J = 3-2 transition masers according to different type of stars (for example, H2O strong, weak and non-detected sources, SiO v = 2, J = 2-1 rare maser detected sources). Our goal is to constrain SiO maser pumping models which are still under debate between collisional and radiative pumping models including the effects of line overlap between the ro-vibrational transitions of SiO and H2O.
(4) Through the development of outflow motion and asymmetry from SiO to H2O maser regions in individual stars at different evolutionary stages, we want to find a clue to the dynamical evolution from AGB to post-AGB stars connected to the development process of asymmetric mass-loss, for example, bipolar outflow and water fountain jet motions. In parallel, we make an effort to examine the cause of large detection rates of SiO v= 2, J = 1-0 only maser emission at late AGB evolutionary stage and different detection rates between SiO and H2O masers in post-AGB RI and LI regions which are obtained from the KVN single dish results.
Using both KVN single dish and VLBI network, we perform regular monitoring of H2O 22 GHz / SiO 43/86/129 GHz bands toward 15 objects of KSP (every one-two months according to their periods). Three years as the first term of KSP are required for covering at least 2 pulsation periods of 15 sources. Single dish monitoring observations at 4 bands go on being performed toward 15 objects for grasping the global features of SiO and H2O masers and for reciprocally complemented researches with VLBI. Total integration time for each target source is required for about 5 hours in order to obtain a sufficient (u, v) coverage for a good quality imaging. Therefore, we need ~350 hrs per year for VLBI monitoring and ~100 hrs for single dish monitoring. Source Frequency Phase Referencing (SFPR) technique will be adopted for registering both H2O and SiO masers using the KVN 4-bands receiving system for simultaneous observations at different bands.
Note: These sources were selected from KVN single dish and VLBI feasibility test observations. R Cas is a spare candidate source. S.A. is the angular separations from maser sources. 1Detected in the KVN calibrator survey (private communication with J. A. Lee). 2Detected in the source frequency phase referencing test observations (n14sc01g, n14sc01h). 3Detected in the calibrator survey in 2014B pilot KSP observations (p14sc01d, p14sc01k and p14sc01o).