Simultaneous observations of SiO and $H_2O$ masers toward AGB and post-AGB stars

We performed simultaneous observations of SiO v=1, 2, $^{29}SiO$ v=0, J=1-0 and $H_2O$ $6_{16}-5_{23}$ maser lines toward 132 AGB and 183 post-AGB stars in order to investigate how evolutionary characteristics from AGB to post-AGB stars appear in these two maser emissions. The observations were carried out from 2011 February to 2012 March using the Korean VLBI Network 21-m radio telescopes. We have detected SiO and/or $H_2O$ maser emission from 29 sources out of 183 post-AGB stars including 19 new detections. Of 132 AGB stars which are mainly selected based on the IRAS Point Source Catalog, we detected SiO and/or $H_2O$ maser emission from 38 stars including 18 newly detected sources. An evolutionary characteristic from AGB to post-AGB stars is discussed in IRAS two-color diagram. It is found that SiO v=2, J=1-0 maser emission without SiO v=1 maser detections was detected from 8 sources among 21 SiO detected post-AGB stars and the intensity of SiO v=2, J=1-0 maser tends to be much stronger than that of SiO v=1. We also found that for the post-AGB stars the maser detection rate of blue group sources (which have higher outflow velocities than red group) are higher than that of red group. Especially, only $H_2O$ maser emission was detected from 7 sources among 94 red group sources without SiO maser detections.