SiO and H2O maser survey toward AGB and post-AGB stars

Abstract

We performed simultaneous observations of SiO v=1, 2, 29SiO v=0, J=1-0 and H2O 616-523 maser lines toward 143 AGB and 164 post-AGB stars in order to investigate how evolutionary characteristics from AGB to post-AGB stars appear in these two maser emission. 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 H2O maser emission from 21 sources out of 164 post-AGB stars including 11 new detections. Of 143 AGB stars, we detected SiO and/or H2O maser emission from 44 stars including 24 newly detected sources. It is found that SiO v=2, J=1-0 maser emission without SiO v=1 maser was detected from 7 sources among 14 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 differently from those of AGB stars. It may be related with the development of hot dust shells according to the evolution of post-AGB stars. We also found that the SiO and H2O maser detection rates of blue group (LI), which have higher outflow velocities and are massive, are higher than those of red group (RI) for the post-AGB stars. Especially, only H2O masers were detected from RI sources, i. e., 6 sources among 91 RI sources showing the different evolutionary stage between LI and RI sources.