Survey of S-type AGB Stars Using the KVN Four-band Receiving System: SMASTES II

Abstract We present the observational results of Simultaneous Multi-mAser Survey Toward Evolved Stars (SMASTES) II for 150 S-type asymptotic giant branch stars. Observations have been performed from 2023 September to 2024 March using the upgraded wide four-band (22/43/86/129 GHz) receiving system of the Korean VLBI Network. For simultaneous observations, 19 molecular lines of H 2 O and multitransitions of SiO masers including several thermal lines were set up together. H 2 O maser was not detected from any stars among 150 S-type stars. For SiO v = 1: J = 1–0, J = 2–1, and J = 3–2 masers were detected from nine, thirteen, and six stars, respectively. For SiO v = 2: J = 1–0, J = 2–1, and J = 3–2 masers were detected from five, two, and two stars, respectively. In particular, for v = 1: J = 1–0, J = 2–1, and J = 3–2 masers were all detected from five stars. For SiO v = 0: J = 1–0, J = 2–1, and J = 3–2 lines in ground vibrational state were detected from five, six, and seven stars, respectively, including the 29 SiO v = 0: J = 1–0 and J = 2–1 lines. For SiO v = 0: J = 1–0, J = 2–1, and J = 3–2 lines were detected in more stars at higher rotational transition lines. The carbon-bearing molecule HCN was detected from four stars. Based on these observational results, we perform statistical analyses on detection rates of maser and thermal lines, maser properties, and kinematics comparing with the results of M-type stars (SMASTES I). The characteristics of maser properties are investigated in the IRAS two-color diagram in relation to the evolutionary stage.