Evolution of the Outflow in the Water Fountain Source IRAS 18043–2116*

Abstract

We present the spectral and spatial evolution of H2O masers associated with the water fountain source IRAS 18043−2116, found in observations with the Nobeyama 45 m Telescope and the Australia Telescope Compact Array. We have found new highest-velocity components of the H2O masers (at the redshifted side V LSR ≃ 376 km s−1 and at the blueshifted side V LSR ≃ −165 km s−1), and the resulting velocity spread of ≃540 km s−1 breaks the speed record of fast jets/outflows in this type of sources. The locations of those components have offsets from the axis joining the two major maser clusters, indicating a large opening angle of the outflow (∼60°). The evolution of the maser cluster separation of ∼2.9 mas yr−1 and the compact (∼0.″2) CO emission source mapped with the Atacama Large Millimeter-submillimeter Array suggest a very short (∼30 yr) timescale of the outflow. We also confirmed an increase in the flux density of the 22 GHz continuum source. The properties of the jet and the continuum sources and their possible evolution in the transition to the planetary nebula phase are further discussed.

Systematic Search for Water Fountain Candidates Using the Databases of Circumstellar Maser Sources

“…The conditions traditionally required to identify WFs are as follows: (1) the velocity range of the 22.235 GHz H 2 O maser emission (i.e., twice the expansion velocity of the molecular jet) exceeds 100 km s −1 , (2) the collimated structure of the molecular jet is confirmed by radio interferometric observations, and (3) the infrared properties are not inconsistent with the status of low-and intermediate-mass evolved stars in terms of color index and morphology. To date, 16 WFs are known (see Appendix E), including several well-studied objects, such as IRAS 16342−3814 (Sahai et al 1999), W43A (Imai et al 2002), IRAS 19134+2131 (Imai et al 2004), IRAS 18286−0959 (Yung et al 2011), and IRAS 18043−2116(Uscanga et al 2023. Since the length and speed of the molecular jet can be obtained from very long baseline interferometry (VLBI) observations, the kinematic timescale of the jet can be calculated.…”

Excited-state OH Masers in the Water Fountain Source IRAS 18460-0151

“…Thus far, 15 WFs have been found by interferometry measurements (Desmurs 2012;Gómez et al 2017). The spatiokinematics of the water masers of the WFs exhibit a broad diversity (Imai et al 2020;Uscanga et al 2023). Given the short dynamical timescales of maser jets (5-100 yr; Imai 2007;Tafoya et al 2020;Imai et al 2023) and high optical obscuration (Suárez et al 2008), WFs are likely to be in a transient phase between the AGB and proto-PN periods (Khouri et al 2021).…”

Water Fountain Sources Monitored in FLASHING

“…We have conducted single-dish monitoring observations of these maser sources in FLASHING with the new capability of simultaneous 22 GHz-and 43 GHz-band observations using the Nobeyama 45 m telescope (Okada et al 2020). Some of them and the masers visible only in the southern hemisphere have also been observed with the Australia Telescope Compact Array (ATCA) (Uscanga et al 2023). If new maser features are detected, follow-up interferometric observations are crucial for their localization (e.g., Imai et al 2020;Uscanga et al 2023).…”

“…Some of them and the masers visible only in the southern hemisphere have also been observed with the Australia Telescope Compact Array (ATCA) (Uscanga et al 2023). If new maser features are detected, follow-up interferometric observations are crucial for their localization (e.g., Imai et al 2020;Uscanga et al 2023).…”