IRAS 18113-2503: the water fountain with the fastest jet?

TL;DR

IRAS 18113-2503 is a post-AGB star with the fastest known jet among water fountain stars, exhibiting a record-high velocity spread and dispersion in its water masers, indicating highly energetic ejection processes.

Contribution

This study reports the discovery of the water fountain star IRAS 18113-2503 with the largest velocity spread and highest jet velocity among known water fountains, expanding understanding of jet dynamics in evolved stars.

Findings

Velocity spread of ~500 km/s in water masers.

Largest velocity dispersion (~170 km/s) within maser lobes.

IRAS 18113-2503 likely has the fastest jet among water fountains.

Abstract

We present Expanded Very Large Array (EVLA) water maser observations at 22 GHz toward the source IRAS 18113-2503. Maser components span over a very high velocity range of ~500 km/s, the second largest found in a Galactic maser, only surpassed by the high-mass star forming region W49N. Maser components are grouped into a blue and a redshifted cluster, separated by 0.12". Further mid-IR and radio data suggest that IRAS 18113-2503 is a post-AGB star, thus a new bona fide member of the rare class of "water fountains". It is the evolved object with the largest total velocity spread in its water masers, and with the highest velocity dispersion within its red- and blue-shifted lobes (~170 km/s). The large total velocity range of emission probably indicates that IRAS 18113-2503 has the fastest jet among the known water fountain stars. On the other hand, the remarkably high velocity dispersion within each lobe may be interpreted in terms of shocks produced by an episode of mass ejection whose velocity increased up to very high values or, alternatively, by projection effects in a jet with a large opening angle and/or precessing motions.