# Recurring OH Flares towards o Ceti: I. location and structure of the 1990s' and 2010s' events

## TL;DR

This study analyzes recurring OH maser flares in o Ceti during the 1990s and 2010s, revealing their locations, structures, and implications for circumstellar models, with a focus on the role of binarity and maser zone dynamics.

## Contribution

It provides detailed spatial and velocity analyses of OH flares in o Ceti, challenging standard models of maser zones and exploring the influence of binarity on maser emission.

## Key findings

- Flares occur within ~40 AU of o Ceti with no preferred orientation.
- OH and H2O masers are likely co-located at similar distances from the star.
- Flaring regions differ from standard OH maser zones, indicating transient emission zones.

## Abstract

We present the analysis of the onset of the new 2010s' OH flaring event detected in the OH ground-state main line at 1665~MHz towards o Ceti and compare its characteristics with those of the 1990s' flaring event. This is based on a series of complementary single-dish and interferometric observations both in OH and H2O obtained with the Nancay Radio telescope (NRT), the Medicina and Effelsberg Telescopes, the European VLBI Network (EVN), and (e)Multi-Element Radio Linked Interferometer Network ((e)MERLIN). We compare the overall characteristics of o Ceti's flaring events with those which have been observed towards other thin-shell Miras, and explore the implication of these events with respect to the standard OH circumstellar-envelope model. The role of binarity in the specific characteristics of o Ceti's flaring events is also investigated. The flaring regions are found to be less than ~400$ +/- 40 mas (i.e., ~40 +/- 4$ AU) either side of o Ceti, with seemingly no preferential location with respect to the direction to the companion Mira B. Contrary to the usual expectation that the OH maser zone is located outside the H2O maser zone, the coincidence of the H2O and OH maser velocities suggests that both emissions arise at similar distances from the star. The OH flaring characteristics of Mira are similar to those observed in various Mira variables before, supporting the earlier results that the regions where the transient OH maser emission occurs are different from the standard OH maser zone.