Long-term polarimetric observations of OH127.8+0.0

TL;DR

This study presents long-term polarimetric monitoring of OH127.8+0.0, revealing a stable magnetic field structure and typical variability patterns of long-period AGB stars over 6.5 years.

Contribution

It provides the first detailed long-term polarimetric observations of OH127.8+0.0, including magnetic field estimation and polarization structure analysis.

Findings

Magnetic field strength estimated at -0.6 mG.

Polarization vectors indicate a regular, radial magnetic field.

Flux variations follow total flux with stable polarization degrees.

Abstract

OH 1612 and 1667 MHz masers from the well known object OH127.8+0.0 were mon- itored in full-polarization mode over a period of 6.5 years and mapped with MERLIN at one epoch. The OH variability pattern of the star is typical of extremely long- period AGB stars. The distance determined from the 1612 MHz light curve and a new measurement of the angular radius is 3.87 (0.28) kpc. At both frequencies, the flux of polarized emission tightly follows the total flux variations while, the degrees of circu- lar and linear polarization are constant within measurement accuracy.. There is net polarization at both lines. The magnetic field strength estimated from a likely Zeeman pair is -0.6 mG at the distance of 5400 au from the star.At the near and far sides of the envelope, the polarization vectors are well aligned implying a regular structure of the magnetic field. The polarization characteristics of the OH maser emission suggest a radial magnetic field which is frozen in the stellar wind.