Rotten Egg Nebula: The magnetic field of a binary evolved star

Abstract

Most of PNe are not spherical. The loss of spherical symmetry occurs somewhere between the AGB and PN phase. The cause of this change of morphology is not yet well known, but magnetic fields are one of the possible agents. Its origin remains to be determined, and potentially requires the presence of a massive companion to the AGB star. Therefore, further detections of the magnetic field around evolved stars (in particular those thought to be part of a binary system) are crucial to improve our understanding of the origin and role of magnetism on evolved stars. One such binaries is the pre-PN OH231.8, around which a magnetic field was detected in the OH maser region of the outer circumstellar envelope. We aim to detect and infer the properties of the magnetic field of this source in the water maser region. We observed the 6_{1,6}-5_{2,3} water maser rotational transition to determine its linear and circular polarization. These emissions are located within the inner regions of OH231.8 (at few tens of AU). We detected 30 water maser features, which occur in two distinct regions that are moving apart with a velocity on the sky of 2.3 mas/year. Taking into account the inclination angle of the source, this corresponds to an average separation velocity of 21 km/s. Based on the velocity gradient of the maser emission, the masers appear to be dragged along the direction of the nebula jet. Linear polarization is present in 3 of the features, and circular polarization was detected in the 2 brightest ones. We found that the strength of the magnetic field is |B_{||}|~45 mG which, when assuming a toroidal magnetic field, implies B~2.5 G on the stellar surface. The morphology of the field is not yet determined, but the high scatter found on the directions of the linear polarization vectors could indicate that the masers occur near the tangent points of a toroidal field.

7 pages, 4 figures

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Cited by in corpus (16)

• Bipolar planetary nebulae from common envelope evolution of binary stars
• Magnetic fields around evolved stars: further observations of H${}_2$O maser polarization
• Through the magnifying glass: ALMA acute viewing of the intricate nebular architecture of OH231.8+4.2
• Circumstellar envelope manifestations in the optical spectra of evolved stars
• Linear polarization of submillimetre masers. Tracing magnetic fields with ALMA
• Magnetic field in IRC+10216 and other C-Rich Evolved Stars
• Submillimeter polarisation and magnetic field properties in the envelopes of proto-planetary nebulae CRL 618 and OH 231.8+4.2
• High-latitude supergiant V5112 Sgr: enrichment of the envelope with heavy s-process metals
• Millimeter polarisation of the protoplanetary nebula OH 231.8+4.2: A follow-up study with CARMA
• Registration of H${}_2$O and SiO masers in the Calabash Nebula, to confirm the Planetary Nebula paradigm
• Radio Stars and Their Lives in the Galaxy
• Time variations of H2O and SiO masers in the proto-Planeatry Nebula OH231.8+4.2
• The detection of heavy metals in the circumstellar envelopes of post-AGB stars
• ALMA reveals the coherence of the magnetic field geometry in OH 231.8+4.2
• Post-AGB nebular studies
• On the Nature of the Protoplanetary Nebula OH\,231.8+4.2