Discovery of the first tau Sco analogues: HD 66665 and HD 63425

TL;DR

This paper reports the discovery of two stars, HD 66665 and HD 63425, that are similar to tau Sco in their UV spectra, magnetic properties, and stellar parameters, providing new insights into magnetic OB stars.

Contribution

It is the first identification of tau Sco analogues, expanding understanding of magnetic massive stars with peculiar wind diagnostics.

Findings

HD 66665 and HD 63425 have UV spectra similar to tau Sco.

Both stars exhibit magnetic fields of comparable strength.

Stellar parameters are consistent with tau Sco, indicating similar physical properties.

Abstract

The B0.2 V magnetic star tau Sco stands out from the larger population of massive OB stars due to its high X-ray activity, peculiar wind diagnostics and highly complex magnetic field. This paper presents the discovery of the first two tau Sco analogues - HD 66665 and HD 63425, identified by the striking similarity of their UV spectra to that of tau Sco. ESPaDOnS spectropolarimetric observations were secured by the Magnetism in Massive Stars CFHT Large Program, in order to characterize the stellar and magnetic properties of these stars. CMFGEN modelling of optical ESPaDOnS spectra and archived IUE UV spectra showed that these stars have stellar parameters similar to those of tau Sco. A magnetic field of similar surface strength is found on both stars, reinforcing the connection between the presence of a magnetic field and wind peculiarities. However, additional phase-resolved observations will be required in order to assess the potential complexity of the magnetic fields, and verify if the wind anomalies are linked to this property.