Constraints on the surface magnetic field strength of Zeta Puppis (HD 668811)

Context: The ubiquitous presence of Discrete Absorption Components (DACs) in the wind-sensitive line of massive stars has been linked to the possible presence of weak complex magnetic fields on their surfaces. Aims: We carry out a simulation of spectropolarimetric signatures corresponding to complex magnetic fields on the star Zeta Puppis (HD 66188) in order to determine the upper limit of the field strength Bmax. Methods: We use the program developed by Kochukhov & Sudnik (2013) to simulate complex field topologies on the Pup surface, distinguishing each topology by the filling factor f and the spot size rs. Then we compute Stokes parameter V through weak field approximation for 20 rotational phases and compare them with the observed profiles obtained by David-Uraz et al. (2014). Varying the field modulus we determine the upper limits of the field strength for each field topology. Results: The upper limits of the field strength are found to be in the range from 400 G to 2400 G. Bmax increases as the spot size decreases, while, at the same spot size, the highest Bmax corresponds to the lowest f. Conclusions: Our upper limits on the field strength are compatible with theoretical predictions by Cantiello et al. (2009). A recent analysis made by Ramiaramanansoa er al. (2017) determined that on Zeta Pup surface there are 2 DACs. For this model, we have determined that Bmax = 400 G. ​