First results of a magnetic survey of classical Cepheids

TL;DR

This study presents initial magnetic field measurements of 25 classical Cepheids, revealing magnetic signatures in some stars with diverse profiles, suggesting complex magnetic phenomena possibly influenced by atmospheric dynamics.

Contribution

First spectropolarimetric survey of classical Cepheids detecting magnetic signatures and exploring their complex profiles and potential origins.

Findings

Magnetic signatures detected in 8 of 15 observed Cepheids.

Profiles show diverse morphologies, some resembling cool supergiants.

Longitudinal magnetic fields are weak, around 1 G.

Abstract

We report recent ESPaDOnS and HARPSpol spectropolarimetric observations from our ongoing magnetic survey of the brightest twenty-five classical Cepheids. Stokes $V$ magnetic signatures are detected in eight of fifteen targets observed to date. The Stokes $V$ profiles show a diversity of morphologies with weak associated longitudinal field measurements of order 1 G. Many of the Stokes $V$ profiles are difficult to interpret in the context of the normal Zeeman effect. They consist of approximately unipolar single or double lobe(s) of positive or negative circular polarization. We hypothesize that these unusual signatures are due to the Zeeman effect modified by atmospheric velocity or magnetic field gradients. In contrast, the Stokes $V$ profiles of Polaris and MY Pup appear qualitatively similar to the complex magnetic signatures of non-pulsating cool supergiants, possibly due to the low pulsation amplitudes of these two stars.