Looking for Magnetic Fields in Kepler Red Giants
Jérôme Ballot (IRAP)

Spectropolarimetric measurements allow us to detect and measure magnetic field through Zeeman effect in stellar photospheres. We observed with the spectropolarimeters Narval (at Telescope Bernard Lyot) and ESPADONS (at CFHT) a few Kepler Red Giants in 2012 and 2013, especially four stars showing depressed bipolar modes. Interestingly, recent seismic studies by Fuller et al. (2015) suggest these stars had a magnetic history. After presenting shortly the technique, I will detail the detections we did and the constraints we put in surface magnetic fields, then I will discuss the origin of these fields by comparing these observations to a broader sample of red giants observed by Aurière et al. (2015).