HD 179949 is an F8V star , orbited by a giant planet at \sim 8 ~ { } R _ { \star } every 3.092514 days .
The system was reported to undergo episodes of stellar activity enhancement modulated by the orbital period , interpreted as caused by Star-Planet Interactions ( SPIs ) .
One possible cause of SPIs is the large-scale magnetic field of the host star in which the close-in giant planet orbits .

In this paper we present spectropolarimetric observations of HD 179949 during two observing campaigns ( 2009 September and 2007 June ) .
We detect a weak large-scale magnetic field of a few Gauss at the surface of the star .
The field configuration is mainly poloidal at both observing epochs .
The star is found to rotate differentially , with a surface rotation shear of \hbox { $d \Omega$ } = 0.216 \pm 0.061 ~ { } \hbox { rad d$ { } ^ { -1 } $ } , corresponding to equatorial and polar rotation periods of 7.62 \pm 0.07 and 10.3 \pm 0.8 d respectively .
The coronal field estimated by extrapolating the surface maps resembles a dipole tilted at \sim 70 \hbox { $ { } ^ { \circ } $ } .
We also find that the chromospheric activity of HD 179949 is mainly modulated by the rotation of the star , with two clear maxima per rotation period as expected from a highly tilted magnetosphere .
In September 2009 , we find that the activity of HD 179949 shows hints of low amplitude fluctuations with a period close to the beat period of the system .