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like many o and b stars , the o7.5iii(n)((f ) ) star @xmath0 per shows very prominent cyclical wind variability in the uv resonance lines ( fig .
1a ) , manifested by discrete absorption components ( dacs ) which migrate from red to blue , and narrow when they approach ( but not reach ) the terminal velocity as measured from saturated wind profiles ( _ e.g. _ ( * ? ? ?
* kaper  1999 ) ) . in @xmath0 per the dac period is 2.09 d. multiwavelength observations of a number of ob stars , including @xmath0 per , have shown that the cyclic behavior is present down to the surface of the star ( ( * ? ? ?
* de jong  1997 ) ) , and that the typical timescale varies with the ( estimated ) rotational timescale .
this strongly argues in favor of a surface phenomenon which perturbs the base of the flow .
two scenarios are proposed : in the so - called corotating interaction region ( cir ) model a perturbation at the surface of the star causes a local increase ( or decrease ) of the radiative force driving the stellar wind , or surface magnetic fields may disturb the outflow , both resulting in a rotationally modulated stellar wind ( see ( * ? ? ?
* cranmer and owocki 1996 ) ) .
a number of coordinated uv and optical observations have confirmed the cir model , including for the case of @xmath0 per , but the origin of the perturbations is not known , which is one of the most challenging problems in stellar wind research of the last decades .
we present here our most recent efforts to measure the magnetic field and the pulsation properties .
previous musicos magnetic measurements of @xmath0 per were presented by ( * ? ? ?
* de jong  ( 2001 ) ) , with no detection . for narval data
the magnetic analysis is essentially the same , applying the least - squares deconvolution method ( ( * ? ? ?
* donati  1997 ) ) to the spectral lines sensitive to magnetic effects .
this yields the longitudinal component of the field , averaged over the facing hemisphere of the star . in fig .
2a and 2b the 45 results are plotted as a function of time .
no zeeman signature was found . as an example , fig .
2c shows the lsd profile of the best exposed spectrum of september 2007 with a s / n = 1960 .
the magnetic values are preliminary , as the used spectral linelist can still be optimized .
we also analysed a number of spectral lines for non - radial pulsations with known period of 3.5 h found in a previous musicos campaign ( ( * ? ? ?
* de jong  1999 ) ) .
the amplitude may have changed during the 9 months between our narval runs , see fig .
1b and 1c .
this obviously needs further investigation , as the impact on the stellar wind may have changed .
cyclical wind variability is an ubiquitous but as yet unexplained feature among ob stars . 
 the o7.5 iii(n)((f ) ) star @xmath0 persei is the brightest representative of this class on the northern hemisphere . as its prominent cyclical wind properties vary on a rotational time scale ( 2 or 4 days ) the star has been already for a long time a serious magnetic candidate . as the cause of this enigmatic behavior non - radial pulsations and/or a surface magnetic field are suggested . 
 we present a preliminary report on our attempts to detect a magnetic field in this star with high - resolution measurements obtained with the spectropolarimeter narval at tbl , france during 2 observing runs of 5 nights in 2006 and 5 nights in 2007 . only upper limits could be obtained , even with the longest possible exposure times . 
 if the star hosts a magnetic field , its surface strength should be less than about 300 g. this would still be enough to disturb the stellar wind significantly . from our new data 
 it seems that the amplitude of the known non - radial pulsations has changed within less than a year , which needs further investigation .