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the effects of structure on wind diagnostics is now widely accepted .
it causes h@xmath0 and radio and ir continuum measurements ( @xmath1   diagnostics ) to _ over_-estimate mass loss rates , @xmath2 .
structure , and its accompanying porosity , can also cause wind line diagnostics to _
under_-estimate @xmath2 ( prinja & massa 2010 ) .
we examine this effect in lightly reddened magellanic cloud o stars by deriving @xmath2s from _ spitzer _ ir excesses , and comparing the results to theoretical expectations from vink et al .
if clumping is significant , we expect the ir excesses to over - estimate the mass loss rates .
furthermore , comparing the lmc and smc results allows us to examine metallicity effects on clumping .
to determine ir excesses , the continua must be corrected for reddening , and this requires the assumption that a portion of the continuum is free of excess and has a known slope , typically @xmath3 . applying
an extinction curve with an inappropriate @xmath4 can introduce enormous errors in the inferred ir excess . in this
regard , lmc and smc o stars have a substantial advantage compared to galactic o stars .
we use a generalization of the lamers & waters ( 1984 ) model which agrees with results from the puls et al .
( 1996 ) fastwind model when similar parameters are used .
we ignore the effects of disks or non - standard , slowly accelerating velocity laws at this time .
for the stellar parameters the following were adopted : for the lmc we used the martins et al .
( 2002 ) calibrations for the stellar parameters , except for luminosities , where a distance modulus of 18.52  mag was used .
we assumed @xmath5 . for the smc we used the massey et al .
( 2009 ) spectral type  @xmath6 calibration , a @xmath7  mag to determine @xmath8 , and the letherer et al .
( 2010 ) @xmath9 grid to determine masses .
when measured terminal velocities , @xmath10 , were not available , we used the vink et al .
( 2001 ) formulae relating escape velocity and @xmath10 .
tlusty ( lanz & hubeny 2003 ) models of the appropriate temperatures , surface gravities and metallicities were used for the bare photospheres , and an @xmath11 extinction curve was assumed throughout ( fitzpatrick & massa 2009 ) .
all of the ir mass loss rates ( see , fig .  1 ) are larger than expected and , as is well known , lmc mass loss rates are larger than smc rates for similar stellar parameters . furthermore , the relative disagreement between the ir , @xmath2(ir ) , and vink et al .
( 2001 ) mass loss rates , @xmath2(vink ) , is similar for the lmc and the smc .
( ir ) , as a function of theoretical expectations , @xmath2(vink ) , for the lmc ( left ) and smc ( right ) . for the lmc ,
p  v results , infer @xmath2s much smaller than @xmath2(vink ) .
the red points depict stars which will be observed by _ hst_. the solid line indicates @xmath2(ir@xmath12(vink ) and the dashed lines give @xmath2(ir@xmath13 and 9@xmath14(vink ) .
, title="fig:",width=240 ] ( ir ) , as a function of theoretical expectations , @xmath2(vink ) , for the lmc ( left ) and smc ( right ) . for the lmc ,
p  v results , infer @xmath2s much smaller than @xmath2(vink ) .
the red points depict stars which will be observed by _ hst_. the solid line indicates @xmath2(ir@xmath12(vink ) and the dashed lines give @xmath2(ir@xmath13 and 9@xmath14(vink ) .
, title="fig:",width=240 ]
@xmath15 ir excesses for lmc and smc o stars are larger than those expected from theory by factors of 3  10 .
+ @xmath15 for lmc stars , the mass loss rates are vastly larger than those expected from uv wind lines ( massa et al .  2003 ,
fullerton et al .  2006 ) .
+ @xmath15 the relative disagreement between theory and observation is similar for both galaxies .
+ @xmath15 if , as expected , clumping causes the disagreement , then its effect appears to be weakly dependent on metallicity .
we use a combination of vjhk and _ spitzer _ [ 3.6 ] , [ 5.8 ] and [ 8.0 ] photometry , to determine ir excesses in a sample of lmc and smc o stars . 
 this sample is ideal for determining excesses because : 1 ) the distances to the stars , and hence their luminosities , are well - determined , and ; 2 ) the very small line of sight reddenings minimize the uncertainties introduced by extinction corrections . 
 we find ir excesses much larger than expected from vink et al .  
 ( 2001 ) mass loss rates . 
 this is in contrast to previous wind line analyses for many of the lmc stars which suggest mass loss rates much less than the vink et al 
 .  predictions . together 
 , these results indicate that the winds of the lmc and smc o stars are strongly structured ( clumped ) .