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Paper text:
we use our non local thermodynamic equilibrium radiative transfer code where the prominence is modelled as a plane - parallel slab standing vertically above the solar surface and moving upward as a solid body ( fig .
[ protu ] ) .
we consider isothermal and isobaric prominence atmospheres only .
other computational details are given in @xcite ( astro - ph/0608221 ) .
the redistribution in frequency during the scattering of the incident photons in resonance lines is best described by the so - called standard partial redistribution ( prd ) approximation : a combination of complete frequency redistribution ( crd ) and coherent scattering in the atom rest frame .
we compare the crd case , where all helium lines are treated in crd , with the prd case , where prd is used for the resonance lines he  i @xmath0584 and 537    and he  ii @xmath1304   .
[ profcrdprd ] shows that there are substantial differences between the crd and prd treatments of the redistribution in frequency .
it is necessary to compute the helium spectrum in prd to compare the calculations with observations .
we compute several prominence models at two different temperatures ( 8000  k and 15000  k ) for velocities between 0 and 400  km  s@xmath2 , keeping other parameters fixed , and using prd .
[ tempint ] shows that there is little difference between the two temperatures for the relative intensity of the he  ii line .
this line is indeed mainly formed by resonant scattering of the incident radiation , as shown in @xcite .
the he  i resonance lines show some sensitivity to the temperature : at high temperatures , collisional excitation becomes non negligible .
the difference between the cold and hot prominences is more evident as the velocity increases .
the contribution of resonant scattering in line formation decreases with increasing velocity . beyond about 200  km s@xmath2
, the thermal contribution dominates the emission .
therefore the emergent intensity becomes almost independent of the velocity .
the he  i 10830 line does not strongly depend on velocity .
the incident radiation coming from the solar disk at this wavelength is a very weak absorption line .
consequently , the doppler effect is virtually unseen in the emergent line .
finally , he  i d3 ( 5876  , not shown ) behaves exactly as he  i 10830 .
figure  [ proft ] illustrates how the line profiles are affected by the velocity at two different temperatures .      at low temperature and low speeds
, we observe an asymmetry in the line profiles of the two resonance lines , with some intensity enhancement in the red part . at high speeds
, a smaller asymmetry still exists . at high temperature , the asymmetry in the line profile is less pronounced than at low temperature . at a given temperature ,
the red wing of the profile first increases , and then decreases , with increasing velocity .
the asymmetries due to the enhanced emission in the red wings are more visible at speeds below 200  km s@xmath2 when thermal emission is negligible .
finally , the reversal at line centre is more pronounced with increasing velocity .
the intensity in this line does not strongly depend on the plasma velocity , due to the very weak incident absorption line .
the emitted intensity in the he  ii line mainly depends on the incident radiation . at a given speed ,
the intensity at line centre is the same for both temperatures .
the line profile becomes broader with temperature .
it is easily seen from figs .
[ tempint ] and [ proft ] that the 304   line intensity decreases rapidly with increasing velocity .
partial redistribution in frequency is necessary to compute the profiles of the helium resonance lines emitted by moving material in prominences .
velocity effects are more visible when thermal emission is low .
together with hydrogen lines the helium lines offer the possibility of a powerful diagnostic of the eruptive prominence plasma . in a future work
, we will infer the full velocity vector by combining doppler dimming / brightening effects on hydrogen and helium lines with the apparent motion of the prominence material brought by soho or future imagers ( e.g. solar - b , stereo ) .
even quiescent solar prominences may become active and sometimes erupt . 
 these events are occasionally linked to coronal mass ejections . 
 however we know very little about the plasma properties during the activation and eruption processes . 
 we present new computations of the helium line profiles emitted by an eruptive prominence . 
 the prominence is modelled as a plane - parallel slab standing vertically above the solar surface and moving upward as a solid body . 
 the helium spectrum is computed with a non local thermodynamic equilibrium radiative transfer code . 
 the effect of doppler dimming / brightening is investigated in the resonance lines of he  i and he  ii formed in the euv , as well as on the he  i @xmath010830   and 5876   lines . 
 we focus on the line profile properties and the resulting integrated intensities . 
 it is shown that the helium lines are very sensitive to doppler dimming effects . 
 we also study the effect of frequency redistribution in the formation mechanisms of the resonance lines and find that it is necessary to use partial redistribution in frequency for the resonance lines .