Context : The eclipsing low-mass X-ray binary X1822-371 is the prototype of the accretion disc corona ( ADC ) sources .
Its inclination angle ( \simeq 82.5 ^ { \circ } ) is high enough that flux from the neutron star is blocked by the edge-on accretion disc .
Because the neutron star ’ s direct emission is hidden , its ADC emission is visible .

Aims : We analyse two Chandra observations and one XMM-Newton observation to study the discrete features in this source and their variation as a function of the orbital phase , deriving constraints on the temperature , density , and location of the plasma responsible for emission lines .

Methods : The HETGS and XMM/Epic-pn observed X1822-371 for 140 and 50 ks , respectively .
We extracted an averaged spectrum and five spectra from five selected orbital-phase intervals that are 0.04-0.25 , 0.25-0.50 , 0.50-0.75 , 0.75-0.95 , and , finally , 0.95-1.04 ; the orbital phase zero corresponds to the eclipse time .
All spectra cover the energy band between 0.35 and 12 keV .

Results : We confirm the presence of local neutral matter that partially covers the X-ray emitting region ; the equivalent hydrogen column is 5 \times 10 ^ { 22 } cm ^ { -2 } and the covered fraction is about 60–65 % .
We identify emission lines from O vii , O viii , Ne ix Ne x , Mg xi , Mg xii , Si xiii , Si xiv , Fe xxv , Fe xxvi , and a prominent fluorescence iron line associated with a blending of Fe i -Fe xv resonant transitions .
The transitions of He-like ions show that the intercombination dominates over the forbidden and resonance lines .
The line fluxes are the highest during the orbital phases between 0.04 and 0.75 .

Conclusions : We discuss the presence of an extended , optically thin corona with optical depth of about 0.01 that scatters the X-ray photons from the innermost region into the line of sight .
The photoionised plasma producing the O viii , Ne ix , Ne x , Mg xi , Mg xii , Si xiii , and Si xiv lines is placed in the bulge at the outer radius of the disc distant from the central source of 6 \times 10 ^ { 10 } cm .
The O vii and the fluorescence iron line are probably produced in the photoionised surface of the disc at inner radii .
Finally , we suggest that the observed local neutral matter is the matter transferred by the companion star that was expelled from the system by the X-ray radiation pressure , which in turn originated in the accretion process onto the neutron star .
( Abridged )