The discovery of the first gravitationally redshifted spectral line from a neutron star ( NS ) by Cottam , Paerels and Mendez has triggered theoretical studies of the physics of atomic line formation in NS atmospheres .
Chang , Bildsten and Wasserman showed that the hydrogenic Fe H \alpha line formed above the photosphere of a bursting NS is intrinsically broad .
We now include rotational broadening within general relativity and compare the resulting profile to that observed during Type I bursts from EXO 0748-676 .
We show that the fine structure splitting of the line precludes a meaningful constraint on the radius .
Our fitting of the data show that the line forming Fe column is { log } _ { 10 } ( N _ { Fe,n = 2 } / { cm ^ { -2 } } ) = 17.9 _ { -0.42 } ^ { +0.27 } and gravitational redshift 1 + z = 1.345 _ { -0.008 } ^ { +0.005 } with 95 % confidence .
We calculate the detectability of this spectral feature for a large range of spins and inclinations assuming that the emission comes from the entire surface .
We find that at 300 ( 600 ) Hz only 10-20 % ( 5-10 % ) of NSs would have spectral features as deep as that seen in EXO 0748-676 .