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We study the capabilities of Lyman $\beta$ and the O I 1027 and 1028 \AA\spectral lines for understanding the properties of the chromosphere andtransition region. The oxygen transitions are located in the wing of Lyman$\beta$ that is a candidate spectral line for the solar missions SolarOrbiter/SPICE and Solar-C (EUVST). We examine general spectroscopic propertiesof the three transitions in the quiet Sun by synthesizing them assumingnon-local thermal equilibrium taking into account partial redistributioneffects. We estimate the heights where the spectral lines are sensitive to thephysical parameters computing the response functions to temperature andvelocity using a 1D semi-empirical atmospheric model. We also synthesize theintensity spectrum using the 3D enhanced network simulation computed with theBIFROST code. The results indicate that Lyman $\beta$ is sensitive to thetemperature from the middle chromosphere to the transition region while it ismainly sensitive to the line-of-sight velocity at the latter atmosphericlayers, around 2000 km above the optical surface. The O I lines form lower inthe middle chromosphere, being sensitive to the LOS velocities at lower heightsthan those covered by Lyman $\beta$. The spatial distribution of intensitysignals computed with the BIFROST atmosphere, as well as the inferredvelocities from the line core Doppler shift confirm the previous results.Therefore, these results indicate that the spectral window at 1025 \AA\contains several spectral lines that complement each other to seamlessly tracethe thermal structure and gas dynamics from the middle chromosphere to thelower transition region.

On the formation of Lyman $\beta$ and the O I 1027 and 1028 \AA\ spectral lines