Analysis of Lyman β and Lyman γ lines in a pre-eruptive and eruptive prominence with <i>Solar Orbiter</i> SPICE observations

ABSTRACT The first dedicated observation of an off-limb prominence by the Spectral Imaging of the Coronal Environment (SPICE) instrument onboard Solar Orbiter took place on 2023 April 15. Our aim is to provide an overview of the potentiality of the diagnostics using these data. We show that we can derive the changes in the physical parameters of the pre-eruptive and eruptive prominence using the Lyman lines. We investigate the integrated intensity and line widths of the Lyman $\beta$ and Lyman $\gamma$ lines, finding variations between the prominence, disc, and coronal regions. The results reflect dynamic changes in density, temperature, and optical thickness. We analyse the spatial and temporal evolution of the Lyman $\beta$ and Lyman $\gamma$ line profiles. Using a simple geometric model, we obtain the radial velocity of this prominence at the early phase of its eruption with the Global Oscillation Network Group H $\alpha$ images. This offers a way of calculating the radial velocity of an eruptive filament from a pair of 2D images. The result helps us understand the potential Doppler effect in line profiles. Overall, the spectral profiles indicate that the eruption enhances spatial and temporal variations in line intensity, reflecting dynamic changes in plasma conditions within the prominence. These findings highlight the diagnostic potential of SPICE observations, and future non-local thermodynamic equilibrium radiative transfer modelling will help to further constrain prominence plasma parameters.