Identification of numerous unidentified photospheric lines in GSC and UCAC4

Identify the atomic transitions responsible for the unidentified photospheric lines listed under “Unidentified photospheric lines” for the PG1159 star GSC and the CO-sdO star UCAC4, including precise species and ionization stages, to improve spectral modeling and abundance analyses of these stars.

Background

The spectra of the PG1159 star GSC and the CO-sdO star UCAC4 show many carbon and oxygen features due to their high C and O abundances, but also numerous lines that could not be identified despite extensive use of atomic databases. The authors suspect many of these features arise from highly excited states of C III, O IV, and O V, indicating gaps in currently available atomic line data for these ions at high excitation.

Resolving these identifications would refine atmospheric models, address blending issues, and support more accurate determinations of stellar parameters and abundances.