2025ApJ...993..246L

Absorption cross sections for ZrO are provided and can be used as a template to interpret spectra of S-type stars. The ZrO spectrum was measured in emission from a carbon furnace at 2700 K and calibrated using synthetic spectra of ⁹⁰Zr¹⁶O. A set of nearly isolated molecular lines has been used for the calibration. We also thoroughly review the literature on the spectroscopy of ZrO. Comparison of the experimental spectrum with currently available line lists revealed issues in ZrO spectral simulation. (a) Within band systems, the relative intensities are not always well reproduced. (b) We identify yet unreported band systems, the strongest ones being E¹Φ-a³Δ and b³Π-X¹Σ⁺; this is to our knowledge the first observation of the theoretically predicted E¹Φ state of ZrO. (c) Three significant band heads in the red are unassigned to this day. We determine spectroscopic constants for E¹Φ (v = 0) and F¹Δ (v = 0, 1) and line lists for associated transitions with Einstein As and oscillator strengths. The C¹Σ⁺-X¹Σ⁺ ab initio transition dipole moment is updated and the line list of this transition is recalculated.