DETECTION OF OH⁺ IN TRANSLUCENT INTERSTELLAR CLOUDS: NEW ELECTRONIC TRANSITIONS AND PROBING THE PRIMARY COSMIC RAY IONIZATION RATE

We present the detection of rotationally resolved electronic transitions in the OH⁺ A³Π–X³Σ⁻ (0, 0) and (1, 0) bands toward CD-32 4348, HD 63804, HD 78344, and HD 80077. These four translucent clouds have been studied in a recent Very Large Telescope/Ultraviolet and Visual Echelle Spectrograph observational run. In total, seven absorption features of OH⁺ are detected, and six of them are identified here for the first time, providing a precise tool to trace OH⁺ in translucent interstellar clouds. An improved set of line positions and oscillator strengths is compiled to support our data interpretation. A dedicated analysis of the observed features in individual targets yields an accurate determination of OH⁺ column densities. The results are applied to estimate the primary cosmic ray ionization rate in the investigated translucent clouds, which yields a typical value of ∼1.0 × 10⁻¹⁶ s⁻¹. In addition, following this work, two of the new interstellar features recently reported by Bhatt and Cami, at ∼3572.65 and 3346.96 Å, can be identified as OH⁺ absorption lines now