Observations and Analysis of CH⁺ Vibrational Emissions from the Young, Carbon-rich Planetary Nebula NGC 7027: A Textbook Example of Chemical Pumping

We discuss the detection of 14 rovibrational lines CH+, obtained toward planetary nebula NGC 7027 with iSHELL spectrograph on NASA's Infrared Telescope Facility (IRTF) Maunakea. Our observations in 3.49–4.13 μm spectral region, a 0375 slit width that provided resolving power λ/Δλ ∼ 80,000, have resulted unequivocal R(0)−R(3) and P(1)−P(10) transitions within v = 1−0 band CH+. The R-branch are anomalously weak relative to P-branch transitions, behavior is explained accurately by rovibronic calculations transition dipole moment reported companion paper. Nine infrared H2 were also detected these observations, comprising S(8), S(9), S(13), S(15) pure rotational lines; O(4)−O(7) 2−1 O(5) line. present photodissociation model, constrained CH+ line fluxes we measured, includes detailed treatment excitation inelastic collisions, optical pumping, chemical ("formation") pumping. latter process found dominate observed model remarkably successful explaining both absolute strengths lines.