The A²Π–X²Σ⁺ Band System of YO

Abstract YO bands are conspicuous in the spectra of S stars. The laboratory spectrum of the A 2 Π–X 2 Σ + electronic transition has been recorded with a Fourier transform spectrometer using a composite-wall hollow cathode lamp source. The A 2 Π–X 2 Σ + transition with <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msup> <mml:mrow> <mml:mi>v</mml:mi> </mml:mrow> <mml:mrow> <mml:mo accent="true">′</mml:mo> </mml:mrow> </mml:msup> <mml:mo>≤</mml:mo> <mml:mn>4</mml:mn> </mml:math> and v ″ ≤ 4 has been rotationally analyzed using the modern spectral fitting program PGOPHER. Vibronic band strengths were calculated using an ab initio transition dipole moment function. A line list for the A 2 Π–X 2 Σ + transition is provided and can be utilized in the modeling of S stars.