Infrared spectroscopy of Mira variables. II - R Leonis, the H2O vibration-rotation bands

Abstract

High-resolution (..delta..sigmaapprox. =0.15 cm/sup -1/) infrared spectra in the 4000--6700 cm/sup -1/ region of the bright Mira variable R Leonis have been searched for stellar water bands. Three bands are readily identified in the spectra, two in the 5300 cm/sup -1/ (1.9..mu..m) region and another in the 6700 cm/sup -1/ (1.5..mu..m) region. Two bands may also be present in the very blended 4000 cm/sup -1/ region (2.5..mu..m). The radial velocities, central depths, and equivalent widths of the lines in the 1.9..mu..m bands were measured.At phases other than maximum light, two separate layers of the atmosphere contribute to the H/sub 2/O spectrum. On the basis of radial velocity, excitation temperature, and broadening of the lines, these two layers are identified with the two CO and OH line-forming regions described by Hinkle (1978a). The water spectrum originates near the boundary layers of the photosphere at T/sub exc/(H/sub 2/O) approx. = 1700 K, and in a cooler, overlying region with T/sub exc/(H/sub 2/O) approx. =1100 K. At maximum light only the 1100 K region contributes H/sub 2/O lines. The photospheric H/sub 2/O radial velocity curve is compared with the photospheric CO and OH curves, and further evidence is presented for a pulsation-shock modelmore » for Mira variables. The details of the 1100 K region velocity curve and equivalent widths are also discussed.Using a curve of growth for a plane-parallel isothermal layer, an approximate column density of 5 x 10/sup 21/ H/sub 2/O molecules cm/sup -2/ through the entire atmosphere of R Leo is derived. Phase-dependent variations in the column density of an order of magnitude occur during the light cycle. Pervious analyses of H/sub 2/O in Mira variables, including those using the 201--000 band at 9400 A, are reviewed.« less