Authors: Fonfria, J. P.; Montiel, E. J.; Cernicharo, J.; DeWitt, C. N.; Richter, M. J.
Journal: ASTRONOMY & ASTROPHYSICS
Publication date: 2020/11/23
Abstract: We report on the detection of hot CO2 in the O-rich asymptotic giant branch star R Leo based on high spectral resolution observations in the range 12.8-14.3 mu m carried out with the Echelon-cross-Echelle Spectrograph (EXES) mounted on the Stratospheric Observatory for Infrared Astronomy (SOFIA). We found similar or equal to 240 CO2 emission lines in several vibrational bands. These detections were possible thanks to a favorable Doppler shift that allowed us to avoid contamination from telluric CO2 features. The highest excitation lines involve levels at an energy of similar or equal to 7000 K. The detected lines are narrow (average deconvolved width similar or equal to 2.5 km s(-1)) and weak (usually less than or similar to 10% the continuum). A ro-vibrational diagram shows that there are three different populations, warm, hot, and very hot, with rotational temperatures of similar or equal to 550, 1150, and 1600 K, respectively. From this diagram, we derived a lower limit for the column density of similar or equal to 2.2 x 10(16) cm(-2). Further calculations based on a model of the R Leo envelope suggest that the total column density can be as large as 7.0 x 10(17) cm(-2) and the abundance with respect to H-2 similar or equal to 2.5 x 10(-5). The detected lines are probably formed due to the de-excitation of CO2 molecules from high energy vibrational states, which are essentially populated by the strong R Leo continuum at 2.7 and 4.2 mu m.