Terahertz water masers. II. Further SOFIA/GREAT detections toward circumstellar outflows, and a multitransition analysis
Following up on our discovery of terahertz water masers, reported in 2017, we report two further detections of water maser emission at frequencies above 1 THz. Using the GREAT instrument on SOFIA, we have detected emission in the 1.296411 THz 827 − 734 transition of water toward two additional oxygen-rich evolved stars, omicron Ceti (Mira) and R Crateris, and obtained an upper limit on the 1.296 THz line emission from U Orionis. Toward these three sources, and toward the red supergiant star VY Canis Majorae from which 1.296 THz line emission was reported previously, we have also observed several lower-frequency (sub)millimeter water maser transitions using the APEX 12 m telescope along with the 22 GHz transition using the Effelsberg 100 m telescope. We have used a simple model to analyze the multitransition data thereby obtained. Adopting, as a prior, independent literature estimates of the mass-loss rates in these four sources and in W Hydrae, we infer water abundances in a remarkably narrow range: n(H2O)/n(H2) = 1.4-2.5 × 10−4. For o Cet, VY CMa, and W Hya, the model is successful in predicting the maser line fluxes to within a typical factor ∼1.6-3. For R Crt and U Ori, the model is less successful, with typical line flux predictions lying an order of magnitude above or below the observations; such discrepancies are perhaps unsurprising given the exponential nature of maser amplification.
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National Aeronautics and Space Administration
Physics and Astronomy
David A. Neufeld, Karl M. Menten, Carlos Durán, Rolf Güsten, Michael J. Kaufman, Alex Kraus, Parichay Mazumdar, Gary J. Melnick, Gisela N. Ortiz-León, Helmut Wiesemeyer, and Friedrich Wyrowski. "Terahertz water masers. II. Further SOFIA/GREAT detections toward circumstellar outflows, and a multitransition analysis" Astrophysical Journal (2021). https://doi.org/10.3847/1538-4357/abc628