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 maser emission at frequencies above 1 THz. Using the GREAT instrument SOFIA, have detected 1.296411 THz $8_{27}-7_{34}$ transition toward additional oxygen-rich evolved stars, omicron Ceti (Mira) and R Crateris, obtained an upper limit 1.296 line from U Orionis. Toward these three sources, red supergiant star VY Canis Majorae which was previously, also observed several lower-frequency (sub)millimeter transitions using APEX 12-m telescope along with 22 GHz Effelsberg 100-m telescope. We used a simple model to analyse multi-transition data thereby obtained. Adopting, as prior, independent literature estimates mass-loss-rates four sources W Hydrae, infer abundances remarkably narrow range: $n({\rm H_2O})/n({\rm H_2}) = 1.4 - 2.5 \times 10^{-4}$. For o Cet, CMa, Hya, is successful predicting fluxes within typical factor $\sim 1.6 3$. Crt Ori, less successful, flux predictions lying order magnitude or below observations; such discrepancies are perhaps unsurprising given exponential nature amplification.