Terahertz Water Masers: II. Further SOFIA/GREAT Detections toward Circumstellar Outflows, and a Multitransition Analysis
| Autor: | Neufeld, David A., Menten, Karl M., Durán, Carlos, Güsten, Rolf, Kaufman, Michael J., Kraus, Alex, Mazumdar, Parichay, Melnick, Gary J., Ortiz-León, Gisela, Wiesemeyer, Helmut, Wyrowski, Friedrich |
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| Rok vydání: | 2020 |
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| Druh dokumentu: | Working Paper |
| DOI: | 10.3847/1538-4357/abc628 |
| Popis: | 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 $8_{27}-7_{34}$ 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 analyse the multi-transition 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: $n({\rm H_2O})/n({\rm H_2}) = 1.4 - 2.5 \times 10^{-4}$. For o Cet, VY CMa, and W Hya, the model is successful in predicting the maser line fluxes to within a typical factor $\sim 1.6 - 3$. 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. Comment: 37 pages, including 10 figures. Accepted for publication in the Astrophysical Journal. Two typos corrected: in two instances the ratio n(H2O)/n(H2) had erroneously been inverted in version 1 |
| Databáze: | arXiv |
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