SOFIA/GREAT Discovery of Terahertz Water Masers

Journal Article · Mon Jul 10 04:00:00 EDT 2017 · Astrophysical Journal

DOI:https://doi.org/10.3847/1538-4357/AA7568· OSTI ID:22876046

Neufeld, David A. ^[1]; Melnick, Gary J. ^[2]; Kaufman, Michael J. ^[3]; Wiesemeyer, Helmut; Güsten, Rolf; Kraus, Alex; Menten, Karl M.; Ricken, Oliver ^[4]; Faure, Alexandre ^[5]

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1. Department of Physics and Astronomy, Johns Hopkins University 3400 North Charles Street, Baltimore, MD 21218 (United States)
2. Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)
3. Department of Physics and Astronomy, San Jose State University, One Washington Square, San Jose, CA 95192-0106 (United States)
4. Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn (Germany)
5. Univ. Grenoble Alpes, IPAG, and CNRS, F-38000 Grenoble (France)

We report the discovery 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{sub 27}−7{sub 34} transition of water toward three oxygen-rich evolved stars: W Hya, U Her, and VY CMa. An upper limit on the 1.296 THz line flux was obtained toward R Aql. Near-simultaneous observations of the 22.23508 GHz 6{sub 16}−5{sub 23} water maser transition were carried out toward all four sources using the Effelsberg 100 m telescope. The measured line fluxes imply 22 GHz/1.296 THz photon luminosity ratios of 0.012, 0.12, and 0.83, respectively, for W Hya, U Her, and VY CMa, values that confirm the 22 GHz maser transition to be unsaturated in W Hya and U Her. We also detected the 1.884888 THz 8{sub 45}−7{sub 52} transition toward W Hya and VY CMa, and the 1.278266 THz 7{sub 43}−6{sub 52} transition toward VY CMa. Like the 22 GHz maser transition, all three of the THz emission lines detected here originate from the ortho-H{sub 2}O spin isomer. Based upon a model for the circumstellar envelope of W Hya, we estimate that stimulated emission is responsible for ∼85% of the observed 1.296 THz line emission, and thus that this transition may be properly described as a terahertz-frequency maser. In the case of the 1.885 THz transition, by contrast, our W Hya model indicates that the observed emission is dominated by spontaneous radiative decay, even though a population inversion exists.

• OSTI ID: 22876046
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 843; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
GHZ RANGE 01-100
ISOMERS
LUMINOSITY
MASERS
MOLECULES
OXYGEN
POPULATION INVERSION
RADIATIVE DECAY
STARS
STIMULATED EMISSION
TELESCOPES
WATER