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| hydroxyl maser | |
|---|---|
| Name | Hydroxyl maser |
| Frequency | 1.665–1.720 GHz typical ground-state transitions |
| Discovery | 1965 (astronomical OH masers) |
| Type | Astrophysical maser |
| Species | Hydroxyl (OH) |
| Typical locations | Star-forming regions, evolved stars, supernova remnants, active galactic nuclei |
hydroxyl maser
Hydroxyl masers are astrophysical maser sources produced by population inversion and stimulated emission in the hydroxyl radical (OH) visible in radio transitions such as 1.665 GHz and 1.667 GHz. They appear in diverse astronomical settings including Orion Nebula, W3(OH), Sgr B2, and circumstellar envelopes around evolved stars like Mira (star)-type variables and IRC+10216, and are detected by facilities such as the Very Large Array, Very Long Baseline Array, Parkes Observatory, and Arecibo Observatory. Observations of hydroxyl masers interact with work by notable observatories and missions including Atacama Large Millimeter/submillimeter Array, Green Bank Telescope, Effelsberg 100-m Radio Telescope, Jodrell Bank Observatory, and the Square Kilometre Array project.
Hydroxyl masers were first identified in the interstellar medium after laboratory maser development by figures associated with Charles H. Townes and early radio discoveries connected to Gordon Stanley, and they complement studies of molecular masers such as water maser sources in regions like W49N and W51. Prominent surveys by teams at National Radio Astronomy Observatory and Cavendish Laboratory mapped OH maser populations in complexes including Taurus Molecular Cloud, Perseus Molecular Cloud, Cepheus A, and Mon R2. OH masers are cataloged alongside maser detections from instruments on missions linked to European Southern Observatory programs and historical data sets from Harvard Smithsonian Center for Astrophysics.
The maser action arises from radiative and collisional pumping schemes leading to non-thermal population inversion in the OH hyperfine ground states, processes studied in theoretical frameworks developed by researchers at Max Planck Institute for Radio Astronomy, University of Manchester, California Institute of Technology, and Princeton University. Pumping routes involve far-infrared photons from dust heated by sources such as Herbig Ae/Be stars, T Tauri stars, and embedded protostars in regions like NGC 7538 and IRAS 16293-2422, or collisional excitation in shocks produced by supernova remnant interactions exemplified by W44 and IC 443. Maser polarization, Zeeman splitting, and magnetic field influence have been interpreted using techniques developed by scientists at Harvard University, Columbia University, University of Cambridge, and University of Tokyo.
OH masers occur in star-forming regions such as W3, Orion KL, S255, and NGC 1333, in circumstellar envelopes of late-type stars including R Doradus and VY Canis Majoris, and in shocked regions near supernova remnants interacting with molecular clouds like W51C. They are also found in extragalactic megamaser environments such as Arp 220, NGC 4258, Mrk 273, and NGC 3079, with surveys by teams at University of Cambridge Cavendish Laboratory and Carnegie Institution extending to systems observed by Hubble Space Telescope and Chandra X-ray Observatory programs. OH masers trace evolutionary stages seen in protostellar clusters like Orion Molecular Cloud and stellar evolution phases studied at Mount Wilson Observatory and by researchers associated with Royal Observatory Edinburgh.
OH maser lines at 1.612 GHz, 1.665 GHz, 1.667 GHz, and 1.720 GHz are targeted with interferometers such as Very Long Baseline Array, European VLBI Network, Long Baseline Array (Australia), and single-dish facilities like Parkes Observatory and Nançay Radio Telescope for spectral-line studies. Techniques including very long baseline interferometry used by groups at Joint Institute for VLBI ERIC and polarization studies led by teams at University of Leeds enable measurement of Zeeman splitting and magnetic fields in sources like W3(OH) and Sgr A* neighborhood. Time-series monitoring campaigns by observers at Daily Telegraph Observatory and networks coordinated through International Astronomical Union working groups track variability, flaring, and proper motions analogous to studies of SiO maser kinematics.
OH maser measurements provide constraints on magnetic fields via Zeeman splitting, gas kinematics in star formation regions, and distances through trigonometric parallax measured with VLBI campaigns by groups at Max Planck Institute for Radio Astronomy, Jet Propulsion Laboratory, National Astronomical Observatory of Japan, and Korea Astronomy and Space Science Institute. Extragalactic OH megamasers inform studies of galaxy mergers such as Antennae Galaxies and starburst systems observed by Spitzer Space Telescope and Herschel Space Observatory, while Galactic OH masers contribute to mapping Galactic structure studies by collaborations linked to Gaia complementary programs and surveys executed by Leiden Observatory teams.
Well-studied Galactic sources include W3(OH), Orion KL, Sgr B2, W49N, and Cep A; evolved-star masers include IRC+10216, VY Canis Majoris, Mira (star), and OH/IR stars cataloged by researchers at Mount Stromlo Observatory and Institute of Astronomy, Cambridge. Extragalactic megamaser hosts include Arp 220, NGC 4258, Mrk 231, and IC 10, with landmark studies by teams affiliated with Caltech, Harvard-Smithsonian Center for Astrophysics, and University of Bonn.
Radiative transfer, non-LTE excitation, and magnetohydrodynamic simulations for OH masers are developed in computational groups at Princeton University, University of California, Berkeley, Max Planck Institute for Astrophysics, CEA Saclay, and National Astronomical Observatory of Japan, integrating inputs from dust models by Institut d'Astrophysique Spatiale and shock chemistry informed by work at University of Oxford. Modeling efforts connect to broader studies of molecular chemistry in regions like Taurus Molecular Cloud and to numerical frameworks used by teams at Lawrence Berkeley National Laboratory and Los Alamos National Laboratory.
Category:Masers