Recently, a joint research team from National Time Service Center (NTSC) of the Chinese Academy of Sciences (CAS), Shanghai Astronomical Observatory (SHAO) of CAS and SKA Observatory used the Shanghai Tianma Radio Telescope to search for 4.7 GHz OH masers in 155 northern star forming regions and discovered eight new sources.
Their findings were published in The Astrophysical Journal on April 4.
OH masers are usually detected towards high-mass (eight times the mass of the Sun) star formation regions. "Observing OH masers at different transitions in the same maser site could place strong constraints on the in-situ physical conditions, such as H2 density, temperature and velocity gradients," said QIAO Haihua, first author of the study.
The researchers investigated the associations between the 18 detected 4.7 GHz OH masers with ground-state OH masers near 1.7 GHz, 6.7 GHz methanol masers and 22 GHz water masers.
They found that the presence of 1665 MHz OH masers was a better indicator of the presence of 4.7 GHz OH masers than 1720 MHz OH masers, and the majority of the 4.7 GHz OH masers were associated with 6.7 GHz methanol and/or 22 GHz water masers.
The formation process of high-mass stars is a fundamental and hot topic in astrophysics. Observations of high-mass star formation processes are hindered by their large distances, high extinction and the short timescales of critical evolutionary phases.
However, OH maser emission arises at radio frequency and is not affected by the dense optical-obscuring gas and dust, which exists at the early stages of high-mass star formation. Thus, the researchers could use OH masers to probe high-mass stars at the earliest stages.
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