Masers at 22GHz
At 22 GHz, the most prominent masers are water (H₂O) masers, specifically:
🔹 Water (H₂O) Maser at 22.23508 GHz
- Transition: 61,6→52,36_{1,6} \rightarrow 5_{2,3} rotational transition of ortho-water.
- Rest Frequency: 22.23508 GHz
- Type: Collisionally pumped
- Maser Class: Often referred to as Class I, though that terminology is more common in methanol masers.
🔍 Astrophysical Contexts
Water masers at 22 GHz are found in a wide variety of environments:
1. Star-Forming Regions
- Examples: Orion KL, W49, W51
- Associated with outflows, shocks, and dense gas in protostellar environments.
2. Evolved Stars
- Found in the circumstellar envelopes of AGB stars, Mira variables, and red supergiants.
- Often used to trace mass-loss processes.
3. Galactic Center and Starburst Galaxies
- Used to map accretion disks and outflows in megamaser galaxies (e.g., NGC 4258).
- These extragalactic H₂O masers are powerful tools for measuring black hole masses and even cosmic distances via geometric parallax.
4. Cometary Impacts and Planetary Atmospheres (Rare)
- Observed occasionally in special circumstances (e.g., impact-induced masers in planetary atmospheres).
🔧 Observational Notes
- 22 GHz masers are very strong, with brightness temperatures up to 101410^{14} K.
- Easily observable with instruments like:
- Very Large Array (VLA)
- Effelsberg 100m
- VLBI arrays (e.g., VLBA)
- Amateur radio telescopes with high-gain dishes and low-noise receivers (though challenging)