Detecting masers associated an amateur radio astronomer
Amateur radio astronomers can indeed detect natural astrophysical masers, though the practical options are limited by sensitivity, equipment, and local regulations. Here’s a breakdown:
1. Hydrogen (H I) Masers
- Frequency: 1420.40575 MHz (21 cm line)
- Notes:
- The 21 cm line is technically a hyperfine transition and can produce maser action in certain interstellar regions, though most emissions are weak thermal signals rather than strong masers.
- Easily detectable with modest antennas like Yagis, small dishes, or simple dipole arrays.
- Common for amateurs as part of radio astronomy projects.
2. Hydroxyl (OH) Masers
- Frequencies: 1612, 1665, 1667, 1720 MHz
- Notes:
- These are stronger astrophysical masers often found in star-forming regions, supernova remnants, or around late-type stars.
- Detecting them requires sensitive receivers and narrowband filters because the signals are often very weak.
- Popular among dedicated amateur setups with SDRs and directional antennas.
3. Water (H₂O) Masers
- Frequency: 22.235 GHz
- Notes:
- These are very bright astrophysical masers associated with star-forming regions and evolved stars.
- Detection is challenging for amateurs due to the high frequency, requiring low-noise amplifiers, high-gain antennas (parabolic dishes), and sometimes microwave waveguides.
- Some advanced amateurs have successfully detected these with 1–3 m dishes and sensitive receivers.
4. Methanol (CH₃OH) Masers
- Frequencies: Commonly 6.7 GHz (class II), 12.2 GHz
- Notes:
- Found in massive star-forming regions.
- Detection is difficult for amateurs because of the higher frequency and weaker flux compared to H₂O masers.
- Requires careful tracking, precise antennas, and often low-noise microwave front ends.
5. Other Molecules
- Molecules like SiO (43 GHz) and ammonia (NH₃, ~24 GHz) masers exist, but these are almost entirely out of reach for amateur setups due to the very high frequencies and extremely low flux densities.
Practical Takeaways for Amateurs
- Most achievable: OH masers at 1.6 GHz and H I regions at 1.42 GHz.
- Advanced: Water masers at 22 GHz with a small dish and good LNA.
- Challenging: Methanol and higher-frequency masers due to atmospheric attenuation and equipment demands.
Many amateur astronomers focus on OH and H₂O masers, often combining SDR receivers with Yagi or small parabolic antennas to track sources like W3(OH), Orion KL, or W49N.
Here’s a detailed table for masers detectable by amateur radio astronomers, including frequency, typical flux ranges, antenna recommendations, and WR waveguide sizes for microwave frequencies. I’ve included practical guidance for amateurs.
| Maser Type | Frequency (GHz) | Typical Flux (Jy) | Common Sources | Amateur Antenna | WR Waveguide (approx.) |
|---|---|---|---|---|---|
| H I (Hyperfine) | 1.4204 | 0.1–10 | Galactic H I regions, Orion Arm | Yagi array or small dish (1–3 m) | — (coax or feed line used; not waveguide) |
| OH | 1.612 / 1.665 / 1.667 / 1.720 | 0.1–100 | W3(OH), OH 127, IRC+10420 | 3–5 m dish or Yagi array | — (coaxial feeds; waveguides not typical at 1.6 GHz) |
| H₂O | 22.235 | 1–10³ | Orion KL, W49N, W3(OH) | ≥1 m dish, Cassegrain or prime focus, LNA | WR-42 (18–26.5 GHz) |
| CH₃OH | 6.668 | 1–100 | W3(OH), NGC 7538 | ≥2 m dish, precise tracking | WR-159 (4.9–7.05 GHz) |
| SiO (rare for amateurs) | 43.122 | 1–50 | Orion KL, VX Sgr | ≥3 m dish, very low-noise LNA | WR-22 (33–50 GHz) |
Notes for Amateurs
- H I and OH masers: Use coaxial feeds with Yagis or small dishes. Waveguides are unnecessary and uncommon below ~4 GHz.
- H₂O masers at 22 GHz: WR-42 waveguide is standard for feeds; dishes ≥1 m with LNAs are recommended. Atmospheric attenuation can be significant—best on clear days.
- Methanol (6.7 GHz): WR-159 is the relevant waveguide for high-efficiency feeds, though some amateurs use coaxial-fed horn antennas.
- SiO and higher-frequency masers: Mostly beyond typical amateur reach, but WR-22 waveguide feeds can be used if dish and LNA are available.