C
International Astronomical Union Spectral Lines of Most Importance Below 300 GHz
At each triennial meeting of the General Assembly, the International Astronomical Union (IAU) reviews carefully the list of astrophysically most important spectral lines that it maintains. The IAU expresses the need to protect these frequency bands from in-band, band-edge, and harmonic emissions, especially from spaceborne transmitters.
In preparation for World Radiocommunication Conference 2000, which revised the allocations above 71 GHz, a millimeter-wavelength working group of the Scientific Committee on Frequency Allocations for Radio Astronomy and Space Science (IUCAF) examined all then-known transitions in the millimeter and submillimeter wavebands. The working group selected a limited number of the astrophysically most important spectral lines to supplement the earlier lists, such as those produced by the IAU, to be used in allocating frequency bands to the Radio Astronomy Service. Spectral lines below 300 GHz are listed in Table C.1. Unless otherwise noted, the suggested minimum band limits are Doppler-shifted frequencies corresponding to radial velocities of ±300 km/s, consistent with line radiation occurring in our Milky Way galaxy. Spectral lines with primary (P), secondary (S), or footnote (F) protection status are noted in Table C.1.
TABLE C.1 The Most Important Spectral Lines Below 300 GHz
Species | Formula | Frequency (GHz) | Suggested Minimum Band (GHz) | Band Allocation Status | Notes (1) |
Deuterium | Di | 0.327384 | 0.327-0.3277 | P | |
Hydrogen | Hi | 1.420406 | 1.370-1.427 | S 1.33-1.40 | 2, 3 |
P 1.40-1.427 | |||||
Hydroxyl radical | OH | 1.612231 | 1.6068-1.6138 | P 1.6106-1.6138 | 4 |
1.665402 | 1.6598-1.6671 | P 1.66-1.67 | 4 | ||
1.667359 | 1.6618-1.6690 | 4 | |||
Hydroxyl radical | OH | 1.720530 | 1.7148-1.7222 | S 1.7188-1.7222 | 3, 4 |
Methyladyne | CH | 3.263794 | 3.2424-3.2671 | S 3.260-3.267 | 3, 4 |
3.335481 | 3.3244-3.3388 | S 3.332-3.339 | 3, 4 | ||
3.349193 | 3.3380-3.3525 | S 3.3458-3.3525 | 3, 4 | ||
Formaldehyde | H2CO | 4.829660 | 4.8136-4.8345 | S 4.8-4.9 | 3, 4 |
Methanol | CH3OH | 6.668518 | 6.6618-6.6752 | S 6.650-6.6752 | 3 |
Helium | 3He+ | 8.665650 | 8.6570-8.6743 | 3, 6 | |
Methanol | CH3OH | 12.178 | 12.17-12.19 | 3, 6 | |
Formaldehyde | H2CO | 14.488 | 14.44-14.50 | S 14.47-14.50 | 3, 4 |
Cyclopropenylidene | C3H2 | 18.343 | 18.28-18.36 | 3, 4, 6 | |
Water vapor | H2O | 22.235 | 22.16-22.26 | F 22.01-22.21 | 3, 4 |
P 22.21-22.50 | |||||
Ammonia | NH3 | 23.694 | 23.61-23.71 | P 23.60-24.00 | 4 |
23.723 | 23.64-23.74 | 4 | |||
23.870 | 23.79-23.89 | 4 | |||
Sulphur monoxide | SO | 30.002 | 29.97-30.03 | 6 | |
Methanol | CH3OH | 36.169 | 36.13-36.21 | P 36-37 | 6 |
Silicon monoxide | SiO | 42.519 | 42.47-42.57 | F 42.77-42.87 | 6, 8 |
42.821 | 42.78-42.86 | F 43.07-43.17 | |||
43.122 | 43.08-43.17 | F 43.37-43.47 | |||
43.424 | 43.38-43.47 | ||||
Dicarbon monosulphide | CCS | 45.379 | 45.33-45.42 | 6 | |
Carbon monosulphide | CS | 48.991 | 48.94-49.04 | P 48.94-49.04 | |
Oxygen | O2 | 61.1 | 56.21-63.06 | P 58.2-59.0 | 5, 6, 7 |
Deuterated water | HDO | 80.578 | 80.50-80.66 | ||
Cyclopropenylidene | C3H2 | 85.339 | 85.05-85.42 | ||
Silicon monoxide | SiO | 86.243 | 86.16-86.33 | P | |
Formylium | H13CO+ | 86.754 | 86.67-86.84 | P | |
Silicon monoxide | SiO | 86.847 | 86.76-86.93 | P | |
Ethynyl radical | C2H | 87.300 | 87.21-87.39 | P | 5 |
Hydrogen cyanide | HCN | 88.632 | 88.34-88.72 | P | 4 |
Formylium | HCO++ | 89.189 | 88.89-89.28 | P | 4 |
Hydrogen isocyanide | HNC | 90.664 | 90.57-90.75 | P | |
Species | Formula | Frequency (GHz) | Suggested Minimum Band (GHz) | Band Allocation Status | Notes (1) |
Diazenylium | N2H+ | 93.174 | 93.08-93.27 | ||
Carbon monosulphide | CS | 97.981 | 97.65-98.08 | 4 | |
Sulfur monoxide | SO | 99.300 | 99.20-99.40 | ||
Methyl acetylene | CH3CCH | 102.5 | 102.39-102.60 | 5 | |
Methanol | CH3OH | 107.014 | 106.91-107.12 | ||
Carbon monoxide | C18O | 109.782 | 109.67-109.89 | P | |
Carbon monoxide | 13CO | 110.201 | 110.83-110.31 | P | 4 |
Carbon monoxide | C17O | 112.359 | 112.25-112.47 | P | 6 |
Cyano radical | CN | 113.500 | 113.39-113.61 | P | 5 |
Carbon monoxide | CO | 115.271 | 114.88-115.39 | P | 4 |
Oxygen | O2 | 118.750 | 118.63-118.87 | P 116-126 | 7 |
Formaldehyde | H213CO | 137.450 | 137.31-137.59 | 6 | |
Formaldehyde | H2CO | 140.840 | 140.69-140.98 | P | |
Carbon monosulphide | CS | 146.969 | 146.48-147.12 | P 146.82-147.12 | |
Nitric oxide | NO | 150.4 | 149.95-150.85 | S 150-151 | 5 |
Methanol | CH3OH | 156.602 | 156.45-156.76 | ||
Water vapor | H2O | 183.310 | 183.13-183.49 | ||
Carbon monoxide | C18O | 219.560 | 219.34-219.78 | P | |
Carbon monoxide | 13CO | 220.399 | 219.67-220.62 | P | 4 |
Cyano radical | CN | 226.600 | 226.37-226.83 | P | 5 |
Cyano radical | CN | 226.800 | 226.57-227.03 | P | 5 |
Carbon monoxide | CO | 230.538 | 229.77-230.77 | P | 4 |
Carbon monosulphide | CS | 244.953 | 244.14-245.20 | 6 | |
Nitric oxide | NO | 250.6 | 250.35-250.85 | P | 5 |
Ethynyl radical | C2H | 262.000 | 261.74-262.26 | 5 | |
Hydrogen cyanide | HCN | 265.886 | 265.00-266.15 | ||
Formylium | HCO++ | 267.557 | 266.66-267.82 | ||
Hydrogen isocyanide | HNC | 271.981 | 271.71-272.25 | ||
Diazenylium | N2H+ | 279.511 | 279.23-279.79 | ||
Carbon monosulphide | CS | 293.912 | 292.93-294.21 | ||
NOTES:
1. If Notes 2 or 4 are not listed, then the band limits are the Doppler-shifted frequencies corresponding to radial velocities of ± 300 km/s (consistent with line radiation occurring in our Milky Way galaxy).
2. An extension to lower frequency of the allocation of 1 400-1 427 MHz is required to allow for the higher Doppler shifts for HI observed in distant galaxies.
3. The current international allocation is not primary and/or does not meet bandwidth requirements. See the Radio Regulations (RR) for more detailed information.
4. Because these line frequencies are also being used for observing other galaxies, the listed bandwidths include Doppler shifts corresponding to radial velocities of up to 1,000 km/s. It should be noted that HI has been observed at frequencies redshifted to 500 MHz, while some lines of the most abundant molecules have been detected in galaxies with velocities up to 50,000 km/s, corresponding to a frequency reduction of up to 17%.
5. There are several closely spaced lines associated with these molecules. The listed bands are wide enough to permit observations of all lines.
6. This line frequency is not mentioned in RR Article 5.
7. These lines are observable only outside the atmosphere.
8. A portion of the “suggested minimum band” for this line extends outside the band allocated to the radio astronomy service. Protection for observations conducted in this portion of the band may not be practicable.
SOURCE: Data and further information can be found in the International Telecommunication Union, RA 314 Series: Preferred Frequency Bands for Radio Astronomical Measurements, June 2003, http://www.itu.int/dms_pubrec/itu-r/rec/ra/R-REC-RA.314-10-200306-I!!PDF-E.pdf.