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JCMT -- the James Clark Maxwell Telescope (JCMT telescope web)
Telescope
15-m diameter telescope
longitude(west) 155 28 47, latitude 19 49 33
altitude of 4092m
The antenna has a lower elevation limit of 5deg, and sources may not be tracked accurately above elevations of about 87deg; the upper limit for position- or beam-switched observations is likely to be 85 or even lower.
pointing accuracies of about arcsec (rms) in both azimuth and elevation
tracking appears to be better than 1 arcsec over periods of an hour or so, and may well be dominated by refraction noise in many cases.
Receiver
SiS mixers, working in four frequency bands:
A: 211-276 GHz
B: 315-370 GHz
C: 430-510 GHz
D: 625-710 GHz
HARP-B: a heterodyne array receiver with 16 elements
345 GHz band.
Here is a table from JCMT web page: link.
| Chan- | Image | Freq. | IF | Bandw. | Efficiencies | HPBW | |||||||||||
| nels | Rej'n? | (GHz) | (GHz) | (K) | (MHz) | η_a | η_mb | η_fss | η_tel | (arcsec) | Notes | ||||||
| A3 | 1 | N | 211-279 | 4.00 | (80) | 1800 | 0.57 | 0.69 | 0.80 | 0.91 | 19.7 | ||||||
| B3 | 2 | Y | 310-370 | 4.00 | 1800 | (0.53) | 0.63 | 0.88 | 0.86 | 13.2 | |||||||
| W/C | 2 | Y | 430-510 | 4.00 | 150 | 1600 | 0.31 | 0.52 | 0.70 | 0.83 | 10.8 | 1 | |||||
| W/D | 2 | Y | 630-710 | 4.00 | 350 | 1600 | (0.20) | (0.30) | (0.60) | (0.65) | (8.0) | 1,2 | |||||
| MPI | 1 | N | 790-840 | 2.54 | 750 | 1000 | (0.15) | (0.25) | (0.50) | (0.60) | (7.0) | 3 | |||||
| Notes: | |||||||||||||||||
| (1) Characterisation ongoing | |||||||||||||||||
| (2) Upgraded mixers installed in 2001 and 2002; re-commissioning still ongoing | |||||||||||||||||
| (3) Available by collaboration with Ronald Stark, MPIfR, Bonn | |||||||||||||||||
Backends
DAS - Digital Autocorrelation Spectrometer
Resolution: 95 kHz - 1.5 MHz
Frequency coverage: 125 - 1800 MHz
ACSIS - designed for the receiver array HARP-B
A configuration table from JCMT web: link.
| No. of | Channel | Spectral | Channels | ||
| Bandwidth | Sub- | spacing | Resolution | per | Notes |
| (MHz) | systems | (kHz) | (kHz)a | subsystemb | |
| Single Polarization (all receivers) | |||||
| 125 | 1 | 78 | 95 | 1600 | 1 |
| 250 | 1 | 156 | 189 | 1600 | |
| 500 | 1 | 313 | 378 | 1600 | |
| 760 | 1 | 625 | 756 | 1216 | 2 |
| 920 | 1 | 625 | 756 | 1472 | |
| 1800 | 2 | 1250 | 1513 | 736 | 3 |
| Dual Polarization (receivers B3, W only) | |||||
| 125 | 2 | 156 | 189 | 800 | 4 |
| 250 | 2 | 313 | 378 | 800 | |
| 500 | 2 | 625 | 756 | 800 | |
| 760 | 2 | 1250 | 1513 | 608 | 2 |
| 920 | 2 | 1250 | 1513 | 736 | 5 |
| aSpectral resolution assumes natural weighting (the default) | |||||
| bActual number of channels per subsystem will be somewhat greater due | |||||
| to edge effects | |||||
| Notes: | |||||
| 1) Best achievable resolution; for receivers used in single-channel mode only. | |||||
| 2) Compressed 920-MHz-band option with an increased overlap between | |||||
| the subbands. | |||||
| 3) Widest band available overall (single polarization only). | |||||
| 4) Best resolution for receivers used in dual-polarization mode. | |||||
| 5) Widest band available overall in dual polarization mode | |||||
Calibration strategy
Use planet to calibrate the flux density. The standard spectra are only for fast check.
Temperatures and efficiencies
For position and beam switch observations, the rms temperature is
TA*(rms) = 2 * Tsys * k / sqrt(t * dnu)
where TA* has been corrected for atmopherical opacity, k = 1.15 is the backend degradation factor of DAS, t is integration time on both target and reference positions in seconds, dnu is the channel width in Hz.
TR*(rms) = TA* / eta_fss
The rms flux fluctuation in Jy can be derived as
S(rms) = 15.6 * TA*(rms) /eta_a
where eta_a is the antenna efficiency which can be found in above table.
More documents on the determination of efficiencies can be found in the JCMT web here.