{"id":164,"date":"2014-11-12T23:47:24","date_gmt":"2014-11-13T09:47:24","guid":{"rendered":"http:\/\/www.eaobservatory.org\/jcmt\/?page_id=164"},"modified":"2026-01-29T10:02:44","modified_gmt":"2026-01-29T20:02:44","slug":"harp","status":"publish","type":"page","link":"https:\/\/www.eaobservatory.org\/jcmt\/instrumentation\/heterodyne\/harp\/","title":{"rendered":"350 GHz band: HARP"},"content":{"rendered":"

\"harp1_lowres\"<\/a><\/p>\n

HARP (Heterodyne Array Receiver Program) is a Single Sideband<\/a> (SSB) array receiver with 16 SIS mixers. HARP can be tuned between 325 and 375 GHz and has a instantaneous bandwidth of ~2 GHz and an Intermediate Frequency (IF) of 5 GHz. The unwanted sideband is terminated on a 20 K load inside the Dewar. The mixers are called receptors and arranged in a 4×4 configuration. The different receptors are separated by 30″ and named H00, H01 … H15. HARP was designed and built by University of Cambridge<\/a> in collaboration with different other groups.<\/p>\n

The half power beam width of each receptor is approximately 14 arcsec. One of the four center receptors is used for pointing and focus<\/a> observations and for pointed observations. This is called the tracking receptor, currently it is H05.<\/p>\n

At 345GHz the main beam efficiency<\/a> \u03b7mb<\/sub> for HARP is 0.64 and \u03b7fss<\/sub> (measured on the Moon in 2006) is 0.77. In April 2015 this efficiency was 0.75.
\nThe aperture efficiency \u03b7a<\/sub> for HARP is 0.52.<\/p>\n

Together with the spectrometer ACSIS<\/a>, HARP is designed to rapidly map large areas. The telescope is scanning in a raster pattern and spectra are read out at a high enough rate to avoid smearing the map. By using the short integration times made available by ACSIS, a map can be done quickly. Combining maps obtained by scanning<\/a> in different ways improves the map uniformity in sensitivity and calibration. It is thus preferable to make several fast maps than one slow one.<\/p>\n

Note that special considerations must be taken into account when observing targets with a strong continuum<\/a> such as the moon, the Sun, or planetary atmospheres.<\/p>\n

Detailed information about this receiver is given by Buckle, J.V., Hills, R.E., Smith, H., et al., 2009, MNRAS 399, 1026<\/a>.<\/p>\n

The figure below shows the atmospheric transmission for the tuning range of HARP for weather bands 1 to 4<\/a>, taken from Buckle et al.<\/a>. The frequencies of some frequently observed molecular transitions are indicated.<\/p>\n

\"harp_transmission_buckle\"<\/a><\/p>\n

The figure below shows the receiver temperature Trx<\/sub> of the tracking receptor H05 of HARP as a function of sky frequency for observations made in 2014. Observations made in the Lower Side Band (LSB) are indicated in purple; observations made in the Upper Side Band (USB) in blue. The drawn line gives the median Trx<\/sub> values which are used in the heterodyne time estimator (HITEC).<\/p>\n

\"HARP_H05_avg_trx_vs_freq\"<\/a><\/p>\n

The following table below gives links to figures with the receiver temperature Trx<\/sub> as a function of sky frequency for 14 of the working receptors from data obtained in 2014, as well as the average Trx<\/sub> at 345.796GHz.<\/p>\n\n\n\n\n\n\n
H12<\/a>
\n160K<\/td>\n		H13<\/td>\nH14*<\/td>\nH15<\/a>
\n175K<\/td>\n<\/tr>\n
H11<\/a>
\n170K<\/td>\n		H10<\/a>
\n152K<\/td>\n		H09<\/a>
\n105K<\/td>\n		H08<\/a>
\n143K<\/td>\n<\/tr>\n
H04<\/a>
\n118K<\/td>\n		H05<\/a>
\n110K<\/td>\n		H06<\/a>
\n182K<\/td>\n		H07<\/a>
\n112K<\/td>\n<\/tr>\n
H03<\/a>
\n185K<\/td>\n		H02<\/a>
\n125K<\/td>\n		H01<\/a>
\n148K<\/td>\n		H00*<\/a><\/em>
\n127K*
\n<\/em><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

*H00, H02, H14 and H15 are not currently operational (January 2026). H13 and H14 were not operational in 2014 when the data for the table was obtained..<\/p>\n

HARP is located in the right Nasmyth focus of the JCMT. The orientation of the array on the sky is determined by the K-mirror<\/a>. The software determines which of the four possible K-mirror angles (with the array in a N-S\/E-W, or user specified direction) allows the longest tracking time.<\/p>\n

Important Notes\/Current status<\/h3>\n