The EMIR multi-band mm-wave receiver for the IRAM 30-m telescope

Abstract

Aims. The prime motivation of this project was to design and build a state-of-art mm-wave heterodyne receiver system to enhance the observing throughput of the IRAM 30-m radiotelescope. More specifically, the requirements were i) state-of-art noise performance for spectroscopic observations; ii) simultaneous dual polarization and dual-frequency observing; iii) coverage of the atmospheric transmission windows from 83 to 360 GHz; iv) compact footprint and minimal maintenance. Methods. Key elements for low noise performance of heterodyne mixers are the superconducting Niobium junctions, operating at 4 K. These junctions are embedded in carefully designed coupling structures; furthermore, since atmospheric radiation is a significant contributor to the system noise budget, all mixers are either sideband separating or sideband rejecting. To achieve low noise, it is also essential to maximize the coupling of the receiver to the astronomical source, and to minimize the coupling to thermal radiation from the ground-based environment; this is achieved through mirror optics that realize a wavelength-independent coupling to the telescope. A flexible configuration of mirrors and frequency selective surfaces permits various combinations of frequency bands, as well as dual-load radiometric calibration. Low noise intermediate frequency amplifiers and bias electronics also play an important role in the system performance. Results. The EMIR receiver in operation at the 30 m telescope offers four frequency bands: B1: 83−117 GHz, B2: 129−174 GHz, B3: 200−267 GHz, and B4: 260−360 GHz. In each band, the two orthogonal polarizations are observed simultaneously. Dual-band combinations B1/2 B1/3, and B2/4 are available. Bands 1 and 4 (also 3 as of Nov.-2011) feature sideband separation. In dual-band configuration, including sideband separation and polarization diplexing, up to eight IF channels are delivered to the spectrometers, totaling up to 64 GHz of signal bandwidth (of which 32 GHz can be transported and processed by spectrometers, status Nov.-2011). The EMIR receiver has been in continuous operation for more than two years and has allowed, through a qualitative jump in performance, observations not possible before, as shown by a few selected examples of astronomical results.

Formation and evolution of interstellar filaments

“…In March 2011, we observed the C 18 O(2−1) and 13 CO(2−1) spectral lines with the HEterodyne Receiver Array (HERA, Schuster et al 2004) and the N 2 H + (1−0) line with the Eight MIxer Receiver (EMIR, a multiband mm-wave receiver, Carter et al 2012) toward the filaments of IC 5146. In addition to single-position spectra taken in the on-off observing mode, we mapped filament 14 in IC 5146 (yellow rectangle in Fig.…”

A simultaneous 3.5 and 1.3 mm polarimetric survey of active galactic nuclei in the northern sky

“…The observations were performed with the XPOL polarimeter (Thum et al 2008) connected to the E090 and E230 EMIR receiver system (Carter et al 2012) on the IRAM 30 m telescope. The advanced design of EMIR allowed us to perform the observations simultaneously at 3.5 mm (86 GHz with the E090 pair of orthogonal receivers) and 1.3 mm (229 GHz with the E230 pair of orthogonal receivers) without loss of a significant amount of signal at either waveband (Thum et al 2008).…”

The CN/C15N isotopic ratio towards dark clouds

“…The VESPA autocorrelator was used as a spectrometer to provide us with high-resolution spectra, namely, 20 kHz or 0.054 km s −1 at 110 GHz. The typical receiver temperature achieved with the EMIR detectors (Carter et al 2012) was ≈ 40 K, resulting in system temperatures ≈ 120 K. Amplitude calibration was performed using the threephase IRAM method typically every 10 min. Pointing and focus sessions using strong continuum sources were repeated every one and two hours respectively.…”