A new design of a cryogenic linear 22-pole ion trap has been constructed and tested. It is essentially a copper housing to which opposite inner walls two electrode sets are attached via sapphire insulators. These stainless steel electrodes are electroformed in one piece to guarantee good heat conduction. Connected to an external coil, they form an LC-circuit of about 19 MHz resonance frequency. This circuit is excited with a rf power supply made of a commercial digital synthesizer followed by a 10 W amplifier. Buffer gas-cooled H(2)D(+) ions have been stored in this trap at a nominal trap temperature of 14 K. Spectroscopy of the ions confirmed that the kinetic (Doppler) temperature is in reasonable agreement with this value.

Context. The THz atmospheric "windows", centered at roughly 1.3 and 1.5 THz, contain numerous spectral lines of astronomical importance, including three high-J CO lines, the [N II] line at 205 µm, and the ground transition of para-H 2 D + . The CO lines are tracers of hot (several 100 K), dense gas; [N II] is a cooling line of diffuse, ionized gas; the H 2 D + line is a non-depleting tracer of cold (∼20 K), dense gas. Aims. As the THz lines benefit the study of diverse phenomena (from high-mass star-forming regions to the WIM to cold prestellar cores), we have built the CO N + Deuterium Observations Receiver (CONDOR) to further explore the THz windows by ground-based observations. Methods. CONDOR was designed to be used at the Atacama Pathfinder EXperiment (APEX) and Stratospheric Observatory For Infrared Astronomy (SOFIA). CONDOR was installed at the APEX telescope and test observations were made to characterize the instrument.Results. The combination of CONDOR on APEX successfully detected THz radiation from astronomical sources. CONDOR operated with typical T rec = 1600 K and spectral Allan variance times of ∼30 s. CONDOR's "first light" observations of CO 13−12 emission from the hot core Orion FIR 4 (= OMC1 South) revealed a narrow line with T MB ≈ 210 K and ∆V ≈ 5.4 km s −1 . A search for [N II] emission from the ionization front of the Orion Bar resulted in a non-detection. Conclusions. The successful deployment of CONDOR at APEX demonstrates the potential for making observations at THz frequencies from ground-based facilities.

Context. Sites of massive star formation have complex internal structures. Local heating by young stars and kinematic processes, such as outflows and stellar winds, generate large temperature and velocity gradients. Complex cloud structures lead to intricate emission line shapes. CO lines from high mass star forming regions are rarely Gaussian and show often multiple peaks. Furthermore, the line shapes vary significantly with the quantum number J up , due to the different probed physical conditions and opacities. Aims. The goal of this paper is to show that the complex line shapes of 12 CO and 13 CO in NGC 2024 showing multiple emission and absorption features, which vary with rotational quantum number J can be explained consistently with a model, whose temperature and velocity structure are based on the well-established scenario of a PDR and the "Blister model". Methods. We present velocity-resolved spectra of seven 12 CO and 13 CO lines ranging from J up = 3 to J up = 13. We combined these data with 12 CO high-frequency data from the ISO satellite and analyzed the full set of CO lines using an escape probability code and a one-dimensional full radiative transfer code. Results. We find that the bulk of the molecular cloud associated with NGC 2024 consists of warm (75 K) and dense (9 × 10 5 cm −3 ) gas. An additional hot (∼300 K) component, located at the interface of the HII region and the molecular cloud, is needed to explain the emission of the high-J CO lines. Deep absorption notches indicate that very cold material (∼20 K) exists in front of the warm material, too. Conclusions. A temperature and column density structure consistent with those predicted by PDR models, combined with the velocity structure of a "Blister model", appropriately describes the observed emission line profiles of this massive star forming region. This case study of NGC 2024 shows that, with physical insights into these complex regions and careful modeling, multi-line observations of 12 CO and 13 CO can be used to derive detailed physical conditions in massive star forming regions.

We are developing a 1.4 THz receiver to explore the far infrared universe, such as probing high mass star forming regions using, e.g., the high J transitions of CO, investigating the warm interstellar medium in N + or probing cold and dense stellar cores in H 2 D + . Due to the poor atmospheric transmission at these frequencies we are planning to use this modular receiver on high altitude ground based observatories, for example the Atacama Pathfinder EXperiment (APEX), and as an additional channel for the German Receiver for Astronomy at Terahertz Frequencies (GREAT) on the Stratospheric Observatory For Infrared Astronomy (SOFIA) located on an airplane. To allow successful astronomical observations under poor atmosphere transmission a low receiver noise temperature and a high receiver stability are mandatory. To achieve a low receiver temperature the main effort is directed to develop phonon-cooled NbTiN HEB mixers. For optimum coupling with the telescope beam and easier alignment we are focussing on waveguide mixers. A phase locked Gunn (114-135 GHz) and three multipliers will be used as the Local Oscillator (LO) of 1370-1500 GHz. A liquid He Dewar will be used for operation on SOFIA and a closed-cycle system with a pulse-tube cooler on APEX. Initially, we are aiming for 1 GHz IF bandwidth (214 kms −1 at 1.4 THz) sufficient for galactic observations. First tests and astronomical observations with a similar but lower frequency HEB at 800 GHz have yielded encouraging results.

The CON+Deuterium Observations Receiver (CONDOR) is a heterodyne receiver that operates between 1250–1530 GHz. Its primary goal is to observe star-forming regions in CO, N+, and H2D+ emission.