Oliver Ricken

4.7-THz Superconducting Hot Electron Bolometer Waveguide Mixer

We present the first superconducting hot electron bolometer (HEB) waveguide mixer operating at 4.7 THz. The 5.5-nm-thick, 300-nm-long, and 3600-nm-wide NbN HEB microbridge is integrated into a normal metal (Au) planar circuit on a 2 μm thick silicon substrate. This circuit is integrated in a 24 μm × 48 μm × 21 μm waveguide cavity and a 14 μm × 7 μm × 200 μm substrate channel, which is directly machined into a CuTe alloy block. The power spectrum of the HEB mixer, measured with a Fourier transform spectrometer, is in good agreement with the results of 3-D EM circuit simulation. Measured mixer performance shows a state-of-the-art double sideband noise temperature of 1100 K, averaged over the IF bandwidth of 0.2-3.5 GHz. The 3-dB noise roll-off is 3.5 GHz. This mixer is used in the German REceiver for Astronomy at Terahertz frequencies (GREAT) at the airborne Stratospheric Observatory for Far Infrared Astronomy (SOFIA).

The upGREAT 1.9 THz multi-pixel high resolution spectrometer for the SOFIA Observatory

We present a new multi-pixel high resolution ( R ≳ 10 7 ) spectrometer for the Stratospheric Observatory for Far-Infrared Astronomy (SOFIA). The receiver uses 2 × 7-pixel subarrays in orthogonal polarization, each in an hexagonal array around a central pixel. We present the first results for this new instrument after commissioning campaigns in May and December 2015 and after science observations performed in May 2016. The receiver is designed to ultimately cover the full 1.8−2.5 THz frequency range but in its first implementation, the observing range was limited to observations of the [CII] line at 1.9 THz in 2015 and extended to 1.83−2.07 THz in 2016. The instrument sensitivities are state-of-the-art and the first scientific observations performed shortly after the commissioning confirm that the time efficiency for large scale imaging is improved by more than an order of magnitude as compared to single pixel receivers. An example of large scale mapping around the Horsehead Nebula is presented here illustrating this improvement. The array has been added to SOFIA’s instrument suite already for ongoing observing cycle 4.

First Supra-THz Heterodyne Array Receivers for Astronomy With the SOFIA Observatory

We present the upGREAT THz heterodyne arrays for far-infrared astronomy. The low-frequency array (LFA) is designed to cover the 1.9-2.5 THz range using 2 × 7-pixel waveguide-based HEB mixer arrays in a dual polarization configuration. The high-frequency array (HFA) will perform observations of the [OI] line at ~ 4.745 THz using a 7-pixel waveguide- based HEB mixer array. This paper describes the common design for both arrays, cooled to 4.5 K using closed-cycle pulse tube technology. We then show the laboratory and telescope characterization of the first array with its 14 pixels (LFA), which culminated in the successful commissioning in May 2015 aboard the SOFIA airborne observatory observing the [CII] fine structure transition at 1.9005 THz. This is the first successful demonstration of astronomical observations with a heterodyne focal plane array above 1 THz and is also the first time high-power closed-cycle coolers for temperatures below 4.5 K are operated on an airborne platform.

Spectroscopically resolved far-IR observations of the massive star-forming region G5.89–0.39

The fine-structure line of [OI] at 63micron is an important diagnostic tool in different fields of astrophysics. However, our knowledge of this line relies on observations with low spectral resolution, and the real contribution of each component (PDR, jet) in complex environment of star-forming regions (SFRs) is poorly understood. We investigate the contribution of jet and PDR emission, and of absorption to the [OI]63micron line towards the ultra-compact H{\sc ii} region G5.89--0.39 and study its far-IR line luminosity in different velocity regimes through [OI], [CII], CO, OH, and H2O. We mapped G5.89--0.39 in [OI] and in CO(16--15) with the GREAT receiver onboard SOFIA. We observed the central position of the source in the OH^2\Pi_{3/2}, J=5/2\toJ=3/2 and ^2\Pi_{1/2}, J=3/2\toJ=1/2 lines. These data were complemented with APEX CO(6-5) and CO(7-6) and HIFI maps and single-pointing observations in [CII], H2O, and HF. The [OI] spectra in G5.89--0.39 are severely contaminated by absorptions from the envelope and from different clouds along the line of sight. Emission is detected only at HV, clearly associated with the compact north-south outflows traced by extremely HV low-J CO. The mass-loss rate and energetics of derived from [OI] agree well with estimates from CO, suggesting that the molecular outflows in G5.89--0.39 are driven by the jet system seen in [OI]. The far-IR line luminosity of G5.89--0.39 is dominated by [OI] at HV; the second coolant in this velocity regime is CO, while [CII], OH and H2O are minor contributors to the cooling in the outflow. Our study shows the importance of spectroscopically resolved data of [OI]63micron for using this line as diagnostic of SFRs. While this was not possible until now, the GREAT receiver onboard SOFIA has recently opened the possibility of detailed studies of this line to investigate its potential for probing different environments.

SOFIA/GREAT Discovery of Terahertz Water Masers

We report the discovery of water maser emission at frequencies above 1 THz. Using the GREAT instrument on SOFIA, we have detected emission in the 1.296411 THz 8(27)-7(34) transition of water toward three oxygen-rich evolved stars: W Hya, U Her, and VY CMa. An upper limit on the 1.296 THz line flux was obtained toward R Aql. Near-simultaneous observations of the 22.23508 GHz 6(16)-5(23) water maser transition were carried out towards all four sources using the Effelsberg 100m telescope. The measured line fluxes imply 22 GHz / 1.296 THz photon luminosity ratios of 0.012, 0.12, and 0.83 respectively for W Hya, U Her, and VY CMa, values that confirm the 22 GHz maser transition to be unsaturated in W Hya and U Her. We also detected the 1.884888 THz 8(45)-7(53) transition toward W Hya and VY CMa, and the 1.278266 THz 7(43)-6(52) transition toward VY CMa. Like the 22 GHz maser transition, all three of the THz emission lines detected here originate from the ortho-H2O spin isomer. Based upon a model for the circumstellar envelope of W Hya, we estimate that stimulated emission is responsible for ~ 85% of the observed 1.296 THz line emission, and thus that this transition may be properly described as a terahertz-frequency maser. In the case of the 1.885 THz transition, by contrast, our W Hya model indicates that the observed emission is dominated by spontaneous radiative decay, even though a population inversion exists.

L1599B: CLOUD ENVELOPE AND C+ EMISSION IN A REGION OF MODERATELY ENHANCED RADIATION FIELD

We study the effects of an asymmetric radiation field on the properties of a molecular cloud envelope. We employ observations of carbon monoxide (12CO and 13CO), atomic carbon, ionized carbon, and atomic hydrogen to analyze the chemical and physical properties of the core and envelope of L1599B, a molecular cloud forming a portion of the ring at approximately 27 pc from the star Lambda Ori. The O III star provides an asymmetric radiation field that produces a moderate enhancement of the external radiation field. Observations of the [CII] fine structure line with the GREAT instrument on SOFIA indicate a significant enhanced emission on the side of the cloud facing the star, while the [Ci], 12CO and 13CO J = 1-0 and 2-1, and 12CO J = 3-2 data from the PMO and APEX telescopes suggest a relatively typical cloud interior. The atomic, ionic, and molecular line centroid velocities track each other very closely, and indicate that the cloud may be undergoing differential radial motion. The HI data from the Arecibo GALFA survey and the SOFIA/GREAT [CII] data do not suggest any systematic motion of the halo gas, relative to the dense central portion of the cloud traced by 12CO and 13CO.

The inception of star cluster formation revealed by [C ii] emission around an Infrared Dark Cloud

We present SOFIA-upGREAT observations of [CII] emission of Infrared Dark Cloud (IRDC) G035.39-00.33, designed to trace its atomic gas envelope and thus test models of the origins of such clouds. Several velocity components of [CII] emission are detected, tracing structures that are at a wide range of distances in the Galactic plane. We find a main component that is likely associated with the IRDC and its immediate surroundings. This strongest emission component has a velocity similar to that of the

Velocity resolved [C ii], [C i], and CO observations of the N159 star-forming region in the Large Magellanic Cloud: a complex velocity structure and variation of the column densities

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Impacts of pure shocks in the BHR71 bipolar outflow

CO(2-1) emission of the IRDC, but offset by

The upGREAT heterodyne array receivers for far Infrared astronomy

\sim3\:{\rm km\:s}^{-1}