For the CCAT Heterodyne Array Instrument (CHAI) we studied the basic components for the local oscillator (LO) distribution in the 4-pixel block, of which 16 units will constitute the 64 pixels in the 455-495 GHz band. A single LO signal is divided by a cascade of on-chip 3 dB power dividers based on superconducting planar transmission lines, implemented in multipixel waveguide mixer blocks. In this article, we present two different types of power dividers, namely, a microstrip Wilkinson and a coplanar waveguide (CPW) 90(degrees) hybrid, which are designed, simulated, and fabricated. Upon integrating them in a two-pixel block with the intended mixers, we observe an unexpected difference in terms of equal power distribution to both mixers. The 90(degrees) phase difference between the outputs of the hybrid, in the presence of standing waves due to an imperfectly terminated isolated port, causes an imbalance between the LO-power transmitted to both mixers. This inequality is frequency-dependent and alternates considerably across the band. The Wilkinson due to its in-phase power division is immune to this effect and therewith demonstrates a significantly more even power transmission to the mixers.

It has long been discussed whether stellar feedback in the form of winds and/or radiation can shred the nascent molecular cloud, thereby controlling the star formation rate. However, directly probing and quantifying the impact of stellar feedback on the neutral gas of the nascent clouds is challenging. We present an investigation of this impact toward the RCW 79 H II region using the ionized carbon line at 158 μm ([C II]) from the FEEDBACK Legacy Survey. We combine this data with information on the dozen ionizing O stars responsible for the evolution of the region, and observe in [C II] for the first time both blue- and redshifted high-velocity gas that reaches velocities of up to 25 km s−1 relative to the bulk emission of the molecular cloud. This high-velocity gas mostly contains neutral gas, and partly forms a fragmented shell, similar to recently found shells in a few Galactic H II regions. However, this shell does not account for all of the observed neutral high-velocity gas. We also find high-velocity gas streaming out of the nascent cloud through holes, and obtain a range of dynamical timescales below 1.0 Myr for the high-velocity gas that is well below the 2.3 ± 0.5 Myr age of the OB cluster. This suggests a different scenario for the evolution of RCW 79, where the high-velocity gas does not solely stem from a spherical expanding bubble, but also from gas recently ablated at the edge of the turbulent molecular cloud into the surrounding interstellar medium through low-pressure holes or chimneys. The resulting mass ejection rate estimate for the cloud is 0.9–3.5 × 10−2 M⊙ yr−1, which leads to short erosion timescales (< 5 Myr) for the nascent molecular cloud. This finding provides direct observational evidence of rapid molecular cloud dispersal.

The CCAT-p Heterodyne Array Instrument (CHAI) is being developed at the I. Physikalisches Institut of the Universität zu Köln. Here we present the proposed architecture of the receiver and the advances made in testing its basic components.

High Resistivity Float-Zone (HRFZ) Silicon is a well-known material employed for optical components at far infrared wavelengths. For accurate design of those components its temperature-dependent refractive index is an important parameter. In this contribution we present the results of transmission measurements in a Fourier Transform Spectrometer of a HRFZ Silicon sample cooled down to 5K to estimate the refractive index at the passage from the mid to the far-IR down to 5K. From room-temperature to 5K the refractive index and absorption coefficient showed a decrease of about 0.83 % and of about 7-15 %, respectively.

FEEDBACK is a SOFIA (Stratospheric Observatory for Infrared Astronomy) legacy program dedicated to study the interaction of massive stars with their environment. It performs a survey of 11 galactic high mass star-forming regions in the 158 mu m (1.9 THz) line of [Cii] and the 63 mu m (4.7 THz) line of [Oi]. We employ the 14 pixel Low Frequency Array and 7 pixel High Frequency Array upGREAT heterodyne instrument to spectrally resolve (0.24 MHz) these far-infrared fine structure lines. With a total observing time of 96h, we will cover similar to 6700 arcmin(2)at 141) angular resolution for the [Cii] line and 63 for the [Oi] line. The observations started in spring 2019 (Cycle 7). Our aim is to understand the dynamics in regions dominated by different feedback processes from massive stars such as stellar winds, thermal expansion, and radiation pressure, and to quantify the mechanical energy injection and radiative heating efficiency. This is an important science topic because feedback of massive stars on their environment regulates the physical conditions and sets the emission characteristics in the interstellar medium (ISM), influences the star formation activity through molecular cloud dissolution and compression processes, and drives the evolution of the ISM in galaxies. The [Cii] line provides the kinematics of the gas and is one of the dominant cooling lines of gas for low to moderate densities and UV fields. The [Oi] line traces warm and high-density gas, excited in photodissociations regions with a strong UV field or by shocks. The source sample spans a broad range in stellar characteristics from single OB stars, to small groups of O stars, to rich young stellar clusters, to ministarburst complexes. It contains well-known targets such as Aquila, the Cygnus X region, M16, M17, NGC7538, NGC6334, Vela, and W43 as well as a selection of Hiiregion bubbles, namely RCW49, RCW79, and RCW120. These [Cii] maps, together with the less explored [Oi] 63 mu m line, provide an outstanding database for the community. They will be made publically available and will trigger further studies and follow-up observations.

C. Risacher1,6∗, R. Güsten, J. Stutzki, H.-W. Hübers, R. Aladro, A. Bell, C. Buchbender, D. Büchel, T. Csengeri, C. Duran, U. U. Graf, R. D. Higgins, C. E. Honingh, K. Jacobs, M. Justen, B. Klein , M. Mertens, Y. Okada, A. Parikka, P. Pütz, N. Reyes, H. Richter, O. Ricken, D. Riquelme, N. Rothbart, N. Schneider, R. Simon, M. Wienold, H. Wiesemeyer, M. Ziebart, P. Fusco, S. Rosner and B. Wohler Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121, Bonn, Germany, crisache@mpifr.de I. Physikalisches Institut der Universität zu Köln, Zülpicher Strasse 77, 50937 Köln, Germany Institute of Optical Sensor Systems, German Aerospace Center (DLR), Rutherfordstr. 2, 12489 Berlin, Germany Departamento de Ingenieŕıa Eléctrica, Universidad de Chile, Santiago, Chile University of Applied Sciences Bonn-Rhein-Sieg, Sankt Augustin, 53757 Germany IRAM, 300 rue de la Piscine, 38406 Saint Martin d’Heres, France NASA Ames Research Center, Moffett Field, CA 94035, USA SETI Institute, Mountain View, CA 94043, USA

Context. Dense highly ionized boundary layers (IBLs) outside of the neutral Photon Dominated Regions (PDRs) have recently been detected via the 122 and 205 μm transitions of ionized nitrogen. These layers have higher densities than in the Warm Ionized Medium (WIM) but less than typically found in H II regions. Observations of [C II] emission, which is produced in both the PDR and IBL, do not fully define the characteristics of these sources. Observations of additional probes which just trace the PDRs, such as the fine structure lines of atomic oxygen, are needed derive their properties and distinguish among different models for [C II] and [N II] emissison. Aims. We derive the properties of the PDRs adjacent to dense highly ionized boundary layers of molecular clouds. Methods. We combine high-spectral resolution observations of the 63 μm [O I] fine structure line taken with the upGREAT HFA-band instrument on SOFIA with [C II] observations to constrain the physical conditions in the PDRs. The observations consist of samples along four lines of sight (LOS) towards the inner Galaxy containing several dense molecular clouds. We interpret the conditions in the PDRs using radiative transfer models for [C II] and [O I]. Results. We have a 3.5-σ detection of [O I] toward one source but only upper limits towards the others. We use the [O I] to [C II] ratio, or their upper limits, and the column density of C+ to estimate the thermal pressure, Pth, in these PDRs. In two LOS the thermal pressure is likely in the range 2–5 × 105 in units of K cm−3, with kinetic temperatures of order 75–100 K and H2 densities, n(H2) ~ 2–4 × 103 cm−3. For the other two sources, where the upper limits on [O I] to [C II] are larger, Pth ≲105 (K cm−3). We have also used PDR models that predict the [O I] to [C II] ratio, along with our observations of this ratio, to limit the intensity of the Far UV radiation field. Conclusions. The [C II] and [N II] emission with either weak, or without any, evidence of [O I] indicates that the source of dense highly ionized gas traced by [N II] most likely arises from the ionized boundary layers of clouds rather than from H II regions.

We present the performance of the upGREAT heterodyne array receivers on the SOFIA telescope after several years of operations. This instrument is a multi-pixel high resolution (R > 10^7) spectrometer for the Stratospheric Observatory for Far-Infrared Astronomy (SOFIA). The receivers use 7-pixel subarrays configured in a hexagonal layout around a central pixel. The low frequency array receiver (LFA) has 2x7 pixels (dual polarization), and presently covers the 1.83-2.06 THz frequency range, which allows to observe the [CII] and [OI] lines at 158 um and 145 um wavelengths. The high frequency array (HFA) covers the [OI] line at 63 um and is equipped with one polarization at the moment (7 pixels, which can be upgraded in the near future with a second polarization array). The 4.7 THz array has successfully flown using two separate quantum-cascade laser local oscillators from two different groups. NASA completed the development, integration and testing of a dual-channel closed-cycle cryocooler system, with two independently operable He compressors, aboard SOFIA in early 2017 and since then, both arrays can be operated in parallel using a frequency separating dichroic mirror. This configuration is now the prime GREAT configuration and has been added to SOFIA's instrument suite since observing cycle 6.

Determining the properties of the warm ionized medium (WIM) at the leading edge of spiral arms is important for understanding its dynamics and cloud formation. The inner edge of the Scutum arm tangency is a unique location in which to disentangle the WIM from other components. We use high spectral resolution [C II] 158 micron and [N II] 205 micron fine structure line observations taken with the upGREAT and GREAT instruments on SOFIA, along with auxiliary HI and 13CO observations. The observations were in and out of the Galactic plane along 18 lines of sight between longitude 30deg and 32deg. We detect strong [N II] emission throughout the Scutum tangency. At VLSR = 110 to 125 km/s, where there is little, if any, 13CO, we could disentangle the [N II] and [C II] emission that arises from the WIM at the inner edge. We find an average electron density, about 0.9 cm{-3} in the plane, and about 0.4 cm{-3} above the plane. For VLSR < 110 km/s there is [N II] emission tracing highly ionized gas throughout the arm's molecular layer. This ionized gas has a high density, n(e) ~ 30 cm{-3}, and a few percent filling factor. Thus, [N II] and [C II] at the Scutum arm tangency reveal a highly ionized gas with about 10 to 20 times those of the interarm WIM, which is best explained by a model in which the interarm WIM is compressed as it falls into the potential well of the arm. The widespread distribution of [N II] in the molecular layers shows that high density ionized gas is distributed throughout the Scutum arm. The n(e) derived from [N II] for these molecular cloud regions are about 30 cm{-3}, and probably arise in the ionized boundary layers of clouds. This [N II] emission from the ionized boundary layers is probably the result of the shock compression of the WIM as it impacts the arm's neutral gas, but some could arise from extended HII regions.

Context. Protostellar jets and outflows are key features of the star-formation process, and primary processes of the feedback of young stars on the interstellar medium. Understanding the underlying shocks is necessary to explain how jet and outflow systems are launched, and to quantify their chemical and energetic impacts on the surrounding medium. Aims. We performed a high-spectral resolution study of the [OI]_(63μm) emission in the outflow of the intermediate-mass Class 0 protostar Cep E-mm. The goal is to determine the structure of the outflow, to constrain the chemical conditions in the various components, and to understand the nature of the underlying shocks, thus probing the origin of the mass-loss phenomenon. Methods. We present observations of the O I ^3P_1 → ^3P_2, OH between ^2Π_(1/2)J = 3/2 and J = 1/2 at 1837.8 GHz, and CO (16–15) lines with the GREAT receiver onboard SOFIA towards three positions in the Cep E protostellar outflow: Cep E-mm (the driving protostar), Cep E-BI (in the southern lobe), and Cep E-BII (the terminal position in the southern lobe). Results. The CO (16–15) line is detected at all three positions. The [OI]_(63μm) line is detected in Cep E-BI and BII, whereas the OH line is not detected. In Cep E-BII, we identify three kinematical components in O I and CO. These were already detected in CO transitions and relate to spatial components: the jet, the HH377 terminal bow-shock, and the outflow cavity. We measure line temperature and line integrated intensity ratios for all components. The O I column density is higher in the outflow cavity than in the jet, which itself is higher than in the terminal shock. The terminal shock is the region where the abundance ratio of O I to CO is the lowest (about 0.2), whereas the jet component is atomic (N(O I)/N(CO) ~ 2.7). In the jet, we compare the [OI]_(63μm) observations with shock models that successfully fit the integrated intensity of 10 CO lines. We find that these models most likely do not fit the [OI]_(63μm) data. Conclusions. The high intensity of O I emission points towards the propagation of additional dissociative or alternative FUV-irradiated shocks, where the illumination comes from the shock itself. A picture emerges from the sample of low-to-high mass protostellar outflows, where similar observations have been performed, with the effects of illumination increasing with the mass of the protostar. These findings need confirmation with more observational constraints and a larger sample.

We present a new multi-pixel high resolution (R ≳ 107) 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.

Atomic fine-structure line emission is a major cooling process in the interstellar medium (ISM). In particular the [C II] 158 mu m line is one of the dominant cooling lines in photon-dominated regions (PDRs). However, it is not confined to PDRs only but can also originate from the ionized gas closely surrounding young massive stars. Here we discuss the question how much of the [C II] emission in the nucleus of the nearby spiral galaxy IC 342 is contributed by PDRs and by the ionized gas. Particularly the correlation of the [C II] line with the also observed [N II] 205 mu m emission line coming exclusively from the H II regions is investigated.The emission coming from the ionized gas shows a kinematic component in addition to the general Doppler signature of the molecular gas. We discuss how this requires an adaptation of our understanding of the geometrical structure of the nucleus of IC 342. Applying predictions from numerical models of H II and PDR regions to derive the contribution from the ionized phase to the total [C II] emission we find that 30-60% of the observed [C II] intensity stems from the ionized gas if both phases contribute.

Context. Atomic fine-structure line emission is a major cooling process in the interstellar medium (ISM). In particular the [C II] 158 mu m line is one of the dominant cooling lines in photon-dominated regions (PDRs). However, it is not confined to PDRs but can also originate from the ionized gas closely surrounding young massive stars. The proportion of the [C II] emission from HII regions relative to that from PDRs can vary significantly.Aims. We investigate the question of how much of the [C II] emission in the nucleus of the nearby spiral galaxy IC 342 is contributed by PDRs and by the ionized gas. We examine the spatial variations of starburst/PDR activity and study the correlation of the [C II] line with the [N II] 205 mu m emission line coming exclusively from the HII regions.Methods. We present small maps of [C II] 158 mu m and [N II] 205 mu m lines recently observed with the GREAT receiver on board SOFIA. We present different methods to utilize the superior spatial and spectral resolution of our new data to infer information on how the gas kinematics in the nuclear region influence the observed line profiles. In particular we present a super-resolution method to derive how unresolved, kinematically correlated structures in the beam contribute to the observed line shapes.Results. We find that the emission coming from the ionized gas shows a kinematic component in addition to the general Doppler signature of the molecular gas. We interpret this as the signature of two bi-polar lobes of ionized gas expanding out of the galactic plane. We then show how this requires an adaptation of our understanding of the geometrical structure of the nucleus of IC 342. Examining the starburst activity we find ratios I([C II]) = I((CO)-C-12(1-0)) between 400 and 1800 in energy units. Applying predictions from numerical models of HII and PDR regions to derive the contribution from the ionized phase to the total [C II] emission we find that 35-90% of the observed [C II] intensity stems from the ionized gas if both phases contribute. Averaged over the central few hundred parsec we find for the [C II] contribution a HII-to-PDR ratio of 70:30.Conclusions. The ionized gas in the center of IC 342 contributes more strongly to the overall [C II] emission than is commonly observed on larger scales and than is predicted. Kinematic analysis shows that the majority of the [C II] emission is related to the strong but embedded star formation in the nuclear molecular ring and only marginally emitted from the expanding bi-polar lobes of ionized gas.

Context. Atomic fine-structure line emission is a major cooling process in the interstellar medium (ISM). In particular the [C II] 158 μm line is one of the dominant cooling lines in photon-dominated regions (PDRs). However, it is not confined to PDRs but can also originate from the ionized gas closely surrounding young massive stars. The proportion of the [C II] emission from H II regions relative to that from PDRs can vary significantly.

OH is a key molecule in H2O chemistry, a valuable tool for probing physical conditions, and an important contributor to the cooling of shock regions. OH participates in the re-distribution of energy from the protostar towards the surrounding ISM. Our aim is to assess the origin of the OH emission from the Cepheus A massive star-forming region and to constrain the physical conditions prevailing in the emitting gas. We thus want to probe the processes at work during the formation of massive stars. We present spectrally resolved observations of OH towards the outflows of Cepheus A with the GREAT spectrometer onboard the SOFIA telescope. Three triplets were observed at 1834.7 GHz, 1837.8 GHz, and 2514.3 GHz (163.4, 163.1, and 119.2 microns), at angular resolutions of 16.3", 16.3", and 11.9", respectively. We present the CO (16-15) spectrum at the same position. We compared the integrated intensities in the redshifted wings to shock models. The two triplets near 163 microns are detected in emission with blending hyperfine structure unresolved. Their profiles and that of CO can be fitted by a combination of 2 or 3 Gaussians. The observed 119.2 microns triplet is seen in absorption, since its blending hyperfine structure is unresolved, but with three line-of-sight components and a blueshifted emission wing consistent with that of the other lines. The OH line wings are similar to those of CO, suggesting that they emanate from the same shocked structure. Under this common origin assumption, the observations fall within the model predictions and within the range of use of our model only if we consider that four shock structures are caught in our beam. Our comparisons suggest that the observations might be consistently fitted by a J-type model with nH > 1e5 cm-3, v > 20 km/s, and with a filling factor of 1. Such a high density is generally found in shocks associated to high-mass protostars.

Context. The fine-structure line of atomic oxygen at 63 mu m ([OI](63) (mu m)) is an important diagnostic tool in different fields of astrophysics: it is for example predicted to be the main coolant in several environments of star-forming regions (SFRs). However, our knowledge of this line relies on observations with low spectral resolution, and the real contribution of each component (photon-dominated region, jet) in the complex environment of SFRs to its total flux is poorly understood.Aims. We investigate the contribution of jet and photon-dominated region emission, and of absorption to the [OI](63 mu m) line towards the hot gas around the ultra-compact HII region G5.89-0.39 and study the far-IR line luminosity of the source in different velocity regimes through spectroscopically resolved spectra of atomic oxygen, [CII], CO, OH, and H2O.Methods. We mapped G5.89-0.39 in [OI](63 mu m) and in CO(16-15) with the GREAT receiver onboard SOFIA. We also observed the central position of the source in the ground-state OH (2)Pi(3/2), J = 5/2 -> J = 3/2 triplet and in the excited OH (2)Pi(1/2), J = 3/2 -> J = 1/2 triplets with SOFIA. These data were complemented with APEX CO(6-5) and CO(7-6) maps and with Herschel/HIFI maps and single-pointing observations in lines of [CII], H2O, and HF.Results. The [OI] spectra in G5.89-0.39 are severely contaminated by absorptions from the source envelope and from different clouds along the line of sight. Emission is detected only at high velocities, and it is clearly associated with the compact north-south outflows traced by extremely high-velocity emission in low-J CO lines. The mass-loss rate and the energetics of the jet system derived from the [OI](63 mu m) line agree well with previous estimates from CO, thus 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 high-velocities; the second coolant in this velocity regime is CO, while [CII], OH and H2O are minor contributors to the total cooling in the outflowing gas. Finally, we derive abundances of different molecules in the outflow: water has low abundances relative to H-2 of 10(-8) - 10(-6), and OH of 10(-8). Interestingly, we find an abundance of HF to H-2 of 10(-8), comparable with measurements in diffuse gas.Conclusions. Our study shows the importance of spectroscopically resolved observations of the [OI](63 mu m) line for using this transition as diagnostic of star-forming regions. While this was not possible until now, the GREAT receiver onboard SOFIA has recently opened the possibility of detailed studies of the [OI](63 mu m) line to investigate the potential of the transition for probing different environments.

The NASA-DLR airborne observatory SOFIA is now performing routine observations, having the German PI instrument (GREAT) as one of its four main instruments. The instrument currently comprises a set of single pixel heterodyne receivers observing in selected frequency windows between 1.25 and 4.7 THz. We are developing new instruments, the upGREAT receivers, which consist of mid-size heterodyne arrays based on superconducting waveguide HEB mixers. The Low Frequency Array (LFA) will cover the 1.9-2.5 THz range using dual polarization 7-pixel HEB arrays. The second receiver, the High Frequency Array (HFA), will observe the [OI] line at ~4.7 THz using a 7-pixel HEB array. We present the status of the LFA receiver, which is in the final stages of integration, testing and characterization. The installation and commissioning aboard SOFIA is planned for May 2015.

The high-resolution far-infrared spectrometer GREAT is now routinely operated onboard the NASA/DLR airborne observatory SOFIA. The instrument runs simultaneously two receivers in science selected frequency windows between 1.25 and 4.7 THz. Because the instrument has seen major upgrades during the last years we will briefly review the present instrument configurations and performances. The extension of GREAT to mid-size heterodyne arrays is under way. The commissioning of our low-frequency array, operating 2 x 7 HEB mixers at 1.9 THz in two polarizations in a hexagonal configuration, was successfully concluded in 2015, and will be available for community projects during SOFIA's cycle 4. A second (high-frequency) array with 7 pixels aiming at the frequency of the [01] fine-structure line at 4.7 THz is under construction, with commissioning planned for late 2016. In more than 60 successful science flights, most of them performing community projects, a wide variety of astrophysical questions has been addressed, with particular interest in velocity-resolved spectroscopy of the most important ISM cooling lines accessible to GREAT, namely the [CII] and [OI] atomic fine-structure and the mid-J CO rotational transitions. On the example of a few selected science cases the performance of the instrument will be illustrated, and the science opportunities with the instrument in its current and near-future configurations will be addressed.

We report on our hot electron bolometer mixer development for the focal plane array extension upGREAT of the German Receiver for Astronomy at Terahertz frequencies (GREAT) operated on SOFIA. For (up)GREAT we have pushed the waveguide technology to 4.7 THz and present RF performance results. We describe the RF planar circuit design, the micro fabrication employing NbN microbridges on 2 μm thin Si membrane substrates and the machining technology used for the waveguides. One of the 4.7 THz mixers was used in the high frequency channel on GREAT in May 2014 and performed as expected from the laboratory characterization.