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The charge density wave (CDW) state is a widespread phenomenon in low-dimensional metals/semimetals. The spectral weight of the associated folded bands (shadow bands) can be an intriguing trigger leading to additional Fermi surface instability and unexplored phase transitions. The rare earth tri-telluride CeTe3 exhibits a single CDW stabilized below ~400 K and antiferromagnetism below ~3 K. The distinct periodicities between the Te-square net, the CeTe block layer, and the CDW give rise to rich shadow band formations. In this work, we reveal the predominant scattering between the original and shadow bands at 4 K, with the scattering within the original bands being relatively suppressed at Fermi energy. This unconventional quasi-particle scattering collectively underscores the vital role of the shadow bands' spectral weight and the hidden matrix element effect, which are crucial for controlling electronic properties in this system. Furthermore, our finding points to the existence of rich and unexplored Fermi surface instabilities, which potentially play a role in controlling the nature of long-range antiferromagnetism at lower temperatures in the presence of finite charge-spin interaction.

Rare earth tri-tellurides (RTe3) are van der Waals (vdW) coupled semimetals ideal for exploring exotic electronic phases. LaTe3 is especially important for understanding the fundamental Fermiology of the RTe3 family because it is non-magnetic and has a simpler charge density wave structure. In this study, we used spectroscopic-imaging scanning tunneling microscopy to measure the Landau levels of LaTe3 with high energy resolution at 300 mK. These measurements were taken under varying magnetic fields up to 15 T, with fine intervals of 0.02 - 0.03 T. Our results reveal a pair of pronounced electron-hole Fermi pockets of similar sizes and evidence of electron-boson coupling in both pockets. Given the strong charge susceptibility typical of low-dimensional conductors, the interactions and instabilities driven by the electron-hole Fermi pockets could be a basis for searching unexplored quantum phases in other antiferromagnetic RTe3 compounds., Comment: This manuscript is accepted by Physical Review B

Analogous to the charged electron-electron pair condensation in superconductors, an excitonic insulator (EI) represents Fermi surface instability due to spontaneous formation and condensation of charge-neutral electron-hole pair (exciton). Unlike in superconductors, however, the charge-neutral nature of exciton makes probing emergent EI phase via macroscopic physical properties generally difficult. Here, we propose a van der Waals coupled antiferromagnetic semiconductor GdGaI (GGI) as a new material category leading to emergent multi-q magnet intertwined with spontaneous exciton formation/condensation. Before excitonic band hybridization, a simple picture for the parent electronic state consists of electron (Gd-derived 5d) and hole (Ga-derived 4p) delocalized bands, together with Gd-derived 4f localized antiferromagnets with S = 7/2 classical nature. Through intra Gd atom 4f-5d Hund's coupling, a notable finding is the emergent minimum length scale (2a) Skyrmion-like spin texture resulting from spontaneous condensation/formation of spin-polarized exciton with BCS-BEC crossover phenomenology. This discovered platform is promising for realizing valuable quantum matter on the nanoscale; our finding will provide significant insight into designing the atomic scale topological magnetism out of itinerant systems., Comment: 23 pages, 10 figures

Context. Recent studies of the optical depth comparing [12CII] and [13CII] line profiles in Galactic star-forming regions revealed strong self-absorption in [12CII] by low excitation foreground material, implying a large column density of C+ corresponding to an equivalent AV of a few, up to about 10 mag. Aims. As the nature and origin of such a large column of cold C+ foreground gas are difficult to explain, it is essential to constrain the physical conditions of this material. Methods. We conducted high-resolution observations of [OI] 63 um and [OI] 145 um lines in M17 SW and Mon R2. The [OI] 145 um transition traces warm PDR-material, while the [OI] 63 um line traces foreground material as manifested by absorption dips. Results. Comparison of both [OI] line profiles with [CII] isotopic lines confirms warm PDR-origin background emission and a significant column of cold foreground material causing self-absorption visible in [12CII] and [OI] 63 um profiles. In M17 SW, the C+ and O column densities are comparable for both layers. Mon R2 exhibits larger O columns compared to C+, indicating additional material where the carbon is neutral or in molecular form. Small-scale spatial variation of the foreground absorption profiles and the large column density (around 1E18 cm-2 ) of the foreground material suggest emission from high-density regions associated with the cloud complex, not a uniform diffuse foreground cloud. Conclusions. The analysis confirms that the previously detected intense [CII] foreground absorption is attributable to a large column of low excitation dense atomic material, where carbon is ionized, and oxygen is in neutral atomic form., Comment: 30 pages, 24 figures

We have implemented a novel method to create simulated [CII] emission line intensity mapping (LIM) data cubes using COSMOS 2020 galaxy catalogue data. It allows us to provide solid lower limits for previous simulation-based model predictions and the expected signal strength of upcoming surveys. We applied [CII]158$\mu$m luminosity models to COSMOS 2020 to create LIM cubes covering a 1.2$\times$1.2 deg$^2$ sky area. These models were derived using galaxy bulk property data from the ALPINE-ALMA survey over the redshift range $4.41 when using FYST parameters. However, our high-redshift results remain inconclusive because of the poor completeness of COSMOS 2020 at $z$>6.3. These predictions will be improved on the basis of future JWST data., Comment: 28 pages, 22 figures, accepted by A&A

We present new $^{13}$CO(1-0), C$^{18}$O(1-0), HCO$^{+}$(1-0) and H$^{13}$CO$^{+}$(1-0) maps from the IRAM 30m telescope, and a spectrally-resolved [CII] 158 $\mu$m map observed with the SOFIA telescope towards the massive DR21 cloud. This traces the kinematics from low- to high-density gas in the cloud which allows to constrain the formation scenario of the high-mass star forming DR21 ridge. The molecular line data reveals that the sub-filaments are systematically redshifted relative to the dense ridge. We demonstrate that [CII] unveils the surrounding CO-poor gas of the dense filaments in the DR21 cloud. We also show that this surrounding gas is organized in a flattened cloud with curved redshifted dynamics perpendicular to the ridge. The sub-filaments thus form in this curved and flattened mass reservoir. A virial analysis of the different lines indicates that self-gravity should drive the evolution of the ridge and surrounding cloud. Combining all results we propose that bending of the magnetic field, due to the interaction with a mostly atomic colliding cloud, explains the velocity field and resulting mass accretion on the ridge. This is remarkably similar to what was found for at least two nearby low-mass filaments. We tentatively propose that this scenario might be a widespread mechanism to initiate star formation in the Milky Way. However, in contrast to low-mass clouds, gravitational collapse plays a role on the pc scale of the DR21 ridge because of the higher density. This allows more effective mass collection at the centers of collapse and should facilitate massive cluster formation., Comment: 32 pages, 28 figures, accepted in ApJ

Fe$_5$GeTe$_2$ is a van der Waals (vdW)-coupled unconventional ferromagnetic metal with a high Curie temperature ($T_C$) exceeding 300 K. The formation of an anomalous ground state significantly below $T_C$ has received considerable attention, resulting in increased interest in understanding the spin-polarized electronic state evolution near the Fermi energy ($E_F$) as a function of temperature. Despite recent extensive studies, a microscopic understanding of the spin-polarized electronic structure around $E_F$ has not yet been established owing to the intrinsic complexity of both the crystal and band structures. In this study, we investigate the temperature dependence of element-specific soft X-ray magnetic circular dichroism (XMCD). A systematic temperature evolution in the XMCD signal from both magnetic Fe and its ligand Te is clearly observed. More importantly, the enhancement in the hybridization between the Fe 3$d$ and Te 5$p$ states in the zero-magnetic field limit is revealed, and we discuss its implications on the possible emergence of an exotic magnetic ground state in Fe$_5$GeTe$_2$., Comment: 12 pages, 4 figures

Magnetic semimetals have increasingly emerged as lucrative platforms hosting spin-based topological phenomena in real and momentum spaces. Of particular interest is the emergence of Berry curvature, whose geometric origin, accessibility from Hall transport experiments, and material tunability, bodes well for new physics and practical devices. Cr1+dTe2, a self-intercalated magnetic transition metal dichalcogenide, TMD, exhibits attractive natural attributes relevant to such applications, including topological magnetism, tunable electron filling, magnetic frustration etc. While recent studies have explored real-space Berry curvature effects in this material, similar considerations of momentum-space Berry curvature are lacking. Here, we systematically investigate the electronic structure and transport properties of epitaxial Cr1+dTe2 thin films over a wide range of doping, d between 0.33 and 0.71. Spectroscopic experiments reveal the presence of a characteristic semi-metallic band region near the Brillouin Zone edge, which shows a rigid band like energy shift as a function of d. Transport experiments show that the intrinsic component of the anomalous Hall effect, AHE, is sizable, and undergoes a sign flip across d. Finally, density functional theory calculations establish a causal link between the observed doping evolution of the band structure and AHE: the AHE sign flip is shown to emerge from the sign change of the Berry curvature, as the semi-metallic band region crosses the Fermi energy. Our findings underscore the increasing relevance of momentum-space Berry curvature in magnetic TMDs and provide a unique platform for intertwining topological physics in real and momentum spaces.

Coherent photoproduction of the neutral pion and eta meson on the deuteron, $\gamma{d}${$\to$}$\pi^0\eta{d}$, has been experimentally studied at incident photon energies ranging from the reaction threshold to 1.15 GeV. The total cross section demonstrates a rapid rise below 1 GeV. The data are underestimated by the existing theoretical calculations based on quasi-free $\pi^0 \eta$ photoproduction on the nucleon followed by deuteron coalescence. At the same time, the data are rather well reproduced by the calculations taking into account the final-state interaction. We have also measured for the first time the differential cross sections: the $\pi^0 \eta$ invariant-mass distribution $d\sigma/dM_{\pi \eta}$, the $\pi^0 d$ invariant-mass distribution $d\sigma/dM_{\pi d}$, the $\eta d$ invariant-mass distribution $d\sigma/dM_{\eta d}$, and the distribution over the deuteron emission angle $d\sigma/d\Omega_d$ in the overall center-of-mass frame. The measured cross section $d\sigma/d\Omega_d$ does not exhibit strongly backward-peaking behavior predicted by the calculations. At all incident energies, an increase in $d\sigma/dM_{\eta d}$ near the $\eta d$ threshold is observed, which indicates a bound or virtual $\eta d$ state resulting from a strong attraction between $\eta$ and a deuteron. The possibilities of using coherent $\pi^0\eta$ photoproduction on a nucleus to study the $\eta$-nuclear interaction are also discussed., Comment: 15 pages, 9 figures

Only recently, OD, the deuterated isotopolog of hydroxyl, OH, has become accessible in the interstellar medium; spectral lines from both species have been observed in the supra-Terahertz and far infrared regime. Here we study rotational lines of OD and OH towards 13 Galactic high-mass star forming regions, with the aim to constrain the OD abundance and infer the deuterium fractionation of OH in their molecular envelopes. We used the Stratospheric Observatory for Infrared Astronomy (SOFIA) to observe the $^2\Pi_{3/2}$ $J=5/2-3/2$ ground-state transition of OD at 1.3 THz ($215~\mu$m) and the rotationally excited OH line at 1.84 THz ($163~\mu$m). We also used published high-spectral-resolution SOFIA data of the OH ground-state transition at 2.51 THz ($119.3~\mu$m). Our results show that absorption from the $^2\Pi_{3/2}$ OD $J=5/2-3/2$ ground-state transition is prevalent in the dense clumps surrounding active sites of high-mass star formation. We performed detailed radiative transfer modelling to investigate the OD abundance profile in the inner envelope for a large fraction of our sample. Our modelling suggests that part of the absorption arises from the denser inner parts, while the bulk of it as seen with SOFIA originates in the outer, cold layers of the envelope for which our constraints on the molecular abundance suggest a strong enhancement in deuterium fractionation. We find a weak negative correlation between the OD abundance and the bolometric luminosity to mass ratio, an evolutionary indicator, suggesting a slow decrease of OD abundance with time. A comparison with HDO shows a similarly high deuterium fractionation for the two species in the cold envelopes, which is of the order of 0.48% for the best studied source, G34.26+0.15. Our results are consistent with chemical models that favour rapid exchange reactions to form OD in the dense cold gas., Comment: 20 pages, 14 figures. Accepted by A&A after refereeing and language corrections. Abstract abbreviated

Revealing the 3D dynamics of HII regions and their associated molecular clouds is important for understanding the longstanding problem as to how stellar feedback affects the density structure and kinematics of the interstellar medium. We employed observations of the HII region RCW 120 in [CII], observed within the SOFIA legacy program FEEDBACK, and the $^{12}$CO and $^{13}$CO (3$\to$2) lines, obtained with APEX. In addition we used HI data from the Southern Galactic Plane Survey. Two radiative transfer models were used to fit the observed data. A line profile analysis with the 1D non-LTE radiative transfer code SimLine proves that the CO emission cannot stem from a spherically symmetric molecular cloud configuration. With a two-layer multicomponent model, we then quantified the amount of warm background and cold foreground gas. There is a deficit of CO emission along the line-of-sight toward the center of the HII region which indicates that the HII region is associated with a flattened molecular cloud. Self-absorption in the CO line may hide signatures of infalling and expanding molecular gas. The [CII] emission arises from an expanding [CII] bubble and from the PDRs. A significant part of [CII] emission is absorbed in a cool (~60-100 K), low-density (<500 cm$^{-3}$) atomic foreground layer with a thickness of a few parsec. We propose that the RCW 120 HII region formed in a flattened molecular cloud and is now bursting out of its parental cloud. The compressed surrounding molecular layer formed a torus around the spherically expanding HII bubble. This scenario can possibly be generalized for other HII bubbles and would explain the observed "flat" structure of molecular clouds associated with HII bubbles. We suggest that the [CII] absorption observed in many star-forming regions is at least partly caused by low-density, cool, HI-envelopes surrounding the molecular clouds.

IRAS 20319+3958 in Cygnus X South is a rare example of a free-floating globule (mass ~240 Msun, length ~1.5 pc) with an internal HII region created by the stellar feedback of embedded intermediate-mass stars, in particular, one Herbig Be star. Here, we present a Herschel/HIFI CII 158 mu map of the whole globule and a large set of other FIR lines (mid-to high-J CO lines observed with Herschel/PACS and SPIRE, the OI 63 mu line and the CO 16-15 line observed with upGREAT on SOFIA), covering the globule head and partly a position in the tail. The CII map revealed that the whole globule is probably rotating. Highly collimated, high-velocity CII emission is detected close to the Herbig Be star. We performed a PDR analysis using the KOSMA-tau PDR code for one position in the head and one in the tail. The observed FIR lines in the head can be reproduced with a two-component model: an extended, non-clumpy outer PDR shell and a clumpy, dense, and thin inner PDR layer, representing the interface between the HII region cavity and the external PDR. The modelled internal UV field of ~2500 Go is similar to what we obtained from the Herschel FIR fluxes, but lower than what we estimated from the census of the embedded stars. External illumination from the ~30 pc distant Cyg OB2 cluster, producing an UV field of ~150-600 G0 as an upper limit, is responsible for most of the CII emission. For the tail, we modelled the emission with a non-clumpy component, exposed to a UV-field of around 140 Go., Comment: accepted by Astronomy & Astrophysics

We present a detailed overview of the science goals and predictions for the Prime-Cam direct detection camera/spectrometer being constructed by the CCAT-prime collaboration for dedicated use on the Fred Young Submillimeter Telescope (FYST). The FYST is a wide-field, 6-m aperture submillimeter telescope being built (first light in mid-2024) by an international consortium of institutions led by Cornell University and sited at more than 5600 meters on Cerro Chajnantor in northern Chile. Prime-Cam is one of two instruments planned for FYST and will provide unprecedented spectroscopic and broadband measurement capabilities to address important astrophysical questions ranging from Big Bang cosmology through reionization and the formation of the first galaxies to star formation within our own Milky Way galaxy. Prime-Cam on the FYST will have a mapping speed that is over ten times greater than existing and near-term facilities for high-redshift science and broadband polarimetric imaging at frequencies above 300 GHz. We describe details of the science program enabled by this system and our preliminary survey strategies., Comment: 61 pages, 16 figures. Resubmitted to ApJSS July 11, 2022

Context. The [CII] 158micron far-infrared fine-structure line is one of the dominant cooling lines of the star-forming interstellar medium (ISM). Hence [CII] emission originates in and thus can be used to trace a range of ISM processes. Velocity-resolved large-scale mapping of [CII] in star-forming regions provides a unique perspective of the kinematics of these regions and their interactions with the exciting source of radiation. Aims. We explore the scientific applications of large-scale mapping of velocity-resolved [CII] observations. With the [CII] observations, we investigate the effect of stellar feedback on the ISM. We present the details of observation, calibration, and data reduction using a heterodyne array receiver mounted on an airborne observatory. Results. A square-degree [CII] map with a spectral resolution of 0.3 km/s is presented. The scientific potential of this data is summarized with discussion of mechanical and radiative stellar feedback, filament tracing using [CII], [CII] opacity effects, [CII] and carbon recombination lines, and [CII] interaction with the large molecular cloud. The data quality and calibration is discussed in detail, and new techniques are presented to mitigate the effects of unavoidable instrument deficiencies (e.g. baseline stability) and thus to improve the data quality. A comparison with a smaller [CII] map taken with the Herschel/Heterodyne Instrument for the Far-Infrared (HIFI) spectrometer is presented.

To investigate the interaction between the nucleon $N$ and nucleon resonance $N(1535)1/2^-$, the $\eta d$ threshold structure connected to the isoscalar $S$-wave $N$-$N(1535)1/2^-$ system has been experimentally studied in the $\gamma{d}${$\to$}$\pi^0\eta{d}$ reaction at incident photon energies ranging from the reaction threshold to 1.15 GeV. A strong enhancement is observed near the $\eta d$ threshold over the three-body phase-space contribution in the $\eta d$ invariant-mass distribution. An analysis incorporating the known isovector resonance $\mathcal{D}_{12}$ with a spin-parity of $2^+$ in the $\pi^0d$ channel reveals the existence of a narrow isoscalar resonance-like structure with $1^-$ in the $\eta d$ system. Using a Flatt\'e parametrization, the mass is found to be $2.427_{-0.006}^{+0.013}$ GeV, close to the $\eta d$ threshold, and the width is $\left(0.029_{-0.029}^{+0.006}{\rm\ GeV}\right)+\left(0.00_{-0.00}^{+0.41}\right) p_\eta c$, where $p_\eta$ denotes the $\eta$ momentum in the rest frame of the $\eta d$ system. The observed structure would be attributed to a predicted isoscalar $1^-$ $\eta NN$ bound state from $\eta NN$ and $\pi NN$ coupled-channel calculation, or an $\eta d$ virtual state owing to strong $\eta d$ attraction., Comment: 6 pages, 3 figures

We investigate near-Fermi-energy (EF) element-specific electronic and spin states of ferromagnetic van der Waals (vdW) metal Fe5GeTe2. The soft x-ray angle-resolved photoemission spectroscopy (SX-ARPES) measurement provides spectroscopic evidence of localized Fe 3d band. We also find prominent hybridization between the localized Fe 3d band and the delocalized Ge/Te p bands. This picture is strongly supported from direct observation of the remarkable spin polarization of the ligand p bands near EF, using x-ray magnetic circular dichroism (XMCD) measurements. The strength of XMCD signal from ligand element Te shows the highest value, as far as we recognize, among literature reporting finite XMCD signal for none-magnetic element in any systems. Combining SX-ARPES and elemental selective XMCD measurements, we collectively point an important role of giant spin polarization of the delocalized ligand Te states for realizing itinerant long-range ferromagnetism in Fe5GeTe2. Our finding provides a fundamental elemental selective view-point for understanding mechanism of itinerant ferromagnetism in low dimensional compounds, which also leads insight for designing exotic magnetic states by interfacial band engineering in heterostructures.

FEEDBACK is a SOFIA 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 LFA and 7 pixel HFA upGREAT instrument to spectrally resolve (0.24 MHz) these FIR structure lines. With an observing time of 96h, we will cover $\sim$6700 arcmin$^2$ at 14.1$''$ angular resolution for the CII line and 6.3$''$ 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. 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 HII region 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.

Magnetic transition metal dichalcogenide (TMD) films have recently emerged as promising candidates to host novel magnetic phases relevant to next-generation spintronic devices. However, systematic control of the magnetization orientation, or anisotropy, and its thermal stability, characterized by Curie temperature (Tc) remains to be achieved in such films. Here we present self-intercalated epitaxial Cr1+{\delta}Te2 films as a platform for achieving systematic/smooth magnetic tailoring in TMD films. Using a molecular beam epitaxy (MBE) based technique, we have realized epitaxial Cr1+{\delta}Te2 films with smoothly tunable over a wide range (0.33-0.82), while maintaining NiAs-type crystal structure. With increasing {\delta}, we found monotonic enhancement of Tc from 160 to 350 K, and the rotation of magnetic anisotropy from out-of-plane to in-plane easy axis configuration for fixed film thickness. Contributions from conventional dipolar and orbital moment terms are insufficient to explain the observed evolution of magnetic behavior with {\delta}. Instead, ab initio calculations suggest that the emergence of antiferromagnetic interactions with {\delta}, and its interplay with conventional ferromagnetism, may play a key role in the observed trends. To our knowledge, this constitutes the first demonstration of tunable Tc and magnetic anisotropy across room temperature in TMD films, and paves the way for engineering novel magnetic phases for spintronic applications.

The aim of the present work is to study structure and gas kinematics in the photodissociation regions (PDRs) around the compact HII regions S235A and S235C. We observe the [CII], [13CII] and [OI] line emission, using SOFIA/upGREAT and complement them by data of HCO+ and CO. We use the [13CII] line to measure the optical depth of the [CII] emission, and find that the [CII] line profiles are influenced by self-absorption, while the [13CII] line remains unaffected by these effects. Hence, for dense PDRs, [13CII] emission is a better tracer of gas kinematics. The optical depth of the [CII] line is up to 10 in S235A. We find an expanding motion of the [CII]-emitting layer of the PDRs into the front molecular layer in both regions. Comparison of the gas and dust columns shows that gas components visible neither in the [CII] nor in low-J CO lines may contribute to the total column across S235A. We test whether the observed properties of the PDRs match the predictions of spherical models of expanding HII region + PDR + molecular cloud. Integrated intensities of the [13CII], [CII] and [OI] lines are well-represented by the model, but the models do not reproduce the double-peaked [CII] line profiles due to an insufficient column density of C+. The model predicts that the [OI] line could be a more reliable tracer of gas kinematics, but the foreground self-absorbing material does not allow using it in the considered regions., Comment: accepted to MNRAS

CeTe3 is a unique platform to investigate the itinerant magnetism in a van der Waals (vdW) coupled metal. Despite chemical pressure being a promising route to boost quantum fluctuation in this system, a systematic study on the chemical pressure effect on Ce3+(4f1) states is absent. Here, we report on the successful growth of a series of Se doped single crystals of CeTe3. We found a fluctuation driven exotic magnetic rotation from the usual easy-axis ordering to an unusual hard-axis ordering. Unlike in localized magnetic systems, near-critical magnetism can increase itinerancy hand-in-hand with enhancing fluctuation of magnetism. Thus, seemingly unstable hard-axis ordering emerges through kinetic energy gain, with the self-consistent observation of enhanced magnetic fluctuation (disorder). As far as we recognize, this order-by-disorder process in fermionic system is observed for the first time within vdW materials. Our finding opens a unique experimental platform for direct visualization of the rich quasiparticle Fermi surface deformation associated with the Fermionic order-by-disorder process. Also, the search for emergent exotic phases by further tuning of quantum fluctuation is suggested as a promising future challenge.

The D/H ratio in cometary water has been shown to vary between 1 and 3 times the Earth's oceans value, in both Oort cloud comets and Jupiter-family comets originating from the Kuiper belt. We present new sensitive spectroscopic observations of water isotopologues in the Jupiter-family comet 46P/Wirtanen carried out using the GREAT spectrometer aboard the Stratospheric Observatory for Infrared Astronomy (SOFIA). The derived D/H ratio of $(1.61 \pm 0.65) \times 10^{-4}$ is the same as in the Earth's oceans. Although the statistics are limited, we show that interesting trends are already becoming apparent in the existing data. A clear anti-correlation is seen between the D/H ratio and the active fraction, defined as the ratio of the active surface area to the total nucleus surface. Comets with an active fraction above 0.5 typically have D/H ratios in water consistent with the terrestrial value. These hyperactive comets, such as 46P/Wirtanen, require an additional source of water vapor in their coma, explained by the presence of subliming icy grains expelled from the nucleus. The observed correlation may suggest that hyperactive comets belong to a population of ice-rich objects that formed just outside the snow line, or in the outermost regions of the solar nebula, from water thermally reprocessed in the inner disk that was transported outward during the early disk evolution. The observed anti-correlation between the active fraction and the nucleus size seems to argue against the first interpretation, as planetesimals near the snow line are expected to undergo rapid growth. Alternatively, isotopic properties of water outgassed from the nucleus and icy grains may be different due to fractionation effects at sublimation. In this case, all comets may share the same Earth-like D/H ratio in water, with profound implications for the early solar system and the origin of Earth's oceans., Comment: 9 pages, 5 figures

Photoproduction of the $\omega$ meson on the proton has been experimentally studied near the threshold. The total cross sections are determined at incident energies ranging from 1.09 to 1.15 GeV. The 1/2 and 3/2 spin-averaged scattering length $a_{\omega p}$ and effective range $r_{\omega p}$ between the $\omega$ meson and proton are estimated from the shape of the total cross section as a function of the incident photon energy: $a_{\omega p} = \left(-0.97^{+0.16_{\rm stat}}_{-0.16_{\rm stat}}{}^{+0.03_{\rm syst}}_{-0.00_{\rm syst}}\right)+i \left(0.07^{+0.15_{\rm stat}}_{-0.14_{\rm stat}}{}^{+0.17_{\rm syst}}_{-0.09_{\rm syst}}\right)$ fm and $r_{\omega p}=\left(+2.78^{+0.68_{\rm stat}}_{-0.54_{\rm stat}}{}^{+0.11_{\rm syst}}_{-0.13_{\rm syst}}\right)+i\left(-0.01^{+0.46_{\rm stat}}_{-0.50_{\rm stat}}{}^{+0.07_{\rm syst}}_{-0.00_{\rm syst}}\right)$ fm, resulting in a repulsive force. The real and imaginary parts for $a_{\omega p}$ and $r_{\omega p}$ are determined separately for the first time. A small $P$-wave contribution does not affect the obtained values., Comment: 6 pages, 4 figures

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., Comment: Accepted to the Journal of Astronomical Instrumentation (SOFIA Special Edition) on 12th November 2018

Coherent double neutral-pion photoproduction on the deuteron, $\gamma{d}${$\to$}$\pi^0\pi^0{d}$, has been experimentally studied at incident photon energies ranging from 0.75 to 1.15 GeV. The total cross section as a function of the $\gamma{d}$ center-of-mass energy shows resonance-like behavior, which peaks at approximately 2.47 and 2.63 GeV. The measured angular distribution of deuteron emission is rather flat, which cannot be reproduced by the kinematics of quasi-free $\pi^0\pi^0$ production with deuteron coalescence. In $\pi^0d $ invariant-mass distributions, a clear peak is observed at $2.14{\pm}0.01$ GeV$/c^2$ with a width of $0.09{\pm}0.01$ GeV$/c^2$. The spin-parity of this state is restricted to $1^+$, $2^+$ or $3^-$ from the angular distributions of the two $\pi^0$s. The present work shows strong evidence for the existence of an isovector dibaryon resonance with a mass of 2.14 GeV$/c^2$. The $2^+$ assignment is consistent with the theoretically predicted ${\cal{D}}_{12}$ state, and also with the energy dependence of the $\pi{d}$ partial-wave amplitude $^3\!P_2$ for the $\pi^{\pm}d${$\to$}$\pi^{\pm}d$ and $\pi^+d${$\to$}${pp}$ reactions., Comment: 12 pages, 6 figures

The total cross sections were measured for coherent double neutral-pion photoproduction on the deuteron at incident energies below 0.9 GeV for the first time. No clear resonance-like behavior is observed in the excitation function for $W_{\gamma d}=2.38$--2.61 GeV, where the $d^*(2380)$ dibaryon resonance observed at COSY is expected to appear. The measured excitation function is consistent with the existing theoretical calculation for this reaction. The upper limit of the total cross section is found to be $0.034$~$\mu$b for the dibaryon resonance at $W_{\gamma d}=2.37$~GeV (90\% confidence level) in the $\gamma d \to \pi^0\pi^0 d$ reaction., Comment: submitted to Physics Letters B

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 x 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., Comment: 7 pages, 11 figures. Accepted for publication in Astronomy & Astrophysics

We have developed an event mixing technique to observe Bose-Einstein correlations (BEC) between two identical neutral pions produced in photo-induced reactions in the non-perturbative QCD energy region. It is found that the missing-mass consistency cut and the pion-energy cut are essential for the event mixing method to effectively extract BEC observables. A Monte Carlo (MC) simulation is used to validate these constraints and confirms the efficiency of this method. Our work paves the way for similar BEC studies at lower energies where the multiplicity of emitted bosons is limited.

This paper presents [CII], [CI] and CO emission line maps of the star-forming regions N66, N25+N26, and N88 in the metal-poor Local Group dwarf galaxy SMC. The spatial and velocity structure of the large HII region N66 reveals an expanding ring of shocked molecular gas centered on the exciting star cluster NGC346, whereas a more distant dense molecular cloud is being eroded by UV radiation from the same cluster. In the N25+N26 and N88 maps, diffuse [CII] emission at a relatively low surface brightness extends well beyond the compact boundaries of the bright emission associated with the [CII] regions. In all regions, the distribution of this bright [CII] emission and the less prominent [CI] emission closely follows the outline of the CO complexes, but the intensity of the [CII] and [CI] emission is generally anticorrelated, which can be understood by the action of photodissociation and photoionization processes. Notwithstanding the overall similarity of CO and [CII] maps, the intensity ratio of these lines varies significantly, mostly due to changes in CO brightness. [CII] emission line profiles are up to 50% wider in velocity than corresponding CO profiles. A radiative transfer analysis shows that the [CII] line is the dominant tracer of (CO-dark) molecular hydrogen in the SMC. CO emission traces only a minor fraction of the total amount of gas. The similarity of the spatial distribution and line profile shape, and the dominance of molecular gas associated with [[CII] rather than CO emission imply that in the low-metallicity environment of the SMC the small amount of dense molecular gas traced by CO is embedded in the much more extended molecular gas traced only by [CII] emission. The contribution from neutral atomic and ionized hydrogen zones is negligible in the star-forming regions observed., Comment: 17 pages, 16 figures, Accepted in A&A

Twelve high schools in Japan (of which six are in Fukushima Prefecture), four in France, eight in Poland and two in Belarus cooperated in the measurement and comparison of individual external doses in 2014. In total 216 high-school students and teachers participated in the study. Each participant wore an electronic personal dosimeter "D-shuttle" for two weeks, and kept a journal of his/her whereabouts and activities. The distributions of annual external doses estimated for each region overlap with each other, demonstrating that the personal external individual doses in locations where residence is currently allowed in Fukushima Prefecture and in Belarus are well within the range of estimated annual doses due to the background radiation level of other regions/countries.

We have mapped the NGC 2023 reflection nebula in [CII] and CO(11--10) with the heterodyne receiver GREAT on SOFIA and obtained slightly smaller maps in 13CO(3--2), CO(3--2), CO(4--3), CO(6--5), and CO(7--6) with APEX in Chile. We use these data to probe the morphology, kinematics, and physical conditions of the C II region, which is ionized by FUV radiation from the B2 star HD37903. The [CII] emission traces an ellipsoidal shell-like region at a position angle of ~ -50 deg, and is surrounded by a hot molecular shell. In the southeast, where the C II region expands into a dense, clumpy molecular cloud ridge, we see narrow and strong line emission from high-J CO lines, which comes from a thin, hot molecular shell surrounding the [CII] emission. The [CII] lines are broader and show photo evaporating gas flowing into the C II region. Based on the strength of the [13CII] F=2--1 line, the [CII] line appears to be somewhat optically thick over most of the nebula with an optical depth of a few. We model the physical conditions of the surrounding molecular cloud and the PDR emission using both RADEX and simple PDR models. The temperature of the CO emitting PDR shell is ~ 90 -- 120 K, with densities of 10^5 -- 10^6 cm^-3, as deduced from RADEX modeling. Our PDR modeling indicates that the PDR layer where [CII] emission dominates has somewhat lower densities, 10^4 to a few times 10^5 cm^-3, Comment: Accepted by A&A

The opening of a spin gap in the orthorhombic compounds CeT$_2$Al$_{10}$ (T = Ru and Os) is followed by antiferromagnetic ordering at $T_N$ = 27 K and 28.5 K, respectively, with a small ordered moment (0.29$-$0.34$\mu_B$) along the $c-$axis, which is not an easy axis of the crystal field (CEF). In order to investigate how the moment direction and the spin gap energy change with 10\% La doping in Ce$_{1-x}$La$_x$T$_2$Al$_{10}$ (T = Ru and Os) and also to understand the microscopic nature of the magnetic ground state, we here report on magnetic, transport, and thermal properties, neutron diffraction (ND) and inelastic neutron scattering (INS) investigations on these compounds. Our INS study reveals the persistence of spin gaps of 7 meV and 10 meV in the 10\% La-doped T = Ru and Os compounds, respectively. More interestingly our ND study shows a very small ordered moment of 0.18 $\mu_B$ along the $b-$axis (moment direction changed compared with the undoped compound), in Ce$_{0.9}$La$_{0.1}$Ru$_2$Al$_{10}$, however a moment of 0.23 $\mu_B$ still along the $c-$axis in Ce$_{0.9}$La$_{0.1}$Os$_2$Al$_{10}$. This contrasting behavior can be explained by a different degree of hybridization in CeRu$_2$Al$_{10}$ and CeOs$_2$Al$_{10}$, being stronger in the latter than in the former. Muon spin rotation ($\mu$SR) studies on Ce$_{1-x}$La$_x$Ru$_2$Al$_{10}$ ($x$ = 0, 0.3, 0.5 and 0.7), reveal the presence of coherent frequency oscillations indicating a long$-$range magnetically ordered ground state for $x$ = 0 to 0.5, but an almost temperature independent Kubo$-$Toyabe response between 45 mK and 4 K for $x$ = 0.7. We will compare the results of the present investigations with those reported on the electron and hole$-$doping in CeT$_2$Al$_{10}$., Comment: 11 pages, 7 figures