arXiv subjects

H. Wiesemeyer

Publications and source records attributed to H. Wiesemeyer.

At least 19 recordsLinked to original sources

arXiv2026

Velocity-resolved [O I] 63,145 um, [C II] 158 um, and OH mapping along the Orion BN/KL explosive outflow and irradiated shocks

Stellar mergers produce explosive outflows that serve as transient sources of IR line luminosity and inject mechanical energy early into the natal molecular cloud. We present the first velocity-resolved maps of the [O I] 63 and 145 um fine-structure line emission from the wide-angle outflow in Orion BN/KL, the nearest explosive outflow. The data were obtained with SOFIA and include sensitive [C II] 158 um and OH maps. They allowed us to disentangle the quiescent cloud gas from the outflow, traced by a broader [O I] component with a line FWHM of about 20-30 km/s and exhibiting a spatial distribution similar to that of the shock-excited H2 emission seen with JWST. The OH 119 um line shows a prominent P-Cygni profile covering 160 km/s, similar to the very broad CO lines. The total [O I] 63 and 145 line luminosity is remarkably high, 86.5 L_sun, comparable to the H2 and CO line luminosities, implying an outflow mass-loss rate of (9.1+/-2.6)x10^-3 M_sun/yr and a mass of 3.3-5.9 M_sun. The [O I] 63 / 145 and [O I] 63 / [C II] 158 intensity ratios reach very high values in the line wings (20-30 and 40-60, respectively), exceeding those found in PDRs. These ratios are consistent with the presence of dense (10^5 to 10^6 cm^-3 ) and warm (~500 K) postshock gas. We analyzed the fine-structure line-wing intensities using magnetized shock models that include UV irradiation, to which the [C II] 158 line intensity is particularly sensitive. We find that the [O I] and [C II] intensities are consistent with emission from dissociative J-type shocks with velocities of 30-40 km/s and preshock gas densities of a few 10^4 cm^-3, illuminated by external UV radiation generated by surrounding fast shocks and possibly by massive (proto)stars in the region. We also report a broad [O I] emission feature around the BN star, which we attribute to an unresolved outflow or wind bow shock.

astro-ph.GA↗

arXiv2026

HyGAL: Characterizing the Galactic ISM with observations of hydrides and other small molecules. III. The absorption lines of [O I], CH, and OH

The HyGAL Stratospheric Observatory for Infrared Astronomy (SOFIA) legacy program aims at characterizing the interstellar medium in the Milky Way using hydrides, [C II], and [O I] absorption lines with the 2.7 m SOFIA telescope toward twenty-five submillimeter-bright Galactic star-forming regions. As part of HyGAL, we investigated correlations among the known H$_2$ tracers -- CH and OH from SOFIA observations, and HCO$^+$ and CCH from ancillary absorption line data from ground-based telescopes. We also examined the abundance variation of neutral atomic oxygen, [O I], observed in absorption. CH, OH, HCO$^+$, and CCH all exhibit strong mutual correlations. OH in particular shows tight correlations with HCO$^+$ and CCH, reflecting their linked chemical and physical pathways. Column density ratios among these H$_2$ tracers are consistent with previous measurements in local diffuse clouds and remain uniform across Galactic environments and velocity intervals. The gas phase oxygen abundance relative to total hydrogen, $\langle X$(O)$\rangle=N$(O)/$N$(H$_{\rm total}$), is $(3.09\pm0.64)\times10^{-4}$, slightly below the elemental solar value but consistent with the previous observations measuring gas-phase abundances. We also find that $N$(HI) decreases toward the regions where the molecular fraction exceeds $f_{H_2}^N \sim 0.5$, marking the onset of the molecular phase. While the atomic oxygen abundance remains roughly constant, the abundances of OH, HCO$^+$, and CCH increase with the molecular fraction. Gas traced by the HCO$^+$ absorption corresponds to higher molecular fractions than that traced by HI and hydride ions, highlighting density variations in the diffuse-to-translucent ISM along different lines of sight.

astro-ph.GA↗

arXiv2025

Faint absorption of the ground state hyperfine-splitting transitions of hydroxyl at 18 cm in the Galactic Disk

The interstellar hydride hydroxyl (OH) is a potential tracer of CO-dark molecular gas. We present new absorption line observations of OH at 18-cm wavelength towards four continuum sources. We compare these to the [CII] line at 1.9 THz obtained with SOFIA, observations of the neutral atomic hydrogen 21 cm line with the VLA, and CO lines obtained with APEX. We trace OH over a large range of molecular hydrogen column densities, and derive OH abundances with respect to molecular and total hydrogen column densities. Increased sensitivity and spectral resolution allowed us to detect weak and narrow features. We identify only one OH absorption component out of 23 without CO counterpart, yet several with intermediate molecular gas fractions. A potential association of [CII] 158 mu m emission with an OH absorption component is seen toward one sightline. Our results confirm that OH absorption traces molecular gas across diffuse and dense environments of the interstellar medium. At the sensitivity limits of the present observations our detection of only one CO-dark molecular gas feature appears in agreement with previous studies. We conclude that if OH absorption was to be used as a CO-dark molecular gas tracer, deeper observations or stronger background targets are necessary to unveil its full potential as a CO-dark molecular gas tracer, and yet it will never be an exclusive tracer of CO-dark molecular gas. For OH hyperfine-splitting transitions in the vicinity of photodissociation regions in W43-South, we detect a spectral and spatial offset between the peak of the inversion of the OH 1612 MHz line and the absorption of the OH 1720 MHz line on the one hand, and the absorption of the OH main lines on the other hand, which provides additional constraints on the interpretation of the OH 18 cm line signatures typical of HII regions.

astro-ph.GA↗

arXiv2025

SOFIA FIFI-LS spectroscopy of DR21 Main: energetics of the spatially-resolved outflow from a high-mass protostar

Massive star formation is associated with energetic processes that may influence the physics and chemistry of parental molecular clouds and impact galaxy evolution. The high-mass protostar DR21 Main in Cygnus X possesses one of the largest and most luminous outflows ever detected in the Galaxy, but the origin of its structure and driving mechanisms is still debated. Our aim is to spatially resolve the far-infrared line emission from DR21 Main and to investigate the gas physical conditions, energetics, and current mass loss rates along its outflow. Far-infrared SOFIA FIFI-LS spectra covering selected high-J CO lines, OH, [O I], [CII] and [O III] lines are analyzed across the almost full extent of the DR21 Main outflow using 2.00' x 3.75' mosaic. The spatial extent of far-infrared emission follows closely the well-known outflow direction of DR21 Main in case of high-J CO, [O I] 63.18 um, and the OH line at 163.13 um. On the contrary, the emission from the [C II] 157.74 um and [O I] 145.53 um lines arises mostly from the eastern part of the outflow, and it is likely linked with a photodissociation region. Comparison of non-LTE radiative transfer models with the observed [O I] line ratios suggest H2 densities of ~10^5 cm^(-3) in the western part of the outflow and ~10^4 cm^(-3) in the East. Such densities are consistent with the predictions of UV-irradiated non-dissociative shock models for the observed ratios of CO and [O I] along the DR21 Main. Main outflow. Assuming that the bulk of emission arises in shocks, the outflow power of DR21 Main of 4.3-4.8x10^2 Lsol and the mass-loss rate of 3.3-3.7x10^(-3) Msol/yr are determined. Observations provide strong support for its origin in outflow shocks, and the stratification of physical conditions along the outflow. The total line cooling provides additional evidence that DR21 Main drives one of the most energetic outflows in the Milky Way.

astro-ph.GA↗

arXiv2025

New submillimetre HCN lasers in carbon-rich evolved stars

Strong laser emission from hydrogen cyanide (HCN) at 805 and 891 GHz has been discovered towards carbon-rich (C-rich) AGB stars, originating from the Coriolis-coupled system between two (1,1^{1e},0) and (0,4^0,0) vibrational states. However, other lines (at 894, 964, 968 and 1055 GHz) in this system remained unexplored due to observational challenges. Using SOFIA/4GREAT observations and Herschel/HIFI archival data, we analyzed the six HCN transitions in eight C-rich AGB stars. We report new HCN transitions show laser action at 964, 968, and 1055 GHz. The 805, 891, and 964 GHz lasers were detected in seven C-rich stars, the 968 GHz laser in six, and the 1055 GHz laser in five, while the 894 GHz line was not detected in any target. Among the detected lasers, the 891 GHz laser is always the strongest, and the 964 GHz laser, like a twin of the 891 GHz line, is the second strongest. Towards IRC+10216, all five HCN laser transitions were observed in six to eight epochs and exhibited significant variations in line profiles and intensities. The cross-ladder lines at 891 and 964 GHz exhibit similar variations, and their intensity changes do not follow the near-infrared light curve (i.e. non-periodic variations). In contrast, the variations of the rotational lines at 805, 968, and 1055 GHz appear to be quasi-periodic, with a phase lag of 0.1 - 0.2 relative to the near-infrared light curve. A comparative analysis indicates that these HCN lasers may be seen as analogues to vibrationally excited SiO and water masers in oxygen-rich stars. We suggest chemical pumping and radiative pumping could play an important role in the production of the cross-ladder HCN lasers, while the quasi-periodic behavior of the rotational HCN laser lines may be modulated by additional collisional and radiative pumping driven by periodic shocks and variations in infrared luminosity. [abridged]

astro-ph.SR↗

arXiv2024

SiO maser polarization and magnetic field in evolved cool stars

Both magnetic fields and photospheric/atmospheric dynamics can be involved in triggering the important mass loss observed in evolved cool stars. Previous works have revealed that these objects exhibit a magnetic field extending beyond their surface. The origin of this magnetic field is still under debate with mechanisms involving a turbulent dynamo, convection, stellar pulsation, and cool spots. Our goal is to estimate the magnetic field strength in the inner circumstellar envelope of six evolved cool stars (five Miras and one Red Supergiant). Combining this work with previous studies, we tentatively constrain the global magnetic field type observed and shed light on the mechanisms at its origin. Using the XPOL polarimeter installed at the IRAM-30 m telescope, we observed the 28 SiO v = 1, J = 2-1 maser line emission and obtained simultaneous spectroscopic measurements of the four Stokes parameters. Applying a careful calibration method for Stokes Q, U, and V, we derive estimates of the magnetic field strength from the circular and linear polarization fractions considering the saturated and unsaturated maser cases under the Zeeman hypothesis. Magnetic field strengths from several Gauss up to several tens of Gauss are derived. These new and more accurate measurements constraining the field strength in the 2-5 stellar radii region better than previous studies and seem to exclude a global poloidal magnetic field type. A combination of a toroidal and a poloidal field is nevertheless not excluded. A variation of the magnetic field strength over a two-months timescale is observed in one Mira star which suggests a possible link to the stellar phase, i.e. with pulsation/photospheric activity.

astro-ph.SR↗

arXiv2022

Phosphine in the Venusian Atmosphere: A Strict Upper Limit from SOFIA GREAT Observations

The presence of phosphine (PH$_3$) in the atmosphere of Venus was reported by Greaves et al. (2021a), based on observations of the J=1-0 transition at 267 GHz using ground-based, millimeter-wave spectroscopy. This unexpected discovery presents a challenge for our understanding of Venus's atmosphere, and has led to a reappraisal of the possible sources and sinks of atmospheric phosphorous-bearing gases. Here we present results from a search for PH$_3$ on Venus using the GREAT instrument aboard the SOFIA aircraft, over three flights conducted in November 2021. Multiple PH$_3$ transitions were targeted at frequencies centered on 533 GHz and 1067 GHz, but no evidence for atmospheric PH$_3$ was detected. Through radiative transfer modeling, we derived a disk-averaged upper limit on the PH$_3$ abundance of 0.8 ppb in the altitude range 75-110 km, which is more stringent than previous ground-based studies.

astro-ph.EP↗

arXiv2022

HyGAL: Characterizing the Galactic ISM with observations of hydrides and other small molecules -- I. Survey description and a first look toward W3(OH), W3 IRS5 and NGC 7538 IRS1

The HyGAL SOFIA legacy program surveys six hydride molecules -- ArH+, OH+, H2O+, SH, OH, and CH -- and two atomic constituents -- C+ and O -- within the diffuse interstellar medium (ISM) by means of absorption-line spectroscopy toward 25 bright Galactic background continuum sources. This detailed spectroscopic study is designed to exploit the unique value of specific hydrides as tracers and probes of different phases of the ISM, as demonstrated by recent studies with the Herschel Space Observatory. The observations performed under the HyGAL program will allow us to address several questions related to the lifecycle of molecular material in the ISM and the physical processes that impact its phase transition, such as: (1) What is the distribution function of the H2 fraction in the ISM? (2) How does the ionization rate due to low-energy cosmic-rays vary within the Galaxy? (3) What is the nature of interstellar turbulence, and what mechanisms lead to its dissipation? This overview discusses the observing strategy, synergies with ancillary and archival observations, the data reduction and analysis schemes adopted; and presents the first results obtained toward three of the survey targets, W3(OH), W3IRS5 and NGC7538IRS1. Robust measurements of the column densities of these hydrides -- obtained through widespread observations of absorption lines-- help address the questions raised, and there is a timely synergy between these observations and the development of theoretical models, particularly pertaining to the formation of H2 within the turbulent ISM. The provision of enhanced HyGAL data products will therefore serve as a legacy for future ISM studies.

astro-ph.GA↗

arXiv2022

SOFIA/GREAT observations of OD and OH rotational lines towards high-mass star forming regions

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 $^2Π_{3/2}$ $J=5/2-3/2$ ground-state transition of OD at 1.3 THz ($215~μ$m) and the rotationally excited OH line at 1.84 THz ($163~μ$m). We also used published high-spectral-resolution SOFIA data of the OH ground-state transition at 2.51 THz ($119.3~μ$m). Our results show that absorption from the $^2Π_{3/2}$ 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.

astro-ph.GA↗

arXiv2021

The distribution of ionized, atomic and PDR gas around S1 in Rho Ophiuchus

The early B star S1 in the Rho Ophiuchus cloud excites an HII region and illuminates a large egg-shaped photodissociation (PDR) cavity. The PDR is restricted to the west and south-west by the dense molecular Rho Oph A ridge, expanding more freely into the diffuse low density cloud to the north-east. We analyze new SOFIA GREAT, GMRT and APEX data together with archival data from Herschel/PACS, JCMT/HARPS to study the properties of the photo-irradiated ionized and neutral gas in this region. The tracers include [C II] at 158 micron, [O I] at 63 and 145 micron, J=6-5 transitions of CO and 13CO, HCO+ (4-3), radio continuum at 610 and 1420 MHz and HI at 21 cm. The PDR emission is strongly red-shifted to the south-east of the nebula, and primarily blue-shifted on the north western side. The [C II] and and [O I]63 spectra are strongly self-absorbed over most of the PDR. By using the optically thin counterparts, [13C II] and [O I]145 respectively, we conclude that the self-absorption is dominated by the warm (>80 K) foreground PDR gas and not by the surrounding cold molecular cloud. We estimate the column densities of C+ and O of the PDR to be 3e18 and 2e19 cm^-2, respectively. Comparison of stellar far-ultraviolet flux and reprocessed infrared radiation suggest enhanced clumpiness of the gas to the north-west. Analysis of the emission from the PDR gas suggests the presence of at least three density components consisting of high density (10^6 cm^-3) clumps, medium density (10^4 cm^-3) and diffuse (10^3 cm^-3) interclump medium. The medium density component primarily contributes to the thermal pressure of the PDR gas which is in pressure equilibrium with the molecular cloud to the west. We find that the PDR is tilted and warped with the south-eastern side of the cavity being denser on the front and the north-western side being denser on the rear.

astro-ph.GA↗

arXiv2020

NGC7538 IRS1 -- an O star driving an ionized jet and giant N-S outflow

NGC 7538 IRS 1 is a very young embedded O star driving an ionized jet and accreting mass with an accretion rate > 10^-4 Msun/year, which is quenching the hypercompact HII region. We use SOFIA GREAT data, Herschel PACS and SPIRE archive data, SOFIA FORCAST archive data, Onsala 20m and CARMA data, and JCMT archive data to determine the properties of the O star and its outflow. IRS 1 appears to be a single O-star with a bolometric luminosity > 1 10^5 Lsun, i.e. spectral type O7 or earlier. We find that IRS 1 drives a large molecular outflow with the blue-shifted northern outflow lobe extending to ~ 280" or 3.6 pc from IRS 1. Near IRS 1 the outflow is well aligned with the ionized jet. The dynamical time scale of the outflow is ~ 1.3 10^5 yr. The total outflow mass is ~ 130 Msun. We determine a mass outflow rate of 1.0 10^-3 Msun/yr, roughly consistent with the observed mass accretion rate. We observe strong high velocity [CII] emission in the outflow, confirming that strong UV radiation from IRS 1 escapes into the outflow lobes and is ionizing the gas. Many O stars may form like low mass stars, but with a higher accretion rate and in a denser environment. As long as the accretion stays high enough to quench the HII region, the star will continue to grow. When the accretion rate drops, the HII region will rapidly start to expand.

astro-ph.GA↗

arXiv2020

FEEDBACK: a SOFIA Legacy Program to Study Stellar Feedback in Regions of Massive Star Formation

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 $μ$m (1.9 THz) line of CII and the 63 $μ$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 $μ$m line, provide an outstanding database for the community. They will be made publically available and will trigger further studies and follow-up observations.

astro-ph.GA↗

arXiv2020

LEGO II: A 3 mm molecular line study covering 100 pc of one of the most actively star-forming portions within the Milky Way Disc

The current generation of (sub)mm-telescopes has allowed molecular line emission to become a major tool for studying the physical, kinematic, and chemical properties of extragalactic systems, yet exploiting these observations requires a detailed understanding of where emission lines originate within the Milky Way. In this paper, we present 60$^{\prime\prime}$ ($\sim$3pc) resolution observations of many 3mm-band molecular lines across a large map of the W49 massive star-forming region ($\sim$100$\times$100pc at 11kpc), which were taken as part of the "LEGO" IRAM-30m large project. We find that the spatial extent or brightness of the molecular line transitions are not well correlated with their critical densities, highlighting abundance and optical depth must be considered when estimating line emission characteristics. We explore how the total emission and emission efficiency (i.e. line brightness per H$_{2}$ column density) of the line emission vary as a function of molecular hydrogen column density and dust temperature. We find that there is not a single region of this parameter space responsible for the brightest and most efficiently emitting gas for all species. For example, we find that the HCN transition shows high emission efficiency at high column density ($10^{22}$cm$^{-2}$) and moderate temperatures (35K), whilst e.g. N$_2$H$^+$ emits most efficiently towards lower temperatures ($10^{22}$cm$^{-2}$; <20K). We determine $X_{\mathrm{CO} (1-0)} \sim 0.3 \times 10^{20} \mathrm{cm^{-2}(Kkms^{-1})^{-1}}$, and $α_{\mathrm{HCN} (1-0)} \sim 30\mathrm{M_\odot(Kkms^{-1}pc^2)^{-1}}$, which both differ significantly from the commonly adopted values. In all, these results suggest caution should be taken when interpreting molecular line emission.

astro-ph.GA↗

arXiv2019

Probing the cold magnetized Universe with SPICA-POL (B-BOP)

SPICA, the cryogenic infrared space telescope recently pre-selected for a `Phase A' concept study as one of the three remaining candidates for ESA's fifth medium class (M5) mission, is foreseen to include a far-infrared polarimetric imager (SPICA-POL, now called B-BOP), which would offer a unique opportunity to resolve major issues in our understanding of the nearby, cold magnetized Universe. This paper presents an overview of the main science drivers for B-BOP, including high dynamic range polarimetric imaging of the cold interstellar medium (ISM) in both our Milky Way and nearby galaxies. Thanks to a cooled telescope, B-BOP will deliver wide-field 100-350 micron images of linearly polarized dust emission in Stokes Q and U with a resolution, signal-to-noise ratio, and both intensity and spatial dynamic ranges comparable to those achieved by Herschel images of the cold ISM in total intensity (Stokes I). The B-BOP 200 micron images will also have a factor ~30 higher resolution than Planck polarization data. This will make B-BOP a unique tool for characterizing the statistical properties of the magnetized interstellar medium and probing the role of magnetic fields in the formation and evolution of the interstellar web of dusty molecular filaments giving birth to most stars in our Galaxy. B-BOP will also be a powerful instrument for studying the magnetism of nearby galaxies and testing galactic dynamo models, constraining the physics of dust grain alignment, informing the problem of the interaction of cosmic rays with molecular clouds, tracing magnetic fields in the inner layers of protoplanetary disks, and monitoring accretion bursts in embedded protostars.

astro-ph.GA↗

arXiv2019

Opening the Treasure Chest in Carina

We have mapped the G287.84-0.82 cometary globule (with the Treasure Chest cluster embedded in it) in the South Pillars region of Carina (i) in [CII], 63micron [OI], and CO(11-10) using upGREAT on SOFIA and (ii) in J=2-1 transitions of CO, 13CO, C18O and J=3-2 transitions of H2CO using the APEX telescope in Chile. We probe the morphology, kinematics, and physical conditions of the molecular gas and the photon dominated regions (PDRs) in G287.84-0.82. The [CII] and [OI] emission suggest that the overall structure of the pillar (with red-shifted photo evaporating tails) is consistent with the effect of FUV radiation and winds from eta-Car and O stars in Trumpler 16. The gas in the head of the pillar is strongly influenced by the embedded cluster, whose brightest member is an O9.5V star, CPD-59 2661. The emission of the [CII] and [OI] lines peak at a position close to the embedded star, while all other tracers peak at another position lying to the north-east consistent with gas being compressed by the expanding PDR created by the embedded cluster. The molecular gas inside the globule is probed with the J=2-1 transitions of CO and isotopologues as well as H2CO, and analyzed using a non-LTE model (escape-probability approach), while we use PDR models to derive the physical conditions of the PDR. We identify at least two PDR gas components; the diffuse part (~10^4 cm^-3) is traced by [CII], while the dense (n~ 2-8x10^5 cm^-3) part is traced by [CII], [OI], CO(11-10). Using the F=2-1 transition of [13CII] detected at 50 positions in the region, we derive optical depths (0.9-5), excitation temperatures of [CII] (80-255 K), and N(C+) of 0.3-1x10^19 cm^-2. The total mass of the globule is ~1000 Msun, about half of which is traced by [CII]. The dense PDR gas has a thermal pressure of 10^7-10^8 K cm^-3, which is similar to the values observed in other regions.

astro-ph.GA↗

arXiv2019

Terrestrial deuterium-to-hydrogen ratio in water in hyperactive comets

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.

astro-ph.EP↗

arXiv2019

Small-scale physical and chemical structure of diffuse and translucent molecular clouds along the line of sight to Sgr B2

The diffuse and translucent molecular clouds traced in absorption along the line of sight to strong background sources have so far been investigated mainly in the spectral domain because of limited angular resolution or small sizes of the background sources. We aim to resolve and investigate the spatial structure of molecular clouds traced by several molecules detected in absorption along the line of sight to SgrB2(N). We have used spectral line data from the EMoCA survey performed with ALMA, taking advantage of the high sensitivity and angular resolution. We identify, on the basis of the spectral analysis of c-C3H2 across the field of view, 15 main velocity components along the line of sight to SgrB2(N) and several components in the envelope of SgrB2. The c-C3H2 column densities reveal two categories of clouds. Clouds in Category I (3 kpc arm, 4 kpc arm, and some GC clouds) have smaller c-C3H2 column densities, smaller linewidths, and smaller widths of their column density PDFs than clouds in Category II (Scutum arm, Sgr arm, and other GC clouds). To investigate the spatial structure we derive opacity maps for the following molecules: c-C3H2, H13CO+, 13CO, HNC, HN13C, HC15N, CS, C34S, 13CS, SiO, SO, and CH3OH. These maps reveal that most molecules trace relatively homogeneous structures that are more extended than the field of view defined by the background continuum emission (about 15", that is 0.08-0.6pc depending on the distance). SO and SiO show more complex structures with smaller clumps of size ~5-8". Our analysis suggests that the driving of the turbulence is mainly solenoidal in the investigated clouds. On the basis of HCO+, we conclude that most line-of-sight clouds towards SgrB2 are translucent, including all clouds where complex organic molecules were recently detected. We also conclude that CCH and CH are good probes of H2 in both diffuse and translucent clouds.

astro-ph.GA↗

arXiv2018

The upGREAT dual frequency heterodyne arrays for SOFIA

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.

astro-ph.IM↗