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R. Güsten

Publications and source records attributed to R. Güsten.

At least 37 records · Page 2Linked to original sources
arXiv2020

Expanding bubbles in Orion A: [CII] observations of M42, M43, and NGC 1977

The Orion Molecular Cloud is the nearest massive-star forming region. Massive stars have profound effects on their environment due to their strong radiation fields and stellar winds. Velocity-resolved observations of the [CII] $158\,μ\mathrm{m}$ fine-structure line allow us to study the kinematics of UV-illuminated gas. Here, we present a square-degree-sized map of [CII] emission from the Orion Nebula complex obtained by the upGREAT instrument onboard SOFIA, covering the entire Orion Nebula (M42) plus M43 and the nebulae NGC 1973, 1975, and 1977. We compare the stellar characteristics of these three regions with the kinematics of the expanding bubbles surrounding them. The bubble blown by the O7V star $θ^1$ Ori C in the Orion Nebula expands rapidly, at $13\,\mathrm{km\,s^{-1}}$. Simple analytical models reproduce the characteristics of the hot interior gas and the neutral shell of this wind-blown bubble and give us an estimate of the expansion time of $0.2\,\mathrm{Myr}$. M43 with the B0.5V star NU Ori also exhibits an expanding bubble structure, with an expansion velocity of $6\,\mathrm{km\,s^{-1}}$. Comparison with analytical models for the pressure-driven expansion of H\,{\sc ii} regions gives an age estimate of $0.02\,\mathrm{Myr}$. The bubble surrounding NGC 1973, 1975, and 1977 with the central B1V star 42 Orionis expands at $1.5\,\mathrm{km\,s^{-1}}$, likely due to the over-pressurized ionized gas as in the case of M43. We derive an age of $0.4\,\mathrm{Myr}$ for this structure. We conclude that the bubble of the Orion Nebula is driven by the mechanical energy input by the strong stellar wind from $θ^1$ Ori C, while the bubbles associated with M43 and NGC 1977 are caused by the thermal expansion of the gas ionized by their central later-type massive stars.

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arXiv2020

An imaging line survey of OMC-1 to OMC-3

Aims: Our aim is to identify the dominant molecular cooling lines and characteristic emission features in the 1.3 mm window of distinct regions in the northern part of the Orion A molecular cloud. By defining and analysing template regions, we also intend to help with the interpretation of observations from more distant sources which cannot be easily spatially resolved. Methods: We analyse an imaging line survey covering the area of OMC-1 to OMC-3 from 200.2 to 281.8 GHz obtained with the PI230 receiver at the APEX telescope. Masks are used to define regions with distinct properties (e.g. column density or temperature ranges) from which we obtain averaged spectra. Lines of 29 molecular species (55 isotopologues) are fitted for each region to obtain the respective total intensity. Results: We find that strong sources like Orion KL have a clear impact on the emission on larger scales. Although not spatially extended, their line emission contributes substantially to spectra averaged over large regions. Conversely, the emission signatures of dense, cold regions like OMC-2 and OMC-3 (e.g. enhanced N$_{2}$H$^{+}$ emission and low HCN/HNC ratio) seem to be difficult to pick up on larger scales, where they are eclipsed by signatures of stronger sources. In all regions, HCO$^{+}$ appears to contribute between 3% and 6% to the total intensity, the most stable value for all bright species. N$_{2}$H$^{+}$ shows the strongest correlation with column density, but not with typical high-density tracers like HCN, HCO$^{+}$, H$_{2}$CO, or HNC. Common line ratios associated with UV illumination, CN/HNC and CN/HCO$^{+}$, show ambiguous results on larger scales, suggesting that the identification of UV illuminated material may be more challenging. The HCN/HNC ratio may be related to temperature over varying scales.

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arXiv2020

[CII] 158 μm self-absorption and optical depth effects

Context. The [CII] 158 μm far-infrared (FIR) fine-structure line is one of the most important cooling lines of the star-forming interstellar medium (ISM). High spectral resolution observations have shown complex structures in the line profiles of the [CII] emission. Aims. Our aim is to determine whether the complex profiles observed in [^{12}CII] are due to individual velocity components along the line-of-sight or to self-absorption based on a comparison of the [^{12}CII] and isotopic [^{13}CII] line profiles. Methods. Deep integrations with the SOFIA/upGREAT 7-pixel array receiver in M43, Horsehead~PDR, Monoceros~R2, and M17~SW allow for the detection of optically thin [^{13}CII] emission lines, along with the [^{12}CII] emission lines, with a high signal-to-noise ratio. We first derived the [^{12}CII] optical depth and the [CII] column density from a single component model. However, the complex line profiles observed require a double layer model with an emitting background and an absorbing foreground. A multi-component velocity fit allows us to derive the physical conditions of the [CII] gas: column density and excitation temperature. Results. We find moderate to high [^{12}CII] optical depths in all four sources and self-absorption of [^{12}CII] in Mon R2 and M17 SW. The high column density of the warm background emission corresponds to an equivalent Av of up to 41 mag. The foreground absorption requires substantial column densities of cold and dense [CII] gas, with an equivalent Av ranging up to about 13 mag. Conclusions. The column density of the warm background material requires multiple photon-dominated region (PDR) surfaces stacked along the line of sight and in velocity. The substantial column density of dense and cold foreground [CII] gas detected in absorption cannot be explained with any known scenario and we can only speculate on its origins

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arXiv2019

Warm gas in protostellar outflows. II. EHV jet and outflows from OMC-2/3

OMC-2/3 is one of the nearest embedded cluster-forming region that includes intermediate-mass protostars at early stages of evolution. A previous CO (3--2) mapping survey towards this region revealed outflow activity related to sources at different evolutionary phases. The present work aims to study the warm gas in the high-velocity emission from several outflows found in CO (3--2) emission by previous observations, determine their physical conditions, and make comparison with previous results in low-mass star-forming regions. We use the CHAMP+ heterodyne array on the APEX telescope to map the CO (6--5) and CO (7--6) emission in the OMC-2 FIR 6 and OMC-3 MMS 1-6 regions, and to observe $^{13}$CO (6--5) at selected positions. We analyze these data together with previous CO (3--2) observations. In addition, we mapped the SiO (5--4) emission in OMC-2 FIR 6. The CO (6--5) emission was detected in most of the outflow lobes in the mapped regions, while the CO (7--6) was found mostly from the OMC-3 outflows. In the OMC-3 MMS 5 outflow, a previously undetected extremely high velocity gas was found in CO (6--5). This extremely high velocity emission arises from the regions close to the central object MMS 5. Radiative transfer models revealed that the high-velocity gas from MMS 5 outflow consists of gas with $n_{\rm H_2}=$10$^4$--10$^{5}$ cm$^{-3}$ and $T>$ 200 K, similar to what is observed in young Class 0 low-mass protostars. For the other outflows, values of $n_{\rm H_2}>$10$^{4}$ cm$^{-3}$ were found. The physical conditions and kinematic properties of the young intermediate-mass outflows presented here are similar to those found in outflows from Class 0 low-mass objects. Due to their excitation requirements, mid$-J$ CO lines are good tracers of extremely high velocity gas in young outflows likely related to jets.

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arXiv2019

APEX Observations of the CO Envelope around the Young FUor-type Star V883 Ori

The accretion-driven outbursts of young FU Orionis-type stars may be a common stage of pre-main sequence evolution and can have a significant impact on the circumstellar environment as it pertains to the growth of solids and eventually planets. This episodic accretion is thought to be sustained by additional gas in-falling from the circumstellar envelope and disk. We present APEX observations of the CO gas in the envelope around V883 Orionis, a young outbursting star. The observations mapped the $^{12}$CO(4-3), $^{12}$CO(3-2), and $^{13}$CO(3-2) lines with the FLASH$^{+}$ instrument and the $^{12}$CO(6-5) line with the SEPIA instrument. We detected high signal-to-noise emission extending out to radii $>10000$ au and calculated integrated fluxes of $1100~\rm Jy~km~s^{-1}$ for $^{12}$CO(6-5), $2400~\rm Jy~km~s^{-1}$ for $^{12}$CO(4-3), $1600~\rm Jy~km~s^{-1}$ for $^{12}$CO(3-2), and $450~\rm Jy~km~s^{-1}$ for $^{13}$CO(3-2). We used the thermo-chemical code P{\small RO}D{\small I}M{\small O} to test several models and find the data are best described by an envelope structure with $\rm M_{env}\approx 0.2-0.4\,M_{\odot}$ and a mass-infall rate of $\rm \dot{M}_{inf}=1-2\times10^{-6}\,M_{\odot}\,yr^{-1}$. We infer that the observed envelope and outflow structure around V883 Ori could be caused by multiple outbursts, consistent with episodic accretion.

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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.

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arXiv2019

Herschel water maps towards the vicinity of the black hole Sgr A*

Aims: We study the spatial distribution and kinematics of water emission in a ~64 pc$^2$ region of the Galactic Center (GC) around Sgr A*. We also analyze the water excitation to derive the physical conditions and water abundances in the CND and the `quiescent clouds'. Methods: We presented the integrated intensity maps of the ortho 1$_{10}-1_{01}$, and para 2$_{02}-1_{11}$ and 1$_{11}-0_{00}$ water transitions observed with the HIFI instrument on board Herschel. To study the water excitation we used ground state ortho and para H$_2^{18}$O transitions. In our study, we also used SPIRE continuum measurements of the CND. Using a non-LTE radiative transfer code, the water line profiles and dust continuum were modeled. We also used a rotating ring model to reproduce the CND kinematics represented by the PV diagram. Results: We identify the water emission arising from the CND, the Western Streamer, and the 20 and 50 km s$^{-1}$ clouds. The ortho water maps show absorption structures in the range of [-220,10] km s$^{-1}$. The PV diagram shows that the 2$_{02}-1_{11}$ H$_2$O emission traces the CND. We derive high X$_{H_2O}$ of $\sim$(0.1-1.3)$\times$10$^{-5}$, V$_t$ of 14-23 km s$^{-1}$ and T$_d$ of 15-45 K for the CND, and the lower X$_{\rm H_2O}$ of 4$\times$10$^{-8}$ and V$_t$ of 9 km s$^{-1}$ for the 20 km s$^{-1}$ cloud. Collisional excitation and dust effects are responsible for the water excitation in the southwest lobe of the CND and the 20 km s$^{-1}$ cloud, whereas only collisions can account for the water excitation in the northeast lobe of the CND. We propose that the water vapor in the CND is caused by grain sputtering by shocks of 10-20 km s$^{-1}$, with some contribution of high temperature and cosmic-ray chemistries plus a PDR chemistry. The low X$_{\rm H_2O}$ derived for the 20 km s$^{-1}$ cloud could be partially a consequence of the water freeze-out on grains.

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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↗
arXiv2018

Velocity resolved [O I] 63 $μ$m emission in the HD 50138 circumstellar disk

HH 50138 is one of the brightest B[e] stars at a distance of $\sim$ 380 pc with strong infrared excess. The star was observed in [O I] 63 $μ$m and [C II] 158 $μ$m with high velocity resolution with upGREAT on SOFIA. The velocity resolved [O I] emission provides evidence for a large gas-disk, $\sim$ 760 au in size, around HD 50138. Whereas previous interferometric observations give strong evidence for a hot gas and dust disk in Keplerian rotation, our bservations are the first to provide unambiguous evidence for a large warm disk around the star. Herschel/PACS observations showed that the [C II] emission is extended, therefore the [C II] emission most likely originates in an ionized gas shell created by a past outflow event. We confirm the isolated nature of HD 50138. It is far from any star forming region and has low proper motion. Neither is there any sign of a remnant cloud from which it could have formed. The extended disk around the star appears carbon poor. It shows OH and [O I] emission, but no CO. The CO abundance appears to be at least an order of magnitude lower than that of OH. Furthermore $^{13}$CO is enriched by more than a factor of five, confirming that the star is not a Herbig Be star. Finally we note that our high spectral resolution [O I] and [C II] observations provide a very accurate heliocentric velocity of the star, 40.8 $\pm$ 0.2 km~s$^{-1}$.

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arXiv2018

A thorough view of the nuclear region of NGC 253 - Combined Herschel, SOFIA and APEX dataset

We present a large set of spectral lines detected in the $40"$ central region of the starburst galaxy NGC 253. Observations were obtained with the three instruments SPIRE, PACS and HIFI on board the Herschel Space Observatory, upGREAT on board of the SOFIA airborne observatory, and the ground based APEX telescope. Combining the spectral and photometry products of SPIRE and PACS we model the dust continuum Spectral Energy Distribution (SED) and the most complete $^{12}$CO Line SED reported so far toward the nuclear region of NGC 253. Properties and excitation of the molecular gas were derived from a three-component non-LTE radiative transfer model, using the SPIRE $^{13}$CO lines and ground based observations of the lower-$J$ $^{13}$CO and HCN lines, to constrain the model parameters. Three dust temperatures were identified from the continuum emission, and three components are needed to fit the full CO LSED. Only the third CO component (fitting mostly the HCN and PACS $^{12}$CO lines) is consistent with a shock/mechanical heating scenario. A hot core chemistry is also argued as a plausible scenario to explain the high-$J$ $^{12}$CO lines detected with PACS. The effect of enhanced cosmic ray ionization rates, however, cannot be ruled out, and is expected to play a significant role in the diffuse and dense gas chemistry. This is supported by the detection of ionic species like OH$^+$ and H$_2$O$^+$, as well as the enhanced fluxes of the OH lines with respect to those of H$_2$O lines detected in both PACS and SPIRE spectrum.

astro-ph.GA↗
arXiv2018

Unveiling the remarkable photodissociation region of M8

Messier 8 is one of the brightest HII regions in the sky. Using SOFIA, APEX 12 m and IRAM 30 m telescopes, we have performed a comprehensive imaging survey of the emission from the [CII], [CI] and CO isotopologues within 1.3 $\times$ 1.3 pc around the dominant Herschel 36 (Her 36) stellar system. To further explore the morphology of the region we compare archival infrared, optical and radio images of the nebula with our newly obtained [CII] and CO data. We perform a quantitative analysis, using both LTE and non-LTE methods to determine the abundances of some of the observed species as well as kinetic temperatures and volume densities. Bright CO, [CII] and [CI] emission has been found towards the HII region and the photodissociation region (PDR) in M8. Our analysis places the bulk of the molecular material in the background of the nebulosity illuminated by the bright stellar systems Her 36 and 9 Sagitarii. Since the emission from all observed atomic and molecular tracers peaks at or close to the position of Her 36, we conclude that the star is still physically close to its natal dense cloud core and heats it. A veil of warm gas moves away from Her 36 toward the Sun and its associated dust contributes to the foreground extinction in the region. One of the most prominent star forming regions in M8, the Hourglass Nebula, is particularly bright due to cracks in this veil close to Her 36. By using radiative transfer modeling of different transitions of CO isotopologues, we obtain H$_{2}$ densities ranging from $\sim 10^{4} - 10^{6}$ cm$^{-3}$ and kinetic temperatures of 100 $-$ 150 K in the bright PDR caused by Her 36.

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arXiv2017

HIFI Spectroscopy of ${\rm H_2O}$ submm Lines in Nuclei of Actively Star Forming Galaxies

We present a systematic survey of multiple velocity-resolved H$_2$O spectra using Herschel/HIFI towards nine nearby actively star forming galaxies. The ground-state and low-excitation lines (E$_{\rm up}\,\le 130\,{\rm K}$) show profiles with emission and absorption blended together, while absorption-free medium-excitation lines ($130\,{\rm K}\, \le\, E_{\rm up}\,\le\,350\,{\rm K}$) typically display line shapes similar to CO. We analyze the HIFI observation together with archival SPIRE/PACS H$_2$O data using a state-of-the-art 3D radiative transfer code which includes the interaction between continuum and line emission. The water excitation models are combined with information on the dust- and CO spectral line energy distribution to determine the physical structure of the interstellar medium (ISM). We identify two ISM components that are common to all galaxies: A warm ($T_{\rm dust}\,\sim\,40-70\,{\rm K}$), dense ($n({\rm H})\,\sim\,10^5-10^6\,{\rm cm^{-3}}$) phase which dominates the emission of medium-excitation H$_2$O lines. This gas phase also dominates the FIR emission and the CO intensities for $J_{\rm up} > 8$. In addition a cold ($T_{\rm dust}\,\sim\,20-30\,{\rm K}$), dense ($n({\rm H})\sim\,10^4- 10^5\,{\rm cm^{-3}}$) more extended phase is present. It outputs the emission in the low-excitation H$_2$O lines and typically also produces the prominent line absorption features. For the two ULIRGs in our sample (Arp 220 and Mrk 231) an even hotter and more compact (R$_s\,\le\,100$ pc) region is present which is possibly linked to AGN activity. We find that collisions dominate the water excitation in the cold gas and for lines with $E_{\rm up}\le300\,{\rm K}$ and $E_{\rm up}\le800\,{\rm K}$ in the warm and hot component, respectively. Higher energy levels are mainly excited by IR pumping.

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arXiv2017

Oxygen budget in low-mass protostars: the NGC1333-IRAS4A R1 shock observed in [OI] at 63 um with SOFIA-GREAT

In molecular outflows from forming low-mass protostars, most oxygen is expected to be locked up in water. However, Herschel observations have shown that typically an order of magnitude or more of the oxygen is still unaccounted for. To test if the oxygen is instead in atomic form, SOFIA-GREAT observed the R1 position of the bright molecular outflow from NGC1333-IRAS4A. The [OI] 63 um line is detected and spectrally resolved. From an intensity peak at +15 km/s, the intensity decreases until +50 km/s. The profile is similar to that of high-velocity (HV) H2O and CO 16-15, the latter observed simultaneously with [OI]. A radiative transfer analysis suggests that ~15% of the oxygen is in atomic form toward this shock position. The CO abundance is inferred to be ~10^-4 by a similar analysis, suggesting that this is the dominant oxygen carrier in the HV component. These results demonstrate that a large portion of the observed [OI] emission is part of the outflow. Further observations are required to verify whether this is a general trend.

astro-ph.SR↗
arXiv2017

ATLASGAL-selected massive clumps in the inner Galaxy: V. Temperature structure and evolution

(Abridged) Aims: We aim to use the progressive heating of the gas caused by the feedback of high-mass young stellar objects (YSOs) to prove the statistical validity of the most common schemes used to define an evolutionary sequence for high-mass clumps, and characterise the sensitivity of different tracers to this process. Methods: From the spectroscopic follow-ups of the ATLASGAL TOP100 sample, we selected several multiplets of CH3CN, CH3CCH, and CH3OH emission lines to derive and compare the physical properties of the gas in the clumps along the evolutionary sequence. Our findings are compared with results obtained from CO isotopologues, dust, and NH3 from previous studies on the same sample. Results: The chemical properties of each species have a major role on the measured physical properties. Low temperatures are traced by NH3, CH3OH, and CO (in the early phases), the warm and dense envelope can be probed with CH3CN, CH3CCH, and, in evolved sources via CO isotopologues. CH3OH and CH3CN are also abundant in the hot cores, and their high-excitation transitions may be good tools to study the kinematics in the hot gas surrounding the YSOs that these clumps are hosting. All tracers show, to different degrees, progressive warming with evolution. The relation between gas temperature and L/M is reproduced by a toy model of a spherical, internally heated clump. Conclusions: The evolutionary sequence defined for the clumps is statistically valid and we could identify the processes dominating in different intervals of L/M. For L/M<2Lsun/Msun a large quantity of gas is still being accumulated and compressed at the bottom of the potential well. Between 2Lsun/Msun 40Lsun/Msun HII regions become common, showing that dissipation of the parental clump dominates.

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arXiv2017

Cold CO gas in the envelopes of FU Orionis-type young eruptive stars

FUors are young stellar objects experiencing large optical outbursts due to highly enhanced accretion from the circumstellar disk onto the star. FUors are often surrounded by massive envelopes, which play a significant role in the outburst mechanism. Conversely, the subsequent eruptions might gradually clear up the obscuring envelope material and drive the protostar on its way to become a disk-only T Tauri star. Here we present an APEX $^{12}$CO and $^{13}$CO survey of eight southern and equatorial FUors. We measure the mass of the gaseous material surrounding our targets. We locate the source of the CO emission and derive physical parameters for the envelopes and outflows, where detected. Our results support the evolutionary scenario where FUors represent a transition phase from envelope-surrounded protostars to classical T Tauri stars.

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arXiv2016

Warm ISM in the Sgr A Complex. I: Mid-J CO, atomic carbon, ionized atomic carbon,and ionized nitrogen sub-mm/FIR line observations with the Herschel-HIFI and NANTEN2/SMART telescopes

We present large-scale submm observations towards the Sgr A Complex covering ~300 arcmin2. These data were obtained in the frame of the HEXGAL Program with the Herschel-HIFI satellite and are complemented with submm observations obtained with the NANTEN2/SMART telescope as part of the NANTEN2/SMART Central Nuclear Zone Survey. The observed species are CO(4-3) observed with the NANTEN2/SMART telescope, and [CI](1-0), [CI](2-1), [NII](1-0), and [CII](3/2-1/2) observed with the Herschel-HIFI satellite. The observations are presented in a 1 km/s spectral resolution and a spatial resolution ranging from 46" to 28". The spectral coverage of the three lower frequency lines is +-200 km/s, while in the two high frequency lines, the upper LSR velocity limit is +94 km/s and +145 km/s for the [NII] and [CII] lines, respectively. The spatial distribution of the emission in all lines is very widespread. The bulk of the CO emission is found towards Galactic latitudes below the Galactic plane, and all the known molecular clouds are identified. Both neutral atomic carbon lines have their brightest emission associated with the +50 km/s cloud. Their spatial distribution at this LSR velocity describes a crescent-shape structure, which is probably the result of interaction with the energetic event (one or several supernovae explosions) that gave origin to the non-thermal Sgr A-East source. The [CII] and [NII] emissions have most of their flux associated with the thermal Arched-Filaments and the H Region and bright spots in [CII] emission towards the Central Nuclear Disk (CND) are detected. Warm Gas at very high (|Vlsr| > 100 km/s) LSR velocities is also detected towards the line of sight to the Sgr A Complex, and it is most probably located outside the region, in the X1 orbits.

astro-ph.GA↗
arXiv2016

Volatile carbon locking and release in protoplanetary disks. A study of TW Hya and HD 100546

The composition of planetary solids and gases is largely rooted in the processing of volatile elements in protoplanetary disks. To shed light on the key processes, we carry out a comparative analysis of the gas-phase carbon abundance in two systems with a similar age and disk mass, but different central stars: HD 100546 and TW Hya. We combine our recent detections of C$^{0}$ in these disks with observations of other carbon reservoirs (CO, C$^{+}$, C$_{2}$H) and gas mass and warm gas tracers (HD, O$^{0}$), as well as spatially resolved ALMA observations and the spectral energy distribution. The disks are modelled with the DALI 2D physical-chemical code. Stellar abundances for HD 100546 are derived from archival spectra. Upper limits on HD emission from HD 100546 place an upper limit on the total disk mass of $\leq0.1\,M_{\odot}$. The gas-phase carbon abundance in the atmosphere of this warm Herbig disk is at most moderately depleted compared to the interstellar medium, with [C]/[H]$_{\rm gas}=(0.1-1.5)\times 10^{-4}$. HD 100546 itself is a $λ\,$Boötis star, with solar abundances of C and O but a strong depletion of rock-forming elements. In the gas of the T Tauri disk TW Hya, both C and O are strongly underabundant, with [C]/[H]$_{\rm gas}=(0.2-5.0)\times 10^{-6}$ and C/O${>}1$. We discuss evidence that the gas-phase C and O abundances are high in the warm inner regions of both disks. Our analytical model, including vertical mixing and a grain size distribution, reproduces the observed [C]/[H]$_{\rm gas}$ in the outer disk of TW Hya and allows to make predictions for other systems.

astro-ph.EP↗
arXiv2016

[CII] 158$μ$m and [NII] 205$μ$m emission from IC 342 - Disentangling the emission from ionized and photo-dissociated regions

Aims: We investigate how much of the [CII] 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 [CII] line with the [NII] 205{\textmu}m emission line coming exclusively from the HII regions. Methods: We present small maps of [CII] and [NII] lines recently observed with the GREAT receiver on board SOFIA. 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 $I([CII])/I(^{12}\mathrm{CO} (1-0))$ 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 [CII] emission we find that 35-90% of the observed [CII] intensity stems from the ionized gas if both phases contribute. Averaged over the central few hundred parsec we find for the [CII] 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 [CII] emission than is commonly observed on larger scales and than is predicted. Kinematic analysis shows that the majority of the [CII] 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.

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