Shock Tracers Research Articles

Sulfur monoxide (SO) as a shock tracer in protoplanetary disks: Case of AB Aurigae

Context. Sulfur monoxide (SO) is known to be a good shock tracer in molecular clouds and protostar environments, but its abundance is difficult to reproduce, even with state-of-the-art astrochemical models. Aims. We investigate the properties of the observed SO emission in the protoplanetary disk of AB Auriga, a Herbig Ae star of 2.4 M⊙ in mass, located at 156 pc. The AB Aur system is unique because it exhibits a dust trap and at least one young putative planet orbiting at about 30 au from the central star. Methods. We reduced ALMA archival data (projects 2019.1.00579.S, 2021.1.00690.S, and 2021.1.01216.S) and analyzed the three detected SO lines (SO 65 − 54, 67 − 56 and 56 − 45). We also used C17O and C18O 2–1 data to complement the interpretation of the SO data. Results. For the three SO lines, the maximum SO emission in the ring is not located in the dust trap. Moreover, the inner radius of the SO ring is significantly larger than the CO emission inner radius, ∼160 au versus ∼90 au. The SO emission traces gas located in part beyond the dust ring. This emission likely originates from shocks at the interface of the outer spirals, observed in CO and scattered light emission, as well as those in the molecular and dust ring. Also, SO is detected within the cavity, at a radius of ∼20 − 30 au and with a rotation velocity compatible with the protoplanet P1. We speculate that this SO emission originates from accretion shocks onto the circumplanetary disk of the putative protoplanet P1. Conclusions. These observations confirm that SO is a good tracer of shocks in protoplanetary disks and could serve as a powerful new tool for detecting embedded (proto)planets.

Fe II] 1.644 µm imaging survey of planetary nebulae with low-ionisation structures

Low-ionisation structures (LISs) are commonly found in planetary nebulae (PNe), but they are still poorly understood. The recent discovery of unforeseen molecular hydrogen gas (H2) has impacted what we think we know about these microstructures and PNe. To obtain an overall understanding of LISs, we carried out an [Fe II] 1.644 µm imagery survey in PNe with LISs, with the aim to detect the [Fe II] 1.644µm emission line, a common tracer of shocks. We present the first detection of [Fe II] 1.644 µmline directly associated with the LISs in four out of five PNe. The theoretical H I 12-4 recombination line was also computed either from the Brγ or the Hβ line and subtracted from the observed narrow-band line fluxes. The [Fe II] 1.644 µm flux ranges from 1 to 40 ×10−15 ergs cm−2 s−1 and the intensity from 2 to 90 ×10−5 erg s−1 cm−2 sr−1. The R(Fe)=[Fe II] 1.644 µm/Brγ line ratio was also computed and found to range between 0.5 and 7. In particular, the [Fe II] 1.644 µm line was detected in NGC 6543 (R(Fe)<0.15), along with the outer pairs of LISs in NGC 7009 (R(Fe)<0.25) and the jet-like LISs in IC 4634 (R(Fe)~1), and in several LISs in NGC 6571 (2<R(Fe)<7). The low R(Fe) result for NGC 6543 is attributed to the UV radiation from the central star. In contrast, the higher values in NGC 6571 and IC 4634 are indicative of shocks. The moderate R(Fe) in NGC 7009 likely indicates the contribution of both mechanisms.

Outflow Driven by a Protoplanet Embedded in the TW Hya Disk

Gas giant planets are formed by gas accretion onto planetary cores in protoplanetary disks. However, direct evidence of this process is still lacking, limiting our understanding of planetary formation processes. During mass accretion, planet-driven outflows may be launched, which could be observable by shock tracers such as sulfur monoxide (SO). We report the detection of SO gas in the protoplanetary disk around TW Hya in archival Atacama Large Millimeter/submillimeter Array observations. The SO J = 87 − 76 emission line is detected at a 6σ significance and localized to the southeast region of the disk with an arc-like morphology. The line center is redshifted with respect to the systemic velocity by ∼5 km s−1. The starting point of the SO emission is located at a planet-carved dust gap at 42 au. We attribute this to an outflow driven by an embedded protoplanet. Indeed, the observed morphology is well reproduced by a ballistic outflow model. The outflow velocity suggests that the outflow launching source has a mass of ∼4M ⊕ and the mass-loss rate is 3 × 10−8–1 × 10−6 M Jup yr−1. With the relation of mass-loss and mass-accretion rates established for protostars, we estimated the mass-accretion rate onto the protoplanet to be 3 × 10−7−1 × 10−5 M Jup yr−1, which matches theoretical predictions for a ∼4M ⊕ planet at this separation. The detection of planet-driven outflow provides us a unique opportunity to directly probe the earliest phase of gas giant planet formation.

The asymmetric bipolar [Fe II] jet and H2 outflow of TMC1A resolved with the JWST NIRSpec Integral Field Unit

Protostellar outflows exhibit large variations in their structure depending on the observed gas emission. To understand the origin of the observed variations, it is important to analyze the differences in the observed morphology and kinematics of the different tracers. The James Webb Space Telescope (JWST) allows us to study the physical structure of the protostellar outflow through well-known near-infrared shock tracers in a manner unrivaled by other existing ground-based and space-based telescopes at these wavelengths. This study analyzes the atomic jet and molecular outflow in the Class I protostar, TMC1A, utilizing spatially resolved Fe II and H2 lines to characterize the morphology and to identify previously undetected spatial features, and compare them to existing observations of TMC1A and its outflows observed at other wavelengths. We identified a large number of Fe II and H2 lines within the G140H, G235H, and G395H gratings of the NIRSpec IFU observations. We analyzed their morphology and position-velocity (PV) diagrams. From the observed Fe II line ratios, the extinction toward the jet is estimated. We detected the bipolar Fe jet by revealing, for the first time, the presence of a redshifted atomic jet. Similarly, the redshifted component of the H2 slower wide-angle outflow was observed. The Fe II and H2 redhifted emission both exhibit significantly lower flux densities compared to their blueshifted counterparts. Additionally, we report the detection of a collimated high-velocity ($ 100$ km $), blueshifted H2 outflow, suggesting the presence of a molecular jet in addition to the well-known wider angle low-velocity structure. The Fe II and H2 jets show multiple intensity peaks along the jet axis, which may be associated with ongoing or recent outburst events. In addition to the variation in their intensities, the H2 wide-angle outflow exhibits a ring-like structure. The blueshifted H2 outflow also shows a left-right brightness asymmetry likely due to interactions with the surrounding ambient medium and molecular outflows. Using the Fe II line ratios, the extinction along the atomic jet is estimated to be between $A_ V $ = 10--30 on the blueshifted side, with a trend of decreasing extinction with distance from the protostar. A similar $A_ V $ is found for the redshifted side, supporting the argument for an intrinsic red-blue outflow lobe asymmetry rather than environmental effects such as extinction. This intrinsic difference revealed by the unprecedented sensitivity of JWST, suggests that younger outflows already exhibit the red-blue side asymmetry more commonly observed toward jets associated with Class II disks.

Absorption and Self-absorption of [C ii] and [O i] Far Infrared Lines toward a Bright Bubble in the Nessie Infrared Dark Cloud

Using the upGREAT instrument on board the Stratospheric Observatory for Infrared Astronomy, we imaged [C ii] 157.74 and [O i] 63.18 μm line emission from a bright photodissociation region (PDR) associated with an ionized bubble located in the Nessie Nebula, a filamentary infrared dark cloud. A comparison with Australia Telescope Compact Array data reveals a classic photodissociation region (PDR) structure, with a uniform progression from ionized gas, to photodissociated gas, and to molecular gas from the bubble’s interior to its exterior. [O i] line emission from the bubble’s PDR reveals self-absorption features. Toward a far-IR bright protostar, both [O i] and [C ii] show an absorption feature at a velocity of −18 km s−1, the same velocity as an unrelated foreground molecular cloud. Since the gas density in typical molecular clouds is well below the [O i] and [C ii] critical densities, the excitation temperatures for both lines are low (∼20 K). The Meudon models demonstrate that the surface of a molecular cloud, externally illuminated by a standard G 0 = 1 interstellar radiation field, can produce absorption features in both transitions. Thus, the commonly observed [O i] and [C ii] self-absorption and absorption features plausibly arise from the subthermally excited, externally illuminated photodissociated envelopes of molecular clouds. The luminous young stellar object AGAL337.916-00.477, located precisely where the expanding bubble strikes the Nessie filament, is associated with two shock tracers: NH3 (3,3) maser emission and SiO 2−1 emission, indicating an interaction between the bubble and the filament. The interaction of the expanding bubble with its parental dense filament has triggered star formation.

FAUST

Context. The origin of the chemical diversity observed around low-mass protostars probably resides in the earliest history of these systems. Aims. We aim to investigate the impact of protostellar feedback on the chemistry and grain growth in the circumstellar medium of multiple stellar systems. Methods. In the context of the ALMA Large Program FAUST, we present high-resolution (50 au) observations of CH3OH, H2CO, and SiO and continuum emission at 1.3 mm and 3 mm towards the Corona Australis star cluster. Results. Methanol emission reveals an arc-like structure at ∼1800 au from the protostellar system IRS7B along the direction perpendicular to the major axis of the disc. The arc is located at the edge of two elongated continuum structures that define a cone emerging from IRS7B. The region inside the cone is probed by H2CO, while the eastern wall of the arc shows bright emission in SiO, a typical shock tracer. Taking into account the association with a previously detected radio jet imaged with JVLA at 6 cm, the molecular arc reveals for the first time a bow shock driven by IRS7B and a two-sided dust cavity opened by the mass-loss process. For each cavity wall, we derive an average H2 column density of ∼7 × 1021 cm−2, a mass of ∼9 × 10−3 M⊙, and a lower limit on the dust spectral index of 1.4. Conclusions. These observations provide the first evidence of a shock and a conical dust cavity opened by the jet driven by IRS7B, with important implications for the chemical enrichment and grain growth in the envelope of Solar System analogues.

Multiple Jets in the Bursting Protostar HOPS 373SW

We present the outflows detected in HOPS 373SW, a protostar undergoing a modest 30% brightness increase at 850 μm. Atacama Large Millimeter/submillimeter Array observations of shock tracers, including SiO 8–7, CH3OH 7k–6k, and 12CO 3–2 emission, reveal several outflow features around HOPS 373SW. The knots in the extremely high-velocity SiO emission reveal the wiggle of the jet, for which a simple model derives a 37° inclination angle of the jet to the plane of the sky, a jet velocity of 90 km s−1, and a period of 50 yr. The slow SiO and CH3OH emission traces U-shaped bow shocks surrounding the two CO outflows. One outflow is associated with the high-velocity jets, while the other is observed to be close to the plane of the sky. The misaligned outflows imply that previous episodic accretion events have either reoriented HOPS 373SW or that it is an unresolved protostellar binary system with misaligned outflows.

The GUAPOS project: G31.41+0.31 Unbiased ALMA sPectral Observational Survey

Context. The astrochemistry of the important biogenic element phosphorus (P) is still poorly understood, but observational evidence indicates that P-bearing molecules are likely associated with shocks. Aims. We study P-bearing molecules and some shock tracers towards one of the chemically richest hot molecular cores, G31.41+0.31, in the framework of the project “G31.41+0.31 Unbiased ALMA sPectral Observational Survey” (GUAPOS), which is being carried out with the Atacama Large Millimeter Array (ALMA). Methods. We observed the molecules PN, PO, SO, SO2, SiO, and SiS through their rotational lines in the spectral range 84.05– 115.91 GHz covered by the GUAPOS project. Results. PN is clearly detected, while PO is tentatively detected. The PN emission arises from two regions southwest of the hot core peak, named regions 1 and 2 here, and is undetected or tentatively detected towards the hot core peak. The PN and SiO lines are very similar both in spatial emission morphology and spectral shape. Region 1 is partly overlapping with the hot core and is warmer than region 2, which is well separated from the hot core and located along the outflows identified in previous studies. The SO, SO2, and SiS emissions are also detected towards the PN-emitting regions 1 and 2, but arise mostly from the hot core. Moreover, the column density ratio SiO/PN remains constant in regions 1 and 2, while SO/PN, SiS/PN, and SO2/PN decrease by about an order of magnitude from region 1 to region 2, indicating that SiO and PN have a common origin even in regions with different physical conditions. The PO/PN ratio in region 2, where PO is tentatively detected, is ~0.6–0.9, which is in line with the predictions of pure shock models. Conclusions. Our study provides robust confirmation of previous observational evidence that PN emission is tightly associated with SiO and is likely a product of shock chemistry, as the lack of a clear detection of PN towards the hot core allows us to rule out relevant formation pathways in hot gas. We propose the PN-emitting region 2 as a new astrophysical laboratory for shock-chemistry studies.

JOYS+: Mid-infrared detection of gas-phase SO2 emission in a low-mass protostar

Context. Thanks to the Mid-InfraRed Instrument (MIRI) on the James Webb Space Telescope (JWST), our ability to observe the star formation process in the infrared has greatly improved. Due to its unprecedented spatial and spectral resolution and sensitivity in the mid-infrared, JWST/MIRI can see through highly extincted protostellar envelopes and probe the warm inner regions. An abundant molecule in these warm inner regions is SO2, which is a common tracer of both outflow and accretion shocks as well as hot core chemistry. Aims. This paper presents the first mid-infrared detection of gaseous SO2 emission in an embedded low-mass protostellar system rich in complex molecules and aims to determine the physical origin of the SO2 emission. Methods. JWST/MIRI observations taken with the Medium Resolution Spectrometer (MRS) of the low-mass protostellar binary NGC 1333 IRAS 2A in the JWST Observations of Young protoStars (JOYS+) program are presented. The observations reveal emission from the SO2 v3 asymmetric stretching mode at 7.35 µm. Using simple slab models and assuming local thermodynamic equilibrium (LTE), we derived the rotational temperature and total number of SO2 molecules. We then compared the results to those derived from high-angular-resolution SO2 data on the same scales (~50–100 au) obtained with the Atacama Large Millimeter/submillimeter Array (ALMA). Results. The SO2 emission from the v3 band is predominantly located on ~50–100 au scales around the mid-infrared continuum peak of the main component of the binary, IRAS 2A1. A rotational temperature of 92 ± 8 K is derived from the v3 lines. This is in good agreement with the rotational temperature derived from pure rotational lines in the vibrational ground state (i.e., v = 0) with ALMA (104 ± 5 K), which are extended over similar scales. However, the emission of the v3 lines in the MIRI-MRS spectrum is not in LTE given that the total number of molecules predicted by a LTE model is found to be a factor of 2 × 104 higher than what is derived for the v = 0 state from the ALMA data. This difference can be explained by a vibrational temperature that is ~100 K higher than the derived rotational temperature of the v = 0 state: Tvib ~ 200 K versus Trot = 104 ± 5 K. The brightness temperature derived from the continuum around the v3 band (~7.35 µm) of SO2 is ~180 K, which confirms that the v3 = 1 level is not collisionally populated but rather infrared-pumped by scattered radiation. This is also consistent with the non-detection of the v2 bending mode at 18–20 µm. The similar rotational temperature derived from the MIRI-MRS and ALMA data implies that they are in fact tracing the same molecular gas. The inferred abundance of SO2 , determined using the LTE fit to the lines of the vibrational ground state in the ALMA data, is 1.0 ± 0.3 × 10−8 with respect to H2, which is on the lower side compared to interstellar and cometary ices (10−8−10−7). Conclusions. Given the rotational temperature, the extent of the emission (~100 au in radius), and the narrow line widths in the ALMA data (~3.5 km s−1), the SO2 in IRAS 2A likely originates from ice sublimation in the central hot core around the protostar rather than from an accretion shock at the disk–envelope boundary. Furthermore, this paper shows the importance of radiative pumping and of combining JWST observations with those from millimeter interferometers such as ALMA to probe the physics on disk scales and to infer molecular abundances.

Shock Excitation in Narrow-line Regions Powered by AGN Outflows

Outflows in an active galactic nucleus (AGN) are considered to play a key role in the evolution of the host galaxy through transfer of a large amount of energy. A narrow-line region (NLR) in the AGN is composed of ionized gas extending from parsec to kiloparsec scales. It has been suggested that shocks are required to ionize the NLR gas. If AGN outflows generate these shocks, they will sweep through the NLR, and the outflow energy will be transferred into a galaxy-scale region. In order to study the contribution of the AGN outflow to the NLR-scale shock, we measure the [Fe ii]λ12570/[P ii]λ11886 line ratio, which is a good tracer of shocks, using near-infrared spectroscopic observations with the Warm INfrared Echelle spectrograph to Realize Extreme Dispersion and sensitivity (WINERED) mounted on the New Technology Telescope. In 13 Seyfert galaxies we observed, the [Fe ii] and [P ii] lines were detected in 12 and 6 targets, respectively. The [Fe ii]/[P ii] ratios in 4 targets were found to be higher than 10, which implies the existence of shocks. We also found that the shock is likely to exist where an ionized outflow, i.e., a blue wing in [S iii]λ9533, is present. Our result implies that the ionized outflow present in an NLR-scale region sweeps through the interstellar medium and generates a shock.

Two-photon Production in Low-velocity Shocks

The Galactic interstellar medium abounds in shocks with low velocities v s ≲ 70 km s−1. Some are descendants of higher velocity shocks, while others start off at low velocity (e.g., stellar bow shocks, intermediate velocity clouds, spiral density waves). Low-velocity shocks cool primarily via Lyα and two-photon continuum, augmented by optical recombination lines (e.g., Hα), forbidden lines of metals and free-bound emission, free–free emission. The dark far-ultraviolet (FUV) sky, aided by the fact that the two-photon continuum peaks at 1400 Å, makes the FUV band an ideal tracer of low-velocity shocks. GALEX FUV images reaffirm this expectation, discovering faint and large interstellar structure in old supernova remnants and thin arcs stretching across the sky. Interstellar bow shocks are expected from fast stars from the Galactic disk passing through the numerous gas clouds in the local interstellar medium within 15 pc of the Sun. Using the bests atomic data available to date, we present convenient fitting formulae for yields of Lyα, two-photon continuum, and Hα for pure hydrogen plasma in the temperature range of 104–105 K. The formulae presented here can be readily incorporated into time-dependent cooling models as well as collisional ionization equilibrium models.

Low-ionization structures in planetary nebulae – III. The statistical analysis of physico-chemical parameters and excitation mechanisms

ABSTRACT Nearly 30 yr after the first detailed studies of low-ionization structures (LISs) in planetary nebulae (PNe), we perform a statistical analysis of their physical, chemical, and excitation properties, by collecting published data in the literature. The analysis was made through the contrast between LISs and high-ionization structures – rims or shells – for a large sample of PNe, in order to highlight significant differences between these structures. Our motivation was to find robust results based on the largest sample of LISs gathered so far. (i) Indeed, LISs have lower electron densities (Ne[S ii]) than the rims/shells. (ii) The nitrogen electron temperatures (Te[N ii]) are similar between the two groups, while a bimodal distribution is observed for the Te based on [O iii] of the rims/shells, although the high- and low-ionization structures have Te[O iii] of similar median values. (iii) No significant variations are observed in total abundances of He, N, O, Ne, Ar, Cl, and S between the two groups. (iv) Through the analysis of several diagnostic diagrams, LISs are separated from rims/shells in terms of excitation. From two large grids of photoionization and shock models, we show that there is an important overlap between both mechanisms, particularly when low-ionization line ratios are concerned. We found a good tracer of high-velocity shocks, as well as an indicator of high- and low-velocity shocks that depends on temperature-sensitive line ratios. In conclusion, both excitation mechanisms could be present; however, shocks cannot be the main source of excitation for most of the LISs of PNe.

ATLASGAL: 3 mm class I methanol masers in high-mass star formation regions

Context. Class I methanol masers are known to be associated with shocked outflow regions around massive protostars, indicating a possible link between the maser properties and those of their host clumps. Aims. The main goals of this study are (1) to search for new class I methanol masers, (2) to statistically study the relationship between class I masers and shock tracers, (3) to compare the properties between class I masers and their host clumps, also as a function of their evolutionary stage, and (4) to constrain the physical conditions that excite multiple class I masers simultaneously. Methods. We analysed the 3 mm wavelength spectral line survey of 408 clumps identified by the APEX Telescope Large Area Survey of the Galaxy (ATLASGAL), which were observed with the IRAM 30-meter telescope, focusing on the class I methanol masers with frequencies near 84, 95, and 104.3 GHz. Results. We detect narrow maser-like features towards 54, 100, and 4 sources in the maser lines near 84, 95, and 104.3 GHz, respectively. Among them, 50 masers at 84 GHz, 29 masers at 95 GHz, and 4 rare masers at 104.3 GHz are new discoveries. The new detections increase the number of known 104.3 GHz masers from five to nine. The 95 GHz class I methanol maser is generally stronger than the 84 GHz maser counterpart. We find nine sources showing class I methanol masers, but no SiO emission, indicating that class I methanol masers might be the only signpost of protostellar outflow activity in extremely embedded objects at the earliest evolutionary stage. Class I methanol masers that are associated with sources that show SiO line wings are more numerous and stronger than those without such wings. The total integrated intensity of class I methanol masers is well correlated with the integrated intensity and velocity coverage of the SiO (2−1) emission. The properties of class I methanol masers are positively correlated with the bolometric luminosity, clump mass, and peak H2 column density of their associated clumps, but are uncorrelated with the luminosity-to-mass ratio, dust temperature, and mean H2 volume density. Conclusions. We suggest that the properties of class I masers are related to shocks traced by SiO. Based on our observations, we conclude that class I methanol masers at 84 and 95 GHz can trace a similar evolutionary stage to the H2O maser, and appear prior to 6.7 and 12.2 GHz methanol and OH masers. Despite their small number, the 104.3 GHz class I masers appear to trace a shorter and more evolved stage compared to the other class I masers.

Imaging Molecular Outflow in Massive Star-forming Regions with HNCO Lines

Protostellar outflows are considered a signpost of star formation. These outflows can cause shocks in the molecular gas and are typically traced by the line wings of certain molecules. HNCO (4–3) has been regarded as a shock tracer because of the high abundance in shocked regions. Here we present the first imaging results of HNCO (4–3) line wings toward nine sources in a sample of 23 massive star-forming regions using the Instituto de Radioastronomía Milimétrica 30 m Telescope. We adopt the velocity range of the full width of HC3N (10–9) and H13CO+ (1–0) emissions as the central emission values, beyond which the emission from HNCO (4–3) is considered to be from line wings. The spatial distributions of the red and/or blue lobes of HNCO (4–3) emission nicely associate with those lobes of HCO+ (1–0) in most of the sources. High-intensity ratios of HNCO (4–3) to HCO+ (1–0) are obtained in the line wings. The derived column density ratios of HNCO to HCO+ are consistent with those previously observed toward massive star-forming regions. These results provide direct evidence that HNCO could trace outflow in massive star-forming regions. This work also implies that the formation of some HNCO molecules is related to shock, either on the grain surface or within the shocked gas.

Shaken or Stirred: The Diffuse Interstellar Medium with Exceptionally High SiO Abundance

Interstellar shocks, a key element of stellar feedback processes, shape the structure of the interstellar medium (ISM) and are essential for the chemistry, thermodynamics, and kinematics of interstellar gas. Powerful, high-velocity shocks are driven by stellar winds, young supernova explosions, more evolved supernova remnants, cloud–cloud collisions, and protostellar outflows, whereas the existence and origin of much-lower-velocity shocks (≲10 km s−1) are not understood. Direct observational evidence for interstellar shocks in diffuse and translucent ISM environments has been especially lacking. We present the most sensitive survey to date of SiO—often considered an unambiguous tracer of interstellar shocks—in absorption, obtained with the Northern Extended Millimeter Array interferometer. We detect SiO in five of eight directions probing diffuse and translucent environments without ongoing star formation. Our results demonstrate that SiO formation in the diffuse ISM (i.e., in the absence of significant star formation and stellar feedback) is more widespread and effective than previously reported. The observed SiO line widths are all ≲4 km s−1, excluding high-velocity shocks as a formation mechanism. Yet, the SiO abundances we detect are mostly 1–2 orders of magnitude higher than those typically assumed in quiescent environments and are often accompanied by other molecular transitions whose column densities cannot be explained with UV-dominated chemical models. Our results challenge the traditional view of SiO production via stellar feedback sources and emphasize the need for observational constraints on the distribution of Si in the gas phase and grain mantles, which are crucial for understanding the physics of grain processing and the diffuse interstellar chemistry.

Shock shaping? Nebular spectroscopy of nova V906 Carinae

ABSTRACT V906 Carinae was one of the best observed novae of recent times. It was a prolific dust producer and harboured shocks in the early evolving ejecta outflow. Here, we take a close look at the consequences of these early interactions through study of high-resolution Ultraviolet and Visual Echelle spectrograph spectroscopy of the nebular stage and extrapolate backwards to investigate how the final structure may have formed. A study of ejecta geometry and shaping history of the structure of the shell is undertaken following a spectral line $\rm {\small SHAPE}$ model fit. A search for spectral tracers of shocks in the nova ejecta is undertaken and an analysis of the ionized environment. Temperature, density, and abundance analyses of the evolving nova shell are presented.

Modeling CO Line Profiles in Shocks of W28 and IC 443

Molecular emission arising from the interactions of supernova remnant (SNR) shock waves and molecular clouds provide a tool for studying the dispersion and compression that might kick-start star formation as well as understanding cosmic-ray production. Purely rotational CO emission created by magnetohydrodynamic shock in the SNR–molecular cloud interaction is an effective shock tracer, particularly for slow-moving, continuous shocks into cold inner clumps of the molecular cloud. In this work, we present a new theoretical radiative transfer framework for predicting the line profile of CO with the Paris–Durham 1D shock model. We generated line profile predictions for CO emission produced by slow, magnetized C shocks into gas of density ∼104 cm−3 with shock speeds of 35 and 50 km s−1. The numerical framework to reproduce the CO line profile utilizes the large velocity gradient (LVG) approximation and the omission of optically thick plane-parallel slabs. With this framework, we generated predictions for various CO spectroscopic observations up to J = 16 in SNRs W28 and IC 443, obtained with SOFIA, IRAM-30 m, APEX, and KPNO. We found that CO line profile prediction offers constraints on the shock velocity and pre-shock density independent of the absolute line brightness and requires fewer CO lines than diagnostics using a rotational excitation diagram.

Sulphur monoxide emission tracing an embedded planet in the HD 100546 protoplanetary disk

Molecular line observations are powerful tracers of the physical and chemical conditions across the different evolutionary stages of star, disk, and planet formation. The high angular resolution and unprecedented sensitivity of the Atacama Large Millimeter Array (ALMA) enables the current drive to detect small-scale gas structures in protoplanetary disks that can be attributed directly to forming planets. We report high angular resolution ALMA Band 7 observations of sulphur monoxide (SO) in the nearby planet-hosting disk around the Herbig star HD 100546. SO is rarely detected in evolved protoplanetary disks, but in other environments, it is most often used as a tracer of shocks. The SO emission from the HD 100546 disk primarily originates from gas within the ≈20 au millimeter-dust cavity and shows a clear azimuthal brightness asymmetry of a factor of 2. In addition, the difference in the line profile shape is significant when these new Cycle 7 data are compared to Cycle 0 data of the same SO transitions. We discuss the different physical and chemical mechanisms that might cause this asymmetry and time variability, including disk winds, disk warps, and a shock triggered by a (forming) planet. We propose that SO is enhanced in the cavity by the presence of a giant planet. The SO asymmetry complements evidence for hot circumplanetary material around giant planet HD 100546 c that is traced via CO ro-vibrational emission. This work sets the stage for further observational and modelling efforts to detect and understand the chemical imprint of a forming planet on its parent disk.

Tracing the chemical footprint of shocks in AGN-host and starburst galaxies with ALMA multi-line molecular studies.

Multi-line molecular observations are an ideal tool for a systematic study of the physico-chemical processes in the Interstellar Medium (ISM), given the wide range of critical densities associated with different molecules and their transitions, and the dependencies of chemical reactions on the energy budget of the system. Recently high spatial resolution of typical shock tracers - SiO, HNCO, and CH3OH - have been studied in the potentially shocked regions in two nearby galaxies: NGC 1068 (an AGN-host galaxy) (Huang et al., Astron. Astrophys., 2022, 666, A102; Huang et al., in prep.) and NGC 253 (a starburst galaxy) (K.-Y. Huang et al., arXiv, 2023, preprint, arXiv:2303.12685, DOI: 10.48550/arXiv.2303.12685). This paper is dedicated to the comparative study of these two distinctively different galaxies, with the aim of determining the differences in their energetics and understanding large-scale shocks in different types of galaxies.

Imaging of HH80-81 Jet in the Near-infrared Shock Tracers H2 and [Fe ii

The HH80-81 system is one of the most powerful jets driven by a massive protostar. We present new near-infrared (NIR) line imaging observations of the HH80-81 jet in the H2 (2.122 μm) and [Fe ii] (1.644 μm) lines. These lines trace not only the jet close to the exciting source but also the knots located farther away. We have detected nine groups of knot-like structures in the jet including HH80 and HH81 spaced 0.2–0.9 pc apart. The knots in the northern arm of the jet show only [Fe ii] emission closer to the exciting source, a combination of [Fe ii] and H2 at intermediate distances, and solely H2 emission farther outwards. Toward the southern arm, all the knots exhibit both H2 and [Fe ii] emission. The nature of the shocks is inferred by combining the NIR observations with radio and X-ray observations from the literature. In the northern arm, we infer the presence of strong dissociative shocks, in the knots located close to the exciting source. The knots in the southern arm that include HH80 and HH81 are explicable as a combination of strong and weak shocks. The mass-loss rates of the knots determined from [Fe ii] luminosities are in the range ∼3.0 × 10−7–5.2 × 10−5 M ⊙ yr−1, consistent with those from massive protostars. Toward the central region, close to the driving source of the jet, we have observed various arcs in H2 emission that resemble bow shocks, and strings of H2 knots that reveal traces of multiple outflows.