CO Molecular Line Research Articles

Effects of Radiative Transfer on the Observed Anisotropy in Magnetohydrodynamic Turbulent Molecular Simulations

We study the anisotropy of centroid and integrated intensity maps with synthetic observations. We perform postprocess radiative transfer including the optically thick regime that was not covered in Hernández-Padilla et al. We consider the emission in various CO molecular lines that range from optically thin to optically thick (12CO, 13CO, C18O, and C17O). The results for the velocity centroids are similar to those in the optically thin case. For instance, the anisotropy observed can be attributed to the Alfvén mode, which dominates over the slow and fast modes when the line of sight is at a high inclination with respect to the mean magnetic field. A few differences arise in the models with higher opacity, where some dependence on the sonic Mach number becomes evident. In contrast to the optically thin case, maps of integrated intensity become more anisotropic in optically thick lines. In this situation the scales probed are restricted, due to absorption, to smaller scales, which are known to be more anisotropic. We discuss how the sonic Mach number can affect the latter results, with highly supersonic cases exhibiting a lower degree of anisotropy.

Exploring fluorine chemical evolution in the Galactic disk: The open cluster perspective

Open clusters are ideal tools for tracing the abundances of different elements because their stars are expected to have the same age, distance, and metallicity. Therefore, they serve as powerful tracers for investigating the cosmic origins of elements. This paper expands on a recent study by us, in which the element fluorine was studied in seven open clusters; here we add six open clusters and eight field stars. The primary objective is to determine the abundance of fluorine (F) to gain insight into its production and evolution. The magnesium (Mg) abundances were derived to categorize the field stars into high and low alpha disk populations. Additionally, cerium (Ce) abundances were determined to better understand the interplay between F and s-process elements. Our goal is to analyze the trend of F abundances across the Galactic disk based on metallicity and age. By comparing observational data with Galactic chemical evolution models, the origin of F can be better understood. The spectra were obtained from the high-resolution near-infrared GIANO-B instrument at the Telescopio Nazionale Galileo (TNG). For the derivation of the stellar parameters and abundances, the Python version of Spectroscopy Made Easy ( PySME ) was used. OH, CN, and CO molecular lines and band heads along with Fe I lines were used to determine the stellar parameters in the H-band region. Two HF lines in the K band ($ 2.28, and 2.33 mu m), three K-band Mg I lines ($ 2.10, 2.11, and 2.15 mu m), and two Ce II lines in the H band ($ 1.66, and 1.71 mu m) were used to derive the abundances of F, Mg, and Ce, respectively. F, Mg, and Ce abundances were derived for 14 stars from 6 OCs, as well as for 8 field stars. The F and Ce abundances were investigated as a function of metallicity, age, and galactocentric distance. We also compared our findings with different Galactic chemical evolution models. Our results indicate that asymptotic giant branch stars and massive stars, including a subset of fast rotators (whose rotation speed likely increases as metallicity decreases), are necessary to explain the cosmic origin of F. This finding is consistent with and, with the large sample size, reinforces the conclusion of our previous study.

Large-field CO (J = 1−0) observations toward SNR G150.3+4.5

Aims. We aim to investigate the molecular environment of the supernova remnant (SNR) G150.3+4.5, and explore its association with ambient molecular clouds (MCs). Methods. We present large-field CO (J = 1−0) molecular line observations toward SNR G150.3+4.5, using the 13.7 m millimeter telescope of the Purple Mountain Observatory. The observations have an angular resolution of ~55″. We analyzed the spatial distribution of MCs in relation to the SNR shell detected in previous Urumqi λ 6 cm radio observations and examined the CO spectra for kinematics information. Results. We find that MCs within the velocity range of [−14, −2] km s−1 are spatially distributed along the radio shell of the SNR. Line broadening and asymmetries are observed in the CO spectra of the clouds. Moreover, we find that the molecular clouds around the shell have systematic velocity gradients in the position–velocity (PV) diagram. Both the morphology alignment and gas kinematics suggest that the SNR is associated with the ambient MCs at ~740 pc. Based on the CO gas distance, the dimension and the age of the SNR are estimated to be 40 pc × 33 pc and 3.8 × 104 yr, respectively. The very high energy emission of 1LHAASO J0428+5531 toward the SNR may originate from the interaction between the SNR and the surrounding MCs.

Disk Wind Feedback from High-mass Protostars. III. Synthetic CO Line Emission

Abstract To test theoretical models of massive star formation it is important to compare their predictions with observed systems. To this end, we conduct CO molecular line radiative transfer post-processing of 3D magnetohydrodynamic simulations of various stages in the evolutionary sequence of a massive protostellar core, including its infall envelope and disk wind outflow. Synthetic position–position–velocity cubes of various transitions of 12CO, 13CO, and C18O emission are generated. We also carry out simulated Atacama Large Millimeter/submillimeter Array (ALMA) observations of this emission. We compare the mass, momentum, and kinetic energy estimates obtained from molecular lines to the true values, finding that the mass and momentum estimates can have uncertainties of up to a factor of 4. However, the kinetic energy estimated from molecular lines is more significantly underestimated. Additionally, we compare the mass outflow rate and momentum outflow rate obtained from the synthetic spectra with the true values. Finally, we compare the synthetic spectra with real examples of ALMA-observed protostars and determine the best-fitting protostellar masses and outflow inclination angles. We then calculate the mass outflow rate and momentum outflow rate for these sources, finding that both rates agree with theoretical protostellar evolutionary tracks.

Stellar Population Astrophysics (SPA) with TNG

Context. The age, evolution, and chemical properties of the Galactic disk can be effectively ascertained using open clusters. Within the large program Stellar Populations Astrophysics at the Telescopio Nazionale Galileo, we specifically focused on stars in open clusters, to investigate various astrophysical topics, from the chemical content of very young systems to the abundance patterns of lesser studied intermediate-age and old open clusters. Aims. We investigate the astrophysically interesting element fluorine (F), which has an uncertain and intriguing cosmic origin. We also determine the abundance of cerium (Ce), as F abundance is expected to correlate with the s-process elements. We intend to determine the trend of F abundance across the Galactic disk as a function of metallicity and age. This will offer insights into Galactic chemical evolution models, potentially enhancing our comprehension of this element’s cosmic origin. Methods. High-resolution near-infrared spectra were obtained using the GIANO-B spectrograph. The Python version of Spectroscopy Made Easy (PySME), was used to derive atmospheric parameters and abundances. The stellar parameters were determined using OH, CN, and CO molecular lines along with Fe I lines. The F and Ce abundances were inferred using two K-band HF lines (λλ 2.28, 2.33 µm) and two atomic H-band lines (λλ 1.66, and 1.71 µm), respectively. Results. Of all the clusters in our sample, only King 11 had not been previously studied through medium- to high-resolution spectroscopy, and our stellar parameter and metallicity findings align well with those documented in the literature. We have successfully inferred F and Ce abundances in all seven open clusters and probed the radial and age distributions of abundance ratios. This paper presents the first F Galactic radial abundance gradient. Our results are also compared with literature estimates and with Galactic chemical evolution models that have been generated using different F production channels. Conclusions. Our results indicate a constant, solar pattern in the [F/Fe] ratios across clusters of different ages, supporting the latest findings that fluorine levels do not exhibit any secondary behavior for stars with solar or above-solar metallicity. However, an exception to this trend is seen in NGC 6791, a metal-rich, ancient cluster whose chemical composition is distinct due to its enhanced fluorine abundance. This anomaly strengthens the hypothesis that NGC 6791 originated in the inner regions of the Galaxy before migrating to its present position. By comparing our sample stars with the predictions of Galactic chemical evolution models, we came to the conclusion that both asymptotic giant branch stars and massive stars, including a fraction of fast rotators that increase with decreasing metallicity, are needed to explain the cosmic origin of F.

Kinematic signatures of planet–disk interactions in vertical shear instability-turbulent protoplanetary disks

Context. Planets are thought to form inside weakly ionized regions of protoplanetary disks, where turbulence creates ideal conditions for solid growth. However, the nature of this turbulence is still uncertain. In fast cooling parts of this zone the vertical shear instability (VSI) can operate, inducing a low level of gas turbulence and large-scale gas motions. Resolving the kinematic signatures of active VSI could reveal the origin of turbulence in planet-forming disk regions. However, an exploration of kinematic signatures of the interplay between VSI and forming planets is needed for a correct interpretation of radio interferometric observations. A robust detection of VSI would lead the way to a deeper understanding of the impact of gas turbulence on planet formation. Aims. The objective of this study is to explore the effect of VSI on the disk substructures triggered by an embedded fairly massive planet. We focus on the impact of this interplay on CO kinematic observations with the ALMA interferometer. Methods. We conducted global 3D hydrodynamical simulations of VSI-unstable disks with and without embedded massive planets, exploring Saturn- and Jupiter-mass cases. We studied the effect of planets on the VSI gas dynamics, and made a comparison with viscous disks. Post-processing the simulations with a radiative transfer code, we examined the kinematic signatures expected in CO molecular line emission, varying disk inclination. Further, we simulated deep ALMA high-resolution observations of our synthetic images, to test the observability of VSI and planetary signatures. Results. The embedded planet produces a damping of the VSI along a radial region, most effective at the disk midplane. For the Saturn case, the VSI modes are distorted by the planet’s spirals producing mixed kinematic signatures. For the Jupiter case, the planet’s influence dominates the overall disk gas kinematics. Conclusions. The presence of massive planets embedded in the disk can weaken the VSI large-scale gas flows, limiting its observability in CO kinematic observations with ALMA.

Polarisation of molecular lines in the circumstellar envelope of the post-asymptotic giant branch star OH 17.7–2.0

Context. The role of magnetic field in shaping planetary nebulae (PNe), either directly or indirectly after being enhanced by binary interaction, has long been a topic of debate. Large-scale magnetic fields around pre-PNe have been inferred from polarisation observations of masers. However, because masers probe very specific regions, it is still unclear if the maser results are representative of the intrinsic magnetic field in the circumstellar envelope (CSE). Aims. Molecular line polarisation of non-maser lines can provide important information about the magnetic field. A comparison between the magnetic field morphology determined from maser observations and that observed in the more diffuse CO gas can reveal if the two tracers probe the same magnetic field. Methods. We compared observations taken with the Atacama Large Millimeter/submillimeter Array (ALMA) of molecular line polarisation around the post-asymptotic giant branch (post-AGB) or pre-PN star OH 17.7−2.0 with previous observations of polarisation in the 1612 MHz OH maser region. Earlier mid-infrared observations indicate that OH 17.7−2.0 is a young bipolar pre-PN, with both a torus and bipolar outflow cavities embedded in a remnant AGB envelope. Results. We detect CO J = 2 − 1 molecular line polarisation at a level of ∼4% that displays an ordered linear polarisation structure. We find that, correcting for Faraday rotation of the OH maser linear polarisation vectors, the OH and CO linearly polarised emission trace the same large-scale magnetic field. A structure function analysis of the CO linear polarisation reveals a plane-of-the-sky magnetic field strength of B⊥ ∼ 1 mG in the CO region, consistent with previous OH Zeeman observations. Conclusions. The consistency of the ALMA CO molecular line polarisation observation with maser observations indicate that both can be used to determine the magnetic field strength and morphology in CSEs. The new observations indicate that the magnetic field has a strong toroidal field component projected on the torus structure and a poloidal field component along the outflow cavity. The existence of a strong, ordered, magnetic-field around OH 17.7−2.0 indicates that the magnetic field is likely involved in the formation of this bipolar pre-PN.

ALMA Band 6 high-resolution observations of the transitional disk around SY Chamaeleontis

Abstract In this study, we reported the results of high-resolution (${0{^{\prime \prime}_{.}}14}$) Atacama Large Millimeter/submillimeter Array (ALMA) observations of the 225 GHz dust continuum and CO molecular emission lines from the transitional disk around SY Cha. Our high-resolution observations clearly revealed the inner cavity and the central point source for the first time. The radial profile of the ring can be approximated by a bright narrow ring superimposed on a fainter wide ring. Furthermore, we found that there is a weak azimuthal asymmetry in dust continuum emission. For gas emissions, we detected 12CO(2–1), 13CO(2–1), and C18O(2–1), from which we estimated the total gas mass of the disk to be 2.2 × 10−4 M ⊙ , assuming a CO/H2 ratio of 10−4. The observations showed that the gas is present inside the dust cavity. The analysis of the velocity structure of the 12CO(2–1) emission line revealed that the velocity is distorted at the location of the dust inner disk, which may be owing to a warping of the disk or radial gas flow within the cavity of the dust disk. High-resolution observations of SY Cha showed that this system is composed of a ring and a distorted inner disk, which may be common, as indicated by the survey of transitional disk systems at a resolution of ${\sim}{0{^{\prime \prime}_{.}}1}$.

Structure and Kinematics of Sh2-138—A Distant Hub-filament System in the Outer Galactic Plane

We present a molecular line study of the Sh2-138 (IRAS 22308+5812) hub-filament system with the aim of investigating its structure and kinematics. Archival CO molecular line data from the Canadian Galactic Plane Survey (CO(J = 1–0)) for the wider region (∼50′ × 50′) and the James Clerk Maxwell Telescope (CO(3–2), 13CO(3–2), and C18O(3–2)) for the central portion (∼5′ × 5′) have been utilized. Analysis of the CO(1–0) spectra for the extended region in conjunction with the identification of the hub and filament using a column density map and the getsf tool, respectively, reveals a complex structure with the spectral extraction for the central position displaying multiple velocity components. Based on the Herschel 70 μm warm dust emission, one of the filaments in the extended region was inferred to be associated with active star formation, and is host to a Bolocam 1.1 mm clump of ∼1606 M ☉. An integrated intensity map of 13CO(3–2) emission, constructed from clumps detected at above 5σ in position–position–velocity space, reveals three filamentary structures (labeled the western filament (W-f), southwestern filament (SW-f), and southeast filament (SE-f)) in the central portion. Velocity gradients observed in 13CO(3–2) position–velocity slices point to longitudinal gas flow along the filaments into the central region. Filaments W-f, SW-f, and SE-f were calculated to have observed line masses of ∼32, 33.5, and 50 M ☉ pc−1, respectively. The cloud was found to be dominated by supersonic and nonthermal motions, with high Mach numbers (≳3) and a low thermal-to-nonthermal pressure ratio (∼0.01–0.1).

The Cassiopeia Filament: A Blown Spur of the Local Arm

We present wide-field and high-sensitivity CO(1–0) molecular line observations toward the Cassiopeia region, using the 13.7 m millimeter telescope of the Purple Mountain Observatory. The CO observations reveal a large-scale highly filamentary molecular cloud within the Galactic region of 132.°0 ≥ l ≥ 122.°0 and −1.°0 ≤ b ≤ 3.°0 and the velocity range from approximately +1 to +4 km s−1. The measured length of the large-scale filament, referred to as the Cassiopeia Filament, is ∼390 pc. The observed properties of the Cassiopeia Filament, such as length, column density, and velocity gradient, are consistent with those synthetic large-scale filaments in the inter-arm regions. Based on its observed properties and location on the Galactic plane, we suggest that the Cassiopeia Filament is a spur of the Local arm, which is formed due to the galactic shear. The western end of the Cassiopeia Filament shows a giant arc-like molecular gas shell, which extends in the velocity range from roughly −1 to +7 km s−1. Finger-like structures, with systematic velocity gradients, are detected in the shell. The CO kinematics suggest that the large shell is expanding at a velocity of ∼6.5 km s−1. Both the shell and finger-like structures outline a giant bubble with a radius of ∼16 pc, which is likely produced by the stellar wind from the progenitor star of a supernova remnant. The observed spectral line widths suggest that the whole Cassiopeia Filament was quiescent initially until its west part was blown by the stellar wind and became supersonically turbulent.

Contributions of Rotation, Expansion and Line Broadening to the Morphology and Kinematics of the Inner CSE of Oxygen-rich AGB Star R Hya

We use archival ALMA observations of the CO(2–1) and SiO(5–4) molecular line emissions of AGB star R Hya to illustrate the relative contributions of rotation, expansion and line broadening to the morphology and kinematics of the circumstellar envelope (CSE) within some ∼70 au (∼0.″5) from the centre of the star. We give evidence for rotation and important line broadening to dominate the inner region, within ∼14 au (∼100 mas) from the centre of the star. The former is about an axis that projects a few degrees west of north and has a projected rotation velocity of a few km s−1. The latter occurs within some 7–14 au (50–100 mas) from the centre of the star, with the line width reaching two to three times its value outside this region. We suggest that it is caused by shocks induced by stellar pulsations and convective cell granulation. We show the importance of properly accounting for the observed line broadening when discussing rotation and evaluating the radial dependence of the rotation velocity.

Mira Ceti, Atypical Archetype

Abstract With the aim of unraveling the complexity of the morphokinematics of the circumstellar envelope (CSE) of Mira Ceti, we review, extend, and in some cases revisit Atacama Large Millimeter/submillimeter Array observations of the emission of the SiO(5–4) and CO(3–2) molecular lines. In addition, we present a detailed analysis of the optically thin 13CO(3–2) emission, which provides several important new results. In agreement with observations at infrared and visible wavelengths, we give evidence for the confinement and probably rotation of a dense gas volume within ∼50 au from the star and for a large SiO line width within ∼15 au. We show that the mass-loss process is episodic and takes the form of clumps having a very low SiO/CO abundance ratio compared with similar oxygen-rich long-period variables, probably a result of depletion on dust grains and photodissociation. We evaluate the mass-loss rate associated with the main clumps and compare it with values obtained from single-dish observations. We argue that the SiO emission observed in the southwestern quadrant is not related to the mechanism of generation of the nascent wind but to a mass ejection that occurred 11 years before the observations. We remark that Mira Ceti is not a good archetype in terms of its wind: models aiming at describing the very complex gas-dust chemistry in action in the CSE of oxygen-rich AGB stars may find it difficult to account for its peculiar features and small variations in the parameters deciding when and where mass loss can proceed significantly.

Large-scale magnetic field in the Monoceros OB 1 east molecular cloud

Context. The role of large-scale magnetic fields in the evolution of star-forming regions remains elusive. Its investigation requires the observational characterization of well-constrained molecular clouds. The Monoceros OB 1 molecular cloud is a large complex containing several structures that have been shown to be engaged in an active interaction and to have a rich star formation history. However, the magnetic fields in this region have only been studied on small scales. Aims. We study the large-scale magnetic field structure and its interplay with the gas dynamics in the Monoceros OB 1 east molecular cloud. Methods. We combined observations of dust polarized emission from the Planck telescope and CO molecular line emission observations from the Taeduk Radio Astronomy Observatory 14-metre telescope. We calculated the strength of the plane-of-sky magnetic field using a modified Chandrasekhar-Fermi method and estimated the mass-over-flux ratios in different regions of the cloud. We used the comparison of the velocity and intensity gradients of the molecular line observations with the polarimetric observations to trace dynamically active regions. Results. The molecular complex shows an ordered large-scale plane-of-sky magnetic field structure. In the northern part, it is mostly orientated along the filamentary structures, while the southern part shows at least two regions with distinct magnetic field orientations. Our analysis reveals a shock region in the northern part right between two filamentary clouds that, in previous studies, were suggested to be involved in a collision. The magnetic properties of the north-main and north-eastern filaments suggest that these filaments once formed a single one, and that the magnetic field evolved together with the material and did not undergo major changes during the evolution of the cloud. In the southern part, we find that either the magnetic field guides the accretion of interstellar matter towards the cloud or it is dragged by the matter falling towards the main cloud. Conclusions. The large-scale magnetic field in the Monoceros OB 1 east molecular cloud is tightly connected to the global structure of the complex. In the northern part, it seems to serve a dynamically important role by possibly providing support against gravity in the direction perpendicular to the field and to the filament. In the southern part, it is probably the most influential factor governing the morphological structure by guiding possible gas inflow. A study of the whole Monoceros OB 1 molecular complex at large scales is necessary to form a global picture of the formation and evolution of the Monoceros OB 1 east cloud and the role of the magnetic field in this process.

Shocked Molecular Hydrogen and Broad CO Lines from the Interacting Supernova Remnant HB 3

Abstract We present the detections of shocked molecular hydrogen (H2) gas in near- and mid-infrared and broad CO in millimeter from the mixed-morphology supernova remnant (SNR) HB 3 (G132.7+1.3) using the Palomar Wide-field InfraRed Camera, the Spitzer GLIMPSE360 and Wide-field Infrared Survey Explorer (WISE) surveys, and the Heinrich Hertz Submillimeter Telescope. Our near-infrared narrow-band filter H2 2.12 μm images of HB 3 show that both Spitzer Infrared Array Camera and WISE 4.6 μm emission originates from shocked H2 gas. The morphology of H2 exhibits thin filamentary structures and a large scale of interaction sites between the HB 3 and nearby molecular clouds. Half of HB 3, the southern and eastern shell of the SNR, emits H2 in a shape of a butterfly or W, indicating the interaction sites between the SNR and dense molecular clouds. Interestingly, the H2 emitting region in the southeast is also co-spatial to the interacting area between HB 3 and the H ii regions of the W3 complex, where we identified star-forming activity. We further explore the interaction between HB 3 and dense molecular clouds with detections of broad CO(3-2) and CO(2-1) molecular lines from the southern and southeastern shell along the H2 emitting region. The widths of the broad lines are 8–20 km s−1; the detection of such broad lines is unambiguous, dynamic evidence of the interactions between the SNR and clouds. The CO broad lines are from two branches of the bright, southern H2 shell. We apply the Paris–Durham shock model to the CO line profiles, which infer the shock velocities of 20–40 km s−1, relatively low densities of 103–4 cm−3, and strong (>200 μG) magnetic fields.

On the Beam Filling Factors of Molecular Clouds

Abstract Imaging surveys of CO and other molecular transition lines are fundamental to measuring the large-scale distribution of molecular gas in the Milky Way. Due to finite angular resolution and sensitivity, however, observational effects are inevitable in the surveys, but few studies are available on the extent of uncertainties involved. The purpose of this work is to investigate the dependence of observations on angular resolution (beam sizes), sensitivity (noise levels), distances, and molecular tracers. To this end, we use high-quality CO images of a large-scale region (258 < l < 497 and ∣b∣ < 5°) mapped by the Milky Way Imaging Scroll Painting (MWISP) survey as a benchmark to simulate observations with larger beam sizes and higher noise levels, deriving corresponding beam filling and sensitivity clip factors. The sensitivity clip factor is defined to be the completeness of observed flux. Taking the entire image as a whole object, we found that 12CO has the largest beam filling and sensitivity clip factors and C18O has the lowest. For molecular cloud samples extracted from images, the beam filling factor can be described by a characteristic size, l 1/4 = 0.762 (in beam size), at which the beam filling factor is approximately 1/4. The sensitivity clip factor shows a similar relationship but is more correlated with the mean voxel signal-to-noise ratio of molecular clouds. This result may serve as a practical reference on beam filling and sensitivity clip factors in further analyses of the MWISP data and other observations.

ATOMIUM: A high-resolution view on the highly asymmetric wind of the AGB starπ1Gruis

The nebular circumstellar environments of cool evolved stars are known to harbour a rich morphological complexity of gaseous structures on different length scales. A large part of these density structures are thought to be brought about by the interaction of the stellar wind with a close companion. The S-type asymptotic giant branch (AGB) starπ1Gruis, which has a known companion at ∼440 au and is thought to harbour a second, closer-by (< 10 au) companion, was observed with the Atacama Large Millimeter/submillimeter Array as part of the ATOMIUMLarge programme. In this work, the brightest CO, SiO, and HCN molecular line transitions are analysed. The continuum map shows two maxima, separated by 0.04″ (6 au). The CO data unambiguously reveal thatπ1Gru’s circumstellar environment harbours an inclined, radially outflowing, equatorial density enhancement. It contains a spiral structure at an angle of ∼38 ± 3° with the line-of-sight. The HCN emission in the inner wind reveals a clockwise spiral, with a dynamical crossing time of the spiral arms consistent with a companion at a distance of 0.04″ from the AGB star, which is in agreement with the position of the secondary continuum peak. The inner wind dynamics imply a large acceleration region, consistent with a beta-law power of ∼6. The CO emission suggests that the spiral is approximately Archimedean within 5″, beyond which this trend breaks down as the succession of the spiral arms becomes less periodic. The SiO emission at scales smaller than 0.5″ exhibits signatures of gas in rotation, which is found to fit the expected behaviour of gas in the wind-companion interaction zone. An investigation of SiO maser emission reveals what could be a stream of gas accelerating from the surface of the AGB star to the companion. Using these dynamics, we have tentatively derived an upper limit on the companion mass to be ∼1.1M⊙.

G133.50+9.01: a likely cloud–cloud collision complex triggering the formation of filaments, cores, and a stellar cluster

ABSTRACT We present compelling observational evidence of G133.50+9.01 being a bona fide cloud–cloud collision candidate with signatures of induced filament, core, and cluster formation. The CO molecular line observations reveal that the G133.50+9.01 complex is made of two colliding molecular clouds with systemic velocities, $\rm -16.9$ and $\rm -14.1\, km\, s^{-1}$. The intersection of the clouds is characterized by broad bridging features characteristic of collision. The morphology of the shocked layer at the interaction front resembles an arc-like structure with enhanced excitation temperature and H2 column density. A complex network of filaments is detected in the Submillimeter Common-User Bolometer Array 2 850 $\rm \mu m$ image with 14 embedded dense cores, all well correlated spatially with the shocked layer. A stellar cluster revealed through an overdensity of identified Classes I and II young stellar objects is found located along the arc in the intersection region corroborating with a likely collision induced origin.

Are the spiral arms in the MWC 758 protoplanetary disc driven by a companion inside the cavity?

ABSTRACT Spiral arms in protoplanetary discs are thought to be linked to the presence of companions. We test the hypothesis that the double spiral arm morphology observed in the transition disc MWC 758 can be generated by an ≈10MJup companion on an eccentric orbit internal to the spiral arms. Previous studies on MWC 758 have assumed an external companion. We compare simulated observations from three-dimensional hydrodynamics simulations of disc–companion interaction to scattered light, infrared and CO molecular line observations, taking into account observational biases. The inner companion hypothesis is found to explain the double spiral arms, as well as several additional features seen in MWC 758 – the arc in the north-west, substructures inside the spiral arms, the cavity in CO isotopologues, and the twist in the kinematics. Testable predictions include detection of fainter spiral structure, detection of a point source south-southeast of the primary, and proper motion of the spiral arms.

Chemical abundances of open clusters from high-resolution infrared spectra – II. NGC 752

ABSTRACT We present a detailed near-infrared chemical abundance analysis of 10 red giant members of the Galactic open cluster NGC 752. High-resolution (R ≃ 45000) near-infrared spectral data were gathered with the Immersion Grating Infrared Spectrograph, providing simultaneous coverage of the complete H and K bands. We derived the abundances of H-burning (C, N, O), α (Mg, Si, S, Ca), light odd-Z (Na, Al, P, K), Fe-group (Sc, Ti, Cr, Fe, Co, Ni), and neutron-capture (Ce, Nd, Yb) elements. We report the abundances of S, P, K, Ce, and Yb in NGC 752 for the first time. Our analysis yields solar-metallicity and solar abundance ratios for almost all of the elements heavier than the CNO group in NGC 752. O and N abundances were measured from a number of OH and CN features in the H band, and C abundances were determined mainly from CO molecular lines in the K band. High-excitation $\rm{C\,\small {I}}$ lines present in both near-infrared and optical spectra were also included in the C abundance determinations. Carbon isotopic ratios were derived from the R-branch band heads of first overtone (2−0) and (3−1) 12CO and (2−0) 13CO lines near 23 440 Å and (3−1) 13CO lines at about 23 730 Å. The CNO abundances and 12C/13C ratios are all consistent with our giants having completed ‘first dredge-up’ envelope mixing of CN-cyle products. We independently assessed NGC 752 stellar membership from Gaia astrometry, leading to a new colour–magnitude diagram for this cluster. Applications of Victoria isochrones and MESA models to these data yield an updated NGC 752 cluster age (1.52 Gyr) and evolutionary stage indications for the programme stars. The photometric evidence and spectroscopic light element abundances all suggest that the most, perhaps all of the programme stars are members of the helium-burning red clump in this cluster.

Chemical abundances of open clusters from high-resolution infrared spectra – I. NGC 6940

We present near-infrared spectroscopic analysis of 12 red giant members of the Galactic open cluster NGC 6940. High-resolution (R$\simeq$45000) and high signal-to-noise ratio (S/N > 100) near-infrared H and K band spectra were gathered with the Immersion Grating Infrared Spectrograph (IGRINS) on the 2.7m Smith Telescope at McDonald Observatory. We obtained abundances of H-burning (C, N, O), ${\alpha}$ (Mg, Si, S, Ca), light odd-Z (Na, Al, P, K), Fe-group (Sc, Ti, Cr, Fe, Co, Ni) and neutron-capture (Ce, Nd, Yb) elements. We report the abundances of S, P, K, Ce, and Yb in NGC 6940 for the first time. Many OH and CN features in the H band were used to obtain O and N abundances. C abundances were measured from four different features: CO molecular lines in the K band, high excitation C I lines present in both near-infrared and optical, CH and $C_2$ bands in the optical region. We have also determined $^{12}C/^{13}C$ ratios from the R-branch band heads of first overtone (2-0) and (3-1) $^{12}CO$ (2-0) $^{13}CO$ lines near 23440 $\overset{\lower.5em\circ}{\mathrm{A}}$ and (3-1) $^{13}CO$ lines at about 23730 $\overset{\lower.5em\circ}{\mathrm{A}}$. We have also investigated the HF feature at 23358.3 $\overset{\lower.5em\circ}{\mathrm{A}}$, finding solar fluorine abundances without ruling out a slight enhancement. For some elements (such as the ${\alpha}$ group), IGRINS data yield more internally self-consistent abundances. We also revisited the CMD of NGC 6940 by determining the most probable cluster members using Gaia DR2. Finally, we applied Victoria isochrones and MESA models in order to refine our estimates of the evolutionary stages of our targets.