Co-propagation of maser emission at 1720 and 4765 MHz

MERLIN observations are presented of OH 4765-MHz and OH 1720-MHz masers in the massive star-forming region W3(OH). Two of the three intense spots of maser emission at 4765 MHz are spatially coincident with two similar spots at 1720 MHz in both left-hand circular (LHC) and right-hand circular (RHC) polarizations, to an accuracy of 15 mas. The spots also overlap in velocity when allowance is made for Zeeman splitting of the 1720-MHz line. We conclude that we have found two examples of masers in different rotational levels of OH which are co-propagating through the same column of gas and experiencing competitive gain effects. The third 4765-MHz maser spot was found to have no overlapping counterpart amongst the 1720-MHz masers

Asymmetric mid-plane gas in ALMA images of HD 100546

In this paper we present new ALMA observations towards the proto-planet hosting transitional disc of Herbig Ae/Be star HD 100546. This includes resolved 1.3 mm continuum, $^{13}$CO and the first detection of C$^{18}$O in this disc, which displays azimuthal asymmetry in regions spatially coincident with structures previously identified in HST images related to spiral arms. The lower limit on the mass of the dust disc is calculated to be 9.6x10$^{-4}$M$_\odot$. A firm lower-limit on the total gas mass calculated from optically thin, mid-plane tracing C$^{18}$O (2-1) emission is 0.018M$_\odot$ assuming ISM abundances. These mass estimates provide an estimate of gas-to-dust ratio in the disc of 19, the ratio will increase if C$^{18}$O is relatively under-abundant in the disc compared to CO and H2. Through deprojection and azimuthal averaging of the image plane we detect 1.3 mm continuum emission out to 290+/-10 au,$^{13}$CO to 390+/-10 au and C$^{18}$O to 300+/-10au. We measure a radially increasing millimetre spectral index between wavelengths of 867$\mu$m and 1.3 mm, which shows that grain sizes increase towards the star, with solid particles growing to cm scales in the inner disc

Planet formation in intermediate-separation binary systems

ABSTRACT We report the first characterization of the individual discs in the intermediate-separation binary systems KK Oph and HD 144668 at millimetre wavelengths. In both systems, the circumprimary and the circumsecondary discs are detected in the millimetre continuum emission, but not in 13CO nor C18O lines. Even though the disc structure is only marginally resolved, we find indications of large-scale asymmetries in the outer regions of the primary discs, most likely due to perturbation by the companion. The derived dust masses are firmly above debris disc level for all stars. The primaries have about three times more dust in their discs than the secondaries. In the case of HD 144668, the opacity spectral index of the primary and secondary differ by a large margin of 0.69, which may be a consequence of the secondary disc being more compact. Upper limits on the gas masses imply less than 0.1 Mjup in any of these discs, meaning that giant planets can no longer form in them. Considering that there have been no massive gas discs identified to date in intermediate-separation binaries (i.e. binaries at a few hundred au separation), this opens space for speculation whether their binarity causes the removal of gas, with tidal interaction truncating the discs and hence shortening the accretion time-scale. More systematic studies in this respect are sorely needed.</jats:p

The Origin of Titan’s External Oxygen:Further Constraints from ALMA Upper Limits on CS and CH₂NH

Titan's atmospheric inventory of oxygen compounds (H2O, CO2, CO) are thought to result from photochemistry acting on externally supplied oxygen species (O+, OH, H2O). These species potentially originate from two main sources: (1) cryogenic plumes from the active moon Enceladus and (2) micrometeoroid ablation. Enceladus is already suspected to be the major O+ source, which is required for CO creation. However, photochemical models also require H2O and OH influx to reproduce observed quantities of CO2 and H2O. Here, we exploit sulphur as a tracer to investigate the oxygen source because it has very different relative abundances in micrometeorites (S/O ~ 10−2) and Enceladus' plumes (S/O ~ 10−5). Photochemical models predict most sulphur is converted to CS in the upper atmosphere, so we use Atacama Large Millimeter/submillimeter Array (ALMA) observations at ~340 GHz to search for CS emission. We determined stringent CS 3σ stratospheric upper limits of 0.0074 ppb (uniform above 100 km) and 0.0256 ppb (uniform above 200 km). These upper limits are not quite stringent enough to distinguish between Enceladus and micrometeorite sources at the 3σ level and a contribution from micrometeorites cannot be ruled out, especially if external flux is toward the lower end of current estimates. Only the high-flux micrometeorite source model of Hickson et al. can be rejected at 3σ. We determined a 3σ stratospheric upper limit for CH2NH of 0.35 ppb, which suggests cosmic rays may have a smaller influence in the lower stratosphere than predicted by some photochemical models. Disk-averaged C3H4 and C2H5CN profiles were determined and are consistent with previous ALMA and Cassini/CIRS measurements

Resolving the ancestry of Austronesian-speaking populations

There are two very different interpretations of the prehistory of Island Southeast Asia (ISEA), with genetic evidence invoked in support of both. The “out-of-Taiwan” model proposes a major Late Holocene expansion of Neolithic Austronesian speakers from Taiwan. An alternative, proposing that Late Glacial/postglacial sea-level rises triggered largely autochthonous dispersals, accounts for some otherwise enigmatic genetic patterns, but fails to explain the Austronesian language dispersal. Combining mitochondrial DNA (mtDNA), Y-chromosome and genome-wide data, we performed the most comprehensive analysis of the region to date, obtaining highly consistent results across all three systems and allowing us to reconcile the models. We infer a primarily common ancestry for Taiwan/ISEA populations established before the Neolithic, but also detected clear signals of two minor Late Holocene migrations, probably representing Neolithic input from both Mainland Southeast Asia and South China, via Taiwan. This latter may therefore have mediated the Austronesian language dispersal, implying small-scale migration and language shift rather than large-scale expansion

ATOMIUM: ALMA tracing the origins of molecules in dust forming oxygen rich M-type stars: Motivation, sample, calibration, and initial results

This overview paper presents atomium, a Large Programme in Cycle 6 with the Atacama Large Millimeter/submillimeter Array (ALMA). The goal of atomium is to understand the dynamics and the gas phase and dust formation chemistry in the winds of evolved asymptotic giant branch (AGB) and red supergiant (RSG) stars. A more general aim is to identify chemical processes applicable to other astrophysical environments. Seventeen oxygen-rich AGB and RSG stars spanning a range in (circum)stellar parameters and evolutionary phases were observed in a homogeneous observing strategy allowing for an unambiguous comparison. Data were obtained between 213.83 and 269.71 GHz at high (0.025-0.050), medium (0.13-0.24), and low (~1) angular resolution. The sensitivity per ~1.3 km s-1 channel was 1.5-5 mJy beam-1, and the line-free channels were used to image the millimetre wave continuum. Our primary molecules for studying the gas dynamics and dust formation are CO, SiO, AlO, AlOH, TiO, TiO2, and HCN; secondary molecules include SO, SO2, SiS, CS, H2O, and NaCl. The scientific motivation, survey design, sample properties, data reduction, and an overview of the data products are described. In addition, we highlight one scientific result - the wind kinematics of the atomium sources. Our analysis suggests that the atomium sources often have a slow wind acceleration, and a fraction of the gas reaches a velocity which can be up to a factor of two times larger than previously reported terminal velocities assuming isotropic expansion. Moreover, the wind kinematic profiles establish that the radial velocity described by the momentum equation for a spherical wind structure cannot capture the complexity of the velocity field. In fifteen sources, some molecular transitions other than 12CO v = 0 J = 2 - 1 reach a higher outflow velocity, with a spatial emission zone that is often greater than 30 stellar radii, but much less than the extent of CO. We propose that a binary interaction with a (sub)stellar companion may (partly) explain the non-monotonic behaviour of the projected velocity field. The atomium data hence provide a crucial benchmark for the wind dynamics of evolved stars in single and binary star models

(Sub)stellar companions shape the winds of evolved stars

Binary interactions dominate the evolution of massive stars, but their role is less clear for low- and intermediate-mass stars. The evolution of a spherical wind from an asymptotic giant branch (AGB) star into a nonspherical planetary nebula (PN) could be due to binary interactions. We observed a sample of AGB stars with the Atacama Large Millimeter/submillimeter Array (ALMA) and found that their winds exhibit distinct nonspherical geometries with morphological similarities to planetary nebulae (PNe). We infer that the same physics shapes both AGB winds and PNe; additionally, the morphology and AGB mass-loss rate are correlated. These characteristics can be explained by binary interaction. We propose an evolutionary scenario for AGB morphologies that is consistent with observed phenomena in AGB stars and PNe

ATOMIUM: halide molecules around the S-type AGB star W Aquilae

Context. S-type asymptotic giant branch (AGB) stars are thought to be intermediates in the evolution of oxygen- to carbon-rich AGB stars. The chemical compositions of their circumstellar envelopes are also intermediate but have not been studied in as much detail as their carbon- and oxygen-rich counterparts. W Aql is a nearby S-type star, with well-known circumstellar parameters, making it an ideal object for in-depth study of less common molecules. Aims. We aim to determine the abundances of AlCl and AlF from rotational lines, which have been observed for the first time towards an S-type AGB star. In combination with models based on PACS observations, we aim to update our chemical kinetics network based on these results. Methods. We analyse ALMA observations towards W Aql of AlCl in the ground and first two vibrationally excited states and AlF in the ground vibrational state. Using radiative transfer models, we determine the abundances and spatial abundance distributions of Al35Cl, Al37Cl, and AlF. We also model HCl and HF emission and compare these models to PACS spectra to constrain the abundances of these species. Results. AlCl is found in clumps very close to the star, with emission confined within 0′′.1 of the star. AlF emission is more extended, with faint emission extending 0′′.2 to 0′′.6 from the continuum peak. We find peak abundances, relative to H2, of 1.7 × 10−7 for Al35Cl, 7 × 10−8 for Al37Cl, and 1 × 10−7 for AlF. From the PACS spectra, we find abundances of 9.7 × 10−8 and ≤10−8, relative to H2, for HCl and HF, respectively. Conclusions. The AlF abundance exceeds the solar F abundance, indicating that fluorine synthesised in the AGB star has already been dredged up to the surface of the star and ejected into the circumstellar envelope. From our analysis of chemical reactions in the wind, we conclude that AlF may participate in the dust formation process, but we cannot fully explain the rapid depletion of AlCl seen inthe wind

The Co-Ordinated radio and infrared survey for high-mass star formation – V. The CORNISH-South survey and catalogue

We present the first high spatial resolution radio continuum survey of the southern Galactic plane. The CORNISH project has mapped the region defined by 295○ < l < 350○; |b| < 1○ at 5.5-GHz, with a resolution of 2.5″ (FWHM). As with the CORNISH-North survey, this is designed to primarily provide matching radio data to the Spitzer GLIMPSE survey region. The CORNISH-South survey achieved a root mean square noise level of ∼ 0.11 mJy beam−1, using the 6A configuration of the Australia Telescope Compact Array (ATCA). In this paper, we discuss the observations, data processing and measurements of the source properties. Above a 7σ detection limit, 4701 sources were detected, and their ensemble properties show similar distributions with their northern counterparts. The catalogue is highly reliable and is complete to 90 per cent at a flux density level of 1.1 mJy. We developed a new way of measuring the integrated flux densities and angular sizes of non-Gaussian sources. The catalogue primarily provides positions, flux density measurements and angular sizes. All sources with IR counterparts at 8μm have been visually classified, utilizing additional imaging data from optical, near-IR, mid-IR, far-IR and sub-millimetre galactic plane surveys. This has resulted in the detection of 524 H II regions of which 255 are ultra-compact H II regions, 287 planetary nebulae, 79 radio stars and 6 massive young stellar objects. The rest of the sources are likely to be extra-galactic. These data are particularly important in the characterization and population studies of compact ionized sources such as UCHII regions and PNe towards the Galactic mid-plane