Using H3+ and H2D+ as probes of star-forming regions

The H3+ and H2D+ ions are important probes of the physical and chemical conditions in regions of the interstellar medium where new stars are forming. This paper reviews how observations of these species and of heavier ions such as HCO+ and H3O+ can be used to derive chemical and kinematic properties of nearby pre-stellar cores, and the cosmic-ray ionisation rate toward more distant regions of high-mass star formation. Future prospects in the field are outlined at the end.Comment: Refereed review, 6 pages, to appear in Phil. Trans. R. Soc.

Impact of Ejecta Temperature and Mass on the Strength of Heavy Element Signatures in Kilonovae

A kilonova, the electromagnetic emission produced by compact binary mergers, is formed through a delicate interplay of physical processes, involving r-process nucleosynthesis and interactions between heavy elements and photons through radiative transfer. This complexity makes it difficult to achieve a comprehensive understanding of kilonova spectra. In this study, we aim to enhance our understanding and establish connections between physical parameters and observables through radiative-transfer simulations. Specifically, we investigate how ejecta temperature and element mass influence the resulting kilonova spectrum. For each species, the strength of its line features depends on these parameters, leading to the formation of a distinct region in the parameter space, dubbed the resonance island, where the line signature of that species is notably evident in the kilonova spectrum. We explore its origin and applications. Among explored r-process elements (31 ≤ Z ≤ 92), we find that four species—SrII, YII, BaII, and CeII—exhibit large and strong resonance islands, suggesting their significant contributions to kilonova spectra at specific wavelengths. In addition, we discuss potential challenges and future perspectives in observable heavy elements and their masses in the context of the resonance island

A Molecular Line Observation toward Massive Clumps Associated with Infrared Dark Clouds

We have surveyed the N2H+ J=1-0, HC3N J=5-4, CCS J_N=4_3-3_2, NH3 (J, K) = (1, 1), (2, 2), (3, 3), and CH3OH J=7-6 lines toward the 55 massive clumps associated with infrared dark clouds by using the Nobeyama Radio Observatory 45 m telescope and the Atacama Submillimeter Telescope Experiment 10 m telescope. The N2H+, HC3N, and NH3 lines are detected toward most of the objects. On the other hand, the CCS emission is detected toward none of the objects. The [CCS]/[N2H+] ratios are found to be mostly lower than unity even in the Spitzer 24 micron dark objects. This suggests that most of the massive clumps are chemically more evolved than the low-mass starless cores. The CH3OH emission is detected toward 18 out of 55 objects. All the CH3OH-detected objects are associated with the Spitzer 24 micron sources, suggesting that star formation has already started in all the CH3OH-detected objects. The velocity widths of the CH3OH J_K=7_0-6_0 A+ and 7_{-1}-6_{-1} E lines are broader than those of N2H+ J=1-0. The CH3OH J_K=7_0-6_0 A+ and 7_{-1}-6_{-1} E lines tend to have broader linewidth in the MSX dark objects than in the others, the former being younger or less luminous than the latter. The origin of the broad emission is discussed in terms of the interaction between an outflow and an ambient cloud.Comment: Accepted to Ap

The Circumstellar Environment of High-Mass Protostellar Objects: IV. C17O Observations and Depletion

We observe 84 candidate young high-mass sources in the rare isotopologues C17O and C18O to investigate whether there is evidence for depletion (freeze-out) towards these objects. Observations of the J=2-1 transitions of C18O and C17O are used to derive the column densities of gas towards the sources and these are compared with those derived from submillimetre continuum observations. The derived fractional abundance suggests that the CO species show a range of degrees of depletion towards the objects. We then use the radiative transfer code RATRAN to model a selection of the sources to confirm that the spread of abundances is not a result of assumptions made when calculating the column densities. We find a range of abundances of C17O that cannot be accounted for by global variations in either the temperature or dust properties and so must reflect source to source variations. The most likely explanation is that different sources show different degrees of depletion of the CO. Comparison of the C17O linewidths of our sources with those of CS presented by other authors reveal a division of the sources into two groups. Sources with a CS linewidth >3 km/s have low abundances of C17O while sources with narrower CS lines have typically higher C17O abundances. We suggest that this represents an evolutionary trend. Depletion towards these objects shows that the gas remains cold and dense for long enough for the trace species to deplete. The range of depletion measured suggests that these objects have lifetimes of 2-4x10^5 years.Comment: 18 pages. Accepted for publication in Astronomy & Astrophysic

The JCMT Spectral Legacy Survey: physical structure of the molecular envelope of the high-mass protostar AFGL2591

The understanding of the formation process of massive stars (>8 Msun) is limited, due to theoretical complications and observational challenges. We investigate the physical structure of the large-scale (~10^4-10^5 AU) molecular envelope of the high-mass protostar AFGL2591 using spectral imaging in the 330-373 GHz regime from the JCMT Spectral Legacy Survey. Out of ~160 spectral features, this paper uses the 35 that are spatially resolved. The observed spatial distributions of a selection of six species are compared with radiative transfer models based on a static spherically symmetric structure, a dynamic spherical structure, and a static flattened structure. The maps of CO and its isotopic variations exhibit elongated geometries on scales of ~100", and smaller scale substructure is found in maps of N2H+, o-H2CO, CS, SO2, CCH, and methanol lines. A velocity gradient is apparent in maps of all molecular lines presented here, except SO, SO2, and H2CO. We find two emission peaks in warm (Eup~200K) methanol separated by 12", indicative of a secondary heating source in the envelope. The spherical models are able to explain the distribution of emission for the optically thin H13CO+ and C34S, but not for the optically thick HCN, HCO+, and CS, nor for the optically thin C17O. The introduction of velocity structure mitigates the optical depth effects, but does not fully explain the observations, especially in the spectral dimension. A static flattened envelope viewed at a small inclination angle does slightly better. We conclude that a geometry of the envelope other than an isotropic static sphere is needed to circumvent line optical depth effects. We propose that this could be achieved in envelope models with an outflow cavity and/or inhomogeneous structure at scales smaller than ~10^4 AU. The picture of inhomogeneity is supported by observed substructure in at least six species.Comment: 17 pages; accepted for publication in A&

Water emission from the high-mass star-forming region IRAS 17233-3606. High water abundances at high velocities

We investigate the physical and chemical processes at work during the formation of a massive protostar based on the observation of water in an outflow from a very young object previously detected in H2 and SiO in the IRAS 17233-3606 region. We estimated the abundance of water to understand its chemistry, and to constrain the mass of the emitting outflow. We present new observations of shocked water obtained with the HIFI receiver onboard Herschel. We detected water at high velocities in a range similar to SiO. We self-consistently fitted these observations along with previous SiO data through a state-of-the-art, one-dimensional, stationary C-shock model. We found that a single model can explain the SiO and H2O emission in the red and blue wings of the spectra. Remarkably, one common area, similar to that found for H2 emission, fits both the SiO and H2O emission regions. This shock model subsequently allowed us to assess the shocked water column density, N(H2O)=1.2x10^{18} cm^{-2}, mass, M(H2O)=12.5 M_earth, and its maximum fractional abundance with respect to the total density, x(H2O)=1.4x10^{-4}. The corresponding water abundance in fractional column density units ranges between 2.5x10^{-5} and 1.2x10^{-5}, in agreement with recent results obtained in outflows from low- and high-mass young stellar objects.Comment: accepted for publication as a Letter in Astronomy and Astrophysic