We present high-resolution (∼300 au) Atacama Large Millimeter/submillimeter Array observations of the massive young stellar object G11.92-0.61 MM 1. We resolve the immediate circumstellar environment ...of MM 1 in 1.3 mm continuum emission and CH3CN emission for the first time. The object divides into two main sources-MM 1a, which is the source of a bipolar molecular outflow, and MM 1b, located 0 57 (1920 au) to the southeast. The main component of MM 1a is an elongated continuum structure, perpendicular to the bipolar outflow, with a size of 0 141 × 0 050 (480 × 170 au). The gas kinematics toward MM 1a probed via CH3CN trace a variety of scales. The lower energy J = 12-11 K = 3 line traces extended, rotating gas within the outflow cavity, while the v8 = 1 line shows a clearly resolved Keplerian rotation signature. Analysis of the gas kinematics and dust emission shows that the total enclosed mass in MM 1a is 40 5 M (where between 2.2 and 5.8 M is attributed to the disk), while MM 1b is <0.6 M . The extreme mass ratio and orbital properties of MM 1a and MM 1b suggest that MM 1b is one of the first observed examples of the formation of a binary star via disk fragmentation around a massive young (proto)star.
The interaction of ionizing and far-ultraviolet radiation with the interstellar medium is of great importance. It results in the formation of regions in which the gas is ionized, beyond which are ...photodissociation regions (PDRs) in which the gas transitions to its atomic and molecular form. Several numerical codes have been implemented to study these two main phases of the interstellar medium either dynamically or chemically. In this paper we present torus-3dpdr, a new self-consistent code for treating the chemistry of three-dimensional photoionization and photodissociation regions. It is an integrated code coupling the two codes torus, a hydrodynamics and Monte Carlo radiation transport code, and 3d-pdr, a PDRs code. The new code uses a Monte Carlo radiative transfer scheme to account for the propagation of the ionizing radiation including the diffusive component as well as a ray-tracing scheme based on the healpix package in order to account for the escape probability and column density calculations. Here, we present the numerical techniques we followed and we show the capabilities of the new code in modelling three-dimensional objects including single or multiple sources. We discuss the effects introduced by the diffusive component of the ultraviolet field in determining the thermal balance of PDRs as well as the effects introduced by a multiple sources treatment of the radiation field. With this new code, three-dimensional synthetic observations for the major cooling lines are possible, for making feasible a detailed comparison between hydrodynamical simulations and observations.
Radiation hydrodynamics (RHD) simulations are used to study many astrophysical phenomena; however, they require the use of simplified radiation transport and thermal prescriptions to reduce ...computational cost. In this paper, we present a systematic study of the importance of microphysical processes in RHD simulations using the example of D-type H ii region expansion. We compare the simplest hydrogen-only models with those that include: ionization of H, He, C, N, O, S and Ne, different gas metallicity, non-LTE metal-line-blanketed stellar spectral models of varying metallicity, radiation pressure, dust and treatment of photodissociation regions. Each of these processes is explicitly treated using modern numerical methods rather than parametrization. In line with expectations, changes due to microphysics in either the effective number of ionizing photons or the thermal structure of the gas lead to differences in D-type expansion. In general, we find that more realistic calculations lead to the onset of D-type expansion at smaller radii and a slower subsequent expansion. Simulations of star-forming regions using simplified microphysics are therefore likely overestimating the strength of radiative feedback. We find that both variations in gas metallicity and the inclusion of dust can affect the ionization front evolution at the 10–20 per cent level over 500 kyr, which could substantially modify the results of simplified 3D models including feedback. Stellar metallicity, radiation pressure and the inclusion of photodissociation regions are all less-significant effects at the 1 per cent level or less, rendering them of minor importance in the modelling the dynamical evolution of H ii regions.
ABSTRACT
Radiative transfer modelling offers a powerful tool for understanding the enigmatic hydrogen emission lines from T Tauri stars. This work compares optical and near-IR spectroscopy of 29 T ...Tauri stars with our grid of synthetic line profiles. The archival spectra, obtained with VLT/X-Shooter, provide simultaneous coverage of many optical and infrared hydrogen lines. The observations exhibit similar morphologies of line profiles seen in other studies. We used the radiative transfer code torus to create synthetic H α, Pa β, Pa γ, and Br γ emission lines for a fiducial T Tauri model that included axisymmetric magnetospheric accretion and a polar stellar wind. The distribution of Reipurth types and line widths for the synthetic H α lines is similar to the observed results. However, the modelled infrared lines are narrower than the observations by ${\approx}80\,{~\rm km\,s}^{-1}$, and our models predict a significantly higher proportion (≈90 per cent) of inverse P-Cygni profiles. Furthermore, our radiative transfer models suggest that the frequency of P-Cygni profiles depends on the ratio of the mass-loss to mass accretion rates and blue-shifted sub-continuum absorption was predicted for mass-loss rates as low as 10−12 M⊙ yr−1. We explore the effect of rotation, turbulence, and the contributions from red-shifted absorption in an attempt to explain the discrepancy in widths. Our findings show that, singularly, none of these effects is sufficient to explain the observed disparity. However, a combination of rotation, turbulence, and non-axisymmetric accretion may improve the fit of the models to the observed data.
We have conducted a programme to determine the fundamental parameters of a substantial number of eclipsing binaries of spectral types O and B in the Small Magellanic Cloud (SMC). New spectroscopic ...data, obtained with the two-degree-field (2dF) multi-object spectrograph on the 3.9-m Anglo-Australian Telescope, have been used in conjunction with photometry from the Optical Gravitational Lens Experiment (OGLE-II) data base of SMC eclipsing binaries. Previously we reported results for 10 systems; in this second and concluding paper we present spectral types, masses, radii, temperatures, surface gravities and luminosities for the components of a further 40 binaries. The uncertainties are typically ±10 per cent on masses, ±4 per cent on radii and ±0.07 on log L. The full sample of 50 OB-type eclipsing systems is the largest single set of fundamental parameters determined for high-mass binaries in any galaxy. We find that 21 of the systems studied are in detached configurations, 28 are in semidetached post-mass-transfer states, and one is a contact binary. The overall properties of the detached systems are consistent with theoretical models for the evolution of single stars with SMC metal abundances (Z ≃ 0.004); in particular, observed and evolutionary masses are in excellent agreement. Although there are no directly applicable published models, the overall properties of the semidetached systems are consistent with them being in the slow phase of mass transfer in case A. About 40 per cent of these semidetached systems show photometric evidence of orbital-phase-dependent absorption by a gas stream falling from the inner Lagrangian point on the secondary star towards the primary star. This sample demonstrates that case-A mass transfer is a common occurrence amongst high-mass binaries with initial orbital periods P ≲ 5 d, and that this slow phase has a comparable duration to the detached phase preceding it. Each system provides a primary distance indicator. We find a mean distance modulus to the SMC of 18.91 ± 0.03 ± 0.1 (internal and external uncertainties; D = 60.6 ± 1.0 ± 2.8 kpc). This value represents one of the most precise available determinations of the distance to the SMC.
We present multidimensional non-local thermodynamic equilibrium radiative transfer models of hydrogen and helium line profiles formed in the accretion flows and the outflows near the star-disc ...interaction regions of classical T Tauri stars (CTTSs). The statistical equilibrium calculations, performed under the assumption of the Sobolev approximation using the radiative transfer code torus, have been improved to include Hei and Heii energy levels. This allows us to probe the physical conditions of the inner wind of CTTSs by simultaneously modelling the robust wind diagnostic line Hei lambda 10830 and the accretion diagnostic lines such as Pa beta , Br gamma and Hei lambda 5876. The code has been tested in 1D and 2D problems, and we have shown that the results are in agreement with established codes. We apply the model to the complex flow geometries of CTTSs. Example model profiles are computed using the combinations of (1) magnetospheric accretion and disc wind, and (2) magnetospheric accretion and the stellar wind. In both cases, the model produces line profiles which are qualitatively similar to those found in observations. Our models are consistent with the scenario in which the narrow blueshifted absorption component of Hei lambda 10830 seen in observations is caused by a disc wind, and the wider blueshifted absorption component (the P-Cygni profile) is caused by a bipolar stellar wind. However, we do not have a strong constraint on the relative importance of the wind and the magnetosphere for the 'emission' component. Our preliminary calculations suggest that the temperature of the disc wind and stellar winds cannot be much higher than similar to 10000K, on the basis of the strengths of hydrogen lines. Similarly the temperature of the magnetospheric accretion cannot be much higher than similar to 10000K. With these low temperatures, we find that the photoionization by high-energy photons (e.g. X-rays) is necessary to produce Hei lambda 10830 in emission and to produce the blueshifted absorption components.
Abstract
We present high-resolution (≲160 au) Atacama Large Millimeter/submillimeter Array (ALMA) 1.3 mm observations of the high-mass prestellar core candidate G11.92−0.61 MM2, which reveal that ...this source is in fact a protobinary system with a projected separation of 505 au. The binary components, MM2E and MM2W, are compact (radii <140 au) sources within the partially optically thick dust emission with
α
0.9 cm−1.3 mm
= 2.47–2.94. The 1.3 mm brightness temperatures,
T
b
= 68.4/64.6 K for MM2E/MM2W, imply internal heating and minimum luminosities
L
*
> 24.7
L
⊙
for MM2E and
L
*
> 12.6
L
⊙
for MM2W. The compact sources are connected by a “bridge” of lower-surface-brightness dust emission and lie within more extended emission that may correspond to a circumbinary disk. The circumprotostellar gas mass, estimated from ∼0.″2 resolution VLA 0.9 cm observations assuming optically thin emission, is 6.8 ± 0.9
M
⊙
. No line emission is detected toward MM2E and MM2W in our high-resolution 1.3 mm ALMA observations. The only line detected is
13
CO
J
= 2–1, in absorption against the 1.3 mm continuum, which likely traces a layer of cooler molecular material surrounding the protostars. We also report the discovery of a highly asymmetric bipolar molecular outflow that appears to be driven by MM2E and/or MM2W in new deep, ∼0.″5 resolution (1685 au) ALMA 0.82 mm observations. This outflow, traced by low-excitation CH
3
OH emission, indicates ongoing accretion onto the protobinary system. Overall, the super-Alfvénic models of Mignon-Risse et al. agree well with the observed properties of the MM2E/MM2W protobinary, suggesting that this system may be forming in an environment with a weak magnetic field.
The TORUS radiation transfer code Harries, T.J.; Haworth, T.J.; Acreman, D. ...
Astronomy and computing,
April 2019, 2019-04-00, Volume:
27
Journal Article
Peer reviewed
Open access
We present a review of the torus radiation transfer and hydrodynamics code. torus uses a 1-D, 2-D or 3-D adaptive mesh refinement scheme to store and manipulate the state variables, and solves the ...equation of radiative transfer using Monte Carlo techniques. A framework of microphysics modules is described, including atomic and molecular line transport in moving media, dust radiative equilibrium, photoionisation equilibrium, and time-dependent radiative transfer. These modules provide a flexible scheme for producing synthetic observations, either from analytical models or as post-processing of hydrodynamical simulations (both grid-based and Lagrangian). A hydrodynamics module is also presented, which may be used in combination with the radiation-transport modules to perform radiation-hydrodynamics simulations. Benchmarking and validation tests of each major mode of operation are detailed, along with descriptions and performance/scaling tests of the various parallelisation schemes. We give examples on the uses of the code in the literature, including applications to low- and high-mass star formation, cluster feedback, and stellar winds, along with an Appendix listing the refereed papers that have used torus.
We present comprehensive models for the Herbig Ae stars MWC 275 and AB Aur that aim to explain their spectral energy distribution (from UV to millimeter) and long-baseline interferometry (from ...near-infrared to millimeter) simultaneously. Data from the literature, combined with new mid- infrared (MIR) interferometry from the Keck Segment Tilting Experiment, are modeled using an axisymmetric Monte Carlo radiative transfer code. Models in which most of the near-infrared (NIR) emission arises from a dust rim fail to fit the NIR spectral energy distribution (SED) and sub-milliarcsecond NIR CHARA interferometry. Following recent work, we include an additional gas emission component with similar size scale to the dust rim, inside the sublimation radius, to fit the NIR SED and long-baseline NIR interferometry on MWC 275 and AB Aur. In the absence of shielding of starlight by gas, we show that the gas-dust transition region in these YSOs will have to contain highly refractory dust, sublimating at similar to 1850 K. Despite having nearly identical structure in the thermal NIR, the outer disks of MWC 275 and AB Aur differ substantially. In contrast to the AB Aur disk, MWC 275 lacks small grains in the disk atmosphere capable of producing significant 10-20 mum emission beyond similar to 7 AU, forcing the outer regions into the "shadow" of the inner disk.
We present multidimensional non-local thermodynamic equilibrium radiative transfer models of hydrogen and helium line profiles formed in the accretion flows and the outflows near the star-disc ...interaction regions of classical T Tauri stars (CTTSs). The statistical equilibrium calculations, performed under the assumption of the Sobolev approximation using the radiative transfer code torus, have been improved to include He i and He ii energy levels. This allows us to probe the physical conditions of the inner wind of CTTSs by simultaneously modelling the robust wind diagnostic line He iλ10830 and the accretion diagnostic lines such as Paβ, Brγ and He iλ5876. The code has been tested in 1D and 2D problems, and we have shown that the results are in agreement with established codes. We apply the model to the complex flow geometries of CTTSs. Example model profiles are computed using the combinations of (1) magnetospheric accretion and disc wind, and (2) magnetospheric accretion and the stellar wind. In both cases, the model produces line profiles which are qualitatively similar to those found in observations. Our models are consistent with the scenario in which the narrow blueshifted absorption component of He iλ10830 seen in observations is caused by a disc wind, and the wider blueshifted absorption component (the P-Cygni profile) is caused by a bipolar stellar wind. However, we do not have a strong constraint on the relative importance of the wind and the magnetosphere for the 'emission' component. Our preliminary calculations suggest that the temperature of the disc wind and stellar winds cannot be much higher than ∼10 000 K, on the basis of the strengths of hydrogen lines. Similarly the temperature of the magnetospheric accretion cannot be much higher than ∼10 000 K. With these low temperatures, we find that the photoionization by high-energy photons (e.g. X-rays) is necessary to produce He iλ10830 in emission and to produce the blueshifted absorption components.
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