Expansion Velocity Research Articles

Failure and deformation characteristics of shale subject to true triaxial stress loading and unloading under water retention and seepage.

A multi-functional true triaxial fluid-structure coupling system was used to conduct water retention and seepage tests of shale under true triaxial loading and unloading stress paths. The stress–strain evolution of shale specimens under different experimental conditions was obtained, and the corresponding deformation and strength were analysed. The evolution and failure characteristics of cracks in shale were obtained by CT scanning images before and after the experiment. The results show that the volumetric strain of shale specimen increases first, then decreases and finally continues to increase with an increase in deviatoric stress under water retention, indicating that the volumetric change has experienced a compaction-expansion-compacting. The σ-ε1 curve of the sample increases first and then decreases, while the deformation in the σ2 direction shows the repeated compression and expansion. In the seepage test, the permeability–strain curve can be divided into two parts before and after fracture according to the σ-ε1 curve. Before fracture, the compression velocity of the specimen in the loading direction exceeds the expansion velocity in the unloading direction, resulting in a decrease in volume and a decrease in permeability. With an increase in deviatoric stress, fractures occur inside the particles and continue to spread from the tip until the fractures break through the shale specimen. The pore fissure area increases and the permeability of the sample increases rapidly. In terms of fracture evolution, for the water retention test, dense tensile and shear cracks appear on the failure plane perpendicular to the σ1 and σ3 directions, and complex shear fracture network appears on the failure plane perpendicular to the σ2 direction. For the seepage test, heavy shear failure occurs throughout the original fracture of the sample. With an increase in the penetration depth, the fracture shape on the failure surface perpendicular to the σ2 direction gradually changes from single to complex.

Common envelope evolution in born-again planetary nebulae – Shaping the H-deficient ejecta of A 30

ABSTRACT Born-again planetary nebulae (PNe) are extremely rare cases in the evolution of solar-like stars. It is commonly accepted that their central stars (CSPN) experienced a very late thermal pulse (VLTP), ejecting H-deficient material inside the evolved H-rich PN. Given the short duration of this event and the fast subsequent evolution of the CSPN, details of the mass ejection are unknown. We present the first morphokinematic model of the H-deficient material surrounding a born-again PN, namely A 30. New San Pedro Mártir observations with the Manchester Echelle Spectrograph were recently obtained to map the inner region of A 30 which are interpreted by means of the software shape in conjunction with HST WFC3 images. The shape morphokinematic model that best reproduces the observations is composed by a disrupted disc tilted 37° with respect to the line of sight and a pair of orthogonal opposite bipolar ejections. We confirm previous suggestions that the structures closer to the CSPN present the highest expansion velocities, that is, the disrupted disc expands faster than the farther bipolar features. We propose that the current physical structure and abundance discrepancy of the H-deficient clumps around the CSPN of A 30 can be explained by a common envelope phase following the VLTP event. Our proposed scenario is also compared with other known born-again PNe (A 58, A 78, HuBi 1, and the Sakurai’s Object).

Measurements of pressure during the forced water entry of a cone into pure and aerated water

The present paper aims at analyzing the pressure distribution arising during water entry of a rigid cone on the free surface of pure water and aerated water initially at rest. For this purpose, impact tests were carried out using a hydraulic machine for a cone with a deadrise angle of 7° and for several impact velocities (5, 7 and 9 m/s) and air volume fractions (0, 0.35 and 1.1%). The impact pressure was measured at four different locations on the cone surface. The evolution of the pressure and the pressure impulse, the pressure maxima and the wetted surface expansion velocity are analyzed. For pure water, the results are in good agreement with the predictions of existing model analytical models of water impact based on Wagner’s theory, with a relative difference smaller than 2% percent for the wetted surface expansion velocity and 8% for the pressure impulse. For aerated water, the measured pressure evolutions are much less repeatable than for pure water and the pressure distribution is no longer axisymmetric and self-similar, likely due to inhomogeneous distributions of the bubbles in the water. Aeration is shown to induce a significant reduction of the impact pressure. A decrease of about 25% (in comparison to pure water) for both the peak pressures and the rate of increase of the pressure impulse was observed for a void volume fraction of 1.1%.

Identifying biomarkers associated with tumor growth rate: a longitudinal preoperative magnetic resonance imaging follow-up of low-grade gliomas.

BackgroundAlthough the influence of molecular biomarkers on the biological behavior of tumor cells has been investigated, their quantitative influence on the velocity of tumor growth remains unclear. This study aimed to identify the molecular biomarkers associated with tumor growth rates in World Health Organization (WHO) grade II gliomas, or low-grade gliomas (LGGs).MethodsPreoperative magnetic resonance imaging (MRI) data of patients with LGGs were retrospectively reviewed. Patients with at least 2 preoperative MRIs taken more than 90 days apart were enrolled. Patients with isocitrate dehydrogenase (IDH) wild-type tumors or with no recorded IDH status were excluded. A linear mixed-effects model was used to assess the velocity of tumor diameter expansion. The effect of biomarker expression on tumor growth rate was assessed using a multivariate linear mixed-effects regression model.ResultsData from 56 patients were used in our study. The overall velocity of diameter expansion (VDE) for LGGs was 2.1 mm/year. Higher expression level of mutant p53 were significantly associated with a higher tumor growth rate (+1.9 mm/year, P<0.01), while higher expression level of alpha-thalassemia/mental retardation syndrome X-linked protein (ATRX) were significantly associated with a lower tumor growth rate (−1.3 mm/year, P<0.01). Tumors with O6-methylguanine-DNA methyltransferase (MGMT) promoter methylation were found to grow significantly more slowly than those with no methylation (−3.1 mm/year, P<0.01). The telomerase reverse transcriptase (TERT) promoter type and expressions levels of Ki-67 and epidermal growth factor receptor (EGFR) showed no significant independent impact on tumor growth rates.ConclusionsThe status of biomarkers is significantly associated with the tumor growth rate in LGGs.

Radioactively Powered Gamma-Ray Transient Associated with a Kilonova from Neutron Star Merger

The association of GW170817/GRB 170817A/AT2017gfo provides the first direct evidence for neutron star mergers as significant sources of r-process nucleosynthesis. A gamma-ray transient (GRT) would be powered by the radioactive decay of the freshly synthesized r-process elements. By analyzing the composition and gamma-ray opacity of the kilonova ejecta in detail, we calculate the lightcurve and spectrum of the GRT for a range of spherically symmetric merger ejecta models with mass M ej = 0.001 to ∼0.05M ⊙ and expansion velocity v ej = 0.1c to ∼0.4c. It is found that the peak of the GRT lightcurve depends on M ej and v ej as and . Most radiating photons are in the 100–3000 keV band and the spectrum peaks at about 800 keV for different nuclear physics inputs. The line features are blurred out by the Doppler broadening effect. Adopting the ejecta parameters reported in the literature, we examine the detection probability of the possible GRT associated with AT2017gfo. We show that the GRT cannot be convincingly detected with either current or proposed missions in the MeV band, such as ETCC and AMEGO. The low gamma-ray flux, together with the extremely low event rate at local universe, makes a discovery of GRTs a great challenge.

Morpho-kinematic Modeling of the Expanding Ejecta of the Extremely Slow Nova V1280 Scorpii

Knowledge of the morphology of nova ejecta is essential for fully understanding the physical processes involved in nova eruptions. We studied the 3D morphology of the expanding ejecta of the extremely slow nova V1280 Sco with a unique light curve. Synthetic line profile spectra were compared to the observed [O iii] λλ4959, 5007 and [N ii] λ5755 emission line profiles in order to find the best-fit morphology, inclination angle, and maximum expansion velocity of the ejected shell. We derive the best-fitting expansion velocity, inclination, and squeeze as km s−1, deg, and using [O iii] line profiles, and km s−1, deg, and using the [N ii] λ5755 line profile. A high inclination angle is consistent with the observational results showing multiple absorption lines originating from clumpy gases, which are produced in dense and slow equatorially focused outflows. Based on additional observational features such as optical flares near the maximum light and dust formation on V1280 Sco, a model of internal shock interaction between slow ejecta and fast wind proposed for the γ-ray emission detected in other novae seems to be applicable to this extremely slow and peculiar nova. Increasing the sample size of novae whose morphology is studied will be helpful in addressing long-standing mysteries in novae such as the dominant energy source to power the optical light at the maximum, optical flares near the maximum, clumpiness of the ejecta, and dust formation.

Deriving Thermonuclear Supernova Properties from Gamma-Ray Line Measurements

We illustrate methods for deriving properties of thermonuclear, or Type Ia, supernovae, including synthesized 56Ni mass, total ejecta mass, ejecta kinetic energy, and 56Ni distribution in velocity, from gamma-ray line observations. We simulate data from a small number of published SNe Ia models for a simple gamma-ray instrument, and measure their underlying properties from straightforward analyses. Assuming spherical symmetry and homologous expansion, we calculate exact line profiles for all 56Co and 56Ni lines at all times, requiring only the variation of mass density and 56Ni mass fraction with expansion velocity as input. By parameterizing these quantities, we iterate the parameters to fit the simulated data. We fit the full profiles of multiple lines, or we integrate over the lines and fit line fluxes only versus time. Line profile fits are more robust, but in either case, we can recover accurately the values of the aforementioned properties of the models simulated, given sufficient signal to noise in the lines. A future gamma-ray mission with line sensitivity approaching 10−6 photons cm−2 s−1 would measure these properties for many SNe Ia, and with unprecedented precision and accuracy for a few per year. Our analyses applied to the reported 56Co lines from SN 2014J favor a low 56Ni mass and low ejecta mass, relative to other estimates.

Bursting Bubbles: Feedback from Clustered Supernovae and the Trade-off Between Turbulence and Outflows

We present an analytic model for clustered supernovae (SNe) feedback in galaxy disks, incorporating the dynamical evolution of superbubbles formed from spatially overlapping SNe remnants. We propose two realistic outcomes for the evolution of superbubbles in galactic disks: (1) the expansion velocity of the shock front falls below the turbulent velocity dispersion of the interstellar medium in the galaxy disk, whereupon the superbubble stalls and fragments, depositing its momentum entirely within the galaxy disk; or (2) the superbubble grows in size to reach the gas scale height, breaking out of the galaxy disk and driving galactic outflows/fountains. In either case, we find that superbubble breakup/breakout almost always occurs before the last Type II SN (≲40 Myr) in the recently formed star cluster, assuming a standard high-end initial mass function slope, and scalings between stellar lifetimes and masses. The threshold between these two cases implies a break in the effective strength of feedback in driving turbulence within galaxies, and a resulting change in the scalings of, for example, star formation rates with gas surface density (the Kennicutt–Schmidt relation) and the star formation efficiency in galaxy disks.

The symbiotic and bipolar nebula M 2-9: Morphological variability of the collimated ionized wind arising from the core

Abstract We studied the central region of bipolar nebula M 2-9 using radio-continuum observations obtained from the Jansky Very Large Array (JVLA) and the Atacama Large Millimeter Array (ALMA) interferometers. This work presents new images at ∼43 GHz (∼7.0 mm) and ∼345 GHz (∼0.9 mm) with angular resolutions of $\sim {0{^{\prime \prime}_{.}}047}$ and ${0{^{\prime \prime}_{.}}09}$, respectively. The continuum emission at ∼43 GHz shows an elongated jet-like structure perpendicular to the ∼345 GHz observation. We conclude that both emissions could correspond to tracing an isothermal collimated fast wind with constant expansion velocity and being driven by the circumstellar ring traced by ALMA. Although this configuration has been discussed within the scope of planetary nebulae models, there is a remarkable fact: the collimated fast wind shows morphological spatial variability. This supports the idea of a symbiotic binary system within the innermost part of M 2-9, which would be composed of a white dwarf and an AGB star. The latter could explain the mirror symmetry observed at larger scales due to their orbital motion.

The Radial Evolution of Magnetic Clouds From Helios to Ulysses

The evolution of a magnetic cloud (MC) from the inner heliosphere to the outer heliosphere has been investigated for decades. Although many studies have reported on the evolution of MCs, there is no relevant statistical study about the continuous parametric evolution of the flux rope model of the Gold–Hoyle solution for MCs from near the Sun to 5.4 au. Based on the velocity-modified uniform-twist force-free flux rope model, in this study we explore the evolution with heliodistance for some parameters from 139 MCs observed by the Helios, Wind, and Ulysses spacecraft. We find a negative/positive correlation between the central axial field strength/the radius of the cross section and the heliodistance. The angle between the axis of the MC and the Sun–spacecraft line (Θ), the expansion velocity (v e ), and the poloidal velocity (v p ) did not show any evident tendency to increase or decrease with the heliodistance. In addition, the number of turns of the magnetic field lines per unit length winding around the magnetic flux rope, τ, shows a weak decrease with heliodistance. Also, there is an evident negative correlation between τ and the radius of the flux rope, R. The axial magnetic flux (F z ) and the magnetic helicity (H m ) show a tendency to decrease within 1 au, after which they remain almost unchanged until 5.5 au. Furthermore, we do not find any evident difference in the parametric properties of MCs on and outside the ecliptic.

Deciphering the Lyman-α emission line: towards the understanding of galactic properties extracted from Lyα spectra via radiative transfer modelling

ABSTRACT Existing ubiquitously in the Universe with the highest luminosity, the Lyman-α (Lyα) emission line encodes abundant physical information about the gaseous medium it interacts with. Nevertheless, the resonant nature of the Lyα line complicates the radiative transfer (RT) modelling of the line profile. We revisit the problem of deciphering the Lyα emission line with RT modelling. We reveal intrinsic parameter degeneracies in the widely used shell model in the optically thick regime for both static and outflowing cases, which suggest the limitations of the model. We also explore the connection between the more physically realistic multiphase, clumpy model, and the shell model. We find that the parameters of a ‘very clumpy’ slab model and the shell model have the following correspondences: (1) the total column density, the effective temperature, and the average radial clump outflow velocity of the clumpy slab model are equal to the H i column density, effective temperature, and expansion velocity of the shell model, respectively; (2) large intrinsic linewidths are required in the shell model to reproduce the wings of the clumpy slab models; (3) adding another phase of hot interclump medium increases peak separation, and the fitted shell expansion velocity lies between the outflow velocities of two phases of gas. Our results provide a viable solution to the major discrepancies associated with Lyα fitting reported in previous literature, and emphasize the importance of utilizing information from additional observations to break the intrinsic degeneracies and interpreting the model parameters in a more physically realistic context.

Low luminosity Type II supernovae – IV. SN 2020cxd and SN 2021aai, at the edges of the sub-luminous supernovae class

ABSTRACT Photometric and spectroscopic data for two Low Luminosity Type IIP Supernovae (LL SNe IIP) 2020cxd and 2021aai are presented. SN 2020cxd was discovered 2 d after explosion at an absolute magnitude of Mr = −14.02 ± 0.21 mag, subsequently settling on a plateau which lasts for ∼120 d. Through the luminosity of the late light curve tail, we infer a synthesized 56Ni mass of (1.8 ± 0.5) × 10−3 M⊙. During the early evolutionary phases, optical spectra show a blue continuum ($T\, \gt $8000 K) with broad Balmer lines displaying a P Cygni profile, while at later phases, Ca ii, Fe ii, Sc ii, and Ba ii lines dominate the spectra. Hydrodynamical modelling of the observables yields $R\, \simeq$ 575 R⊙ for the progenitor star, with Mej = 7.5 M⊙ and $E\, \simeq$ 0.097 foe emitted during the explosion. This low-energy event originating from a low-mass progenitor star is compatible with both the explosion of a red supergiant (RSG) star and with an Electron Capture Supernova arising from a super asymptotic giant branch star. SN 2021aai reaches a maximum luminosity of Mr = −16.57 ± 0.23 mag (correcting for AV = 1.92 mag), at the end of its remarkably long plateau (∼140 d). The estimated 56Ni mass is (1.4 ± 0.5) × 10−2 M⊙. The expansion velocities are compatible with those of other LL SNe IIP (few 103 km s−1). The physical parameters obtained through hydrodynamical modelling are $R\, \simeq$ 575 R⊙, Mej = 15.5 M⊙, and E = 0.4 foe. SN 2021aai is therefore interpreted as the explosion of an RSG, with properties that bridge the class of LL SNe IIP with standard SN IIP events.

Numerical Simulation and Experimental Verification of Phase Change Buoyancy Control System

Phase change buoyancy control systems (PBCS) driven by phase change materials have unique advantages over conventional hydraulically actuated buoyancy control systems, especially in their high adaptability for deep-sea exploration and seamless interaction with humans. Studying the heat transfer process and working mechanism of PBCS is helpful to research the precise control mode of the phase change buoyancy regulation system. In this study, we chose paraffin wax as the phase change material for PBCS. A buoyancy generator for phase change buoyancy regulation is designed and manufactured. By studying the relation between its expansion volume and heating time and heat input, the mathematical model of the volume change of PBCS is established. We obtain the calculation results of the PBCS working process by using the computer-aided software MATLAB. Experimental results show that the theoretical volume expansion velocity and volume expansion rate of paraffin are almost consistent with the experimental results. The mathematical calculation model is available and has a significant reference value for further research on the theoretical basis of the diving depth control of PBCS.

A kinematical study of the dwarf irregular galaxy NGC 1569 and its supernova remnants

ABSTRACT We present Fabry-Pérot observations in the H α and [S ii] lines to study the kinematics of the Magellanic-type dwarf irregular galaxy NGC 1569, these observations allowed us to compute the H α velocity field of this galaxy. Doing a detailed analysis of the velocity along the line of sight and H α velocity profiles, we identified the origin of most of the motions in the innermost parts of the galaxy and discarded the possibility of deriving a rotation curve that traces the gravitational well of the galaxy. We analysed the kinematics of the ionized gas around 31 supernova remnants previously detected in NGC 1569 by other authors, in optical and radio emission. We found that the H α velocity profiles of the supernova remnants are complex indicating the presence of shocks. Fitting these profiles with several Gaussian functions, we computed their expansion velocities which rank from 87 to 188 km s−1 confirming they are supernova remnants. Also, we determined the physical properties such as electron density, mechanical energy, and kinematic age for 30 of the 31 supernova remnants and found they are in the radiative phase with an energy range from 1 to 39 × 1050 erg s−1 and an age from 2.3 to 8.9 × 104 yr. Finally, we estimated the Surface Brightness–Diameter (Σ–D) relation for NGC 1569 and obtained a slope β = 1.26 ± 0.2, comparable with the β value obtained for supernova remnants in galaxies M31 and M33.

Factors Associated With Long-term Survival in Women Who Get Pregnant After Surgery for WHO Grade II Glioma.

Women with a World Health Organization grade II glioma (GIIG) often question clinicians about the effects of pregnancy on their disease. Previous reports have indicated a higher risk of glioma progression during and after pregnancy. Here, the aim was to investigate postpregnancy outcomes and predictive factors affecting overall survival in female patients who underwent GIIG surgery. Inclusion criteria were adult women who have been pregnant after a GIIG resection and with a stable oncologic status at the time of pregnancy (no ongoing oncologic treatment, no contrast enhancement, no debilitating clinical condition). Relevant cases were identified from a databank (1998-2021) of patients who underwent surgical resection for a histologically confirmed GIIG in our department. Among 345 women with GIIG in their reproductive years (age <45 years), 16 patients (4.6%, mean age at delivery 30.9 ± 5.1 years) were pregnant (twice in 5 cases). The mean interval between the last oncologic treatment (surgery alone in 11 patients, surgery followed by chemotherapy and/or radiotherapy in 5 patients) and pregnancy was 3.5 years (range 0.75-10 years). Two patients experienced seizures during pregnancy. The delivery was vaginal and uneventful in all cases but 1 (1 caesarean). All children had normal mental and physical development. The glioma behavior changed in 7 patients (43.7%), with an acceleration of the velocity of diameter expansion and/or the occurrence of a contrast enhancement during or within 3 months after pregnancy, resulting in medical treatment and/or reoperation in the early postpartum period in 7 cases. The median clinical follow-up from delivery was 5.3 years (range 1.25-11.6 years). Four other patients received delayed adjuvant therapy for glioma progression. Seven patients (43.7%) died at a median time from delivery of 3.9 years (range 1.25-5.9 years). Overall, the median survival from delivery was 5.75 years. A crucial finding is that patients who underwent a complete surgical resection and patients with stable lesions before pregnancy lived longer (log rank, p = 0.046 and p = 0.0026, respectively). Tumor residual volume and tumor speed growth are strong predictive factors conditioning postpregnancy long-term survival in patients with GIIG. Identifying patients at risk is critical to provide relevant counsel to women with GIIG with a desire for motherhood.

Ultracold neutral plasma expansion in a strong uniform magnetic field.

In strongly magnetized neutral plasmas, electron motion is reduced perpendicular to the magnetic field direction. This changes dynamical plasma properties such as temperature equilibration, spatial density evolution, electron pressure, and thermal and electrical conductivity. In this paper we report measurements of free plasma expansion in the presence of a strong magnetic field. We image laser-induced fluorescence from an ultracold neutral Ca^{+} plasma to map the plasma size as a function of time for a range of magnetic field strengths. The asymptotic expansion velocity perpendicular to the magnetic field direction falls rapidly with increasing magnetic field strength. We observe that the initially Gaussian spatial distribution remains Gaussian throughout the expansion in both the parallel and perpendicular directions. We compare these observations with a diffusion model and with a self-similar expansion model and show that neither of these models reproduces the observed behavior over the entire range of magnetic fields used in this study. Modeling the expansion of a magnetized ultracold plasma poses a nontrivial theoretical challenge.

Plume characteristics of polymeric material doped with different metal particles under pulsed laser irradiation

The polymer emerges as a promising propellant for laser propulsion, which is expected to achieve high specific impulse and momentum coupling coefficient. However, the low laser absorptivity of polymer deteriorates its further application. Metals can improve the laser absorption of laser energy, contributing to better propulsion performance. This paper investigated the influence of different alloy particles (Cu-Zn, Al-Si, Ni-Ti, Co-Cr) on the plume characteristics of polymeric material under laser irradiation. The plume images, length, area, and relative intensity distribution of the doped sample were analyzed and compared. It is found that each alloy particle could contribute to the stable and massive formation of the ablation plume. When laser irradiates these doped samples, an obvious jet was generated from the ablation surface, and there was an additional expansion cluster at the end of the jet. Compared to other samples, the target filled with Al-Si witnessed the maximal plume length of 13 cm, expansion velocity of 26 m/s, and plume area of 33 cm2. Besides, the higher doping ratio contributed to the larger plume length while the smaller plume area in general, but the doping ratio had little effect on the plume length and area for the short laser-material interaction process.

Breaking Orion's Veil with fossil outflows

Context. The role of feedback in the self-regulation of star formation is a fundamental question in astrophysics. The Orion Nebula is the nearest site of ongoing and recent massive star formation. It is a unique laboratory for the study of stellar feedback. Recent SOFIA [C II] 158 μm observations have revealed an expanding bubble, the Veil shell, that is powered by stellar winds and ionization feedback. Aims. We have identified a protrusion-like substructure in the northwestern portion of the Orion Veil shell that may indicate additional, highly directional feedback mechanisms. Our goal is to investigate the origin of the protrusion by quantifying its possible driving mechanisms. Methods. We use the [C II] 158 μm map of the Orion Nebula obtained with the upGREAT instrument on board SOFIA. The spectral and spatial resolution of the observations are 0.3 km s−1 and 16", respectively. The velocity-resolved [C II] observations allow us to construct position-velocity (pv) diagrams to measure the morphology and the expansion velocity of the protrusion. For the morphology, we also use new observations of 12CO and 13CO J = 2-1 (to trace molecular gas), Spitzer 8 μm observations (to trace the far-ultraviolet-illuminated surfaces of photodissociation regions), and Hα observations (to trace ionized gas). For the kinematics, we perform a line-profile analysis of [C II], 13CO, and 12CO at 12 positions, covering the entire protrusion. To quantify the stellar feedback, we estimate the mass of the protrusion by fitting the dust thermal emission. We compare the kinetic energy with the stellar wind of θ1 Ori C and the momentum of the outflows of massive protostars to investigate the driving mechanism of the protrusion. Results. The pv diagrams reveal two half-shells expanding at velocities of +6 km s−1 and +12 km s−1. We find that the protrusion has a diameter of ~1.3 pc with a ~45 M⊙ shell expanding at +12 km s−1 at the northwestern rim of the Veil. The thickness of the expanding shell is ~0.1 pc. Using the mass in the limb-brightened shell and the maximum expansion velocity, we calculate the kinetic energy and the momentum of the protrusion to be ~7 × 1046 erg and 540 M⊙ km s−1, respectively. We consider three possible origins for this protrusion: fossil outflow cavities created by jets and outflows during the protostellar accretion phase, preexisting "clumpiness" in the OMC-1 core, and the stellar wind during the main-sequence phase. Based on the energetics and the morphology, we conclude that the northwestern part of the preexisting cloud was locally perturbed by outflows ejected from massive protostars in the Trapezium cluster. This suggests that the protrusion of the Veil is the result of mechanical rather than radiative feedback. Furthermore, we argue that the location of the protrusion is a suitable place to break Orion's Veil owing to the photo-ablation from the walls of the protrusion. Conclusions. We conclude that the outflows of massive protostars can influence the morphology of the future H II region and even cause breakages in the ionization front. Specifically, the interaction of stellar winds of main-sequence stars with the molecular core preprocessed by the protostellar jet is important.

The Rapidly Evolving Asymptotic Giant Branch Star, V Hya: ALMA Finds a Multiring Circus with High-velocity Outflows

We have observed the mass-losing carbon star V Hya that is apparently transitioning from an asymptotic giant branch star to a bipolar planetary nebula, at an unprecedented angular resolution of ∼0.″4–0.″6 with the Atacama Large Millimeter/submillimeter Array. Our 13CO and 12CO (J = 3–2 and J = 2–1) images have led to the discovery of a remarkable set of six expanding rings within a flared, warped disk structure undergoing dynamical expansion (DUDE) that lies in the system’s equatorial plane. We also find, for the first time, several bipolar, high-velocity outflows, some of which have parabolic morphologies, implying wide-opening angles, while one (found previously) is clumpy and highly collimated. The latter is likely associated with the high-velocity bullet-like ejections of ionized gas from V Hya; a possible molecular counterpart to the oldest of the four bullets can be seen in the 12CO images. We find a bright, unresolved central source of continuum emission (FWHM size ≲165 au); about 40% of this emission can be produced in a standard radio photosphere, while the remaining 60% is likely due to thermal emission from very large (millimeter-sized) grains, having mass ≳10−5 M ⊙. We have used a radiative transfer model to fit the salient characteristics of the DUDE’s 13CO and 12CO emission out to a radius of 8″ (3200 au) with a flared disk of mass 1.7 × 10−3 M ⊙, whose expansion velocity increases very rapidly with the radius inside a central region of size ∼200 au, and then more slowly outside it, from 9.5 to 11.5 km s−1. The DUDE’s underlying density decreases radially, interspersed with local increases that represent the observationally well-characterized innermost three rings.

Statistical Properties of the Nebular Spectra of 103 Stripped-envelope Core-collapse Supernovae*

Abstract We present an analysis of the nebular spectra of 103 stripped-envelope (SE) supernovae (SNe) collected from the literature and observed with the Subaru Telescope from 2002 to 2012, focusing on [O i] λλ6300, 6363. The line profile and width of [O i] are employed to infer the ejecta geometry and the expansion velocity of the inner core; these two measurements are then compared with the SN subtypes, and further with the [O i]/[Ca ii] ratio, which is used as an indicator of the progenitor CO core mass. Based on the best-fit results of the [O i] profile, the objects are classified into different morphological groups, and we conclude that the deviation from spherical symmetry is a common feature for all types of SESNe. There is a hint (at the ∼1σ level) that the distributions of the line profile fractions are different between canonical SESNe and broad-line SNe Ic. A correlation between [O i] width and [O i]/[Ca ii] is discerned, indicating that the oxygen-rich material tends to expand faster for objects with a more massive CO core. Such a correlation can be utilized to constrain the relation between the progenitor mass and the kinetic energy of the explosion. Further, when [O i]/[Ca ii] increases, the fraction of objects with Gaussian [O i] profile increases, while those with double-peaked profile decreases. This phenomenon connects ejecta geometry and the progenitor CO core mass.