Outflow Velocity Research Articles

Transient obscuration event captured in NGC 3227

The relationship between warm absorber (WA) outflows of active galactic nuclei and nuclear obscuration activities caused by optically thick clouds (obscurers) crossing the line of sight is still unclear. NGC 3227 is a suitable target for studying the properties of both WAs and obscurers because it matches the following selection criteria: WAs in both ultraviolet (UV) and X-rays, suitably variable, bright in UV and X-rays, and adequate archival spectra for making comparisons with the obscured spectra. In the aim of investigating WAs and obscurers of NGC 3227 in detail, we used a broadband spectral-energy-distribution model that is built in findings of the first paper in our series together with the photoionization code of SPEX software to fit the archival observational data taken by XMM-Newton and NuSTAR in 2006 and 2016. Using unobscured observations, we find four WA components with different ionization states (log ξ [erg cm s−1] ∼ −1.0, 2.0, 2.5, 3.0). The highest-ionization WA component has a much higher hydrogen column density (∼1022 cm−2) than the other three components (∼1021 cm−2). The outflow velocities of these WAs range from 100 to 1300 km s−1, and show a positive correlation with the ionization parameter. These WA components are estimated to be distributed from the outer region of the broad line region (BLR) to the narrow line region. It is worth noting that we find an X-ray obscuration event in the beginning of the 2006 observation, which was missed by previous studies. We find that it can be explained by a single obscurer component. We also study the previously published obscuration event captured in one observation in 2016, which needs two obscurer components to fit the spectrum. A high-ionization obscurer component (log ξ ∼ 2.80; covering factor Cf ∼ 30%) only appears in the 2016 observation, which has a high column density (∼1023 cm−2). A low-ionization obscurer component (log ξ ∼ 1.0 − 1.9; Cf ∼ 20%−50%) exists in both 2006 and 2016 observations, which has a lower column density (∼1022 cm−2). These obscurer components are estimated to reside within the BLR by their crossing time of transverse motions. The obscurers of NGC 3227 are closer to the center and have larger number densities than the WAs, which indicate that the WAs and obscurers might have different origins.

Repeating Gas Ejection Events from Comet 45P/Honda–Mrkos–Pajdušáková

Abstract Studying materials released from Jupiter-family comets (JFCs)—as seen in their inner comae, the envelope of gas and dust that forms as the comet approaches the Sun—improves the understanding of their origin and evolutionary history. As part of a coordinated, multiwavelength observing campaign, we observed comet 45P/Honda–Mrkos–Pajdušáková during its close approach to Earth in 2017 February. Narrowband observations were taken using the Bok 90″ telescope at Kitt Peak National Observatory on February 16 and 17 UT, revealing gas and dust structures. We observed different jet directions for different volatile species, implying source region heterogeneity, consistent with other ground-based and in situ observations of other comet nuclei. A repeating feature visible in CN and C2 images on February 16 was also observed on February 17 with an interval of 7.6 ± 0.1 hr, consistent with the rotation period of the comet derived from Arecibo Observatory radar observations. The repeating feature’s projected gas velocity away from the nucleus is 0.8 km s−1, with an outflow velocity of 0.5 km s−1. A bright compact spot adjacent to the nucleus provides a lower limit of the amount of material released in one cycle of ∼9.2 kg, depending on composition—a quantity small enough to be produced by repeated exposure of nucleus ices to sunlight. This repeating CN jet, forming within 400 km of the nucleus, may be typical of inner-coma behavior in JFCs; however, similar features could be obscured by other processes and daughter product species when viewed from distances further than the scale length of CN molecules.

The Dipolar Solar Minimum Corona

The large-scale configuration of the UV solar corona at the minimum activity between solar cycles 22 and 23 is explored in this paper. Exploiting a large sample of spectroscopic observations acquired by the Ultraviolet Coronagraph Spectrometer aboard the Solar and Heliospheric Observatory in the two-year period of 1996–1997, this work provides the first-ever monochromatic O vi 1032 Å image of the extended corona, and the first-ever two-dimensional maps of the kinetic temperature of oxygen ions and the O vi1037/1032 Å doublet intensity ratio (a proxy for the outflow velocity of the oxygen component of the solar wind), statistically representative of solar minimum conditions. A clear dipolar magnetic structure, both equator- and axis-symmetric, is distinctly shown to shape the solar minimum corona, both in UV emission and in temperature and expansion rate. This statistical approach allows for robust establishment of the key role played by the magnetic field divergence in modulating the speed and temperature of the coronal flows, and identification of the coronal sources of the fast and slow solar wind.

First light observations of the solar wind in the outer corona with the Metis coronagraph

In this work, we present an investigation of the wind in the solar corona that has been initiated by observations of the resonantly scattered ultraviolet emission of the coronal plasma obtained with UVCS-SOHO, designed to measure the wind outflow speed by applying Doppler dimming diagnostics. Metis on Solar Orbiter complements the UVCS spectroscopic observations that were performed during solar activity cycle 23 by simultaneously imaging the polarized visible light and the H I Lyman-α corona in order to obtain high spatial and temporal resolution maps of the outward velocity of the continuously expanding solar atmosphere. The Metis observations, taken on May 15, 2020, provide the first H I Lyman-α images of the extended corona and the first instantaneous map of the speed of the coronal plasma outflows during the minimum of solar activity and allow us to identify the layer where the slow wind flow is observed. The polarized visible light (580–640 nm) and the ultraviolet H I Lyα (121.6 nm) coronal emissions, obtained with the two Metis channels, were combined in order to measure the dimming of the UV emission relative to a static corona. This effect is caused by the outward motion of the coronal plasma along the direction of incidence of the chromospheric photons on the coronal neutral hydrogen. The plasma outflow velocity was then derived as a function of the measured Doppler dimming. The static corona UV emission was simulated on the basis of the plasma electron density inferred from the polarized visible light. This study leads to the identification, in the velocity maps of the solar corona, of the high-density layer about ±10° wide, centered on the extension of a quiet equatorial streamer present at the east limb – the coronal origin of the heliospheric current sheet – where the slowest wind flows at about 160 ± 18 km s−1 from 4 R⊙ to 6 R⊙. Beyond the boundaries of the high-density layer, the wind velocity rapidly increases, marking the transition between slow and fast wind in the corona.

Effects of the Solar Wind Dynamic Pressure on the Martian Topside Ion Distribution: Implications on the Variability of Bulk Ion Outflow

Abstract With the aid of the ion densities measured by the Neutral Gas and Ion Mass Spectrometer and the solar wind dynamic pressures measured by the Solar Wind Ion Analyzer on board the Mars Atmosphere and Volatile EvolutioN, we investigate the modulation of a sequence of ion species in the Martian topside ionosphere by the upstream solar wind condition. Almost all ion species, except for CO 2 + and OCOH+, are very sensitive to the variation of the solar wind condition, and their densities decrease with increasing solar wind dynamic pressure. The response of the topside ion distribution to the variation of the solar wind condition is also found to be remarkably related to the magnetic field orientation, in that the solar wind modulation occurs mainly over regions with near-horizontal field lines. These observations imply substantially enhanced outflow velocities for all ion species under high solar wind dynamic pressures when the ambient magnetic fields are near-horizontal.

Outflows from GRB hosts are ubiquitous: Kinematics of z < 0.3 GRB-SN hosts resolved with FLAMES

The hosts of long duration gamma-ray bursts (GRBs) are predominantly starburst galaxies at subsolar metallicity. At redshifts z < 1, this implies that most of them are low-mass galaxies similar to the populations of blue compact dwarfs and dwarf irregulars. What triggers the massive star-formation needed for producing a GRB progenitor is still largely unknown, as are the resolved gas properties and kinematics of these galaxies and their formation history. Here we present a sample of six spatially resolved GRB hosts at z < 0.3 observed with 3D spectroscopy at high spectral resolution (R = 8000−13 000) using FLAMES/VLT. We analyzed the resolved gas kinematics of the full sample and the abundances in a subsample with strong enough emission lines. Only two galaxies show a regular disk-like rotation field, another two are dispersion-dominated, and the remaining ones have two narrow emission components associated with different parts of the galaxy but no regular rotation field, which might indicate a recent merger. All galaxies show evidence for broad components underlying the main emission peak with σ of 50−110 km s−1. This broad component is more metal-rich than the narrow components, it is blueshifted in most cases, and it follows a different velocity structure. We find a weak correlation between the star-formation rate and the width of the broad component, its flux compared to the narrow component, and the maximum outflow velocity of the gas, but we do not find any correlation with the star-formation density, metallicity or stellar mass. We hence associate this broad component with a metal-rich outflow from star-forming regions in the host. The GRB is not located in the brightest region of the host, but is always associated with some star-forming region showing a clear wind component. Our study shows the great potential of 3D spectroscopy to study the star-formation processes and history in galaxies hosting extreme transients, the need for high signal-to-noise, and the perils using unresolved or only partially resolved data for these kinds of studies.

ALMA Imaging of a Galactic Molecular Outflow in NGC 4945

Abstract We present the ALMA detection of molecular outflowing gas in the central regions of NGC 4945, one of the nearest starbursts and also one of the nearest hosts of an active galactic nucleus (AGN). We detect four outflow plumes in CO J = 3 − 2 at ∼0.″3 resolution that appear to correspond to molecular gas located near the edges of the known ionized outflow cone and its (unobserved) counterpart behind the disk. The fastest and brightest of these plumes has emission reaching observed line-of-sight projected velocities of over 450 km s−1 beyond systemic, equivalent to an estimated physical outflow velocity v ≳ 600 km s−1 for the fastest emission. Most of these plumes have corresponding emission in HCN or HCO+ J = 4 − 3. We discuss a kinematic model for the outflow emission where the molecular gas has the geometry of the ionized gas cone and shares the rotation velocity of the galaxy when ejected. We use this model to explain the velocities we observe, constrain the physical speed of the ejected material, and account for the fraction of outflowing gas that is not detected due to confusion with the galaxy disk. We estimate a total molecular mass outflow rate M ̇ mol ∼ 20 M ⊙ yr−1 flowing through a surface within 100 pc of the disk midplane, likely driven by a combination of the central starburst and AGN.

Massive Molecular Outflow and 100 kpc Extended Cold Halo Gas in the Enormous Lyα Nebula of QSO 1228+3128

Abstract The link between the circumgalactic medium (CGM) and the stellar growth of massive galaxies at high-z depends on the properties of the widespread cold molecular gas. As part of the SUPERCOLD-CGM survey (Survey of Protocluster ELANe Revealing CO/[C i] in the Lyα-Detected CGM), we present the radio-loud QSO Q1228+3128 at z = 2.2218, which is embedded in an enormous Lyα nebula. ALMA+ACA observations of CO(4–3) reveal both a massive molecular outflow, and a more extended molecular gas reservoir across ∼100 kpc in the CGM, each containing a mass of M H2 ∼ 4–5 × 1010 M ⊙. The outflow and molecular CGM are aligned spatially, along the direction of an inner radio jet. After reanalysis of Lyα data of Q1228+3128 from the Keck Cosmic Web Imager, we found that the velocity of the extended CO agrees with the redshift derived from the Lyα nebula and the bulk velocity of the massive outflow. We propose a scenario where the radio source in Q1228+3128 is driving the molecular outflow and perhaps also enriching or cooling the CGM. In addition, we found that the extended CO emission is nearly perpendicular to the extended Lyα nebula spatially, indicating that the two gas phases are not well mixed, and possibly even represent different phenomena (e.g., outflow versus infall). Our results provide crucial evidence in support of predicted baryonic recycling processes that drive the early evolution of massive galaxies.

SOFIA upGREAT/FIFI-LS Emission-line Observations of Betelgeuse during the Great Dimming of 2019/2020

Abstract We report NASA-DLR SOFIA upGREAT circumstellar [O i] 63.2 μm and [C ii] 157.7 μm emission profiles and FIFI-LS [O i] 63.2 μm, [O i] 145.5 μm, and [C ii] 157.7 μm fluxes obtained shortly after Betelgeuse’s 2019/2020 Great Dimming event. Haas et al. noted a potential correlation between the [O i] 63.2 μm flux and V magnitude based on three Kuiper Airborne Observatory observations made with the CGS and FIFI instruments. The FIFI observation was obtained when V ≃ 0.88 and revealed a 3σ non-detection at a quarter of the previous CGS flux measurement made when V ≃ 0.35. A potential explanation could be a change in dust-gas drag heating by circumstellar silicates caused by variations in the photospheric radiation field. SOFIA observations provide a unique test of this correlation because the V-band brightness went to its lowest value on record, V ≃ 1.61, with the SOFIA observations being made when V FIFI−LS ≃ 1.51 and V upGREAT ≃ 1.36. The upGREAT spectra show a [O i] 63.2 μm flux larger than previous space observatory measurements obtained when V ≃ 0.58. The profile is consistent with formation in the slower, more turbulent inner S1 outflow, while the [C ii] 157.7 μm profile is consistent with formation farther out in the faster S2 outflow. Modeling of dust-gas drag heating, combined with 25 yr of Wing three-filter and V photometry, reveals that it is unlikely that the S1 circumstellar envelope and [O i] 63.2 μm fluxes are dominated by the dust-gas drag heating and that another heating source is also active. The [O i] 63.2 μm profile is hard to reconcile with existing outflow velocity models.

Abstract 10027: Pulsatile Load, Rather Than Cardiac Power Output, for the Right Ventricle Determines the Prognosis in Heart Failure Patients

Background: Although cardiac power output (CPO), a parameter of cardiac performance, for the left ventricle (LV) is reported to be a powerful prognostic indicator in heart failure (HF), significance of the right ventricular (RV) CPO in HF has not been elucidated. On the other hand, RV pulsatile load stands for one of the prognostic markers in HF. We thus investigated the relationship of the RV CPO and pulsatile load to the outcome in HF. Methods: Right heart catheterization and echocardiography were performed in 231 HF patients (62±16 years, LV ejection fraction 42±18%). Invasive and noninvasive CPOs were calculated from mean systemic or pulmonary arterial pressures and cardiac output for the LV and RV. LV CPO was then corrected by LV mass (LV CPO/M). Pulmonary artery compliance (PAC) and the ratio of acceleration time to ejection time (AcT/ET) of the RV outflow velocity were used as parameters of RV pulsatile load. Cardiac death, HF hospitalization, ventricular arrhythmia and LVAD implantation after the examination were recorded. Results: Noninvasive CPOs were moderately correlated with invasive ones (LV: R=0.73, RV: R=0.58, P <0.001 for both). During a median follow-up period of 441 days, cardiac events occurred in 57 patients. Using the cut-off of median values, lower LV CPO/M was associated with higher event rates, however, RV CPO did not discriminate the risk of future cardiac events. In contrast, higher RV pulsatile load was associated with higher event rates regardless of the level of LV CPO/M ( Figure ). In multivariable Cox proportional hazard analyses, echocardiographic LV CPO/M and AcT/ET both determined cardiac events independently of age, NYHA classification, LV ejection fraction and plasma brain natriuretic peptide levels. Conclusion: Pulsatile load, rather than CPO, for the RV was associated with cardiac events in HF. Furthermore, combination of echocardiographic LV CPO/M and AcT/ET could become a novel noninvasive prognostic indicator in HF patients.

Abstract 9220: Employing a Convolutional Neural Network Facilitates Unsupervised Clustering of Aortic Outflow Velocity Profiles from Patients With Severe Aortic Stenosis

Introduction: The aortic outflow velocity profile is key to diagnose severe aortic stenosis (AS), and its shape reflects both aortic valve obstruction and left ventricular contractility. Hypothesis: Hypothesizing that aortic outflow velocity profiles contain more valuable information than can be captured by the human eye, features of the complex geometry of Doppler tracings were extracted by a convolutional neural network (CNN) pre-trained on big data (transfer learning). Methods: After pre-training a CNN (VGG-16) on a large data set (ImageNet data set; 14 million images belonging to 1,000 classes), the convolutional part was employed to transform Doppler tracings to 1D arrays. Principal component analysis (PCA) and k-means clustering of those 1D arrays were performed, and association between cluster and 2-year all-cause mortality was hereinafter assessed. Among 366 eligible patients with pre-procedural echocardiography and right heart catheterization prior to transcatheter aortic valve replacement (TAVR) for severe AS, good quality Doppler tracings from 101 patients were analyzed. Results: Among 101 patients (mean age: 79.3 ± 6.78 years; 49 [48.5%] women), estimated 2-year survival was 83.0% (95% CI: 75.1-91.7%). The convolutional part of the pre-trained VGG-16 model in conjunction with PCA and k-means clustering distinguished 2 shapes of aortic outflow velocity profiles. Kaplan-Meier analysis revealed that mortality in patients from cluster 2 (n = 40 [39.6%]) was significantly increased (HR for 2-year mortality: 3 [95% CI: 1-8.9]). Apart from reduced cardiac output and mean aortic valve gradient (AVG mean ), patients from cluster 2 were also characterized by signs of pulmonary hypertension, impaired right ventricular function and right atrial enlargement. Conventional dichotomization according to AVG mean confirmed that patients with AVG mean < 40 mmHg (n = 54 [53.5%]) decease earlier, but no statistical significance was reached (HR for 2-year mortality: 1.8 [95% CI: 0.59-5.2]). Conclusions: This is a proof-of-principle that transfer learning aids in agnostic interpretation of aortic outflow velocity profiles, thereby holding the promise to refine prognostic resolution for survival after TAVR.

Optical spectroscopic observations of a symbiotic star MWC 560 in the mass accumulation phase

Abstract There are about a dozen symbiotic stars known to produce high-velocity jets during outbursts. MWC 560 (V694 Mon) is a symbiotic star that seems to show a permanent jet. After showing an unexpected brightening in 2018 November, it has continued to brighten until 2021 and is currently in the brightest state ever. We have been conducting long-term high-dispersion spectroscopic monitoring of this object since 2016 March. An emission wing with vFWHM ≈ 700 km s−1 in the hydrogen Balmer line at an unexpected brightening event in 2018 was reported by Ando et al. (2021, PASJ, 73, L1). In subsequent continuous observations, this emission wing was no longer seen on 2019 February 6. The absorption lines seen in the hydrogen Balmer lines are gradually deepening and spreading to the slower side of the velocity, and the outflow velocity is becoming slower. The expanding component generated by the outburst was initially observed in the emission wing just after the 2018 outburst, got gradually cooler, and was observed in the absorption line after 2019.

Left atrial appendage shape impacts on the left atrial flow hemodynamics: A numerical hypothesis generating study on two cases

Background and objectivesThe left atrial appendage (LAA) is the most common region for thrombus formation in atrial fibrillation (AF). Morphological parameters such as shape, size, and LAA volume can cause insufficient effectiveness of available therapeutic options. This study aimed to examine blood flow inside LAA and its removal effects. Computational fluid dynamic (CFD) simulations were carried out on two patients with different morphologies. MethodsTwo patients' CT was used to reconstruct the 3D geometries of the left atrium (LA) and left atrial appendage (LAA). Then, the geometries were refined in the mentioned software, and the LAA in some models was removed. Next, in generated 3D volume mesh, sinus rhythm (SR) and atrial fibrillation (AF) outflow velocity were imposed at the mitral valve as boundary conditions. Finally, CFD simulation was conducted to analyzing blood flow within LA with/without LA. ResultsThe results confirmed that velocity and vorticity decreased under AF conditions inside the LA domain for both patients. However, removing LAA may cause unpredictable consequences, due to different shape and volume of LAA. LAA removal had insignificant effects on velocity and vorticity within LA in SR-mitral outflow. However, removing LAA increased the blood flow rate by 9.15% and vorticity by 7.27% for patient one under AF rhythm (SR)-outflow. In contrast, for patient two, LAA removal in both AF and SR decreased velocity and vorticity within the LA domain. In SR-mitral outflow, velocity dropped by 18.8 %, and vorticity by 13.2%. Also, under AF velocity and vorticity decreased by 23.33% and 18.6% respectively. Meanwhile, the results indicated that the vorticity magnitude increased inside the LAA under AF associated with the risk of thrombus formation, particularly for patient one under AF. The distal part of LAA in both patients was the most common region for blood stasis because of the lowest velocity magnitude. ConclusionOverall, the morphology of LAA could be the critical parameter to determine the possibility of thrombosis formation, particularly under AF conditions. High volume, low blood flow velocity and two-lobe-appendage are more likely to have blood stasis. Furthermore, the morphology difference can affect the LAA removal result and make it more complicated. So, it could be challenging to generalize LAA removal as a therapeutic option for different patients. The implication of this CFD observation needs more investigation.

Mass-loading and non-spherical divergence in hot galactic winds: implications for X-ray observations

ABSTRACT Cool clouds are expected to be destroyed and incorporated into hot supernova-driven galactic winds. The mass-loading of a wind by the cool medium modifies the bulk velocity, temperature, density, entropy, and abundance profiles of the hot phase relative to an unmass-loaded outflow. We provide general equations and limits for this physics that can be used to infer the rate of cool gas entrainment from X-ray observations, accounting for non-spherical expansion. In general, mass-loading flattens the density and temperature profiles, decreases the velocity and increases the entropy if the Mach number is above a critical value. We first apply this model to a recent high-resolution galactic outflow simulation where the mass-loading can be directly inferred. We show that the temperature, entropy, and composition profiles are well matched, providing evidence that this physics sets the bulk hot gas profiles. We then model the diffuse X-ray emission from the local starburst M82. The non-spherical (more cylindrical) outflow geometry is directly taken from the observed X-ray surface brightness profile. These models imply a total mass-loading rate that is about equal to that injected in the starburst ≃ 10 M⊙ yr−1, and they predict an asymptotic hot wind velocity of $\sim 1000\, {\rm km \ s^{-1}}$, which is ∼1.5–2 times smaller than previous predictions. We also show how the observed entropy profile can be used to constrain the outflow velocity, making predictions for future missions like XRISM. We argue that the observed X-ray limb brightening may be explained by mass-loading at the outflow’s edges.

Affecting mechanism of partition boards on hydrogen dispersion in confined space with symmetrical lateral openings

Dispersion and natural ventilation of hydrogen leaked at the floor center of a confined space are analytically and numerically studied in this contribution. Two symmetrical openings located atop two opposite walls and several sets of partition boards with varying heights, 0–1.0 m with 0.2 m increment, mounted under the ceiling were designed to examine their effects on ventilation efficiency. Without partition boards, a semi-analytical model combining a modified buoyancy ceiling jet theory and zone model was established to predict the key parameters at steady stage. The analytical predictions were compared with numerical results. 15 monitors were predesigned at an opening and the channels separated by the partition boards to collect the velocity and hydrogen concentration evolutions. The results show that the existence of the partition boards significantly promotes the ventilation efficiency by decreasing the hydrogen concentration in the confined space, constraining the flammable regime into a smaller volume, and increasing both the inflow and outflow velocities. Better ventilation efficiency is achieved by higher partition boards until a critical height after which no appreciable improvement can be gained. Applying the partition boards considerably shortens the developing stage of the dispersion process and intensifies the turbulence of outflow. Conclusions obtained in current work may benefit the natural ventilation system and building structure design for hydrogen safety in practical applications.

The angular momentum structure of cosmic ray driven galactic outflows triggered by stream accretion

Abstract We investigate the impact of gas accretion in streams on the evolution of disc galaxies, using magneto-hydrodynamic simulations including advection and anisotropic diffusion of cosmic rays generated by supernovae as the only source of feedback. Stream accretion has been suggested as an important galaxy growth mechanism in cosmological simulations and we vary their orientation and angular momentum in idealised setups. We find that accretion streams trigger the formation of galactic rings and enhanced star formation. The star formation rates and consequently the cosmic ray driven outflow rates are higher for low angular momentum accretion streams, which also result in more compact, lower angular momentum discs. The cosmic ray generated outflows show a characteristic structure. At low outflow velocities (<50 km s−1) the angular momentum distribution is similar to the disk and the gas is in a fountain flow. Gas at high outflow velocities (>200 km s−1), penetrating deep into the halo, has close to zero angular momentum, and originates from the centre of the galaxies. As the mass loading factors of the cosmic ray driven outflows are of order unity and higher, we conclude that this process is important for the removal of low angular momentum gas from evolving disk galaxies and the transport of, potentially metal enriched, material from galactic centres far into the galactic haloes.

Radio Observations of an Ordinary Outflow from the Tidal Disruption Event AT2019dsg

Abstract We present detailed radio observations of the tidal disruption event (TDE) AT2019dsg, obtained with the Karl G. Jansky Very Large Array (VLA) and the Atacama Large Millimeter/submillimeter Array (ALMA), and spanning 55–560 days post disruption. We find that the peak brightness of the radio emission increases until ∼200 days and subsequently begins to decrease steadily. Using a standard equipartition analysis, including the effects of synchrotron cooling as determined by the joint VLA–ALMA spectral energy distributions, we find that the outflow powering the radio emission is in roughly free expansion with a velocity of ≈0.07 c, while its kinetic energy increases by a factor of about 5 from 55 to 200 days and plateaus at ≈4.4 × 1048 erg thereafter. The ambient density traced by the outflow declines as radius ≈R −1.7 on a scale of ≈(1–4) × 1016 cm (≈6300–25,000 R s ), followed by a steeper decline to ≈7 × 1016 cm (≈44,000 R s ). Allowing for a collimated geometry, we find that to reach even mildly relativistic velocities (Γ = 2) the outflow requires an opening angle of θ j ≈ 2°, which is narrow even by the standards of gamma-ray burst jets; a truly relativistic outflow requires an unphysically narrow jet. The outflow velocity and kinetic energy in AT2019dsg are typical of previous non-relativistic TDEs, and comparable to those from type Ib/c supernovae, raising doubts about the claimed association with a high-energy neutrino event.

The Effect of Parameter Variation on Spiral Flow Inducing Cannula Performances

Spiral flow-inducing cannula has been shown in previous research to exhibit a considerable effect on flow hemodynamic. However, there is still room for improvement. In this study, several design variations were tested to determine which variants were the best in terms of flow reduction. Computational Fluid Dynamics (CFD) software was used to simulate flow within a spiral flow-inducing cannula with several variations from chamber width and angle differences. The variants were compared against each other by using several flow parameters and a selection method was employed to determine which model was the best. It was found that a variant that has the widest chamber (14 mm) and biggest angle opening (70°) from the chamber to the cannula tube was the best in several parameters, and as such was chosen as the best variant. When compared with the standard straight cannula, the reduction in flow output was recorded to be 30% which is deemed significantly. In conclusion, spiral flow cannula recorded better hemodynamic effects with lower outflow velocity and wall shear stress value.

Numerical investigation of air curtain jet effect on the upper layer temperature evolution of a compartment fire and its transition

• Air curtain effect on the compartment fire evolution investigated. • Inside temperature obtained for different opening size and air curtain conditions. • Upper layer temperature transition due to the presence of air curtain observed. • Correlation of the critical heat release rate with the new Froude numer proposed. This paper investigates the upper layer temperature evolution of a compartment fire and its transition behavior with air curtain jet conditions. Based on FDS simulation, a series of full scale models with a fire compartment of 4 m × 4 m × 4 m are set up. During simulation, different heat release rates, opening sizes and air curtain jet velocities are considered, while the upper layer temperature evolution inside the compartment is recorded by thermocouple trees. It could be seen from the results that the evolution of upper layer temperature could be distinguished into the rapid growth regime and the moderate developing regime, indicating the combustion transition inside the compartment. The normalized critical heat release rates of such transition are all around 0.6 for the compartment fire cases without air curtain jet condition, however the presence of air curtain would change the compartment flows resulting in the difference of the temperature inside and the critical condition of the transition. A new Froude Number v jet gH in relation to the air curtain jet velocity and the characteristic outflow velocity is defined, and finally a linear correlation of the normalized critical heat release rate with Froude Number v jet gH is well proposed.

DEATHSTAR: nearby AGB stars with the Atacama Compact Array

Aims. We aim to constrain the sizes of, and investigate deviations from spherical symmetry in, the CO circumstellar envelopes (CSEs) of 16 S-type stars, along with an additional 7 and 4 CSEs of C-type and M-type AGB stars, respectively. Methods. We map the emission from the CO J = 2–1 and 3–2 lines observed with the Atacama Compact Array (ACA) and its total power (TP) antennas, and fit with a Gaussian distribution in the uv- and image planes for ACA-only and TP observations, respectively. The major axis of the fitted Gaussian for the CO(2–1) line data gives a first estimate of the size of the CO-line-emitting CSE. We investigate possible signs of deviation from spherical symmetry by analysing the line profiles and the minor-to-major axis ratio obtained from visibility fitting, and by investigating the deconvolved images. Results. The sizes of the CO-line-emitting CSEs of low-mass-loss-rate (low-MLR) S-type stars fall between the sizes of the CSEs of C-stars, which are larger, and those of M-stars, which are smaller, as expected because of the differences in their respective CO abundances and the dependence of the photodissociation rate on this quantity. The sizes of the low-MLR S-type stars show no dependence on circumstellar density, as measured by the ratio of the MLR to terminal outflow velocity, irrespective of variability type. The density dependence steepens for S-stars with higher MLRs. While the CO(2–1) brightness distribution size of the low-density S-stars is in general smaller than the predicted photodissociation radius (assuming the standard interstellar radiation field), the measured size of a few of the high-density sources is of the same order as the expected photodissociation radius. Furthermore, our results show that the CO CSEs of most of the S-stars in our sample are consistent with a spherically symmetric and smooth outflow. For some of the sources, clear and prominent asymmetric features are observed which are indicative of intrinsic circumstellar anisotropy. Conclusions. As the majority of the S-type CSEs of the stars in our sample are consistent with a spherical geometry, the CO envelope sizes obtained in this paper will be used to constrain detailed radiative transfer modelling to directly determine more accurate MLR estimates for the stars in our sample. For several of our sources that present signs of deviation from spherical symmetry, further high-resolution observations would be necessary to investigate the nature of, and the physical processes behind, these asymmetrical structures. This will provide further insight into the mass-loss process and its related chemistry in S-type AGB stars.