Expansion Velocity Research Articles

Three-component modelling of O-rich AGB star winds

Stellar winds of cool and pulsating asymptotic giant branch (AGB) stars enrich the interstellar medium with large amounts of processed elements and various types of dust. We present the first study on the influence of gas-to-dust drift on ab initio simulations of stellar winds of M-type stars driven by radiation pressure on forsterite particles. Our study is based on our radiation hydrodynamic model code T-800 that includes frequency-dependent radiative transfer, dust extinction based on Mie scattering, grain growth and ablation, gas-to-dust drift using one mean grain size, a piston that simulates stellar pulsations, and an accurate high spatial resolution numerical scheme. To enable this study, we calculated new gas opacities based on the EXOMOL database, and we extended the model code to handle the formation of minerals that may form in M-type stars. We determine the effects of drift by comparing drift models to our new and extant non-drift models. Three out of four new drift models show high drift velocities, 87–310 km s−1. Our new drift model mass-loss rates are 1.7–13 per cent of the corresponding values of our non-drift models, but compared to the results of two extant non-drift models that use the same stellar parameters, these same values are 0.33–1.5 per cent. Meanwhile, a comparison of other properties such as the expansion velocity and grain size show similar values. Our results, which are based on single-component forsterite particles, show that the inclusion of gas-to-drift is of fundamental importance in stellar wind models driven by such transparent grains. Assuming that the drift velocity is insignificant, properties such as the mass-loss rate may be off from more realistic values by a factor of 50 or more.

SN 2023ixf—Temporal Development of Hα Emission

I present a series of spectra of the Type II supernova SN 2023ixf in M101 covering a temporal period of 6 weeks. The latest spectra show a prominent Hα P-Cygni profile with an expansion velocity of 7100 km s−1. In addition to an expanding gas shell, evidence of a possible additional absorption was found. This could be interpreted as an asymmetrical feature in the expanding material of the supernova.

Quantifying the energetics of molecular superbubbles in PHANGS galaxies

Context. Star formation and stellar feedback are interlinked processes that redistribute energy, turbulence, and material throughout galaxies. Because young and massive stars form in spatially clustered environments, they create pockets of expanding gas termed superbubbles, which retain information about the physical processes that drive them. As these processes play a critical role in shaping galaxy discs and regulating the baryon cycle, measuring the properties of superbubbles provides important input for galaxy evolution models. Aims. With the wide coverage and high angular resolution (∼50–150 pc) of the PHANGS–ALMA 12CO (J = 2−1) survey, we can now resolve, identify and characterise a statistically representative number of superbubbles using molecular gas in nearby galaxies. Methods. We identify superbubbles by requiring spatial correspondence between shells in CO with stellar populations identified in PHANGS–HST. Then, by combining the properties of the stellar populations with the CO, we quantify the energetics of the stars and constrain feedback models. We visually find 325 cavities across 18 PHANGS–ALMA galaxies, 88 of which have clear superbubble signatures (unbroken shells, central clusters, kinematic signatures of expansion). We measure their radii and expansion velocities using CO (2–1) to dynamically derive their ages and the mechanical power driving the bubbles, which we use to compute the expected properties of the parent stellar populations driving the bubbles. Results. We find consistency between the predicted and derived stellar ages and masses of the stellar populations if we use a supernova (SN) model that injects energy with a coupling efficiency of ∼10%. Not only does this confirm that molecular gas accurately traces superbubble properties, but it also provides key observational constraints for superbubble models. We also find evidence that the bubbles are sweeping up gas as they expand, and speculate that these sites have the potential to host new generations of stars. Conclusions. This work demonstrates that molecular superbubbles provide novel quantitative constraints on SNe feedback efficiencies and gas clearing times, and represent a promising environment to search for the propagation of star formation, all of which are needed to understand what sets the observed star formation rates in galaxies.

Influence of pressure and pulse energy on the expansion dynamics of nanoparticle-enhanced laser produced plasma

In the present work, we have studied the influence of pressure and pulse energy on the expansion dynamics of nanoparticle-enhanced laser produced plasma (NELPP) for two different metals, copper and aluminum. The targets were ablated using a Q-switched Nd:YAG laser operating at its primary wavelength of 1064 nm. The plasma imaging was recorded using the fast-gated ICCD camera. Although spectroscopic investigation of signal enhancement of emission line intensities in presence of nanoparticles (NPs), nanoparticle enhanced LIBS (NELIBS), has been performed extensively, expansion dynamics for NELIBS is not yet studied. We have carried out a detailed investigation of the plume propagation of NELPP for different pulse energies and ambient pressures. Temporal evolution of the distance of propagation of the plume front at different laser fluences and pressures shows a good agreement with the existing theoretical models. By comparing different plume propagation parameters, such as diameter, aspect ratio and expansion velocity, we have shown that the NELPP plume shows similar behavior as of LPP and its evolution can be explained with the existing models. Hence NPs, though influence the ablation process, do not alter the overall plume dynamics during the course of plasma evolution as observed for the two metals.

Three-phase contact formation between an air bubble and solid surfaces with different hydrophobicity degrees in liquid

Interactions between gas bubbles and solid particles are crucial in numerous industrial processes, including froth flotation, in which particle-bubble attachment plays a vital role. The process efficiency depends on differences in the surface wettability (i.e., hydrophobicity, expressed by the contact angle) of separated particles. This study aimed to investigate the influence of surface hydrophobicity and zeta potential on the formation of a three-phase contact (TPC) between a single air bubble and planar glass surfaces. Different degrees of hydrophobicity were achieved by esterification with a range of alcohols and time. The interaction between the bubble and surface was monitored using a high-speed camera with a time resolution of 1 ms, allowing for measurements of the time of thin liquid film drainage, time and diameter of TPC formation, TPC line expansion velocity, and dynamic contact angles. The observations suggest that TPC formation occurs when the solid surface has a sufficient degree of hydrophobicity (critical contact angle) and is dependent on the differences in zeta potential values between the air bubble and the solid surface in water. When both surfaces are negatively charged, the limiting value of the water contact angle is ca. 35°, whereas for oppositely charged surfaces, the value slightly decreases to ca. 31°. The results show that increasing surface hydrophobicity enhances the bubble adhesion effectiveness by increasing both the propagation velocity of the TPC perimeter and its size (measured by the diameter of the formed TPC). The article also discusses the mechanism of bubble-solid adhesion in relation to the hydrophobicity and zeta potential of the solid surface based on the obtained results.

The motion and distribution characteristics of cathode spot and its influence on plasma parameters

Cathode spots and plasma are the key factors affecting the breaking capacity of vacuum switches. In order to analyze the motion and distribution characteristics of cathode spot and its influence on plasmas, the experiments of cathode spot observation and plasma diagnosis were conducted in this paper. The cathode spot images were captured by ultra high-speed camera. Based on the continuous spectrum theory, the electron density was measured by the colorimetric thermometry. According to the cathode spot images and method of cathode spot recognition, the parameters of cathode spots including number, size and current were obtained. The changes of these parameters with arcing time and current amplitude were analyzed. The dependence of the cathode spots average size on spot current and spot expansion velocity was discussed. The axial and radial distributions of electron density were obtained which is related to the cathode spot distribution on the cathode surface. The significant fluctuation in the radial direction for electron density was observed.

Hα kinematics of superbubbles and supernova remnants of the dwarf galaxy NGC 4214

ABSTRACT We analysed the ionized gas kinematics of the dwarf galaxy NGC 4214 using high resolution Fabry–Perot interferometry observations and present a set of narrowband images in the Hα, [S ii] λ6717 Å, [N ii] λ6584 Å, and [O iii] λ5007 Å emission lines. The high-resolution Fabry–Perot observations of the Hα emission line, allowed us to derive the velocity field, the velocity dispersion σ, and the rotation curve of the galaxy. We also present for the first time, 3D kinematic maps of the complexes NGC 4214-I and NGC 4214-II and analysed the kinematics of the ionized gas of two new superbubbles, as well as the supernova remnants previously detected in this galaxy by other authors, in radio, optical, and X-ray emission. We computed the expansion velocities of the superbubbles and supernova remnants fitting their velocity profiles and obtained their respective physical parameters. We found that the superbubbles have an expansion velocity of ∼50 km s −1, dynamical age about ∼2 Myr and wind luminosity LW of ∼9 × 1038 erg s−1 produced probably by massive stars in OB associations. For supernova remnants, their expansion velocities are between ∼48 and ∼80 km s−1 with ages of about 104 yr and kinetic energy of about 1051 erg assuming they are in the radiative phase of evolution.

Pulsation-induced Spectroscopic Variability of IRAS Z02229+6208

Monitoring of high-resolution spectra in the optical and near-infrared wavelength region was carried out for the early post-AGB stage star IRAS Z02229+6208 with the CARMENES instrument to reveal spectroscopic variability over the pulsation cycle of 154 days. Significant changes are seen in both the intensity and position of carbon-bearing molecular lines. Strong and broad CN red system lines, blueshifted up to 9.4 km s−1 relative to the stellar photosphere, are seen near the light minimum. Near the light maxima, the molecular features are weak and most of them are in emission, e.g., broad emissions in the CN red system (0,0) lines are seen. A site of formation of molecular absorptions and emissions appears to be an extended atmosphere of a cool post-AGB star affected by stellar pulsation. In addition, we observed narrow absorption lines of the C2 Phillips (2, 0), (3, 0) system and the CN red system (2,0), most likely related to the circumstellar envelope produced during the evolution on the asymptotic giant branch (AGB). An expansion velocity of the circumstellar shell was found to be V exp = −11.1 km s−1 relative to the stellar mass center, in agreement with that estimated before from CO lines. The observed spectroscopic variability seems to be typical for pulsating early post-AGB stage stars.

Near-infrared evolution of the equatorial ring of SN 1987A

We used adaptive optics imaging and integral field spectroscopy from the Very Large Telescope, together with images from the Hubble Space Telescope, to study the near-infrared (NIR) evolution of the equatorial ring (ER) of SN 1987A. We studied the NIR flux and morphology over time in order to lay the groundwork for James Webb Space Telescope observations of the system. We also studied the differences in the interacting ring structure and flux between optical, NIR, and other wavelengths, and between line and continuum emission, to constrain the underlying physical processes. For the most part, the evolution is similar in the NIR and optical. The morphology of the ER has been skewed toward the west side (with roughly two-thirds of the NIR emission originating there) since around 2010. A steady decline in the ER flux, broadly similar to the mid-infrared and the optical, has been ongoing since roughly this time as well. The expansion velocity of the ER hotspots in the NIR is fully consistent with the optical. However, continuum emission forms roughly 70% of the NIR luminosity, and has been stronger outside the hotspot-defined extent of the ER (relative to the hotspots themselves) than the optical emission or the NIR line emission since 2012–2013, suggesting a faster-expanding continuum component. We find that this outer NIR emission can have a significant synchrotron contribution. Even if emission from hot dust (~2000 K) is dominant within the ER, the mass of this dust must be vanishingly small (a few times 10−12 M⊙) compared to the total dust mass in the ER (≳10−5 M⊙) to account for the observed HKs flux. The NIR continuum emission, however, expands more slowly than the more diffuse 180-K dust emission that dominates in the MIR, indicating a different source, and the same hot dust component cannot account for the J-band emission.

The Core Starbursts of the Galaxy NGC 3628: Radio Very Long Baseline Interferometry and X-Ray Studies

We present radio very long baseline interferometry (VLBI) and X-ray studies of the starburst galaxy NGC 3628. The VLBI observation at 1.5 GHz reveals seven compact (0.7−7 pc) radio sources in the central ∼250 pc region of NGC 3628. Based on their morphology, high radio-brightness temperatures (105–107 K), and steep radio spectra, none of these seven sources can be associated with active galactic nuclei (AGNs); instead, they can be identified as supernova remnants (SNRs), with three of them appearing consistent with partial shells. Notably, one of them (W2) is likely a nascent radio supernova (SN) and appears to be consistent with the star formation rate of NGC 3628 when assuming a canonical initial mass function. The VLBI observation provides the first precise measurement of the diameter of the radio sources in NGC 3628, which allow us to fit a well-constrained radio surface brightness—diameter (Σ–D) correlation by including the detected SNRs. Furthermore, future VLBI observations can be conducted to measure the expansion velocity of the detected SNRs. In addition to our radio VLBI study, we analyze Chandra and XMM-Newton spectra of NGC 3628. The spectral fitting indicates that the SNR activities could well account for the observed X-ray emissions. Along with the Chandra X-ray image, it further reveals that the X-ray emission is likely maintained by the galactic-scale outflow triggered by SN activities. These results provide strong evidence that SN-triggered activities play a critical role in generating both radio and X-ray emissions in NGC 3628.

Testing the Dynamics of Flight for the Products of Explosion for a Warhead with a Weight of 250 kg

This study presents the results of the testing of the explosion process of a warhead with a weight of 250 kg, filled with 87 kg of TNT with 20% of aluminium dust, in two configurations: with horizontal and vertical alignment of the warheads longitudinal axis, and with the centre of length of the warhead body located at a height of approx. 1 m above the ground. Four warheads were detonated in each configuration. The horizontal configuration allowed the collection of some amount of the fragments from the ground, with sizes and spatial distribution of the fragments corresponding to the location on the body from which they came, with the largest fragments from the central part of the shell measuring approximately 9 30 280 mm. For the vertical configuration, the warheads nose was pointed downwards, with an up-down excitation. In both configurations, the explosion process was recorded from a distance of 300 m using a PHANTOM fast camera with a time resolution (frame interval) of 55 s to 133 s: for the horizontal configuration along the bodys longitudinal axis, for the vertical configuration perpendicular to this axis. In the vertical configuration, the bodys expansion process was recorded using short-circuit sensors spaced every 5 mm along the flight radius. The sensors sent short-circuit signals to the time meter, whereas the first sensor was installed at a distance of approx. 1 mm from the body surface and was used to initiate the processes of time counting and recording the overpressure diagrams over time at the front of the explosion/shock (FU) wave. The recorded expansion velocity was approx. 1300 m/s, with the shell radius increasing by 20 mm. Overpressure at the front of the FU was measured by PCB pencil-tip piezoelectric sensors (CzP). Every sensor had two active surfaces arranged in tandem at a distance of 100 mm, which made it possible to determine the local FU velocity. Signals from CzP were recorded every 200 ns using a DEWETRON recorder with software allowing their initial and further processing. Three sensors were spaced 8 m from each other, whereas the first was located 8 m to 10 m from the warheads longitudinal axis. Under a row of the sensors a thick-wall steel pipe was placed to protect the sensors from destruction by the fragments. The determined local FU velocities varied from approx. (590 m/s to 740 m/s) at a distance of approx. 8 m from the epicentre up to approx. 370 m/s at a distance of approx. 26 m from the epicentre; the overpressure measured values varied from approx. (230 kPa to 550 kPa) at a distance of approx. 8 m to approx. 22 kPa at a distance of approx. 26 m from the epicentre; satisfying conformance of the velocity and pressure values under the flat FU model was found. The FU trajectory was also taken from the video recording the velocities measured varied from approx. 2,650 m/s at a distance of 0.3 m to approx. 670 m/s at a distance of 6 m from the epicentre, which corresponds to the CzP data. The fragments flying next to the CzP, generally with the highest mass to effective transverse surface ratio, left traces of their conical FU on the CzP overpressure records, which allowed the determination of average velocities for some of them across the access path to the CzP, whereas these velocities ranged from approx. 1700 m/s at a distance of approx. 8 m and (1500 m/s to 1600 m/s) at a distance of 16 m to approx. 1300 to 1400 m/s at a distance of 26 m from the epicentre. Average access velocities of the selected fragments to the field marks were determined on the basis of the video recording ranged from approx. 1800 m/s at a distance of 5 m to approx. 1500 m/s at a distance of 20 m from the explosion epicentre.

NGC 2022, a case study of a multiple-shell planetary nebula

ABSTRACT We present a detailed study of the physical properties, history of mass loss, and chemical abundances of the planetary nebula NGC 2022. New imaging observations obtained with the OAJ/JAST80 and NOT/ALFOSC confirm the presence of a faint ∼88 arcsec halo surrounding a double-layered elliptical structure that consists of a bright 21.4 × 16.7 arcsec inner shell and a 32 arcsec diameter envelope. The long-slit high-dispersion echelle observations obtained with MES on the OAN-SPM 2.1-m telescope can be well described by a shape model with expansion velocities of 43 ± 3 and 34 ± 3 km s−1 along the major and minor axes of the elliptical inner shell, respectively. In addition, a deep long-slit high-dispersion echelle observation made with the KPNO 4-m telescope detected line-splitting in the faint halo, revealing an expansion velocity of 15.5 ± 2 km s−1. We have also used new intermediate-dispersion optical spectra with the NOT, complemented with IUE data, to study the chemical abundances of each shell. The abundances of the three shells are typical of a Type II in the Peimbert classification of PNe and do not exhibit any notable anomalies. Finally, we estimate the total mass of NGC 2022 to be ≈0.9 M⊙, which consists of 0.64 M⊙ from the CSPN and 0.1, 0.11, and 0.1 × $f_{\mathrm{halo}}^{1/2}$ M⊙ from the ionized inner shell, outer shell, and halo, respectively.

Distinguishing evaporation-like and boiling-like modes of pseudo-boiling in supercritical pressures

In this study, we identify whether evaporation-like (EL) mode and boiling-like (BL) mode occur under supercritical pressures by investigating the heat transfer of platinum (Pt) and nickel-chromium (NiCr) wires, with a length of 22.0 mm and diameter of 70 μm, in carbon dioxide liquid at 8 and 10 MPa. Using a direct photographic technique based on the light refractive principle, we analyse the brighter/darker pattern in a varied-density field. The vapor–liquid interface is quantified using the grey extraction method. Our results show that beyond the limit of natural convection (NC), only the EL mode is identified for the Pt wire. However, for the NiCr wire, the EL mode, the transition from EL to BL (TEB) mode, and the BL mode are observed. The opposing gravity and drag forces cause downward bending of the Pt wire and upward bending of the NiCr wire. In the TEB region, the varying importance of interfacial expansion velocity over the buoyancy velocity accounts for the piston motion of the NiCr wire. During falling of the wire, the lighter fluid penetrating the heavier fluid causes interfacial instability to trigger the intermittent BL heat transfer. Beyond the TEB region, continuous BL heat transfer is observed. We introduce the small-perturbation theory to achieve a new non-dimensional parameter, H3. For the Pt wire, a smaller (either negative or positive) H3 explains why only the EL mode appears. For the NiCr wire, the negative H3 in the TEB region proves that the intermittent BL heat transfer is caused by the piston motion of the wire, but the positive and ∼30 times larger H3 indicates that the continuous BL heat transfer is caused by the temporal-spatial temperature variations. Furthermore, we observe that the BL mode occurs in a vapor-like layer instead of wall cavities, which is different from subcritical boiling. The BL mode displays random and disordered features, like those of subcritical boiling. This work elaborately explores common and uncommon features between supercritical pseudo-boiling and subcritical boiling, and uncovers the secret of two modes of pseudo-boiling.

Evaluation of a nnU-Net type automated clinical volumetric tumor segmentation tool for diffuse low-grade glioma follow-up

Background and purposeDiffuse low-grade gliomas (DLGG) are characterized by a slow and continuous growth and always evolve towards an aggressive grade. Accurate prediction of the malignant transformation is essential as it requires immediate therapeutic intervention. One of its most precise predictors is the velocity of diameter expansion (VDE). Currently, the VDE is estimated either by linear measurements or by manual delineation of the DLGG on T2 FLAIR acquisitions. However, because of the DLGG's infiltrative nature and its blurred contours, manual measures are challenging and variable, even for experts. Therefore we propose an automated segmentation algorithm using a 2D nnU-Net, to 1) gain time and 2) standardize VDE assessment. Materials and MethodsThe 2D nnU-Net was trained on 318 acquisitions (T2 FLAIR & 3DT1 longitudinal follow-up of 30 patients, including pre- & post-surgery acquisitions, different scanners, vendors, imaging parameters…). Automated vs. manual segmentation performance was evaluated on 167 acquisitions, and its clinical interest was validated by quantifying the amount of manual correction required after automated segmentation of 98 novel acquisitions. ResultsAutomated segmentation showed a good performance with a mean Dice Similarity Coefficient (DSC) of 0.82±0.13 with manual segmentation and a substantial concordance between VDE calculations. Major manual corrections (i.e., DSC<0.7) were necessary only in 3/98 cases and 81% of the cases had a DSC>0.9. ConclusionThe proposed automated segmentation algorithm can successfully segment DLGG on highly variable MRI data. Although manual corrections are sometimes necessary, it provides a reliable, standardized and time-winning support for VDE extraction to asses DLGG growth.

Effects of anode material on the evolution of anode plasma and characteristics of intense electron beam diode

In this paper, three kinds of materials including graphite, titanium (Ti) and molybdenum (Mo) are used as anodes to figure out the influence factors of anode material on the characteristics of the intense electron beam diode. The results show that the characteristics of diode are mainly determined by the cathode plasma motion under a 15 mm diode gap, in which the typical electron beam parameters are 280 kV, 3.5 kA. When the diode gap is reduced to 5 mm, the voltage of the electron beam reduces to about 200 kV, and its current increases to more than 8.2 kA. It is calculated that the surface temperatures of Ti and Mo anodes are higher than their melting points. The diode plasma luminescence images show that Ti and Mo anodes produce plasmas soon after the bombardment of electron beams. Ti and Mo lines are respectively found in the plasma composition of Ti and Mo anode diodes. Surface melting traces are also observed on Ti and Mo anodes by comparing the micromorphologies before and after bombardment of the electron beam. These results suggest that the time of anode plasma generation is closely related to the anode material. Compared with graphite, metal Ti and Mo anodes are more likely to produce large amounts of plasma due to their more significant temperature rise effect. According to the moment that anode plasma begins to generate, the average expansion velocities of cathode and anode plasma are estimated by fitting the improved space-charge limited flow model. This reveals that generation and motion of the anode plasma significantly affect the characteristics of intense electron beam diode.

Study on the cylinder test of aluminized explosives with different content of Al powder

To investigate the effect of the content of Al powder on the acceleration ability of the aluminized explosives, a series of 25mm cylinder experiments was conducted, and the content of Al/LiF powder is 0%, 15%, 30%. The radial expansion velocities of the cylinder wall were measured through the Photonic Doppler Velocimetry (PDV) system. The cylinder experiments verify that Al powder could react with detonation products to release energy, which enhance the accelerating ability of explosives. By comparing the different content of Al powder of aluminized explosives, it is found that the accelerating ability of aluminized explosives is related to the content of Al powder, and the optimal content of Al powder is 15% in this experiment. By comparing the same content of Al/LiF powder, it is indicated that the reaction delay time of Al powder in RDX80/Al15 explosive does not exceed 2.8µs, and as RDX65/Al30, the reaction delay time is less than 3µs. Finally, through normalization method, the specific reaction delay time of Al powder are 0.147 and 0.203, with the content of Al powder 15% and 30%.

Inferring the Progenitor Mass–Kinetic Energy Relation of Stripped-envelope Core-collapse Supernovae from Nebular Spectroscopy

The relation between the progenitor mass and the kinetic energy of the explosion is a key toward revealing the explosion mechanism of stripped-envelope core-collapse supernovae (SESNe). Here, we present a method to derive this relation using the nebular spectra of SESNe, based on the correlation between [O i]/[Ca ii], which is an indicator of progenitor mass, and the width of [O i], which measures the expansion velocity of the oxygen-rich material. To explain the correlation, the kinetic energy (E K) is required to be positively correlated with the progenitor mass as represented by the CO core mass (M CO). We demonstrate that SNe IIb/Ib and SNe Ic/Ic-BL follow the same M CO–E K scaling relation, which suggests that helium-rich and helium-deficient SNe share the same explosion mechanism. The M CO–E K relation derived in this work is compared with the ones derived from early phase observations. The results are largely in good agreement. Combined with early phase observations, the method presented in this work provides a chance to scan through the ejecta from the outermost region to the dense inner core, which is important to reveal the global properties of the ejecta and constrain the explosion mechanism of core-collapse SNe.

Theoretical study of the void collapse and shear band formation mechanism for β‐HMX

AbstractBased on molecular dynamics simulation, we obtain a shear band formation mechanism for β‐HMX. The shock wave reflected at void face induces rarefaction wave, and the velocity difference between rarefaction wave zone and shock wave zone induces slipping. A set of physical models are developed to describe the wave reflection, shear band expansion and energy dissipation. The orientation angle, face indices, expansion velocity and formation energy of shear bands are calculated. A complete physical picture for shear band formation is obtained.

Faint but Not Forgotten. I. First Results from a Search for Astrospheres around AGB Stars in the Far-ultraviolet

Using the GALEX archive, we have discovered extended structures around ten asymptotic giant branch (AGB) stars (out of a total 92 searched) emitting in the far-ultraviolet (FUV) band. In all but one, we find the typical morphology expected for a spherical wind moving relative to, and interacting with, the interstellar medium (ISM) to produce an astrosphere. The exception is V Hya whose mass ejection is known to be highly aspherical, where we find evidence of its large parabolic outflows interacting with the ISM, and its collimated, extreme velocity outflows interacting with the circumstellar medium. For eight objects with relatively large proper motions, we find (as expected) that the termination-shock region lies in a hemisphere that contains the proper motion vector. Radial intensity cuts for each source have been used to locate the termination shock and the astropause’s outer edge. In a few objects, the cuts also reveal faint emission just outside the astropause that likely arises in shocked ISM material. We have used these data, together with published mass-loss rates and wind expansion velocities, to determine the total mass lost and duration for each source—we find that the duration of and total mass in the shocked wind are significantly larger than their corresponding values for the unshocked wind. The combination of FUV and far-IR data on AGB astrospheres provides a unique database for theoretical studies (numerical simulations) of wind–ISM interactions. We show that a Cyclical Spatial Heterodyne Spectrometer on a small space-based telescope can provide high-resolution spectra of astrospheres to confirm the emission mechanism.

Volumetric Rates of Luminous Red Novae and Intermediate-luminosity Red Transients with the Zwicky Transient Facility

Luminous red novae (LRNe) are transients characterized by low luminosities and expansion velocities, and they are associated with mergers or common-envelope ejections in stellar binaries. Intermediate-luminosity red transients (ILRTs) are an observationally similar class with unknown origins, but they are generally believed to be either electron-capture supernovae in super-asymptotic giant branch stars or outbursts in dusty luminous blue variables (LBVs). In this paper, we present a systematic sample of eight LRNe and eight ILRTs detected as part of the Census of the Local Universe (CLU) experiment on the Zwicky Transient Facility (ZTF). The CLU experiment spectroscopically classifies ZTF transients associated with nearby (<150 Mpc) galaxies, achieving 80% completeness for m r < 20 mag. Using the ZTF-CLU sample, we derive the first systematic LRNe volumetric rate of Mpc−3 yr−1 in the luminosity range −16 ≤ M r ≤ −11 mag. We find that, in this luminosity range, the LRN rate scales as —significantly steeper than the previously derived scaling of L −1.4±0.3 for lower-luminosity LRNe (M V ≥ −10 mag). The steeper power law for LRNe at high luminosities is consistent with the massive merger rates predicted by binary population synthesis models. We find that the rates of the brightest LRNe (M r ≤ −13 mag) are consistent with a significant fraction of them being progenitors of double compact objects that merge within a Hubble time. For ILRTs, we derive a volumetric rate of Mpc−3 yr−1 for M r ≤ −13.5 mag, which scales as . This rate is ∼1%–5% of the local core-collapse supernova rate and is consistent with theoretical ECSN rate estimates.