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Habitability at the surface of a planet depends on having an atmosphere long enough for life to develop. The loss of atmosphere to space is an important component in assessing planetary surface habitability. Current models of atmospheric escape from exoplanets are not well constrained by observations. Atmospheric escape observations from the terrestrial planets are available in public data archives. We recast oxygen escape rates from Earth derived from an instrument on Dynamics Explorer‐1 as function of solar wind and compare them to similar data from Mars. Analysis demonstrates that oxygen escape rates from Mars are not as sensitive to variations in solar power components as those from Earth. Available data from Venus can confirm or refute the assertion that oxygen escape from magnetized planets is more sensitive than that from unmagnetized planets. Plain Language Summary: Habitability of a planet depends on having an atmosphere long enough for life to develop. NASA and ESA data archives contain information about atmospheric escape from the terrestrial planets. For these planets oxygen ions dominate atmospheric escape. The data archives are just beginning to be analyzed and presented in a form that allows comparison with, and validation of, models of the interaction of stellar winds with exoplanets. We derive oxygen escape rates from Earth as a function of solar power components from a recasting of Dynamics Explorer‐1 data and compare them to similar data from Mars. Our analysis demonstrates that oxygen escape rates from Mars are not as sensitive to variations in the solar power components as those from Earth. These data and similar data from Venus will prove to be important constrains on models of stelar wind/atmosphere interactions and atmospheric escape from exoplanets. Key Points: We recast oxygen escape rates from Earth derived from an instrument on Dynamics Explorer‐1 as a function of solar energy inputsWe compare escape rates for a magnetized planet (Earth) and an unmagnetized planet (Mars) as a function of solar energy inputsOxygen escape rates from Mars are not as sensitive to variations in the solar power components as those from Earth [ABSTRACT FROM AUTHOR]

Mixed-morphology supernova remnants (MMSNRs) are characterized by a shell-like morphology in the radio and centrally peaked thermal emission in the X-ray band. The nature of this peculiar class of supernova remnants (SNRs) remains a controversial issue. In this work, by pairing the predictions of stellar evolution theory with two-dimensional hydrodynamic simulations, we show that the mixed morphology properties of an SNR can arise by the interaction of the SNR with the circumstellar medium shaped by a red supergiant progenitor star, embedded in a dense environment. As a study case, we model the circumstellar medium formation and the subsequent interaction of the SNR with it of a |$15~\rm {\rm M}_{\odot }$| progenitor star. The reflected shock, formed by the collision of the SNR with the density walls of the surrounding circumstellar cavity, accumulates and re-shocks the supernova ejecta at the centre of the remnant, increasing its temperature so that the gas becomes X-ray bright. Such a formation mechanism may naturally explain the nature of MMSNRs resulted from Type II supernovae without the demand of additional physical mechanisms and/or ambient medium inhomogeneities. We discuss alternative evolutionary paths that potentially could be ascribed for the MMSNR formation within the framework of the reflected shock model. [ABSTRACT FROM AUTHOR]

We address the challenge of running thermally pulsing-(super)asymptotic giant branch [TP-(S)AGB] models, with a 1D hydrostatic stellar evolution code, without suffering instabilities that terminate the evolution. We investigate two instabilities that usually occur during the luminosity peak following a thermal pulse: the hydrogen recombination instability and the Fe-peak instability. Both instabilities occur when the stellar mass is significantly reduced (⁠|$M \lesssim M_\mathrm{i}/2$|⁠) at the end of the TP-(S)AGB in our models with initial mass |$M_\mathrm{i}\gtrsim 2~\mathrm{M}_\odot$|⁠. The hydrogen recombination instability occurs due to the difficulty of modelling a thermally and dynamically unstable envelope in a 1D hydrostatic code, and is prevented by damping the energy released by hydrogen recombination in the outer envelope. The Fe-peak instability occurs when the radiation pressure drops at the base of the convective envelope and is prevented by boosting the convective energy transport in this region. We provide custom routines to prevent these instabilities in the stellar evolution code mesa. The impact of these routines on the stellar structure is minimized so as to not affect the efficiency of third dredge-up, hot-bottom burning, or the wind mass-loss rate. We find only a modest reduction in third dredge-up efficiency at small envelope masses (⁠|$M_\mathrm{env}\lesssim 1.0~\mathrm{M}_\odot$|⁠). Consequently, our |$M_\mathrm{i}=5~\mathrm{M}_\odot$| star, with hot-bottom burning, becomes a carbon star for the last |$\sim 10~{{\ \rm per\ cent}}$| of its thermally pulsing lifetime. The largest stellar radii are reached during the final thermal pulses, which may have important consequences for binary–star interactions. [ABSTRACT FROM AUTHOR]

Massive stars in the red supergiant (RSG) phase are known to undergo strong mass-loss through winds and observations indicate that a substantial part of this mass-loss could be driven by localized and episodic outflows. Various mechanisms have been considered to explain this type of mass-loss in RSGs, but these models often focus on single-star evolution. However, massive stars commonly evolve in binary systems, potentially interacting with their companions. Motivated by observations of the highly asymmetric circumstellar ejecta around the RSG VY CMa, we investigate a scenario where a companion on an eccentric orbit grazes the surface of an RSG at periastron. The companion ejects part of the outer RSG envelope, which radiatively cools, reaching the proper conditions for dust condensation and eventually giving rise to dust-driven winds. Using simple treatments for radiative cooling and dust-driven winds, we perform three-dimensional smoothed particle hydrodynamic simulations of this scenario with a |$20\, {\rm M}_\odot$| RSG and a |$2\, {\rm M}_\odot$| companion. We follow the evolution of the binary throughout a total of 14 orbits and observe that the orbit tightens after each interaction, in turn enhancing the mass-loss of subsequent interactions. We show that one such grazing interaction yields outflows of |$3\times 10^{-4}\, {\rm M}_\odot$|⁠ , which later results in wide asymmetric dusty ejecta, carrying a total mass of |$0.185\, {\rm M}_\odot$| by the end of simulations. We discuss the implications for the evolution of the binary, potential observational signatures, as well as future improvements of the model required to provide sensible predictions for the evolution of massive binaries. [ABSTRACT FROM AUTHOR]

Wind Roche-lobe overflow (WRLOF) is a mass-transfer mechanism proposed by Mohamed and Podsiadlowski for stellar binaries wherein the wind acceleration zone of the donor star exceeds its Roche-lobe radius, allowing stellar wind material to be transferred to the accretor at enhanced rates. WRLOF may explain characteristics observed in blue lurkers and blue stragglers. While WRLOF has been implemented in rapid population synthesis codes, it has yet to be explored thoroughly in detailed binary models such as MESA (a 1D stellar evolution code), and over a wide range of initial binary configurations. We incorporate WRLOF accretion in MESA to investigate wide low-mass binaries at solar metallicity. We perform a parameter study over the initial orbital periods and stellar masses. In most of the models where we consider angular momentum transfer during accretion, the accretor is spun up to the critical (or breakup) rotation rate. Then we assume the star develops a boosted wind to efficiently reduce the angular momentum so that it could maintain subcritical rotation. Balanced by boosted wind loss, the accretor only gains ∼2% of its total mass, but can maintain a near-critical rotation rate during WRLOF. Notably, the mass-transfer efficiency is significantly smaller than in previous studies in which the rotation of the accretor is ignored. We compare our results to observational data of blue lurkers in M67 and find that the WRLOF mechanism can qualitatively explain the origin of their rapid rotation, their location on the H-R diagram, and their orbital periods. [ABSTRACT FROM AUTHOR]

Spectroscopic observations have shown for decades that the Wolf–Rayet (WR) phenomenon is ubiquitous among stars with different initial masses. Although much effort to understand the winds from massive WR stars has been presented in the literature, not much has been done for such type of stars in the low-mass range. Here we present an attempt to understand the winds from [WR]-type stars using results from spectral analyses with the full non-local thermodynamic equilibrium stellar atmosphere code PoWR. These results are put into context with the properties of massive WR stars. We found that WC + [WC] stars and WO + [WO] stars create independent sequences in the mass-loss rate (⁠|$\dot{M}$|⁠) and modified wind momentum (D mom) versus luminosity (L) diagrams. Our analysis indicates that even when the winds of WR and [WR] stars become optically thin, there is no breakdown of the general mass-loss trend, contrary to the observed 'weak wind phenomenon' in OB stars. We report that all WR-type stars studied here broadly define single sequences in the wind efficiency (η) versus transformed mass-loss rate (⁠|$\dot{M}_\mathrm{t}$|⁠), the |$\dot{M}_\mathrm{t}$| – T eff diagram, and the |$(L, T_\mathrm{eff}, \dot{M})$| space, which suggest these to be fundamental properties of the WR phenomenon (regardless of the mass range), at least for WR-type stars of the O and C sequences. Our analytical estimations could drive computations of future stellar evolution models for WR-type stars. [ABSTRACT FROM AUTHOR]

We present a set of controlled hydrodynamical simulations to study the effects of strong galactic outflows on the density and temperature structures, and associated X-ray signatures, of extra-planar and circumgalactic gas. We consider three initial state models, isothermal, isentropic, and rotating cooling-flow, for the hot circumgalactic medium (CGM) into which the outflows are driven. The energy sources are either stellar winds and supernovae, or active galactic nuclei. We consider energy injection rates in the range |$10^{40} \lt \dot{E}_{\rm inj} \lt 10^{44.5}$| erg s−1, and compute the time-dependent soft X-ray (0.5–2 keV) surface brightness. For |$\dot{E}_{\rm inj} \gtrsim 10^{41} {\small --} 10^{42}$| erg s−1, with the exact threshold depending on the initial CGM state, the X-ray response is dominated by dense hot gas in the forward shock that eventually fades into the CGM as a sound wave. The shock surrounds an inner hot bubble leading to a radial flattening of the X-ray surface brightness. For lower energy injection rates, the X-ray surface brightness of the initial CGM state is almost unaffected. We present analytical approximations for the outflow shock propagation and the associated X-ray emissions. [ABSTRACT FROM AUTHOR]

Stellar rotation at early ages plays a crucial role in the survival of primordial atmospheres around Earth-mass exoplanets. Earth-like planets orbiting fast-rotating stars may undergo complete photoevaporation within the first few hundred Myr driven by the enhanced stellar XUV [X-rays and extreme ultraviolet (EUV)] radiation, while planets orbiting slow-rotating stars are expected to experience difficulty in losing their primordial envelopes. Besides the action of stellar radiation, stellar winds induce additional erosion on these primordial atmospheres, altering their morphology, extent, and causing supplementary atmospheric losses. In this paper, we study the impact of activity-dependent stellar winds on primordial atmospheres to evaluate the extent to which the action of these winds can be significant in the whole planetary evolution at early evolutionary stages. We performed 3D magnetohydrodynamical (MHD) simulations of the interaction of photoevaporating atmospheres around unmagnetized Earth-mass planets in the time span between 50 and 500 Myr, analysing the joint evolution of stellar winds and atmospheres for both fast- and slow-rotating stars. Our results reveal substantial changes in the evolution of primordial atmospheres when influenced by fast-rotating stars, with a significant reduction in extent at early ages. In contrast, atmospheres embedded in the stellar winds from slow-rotating stars remain largely unaltered. The interaction of the magnetized stellar winds with the ionized upper atmospheres of these planets allows us to evaluate the formation and evolution of different MHD structures, such as double bow shocks and induced magnetospheres. This work will shed light on the first evolutionary stages of Earth-like exoplanets, which are of crucial relevance in terms of planet habitability. [ABSTRACT FROM AUTHOR]

We developed a grid of stellar rotation models for low-mass and solar-type classical T Tauri stars (CTTS; 0.3 M ⊙ < M * < 1.2 M ⊙). These models incorporate the star–disk interaction and magnetospheric ejections to investigate the evolution of the stellar rotation rate as a function of the mass of the star M *, the magnetic field (B *), and stellar wind ( M ̇ wind ). We compiled and determined stellar parameters for 208 CTTS, such as projected rotational velocity v sin (i) , mass accretion rate M ̇ acc , stellar mass M *, ages, and estimated rotational periods using Transiting Exoplanet Survey Satellite (TESS) data. We also estimated a representative value of the mass-loss rate for our sample using the [O i ] λ 6300 spectral line. Our results confirm that v sin (i) measurements in CTTS agree with the rotation rates provided by our spin models in the accretion-powered stellar winds picture. In addition, we used the approximate Bayesian computation technique to explore the connection between the model parameters and the observational properties of CTTS. We find that the evolution of v sin (i) with age might be regulated by variations in (1) the intensity of B * and (2) the fraction of the accretion flow ejected in magnetic winds, removing angular momentum from these systems. The youngest stars in our sample (∼1 Myr) show a median branching ratio M ̇ wind / M ̇ acc ∼ 0.16 and median B * ∼ 2000 G, in contrast to ∼0.01 and 1000 G, respectively, for stars with ages ≳3 Myr. [ABSTRACT FROM AUTHOR]

We report on a multiwavelength study of the Wolf–Rayet star [KSF2015] 1381-19L, which is located in the solar metallicity region (Z = 0.014) of the Milky Way, strongly obscured by interstellar dust. We perform a detailed characterization of the stellar atmosphere by fitting the spectral emission lines observed in the optical and near-infrared (NIR) bands, using CMFGEN. The best-fitted spectroscopic model indicates a highly luminous (105.89 L ⊙) star with a large radius (15 R ⊙) and effective temperature, wind terminal velocity, and chemical composition similar to those of Galactic WC9-dusty (WC9d)-type stars. The atmospheric ionization structure shows coexisting ionization states of different elements, simultaneously affecting the opacity and thermal electron balance. Fitting of the spectral energy data reveals high interstellar optical extinction (A V = 8.87), while the IR extinction is found to be comparatively lower ( A K s = 0.98 ). We do not detect any excess emission at NIR wavelengths due to dust. Upon comparison of our results with the GENEVA single-star evolutionary models (Z = 0.014), we identify the best possible progenitors (a rotating star of 67 M ⊙ and a nonrotating star of 90 M ⊙). [ABSTRACT FROM AUTHOR]

Auroral emission lines result from the interaction between magnetic field and stellar wind, offering valuable insights into physical properties and processes occurring within magnetospheres of celestial bodies. While extensively studied in planetary and exoplanetary atmospheres, in ultracool dwarfs, and as radio emission from early-type stars, the presence of specific auroral emission lines in hot star spectra remains unexplored. In this study, we utilized tlusty code to simulate the auroral lines, while modelling the effect of the interaction between stellar wind and magnetosphere through X-ray irradiation. Utilizing high-resolution synthetic spectra generated from model atmospheres, we identified potential candidate lines indicative of auroral emission, which were absent in non-irradiated spectra. Emission lines in synthetic spectra were present primarily in the infrared domain. The most prominent line generated by irradiation was He  ii 69458 Å, which appeared in all our model atmospheres with effective temperatures ranging from 15 kK to 30 kK. We also calculated the minimum irradiation required to detect emission in this most prominent line. The presence of emission lines was interpreted by considering changes in the population of different excited states of given atoms. Besides the appearance of infrared emission lines, high-energy irradiation causes infrared excess. To complement our simulations, we also searched for auroral lines in Far Ultraviolet Spectroscopic Explorer (FUSE) observations, which are deposited in the Multimission Archive at Space Telescope catalogue. The comparison of observed spectra with synthetic spectra did not identify any possible candidate emission lines in FUSE spectra. [ABSTRACT FROM AUTHOR]

The large number of gravitational wave (GW) detections have revealed the properties of the merging black hole binary population, but how such systems are formed is still heavily debated. Understanding the imprint of stellar physics on the observable GW population will shed light on how we can use the GW data, along with other observations, to constrain the poorly understood evolution of massive binaries. We perform a parameter study on the classical isolated binary formation channel with the population synthesis code seba to investigate how sensitive the properties of the coalescing binary black hole population are on the uncertainties related to first phase of mass transfer and stellar winds. We vary five assumptions: (1) and (2) the mass transfer efficiency and the angular momentum loss during the first mass transfer phase, (3) the mass transfer stability criteria for giant donors with radiative envelopes, (4) the effective temperature at which an evolved star develops a deep convective envelope, and (5) the mass-loss rates of stellar winds. We find that current uncertainties related to first phase of mass transfer have a huge impact on the relative importance of different dominant channels, while the observable demographics of GW sources are not significantly affected. Our varied parameters have a complex, interrelated effect on the population properties of GW sources. Therefore, inference of massive binary physics from GW data alone remains extremely challenging, given the large uncertainties in our current models. [ABSTRACT FROM AUTHOR]

The remnant of the historical supernova 1181 is claimed to be associated with a white dwarf merger remnant J005311. The supernova remnant (SNR) shock, and a termination shock expected to be formed by the intense wind of J005311, are potential sites for radio emission via synchrotron emission from shock-accelerated electrons. In this paper, we estimate the radio emission from these two shocks, and find the peak radio flux to be 0.1–10 mJy (at 0.01–1 GHz) in the outer SNR shock and 0.01–0.1 mJy (at 1–10 GHz) in the inner termination shock. We also search for radio emission from this source in the archival data of the Karl G. Jansky Very Large Array (VLA) Sky Survey at 3 GHz, the NRAO VLA Sky Survey at 1.4 GHz and the Canadian Galactic Plane Survey at 408 MHz, finding no significant detection. While targeted observations with higher sensitivity are desired, we particularly encourage those at higher frequency and angular resolution to probe the inner termination shock and its evolution. [ABSTRACT FROM AUTHOR]

We have studied the stability of C59 anions as a function of time, from their formation on femtosecond timescales to their stabilization on second timescales and beyond, using a combination of theory and experiments. The C 59 − fragments were produced in collisions between C60 fullerene anions and neutral helium gas at a velocity of 90 km s−1 (corresponding to a collision energy of 166 eV in the center-of-mass frame). The fragments were then stored in a cryogenic ion beam storage ring at the DESIREE facility, where they were followed for up to 1 minute. Classical molecular dynamics simulations were used to determine the reaction cross section and the excitation energy distributions of the products formed in these collisions. We find that about 15% of the C 59 − ions initially stored in the ring are intact after about 100 ms and that this population then remains intact indefinitely. This means that C60 fullerenes exposed to energetic atoms and ions, such as stellar winds and shock waves, will produce stable, highly reactive products, like C59, that are fed into interstellar chemical reaction networks. [ABSTRACT FROM AUTHOR]

Stellar winds of massive (⁠|$\gtrsim 9\, \mathrm{M_\odot }$|⁠) and very massive (⁠|$\gtrsim 100\, \mathrm{M_\odot }$|⁠) stars may play an important role in the metal-enrichment during the formation of star clusters. With novel high-resolution hydrodynamical griffin -project simulations, we investigate the rapid recycling of stellar wind-material during the formation of massive star clusters up to |$M_\mathrm{cluster}\sim 2\times 10^5\, \mathrm{M_\odot }$| in a low-metallicity dwarf galaxy starburst. The simulation realizes new stars from a stellar initial mass function (IMF) between |$0.08$| and |$\sim 400\, \mathrm{M_\odot }$| and follows stellar winds, radiation and supernova-feedback of single massive stars with evolution tracks. Star clusters form on time-scales less than ∼5 Myr, and their supernova-material is very inefficiently recycled. Stellar wind-material, however, is trapped in massive clusters resulting in the formation of stars self-enriched in Na, Al, and N within only a few Myr. Wind-enriched (second population, 2P) stars can be centrally concentrated in the most massive clusters (⁠|$\gtrsim 10^4\, \mathrm{M_\odot }$|⁠) and the locked wind-material increases approximately as |$M_\mathrm{cluster}^{2}$|⁠. These trends resemble the characteristics of observed 2P stars in globular clusters (GCs). We fit scaling relations to the lognormal distributed wind-mass fractions and extrapolate to possible GC progenitors of |$M_\mathrm{cluster}=10^7\, \mathrm{M_\odot }$| to investigate whether a dominant 2P could form. This can only happen if the IMF is well-sampled, single massive stars produce at least a factor of a few more enriched winds, for example, through a top-heavy IMF, and a significant fraction of the first population (unenriched) stars is lost during cluster evolution. [ABSTRACT FROM AUTHOR]

Cosmic rays are highly energetic messengers propagating in magnetized plasma, which are, possibly but not exclusively, accelerated at astrophysical shocks. Amongst the variety of astrophysical objects presenting shocks, the huge circumstellar stellar wind bubbles forming around very massive stars, are potential non-thermal emitters. We present the 1D magneto-hydrodynamical simulation of the evolving magnetized surroundings of a single, OB-type main-sequence |$60\, \rm {\rm M}_{\odot }$| star, which is post-processed to calculate the re-acceleration of pre-existing non-thermal particles of the Galactic cosmic ray background. It is found that the forward shock of such circumstellar bubble can, during the early phase (⁠|$1\, \rm Myr$|⁠) of its expansion, act as a substantial re-accelerator of pre-existing interstellar cosmic rays. This results in an increasing excess emission flux by a factor of 5, the hadronic component producing γ-rays by π0 decay being more important than those by synchrotron and inverse Compton radiation mechanisms. We propose that this effect is at work in the circumstellar environments of massive stars in general and we conjecture that other nebulae such as the stellar wind bow shocks of runaway massive stars also act as Galactic cosmic ray re-accelerators. Particularly, this study supports the interpretation of the enhanced hadronic emission flux measured from the surroundings of κ Ori as originating from the acceleration of pre-existing particles at the forward shock of its wind bubble. [ABSTRACT FROM AUTHOR]

The magnetic field in the O9.7 V star HD 54879 has been monitored for almost a decade. Spectropolarimetric observations reveal a rather strong mean longitudinal magnetic field that varies with a period of about 7.41 years. Observations in the Hα$$ \alpha $$ line show a variation with the same period, while the Hβ$$ \beta $$ line shows only little variation. Assuming the periodic variation to be caused by a slow rotation and a dipolar magnetic field, we find a magnetic field strength of ≥$$ \ge $$2 kG at the magnetic poles. With the relatively low mass loss rate of 10−9M⊙$$ {10}^{-9}{M}_{\odot } $$ year−1, this star is a case of extremely strong magnetic confinement. Both theoretical arguments and numerical simulations indicate the presence of an extended disk of increased gas density in the equatorial plane of the magnetic field, where gas from the line‐driven stellar wind is trapped. This disk is likely to be the origin of the observed Hα$$ \alpha $$ emission, which peaks together with the strongest line‐of‐sight magnetic field. The profile of the Hα$$ \alpha $$ line is resolved in several components and shows a remarkable variability with the rotation period. [ABSTRACT FROM AUTHOR]

Stellar feedback plays a crucial role in regulating baryon cycles of a galactic ecosystem, and may manifest itself in the formation of superbubbles in the interstellar medium. In this work, we used a set of high-resolution simulations to systematically study the properties and evolution of superbubbles in galactic environments. The simulations were based on the SMUGGLE galaxy formation framework using the hydrodynamical moving-mesh code arepo , reaching a spatial resolution of |$\sim 4 \, \rm pc$| and mass resolution of |$\sim 10^3 \, \rm M_{\odot }$|⁠. We identified superbubbles and tracked their time evolution using the parent stellar associations within the bubbles. The X-ray luminosity-size distribution of superbubbles in the fiducial run is largely consistent with the observations of nearby galaxies. The size of superbubbles shows a double-peaked distribution, with the peaks attributed to early feedback (radiative and stellar wind feedback) and supernova feedback. The early feedback tends to suppress the subsequent supernova feedback, and it is strongly influenced by star formation efficiency, which regulates the environmental density. Our results show that the volume filling factor of hot gas (T > 105.5 K) is about |$12~{{\ \rm per\ cent}}$| averaged over a region of 4 kpc in height and 20 kpc in radius centred on the disc of the galaxy. Overall, the properties of superbubbles are sensitive to the choice of subgrid galaxy formation models and can, therefore, be used to constrain these models. [ABSTRACT FROM AUTHOR]

In eclipsing X-ray binary systems, the direct X-ray emission is blocked by the companion star during the eclipse. We observe only reprocessed emission that contains clues about the environment of the compact object and its chemical composition, ionization levels, etc. We have found flares in some X-ray binaries during their eclipses. The study of eclipse flares provides additional clues regarding the size of the reprocessing region and helps distinguish between different components of the X-ray spectrum observed during the eclipse. In the archival data, we searched for flares during eclipses of high-mass X-ray binaries and found flares in three sources: Vela X-1, LMC X-4, and 4U 1700−37. Comparing spectral properties of the eclipse flare and non-flare data, we found changes in the power-law photon index in all three sources and multiple emission lines in Vela X-1 and 4U 1700-37. The fluxes of prominent emission lines showed a similar increase as the overall X-ray flux during the eclipse flare, suggesting the lines originate in the binary environment and not in the interstellar medium. We also observed a soft excess in 4U 1700-37 that remains unchanged during both eclipse flare and non-flare states. Our analysis suggests that this emission originates from the extremely thin shell of the stellar wind surrounding the photosphere of its companion star. The detection of short (100–200 s) count-rate doubling time-scale in 4U 1700−37 and LMC X-4 indicates that the eclipse reprocessing occurs in a region larger than, but comparable to the size of the companion star. [ABSTRACT FROM AUTHOR]

We fit the high-resolution Chandra X-ray spectra of the O supergiant ζ Puppis using the variable boundary condition (VBC) line model to test the stability of its mass-loss rate between two epochs of observation: 2000 March and 2018 July – 2019 August. At issue is whether the observed variations are induced by global changes in the cool (unshocked) wind itself or are isolated to the local pockets of hot gas (i.e. changes in the frequency and location of the shocks). Evidence in the literature favoured the possibility of a 40 per cent increase in the mass flux of the entire stellar wind, based on X-ray reabsorption from a line-deshadowing-instability-inspired parametrization, whereas our fit parameters are consistent with a constant mass flux with a change in the velocity variations that determine the locations where shocks form. Our results suggest the shocks in the more recent data are formed at somewhat larger radii, mimicking the enhanced blueshifts and increased line fluxes interpreted in the previous analysis as being due to increases in both the X-ray generation and reabsorption from an overall stronger wind. [ABSTRACT FROM AUTHOR]

Outflows play a pivotal role in star formation as one of its most visible markers and a means of transporting mass, momentum, and angular momentum from the infalling gas into the surrounding molecular cloud. Their wide reach (at least thousands of astrnomical units) is a contrast to typical disk sizes (∼10–100 au). We employ high-resolution three-dimensional nested-grid nonideal magnetohydrodynamic (MHD) simulations to study outflow properties in the Class 0 phase. We find that no disk wind is driven from the extended centrifugal disk that has weak magnetic coupling. The low-velocity winds emerge instead from the infalling magnetic pseudodisk. Much of the disk actually experiences an infall of matter rather than outflowing gas. Some of the pseudodisk wind (PD-wind) moves inward to regions above the disk and either falls onto the disk or proceeds upward. The upward flow gives the impression of a disk wind above a certain height even if the gas is originally emerging from the pseudodisk. The PD-wind has the strongest flow coming from a disk interaction zone that lies just outside the disk and is an interface between the inwardly advected magnetic field of the pseudodisk and the outwardly diffusing magnetic field of the disk. The low-velocity wind exhibits the features of a flow driven by the magnetic pressure gradient force in some regions and those of a magnetocentrifugal wind in other regions. We interpret the structure and dynamics of the outflow zone in terms of the basic physics of gravity, angular momentum, magnetic fields, and nonideal MHD. [ABSTRACT FROM AUTHOR]

We present time-series linear-polarization observations of the bright O4 supergiant ζ Puppis. The star is found to show polarization variation on time-scales of around an hour and longer. Many of the observations were obtained contemporaneously with Transiting Exoplanet Survey Satellite (TESS) photometry. We find that the polarization varies on similar time-scales to those seen in the TESS light curve. The previously reported 1.78-d photometric periodicity is seen in both the TESS and polarization data. The amplitude ratio of photometry to polarization is ∼9 for the periodic component and the polarization variation is oriented along position angle ∼70°–160°. Higher frequency stochastic variability is also seen in both data sets with an amplitude ratio of ∼19 and no preferred direction. We model the polarization expected for a rotating star with bright photospheric spots and find that models that fit the photometric variation produce too little polarization variation to explain the observations. We suggest that the variable polarization is more likely the result of scattering from the wind, with corotating interaction regions producing the periodic variation and a clumpy outflow producing the stochastic component. The Hα emission line strength was seen to increase by 10 per cent in 2021 with subsequent observations showing a return to the pre-2018 level. [ABSTRACT FROM AUTHOR]

Context. Several studies suggest that the emission properties of a star can be significantly affected by its interaction with a nearby planet through magnetic fields or interaction between their respective winds. However, the actual observability of these effects remains a subject of debate. An illustrative example is the HD 189733A system: certain characteristics of its emissions have been interpreted as indicative of ongoing interactions between the star and its associated planet. Other studies attribute these characteristics to the coronal activity of the star. Aims. In this study we aimed to investigate whether the observed stellar X-ray flare events, which appear to be in phase with the planetary period in the HD 189733A system, could be attributed to the accretion of the planetary wind onto the stellar surface or if they resulted from an interaction between the planetary and stellar winds. Methods. We developed a 3D magnetohydrodynamic model with the PLUTO code that describes the system HD 189733A , including the central host star and its hot Jupiter along with their respective winds. The effects of gravity and the magnetic fields of both the star and the planet are taken into account. Results. Our analysis reveals that, in the cases examined in this study, the accretion scenario is only viable when the stellar magnetic field strength is at 5 G and the planetary magnetic field strength is at 1 G. In this scenario, the Rayleigh-Taylor instabilities lead to the formation of an accretion column that connects the star to the planet. Once formed the accretion column remains stable for the duration of the simulation. The accretion column produces an accretion rate of the order of 1012 g s−1 and shows an average density of about 107 cm−3. In the other case explored, the accretion column does not form because the Rayleigh-Taylor instability is suppressed by the stronger magnetic field intensities assumed for both the star and the planet. We synthesized the emission resulting from the shocked planetary wind and found that the total X-ray emission ranges from 5 × 1023 to 1024 erg s−1. Conclusions. In the case of accretion, the emission originating from the hotspot cannot be distinguished from the coronal activity. Also, the interaction between the planetary and stellar winds cannot be responsible for the X-ray emission, as the total emission produced is about four orders of magnitude lower than the average X-ray luminosity of the star. [ABSTRACT FROM AUTHOR]

We present low-frequency radio observations of the Galactic symbiotic recurrent nova RS Ophiuchi during its 2021 outburst. The observations were carried out with the upgraded Giant Metrewave Radio Telescope spanning a frequency range of 0.15–1.4 GHz during 23–287 d post the outburst. The average value of the optically thin spectral index is α ∼ −0.4 (F ν ∝ να), indicating a non-thermal origin of the radio emission at the observed frequencies. The radio light curves are best represented by shock-driven synchrotron emission, initially absorbed by a clumpy ionized circumbinary medium. We estimate the mass-loss rate of the red giant companion star to be |$\dot{M} \sim$| 7.5 × 10−8 M⊙ yr−1 for an assumed stellar wind velocity of 20 km s−1. The 0.15–1.4 GHz radio light curves of the 2021 outburst are systematically brighter than those of the 2006 outburst. Considering similar shock properties between the two outbursts, this is indicative of a relatively higher particle number density in the synchrotron emitting plasma in the current outburst. [ABSTRACT FROM AUTHOR]

We simulate the formation of second-generation (SG) stars in young clusters with masses of 105 and |$10^6\, \mathrm{M}_{\odot }$| within |$30\!-\!100\, \mathrm{Myr}$| after the formation of clusters. We assume the clusters move through a uniform interstellar medium with gas densities of 10−24 and |$10^{-23}\, \mathrm{g\, cm}^{-3}$| and consider the stellar winds from asymptotic giant branch (AGB) stars, gas accretion on to the cluster, ram pressure, star formation, and photoionization feedback of our stellar systems including binary stars. We find that SG stars can be formed only within the |$10^6\, \mathrm{M}_{\odot }$| cluster in the high-density simulation, where the cluster can accrete sufficient pristine gas from their surrounding medium, leading to efficient cooling required for the ignition of SG formation and sufficient dilution of the AGB ejecta. Hence, our results indicate that a denser environment is another requirement for the AGB scenario to explain the presence of multiple populations in globular clusters. On the other hand, the ionizing feedback becomes effective in heating the gas in our low-density simulations. As a result, the clusters cannot accumulate a considerable amount of pristine gas at their centre. The gas mass within the clusters in these simulations is similar to that in young massive clusters (YMCs). Hence, our studies can provide a possible reason for the lack of gas, star formation, and SG stars in YMCs. Our results indicate that the ionizing stellar feedback is not a severe problem for SG formation; rather, it can help the AGB scenario to account for some observables. [ABSTRACT FROM AUTHOR]

Depending on the distance of the exoplanet from the central star and the properties of this star, different regimes of stellar wind flow around it arise. If the exoplanet is located at a distance up to the Alfvén radius, where the wind speed is equal to the Alfvén speed, or the Alfvén Mach number , the exoplanet generates Alfvén wings. If it is situated beyond the Alfvén radius, a comet-like magnetosphere appears, similar to that of the planets of the Solar System. The paper examines how the transition from one flow regime to another can be described on the base of a paraboloid model of the magnetospheric magnetic field using the example of exoplanet HD 209458b. [ABSTRACT FROM AUTHOR]

Solar-type stars form with a wide range of rotation rates Ω. A wide Ω range persists until a stellar age of t  ∼ 0.6 Gyr, after which solar-type stars exhibit Skumanich spin-down where Ω ∝  t −1/2. Rotational evolution models incorporating polytropic stellar winds struggle to simultaneously reproduce these two regimes, namely the initially wide Ω range and the Skumanich spin-down without imposing an a priori cap on the wind mass-loss rate. We show that a three-dimensional wind model driven by Alfvén waves and observational data yields wind torques that agree with the observed age distribution of Ω. In our models of the Sun and 27 open cluster stars aged from 0.04 to 0.6 Gyr that have observationally derived surface magnetic maps and rotation rates, we find evidence of exponential spin-down in young stars that are rapid rotators and Skumanich spin-down for slow rotators. The two spin-down regimes emerge naturally from our data-driven models. Our modelling suggests that the observed age distribution of stellar rotation rates Ω arises as a consequence of magnetic field strength saturation in rapid rotators. [ABSTRACT FROM AUTHOR]

The nearby supernova 1987A was accompanied by a burst of neutrino emission, which indicates that a compact object (a neutron star or black hole) was formed in the explosion. There has been no direct observation of this compact object. In this work, we observe the supernova remnant with JWST spectroscopy, finding narrow infrared emission lines of argon and sulfur. The line emission is spatially unresolved and blueshifted in velocity relative to the supernova rest frame. We interpret the lines as gas illuminated by a source of ionizing photons located close to the center of the expanding ejecta. Photoionization models show that the line ratios are consistent with ionization by a cooling neutron star or a pulsar wind nebula. The velocity shift could be evidence for a neutron star natal kick. [ABSTRACT FROM AUTHOR]

Only 3–4 per cent of Galactic O stars are observed to display the emission features representative of the OBe phenomenon, compared to Galactic B stars, which display these characteristics in 25–35 per cent of B0 and B1 stars. We present new observations of the high-mass O star, VES 735, which confirms its classification as one of these rare emission-line stars. These are its first recorded observations that display strong spectroscopic variations in nearly 30 yr of monitoring, with the H α profile exhibiting a 10-fold increase in emission compared to observations taken between 1996 and 2014 and having variations which show episodes of inflowing and outflowing material. These observations, coupled with photometric variations in the visible and infrared, show behaviour that is consistent with the mass reservoir effect for viscous decretion discs. We propose that in 2015 VES 735 began an approximately 3 yr event in which mass was being injected into the circumstellar environment followed by re-accretion towards the star. We also find evidence that the re-accretion may have been interrupted with another, smaller, mass-injection event based on observations in 2022 and 2023. Observational cadences ranging from hours to months show no evidence that VES 735 is part of a binary system, making it an ideal candidate for future observations to further investigate the evolution of high-mass stars and the OBe phenomenon as it pertains to their circumstellar environment. [ABSTRACT FROM AUTHOR]

We present new analytical solutions for the evolution of protoplanetary discs (PPDs) where magnetohydrodynamic (MHD) wind-driven processes dominate. Our study uses a 1D model which incorporates equations detailing angular momentum extraction by MHD winds and mass-loss rates. Our solutions demonstrate that the disc retains its initial state during the early phases; however, it rapidly evolves towards a self-similar state in the later stages of disc evolution. The total disc mass undergoes a continuous decline over time, with a particularly rapid reduction occurring beyond a certain critical time threshold. This gradual decrease in mass is influenced by the wind parameters and the initial surface density of the disc. In the MHD wind-dominated regime, we show that the disc's lifespan correlates positively with the magnetic lever arm up to a certain threshold, irrespective of the initial disc size. PPDs with a larger magnetic lever arm are found to maintain significantly higher total disc mass over extended periods compared to their counterparts. The mass ejection-to-accretion ratio increases in efficient wind scenarios and is further amplified by a steeper initial surface density profile. Our analysis also reveals varied evolutionary trajectories in the plane of accretion rate and total disc mass, influenced by magnetic parameters and initial disc size. In scenarios with efficient MHD winds, discs with bigger sizes have extended operation time for mechanisms governing planet formation. [ABSTRACT FROM AUTHOR]

We present Atacama Large Millimeter/sub-millimeter Array (ALMA) Cycle-5 observations of HBC 494, as well as calculations of the kinematic and dynamic variables which represent the object's wide-angle bipolar outflows. HBC 494 is a binary FU Orionis type object located in the Orion A molecular cloud. We take advantage of combining the ALMA main array, Atacama Compact Array (ACA), and Total Power (TP) array in order to map HBC 494's outflows and thus, estimate their kinematic parameters with higher accuracy in comparison to prior publications. We use 12CO, 13CO, C18O, and SO observations to describe the object's outflows, envelope, and disc, as well as estimate the mass, momentum, and kinetic energy of the outflows. After correcting for optical opacity near systemic velocities, we estimate a mass of 3.0 × 10−2 M⊙ for the southern outflow and 2.8 × 10−2 M⊙ for northern outflow. We report the first detection of a secondary outflow cavity located approximately 15 arcsec north of the central binary system, which could be a remnant of a previous large-scale accretion outburst. Furthermore, we find CO spatial features in HBC 494's outflows corresponding to position angles of ∼35° and ∼145°. This suggests that HBC 494's outflows are most likely a composite of overlapping outflows from two different sources, i.e. HBC 494a and HBC 494b, the two objects in the binary system. [ABSTRACT FROM AUTHOR]

Accurate determination of mass-loss rates from massive stars is important to understand stellar and galactic evolution and enrichment of the interstellar medium. Large-scale structure and variability in stellar winds have significant effects on mass-loss rates. Time-series observations provide direct quantification of such variability. Observations of this nature are available for some Galactic early supergiant stars but not yet for stars in lower metallicity environments such as the Magellanic Clouds. We utilize ultraviolet spectra from the Hubble Space Telescope ULLYSES program to demonstrate that the presence of structure in stellar winds of supergiant stars at low metallicities may be discerned from single-epoch spectra. We find evidence that, for given stellar luminosities and mean stellar wind optical depths, structure is more prevalent at higher metallicities. We confirm, at Large Magellanic Cloud (0.5 Z ⊙), Small Magellanic Cloud (0.2 Z ⊙), and lower (0.14–0.1 Z ⊙) metallicities, earlier Galactic results that there does not appear to be correlation between the degree of structure in stellar winds of massive stars and stellar effective temperature. Similar lack of correlation is found with regard to terminal velocity of stellar winds. Additional and revised values for radial velocities of stars and terminal velocities of stellar winds are presented. Direct evidence of temporal variability, on time-scales of several days, in stellar wind at low metallicity is found. We illustrate that narrow absorption components in wind-formed profiles of Galactic OB stellar spectra remain common in early B supergiant spectra at low metallicities, providing means for better constraining hot, massive star mass-loss rates. [ABSTRACT FROM AUTHOR]

The similarity in physical conditions in the winds of low-mass post-asymptotic giant branch stars and evolved massive stars leads to the appearance of an interesting phenomenon of spectral mimicry. Because of this, the discovery of every new star with a Wolf–Rayet (WR) spectrum requires a special study of its evolutionary status before it can be included in the list of Galactic WR stars. A couple of years ago, LAMOST J040901.83+323955.6 (hereafter J0409+3239) was selected as a WR star in the LAMOST spectroscopic data base by machine-learning methods. In this work, we investigate its evolutionary status. After analysing the spatial location of J0409+3239  in the Galaxy and its position in the colour–magnitude diagram, we conclude that J0409+3239  is instead a low-mass object displayng the WR phenomenon. Its luminosity is |$L*=1000~\rm L_\odot$| and its effective temperature is T eff = 40 000 K. Using new and archival photometric data, we detected irregular variability on time-scales from hours to tens of days with an amplitude of up to ~0.2 mag. A comparison of the spectrum obtained in 2022 with that from 2014 also shows evidence of spectral variability. The absence of a clearly detected circumstellar nebula prevents the classification of J0409+3239  as [WR], namely as the central star of a planetary nebula (CSPN). However, the position of J0409+3239 on the Hertzsprung–Russell diagram suggests that this object  is a low-mass star caught in a rare transitional phase to CSPN. Estimation of the J0409+3239  mass based on evolutionary tracks shows that it is less than |$0.9~\rm M_\odot$|⁠ , and thus that the age of the Galaxy is barely sufficient for the star to have evolved to its current stage. [ABSTRACT FROM AUTHOR]

Galaxies comprise intricate networks of interdependent processes which together govern their evolution. Central among these are the multiplicity of feedback channels, which remain incompletely understood. One outstanding problem is the understanding and modelling of the multiphase nature of galactic winds, which play a crucial role in galaxy formation and evolution. We present the results of three-dimensional magnetohydrodynamical simulations of tall–box interstellar medium (ISM) patches with clustered supernova-driven outflows. Dynamical fragmentation of the ISM during superbubble breakout seeds the resulting hot outflow with a population of cool clouds. We focus on analyzing and modelling the origin and properties of these clouds. Their presence induces large-scale turbulence, which, in turn, leads to complex cloud morphologies. Cloud sizes are well described by a power-law distribution and mass growth rates can be modelled using turbulent radiative mixing layer theory. Turbulence provides significant pressure support in the clouds, while magnetic fields only play a minor role. We conclude that many of the physical insights and analytic scalings derived from idealized small-scale simulations of turbulent radiative mixing layers and cloud–wind interactions are directly translatable and applicable to these larger scale cloud populations. This opens the door to developing effective subgrid recipes for their inclusion in global-scale galaxy models where they are unresolved. [ABSTRACT FROM AUTHOR]

The Thermally Pulsing- (Super) Asymptotic Giant Branch is a late stage in the evolution of low- and intermediate-mass stars. These stars undergo strong wind mass-loss and diverse nucleosynthesis. Third dredge-up events, that occur following thermal pulses, are responsible for enriching the surfaces of Asymptotic Giant Branch stars, hence an understanding of this process is crucial for constraining galactic chemical evolution. Using a custom numerical scheme, we investigate the temporal and spatial resolution required to resolve the third dredge-up in the 1D stellar evolution code mesa. With mesa 's default controls, the third dredge-up efficiency is underestimated by as much as |$\approx 76~{{\ \rm per\ cent}}$|⁠. In stars that undergo hot third dredge-up (M ≳ 6 M⊙), the third dredge-up efficiency is overestimated by |$\approx 55~{{\ \rm per\ cent}}$|⁠. The Thermally Pulsing- (Super) Asymptotic Giant Branch (TP-(S)AGB) evolution is computed for models with initial masses 1 ≤ M i/M⊙ ≤ 8 at Solar metallicity (Z = 0.014). The minimum initial mass for carbon stars falls in the range 1.5–1.75 M⊙, compatible with observations. The use of mesa for TP-(S)AGB evolution is validated by comparison to the widely used monash models which show good agreement in the maximum third dredge-up efficiency at initial masses M i > 2 M⊙. We also compare the third dredge-up efficiency in models produced using two independent stellar evolution codes, fruity and aton , which were computed with various differences in input physics including mass-loss, and which exhibit weaker third dredge-up episodes. [ABSTRACT FROM AUTHOR]

The ability to determine galaxy properties such as masses, ages, and star formation rates robustly is critically limited by the ability to measure dust attenuation accurately. Dust reddening is often characterized by comparing observations to models of either nebular recombination lines or the UV continuum. Here, we use a new technique to measure dust reddening by exploiting the He ii λ 1640 and λ 4686 emission lines originating from the stellar winds of Wolf–Rayet stars. The intrinsic line ratio is determined by atomic physics, enabling an estimate of the stellar reddening similar to how the Balmer lines probe gas-emission reddening. The He ii line ratio is measured from UV and optical spectroscopy using the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope for eight nearby galaxies hosting young massive star clusters. We compare our results to dust reddening values estimated from UV spectral slopes and from Balmer line ratios and find tentative evidence for systematic differences. The reddening derived from the He ii lines tends to be higher, whereas that from the UV continuum tends to be lower. A larger sample size is needed to confirm this trend. If confirmed, this may indicate an age sequence probing different stages of dust clearing. Broad He ii lines have also been detected in galaxies more distant than in our sample, providing the opportunity to estimate the dust reddening of the youngest stellar populations out to distances of ∼100 Mpc. [ABSTRACT FROM AUTHOR]

We investigate the nebular emission produced by young stellar populations using the new galsevn model based on the combination of the sevn population-synthesis code including binary-star processes and the galaxev code for the spectral evolution of stellar populations. Photoionization calculations performed with the cloudy code confirm that accounting for binary-star processes strongly influences the predicted emission-line properties of young galaxies. In particular, we find that our model naturally reproduces the strong He  ii  λ4686/H β ratios commonly observed at high H β equivalent widths in metal-poor, actively star-forming galaxies, which have proven challenging to reproduce using previous models. Including bursty star formation histories broadens the agreement with observations, while the most extreme He  ii  λ1640 equivalent widths can be reproduced by models dominated by massive stars. galsevn also enables us to compute, for the first time in a way physically consistent with stellar emission, the emission from accretion discs of X-ray binaries (XRBs) and radiative shocks driven by stellar winds and supernova explosions. We find that these contributions are unlikely to prominently affect the predicted He  ii  λ4686/H β ratio, and that previous claims of a significant contribution by XRBs to the luminosities of high-ionization lines are based on models predicting improbably high ratios of X-ray luminosity to star formation rate, inconsistent with the observed average luminosity function of XRBs in nearby galaxies. The results presented here provide a solid basis for a more comprehensive investigation of the physical properties of observed galaxies with galsevn using Bayesian inference. [ABSTRACT FROM AUTHOR]

We present proper-motion measurements and long-slit spectroscopy of the Mg  ii nebula around η Carinae obtained with the Wide Field Camera 3 and Space Telescope Imaging Spectrograph (STIS) aboard the Hubble Space Telescope. Detailed kinematics of the Mg  ii -emitting material constrain the geometry and history of mass-loss from η Car, and provide estimated ejection dates, assuming linear, ballistic motions. These measurements show that the neutral gas immediately outside the Homunculus – i.e. material into which the Homunculus is now expanding – was expelled over several decades prior to the Great Eruption, thus representing unshocked pre-eruption stellar wind. Material outside the Homunculus is therefore not part of a Hubble-like flow from the Great Eruption itself. This result discriminates between versions of merger-in-a-triple models for η Car. The STIS spectrum of Mg  ii -emitting gas along the projected outflow axis displays radial velocities consistent with bipolar expansion, redshifted several hundred km s−1 towards the northwest, similarly blueshifted towards the southeast, and with low internal velocity dispersion. The η Car system was therefore losing mass in a relatively fast, low-density polar wind for several decades that probably traces the critical inspiral phase preceding a merger event. [ABSTRACT FROM AUTHOR]

Cir X-1 is an unusual X-ray binary, which has resumed periodic outbursts since August 2019. We investigate the post-quiescence spectral properties of Cir X-1 at orbital phase around the periastron using NICER and NuSTAR X-ray observatories after the resumption of outbursts. We identify two distinct classes of spectral properties. The first class exhibits highly ionized absorption, whereas the second class does not. We suggest that the ionized absorption originates from the shelter of the disc wind, while the low-ionized/neutral absorption arises from the companion's stellar wind. We also suggest that the disc wind may be always present in both classes, and a warped precession disc could alter the visibility of the disc wind. [ABSTRACT FROM AUTHOR]

We analyse the XMM – Newton RGS spectra of Wolf–Rayet (WR) 140, an archetype long-period eccentric WR+O colliding wind binary. We evaluate the spectra of O and Fe emission lines and find that the plasmas emitting these lines have the largest approaching velocities with the largest velocity dispersions between phases 0.935 and 0.968 where the inferior conjunction of the O star occurs. This behaviour is the same as that of the Ne line-emission plasma presented in our previous paper. We perform a diagnosis of the electron number density n e using the He-like triplet lines of O and Ne-like Fe–L lines. The former results in a conservative upper limit of n e ≲ 1010–1012 cm−3 on the O line-emission site, while the latter cannot impose any constraint on the Fe line-emission site because of statistical limitations. We calculate the line-of-sight velocity and its dispersion separately along the shock cone. By comparing the observed and calculated line-of-sight velocities, we update the distance of the Ne line-emission site from the stagnation point. By assuming radiative cooling of the Ne line-emission plasma using the observed temperature and the local stellar wind density, we estimate that the line-emission site extends along the shock cone by at most ±58 per cent (phase 0.816) of the distance from the stagnation point. In this framework, the excess of the observed velocity dispersion over that calculated is ascribed to turbulence in the hot-shocked plasma at earlier orbital phases of 0.816, 0.912, and 0.935, with the largest velocity dispersion of 340-630 km s−1 at phase 0.912. [ABSTRACT FROM AUTHOR]

B[e] type stars are characterized by strong emission lines, photometric, and spectroscopic variabilities and unsteady mass-loss rates. MWC 137 is a galactic B[e] type star situated in the constellation Orion. Recent photometric observation of MWC 137 by TESS has revealed variabilities with a dominant period of 1.9 d. The origin of this variability is not known but suspected to be from stellar pulsation. To understand the nature and origin of this variability, we have constructed three different set of models of MWC 137 and performed non-adiabatic linear stability analysis. Several low order modes are found to be unstable in which models having mass in the range of 31–34 M⊙ and 43–46 M⊙ have period close to 1.9 d. The evolution of instabilities in the non-linear regime for model having solar chemical composition and mass of 45 M⊙ leads to finite amplitude pulsation with a period of 1.9 d. Therefore, in the present study we confirm that this variability in MWC 137 is due to pulsation. Evolutionary tracks passing through the location of MWC 137 in the Hertzsprung–Russell diagram indicate that the star is either in post main sequence evolutionary phase or about to enter in this evolutionary phase. [ABSTRACT FROM AUTHOR]

Asymptotic giant branch (AGB) stars experience heavy episodes of mass-loss through a slow stellar wind during the thermal pulse phase that form large, pc-scale structures around them. As the AGB stellar wind interacts with the interstellar medium (ISM), the otherwise isotropic ejecta gets distorted, resulting in asymmetric shapes, bow-shock structures and, in the case of fast motion relative to the surrounding ISM, extended wakes and tails as unexpectedly detected in GALEX ultraviolet (UV) images of o  Cet, also known as Mira. Since that discovery, another fourteen AGB stars have been reported to exhibit extended UV emission around them. Here, we present the discovery of extended UV emission around another three AGB stars, namely R For, R Hor, and DM Tuc. The analysis of the overall properties of the regions of extended UV emission indicates that these are preferentially detected in closer AGB stars far away from the Galactic plane, i.e. sources less extincted. Faster AGB stars tend to have more elongated shapes, with bow-shocks and wakes or tails of material, while AGB stars farther away from the Galactic plane tend to be surrounded by larger regions of UV emission. [ABSTRACT FROM AUTHOR]

Stellar radio emission can measure a star's magnetic field strength and structure, plasma density, and dynamics, and the stellar wind pressure impinging on exoplanet atmospheres. However, properly interpreting the radio data often requires temporal baselines that cover the rotation of the stars, orbits of their planets, and any longer-term stellar activity cycles. Here we present our monitoring campaign on the young, active M dwarf AU Microscopii with the Australia Telescope Compact Array between 1.1 and 3.1 GHz. With over 250 h of observations, these data represent the longest radio monitoring campaign on a single main-sequence star to date. We find that AU Mic produces a wide variety of radio emission, for which we introduce a phenomenological classification scheme predicated on the polarisation fraction and time-frequency structure of the emission. Such a classification scheme is applicable to radio emission from other radio-bright stars. The six types of radio emission detected on AU Mic can be broadly categorised into five distinct types of bursts, and broadband quiescent emission. We find that the radio bursts are highly circularly polarised and periodic with the rotation period of the star, implying that the emission is beamed. It is therefore most likely produced by the electron cyclotron maser instability. We present a model to show that the observed pattern of emission can be explained by emission from auroral rings on the magnetic poles. The total intensity of the broadband emission is stochastic, but we show that its circular polarisation fraction is also periodic with the rotation of the star. Such a periodicity in the polarised fraction of emission has not been observed on an M dwarf before. We present a qualitative model to describe the periodicity in the polarisation fraction of the broadband emission, using low-harmonic gyromagnetic emission. Using a simple qualitative model, we infer a magnetic obliquity of at least 20° from the observed variation in polarisation fraction. Finally, we show that the radio emission might be evolving on long timescales, hinting at a potential stellar magnetic activity cycle. [ABSTRACT FROM AUTHOR]

Context. V1309 Sco is an example of a red nova, a product of the merger between non-compact stars. V1309 Sco is particularly important within the class of red novae due to the abundance of photometric data of the progenitor binary before the merger. Aims. We aim to investigate the spatio-kinematic and chemical properties of the circumstellar environment, including deriving the physical conditions and establishing the origins of the different circumstellar components. Methods. We used radiative transfer modelling of molecular emission in sub-millimetre spectra to examine the properties of the molecular gas, and we used forbidden line diagnostics from optical spectra to constrain the electron density and temperature using forbidden line diagnostics. We compared line intensities from shock models to observations to look for and constrain shocks. Results. We derived a new kinematical distance of 5.6 kpc to the source. The detection of ro-vibrational H2 and sub-millimetre HCO+ emission in 2016 and 2019, respectively, indicate active shock interactions within the circumstellar environment. The velocity profiles of both H2 and HCO+, as well as the moment-1 maps of sub-millimetre CO and 29SiO, indicate a bipolar structure that may be asymmetric. The sub-millimetre and optical molecular emission exhibits temperatures of 35–113 and 200 K, respectively, whilst the atomic gas is much hotter, with temperatures of 5–15 kK, which may be due to shock heating. Conclusions. The detection of a bipolar structure in V1309 Sco indicates further similarities with the structure of another Galactic red nova, V4332 Sgr. It provides evidence that bipolar structures may be common in red novae. All collected data are consistent with V1309 Sco being a kinematically and chemically complex system. [ABSTRACT FROM AUTHOR]

Context. During the first four all-sky surveys eRASS:4, which was carried out from December 2019 to 2021, the extended Roentgen Survey with an Imaging Telescope Array (eROSITA) on board the Spektrum-Roentgen-Gamma (Spektr-RG, SRG) observed the Galactic H II region, the Carina nebula. Aims. We analysed the eRASS:4 data to study the distribution and spectral properties of the hot interstellar plasma and the bright stellar sources in the Carina nebula. Methods. The spectral extraction regions of the diffuse emission were defined based on the X-ray spectral morphology and multi-wavelength data. The spectra were fit with a combination of thermal and non-thermal emission models. The X-ray bright point sources in the Carina nebula are the colliding wind binary η Car, several O stars, and Wolf–Rayet (WR) stars. We extracted the spectra of the brightest stellar sources, which can be well fit with a multi-component thermal plasma model. Results. The spectra of the diffuse emission in the brighter parts of the Carina nebula are well reproduced by two thermal models, a lower-temperature component (~0.2 keV) and a higher-temperature component (0.6–0.8 keV). An additional non-thermal component dominates the emission above ~1 keV in the Central region around η Car and the other massive stars. Significant orbital variation in the X-ray flux was measured for η Car, WR 22, and WR 25. η Car requires an additional time-variable thermal component in the spectral model, which is associated with the wind-wind collision zone. Conclusions. Properties such as temperature, pressure, and luminosity of the X-ray emitting plasma in the Carina nebula derived from the eROSITA data are consistent with theoretical calculations of emission from superbubbles. This confirms that the X-ray emission is caused by the hot plasma inside the Carina nebula that has been shocked-heated by the stellar winds of the massive stars, in particular, of η Car. [ABSTRACT FROM AUTHOR]

We present the results from an analysis of data from an XMM–Newton observation of the accreting high-mass X-ray binary pulsar GX 301−2. Spectral analysis in the non-flaring segment of the observation revealed that the equivalent width of the iron fluorescence emission is correlated with the observed absorption column density and the ratio of the iron Kβ and Kα line strength varied with the flux of the source. Coherent pulsations were detected with the spin period of the pulsar of 687.9 ± 0.1 s, and a secondary pulsation was also detected with a period of 671.8 ± 0.2 s, most prominent in the energy band of the iron line. At the spin period of the neutron star, the pulsation of the iron line has a low amplitude and the profile is different from the continuum. Pulse phase-resolved spectroscopy also revealed pulsations of the iron emission line during the non-flaring segment of the light curve. At the secondary period, both the iron line and the continuum have nearly identical pulse fraction and pulse profile. The additional periodicity can be attributed to the beat frequency between the spin of the neutron star and the Keplerian frequency of a stellar wind clump in retrograde motion around the neutron star. Reprocessed X-ray emissions originating from the clump can produce the observed secondary pulsations both in the continuum and the iron fluorescence line. The clump rotating around the neutron star is estimated to be approximately five lt-s away from the neutron star. [ABSTRACT FROM AUTHOR]

Supernova remnants are the nebular leftover of defunct stellar environments, resulting from the interaction between a supernova blastwave and the circumstellar medium shaped by the progenitor throughout its life. They display a large variety of non-spherical morphologies such as ears that shine non-thermally. We have modelled the structure and the non-thermal emission of the supernova remnant G1.9 + 0.3 through 3D magnetohydrodynamic numerical simulations. We propose that the peculiar ear-shaped morphology of this supernova remnant results from the interaction of its blast wave with a magnetized circumstellar medium, which was previously asymmetrically shaped by the past stellar wind emanating from the progenitor star or its stellar companion. We created synthetic non-thermal radio and X-ray maps from our simulated remnant structure, which are in qualitative agreement with observations, forming ears on the polar directions. Our synthetic map study explains the discrepancies between the measured non-thermal radio and X-ray surface brightness distributions assuming that the inverse Compton process produces the observed X-ray emission. [ABSTRACT FROM AUTHOR]

As the industry transitions toward Floating Offshore Wind Turbines (FOWT) in greater depths, conventional chain mooring lines become impractical, prompting the adoption of synthetic fiber ropes. Despite their advantages, these mooring lines present challenges in inspection due to their exterior jacket, which prevents visual assessment. The current study focuses on vibration-based Structural Health Monitoring (SHM) in FOWT synthetic mooring lines under uncertainty arising from varying Environmental and Operational Conditions (EOCs). Six damage detection methods are assessed, utilizing either multiple models or a single functional model. The methods are based on Vector Autoregressive (VAR) or Transmittance Function Autoregressive with exogenous input (TF-ARX) models. All methods are evaluated through a Monte Carlo study involving 1100 simulations, utilizing acceleration signals generated from a finite element model of the OO-Star Wind Floater Semi 10 MW wind turbine. With signals from only two measuring positions, the methods demonstrate excellent results, detecting the stiffness reduction of a mooring line at levels 10% through 50%. The methods are also tested for healthy cases, with those utilizing TF-ARX models achieving zero false alarms, even for EOCs not encountered in the training data. [ABSTRACT FROM AUTHOR]

It is commonly believed that accretion discs are truncated and their inner regions are described by advection dominated accretion flows (ADAFs) in the hard spectral state of black hole X-ray binaries. However, the increasing occurrence of a relativistically blurred Fe K α line together with a hard continuum points to the existence of a thin disc located near the innermost stable circular orbit (ISCO). Assuming the accretion in the hard state is via an ADAF extending to near 100 Schwarzschild radii, which is supplied by either a stellar wind from a companion star or resulting from an evaporated disc, we study the possible condensation of the hot gas during its accretion towards the black hole. It is found that a small fraction of the ADAF condenses into a cold disc as a consequence of efficient radiative cooling at small distances, forming a disc-corona configuration near the ISCO. This takes place for low accretion rates corresponding to luminosities ranging from ∼10−3 to a few per cent of the Eddington luminosity. The coexistence of the weak inner disc and the dominant hot accretion flow provides a natural explanation of the broad K α line in the hard state. Detailed computations demonstrate that such accretion flows produce a hard X-ray spectrum accompanied by a weak disc component with a negative correlation between the 2 and 10 keV photon index and the Eddington ratio. The predicted spectrum of Cygnus X-1 and the correlation between the photon index and the Eddington ratio are in good agreement with observations. [ABSTRACT FROM AUTHOR]