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The spin evolution of main sequence stars has long been of interest for basic stellar evolution, stellar aging, stellar activity, and consequent influence on companion planets. Observations of older than solar late-type main-sequence stars have been interpreted to imply that a change from a dipole-dominated magnetic field to one with more prominent higher multipoles might be necessary to account for the data. The spin-down models that lead to this inference are essentially tuned to the sun. Here we take a different approach which considers individual stars as fixed points rather than just the Sun. We use a time-dependent theoretical model to solve for the spin evolution of low-mass main-sequence stars that includes a Parker-type wind and a time-evolving magnetic field coupled to the spin. Because the wind is exponentially sensitive to the stellar mass over radius and the coronal base temperature, the use of each observed star as a separate fixed point is more appropriate and, in turn, produces a set of solution curves that produces a solution envelope rather than a simple line. This envelope of solution curves, unlike a single line fit, is consistent with the data and does not unambiguously require a modal transition in the magnetic field to explain it., 8 pages, 4 figures; Accepted for publication in MNRAS

It has long been speculated that jet feedback from accretion onto the companion during a common envelope (CE) event could affect the orbital evolution and envelope unbinding process, but this conjecture has heretofore remained largely untested. We present global 3D hydrodynamical simulations of CE evolution (CEE) that include a jet subgrid model and compare them with an otherwise identical model without a jet. Our binary consists of a $2M_\odot$ red giant branch primary and a $1M_\odot$ or $0.5M_\odot$ main sequence or white dwarf secondary companion modeled as a point particle. We run the simulations for 10 orbits (40 days). Our jet model adds mass at a constant rate $\dot{M}_\mathrm{j}$ of order the Eddington rate, with maximum velocity $v_\mathrm{j}$ of order the escape speed, to two spherical sectors with the jet axis perpendicular to the orbital plane, and supplies kinetic energy at the rate $\sim\dot{M}_\mathrm{j} v_\mathrm{j}^2/40$. We explore the influence of the jet on orbital evolution, envelope morphology and envelope unbinding, and assess the dependence of the results on jet mass-loss rate, launch speed, companion mass, opening angle, and whether or not subgrid accretion is turned on. In line with our theoretical estimates, we find that in all cases the jet becomes choked around the time of first periastron passage. We also find that jets lead to increases in unbound mass of up to $\sim10\%$, as compared to simulations which do not include a jet., Comment: 16 pages, 8 figures

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Magnetic fields provide an important probe of the thermal, material, and structural history of planetary and sub-planetary bodies. Core dynamos are a potential source of magnetic fields for differentiated bodies, but evidence of magnetization in undifferentiated bodies requires a different mechanism. Here we study the amplified field provided by the stellar wind to an initially unmagnetized body using analytic theory and numerical simulations, employing the resistive MHD AstroBEAR adaptive mesh refinement (AMR) multiphysics code. We obtain a broadly applicable scaling relation for the peak magnetization achieved once a wind advects, piles-up, and drapes a body with magnetic field, reaching a quasi-steady state. We find that the dayside magnetic field for a sufficiently conductive body saturates when it balances the sum of incoming solar wind ram, magnetic, and thermal pressures. Stronger amplification results from pileup by denser and faster winds. Careful quantification of numerical diffusivity is required for accurately interpreting the peak magnetic field strength from simulations, and corroborating with theory. As specifically applied to the Solar System, we find that early solar wind-induced field amplification is a viable source of magnetization for observed paleointensities in meteorites from some undifferentiated bodies. This mechanism may also be applicable to other Solar System bodies, including metal-rich bodies to be visited in future space missions such as the asteroid (16) Psyche., 12 pages, 6 figures, accepted by MNRAS

Full list of authors: De Marco, Orsola; Akashi, Muhammad; Akras, Stavros; Alcolea, Javier; Aleman, Isabel; Amram, Philippe; Balick, Bruce; De Beck, Elvire; Blackman, Eric G.; Boffin, Henri M. J.; Boumis, Panos; Bublitz, Jesse; Bucciarelli, Beatrice; Bujarrabal, Valentin; Cami, Jan; Chornay, Nicholas; Chu, You-Hua; Corradi, Romano L. M.; Frank, Adam; García-Hernández, D. A.; García-Rojas, Jorge; García-Segura, Guillermo; Gómez-Llanos, Veronica; Gonçalves, Denise R.; Guerrero, Martín A.; Jones, David; Karakas, Amanda I.; Kastner, Joel H.; Kwok, Sun; Lykou, Foteini; Manchado, Arturo; Matsuura, Mikako; McDonald, Iain; Miszalski, Brent; Mohamed, Shazrene S.; Monreal-Ibero, Ana; Monteiro, Hektor; Montez, Rodolfo; Baez, Paula Moraga; Morisset, Christophe; Nordhaus, Jason; Mendes de Oliveira, Claudia; Osborn, Zara; Otsuka, Masaaki; Parker, Quentin A.; Peeters, Els; Quint, Bruno C.; Quintana-Lacaci, Guillermo; Redman, Matt; Ruiter, Ashley J.; Sabin, Laurence; Sahai, Raghvendra; Contreras, Carmen Sánchez; Santander-García, Miguel; Seitenzahl, Ivo; Soker, Noam; Speck, Angela K.; Stanghellini, Letizia; Steffen, Wolfgang; Toalá, Jesús A.; Ueta, Toshiya; Van de Steene, Griet; Van Winckel, Hans; Ventura, Paolo; Villaver, Eva; Vlemmings, Wouter; Walsh, Jeremy R.; Wesson, Roger; Zijlstra, Albert A., Planetary nebulae—the ejected envelopes of red giant stars—provide us with a history of the last, mass-losing phases of 90% of stars initially more massive than the Sun. Here we analyse images of the planetary nebula NGC 3132 from the James Webb Space Telescope (JWST) Early Release Observations. A structured, extended hydrogen halo surrounding an ionized central bubble is imprinted with spiral structures, probably shaped by a low-mass companion orbiting the central star at about 40–60 au. The images also reveal a mid-infrared excess at the central star, interpreted as a dusty disk, which is indicative of an interaction with another closer companion. Including the previously known A-type visual companion, the progenitor of the NGC 3132 planetary nebula must have been at least a stellar quartet. The JWST images allow us to generate a model of the illumination, ionization and hydrodynamics of the molecular halo, demonstrating the power of JWST to investigate complex stellar outflows. Furthermore, new measurements of the A-type visual companion allow us to derive the value for the mass of the progenitor of a central star with excellent precision: 2.86 ± 0.06 M⊙. These results serve as pathfinders for future JWST observations of planetary nebulae, providing unique insight into fundamental astrophysical processes including colliding winds and binary star interactions, with implications for supernovae and gravitational-wave systems. © 2022, The Author(s), under exclusive licence to Springer Nature Limited., We acknowledge the International Astronomical Union that oversees the work of Commission H3 on Planetary Nebulae. It is through the coordinating activity of this committee that this paper came together. S.A. acknowledges support under the grant 5077 financed by IAASARS/NOA. J.A. and V.B. acknowledge support from the EVENTs/Nebulae-Web research programme, Spanish AEI grant PID2019-105203GB-C21. I.A. acknowledges the support of CAPES, Brazil (Finance Code 001). E.D.B. acknowledges financial support from the Swedish National Space Agency. E.G.B. acknowledges NSF grants AST-1813298 and PHY-2020249. J.C. and E.P. acknowledge support from an NSERC Discovery Grant. G.G.-S. thanks M. L. Norman and the Laboratory for Computational Astrophysics for the use of ZEUS-3D. D.A.G.-H. and A.M. acknowledge support from the ACIISI, Gobierno de Canarias and the European Regional Development Fund (ERDF) under grant with reference PROID2020010051 as well as from the State Research Agency (AEI) of the Spanish Ministry of Science and Innovation (MICINN) under grant PID2020-115758GB-I00. J.G.-R. acknowledges support from Spanish AEI under Severo Ochoa Centres of Excellence Programme 2020-2023 (CEX2019-000920-S). J.G.-R. and V.G.-L. acknowledge support from ACIISI and ERDF under grant ProID2021010074. D.R.G. acknowledges the CNPq grant 313016/2020-8. M.A.G. acknowledges support of grant PGC2018-102184-B-I00 of the Ministerio de Educación, Innovación y Universidades cofunded with FEDER funds and from the State Agency for Research of the Spanish MCIU through the ‘Center of Excellence Severo Ochoa’ award to the Instituto de Astrofísica de Andalucía (SEV-2017-0709). D.J. acknowledges support from the Erasmus+ programme of the European Union under grant number 2020-1-CZ01-KA203-078200. A.I.K. and Z.O. were supported by the Australian Research Council Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), through project number CE170100013. This research is/was supported by an Australian Government Research Training Program (RTP) Scholarship. M.M. and R.W. acknowledge support from STFC Consolidated grant (2422911). C.M. acknowledges support from UNAM/DGAPA/PAPIIT under grant IN101220. S.S.M. acknowledges funding from UMiami, the South African National Research Foundation and the University of Cape Town VC2030 Future Leaders Award. J.N. acknowledges support from NSF grant AST-2009713. C.M.d.O. acknowledges funding from FAPESP through projects 2017/50277-0, 2019/11910-4 e 2019/26492-3 and CNPq, process number 309209/2019-6. J.H.K. and P.M.B. acknowledge support from NSF grant AST-2206033 and a NRAO Student Observing Support grant to Rochester Institute of Technology. M.O. was supported by JSPS Grants-in-Aid for Scientific Research(C) (JP19K03914 and 22K03675). Q.A.P. acknowledges support from the HKSAR Research grants council. Vera C. Rubin Observatory is a Federal project jointly funded by the National Science Foundation (NSF) and the Department of Energy (DOE) Office of Science, with early construction funding received from private donations through the LSST Corporation. The NSF-funded LSST (now Rubin Observatory) Project Office for construction was established as an operating centre under the management of the Association of Universities for Research in Astronomy (AURA). The DOE-funded effort to build the Rubin Observatory LSST Camera (LSSTCam) is managed by SLAC National Accelerator Laboratory (SLAC). A.J.R. was supported by the Australian Research Council through award number FT170100243. L.S. acknowledges support from PAPIIT UNAM grant IN110122. C.S.C.’s work is part of I+D+i project PID2019-105203GB-C22 funded by the Spanish MCIN/AEI/10.13039/501100011033. M.S.-G. acknowledges support by the Spanish Ministry of Science and Innovation (MICINN) through projects AxIN (grant AYA2016-78994-P) and EVENTs/Nebulae-Web (grant PID2019-105203GB-C21). R.S.’s contribution to the research described here was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. J.A.T. thanks the Marcos Moshisnky Fundation (Mexico) and UNAM PAPIIT project IA101622. E.V. acknowledges support from the ‘On the rocks II project’ funded by the Spanish Ministerio de Ciencia, Innovación y Universidades under grant PGC2018-101950-B-I00. A.A.Z. acknowledges support from STFC under grant ST/T000414/1. This research made use of Photutils, an Astropy package for detection and photometry of astronomical sources83, of the Spanish Virtual Observatory (https://svo.cab.inta-csic.es) project funded by MCIN/AEI/10.13039/501100011033/ through grant PID2020-112949GB-I00 and of the computing facilities available at the Laboratory of Computational Astrophysics of the Universidade Federal de Itajubá (LAC-UNIFEI, which is maintained with grants from CAPES, CNPq and FAPEMIG).

Despite spatial and temporal fluctuations in turbulent astrophysical systems, mean-field theories can be used to describe their secular evolution. However, observations taken over time scales much shorter than dynamical time scales capture a system in a single state of its turbulence ensemble. Comparing with mean-field theory can falsify the latter only if the theory is additionally supplied with a quantified precision. The central limit theorem provides appropriate estimates to the precision only when fluctuations contribute linearly to an observable and with constant coherent scales. Here we introduce an error propagation formula that relaxes both limitations, allowing for nonlinear functional forms of observables and inhomogeneous coherent scales and amplitudes of fluctuations. The method is exemplified in the context of accretion disc theories, where inhomogeneous fluctuations in the surface temperature are propagated to the disc emission spectrum--the latter being a nonlinear and non-local function of the former. The derived precision depends non-monotonically on emission frequency. Using the same method, we investigate how binned spectral fluctuations in telescope data change with the spectral resolving power. We discuss the broader implications for falsifiability of a mean-field theory., Comment: 10 pages, 4 figures; accepted by MNRAS

The role of charge exchange in shaping exoplanet photoevaporation remains a topic of contention. Exchange of electrons between stellar wind protons from the exoplanet's host star and neutral hydrogen from the planet's wind has been proposed as a mechanism to create "energetic neutral atoms" (ENAs), which could explain the high absorption line velocities observed in systems where mass loss is occurring. In this paper we present results from 3D hydrodynamic simulations of the mass loss of a planet similar to HD 209458b. We self-consistently launch a planetary wind by calculating the ionization and heating resulting from incident high-energy radiation, inject a stellar wind into the simulation, and allow electron exchange between the stellar and planetary winds. We predict the potential production of ENAs by the wind-wind interaction analytically, then present the results of our simulations, which confirm the analytic limits. Within the limits of our hydrodynamic simulation, we find that charge exchange with the stellar wind properties examined here is unable to explain the absorption observed at high Doppler velocities., arXiv admin note: text overlap with arXiv:1906.00075

Magnetic reconnection converts magnetic energy into thermal and kinetic energy in plasma. Among numerous candidate mechanisms, ion acoustic instabilities driven by the relative drift between ions and electrons, or equivalently electric current, have been suggested to play a critical role in dissipating magnetic energy in collisionless plasmas. However, their existence and effectiveness during reconnection have not been well understood due to ion Landau damping and difficulties in resolving the Debye length scale in the laboratory. Here we report a sudden onset of ion acoustic bursts measured by collective Thomson scattering in the exhaust of anti-parallel magnetically driven reconnection using high-power lasers. The ion acoustic bursts are followed by electron acoustic bursts with electron heating and bulk acceleration. We reproduce these observations with 1D and 2D particle-in-cell simulations in which electron outflow jet drives ion-acoustic instabilities, forming double layers. These layers induce electron two-stream instabilities that generate electron acoustic bursts and energize electrons. Our results demonstrate the importance of ion and electron acoustic dynamics during reconnection when ion Landau damping is ineffective, a condition applicable to a range of astrophysical plasmas including near-Earth space, stellar flares, and black hole accretion engines.

The Moon lacked a long-lived magnetic field of internal origin, and this allowed solar wind volatiles to accumulate in its soils., Determining the presence or absence of a past long-lived lunar magnetic field is crucial for understanding how the Moon’s interior and surface evolved. Here, we show that Apollo impact glass associated with a young 2 million–year–old crater records a strong Earth-like magnetization, providing evidence that impacts can impart intense signals to samples recovered from the Moon and other planetary bodies. Moreover, we show that silicate crystals bearing magnetic inclusions from Apollo samples formed at ∼3.9, 3.6, 3.3, and 3.2 billion years ago are capable of recording strong core dynamo–like fields but do not. Together, these data indicate that the Moon did not have a long-lived core dynamo. As a result, the Moon was not sheltered by a sustained paleomagnetosphere, and the lunar regolith should hold buried 3He, water, and other volatile resources acquired from solar winds and Earth’s magnetosphere over some 4 billion years.

We compute the forces, torque and rate of work on the companion-core binary due to drag in global simulations of common envelope (CE) evolution for three different companion masses. Our simulations help to delineate regimes when conventional analytic drag force approximations are applicable. During and just prior to the first periastron passage of the in-spiral phase, the drag force is reasonably approximated by conventional analytic theory and peaks at values proportional to the companion mass. Good agreement between global and local 3D "wind tunnel" simulations, including similar net drag force and flow pattern, is obtained for comparable regions of parameter space. However, subsequent to the first periastron passage, the drag force is up to an order of magnitude smaller than theoretical predictions, quasi-steady, and depends only weakly on companion mass. The discrepancy is exacerbated for larger companion mass and when the inter-particle separation reduces to the Bondi-Hoyle-Lyttleton accretion radius, creating a turbulent thermalized region. Greater flow symmetry during this phase leads to near balance of opposing gravitational forces in front of and behind the companion, hence a small net drag. The reduced drag force at late times helps explain why companion-core separations necessary for envelope ejection are not reached by the end of limited duration CE simulations., 14 pages, 8 figures, MNRAS in press

The Magnetorotational Instability (MRI) has long been considered a plausibly ubiquitous mechanism to destabilize otherwise stable Keplerian flows to support radially outward transport of angular momentum. Such an efficient transport process would allow fast accretion in astrophysical objects such as stars and black holes to release copious kinetic energy that powers many of the most luminous sources in the universe. But the standard MRI under a purely vertical magnetic field has heretofore never been directly measured despite numerous efforts over more than a decade. Here we report an unambiguous laboratory demonstration of the spring-mass analogue to the standard MRI by comparing motion of a spring-tethered ball within different rotating flows. The experiment corroborates the theory: efficient outward angular momentum transport manifests only for cases with a weak spring in quasi-Keperian flow. Our experimental method accomplishes this in a new way, thereby connecting solid and fluid mechanics to plasma astrophysics., Comment: 7 pages; 4 figures; accepted by Communications Physics

Collisional self-interactions occurring in protostellar jets give rise to strong shocks, the structure of which can be affected by radiative cooling within the flow. To study such colliding flows, we use the AstroBEAR AMR code to conduct hydrodynamic simulations in both one and three dimensions with a power law cooling function. The characteristic length and time scales for cooling are temperature dependent and thus may vary as shocked gas cools. When the cooling length decreases sufficiently rapidly the system becomes unstable to the radiative shock instability, which produces oscillations in the position of the shock front; these oscillations can be seen in both the one and three dimensional cases. Our simulations show no evidence of the density clumping characteristic of a thermal instability, even when the cooling function meets the expected criteria. In the three-dimensional case, the nonlinear thin shell instability (NTSI) is found to dominate when the cooling length is sufficiently small. When the flows are subjected to the radiative shock instability, oscillations in the size of the cooling region allow NTSI to occur at larger cooling lengths, though larger cooling lengths delay the onset of NTSI by increasing the oscillation period., Comment: 12 pages, 21 figures. Accepted for publication in MNRAS

The shear-current effect (SCE) of mean-field dynamo theory refers to the combination of a shear flow and a turbulent coefficient $\beta_{21}$ with a favorable negative sign for exponential mean-field growth, rather than positive for diffusion. There have been long standing disagreements among theoretical calculations and comparisons of theory with numerical experiments as to the sign of kinetic ($\beta^u_{21}$) and magnetic ($\beta^b_{21}$) contributions. To resolve these discrepancies, we combine an analytical approach with simulations, and show that unlike $\beta^b_{21}$, the kinetic SCE $\beta^u_{21}$ has a strong dependence on the kinetic energy spectral index and can transit from positive to negative values at $\mathcal{O}(10)$ Reynolds numbers if the spectrum is not too steep. Conversely, $\beta^b_{21}$ is always negative regardless of the spectral index and Reynolds numbers. For very steep energy spectra, the positive $\beta^u_{21}$ can dominate even at energy equipartition $u_\text{rms}\simeq b_\text{rms}$, resulting in a positive total $\beta_{21}$ even though $\beta^b_{21}0$ and an inconclusive overall sign of $\beta_{21}$ for $\mathcal{O}(10)$ Reynolds numbers. The transient behavior of $\beta^u_{21}$ is demonstrated using the kinematic test-field method. We compute dynamo growth rates for cases with or without rotation, and discuss opportunities for further work., Comment: 17 pages, 12 figures; accepted by MNRAS

We present the first results from comprehensive, near-UV-to-near-IR Hubble Space Telescope Wide Field Camera 3 (WFC3) emission-line imaging studies of two young planetary nebulae (PNe), NGC 7027 and NGC 6302. These two objects represent key sources for purposes of understanding PNe shaping processes. Both nebulae feature axisymmetric and point-symmetric (bipolar) structures and, despite hot central stars and high nebular excitation states, both harbor large masses of molecular gas and dust. The sweeping wavelength coverage of our Cycle 27 Hubble Space Telescope (HST)/WFC3 imaging surveys targeting these two rapidly evolving PNe will provide a battery of essential tests for theories describing the structural and chemical evolution of evolved star ejecta. Here, we present initial color overlays for selected images, and we highlight some of the first results gleaned from the surveys.

Common envelope (CE) evolution is a critical but still poorly understood progenitor phase of many high-energy astrophysical phenomena. Although 3D global hydrodynamic CE simulations have become more common in recent years, those involving an asymptotic giant branch (AGB) primary are scarce, due to the high computational cost from the larger dynamical range compared to red giant branch (RGB) primaries. But CE evolution with AGB progenitors is desirable to simulate because such events are the likely progenitors of most bi-polar planetary nebulae (PNe), and prominent observational testing grounds for CE physics. Here we present a high resolution global simulation of CE evolution involving an AGB primary and $1\,\mathrm{M}_\odot$ secondary, evolved for $20$ orbital revolutions. During the last $16$ of these orbits, the envelope unbinds at an almost constant rate of about $0.1$-$0.2\,\mathrm{M}_\odot\,\mathrm{yr}^{-1}$. If this rate were maintained, the envelope would be unbound in less than $10\,\mathrm{yr}$. The dominant source of this unbinding is consistent with inspiral; we assess the influence of the ambient medium to be subdominant. We compare this run with a previous run that used an RGB phase primary evolved from the same $2\,\mathrm{M}_\odot$ main sequence star to assess the influence of the evolutionary state of the primary. When scaled appropriately, the two runs are quite similar, but with some important differences., 12 pages, 12 figures, published in MNRAS

Significance The age and early history of Earth’s geomagnetic field can provide insight into the evolution of the core and atmosphere. But measurement of Hadean zircons—the oldest known terrestrial materials—and the determination of the antiquity of their magnetizations are amongst the most challenging endeavors in paleomagnetism. New paleomagnetic, electron microscope, geochemical, and paleointensity data indicate the presence of primary magnetite inclusions in select zircons. These data support the presence of the geomagnetic field, and associated shielding of the atmosphere from the solar wind, ∼4.2 billion years ago. A relatively strong field recorded by these zircons at ∼4 billion years ago may be a signal that chemical precipitation in the core was powering the geodynamo., Determining the age of the geomagnetic field is of paramount importance for understanding the evolution of the planet because the field shields the atmosphere from erosion by the solar wind. The absence or presence of the geomagnetic field also provides a unique gauge of early core conditions. Evidence for a geomagnetic field 4.2 billion-year (Gy) old, just a few hundred million years after the lunar-forming giant impact, has come from paleomagnetic analyses of zircons of the Jack Hills (Western Australia). Herein, we provide new paleomagnetic and electron microscope analyses that attest to the presence of a primary magnetic remanence carried by magnetite in these zircons and new geochemical data indicating that select Hadean zircons have escaped magnetic resetting since their formation. New paleointensity and Pb-Pb radiometric age data from additional zircons meeting robust selection criteria provide further evidence for the fidelity of the magnetic record and suggest a period of high geomagnetic field strength at 4.1 to 4.0 billion years ago (Ga) that may represent efficient convection related to chemical precipitation in Earth’s Hadean liquid iron core.

The kinetic energy of supersonic turbulence within interstellar clouds is subject to cooling by dissipation in shocks and subsequent line radiation. The clouds are therefore susceptible to a condensation process controlled by the specific entropy. In a form analogous to the thermodynamic entropy, the entropy for supersonic turbulence is proportional to the log of the product of the mean turbulent velocity and the size scale. We derive a dispersion relation for the growth of entropic instabilities in a spherical self-gravitating cloud and find that there is a critical maximum dissipation time scale, about equal to the crossing time, that allows for fragmentation and subsequent star formation. However, the time scale for the loss of turbulent energy may be shorter or longer, for example with rapid thermal cooling or the injection of mechanical energy. Differences in the time scale for energy loss in different star-forming regions may result in differences in the outcome, for example, in the initial mass function., To be published in MNRAS

Many stars harbour multi-planet systems. As these stars expand late in their evolutions, the innermost planet may be engulfed, leading to a common envelope (CE) event. Even if this is insufficient to eject the envelope, it may expand the star further, causing additional CE events, with the last one unbinding what remains of the envelope. This multi-planet CE scenario may have broad implications for stellar and planetary evolution across a range of systems. We develop a simplified version and show that it may be able to explain the recently observed planet WD 1856 b., Comment: 5 pages, 2 figures, accepted for publication in MNRAS Letters

The photoionization-driven evaporation of planetary atmospheres has emerged as a potentially fundamental process for planets on short period orbits. While 1-D studies have proven the effectiveness of stellar fluxes at altering the atmospheric mass and composition for sub-Jupiter mass planets, there remains much that is uncertain with regard to the larger-scale, multidimensional nature of such "planetary wind" flows. In this paper we use a new radiation-hydrodynamic platform to simulate atmospheric evaporative flows. Using the AstroBEAR AMR multiphysics code in a co-rotating frame centered on the planet, we model the transfer of ionizing photons into the atmosphere, the subsequent launch of the wind and the wind's large scale evolution subject to tidal and non-inertial forces. We run simulations for planets of 0.263 and 0.07 Jupiter masses and stellar fluxes of $2 \times 10^{13}$ and $2 \times 10^{14}$ photons/cm^2/s. Our results reveal new, potentially observable planetary wind flow patterns, including the development, in some cases, of an extended neutral tail lagging behind the planet in its orbit.

The extent to which a magnetosphere protects its planetary atmosphere from stellar wind ablation depends upon how well it prevents energy and momentum exchange with the atmosphere and how well it traps otherwise escaping plasma. We focus on the former, and provide a formalism for estimating approximate upper limits on mass, energy, and momentum capture, and use them to constrain loss rates. Our approach quantifies a competition between the local deflection of incoming plasma by a planetary magnetic field and the increase in area for solar wind mass capture provided by this magnetosphere when the wind and planetary fields incur magnetic reconnection. Solar wind capture can be larger for a magnetized planet versus an unmagnetized planet with small ionosphere, even if the rate of energy transfer is less. We find this to be the case throughout Earth's history since the lunar forming impact-- the likely start of the geodynamo. Focusing of incoming charged particles near the magnetic poles can increase the local energy flux for a strong enough planetary field and weak enough wind, and we find that this may be the case for Earth's future. The future protective role of Earth's magnetic field would then depend on its ability to trap outgoing plasma. This competition between increased collection area and reduced inflow speed from a magnetosphere is likely essential in determining the net protective role of planetary fields and its importance in sustaining habitability, and can help explain the current ion loss rates from Mars, Venus and Earth., 10 pages; 2 figures; accepted and in press, MNRAS

Common envelope evolution (CEE) is presently a poorly understood, yet critical, process in binary stellar evolution. Characterizing the full 3D dynamics of CEE is difficult in part because simulating CEE is so computationally demanding. Numerical studies have yet to conclusively determine how the envelope ejects and a tight binary results, if only the binary potential energy is used to propel the envelope. Additional power sources might be necessary and accretion onto the inspiraling companion is one such source. Accretion is likely common in post-asymptotic giant branch (AGB) binary interactions but how it operates and how its consequences depend on binary separation remain open questions. Here we use high resolution global 3D hydrodynamic simulations of CEE with the adaptive mesh refinement (AMR) code AstroBEAR, to bracket the range of CEE companion accretion rates by comparing runs that remove mass and pressure via a subgrid accretion model with those that do not. The results show that if a pressure release valve is available, super-Eddington accretion may be common. Jets are a plausible release valve in these environments, and they could also help unbind and shape the envelopes., Comment: 14 pages, submitted to MNRAS

Using 3D radiation-hydrodynamic simulations and analytic theory, we study the orbital evolution of asymptotic-giant-branch (AGB) binary systems for various initial orbital separations and mass ratios, and thus different initial accretion modes. The time evolution of binary separations and orbital periods are calculated directly from the averaged mass loss rate, accretion rate and angular momentum loss rate. We separately consider spin-orbit synchronized and zero spin AGB cases. We find that the the angular momentum carried away by the mass loss together with the mass transfer can effectively shrink the orbit when accretion occurs via wind-Roche-lobe overflow. In contrast, the larger fraction of mass lost in Bondi-Hoyle-Lyttleton accreting systems acts to enlarge the orbit. Synchronized binaries tend to experience stronger orbital period decay in close binaries. We also find that orbital period decay is faster when we account for the nonlinear evolution of the accretion mode as the binary starts to tighten. This can increase the fraction of binaries that result in common envelope, luminous red novae, Type Ia supernovae and planetary nebulae with tight central binaries. The results also imply that planets in the the habitable zone around white dwarfs are unlikely to be found., 10 pages, 10 figures and 6 tables submitted to MNRAS

We revisit the nature of large dips in flux from extinction by dusty circumstellar material that is observed by Kepler for many young stars in the Upper Sco and $\rho$ Oph star formation regions. These young, low-mass "dipper" stars are known to have low accretion rates and primarily host moderately evolved dusty circumstellar disks. Young low mass stars often exhibit rotating star spots that cause quasi-periodic photometric variations. We found no evidence for periods associated with the dips that are different from the star spot rotation period in spectrograms constructed from the light curves. The material causing the dips in most of these light curves must be approximately corotating with the star. We find that disk temperatures computed at the disk corotation radius are cool enough that dust should not sublime. Crude estimates for stellar magnetic field strengths and accretion rates are consistent with magnetospheric truncation near the corotation radius. Magnetospheric truncation models can explain why the dips are associated with material near corotation and how dusty material is lifted out of the midplane to obscure the star which would account for the large fraction of young low mass stars that are dippers. We propose that variations in disk orientation angle, stellar magnetic field dipole tilt axis, and disk accretion rate are underlying parameters accounting for differences in the dipper light curves.

We present new methods to solve the Riemann problem both exactly and approximately for general equations of state (EoS) to facilitate realistic modeling and understanding of astrophysical flows. The existence and uniqueness of the new exact general EoS Riemann solution can be guaranteed if the EoS is monotone regardless of the physical validity of the EoS. We confirm that: (1) the solution of the new exact general EoS Riemann solver and the solution of the original exact Riemann solver match when calculating perfect gas Euler equations; (2) the solution of the new Harten-Lax-van Leer-Contact (HLLC) general EoS Riemann solver and the solution of the original HLLC Riemann solver match when working with perfect gas EoS; and (3) the solution of the new HLLC general EoS Riemann solver approaches the new exact solution. We solve the EoS with two methods, one is to interpolate 2D EoS tables by the bi-linear interpolation method, and the other is to analytically calculate thermodynamic variables at run-time. The interpolation method is more general as it can work with other monotone and realistic EoS while the analytic EoS solver introduced here works with a relatively idealized EoS. Numerical results confirm that the accuracy of the two EoS solvers is similar. We study the efficiency of these two methods with the HLLC general EoS Riemann solver and find that analytic EoS solver is faster in the test problems. However, we point out that a combination of the two EoS solvers may become favorable in some specific problems. Throughout this research, we assume local thermal equilibrium., 42 pages, 19 figures, accepted by the Journal of Computational Physics. Corrected some grammatical errors and a typo in the latest version

Molecular cloud complexes exhibit both (i) an unfettered Larson-type spectrum over much of their dynamic range, whilst (ii) still producing a much lower star-formation rate than were this cascade to remain unfettered all the way down to star-forming scales. Here we explain the compatibility of these attributes with minimalist considerations of a mass-conserving fragmentation cascade, combined with estimates of stellar feedback. Of importance is that the amount of feedback needed to abate fragmentation and truncate the complex decreases with decreasing scale. The scale at which the feedback momentum matches the free-fall momentum marks a transition scale below most of the cascade is truncated and the molecular cloud complex dissipated. For a $10^6M_\odot$ GMC complex starting with radius of $\sim 50$pc, the combined feedback from young stellar objects, supernovae, radiation, and stellar winds for a GMC cloud complex can truncate the cascade within an outer free-fall time but only after the cascade reaches parsec scales., Comment: 6 pages, accepted by MNRAS

The role of radiation pressure in shaping exoplanet photoevaporation remains a topic of contention. Radiation pressure from the exoplanet’s host star has been proposed as a mechanism to drive the escaping atmosphere into a ‘cometary’ tail and explain the high velocities observed in systems where mass-loss is occurring. In this paper, we present results from high-resolution 3D hydrodynamic simulations of a planet similar to HD 209458b. We self-consistently launch a wind flowing outwards from the planet by calculating the ionization and heating resulting from incident high-energy radiation, and account for radiation pressure. We first present a simplified calculation, setting a limit on the Lyman-α flux required to drive the photoevaporated planetary material to larger radii and line-of-sight velocities. We then present the results of our simulations, which confirm the limits determined by our analytic calculation. We thus demonstrate that, within the limits of our hydrodynamic simulation and for the Lyman-α fluxes expected for HD 209458, radiation pressure is unlikely to significantly affect photoevaporative winds or to explain the high velocities at which wind material is observed, though further possibilities remain to be investigated.

Volume complete sky surveys provide evidence for a binary origin for the formation of isolated white dwarfs with magnetic fields in excess of a MegaGauss. Interestingly, not a single high-field magnetic white dwarf has been found in a detached system suggesting that if the progenitors are indeed binaries, the companion must be removed or merge during formation. An origin scenario consistent with observations involves the engulfment, inspiral, and subsequent tidal disruption of a low-mass companion in the interior of a giant star during a common envelope phase. Material from the shredded companion forms a cold accretion disc embedded in the hot ambient around the proto-white dwarf. Entrainment of hot material may evaporate the disc before it can sufficiently amplify the magnetic field, which typically requires at least a few orbits of the disc.Using three-dimensional hydrodynamic simulations of accretion discs with masses between 1 and 10 times the mass of Jupiter inside the core of an Asymptotic Giant Branch star, we find that the discs survive for at least 10 orbits (and likely for 100 orbits), sufficient for strong magnetic fields to develop., Comment: Submitted to MNRAS

The association of starspots with magnetic fields leads to an expectation that quantities which correlate with magnetic field strength may also correlate with {starspot} coverage. Since younger stars spin faster and are more magnetically active, assessing whether {starspot} coverage correlates with shorter rotation periods and stellar youth tests these principles. Here we analyze the {starspot} covering fraction versus stellar age for M{-}, G{-}, K{-}, and F{-}type stars based on previously determined variability and rotation periods of over 30,000 {\textit{Kepler}} main-sequence stars. We determine the correlation between age and variability using single and dual power law best fits. We find that {starspot} coverage does indeed decrease with age. Only when the data {are} binned in an effort to remove the effects of activity cycles of individual stars, do statistically significant power law fits emerge for each stellar type. {Using bin averages,} we then find that the {starspot} covering fraction scales with the {X}-ray to bolometric ratio to the power $\lambda$ with {$0.22\pm 0.03 < \lambda < 0.32\pm 0.09$} for {G-type} stars of rotation period below 15 days and for the full range of F{-} and M{-type} stars. For K{-}type stars, we find two branches of $\lambda$ separated by variability bins, with the lower branch showing nearly constant starspot coverage and the upper branch {$\lambda \sim 0.35\pm 0.04$.} G{-}type stars with periods longer than $15$ days exhibit a transition to steeper power law of {$ \lambda \sim 2.4 \pm 1.0$.} The potential connection to previous rotation-age measurements suggesting a magnetic breaking transition at the solar age, corresponding to period of $24.5$ is also of interest., Comment: 10 Pages, 7 figures, accepted by MNRAS

Megagauss magnetic fields were generated by a current flowing through a U-shaped coil connecting two parallel copper foils. Two kJ-class lasers at various pulse widths from 2 ns to 9.9 ns passed through holes in the front foil and were focused on the back foil with an intensity of ∼ 1.7 × 10 16 W/cm2. The coil current and resulting magnetic fields were characterized using ultrafast proton radiography, timed at the end of the laser pulses. The measurements show that magnetic field strength decays with increasing laser pulse width. A lumped-circuit model was developed and showed consistency with the experimental measurements, demonstrating an ion shorting effect: as the ion current neutralizes the electron current contribution to interplate voltage, the coil current peaks on a timescale close to the ion transit time t i = d / v ion. FLASH simulations of the coil current are performed, and the calculated resistance values are used to constrain ion speed as a function of hot electron temperature.

We study the dynamo generation (exponential growth) of large scale (planar averaged) fields in unstratified shearing box simulations of the magnetorotational instability (MRI). In contrast to previous studies restricted to horizontal ($x$-$y$) averaging, we demonstrate the presence of large scale fields when either horizontal or vertical ($y$-$z$) averaging is employed. By computing planar averaged fields and power spectra, we find large scale dynamo action in the early MRI growth phase---a previously unidentified feature. Fast growing horizontal low modes and fiducial vertical modes over a narrow range of wave numbers amplify these planar averaged fields in the MRI growth phase, before turbulence sets in. The large scale field growth requires linear fluctuations but not nonlinear turbulence (as defined by mode-mode coupling) and grows as a direct global mode of the MRI. Only by vertical averaging, can it be shown that the growth of horizontal low wavenumber MRI modes directly feed-back to the initial vertical field providing a clue as to why the large scale vertical field sustains against turbulent diffusion in the saturation regime. We compute the terms in the planar averaged mean field equations to identify the individual contributions to large scale field growth for both vertical and horizontal averaging. The large scale fields obtained from such vertical averaging are found to compare well with global cylindrical simulations and quasilinear analytical analysis from a previous study by Ebrahimi \& Blackman. We discuss the potential implications of these new results for understanding large scale MRI dynamo saturation and turbulence., 12 pages, 9 figues, submitted to MNRAS, comments are welcome

Recent observations of the L2 Puppis system suggest that this Mira-like variable may be in the early stages of forming a bipolar planetary nebula (PN). As one of nearest and brightest AGB stars, thought be a binary, L2 Puppis serves as a benchmark object for studying the late-stages of stellar evolution. We perform global, three-dimensional, adaptive-mesh-refinement hydrodynamic simulations of the L2 Puppis system with AstroBEAR. We use the radiative transfer code RADMC-3D to construct the broad-band spectral-energy-distribution (SED) and synthetic observational images from our simulations. Given the reported binary parameters, we are able to reproduce the current observational data if a short pulse of dense material is released from the AGB star with a velocity sufficient to escape the primary but not the binary. Such a situation could result from a thermal pulse, be induced by a periastron passage of the secondary, or could be launched if the primary ingests a planet., 6 pages, 12 figures, submitted to MNRAS

Late-type main sequence stars exhibit an x-ray to bolometric flux ratio that depends on ${\tilde Ro}$, the ratio of rotation period to convective turnover time, as ${\tilde Ro}^{-\zeta}$ with $2\le \zeta \le 3$ for ${\tilde Ro} >0.13$, but saturates with $|\zeta, Comment: 12 pages, 5 figures; published in MNRAS; this version updated to correct some typographical errors identified in a post-publication erratum

The possibility that mass ejected during Asymptotic Giant Branch (AGB) stellar evolution phases falls back towards the star has been suggested in applications ranging from the formation of accretion disks to the powering of late-thermal pulses. In this paper, we seek to explicate the properties of fallback flow trajectories from mass-loss events. We focus on a transient phase of mass ejection with sub-escape speeds, followed by a phase of a typical AGB wind. We solve the problem using both hydrodynamic simulations and a simplified one-dimensional analytic model that matches the simulations. For a given set of initial wind characteristics, we find a critical shell velocity that distinguishes between "shell fallback" and "shell escape". We discuss the relevance of our results for both single and binary AGB stars. In particular, we discuss how our results help to frame further studies of fallback as a mechanism for forming the substantial population of observed post-AGB stars with dusty disks., 7 pages, 13 figures, accepted by MNRAS on Jan. 4th 2016

The morphologies of planetary nebula have long been believed to be due to wind shaping processes in which a &ldquo, fast wind&rdquo, from the central star impacts a previously ejected envelope. It is assumed that asymmetries existing in the &ldquo, slow wind&rdquo, envelope would lead to inertial confinement, shaping the resulting interacting wind flow. We present new results demonstrating the effectiveness of Common Envelope Evolution (CEE) at producing aspherical envelopes which, when impinged upon by a spherical fast stellar wind, produce highly bipolar, jet-like outflows. We have run two simple cases using the output of a single PHANTOM SPH CEE simulation. Our work uses the Adaptive Mesh Refinement code AstroBEAR to track the interaction of the fast wind and CEE ejecta allows us to follow the morphological evolution of the outflow lobes at high resolution in 3-D. Our two models bracket low and high momentum output fast winds. We find the interaction leads to highly collimated bipolar outflows. In addition, the bipolar morphology depends on the fast wind momentum injection rate. With this dependence comes the initiation of significant symmetry breaking between the top and bottom bipolar lobes. Our simulations, though simplified, confirm the long-standing belief that CEE can plan a major role in PPN and PN shaping. These simulations are intended as an initial exploration of the post-CE/PPN flow patterns that can be expected from central source outflows and CE ejecta.

Mean field electrodynamics (MFE) facilitates practical modeling of secular, large scale properties of astrophysical or laboratory systems with fluctuations.Practitioners commonly assume wide scale separation between mean and fluctuating quantities, to justify equality of ensemble and spatial or temporal averages.Often however, real systems do not exhibit such scale separation. This raises two questions: (I) what are the appropriate generalized equations of MFE in the presence of mesoscale fluctuations? (II) how precise are theoretical predictions from MFE? We address both by first deriving the equations of MFE for different types of averaging, along with mesoscale correction terms that depend on the ratio of averaging scale to variation scale of the mean. We then show that even if these terms are small, predictions of MFE can still have a significant precision error. This error has an intrinsic contribution from the dynamo input parameters and a filtering contribution from differences in the way observations and theory are projected through the measurement kernel.Minimizing the sum of these contributions can produce an optimal scale of averaging that makes the theory maximally precise.The precision error is important to quantify when comparing to observations because it quantifies the resolution of predictive power. We exemplify these principles for galactic dynamos, comment on broader implications, and identify possibilities for further work., 35 pages, 10 figures. Published in Journal of Plasma Physics; Mar. 21 2019: Typos of a sign in (3.6) and indices of $\xi$ in the paragraphs containing (B7)-(B9) corrected

Observations of transiting extra-solar planets provide rich sources of data for probing the in-system environment. In the WASP-12 system, a broad depression in the usually-bright MgII h&k lines has been observed, in addition to atmospheric escape from the extremely hot Jupiter WASP-12b. It has been hypothesized that a translucent circumstellar cloud is formed by the outflow from the planet, causing the observed signatures. We perform 3D hydrodynamic simulations of the full system environment of WASP-12, injecting a planetary wind and stellar wind from their respective surfaces. We find that a torus of density high enough to account for the lack of MgII h&k line core emission in WASP-12 can be formed in approximately 13 years. We also perform synthetic observations of the Lyman-alpha spectrum at different points in the planet's orbit, which demonstrate that significant absorption occurs at all points in the orbit, not just during transits, as suggested by the observations.

Transport coefficients in turbulence are comprised of correlation functions between turbulent fluctuations and efficient methods to calculate them are desirable. For example, in mean field dynamo theories used to model the growth of large scale magnetic fields of stars and galaxies, the turbulent electromotive force is commonly approximated by a series of tensor products of turbulent transport coefficients with successively higher order spatial derivatives of the mean magnetic field. One ingredient of standard models is the kinematic coefficient of the zeroth order term, namely the averaged kinetic pseudotensor $\bm{\alpha}$, that converts toroidal to poloidal fields. Here we demonstrate an efficient way to calculate this quantity for rotating stratified turbulence, whereby the pre-averaged quantity is calculated for the motion of a single plume, and the average is then taken over an ensemble of plumes of different orientations. We calculate the plume dynamics in the most convenient frame, before transforming back to the lab frame and averaging. Our concise configuration space calculation gives essentially identical results to previous lengthier approaches. The present application exemplifies what is a broadly applicable method., Comment: 6 pages; 1 figure; accepted by MNRAS Letters

Star formation can be triggered by compression from wind or supernova driven shock waves that sweep over molecular clouds. In a previous work we used Adaptive Mesh Refinement (AMR) simulation methods, including sink particles, to simulate the full collapse of a stable Bonnor–Ebert sphere subjected to a passing shock. We tracked the flow of cloud material after a star (a sink particle) had formed. For rotating clouds we observed the formation of disks which then interact with the post-shock flow. In this paper we take the next step forward in complexity, presenting first results of simulations that include a magnetized cloud. Our results show that after a disk is formed a collimated magneto-centrifugal outflow is launched. The outflow is bipolar but asymmetric, due to interactions with the shocked flow. We explore the influence of the outflows on the post-triggering collapse dynamics.