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Jason Nordhaus

Publications and source records attributed to Jason Nordhaus.

31 records · Page 2Linked to original sources
arXiv2018

Accretion in common envelope evolution

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.

astro-ph.SR↗
arXiv2017

Wind-accelerated orbital evolution in binary systems with giant stars

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.

astro-ph.SR↗
arXiv2017

Mass Transfer and Disc Formation in AGB Binary Systems

We investigate mass transfer and the formation of disc in binary systems using a combination of numerical simulations and theory. We consider six models distinguished by binary separation, secondary mass and outflow mechanisms. Each system consists of an asymptotic-giant-branch (AGB) star and an accreting secondary. The AGB star loses its mass via a wind. In one of our six models, the AGB star incurs a short period of outburst. In all cases, the secondary accretes part of the ejected mass and also influences the mass-loss rate of the AGB star. The ejected mass may remain gravitationally bound to the binary system and form a circumbinary disk, or contribute to an accretion disk around the secondary. In other cases, the ejecta will escape the binary system. The accretion rate on to the secondary changes non-linearly with binary separation. In our closest binary simulations, our models exemplify the wind Roche lobe overflow while in our wide binary cases, the mass transfer exhibits Bondi-Hoyle accretion. The morphologies of the outflows in the binary systems are varied. The variety may provide clues to how the late AGB phase influences planetary nebulae shaping. We employ the adaptive-mesh-refinement code ASTROBEAR for our simulations and include ray-tracing, radiation transfer, cooling and dust formation. To attain the highest computational efficiency and the most stable results, all simulations are run in the corotating frame.

astro-ph.SR↗
arXiv2016

Three-dimensional hydrodynamic simulations of L2 Puppis

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.

astro-ph.SR↗
arXiv2016

Radio Emission from Red-Giant Hot Jupiters

When planet-hosting stars evolve off the main sequence and go through the red-giant branch, the stars become orders of magnitudes more luminous and, at the same time, lose mass at much higher rates than their main-sequence counterparts. Accordingly, if planetary companions exist around these stars at orbital distances of a few AU, they will be heated up to the level of canonical hot Jupiters and also be subjected to a dense stellar wind. Given that magnetized planets interacting with stellar winds emit radio waves, such "Red-Giant Hot Jupiters" (RGHJs) may also be candidate radio emitters. We estimate the spectral auroral radio intensity of RGHJs based on the empirical relation with the stellar wind as well as a proposed scaling for planetary magnetic fields. RGHJs might be intrinsically as bright as or brighter than canonical hot Jupiters and about 100 times brighter than equivalent objects around main-sequence stars. We examine the capabilities of low-frequency radio observatories to detect this emission and find that the signal from an RGHJ may be detectable at distances up to a few hundred parsecs with the Square Kilometer Array.

astro-ph.EP↗
arXiv2016

The Creation of AGB Fallback Shells

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.

astro-ph.SR↗
arXiv2015

A call for a paradigm shift from neutrino-driven to jet-driven core-collapse supernova mechanisms

Three-dimensional (3D) simulations in recent years have shown severe difficulties producing 10^51 erg explosions of massive stars with neutrino based mechanisms while on the other hand demonstrated the large potential of mechanical effects, such as winds and jets in driving explosions. In this paper we study the typical time-scale and energy for accelerating gas by neutrinos in core-collapse supernovae (CCSNe) and find that under the most extremely favorable (and probably unrealistic) conditions, the energy of the ejected mass can reach at most 5X10^50 erg. More typical conditions yield explosion energies an order-of-magnitude below the observed 10^51 erg explosions. On the other hand, non-spherical effects with directional outflows hold promise to reach the desired explosion energy and beyond. Such directional outflows, which in some simulations are produced by numerical effects of 2D grids, can be attained by angular momentum and jet launching. Our results therefore call for a paradigm shift from neutrino-based explosions to jet-driven explosions for CCSNe.

astro-ph.SR↗
arXiv2014

Dusty Disks Around Central Stars of Planetary Nebulae

Only a few percent of cool, old white dwarfs (WDs) have infrared excesses interpreted as originating in small hot disks due to the infall and destruction of single asteroids that come within the star's Roche limit. Infrared excesses at 24 micron were also found to derive from the immediate vicinity of younger, hot WDs, most of which are still central stars of planetary nebulae (CSPN). The incidence of CSPN with this excess is 18%. The Helix CSPN, with a 24 micron excess, has been suggested to have a disk formed from collisions of Kuiper belt-like objects (KBOs). In this paper, we have analyzed an additional sample of CSPN to look for similar infrared excesses. These CSPN are all members of the PG 1159 class and were chosen because their immediate progenitors are known to often have dusty environments consistent with large dusty disks. We find that, overall, PG 1159 stars do not present such disks more often than other CSPN, although the statistics (5 objects) are poor. We then consider the entire sample of CSPN with infrared excesses, and compare it to the infrared properties of old WDs, as well as cooler post-AGB stars. We conclude with the suggestion that the infrared properties of CSPN more plausibly derive from AGB-formed disks rather than disks formed via the collision of KBOs, although the latter scenario cannot be ruled out. We finally remark that there seems to be an association between CSPN with a 24 micron excess and confirmed or possible binarity of the central star.

astro-ph.SR↗
arXiv2013

Size of discs formed by wind accretion in binaries can be underestimated if the role of wind-driving force is ignored

Binary systems consisting of a secondary accreting form a wind-emitting primary are ubiquitous in astrophysics. The phenomenology of such Bondi-Hoyle-Lyttleton (BHL) accretors is particularly rich when an accretion disc forms around the secondary. The outer radius of such discs is commonly estimated from the net angular momentum produced by a density variation of material across the BHL or Bondi accretion cylinder, as the latter is tilted with respect to the direction to the primary due to orbital motion. But this approach has ignored the fact that the wind experiences an outward driving force that the secondary does not. In actuality, the accretion stream falls toward a retarded point in the secondary's orbit as the secondary is pulled toward the primary relative to the stream. The result is a finite separation or "accretion stream impact parameter" (ASIP) separating the secondary and stream. When the orbital radius a_o exceeds the BHL radius r_b, the ratio of outer disc radius estimated as the ASIP to the conventional estimate a_o^{1/2}/r_b^{1/2}>1. We therefore predict that discs will form at larger radii from the secondary than traditional estimates. This agrees with the importance of the ASIP emphasized by Huarte-Espinosa et al. (2013) and the practical consequence that resolving the initial outer radius of such an accretion disc in numerical simulations can be less demanding than what earlier estimates would suggest.

astro-ph.HE↗
arXiv2013

The Formation and Evolution of Wind-Capture Disks In Binary Systems

We study the formation, evolution and physical properties of accretion disks formed via wind capture in binary systems. Using the AMR code AstroBEAR, we have carried out high resolution 3D simulations that follow a stellar mass secondary in the co-rotating frame as it orbits a wind producing AGB primary. We first derive a resolution criteria, based on considerations of Bondi-Hoyle flows, that must be met in order to properly resolve the formation of accretion disks around the secondary. We then compare simulations of binaries with three different orbital radii (10, 15, 20 AU). Disks are formed in all three cases, however the size of the disk and, most importantly, its accretion rate decreases with orbital radii. In addition, the shape of the orbital motions of material within the disk becomes increasingly elliptical with increasing binary separation. The flow is mildly unsteady with "fluttering" around the bow shock observed. The disks are generally well aligned with the orbital plane after a few binary orbits. We do not observe the presence of any large scale, violent instabilities (such as the flip-flop mode). For the first time, moreover, it is observed that the wind component that is accreted towards the secondary has a vortex tube-like structure, rather than a column-like one as it was previously thought. In the context of AGB binary systems that might be precursors to Pre-Planetary and Planetary Nebula, we find that the wind accretion rates at the chosen orbital separations are generally too small to produce the most powerful outflows observed in these systems if the companions are main sequence stars but marginally capable if the companions are white dwarfs. It is likely that many of the more powerful PPN and PN involve closer binaries than the ones considered here. The results also demonstrate principles of broad relevance to all wind-capture binary systems.

astro-ph.SR↗
arXiv2012

Dimensional Dependence of the Hydrodynamics of Core-Collapse Supernovae

The multidimensional character of the hydrodynamics in core-collapse supernova (CCSN) cores is a key facilitator of explosions. Unfortunately, much of this work has necessarily been performed assuming axisymmetry and it remains unclear whether or not this compromises those results. In this work, we present analyses of simplified two- and three-dimensional CCSN models with the goal of comparing the multidimensional hydrodynamics in setups that differ only in dimension. Not surprisingly, we find many differences between 2D and 3D models. While some differences are subtle and perhaps not crucial to understanding the explosion mechanism, others are quite dramatic and make interpreting 2D CCSN models problematic. In particular, we find that imposing axisymmetry artificially produces excess power at the largest spatial scales, power that has been deemed critical in the success of previous explosion models and has been attributed solely to the standing accretion shock instability. Nevertheless, our 3D models, which have an order of magnitude less power on large scales compared to 2D models, explode earlier. Since we see explosions earlier in 3D than in 2D, the vigorous sloshing associated with the large scale power in 2D models is either not critical in any dimension or the explosion mechanism operates differently in 2D and 3D. Possibly related to the earlier explosions in 3D, we find that about 25% of the accreted material spends more time in the gain region in 3D than in 2D, being exposed to more integrated heating and reaching higher peak entropies, an effect we associate with the differing characters of turbulence in 2D and 3D. Finally, we discuss a simple model for the runaway growth of buoyant bubbles that is able to quantitatively account for the growth of the shock radius and predicts a critical luminosity relation.

astro-ph.SR↗
arXiv2010

A New Method for Determining the Milky Way Bar Pattern Speed

Previous work has related the Galactic bar to structure in the local stellar velocity distribution. Here we show that the bar also influences the spatial gradients of the velocity vector via the Oort constants. By numerical integration of test-particles we simulate measurements of the Oort C value in a gravitational potential including the Galactic bar. We account for the observed trend that C is increasingly negative for stars with higher velocity dispersion. By comparing measurements of C with our simulations we improve on previous models of the bar, estimating that the bar pattern speed is Omega_b/Omega_0=1.87\pm0.04, where Omega_0 is the local circular frequency, and the bar angle lies within 20[deg]<phi_0<45[deg]. We find that the Galactic bar affects measurements of the Oort constants A and B less than ~2 km/s/kpc for the hot stars.

astro-ph.GA↗