Envelope Evolution Research Articles

Unexpectedly high formation rate of merging binary black holes in open clusters

AbstractGravitational wave direct detections suggest that 30 M⊙ binary black holes (BBHs) commonly exist in the universe. One possible formation scenario of such BBHs is dynamical three-body encounters in dense star clusters. We performed a series of direct N-body simulations with a mass of 2500 and 10000 M⊙ and found a new channel for the formation of BBHs which is dominant in open clusters. In open clusters, the core-collapse time is shorter than in globular clusters, and therefore massive main-sequence (MS) binaries can form before they evolve to BHs. These MS binaries experience common envelope evolution and evolve to hard BBHs, which can merge within the Hubble time. The number of BBH mergers per unit mass obtained from our simulations reached 20–50 % of that for globular clusters, assuming an initial cluster mass function. Thus, open clusters can be a dominant formation site of hard BBHs.

Energy budget and core-envelope motion in common envelope evolution

We analyze a 3D hydrodynamic simulation of common envelope evolution to understand how energy is transferred between various forms and whether theory and simulation are mutually consistent given the setup. Virtually all of the envelope unbinding in the simulation occurs before the end of the rapid plunge-in phase, here defined to coincide with the first periastron passage. In contrast, the total envelope energy is nearly constant during this time because positive energy transferred to the gas from the core particles is counterbalanced by the negative binding energy from the closer proximity of the inner layers to the plunged-in secondary. During the subsequent slow spiral-in phase, energy continues to transfer to the envelope from the red giant core and secondary core particles. We also propose that relative motion between the centre of mass of the envelope and the centre of mass of the particles could account for the offsets of planetary nebula central stars from the nebula's geometric centre.

Study of orbit properties and intense beam dynamics in a high current separated sector proton cyclotron

This paper outlines a simple method based on analytical formulations to find out the physics design of a separated sector cyclotron. Formulations are developed to determine the magnet sector shape and equilibrium orbit properties for a chosen orbital frequency and a peak magnetic field in the magnet sector. Stability analysis of single particle motion without space charge effect has been performed and allowed values of sector angles are determined. The dynamics of space charge dominated beam in the separated sector proton cyclotron are explored by using beam envelope equations that includes radial and longitudinal coupling. Evolution of the rms beam envelopes and emittances has been studied as a function of the beam current for various sector geometry. The envelope equations and perturbed equations of motion around the matched beam envelopes have been utilized to obtain the matched beam conditions at different values of the beam current.

Evidence for bimodal orbital separations of white dwarf–red dwarf binary stars

We present the results of a radial velocity survey of 20 white dwarf plus M dwarf binaries selected as a follow up to a \textit{Hubble Space Telescope} study that aimed to spatially resolve suspected binaries. Our candidates are taken from the list of targets that were spatially unresolved with \textit{Hubble}. We have determined the orbital periods for 16 of these compact binary candidates. The period distribution ranges from 0.14 to 9.16\,d and peaks near 0.6\,d. The original sample therefore contains two sets of binaries, wide orbits ($\approx100-1000$\,au) and close orbits ($\lesssim1-10$\,au), with no systems found in the $\approx10-100$\,au range. This observational evidence confirms the bimodal distribution predicted by population models and is also similar to results obtained in previous studies. We find no binary periods in the months to years range, supporting the post common envelope evolution scenario. One of our targets, WD\,1504+546, was discovered to be an eclipsing binary with a period of 0.93\,d.

Signs of accretion in the white dwarf + brown dwarf binary NLTT5306

We present new XSHOOTER spectra of NLTT5306, a 0.44 $\pm$ 0.04\msun white dwarf in a short period (101\,min) binary system with a brown dwarf companion that is likely to have previously undergone common envelope evolution. We have confirmed the presence of H$\alpha$ emission and discovered Na I absorption associated with the white dwarf. These observations are indicative of accretion. Accretion is typically evidenced by high energy emission in the UV and X-ray regime. However our \textit{Swift} observations covering the full orbital period in three wavebands (uvw1, uvm2, uvw2) revealed no UV excess or modulation. We used the X-ray non-detection to put an upper limit on the accretion rate of 2$\times$10$^{-15}$\msun yr$^{-1}$. We compare NLTT5306 to similar accreting binaries with brown dwarf donors and suggest the inferred accretion rate could be from wind accretion or accretion from a debris/dust disk. The lack of evidence for a disk implies NLTT5306 is magnetically funnelling a weak wind from a potentially low gravity brown dwarf. The upper limit on the accretion rate suggests a magnetic field as low as 0.45\,kG would be sufficient to achieve this. If confirmed this would constitute the first detection of a brown dwarf wind and could provide useful constraints on mass loss rates.

On the formation of neutron stars via accretion-induced collapse in binaries

We investigate evolutionary pathways leading to neutron star formation through the collapse of oxygen-neon white dwarf (ONe WD) stars in interacting binaries. We consider (1) non-dynamical mass transfer where an ONe WD approaches the Chandrasekhar mass leading to accretion-induced collapse (AIC) and (2) dynamical timescale merger-induced collapse (MIC) between an ONe WD and another WD. We present rates, delay times, and progenitor properties for two different treatments of common envelope evolution. We show that AIC neutron stars are formed via many different channels and the most dominant channel depends on the adopted common envelope physics. Most AIC and MIC neutron stars are born shortly after star formation, though some have delay times >10 Gyr. The shortest delay time (25-50 Myr) AIC neutron stars have stripped-envelope, compact, helium-burning star donors, though many prompt AIC neutron stars form via wind-accretion from an asymptotic giant branch star. The longest delay time AIC neutron stars, which may be observed as young milli-second pulsars among globular clusters, have a red giant or main sequence donor at the time of NS formation and will eventually evolve into NS + helium WD binaries. We discuss AIC & MIC binaries as potential gravitational wave sources for LISA. Neutron stars created via AIC undergo a LMXB phase, offering an electromagnetic counterpart for those shortest orbital period sources that LISA could identify. The formation of neutron stars from interacting WDs in binaries is likely to be a key mechanism for the production of LIGO/Virgo gravitational wave sources (NS-NS and BH-NS mergers) in globular clusters.

On the requirement for a high resolution spectrograph to investigate the multiplicity of massive stars with the 3.6-m Devasthal Optical Telescope

The investigation of the multiplicity of massive stars constitutes a key aspect of their understanding. On the one hand, the evolution of short period systems can be tremendously influenced by the companion, for instance through mass exchange or common envelope evolution. On the other hand, the wind-wind interaction region in massive multiple systems is the seat of a high level physics, including strong thermal X-ray emission, particle acceleration and non-thermal emission processes. The description and understanding of these processes require the accurate determination of orbital parameters, notably through spectroscopic studies. In this context, it is timely to anticipate some relevant applications of a high resolution spectrograph (HRS) to be mounted on the Devasthal Optical Telescope, emphasizing its potential complementarity with other Indian facilities such as the GMRT and Astrosat.

Variable jets at the termination of the common envelope evolution

I propose that at the termination of the common envelope evolution (CEE) the companion to the giant star might launch jets that have variable directions and intensities, hence the jets shape the inner zones of the descendant nebula causing it to lose any type of symmetry. This might account for some of the chaotic departures from axisymmetric structures in some planetary nebulae. I base my study on the assumption that at the termination of the CEE the binary interaction forms a circumbinary thick disk that feeds the companion via an accretion disk that launches opposite jets. I consider two processes that might lead to the development of Rayleigh-Taylor instabilities that lead to chaotic accretion flow on to the companion. The chaotic accretion flow leads to a variable accretion disk around the companion, hence to variable jets. In the first process the jets inflate low-density hot bubbles in the inner regions of the envelope. In the second process the inner boundary of the thick circumbinary disk, that faces the center, cools by radiation thus leading to a temperature, and hence also a pressure, increase with radius. The opposite pressure and density gradients lead to Rayleigh-Taylor instabilities. This study further underlines the importance of exploring the termination phase of the CEE to the understanding of the entire CEE and its outcomes.

Physical and Chemical Conditions of the Protostellar Envelope and the Protoplanetary Disk in HL Tau

Abstract We report our Submillimeter Array (SMA) observations of the Class I–II protostar HL Tau in 13CO (2–1), C18O (2–1), SO(56–45), and 1.3 mm dust-continuum emission and our analyses of the ALMA long baseline data of HCO+ (1–0) emission. The 1.3 mm continuum emission observed with the SMA shows compact (∼0.″8 × 0.″5) and extended (∼6.″5 × 4.″3) components, tracing the protoplanetary disk and the protostellar envelope, respectively. The 13CO, C18O, and HCO+ show a compact (∼200 au) component at velocities higher than 3 km s−1 from the systemic velocity and an extended (∼1000 au) component at lower velocities. The high-velocity component traces the Keplerian rotating disk, and the low-velocity component traces the infalling envelope. The HCO+ high-velocity component is fitted with a Keplerian disk model with a central stellar mass of 1.4 M ⊙. The radial intensity profiles of 13CO and C18O along the disk major axis are fitted with a disk+envelope model, and the gas masses of the disk and envelope are estimated to be (2–40) × 10–4 M ⊙ and M ⊙, respectively. The disk dust mass has been estimated to be (1–3) × 10−3 M ⊙ in the literature. Thus, our estimated disk gas mass suggests that the gas-to-dust mass ratio in the disk is <10, a factor of 10 lower than the estimated ratio in the envelope. We discuss possible gas depletion or CO depletion in the planet-forming candidate HL Tau in the context of disk and envelope evolution.

On the Role of Supernova Kicks in the Formation of Galactic Double Neutron Star Systems

Abstract In this work we focus on a group of Galactic double neutron star (DNS) systems with long orbital periods of ≳1 day and low eccentricities of ≲0.4. The feature of these orbital parameters is used to constrain the evolutionary processes of progenitor binaries and the supernova (SN) kicks of the second born NSs. Adopting that the mass transfer during primordial binary evolution is highly nonconservative (rotation-dependent), the formation of DNS systems involves a double helium star binary phase, the common envelope (CE) evolution initiates before the first NS formation. During the CE evolution the binary orbital energy is obviously larger when using a helium star rather than an NS to expel the donor envelope, this can help explain the formation of DNS systems with long periods. SN kicks at NS birth can lead to eccentric orbits and even the disruption of binary systems, and the low eccentricities require that the DNSs receive a small natal kick at the second collapse. Compared with the overall distribution of orbital parameters for observed DNS binaries, we propose that the second born NSs in most DNS systems are subject to small natal kicks with the Maxwellian dispersion velocity of less than 80 km s−1, which can provide some constraints on the SN explosion processes. The mass distribution of DNS binaries is also briefly discussed. We suggest that the rotation-dependent mass transfer mode and our results about SN kicks should be applied to massive binary evolution and population synthesis studies.

A particle-conserved weighted-average oscillator model for trapped particles in long-time nonlinear Landau damping

A normalized weighting function model for the average period of particles trapped in the potential wells of waves undergoing nonlinear Landau damping is considered. The model preserves the conservation properties of the trapped particles and relates them to the evolution of the wave envelope. It is valid when there are more shallowly trapped particles than deeply trapped particles, such as in long-time nonlinear Landau damping, as well as stabilities due to trapped particles at long times. The model is also useful for estimating the validity of the often invoked assumption that most trapped particles in nonlinear waves are deeply trapped.

Planetary Nebulae Shaped by Common Envelope Evolution

The morphologies of planetary nebula have long been believed to be due to wind shaping processes in which a “fast wind” from the central star impacts a previously ejected envelope. It is assumed that asymmetries existing in the “slow wind” 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.

Origin of magnetic fields in cataclysmic variables

In a series of recent papers, it has been proposed that high field magnetic white dwarfs are the result of close binary interaction and merging. Population synthesis calculations have shown that the origin of isolated highly magnetic white dwarfs is consistent with the stellar merging hypothesis. In this picture, the observed fields are caused by an alpha-Omega dynamo driven by differential rotation. The strongest fields arise when the differential rotation equals the critical break-up velocity and result from the merging of two stars (one of which has a degenerate core) during common envelope evolution or from the merging of two white dwarfs. We now synthesise a population of binary systems to investigate the hypothesis that the magnetic fields in the magnetic cataclysmic variables also originate during stellar interaction in the common envelope phase. Those systems that emerge from common envelope more tightly bound form the cataclysmic variables with the strongest magnetic fields. We vary the common envelope efficiency parameter and compare the results of our population syntheses with observations of magnetic cataclysmic variables. We find that common envelope interaction can explain the observed characteristics of these magnetic systems if the envelope ejection efficiency is low.

The Morphology of the Outflow in the Grazing Envelope Evolution

We study the grazing envelope evolution (GEE), where a secondary star, which orbits the surface of a giant star, accretes mass from the giant envelope and launches jets. We conduct simulations of the GEE with different half-opening angles and velocities, and simulate the onset phase and the spiralling-in phase. We discuss the resulting envelope structure and the outflow geometry. We find in the simulations of the onset phase with narrow jets that a large fraction of the ejected mass outflows along the polar directions. The mass ejected at these directions has the fastest velocity and the highest angular momentum magnitude. In the simulations of the spiralling-in phase, a large fraction of the ejected mass concentrates around the orbital plane. According to our findings, the outflow with the highest velocity is closer to the poles as we launch narrower jets. The outflow has a toroidal shape accompanied by two faster rings, one ring at each side of the equatorial plane. The interaction of the jets with the giant envelope causes these outflow structures, as we do not include in our simulations the secondary star gravity and the envelope self-gravity.

Experimental study of the stabilization mechanism of a lifted Diesel-type flame using combined optical diagnostics and laser-induced plasma ignition

The understanding of the stabilization process of Diesel spray flames is a key challenge because of its effect on pollutant emissions. In particular, the close relationship between lift-off length and soot production is now well established. However, different stabilization mechanisms have been proposed and are still under debate. The objective of this paper is to provide an experimental contribution to the investigation of these governing mechanisms. Combustion of a Diesel spray issued from a single-hole nozzle (90 µm orifice, ECN spray A injector) was studied in a constant-volume precombustion vessel using a combination of optical diagnostic techniques. Simultaneous high frame rate (6kfps) schlieren, 355 LIF (excitation at 355 nm and maximum collection at 430 nm) and high-temperature chemiluminescence (collection from 400 nm to 490 nm) or OH* chemiluminescence (collection at 310 nm and frame rate at 60kfps) are respectively used to follow the evolution of the gaseous jet envelope, formaldehyde location and lift-off position. Additional experiments are performed where the ignition of the mixture is forced at a location upstream of the natural lift off position by laser-induced plasma ignition (at 1064 nm). The evolution of the lift-off position until its return to the natural steady-state position is then studied for different ambient temperatures (800 K to 850 K), densities (11 kg/m3 to 14.8 kg/m3) and rail pressures (100 MPa to 150 MPa) using the same set of optical diagnostics. The analysis of the evolution of the lift off position without laser ignition reveals two main types of behaviors: sudden jumps in the upstream direction and more progressive displacement towards the downstream direction. While the former is attributed to auto-ignition events, the latter is studied through the forced laser ignition results. It is found that the location of formaldehyde greatly impacts the return velocity of the lift-off position: if laser ignition occurs upstream of the zone where formaldehyde is naturally present, the lift-off position convects rapidly until it reaches the region where formaldehyde is present and then returns more slowly towards its natural position, suggesting that cool-flame products greatly assist lift-off stabilization. The average return velocity in this second stage depends on the operating conditions.

The scatter of the M dwarf mass–radius relationship

M dwarfs are prime targets in the hunt for habitable worlds around other stars. This is due to their abundance as well as their small radii and low masses and temperatures, which facilitate the detection of temperate, rocky planets in orbit around them. However, the fundamental properties of M dwarfs are difficult to constrain, often limiting our ability to characterise the planets they host. Here we test several theoretical relationships for M dwarfs by measuring 23 high precision, model-independent masses and radii for M dwarfs in binaries with white dwarfs. We find a large scatter in the radii of these low-mass stars, with 25 per cent having radii consistent with theoretical models while the rest are up to 12 per cent over-inflated. This scatter is seen in both partially- and fully-convective M dwarfs. No clear trend is seen between the over-inflation and age or metallicity, but there are indications that the radii of slowly rotating M dwarfs are more consistent with predictions, albeit with a similar amount of scatter in the measurements compared to more rapidly rotating M dwarfs. The sample of M dwarfs in close binaries with white dwarfs appears indistinguishable from other M dwarf samples, implying that common envelope evolution has a negligible impact on their structure. We conclude that theoretical and empirical mass-radius relationships lack the precision and accuracy required to measure the fundamental parameters of M dwarfs well enough to determine the internal structure and bulk composition of the planets they host.

Radiating the Hydrogen Recombination Energy during Common Envelope Evolution

Abstract Using the stellar evolution code Modules for Experiments in Stellar Astrophysics (MESA), we show that most of the hydrogen recombination energy that is released as the envelope expands during a regular common envelope evolution—namely, the initial dynamical phase or plunge-in phase—is radiated, and hence substantially increases the stellar luminosity. Only about 10% of the hydrogen recombination energy might be used to remove the envelope. We show that the key property of energy transport is that when convection becomes inefficient in the outer parts of the envelope, where the ionization degree of hydrogen falls below about 30%, photon diffusion becomes very efficient and removes the recombination energy. The expanding envelope absorbs most of the gravitational energy that is released by the spiraling-in process of the secondary star inside the common envelope, and so it is the hydrogen recombination energy that is responsible for most of the luminosity increase of the system. The recombination energy of hydrogen adds only a small fraction of the energy required to remove the common envelope, and hence does not play a significant role in the ejection of the envelope.

Are there pre-main-sequence/black hole X-ray binaries?

A large fraction of black-hole low-mass X-ray binaries (BHLMXBs) are in short period orbits, which require strong orbital angular momentum loss during the previous evolutionary stage. Ivanova put forward the possibility that some of the BHLMXBs may harbour pre-main-sequence (pre-MS) donor stars, in order to explain the Li-overabundances in three BHLMXBs. In this work we investigate the evolution of low-mass pre-MS stars in binaries with a BH companion. We calculate the evolution of the spin and orbital periods, the stellar radius and the Roche lobe radius during the pre-MS stage with the stellar evolution code mesa. We find that, because of the relatively slow rotation of the pre-MS star after the common envelope evolution and the long turnover time in the pre-MS stars, tidal torque is not always able to synchronize the pre-MS star, so the spin periods are generally longer than the orbital periods. Mass transfer can occur only for stars with mass larger than ∼1.2 M , which experience expansion due to nuclear reaction after the Hayashi contraction phase. The effective temperatures and orbital periods of these systems do not match the observations of BHLMXBs. Our results show that the observed BHLMXBs with lithium overabundances are unlikely to host pre-MS donor stars.

Oxygen-neon-rich merger during common envelope evolution

We conduct a population synthesis study of the common envelope evolution (CEE) of a white dwarf (WD) and an asymptotic giant branch (AGB) star and find that the potential number of type Ia supernovae (SNe Ia) from the core degenerate (CD) and from the double degenerate (DD) scenarios are of the same order of magnitude. For the CD scenario we consider cases where a carbon oxygen rich (CO) AGB core and a CO WD merge during the CEE and leave a WD remnant with a mass of >1.35Mo, and for the DD scenario we count surviving CO WD binary systems that merge within a time of 10 Gyr. When either the AGB core or the WD are oxygen neon rich (ONe) we assume that the outcome might be a peculiar SN Ia. We find that the number of potential peculiar SNe Ia in the channels we study, that do not include peculiar SNe Ia that involve helium WDs or helium donors, is non-negligible, but less than the number of normal SNe Ia. If a SN Ia or a peculiar SN Ia explosion takes place within about million year after CEE, whether in the CD scenario or in the DD scenario, a massive circumstellar matter is present at explosion time. Our results are compatible with the suggestion that Chandrasekhar-mass SNe Ia mostly come from the CD scenario, and sub-Chandrasekhar SNe Ia mostly come from the DD scenario.

Surveying Planetary Nebulae Central Stars for Close Binaries: Constraining Evolution of Central Stars Based on Binary Parameters

The increase in discovered close binary central stars of planetary nebulae is leading to a sufficiently large sample to begin to make broader conclusions about the effect of close binary stars on common envelope evolution and planetary nebula formation. Herein I review some of the recent results and conclusions specifically relating close binary central stars to nebular shaping, common envelope evolution off the red giant branch, and the total binary fraction and double degenerate fraction of central stars. Finally, I use parameters of known binary central stars to explore the relationship between the proto-planetary nebula and planetary nebula stages, demonstrating that the known proto-planetary nebulae are not the precursors of planetary nebulae with close binary central stars.