Standard Evolution Models Research Articles

Is the low-energy tail of shock-accelerated protons responsible for over-ionized plasma in supernova remnants?

Abstract Over-ionized, recombining plasma is an emerging class of X-ray bright supernova remnants (SNRs). This unique thermal state, where the ionization temperature ($T_{\rm z}$) is significantly higher than the electron temperature ($T_{\rm e}$), is not expected from the standard evolution model that assumes a point explosion in a uniform interstellar medium, thus requiring a new scenario for the dynamical and thermal evolution. A recently proposed idea attributes the over-ionization state to additional ionization contribution from the low-energy tail of shock-accelerated protons. However, this new scenario has been left untested, especially from the atomic physics point of view. We report calculation results of the proton impact ionization rates of heavy-element ions in ejecta of SNRs. We conservatively estimate the requirement for accelerated protons, and find that their relative number density to thermal electrons needs to be higher than $5\ (k T_{\rm e}/1\:\mbox{keV})\%$ in order to explain the observed over-ionization degree at $T_{\rm z}/T_{\rm e} \ge 2$ for K-shell emission. We conclude that the proton ionization scenario is not feasible because such a high abundance of accelerated protons is prohibited by the injection fraction from thermal to non-thermal energies, which is expected to be $\sim\! 1\%$ at most.

Chemical evolution of a young super star cluster at the Sunburst Arc

ABSTRACT Recent observations of high-redshift galaxies have revealed starburst galaxies with excessive amounts of nitrogen, well above that expected in standard evolutionary models. The Sunburst Arc galaxy, particularly its young and massive star cluster, represents the closest ($z=2.4$) and brightest of these as a strongly lensed object. In this work, we study the chemical history of this star cluster to determine the origin of the elevated gas-phase nitrogen using a chemical evolution model. Our model includes the enrichment of OB stars through stellar winds and core-collapse supernovae assuming that massive stars ($M\gt 25$ $\mathrm{ M}_\odot$) collapse directly into black holes at the end of their lives. We fit the model parameters to the observed chemical abundances of the Sunburst Arc cluster: O/H, C/O, and N/O. We find that the observed chemical abundances can be explained by models featuring intense star formation events, characterized by rapid gas accretion and high star formation efficiencies. Additionally, the stellar population contributing to the gas enrichment must exclude Wolf–Rayet stars. These conditions might be present in other nitrogen-rich objects as their similar chemical abundances suggest a common history. As previous studies have proposed the presence of Wolf–Rayet stars in the new nitrogen-rich objects, further research using chemodynamic modeling is necessary to ascertain the true nature of these objects.

The cataclysmic variable orbital period gap: More evident than ever

Recently, large and homogeneous samples of cataclysmic variables identified by the Sloan Digital Sky Survey (SDSS) were published. In these samples, the famous orbital period gap, which is a dearth of systems in the orbital period range $ and the defining feature of most evolutionary models for has been claimed not to be clearly present. If true, this finding would completely change our picture of evolution. In this Letter we focus on potential differences with respect to the orbital period gap between in which the magnetic field of the white dwarf is strong enough to connect with that of the donor star, so-called polars, and non-polar as the white dwarf magnetic field in polars has been predicted to reduce the strength of angular momentum loss through magnetic braking. We separated the SDSS I-IV sample of into polars and non-polar systems and performed statistical tests to evaluate whether the period distributions are bimodal as predicted by the standard model for evolution or not. We also compared the SDSS\,I-IV period distribution of non-polars to that of other samples of cvs. We confirm the existence of a period gap in the SDSS\,I-IV sample of non-polar with $>98$ per cent confidence. The boundaries of the orbital period gap are $147$ and $191$ minutes, with the lower boundary being different to previously published values ($129$\,min). The orbital period distribution of polars from SDSS I-IV is clearly different and does not show a similar period gap. The SDSS samples as well as previous samples of are consistent with the standard theory of evolution. Magnetic braking does indeed seem get disrupted around the fully convective boundary, which causes a detached phase during evolution. In polars, the white dwarf magnetic field reduces the strength of magnetic braking and consequently the orbital period distribution of polars does not display an equally profound and extended period gap as non-polars. It remains unclear why the breaking rates derived from the rotation of single stars in open clusters favour prescriptions that are unable to explain the orbital period distribution of cvs.

Social Conflict and the Evolution of Unequal Conventions

Abstract We propose a theory of social norms (or conventions) that implement substantial levels of inequality between men and women, ethnic groups, and classes and that persist over long periods of time despite being inefficient and not supported by formal institutions. Consistent with historical cases, we extend the standard asymmetric stochastic evolutionary game model to allow subpopulation sizes to differ and idiosyncratic rejection of a status quo convention to be intentional to some degree (rather than purely random as in the standard evolutionary models). In this setting, if idiosyncratic play is sufficiently intentional and the subordinate class is sufficiently large relative to the elite, then risk-dominated conventions that are both more unequal and inefficient relative to alternative conventions will be stochastically stable and may persist for long periods. We show that the same is true in a general bipartite network of the population if most of the subordinate groups interactions are local, while the elite is more “cosmopolitan”. We apply the model to the evolution of wage conventions on the bipartite network of workers and employers, and find that an unequal monopsonistic wage convention is robust to the idiosyncratic play of workers that otherwise might displace it.

Strongly magnetized accretion in two ultracompact binary systems

ABSTRACT We present the discoveries of two of AM CVn systems, Gaia14aae and SDSS J080449.49+161624.8, which show X-ray pulsations at their orbital periods, indicative of magnetically collimated accretion. Both also show indications of higher rates of mass transfer relative to the expectations from binary evolution driven purely by gravitational radiation, based on existing optical data for Gaia14aae, which show a hotter white dwarf temperature than expected from standard evolutionary models, and X-ray data for SDSS J080449.49+161624.8 which show a luminosity 10−100 times higher than those for other AM CVn at similar orbital periods. The higher mass transfer rates could be driven by magnetic braking from the disc wind interacting with the magnetosphere of the tidally locked accretor. We discuss implications of this additional angular momentum transport mechanism for evolution and gravitational wave detectability of AM CVn objects.

TIC 43152097 The first eclipsing binary in NGC 2232

We report the discovery of a low-mass totally eclipsing system in the young (age ≃ 28 Myr) open cluster NGC 2232, during an examination of their TESS photometry. The follow-up study of this detached system, TIC 43152097, is based on photometry and high-resolution spectra from the literature and collected by us. The radial velocity of the center of mass and the photospheric lithium abundance of the binary components confirm its membership to NGC 2232. By analyzing the existing photometric and spectroscopic data, we obtain orbital elements and fundamental stellar parameters for the two stars. The primary component of TIC 43152097 is a late F-type dwarf (Teff = 6070 K), while the lower-mass secondary is a late K-type star (Teff = 4130 K) that is still in the pre-main-sequence phase. The precise measurements of the radii, masses, and effective temperatures, enabled by the simultaneous solution of light and radial velocity curves, indicate radius inflation for the K-type component, which turns out to be 7–11% larger than that predicted by standard evolutionary models. More sophisticated models incorporating both the inhibition of convective energy transport caused by sub-photospheric magnetic fields and the effects of cool starspots covering a substantial fraction of the stellar surface (30–60%) allow the position of the secondary component to be reproduced in the Hertzsprung–Russell and mass–radius diagrams.

On the Relationship between Design and Evolution

A longstanding question in science and religion is whether standard evolutionary models are compatible with the claim that the world was designed. In The Compatibility of Evolution and Design, theologian E. V. Rope Kojonen constructs a powerful argument that not only are evolution and design compatible, but that evolutionary processes (and biological data) strongly point to design. Yet Kojonen’s model faces several difficulties, each of which raise hurdles for his understanding of how evolution and design can be harmonized. First, his argument for design (and its compatibility with evolution) relies upon a particular view of nature in which fitness landscapes are “fine-tuned” to allow proteins to evolve from one form to another by mutation and selection. But biological data run contrary to this claim, which poses a problem for Kojonen’s design argument (and, as such, his attempt to harmonize design with evolution). Second, Kojonen appeals to the bacterial flagellum to strengthen his case for design, yet the type of design in the flagellum is incompatible with mainstream evolutionary theory, which (again) damages his reconciliation of design with evolution. Third, Kojonen regards convergent evolution as notable positive evidence in favor of his model (including his version of design), yet convergent evolution actually harms the justification of common ancestry, which Kojonen also accepts. This, too, mars his reconciliation of design and evolution. Finally, Kojonen’s model damages the epistemology that undergirds his own design argument as well as the design intuitions of everyday “theists on the street”, whom he seeks to defend. Thus, despite the remarkable depth, nuance, and erudition of Kojonen’s account, it does not offer a convincing reconciliation of ‘design’ and ‘evolution’.

Catastrophe by Design in Population Games: A Mechanism to Destabilize Inefficient Locked-in Technologies

In multi-agent environments in which coordination is desirable, the history of play often causes lock-in at sub-optimal outcomes. Notoriously, technologies with significant environmental footprint or high social cost persist despite the successful development of more environmentally friendly and/or socially efficient alternatives. The displacement of the status quo is hindered by entrenched economic interests and network effects. To exacerbate matters, the standard mechanism design approaches based on centralized authorities with the capacity to use preferential subsidies to effectively dictate system outcomes are not always applicable to modern decentralized economies. What other types of mechanisms are feasible? In this article, we develop and analyze a mechanism that induces transitions from inefficient lock-ins to superior alternatives. This mechanism does not exogenously favor one option over another; instead, the phase transition emerges endogenously via a standard evolutionary learning model, Q-learning, where agents trade off exploration and exploitation. Exerting the same transient influence to both the efficient and inefficient technologies encourages exploration and results in irreversible phase transitions and permanent stabilization of the efficient one. On a technical level, our work is based on bifurcation and catastrophe theory, a branch of mathematics that deals with changes in the number and stability properties of equilibria. Critically, our analysis is shown to be structurally robust to significant and even adversarially chosen perturbations to the parameters of both our game and our behavioral model.

Magneto-convective Modeling of Low-mass Pre-main Sequence Stars: Postponing the Depletion of Lithium

Standard evolutionary models of pre-main sequence (PMS) low-mass stars often predict radii R and Li abundances A(7Li) which are too small to agree with empirical data, while effective temperatures T eff are predicted to be too large. There are also discrepancies in replicating the stellar age. Discrepancies in R, T eff, and A(7Li) are reported by Stassun et al. for both components (A/B) of the eclipsing binary 2M1222-57 belonging to the young Lower Centaurus Crux association. Using the output of a magneto-convective stellar evolution model which we applied in an early study (in 2010) of PMS stars in a different young association, we show that the discrepancies reported by Stassun et al. in the 2M1222-57 system are alleviated. The models are instructive in showing why larger lithium abundances occur in magnetic PMS stars: it takes longer for the central gas in such a star to become hot enough to destroy lithium.

Correlating Changes in Spot Filling Factors with Stellar Rotation: The Case of LkCa 4

We present a multi-epoch spectroscopic study of LkCa 4, a heavily spotted non-accreting T Tauri star. Using SpeX at NASA’s Infrared Telescope Facility (IRTF), 12 spectra were collected over five consecutive nights, spanning ≈1.5 stellar rotations. Using the IRTF SpeX Spectral Library, we constructed empirical composite models of spotted stars by combining a warmer (photosphere) standard star spectrum with a cooler (spot) standard weighted by the spot filling factor, f spot. The best-fit models spanned two photospheric component temperatures, T phot = 4100 K (K7V) and 4400 K (K5V), and one spot component temperature, T spot = 3060 K (M5V) with an A V of 0.3. We find values of f spot to vary between 0.77 and 0.94 with an average uncertainty of ∼0.04. The variability of f spot is periodic and correlates with its 3.374 day rotational period. Using a mean value for f mean spot to represent the total spot coverage, we calculated spot corrected values for T eff and L ⋆. Placing these values alongside evolutionary models developed for heavily spotted young stars, we infer mass and age ranges of 0.45–0.6 M ⊙ and 0.50–1.25 Myr, respectively. These inferred values represent a twofold increase in the mass and a twofold decrease in the age as compared to standard evolutionary models. Such a result highlights the need for constraining the contributions of cool and warm regions of young stellar atmospheres when estimating T eff and L ⋆ to infer masses and ages as well as the necessity for models to account for the effects of these regions on the early evolution of low-mass stars.

Can models of evolutionary transition clarify the debates over the Neolithic Revolution?

The 'Neolithic Revolution,' sometimes referred to as the emergence of agriculture at its earliest in the southern Levant, is the most significant shift in human history, shaping the world we live in today. Yet, after 100 years of study, its major cause, tempo (gradual or revolutionary), and impact of human intentionality remain disputed. Here, we examine the research potential of an evolutionary transition in individuality (ETI) to clarify this dramatic shift. Applying an ETI research perspective reveals how different causes and conditions lead to the same result, enabling a holistic view rather than a reduction of 'Neolithic' to 'agriculture,' or to one major climatic condition, inheritance system or standard evolutionary model, thus allowing us to clarify and bypass some of these heated, unresolved disputes. Additionally, unlike current archaeological emphasis on 'where,' 'when,' 'why' and 'how' questions, the ETI perspective offers a productive path for resolving a fundamental preliminary anomaly: why and how could the Neolithic lifeway evolve at all, given the selfish interest of individuals in a hunter-gatherer group? We do not intend to solve the shift to Neolithic lifeways, only to offer a fresh lens for examining it, emphasizing the relevance of tracking within and between group differences. This article is part of the theme issue 'Human socio-cultural evolution in light of evolutionary transitions'.

Magnetic braking saturates: evidence from the orbital period distribution of low-mass detached eclipsing binaries from ZTF

ABSTRACT We constrain the orbital period (Porb) distribution of low-mass detached main-sequence eclipsing binaries (EBs) with light-curves from the Zwicky Transient Facility (ZTF), which provides a well-understood selection function and sensitivity to faint stars. At short periods (Porb ≲ 2 d), binaries are predicted to evolve significantly due to magnetic braking (MB), which shrinks orbits and ultimately brings detached binaries into contact. The period distribution is thus a sensitive probe of MB. We find that the intrinsic period distribution of low-mass (0.1 ≲ M1/M⊙ < 0.9) binaries is basically flat (${\rm d}N/{\rm d}P_{\rm orb} \propto P_{\rm orb}^0$) from Porb = 10 d down to the contact limit. This is strongly inconsistent with predictions of classical MB models based on the Skumanich relation, which are widely used in binary evolution calculations and predict ${\rm d}N/{\rm d}P_{\rm orb} \propto P_{\rm orb}^{7/3}$ at short periods. The observed distributions are best reproduced by models in which the magnetic field saturates at short periods with a MB torque that scales roughly as $\dot{J}\propto P_{\rm orb}^{-1}$, as opposed to $\dot{J} \propto P_{\rm orb}^{-3}$ in the standard Skumanich law. We also find no significant difference between the period distributions of binaries containing fully and partially convective stars. Our results confirm that a saturated MB law, which was previously found to describe the spin-down of rapidly rotating isolated M dwarfs, also operates in tidally locked binaries. We advocate using saturated MB models in binary evolution calculations. Our work supports previous suggestions that MB in cataclysmic variables (CVs) is much weaker than assumed in the standard evolutionary model, unless mass transfer leads to significant additional angular momentum loss in CVs.

Magnetic Fields in Low-mass Stars Increase Photometric Masses, Thereby Reducing Inferred Radius Inflation

Standard evolution models of a given age provide a relationship between stellar mass and T eff. Based on this, Cruz et al. have derived stellar masses and radii for a sample of Kepler stars using photometry alone: their radii are found to be inflated by up to 100% relative to standard models. However, magnetic fields distort the M–T eff relationship in a systematic way: here, we quantify this distortion, and show that radius inflations in the Cruz et al. stars are likely to be significantly smaller than 100%.

The evolution of altruism and the units of selection problem

In this paper, I will address one of the main issues in the philosophy of biology: the evolution of altruism and cooperation and the related problem of the units of selection. Starting from the so-called paradox of altruism, I will critically examine standard evolutionary models for the resolution of that paradox, and the explanation of altruism. I review and assess the following models of selection: the traditional model of group selection, gene?s eye view, kin selection, direct reciprocity (reciprocal altruism), indirect reciprocity, and the updated version of group selection, namely Sober and Wilson?s model of multilevel selection. In the final section, I will try to explain why is the dismissal of multilevel selection based on its explanatory complexity so common, and why inclusive fitness theory and direct reciprocity are generally sufficient to explain a good part of biological phenomena related to altruism and cooperation.

Transients from the Cataclysmic Deaths of Cataclysmic Variables

Abstract We explore the observational appearance of the merger of a low-mass star with a white dwarf (WD) binary companion. We are motivated by recent work finding that multiple tensions between the observed properties of cataclysmic variables (CVs) and standard evolution models are resolved if a large fraction of CV binaries merge as a result of unstable mass transfer. Tidal disruption of the secondary forms a geometrically thick disk around the WD, which subsequently accretes at highly super-Eddington rates. Analytic estimates and numerical hydrodynamical simulations reveal that outflows from the accretion flow unbind a large fraction ≳90% of the secondary at velocities ∼500–1000 km s−1 within days of the merger. Hydrogen recombination in the expanding ejecta powers optical transient emission lasting about a month with a luminosity ≳1038 erg s−1, similar to slow classical novae and luminous red novae from ordinary stellar mergers. Over longer timescales the mass accreted by the WD undergoes hydrogen shell burning, inflating the remnant into a giant of luminosity ∼300–5000 L ⊙, effective temperature T eff ≈ 3000 K, and lifetime ∼104–105 yr. We predict that ∼103–104 Milky Way giants are CV merger products, potentially distinguishable by atypical surface abundances. We explore whether any Galactic historical slow classical novae are masquerading CV mergers by identifying four such post-nova systems with potential giant counterparts for which a CV merger origin cannot be ruled out. We address whether the historical transient CK Vul and its gaseous/dusty nebula resulted from a CV merger.

Testing the intrinsic scatter of the asteroseismic scaling relations with Kepler red giants

ABSTRACT Asteroseismic scaling relations are often used to derive stellar masses and radii, particularly for stellar, exoplanet, and Galactic studies. It is therefore important that their precisions are known. Here we measure the intrinsic scatter of the underlying seismic scaling relations for Δν and νmax, using two sharp features that are formed in the H–R diagram (or related diagrams) by the red giant populations. These features are the edge near the zero-age core-helium-burning phase, and the strong clustering of stars at the so-called red giant branch bump. The broadening of those features is determined by factors including the intrinsic scatter of the scaling relations themselves, and therefore it is capable of imposing constraints on them. We modelled Kepler stars with a Galaxia synthetic population, upon which we applied the intrinsic scatter of the scaling relations to match the degree of sharpness seen in the observation. We found that the random errors from measuring Δν and νmax provide the dominating scatter that blurs the features. As a consequence, we conclude that the scaling relations have intrinsic scatter of $\sim 0.5$ (Δν), $\sim 1.1$ (νmax), $\sim 1.7$ (M), and $\sim 0.4{{\ \rm per\ cent}}$ (R), for the SYD pipeline measured Δν and νmax. This confirms that the scaling relations are very powerful tools. In addition, we show that standard evolution models fail to predict some of the structures in the observed population of both the HeB and RGB stars. Further stellar model improvements are needed to reproduce the exact distributions.

The origins of mindreading: how interpretive socio-cognitive practices get off the ground

Recent accounts of mindreading—i.e., the human capacity to attribute mental states to interpret, explain, and predict behavior—have suggested that it has evolved through cultural rather than biological evolution. Although these accounts describe the role of culture in the ontogenetic development of mindreading, they neglect the question of the cultural origins of mindreading in human prehistory. We discuss four possible models of this, distinguished by the role they posit for culture: (1) the standard evolutionary psychology model (Carruthers), (2) the individualist empiricist model (Wellman, Gopnik), (3) the cultural empiricist model (Heyes), and (4) the radical socio-cultural constructivist model, which we favor. We motivate model (4) by arguing that many forms of mental state ascription do not serve the function of simply describing inner states causally responsible for the behavior of a cognitive agent; rather, they relate the agent to her environment by characterizing her practical commitments. Making these practical commitments explicit has an important regulatory function in that it supports action coordination and alignment on joint goals. We propose a model of how the ascription of mental states may have evolved as a linguistic device to perform exactly this function of making agents’ practical commitments explicit.

Key role of recombination in evolutionary processes with migration between two habitats.

Recombination is one of the leading forces of evolutionary dynamics. Although the importance of both recombination and migration in evolution is well recognized, there is currently no exact theory of evolutionary dynamics for large genome models that incorporates recombination, mutation, selection (quasispecies model with recombination), and spatial dynamics. To address this problem, we analyze the simplest spatial evolutionary process, namely, evolution of haploid populations with mutation, selection, recombination, and unidirectional migration, in its exact analytical form. This model is based on the quasispecies theory with recombination, but with replicators migrating from one habitat to another. In standard evolutionary models involving one habitat, the evolutionary processes depend on the ratios of fitness for different sequences. In the case of migration, we consider the absolute fitness values because there is no competition for resources between the population of different habitats. In the standard model without epistasis, recombination does not affect the mean fitness of the population. When migration is introduced, the situation changes drastically such that recombination can affect the mean fitness as strongly as mutation, as has been observed by Li and Nei for a few loci model without mutations. We have solved our model in the limit of large genome size for the fitness landscapes having different peaks in the first and second habitats and obtained the total population sizes for both habitats as well as the proportion of the population around two peak sequences in the second habitat. We identify four phases in the model and present the exact solutions for three of them.

Wind Roche lobe overflow as a way to make Type Ia supernovae from the widest symbiotic systems

Symbiotic stars are interacting binaries with one of the longest orbital periods. Since they can contain a massive white dwarf with a high accretion rate they are considered a possible type Ia supernovae (SNe Ia) progenitors. Among symbiotic binaries there are systems containing a Mira donor, which can have orbital periods of a few tens of years and more. This subclass of symbiotic stars due to their very large separation usually was not considered promising SNe Ia progenitors. We analysed evolution of one of the well studied symbiotic star with a Mira donor, V407 Cyg. We showed that the standard evolution model predicts that the system will not become a SN Ia. However, by simply adding a Wind Roche Lobe Overflow as one of the mass transfer modes we predict that the white dwarf in V407 Cyg will reach the Chandrasekhar limit in 40-200 Myr.

Changing-Look AGNs or Short-Lived Radio Sources?

The evolution of extragalactic radio sources has been a fundamental problem in the study of active galactic nuclei for many years. A standard evolutionary model has been created based on observations of a wide range of radio sources. In the general scenario of the evolution, the younger and smaller Gigahertz-Peaked Spectrum (GPS) and Compact Steep Spectrum (CSS) sources become large-scale FRI and FRII objects. However, a growing number of observations of low power radio sources suggests that the model cannot explain all their properties and there are still some aspects of the evolutionary path that remain unclear. There are indications, that some sources may be short-lived objects on timescales of $10^4$ - $10^5$ years. Those objects represent a new population of active galaxies. Here, we present the discovery of several radio transient sources on timescales of 5-20 years, largely associated with renewed AGN (Active Galactic Nucleus) activity. These changing-look AGNs possibly represent behaviour typical for many active galaxies.