Effects Of Binary Stars Research Articles

The effects of binary stars on galaxies and metal-enriched gas during reionization

ABSTRACT Binary stars are abundant in nearby galaxies, but are typically unaccounted for in simulations of the high-redshift Universe. Stellar population synthesis models that include the effects of binary evolution result in greater relative abundances of ionizing photons that could significantly affect the ambient ionizing background during the epoch of hydrogen reionization, additionally leading to differences in galaxy gas content and star formation. We use hydrodynamic cosmological simulations including in situ multifrequency radiative transfer to evaluate the effects of a high binary fraction in reionization-era galaxies on traits of the early intergalactic medium and the abundance of H i and He ii ionizing photons. We further extend this to analyse the traits of enriched gas. In comparing metrics generated using a fiducial simulation assuming single stars with one incorporating a high binary fraction, we find that binary stars cause H i reionization to complete earlier and at an accelerated pace, while also increasing the abundances of high-ionization metals (C iv and Si iv) in simulated absorption spectra while reducing the abundance of low-ionization states (O i, Si ii, and C ii). However, through increased photoheating of galactic and circumgalactic gas, they simultaneously reduce the rate of star formation in low-mass galaxies, slowing the ongoing process of enrichment and suppressing their own ionizing background. This potentially contributes to a slower He ii reionization process at $z\ge 5$, and further indicates that self-regulation of galaxies could be underestimated when neglecting binary stellar evolution.

The dynamics of the globular cluster NGC 3201 out to the Jacobi radius

ABSTRACT As part of a chemodynamical survey of five nearby globular clusters with 2dF/AAOmega on the Anglo-Australian Telescope (AAT), we have obtained kinematic information for the globular cluster NGC 3201. Our new observations confirm the presence of a significant velocity gradient across the cluster which can almost entirely be explained by the high proper motion of the cluster (${\sim}9\, \mathrm{mas\, yr^{-1}}$). After subtracting the contribution of this perspective rotation, we found a remaining rotation signal with an amplitude of ${\sim}1\, \mathrm{km\, s^{-1}}$ around a different axis to what we expect from the tidal tails and the potential escapers, suggesting that this rotation is internal and can be a remnant of its formation process. At the outer part, we found a rotational signal that is likely a result from potential escapers. The proper motion dispersion at large radii reported by Bianchini et al. ($3.5\pm 0.9\, \mathrm{km\, s^{-1}}$) has previously been attributed to dark matter. Here, we show that the LOS dispersion between 0.5 and 1 Jacobi radius is lower ($2.01\pm 0.18\, \mathrm{km\, s^{-1}}$), yet above the predictions from an N-body model of NGC 3201 that we ran for this study ($1.48\pm 0.14\, \mathrm{km\, s^{-1}}$). Based on the simulation, we find that potential escapers cannot fully explain the observed velocity dispersion. We also estimate the effect on the velocity dispersion of different amounts of stellar-mass black holes and unbound stars from the tidal tails with varying escape rates and find that these effects cannot explain the difference between the LOS dispersion and the N-body model. Given the recent discovery of tidal tail stars at large distances from the cluster, a dark matter halo is an unlikely explanation. We show that the effect of binary stars, which is not included in the N-body model, is important and can explain part of the difference in dispersion. We speculate that the remaining difference must be the result of effects not included in the N-body model, such as initial cluster rotation, velocity anisotropy, and Galactic substructure.

The Unexpected Kinematics of Multiple Populations in NGC 6362: Do Binaries Play a Role?*

Abstract We present a detailed analysis of the kinematic properties of the multiple populations (MPs) in the low-mass Galactic globular cluster (GC) NGC 6362 based on a sample of about 500 member stars for which radial velocities (RVs), and Fe and Na abundances have been homogeneously derived. At distances from the cluster center larger than about 0.5r h , we find that first-generation (FG–Na-poor) and second-generation (SG–Na-rich) stars show hints of different line-of-sight velocity dispersion profiles, with FG stars being dynamically hotter. This is the first time that differences in the velocity dispersion of MPs are detected using only RVs. While kinematic differences between MPs in GCs are usually described in terms of anisotropy differences driven by the different radial distributions, this explanation hardly seems viable for NGC 6362, where SG and FG stars are spatially mixed. We demonstrate that the observed difference in the velocity dispersion profiles can be accounted for by the effect of binary stars. In fact, thanks to our multi-epoch RV measurements, we find that the binary fraction is significantly larger in the FG sample (f ∼ 14%) than in the SG population (f < 1%), and we show that such a difference can inflate the velocity dispersion of FG with respect to SG by the observed amount in the relevant radial range. Our results nicely match the predictions of state-of-the art N-body simulations of the co-evolution of MPs in GCs that include the effects of binaries.

The Effects of Binary Stars on the Color–Magnitude Diagrams of Young-age Massive Star Clusters

Abstract Extended main-sequence turnoffs (eMSTO) have been observed in the color–magnitude diagram (CMD) of intermediate-age and young star clusters. The origin of the eMSTO phenomenon is still highly debated. Calculations show that the blue and faint (BF) stars in the CMD of NGC 1866 are hydrogen main-sequence (MS) + naked He-star systems. The He star derives from the massive star of a binary system. The BF stars and the red and faint MSTO stars belong to the same stellar population. The values of m F336W and m F336W −m F814W of the BF stars are mainly determined by the masses of He stars and H-MS stars, respectively. The behaviors of the BF stars in the CMD are well explained by the H-MS+He-star systems. The BF stars provide a strict restriction on the age of the stellar population. Moreover, the bimodal MS of NGC 1866 can also be reproduced by a younger binary population. The calculations show that part of the blue and bright (BB) MS stars of NGC 1866 are H-MS+He-star systems, H-MS+white dwarf systems, and merged stars in a binary scenario. The H-MS stars of the H-MS+He-star systems for the BB stars are significantly more massive than those of the BF stars. Once the H-MS+He-star systems and their membership in NGC 1866 are confirmed, the extended star formation histories and the effects of binaries can be confirmed in the young star cluster.

The effect of binary stars on photometric redshift for galaxies at z ~ 2.0

AbstractEvolutionary population synthesis (EPS) models play an important role in many studies on the formation and evolution of galaxy. The poorly calibration for some stellar evolution stages in EPS models can lead to uncertainty of the parameter determinations for galaxies. By means of the HyperZ code and a set of theoretical galaxy template, which are built on the EPS models with and without binary interactions, we present photometric redshift (photo-z) estimates for passive galaxy sample at redshift z ~ 2.0. The passive galaxy sample is selected from Fang et al., and they also provide the redshift for these passive galaxies. By comparing the photo-z determined from EPS models with and without binary interactions, we find that the binary interactions have little effect in the photo-z determinations.

The effects of binary stars on the colors of galaxies at z~2.0

AbstractUsing the Monte Carlo simulations and a set of theoretical galaxy templates, which are built on the Yunnan evolutionary population synthesis models with and without binary interactions, we compare the optical color-color (C-C) relations for passive and star-forming galaxies at redshift z~2.0, and study the effect of binary interactions on this relation. We find that the influence of binary interactions on the C-C relation is insignificant for passive galaxies at z~2.0.

Open cluster stability and the effects of binary stars

The diagnostic age versus mass-to-light ratio diagram is often used in attempts to constrain the shape of the stellar initial mass function (IMF) and the potential longevity of extragalactic young to intermediate-age massive star clusters. Here, we explore its potential for Galactic open clusters. On the basis of a small, homogenised cluster sample, we provide useful constraints on the presence of significant binary fractions. Using the massive young Galactic cluster Westerlund 1 as a key example, we caution that stochasticity in the IMF introduces significant additional uncertainties. We conclude that, for an open cluster to survive for any significant length of time, and in the absence of substantial external perturbations, it is necessary but not sufficient to be located close to or (in the presence of a significant binary population) somewhat below the predicted photometric evolutionary sequences for “normal” simple stellar populations, although such a location may be dominated by a remaining “bound” cluster core and thus not adequately reflect the overall cluster dynamics.

Luminosity-colour relations for thin-disc main-sequence stars

In this study we present the absolute magnitude calibrations of thin-disc main-sequence stars in the optical (M V ), and in the near-infrared (Mj). Thin-disc stars are identified by means of Padova isochrones, and absolute magnitudes for the sample are evaluated via the newly reduced Hipparcos data. The obtained calibrations cover a large range of spectral types: from A0 to M4 in the optical and from A0 to M0 in the near-infrared. Also, we discuss the effects of binary stars and evolved stars on the absolute magnitude calibrations. The usage of these calibrations can be extended to the estimation of galactic model parameters for the thin disc individually, in order to compare these parameters with the corresponding ones estimated by Χ 2 min statistics (which provides galactic model parameters for thin and thick discs and halo simultaneously) to test any degeneracy between them. The calibrations can also be used in other astrophysical researches where distance plays an important role in that study.

The role of binary stars in stellar population synthesis

AbstractMore than about 50% stars are in binaries, but the effects of binary evolution were not taken into account in most previous stellar population synthesis studies. In fact, binaries can affect the integrated peculiarities such as spectral energy distributions (SEDs), colours, and line-strength indices of populations. With the effects of binary stars taken into account, some new results for stellar population studies will be shown. We discuss how binaries affect the colours and Lick indices of simple stellar populations, and the measurement of stellar ages and metallicities.

ITAL]Hubble Space Telescope[/ITAL] Observations of the Central-Cusp Globular Cluster NGC 6752: the Effect of Binary Stars on the Luminosity Function in the Core

We consider the effect of binary stars on the main-sequence luminosity functions observed in the core of globular clusters, with specific reference to NGC 6752. We find that mass segregation results in an increased binary fraction at fainter magnitudes along the main sequence. If this effect is not taken into account when analyzing luminosity functions, erroneous conclusions can be drawn regarding the distribution of single stars and the dynamical state of the cluster. In the core of NGC 6752, our Hubble Space Telescope data reveal a flat luminosity function (LF), in agreement with previous results. However, when we correct for the increasing binary fraction at faint magnitudes, the LF begins to fall immediately below the turnoff. This effect appears to be confined to the inner core radius of the cluster.

Measuring the Dark Matter Scale of Local Group Dwarf Spheroidals

We reanalyze published Draco and Ursa Minor dwarf spheroidal (dSph) stellar velocity data. Previous studies of dSph stellar distributions have concentrated principally on the spatial distribution of stars or on computation of a global velocity dispersion. A detailed understanding of the spatial behavior of the velocity distribution, however, is necessary to distinguish among competing theories of dSph dynamics. Here we apply a maximum-likelihood technique to fit the set of individual velocity measurements to a global distribution. Rather than calculating mean local velocity dispersions in regions where the data are sparse, this technique has the advantage of using the velocity measurements individually. We confirm earlier findings of a radial falloff in the velocity distribution of UMi, which is consistent with a mass-follows-light (MFL) King model. We also confirm an apparent radial rise in the velocity dispersion of Draco. However, these data do not suffice to distinguish among extended halo and MFL models. Finally, we perform simulations to determine the number of additional observations required to clearly differentiate between different dynamical models. Only ~10–20 additional observations at 0.75 times the tidal radius would be required to distinguish clearly between an MFL distribution and an extended halo or disrupted remnant model with a flat or radially rising velocity dispersion. We describe a method for treating the effect of binary stars, which may be a source of contamination.

Effect of binary stars on the dynamical evolution of stellar clusters. II - Analytic evolutionary models

view Abstract Citations (89) References (4) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Effect of binary stars on the dynamical evolution of stellar clusters. II. Analytic evolutionary models. Hills, J. G. Abstract Analytical models are used to compute the evolution of the core of a stellar system due simultaneously to stellar evaporation, which causes the system (core) to contract, and to its binaries, which cause it to expand by progressively decreasing its binding energy. The evolution of the system is determined by two parameters: the initial number of stars in the system and the fraction of its stars which are binaries. For a fixed binary fraction, stellar evaporation initially dominates the dynamical evolution if the initial number is sufficiently large, due to the fact that the rate of evaporation is determined chiefly by long-range encounters which increase in importance as the number of stars in the system increases. If stellar evaporation initially dominates, the system first contracts, but as the number of remaining stars in the system decreases by evaporation, the system reaches a minimum radius and a maximum density, and then it expands monotonically as the number of remaining stars decreases further. Open clusters expand monotonically from the beginning if they have anything approaching average Population I binary frequencies. Globular clusters are highly deficient in binaries in order to have formed and retained the high-density stellar cores observed in most of them. The binary fraction for these systems is estimated to be no more than 0.15. Publication: The Astronomical Journal Pub Date: December 1975 DOI: 10.1086/111842 Bibcode: 1975AJ.....80.1075H Keywords: Astronomical Models; Binary Stars; Mass Transfer; Star Clusters; Stellar Evolution; Stellar Systems; Evaporation; Globular Clusters; Graphs (Charts); Gravitational Collapse; Open Clusters; Star Distribution; Astrophysics full text sources ADS |