Regular Star Research Articles

Anomalous double-mode RR Lyrae stars in the Magellanic Clouds

We report the discovery of a new subclass of double-mode RR Lyrae stars in the Large and Small Magellanic Clouds. The sample of 22 pulsating stars have been extracted from the latest edition of the OGLE collection of RR Lyrae variables in the Magellanic System. The stars pulsating simultaneously in the fundamental (F) and first-overtone (1O) modes have distinctly different properties than regular double-mode RR Lyrae variables (RRd stars). The $P_{1O}/P_F$ period ratios of our anomalous RRd stars are within a range 0.725-0.738, while "classical" double-mode RR Lyrae variables have period ratios in the range 0.742-0.748. In contrast to the typical RRd stars, in the majority of the anomalous pulsators the F-mode amplitudes are higher than the 1O-mode amplitudes. The light curves associated with the F-mode in the anomalous RRd stars show different morphology than the light curves of, both, regular RRd stars and single-mode RRab stars. Most of the anomalous double-mode stars show long-term modulations of the amplitudes (Blazhko-like effect). Translating the period ratios into the abundance parameter, Z, we find for our stars Z in the range (0.002,0.005) - an order of magnitude higher values than typical for RR Lyrae stars. The mass range of the RRd stars inferred from the $W_I$ vs. $P_F$ diagram is (0.55-0.75) of the solar mass. These parameters cannot be accounted for with single star evolution assuming a Reimers-like mass loss. Much greater mass loss caused by interaction with other stars is postulated. We blame the peculiar pulsation properties of our stars to the parametric resonance instability of the 1O-mode to excitation of the F- and 2O-modes as with the inferred parameters of the stars $2\omega_{\rm 1O}\approx\omega_{\rm F}+\omega_{\rm 2O}$.

THE CHEMICAL EVOLUTION OF THE BOÖTES I ULTRA-FAINT DWARF GALAXY*

ABSTRACT We present chemical abundance measurements of two metal-poor red giant stars in the ultra-faint dwarf galaxy Boötes I, based on Magellan/MIKE high-resolution spectra. For Boo-980, with , we present the first elemental abundance measurements, while Boo-127, with , shows abundances in good agreement with previous measurements. Light and iron-peak element abundance ratios in the two Boötes I stars, as well as those of most other Boötes I members, collected from the literature, closely resemble those of regular metal-poor halo stars. Neutron-capture element abundances Sr and Ba are systematically lower than the main halo trend and also show a significant abundance spread. Overall, this is similar to what has been found for other ultra-faint dwarf galaxies. We apply corrections to the carbon abundances (commensurate with stellar evolutionary status) of the entire sample and find 21% of stars to be carbon-enhanced metal-poor (CEMP) stars, compared to 13% without using the carbon correction. We reassess the metallicity distribution functions for the CEMP stars and non-CEMP stars, and confirm earlier claims that CEMP stars might belong to a different, earlier population. Applying a set of abundance criteria to test to what extent Boötes I could be a surviving first galaxy suggests that it is one of the earliest assembled systems that perhaps received gas from accretion from other clouds in the system, or from swallowing a first galaxy or building block type object. This resulted in the two stellar populations observable today.

Radiative feedback and cosmic molecular gas: the role of different radiative sources

We present results from multifrequency radiative hydrodynamical chemistry simulations addressing primordial star formation and related stellar feedback from various populations of stars, stellar energy distributions (SEDs) and initial mass functions. Spectra for massive stars, intermediate-mass stars and regular solar-like stars are adopted over a grid of 150 frequency bins and consistently coupled with hydrodynamics, heavy-element pollution and non-equilibrium species calculations. Powerful massive population III stars are found to be able to largely ionize H and, subsequently, He and He$^+$, causing an inversion of the equation of state and a boost of the Jeans masses in the early intergalactic medium. Radiative effects on star formation rates are between a factor of a few and 1 dex, depending on the SED. Radiative processes are responsible for gas heating and photoevaporation, although emission from soft SEDs has minor impacts. These findings have implications for cosmic gas preheating, primordial direct-collapse black holes, the build-up of "cosmic fossils" such as low-mass dwarf galaxies, the role of AGNi during reionization, the early formation of extended disks and angular-momentum catastrophe.

On the structure of periodic complex Horadam orbits

Numerous geometric patterns identified in nature, art or science can be generated from recurrent sequences, such as for example certain fractals or Fermat’s spiral. Fibonacci numbers in particular have been used to design search techniques, pseudo random-number generators and data structures. Complex Horadam sequences are a natural extension of Fibonacci sequence to complex numbers, involving four parameters (two initial values and two in the defining recursion), therefore successive sequence terms can be visualized in the complex plane. Here, a classification of the periodic orbits is proposed, based on divisibility relations between orders of generators (roots of the characteristic polynomial). Regular star polygons, bipartite graphs and multi-symmetric patterns can be recovered for selected parameter values. Some applications are also suggested.

Star fruit toxicity: a cause of both acute kidney injury and chronic kidney disease: a report of two cases.

BackgroundStar fruit (Averrhoa carambola) is commonly consumed as a herbal remedy for various ailments in tropical countries. However, the dangers associated with consumption of star fruit are not commonly known. Although star fruit induced oxalate nephrotoxicity in those with existing renal impairment is well documented, reports on its effect on those with normal renal function are infrequent. We report two unique clinical presentation patterns of star fruit nephrotoxicity following consumption of the fruit as a remedy for diabetes mellitus—the first, in a patient with normal renal function and the second case which we believe is the first reported case of chronic kidney disease (CKD) due to prolonged and excessive consumption of star fruits.Case presentationThe first patient is a 56-year-old female diabetic patient who had normal renal function prior to developing acute kidney injury (AKI) after consuming large amount of star fruit juice at once. The second patient, a 60-year-old male, also diabetic presented with acute on chronic renal failure following ingestion of a significant number of star fruits in a short duration with a background history of regular star fruit consumption over the past 2–3 years. Both had histologically confirmed oxalate induced renal injury. The former had histological features of acute tubulo-interstitial disease whilst the latter had acute-on-chronic interstitial disease; neither had histological evidence of diabetic nephropathy. Both recovered over 2 weeks without the need for haemodialysis.ConclusionThese cases illustrate the importance of obtaining the patient’s detailed history with respect to ingestion of herbs, traditional medication and health foods such as star fruits especially in AKI or CKD of unknown cause.Electronic supplementary materialThe online version of this article (doi:10.1186/s13104-015-1640-8) contains supplementary material, which is available to authorized users.

Globular clusters as the relics of regular star formation in ‘normal’ high-redshift galaxies

We present an end-to-end, two-phase model for the origin of globular clusters (GCs). In the model, populations of stellar clusters form in the high-pressure discs of high-redshift ($z>2$) galaxies (a rapid-disruption phase due to tidal perturbations from the dense interstellar medium), after which the galaxy mergers associated with hierarchical galaxy formation redistribute the surviving, massive clusters into the galaxy haloes, where they remain until the present day (a slow-disruption phase due to tidal evaporation). The high galaxy merger rates of $z>2$ galaxies allow these clusters to be `liberated' into the galaxy haloes before they are disrupted within the high-density discs. This physically-motivated toy model is the first to include the rapid-disruption phase, which is shown to be essential for simultaneously reproducing the wide variety of properties of observed GC systems, such as their universal characteristic mass-scale, the dependence of the specific frequency on metallicity and galaxy mass, the GC system mass-halo mass relation, the constant number of GCs per unit supermassive black hole mass, and the colour bimodality of GC systems. The model predicts that most of these observables were already in place at $z=1$-$2$, although under rare circumstances GCs may still form in present-day galaxies. In addition, the model provides important constraints on models for multiple stellar populations in GCs by putting limits on initial GC masses and the amount of pristine gas accretion. The paper is concluded with a discussion of these and several other predictions and implications, as well as the main open questions in the field.

Translational diffusion coefficient of wormlike regular three-arm stars

The translational diffusion coefficient D or (effective) hydrodynamic radius RH of the regular three-arm star Kratky–Porod (KP) wormlike chain is evaluated. The behavior of the ratio gH of RH of the star to that of the corresponding linear chain is examined as a function of the (reduced) contour length L and (reduced) hydrodynamic diameter db.

Precise Synthesis of Novel Star-Branched Polymers Containing Reactive Poly(1,4-divinylbenzene) Arm(s) by Linking Reaction of Living Anionic Poly(1,4-divinylbenzene) with Chain-(α-Phenyl acrylate)-Functionalized Polymers

We have synthesized several star-branched polymers having poly(1,4-divinylbenzene) (PDVB) segment(s) by quantitatively linking the 1,1-diphenylethylene-stabilized living anionic PDVB with the chain-(α-phenyl acrylate)-functionalized polymers. The synthesized polymers were the A3 regular star PDVB, A2B, AB2, ABC, ABCD, and A4B μ-star polymers. The A arm is the PDVB segment, while the B, C, or D arm is either a polystyrene, poly(methyl methacrylate), poly(α-methylstyrene), or poly(2-vinylpyridine) segment. These polymers are the first successful highly reactive PDVB-containing well-defined star-branched polymers, whose pendant vinyl groups are capable of undergoing various postfunctionalization reactions to introduce additional functionalities.

Proof Without Words: The Vertex Angle Sum of a Regular Star Polygon

SummaryWe visually prove the formula for the vertex angle sum of a regular star polygon.

Regular weakly star closed sets in bigeneralized topological spaces

The main purpose of this paper is to introduce the concept of a new class of set called μ(m,n)-regular weakly star closed (briefly μ(m,n)-rw ∗closed) set in bigeneralized topological spaces. Here, basic properties of μ(m,n)-rw ∗-closed sets are discussed and relationships among other type of weakly closed sets in bigeneralized topological spaces are investigated.

Regular weakly star closed sets in bigeneralized topological spaces: revisited

Regular weakly star closed sets in bigeneralized topological spaces: revisited

Regular weakly star closed sets in generalized topological spaces

Regular weakly star closed sets in generalized topological spaces

Globular cluster formation in the context of galaxy formation and evolution

The formation of globular clusters (GCs) remains one of the main unsolved problems in star and galaxy formation. The past decades have seen important progress in constraining the physics of GC formation from a variety of directions. In this article, we discuss the latest constraints obtained from studies of present-day GC populations, the formation of young massive clusters (YMCs) in the local Universe, and the observed, large-scale conditions for star and cluster formation in high-redshift galaxies. The main conclusion is that the formation of massive, GC progenitor clusters is restricted to high-pressure environments similar to those observed at high redshift and at the sites of YMC formation in the local Universe. However, the correspondingly high gas densities also lead to efficient cluster disruption by impulsive tidal shocks, which limits the survival of GCs progenitor clusters. As a result, the long-term survival of GC progenitor clusters requires them to migrate into the host galaxy halo on a short time-scale. It is proposed that the necessary cluster migration is facilitated by the frequent galaxy mergers occurring at high redshift. We use the available observational and theoretical constraints to condense the current state of the field into a coherent picture of GC formation, in which regular star and cluster formation in high-redshift galaxies naturally leads to the GC populations observed today.

Characteristics of bright ab-type RR Lyrae stars from the ASAS and WASP surveys

In this article, we present results based on high-density, high-precision Wide-Angle Search for Planets (WASP) light curves supplemented with lower-precision photometry from the All-Sky Automated Survey (ASAS) for 268 RR Lyrae stars (176 regular, 92 Blazhko). Light curves were Fourier-decomposed and coefficients from WASP were transformed to the ASAS standard using 24 common stars. Coefficients were then compared with similar data from Galactic globular clusters, the Galactic bulge and the Large and Small Magellanic Clouds (LMC and SMC). Using Fourier coefficients, we also calculated physical parameters via standard equations from the literature. We confirmed the results of previous authors, including lower amplitudes and longer rise times for Blazhko stars. It was found that in the $R_{31}$ vs. $R_{21}$ plot the location of a star depends mainly on its metallicity and that Blazhko stars prefer a different location than modulation-free stars. Field and globular-cluster RR Lyrae variables have a different $\phi_{21}$ and $\phi_{31}$ than stars in the LMC, SMC and in Galactic bulge. Although there are some weak indications that Blazhko stars could prefer a slightly lower metallicity and shorter periods, no convincing proof was found. The most interesting highlight is the identification of a very recently proposed new group of metal-rich RR Lyrae type stars. These low-luminous, metal-strong variables, which comprise both Blazhko and regular stars, have shorter periods and about a 180 K higher temperature at constant $(B-V)_{0}$ than the rest of the stars in the sample.

Can the Branching Exponent Reliably Relate the Branching Indexes?

Randomly branched Gaussian chains, including regular and random stars, were modeled. The chains were generated by repeated random movement of the end‐point in a cubic grid. The radius‐of‐gyration‐ and viscosity‐volume branching indexes, g and g′, were calculated for randomly branched molecules and compared with the data taken from the literature. The dependence of g′ on g, constructed from our data as well as from those by Kurata and Fukatsu, appears linear. The experimental data taken from the literature do not contradict this finding. On the other hand, the values of the branching exponent ϵ are highly scattered and a reliable average cannot be found. This findings support the value of the branching exponent of ϵ = 1, relating g and g′, proposed also by other authors.

Why I-Love-Q: Explaining why universality emerges in compact objects

Black holes are said to have no hair because all of their multipole moments can be expressed in terms of just their mass, charge and spin angular momentum. The recent discovery of approximately equation-of-state-independent relations among certain multipole moments in neutron stars suggests that they are also approximately bald. We here explore the yet unknown origin for this universality. First, we investigate which region of the neutron star's interior and of the equation of state is most responsible for the universality. We find that the universal relation between the moment of inertia and the quadrupole moment is dominated by the star's outer-core, a shell of width (50-95)% of the total radius, which corresponds to the density range $(10^{14}$-$10^{15})$g/cm$^3$. Second, we study the impact on the universality of approximating stellar isodensity contours as self-similar ellipsoids. An analytical calculation in the Newtonian limit reveals that the shape of the ellipsoids does not affect the universal relations, but relaxing the self-similarity assumption can completely destroy it. Third, we investigate the eccentricity profiles of rotating relativistic stars and find that the ellipticity is roughly constant, with variations of roughly (20-30)% in the region that matters to the universal relations. Fourth, we repeat the above analysis for non-compact, regular stars and find that the ellipticity is not constant, with variations that easily exceed 100% and universality is lost. These findings suggest that universality arises as an emergent approximate symmetry: as one flows in the stellar-structure phase space from non-compact star region to the relativistic star region, the eccentricity variation inside stars decreases, leading to approximate self-similarity in their isodensity contours, which then leads to the universal behavior observed in their exterior multipole moments.

AF4/MALS/QELS/DRI characterization of regular star polymers and their "span analogs".

Asymmetric flow field-flow fractionation (AF4) coupled with multi-angle static and quasi-elastic light scattering and differential refractive index detectors, was employed for the separation and characterization of regular star-shaped polystyrenes and their linear and span analogs in tetrahydrofuran. Stars with different arm lengths were separated from each other by employing a binary slope cross-flow gradient. Cross-flow optimization enabled fast separation of polystyrenes in two- and three-component blends. Macromolecular parameters were obtained by using light-scattering and refractive index detection, and properties of polystyrenes with different molecular architectures were compared. To our knowledge, this is the first report on the separation of star polymers by AF4. Novel characterization approaches for stars are important from both applied and fundamental standpoints, as these macromolecules are valued for their tribological, drug delivery, catalytic and coating capabilities, and also serve as model compounds for the structured study of long-chain branching and its effects in polymers.

Random packing of regular polygons and star polygons on a flat two-dimensional surface.

Random packing of unoriented regular polygons and star polygons on a two-dimensional flat continuous surface is studied numerically using random sequential adsorption algorithm. Obtained results are analyzed to determine the saturated random packing ratio as well as its density autocorrelation function. Additionally, the kinetics of packing growth and available surface function are measured. In general, stars give lower packing ratios than polygons, but when the number of vertexes is large enough, both shapes approach disks and, therefore, properties of their packing reproduce already known results for disks.

Are globular clusters the natural outcome of regular high-redshift star formation?

AbstractWe summarise the recent progress in understanding the formation and evolution of globular clusters (GCs) in the context of galaxy formation and evolution. It is discussed that an end-to-end model for GC formation and evolution should capture four different phases: (1) star and cluster formation in the high-pressure interstellar medium of high-redshift galaxies, (2) cluster disruption by tidal shocks in the gas-rich host galaxy disc, (3) cluster migration into the galaxy halo, and (4) the final evaporation-dominated evolution of GCs until the present day. Previous models have mainly focussed on phase 4. We present and discuss a simple model that includes each of these four steps – its key difference with respect to previous work is the simultaneous addition of the high-redshift formation and early evolution of young GCs, as well as their migration into galaxy haloes. The new model provides an excellent match to the observed GC mass spectrum and specific frequency, as well as the relations of GCs to the host dark matter halo mass and supermassive black hole mass. These results show (1) that the properties of present-day GCs are reproduced by assuming that they are the natural outcome of regular high-redshift star formation (i.e. they form according to same physical processes that govern massive cluster formation in the local Universe), and (2) that models only including GC evaporation strongly underestimate their integrated mass loss over a Hubble time.

Dissolution behaviors of waxy maize amylopectin in aqueous-DMSO solutions containing NaCl and CaCl2

Dissolution behavior and molecular conformation of waxy maize amylopectin in aqueous DMSO solutions containing different amounts of water and salts (NaCl or CaCl2 up to 0.2 M) were characterized using multi-angle laser light scattering (MALLS; micro-batch mode) and dynamic light scattering (DLS) detectors. The solubility of amylopectin decreased and the molecular size measured increased when the water content in the DMSO increased, indicating that amylopectin chains tended to be less dissociated or aggregate by the excess amount of water. The amylopectin in aqueous DMSO solutions (10–50% water) had a spherical shape with a regular star structure, but the individual amylopectin chains were not affected by water content. Minor addition of salts facilitated the dissolution of amylopectin in aqueous DMSO solutions, possibly due to water cluster formation by the salt ions. However, a minute presence of salts (0.01 and 0.05 M) could induce the chain association even in 90% DMSO solution.