Building on the recent release of a new \emph{Gaia}-based blue straggler star catalog in Galactic open star clusters (OCs), we explored the properties of these stars in a cluster sample spanning a ...wide range in fundamental parameters. We employed \emph{Gaia} EDR3 to assess the membership of any individual blue or yellow straggler to their parent cluster. We then made use of the \texttt{ASteCA} code to estimate the fundamental parameters of the selected clusters, in particular, the binary fraction. With all this at hand, we critically revisited the relation of the blue straggler population and the latter. For the first time, we found a correlation between the number of blue stragglers and the host cluster binary fraction and binaries. This supports the hypothesis that binary evolution is the most viable scenario of straggler formation in Galactic star clusters. The distribution of blue stragglers in the Gaia color-magnitude diagram was then compared with a suite of composite evolutionary sequences derived from binary evolutionary models that were run by exploring a range of binary parameters: age, mass ratio, period, and so forth. The excellent comparison between the bulk distribution of blue stragglers and the composite evolutionary sequences loci further supports the binary origin of most stragglers in OCs and paves the way for a detailed study of individual blue stragglers
We present radial velocity observations of four extremely low-mass (0.2 Msol) white dwarfs. All four stars show peak-to-peak radial velocity variations of 540 - 710 km/s with 1.0 - 5.9 hr periods. ...The optical photometry rules out main-sequence companions. In addition, no milli-second pulsar companions are detected in radio observations. Thus the invisible companions are most likely white dwarfs. Two of the systems are the shortest period binary white dwarfs yet discovered. Due to the loss of angular momentum through gravitational radiation, three of the systems will merge within 500 Myr. The remaining system will merge within a Hubble time. The mass functions for three of the systems imply companions more massive than 0.46 Msol; thus those are carbon/oxygen core white dwarfs. The unknown inclination angles prohibit a definitive conclusion about the future of these systems. However, the chance of a supernova Ia event is only 1% to 5%. These systems are likely to form single R Coronae Borealis stars, providing evidence for a white dwarf + white dwarf merger mechanism for these unusual objects. One of the systems, SDSS J105353.89+520031.0 has a 70% chance of having a low-mass white dwarf companion. This system will probably form a single helium-enriched subdwarf O star. All four white dwarf systems have unusal mass ratios of < 0.2-0.8 that may also lead to the formation of AM CVn systems.
Equine viral arteritis (EVA) is a contagious viral disease that frequently causes mild or subclinical infections in adult horses. Only one EAV serotype has been described. However, there are ...differences in antigenicity, pathogenicity and neutralization characteristics of virus field strains. The interaction of two viral proteins, GP5 and M, is critical for infectivity and amino acid changes in the GP5 sequences have an effect on the neutralizing phenotype, regardless the effects of other viral proteins. The objective of the present study was to evaluate the neutralization phenotypes of the 5 unique Argentine EAV strains reported and to compare them with the neutralization phenotypes of the EAV-UCD reference strain, with special emphasis on the analysis of M and GP5 proteins. The strains had a similar neutralization phenotype pattern when anti-EAV serum, derived from EAV seropositive horses, was used in the analysis. Meanwhile, low titers were observed when equine polyclonal anti-EAV reference sera were used in the assay. Argentine strains have almost the same amino acid substitutions, with the exception of LP01 strain, that mainly involves the first variable region V1, especially in neutralization sites B and C. However, they are fairly different from the EAV-UCD strain. Nevertheless, the nucleotide and amino acid differences observed among the Argentine strains LP02/R, LP02/C, LP02/P and LP-LT-ARG did not show any variations in the neutralization phenotype.La arteritis viral equina (AVE) ocasiona infecciones, en su mayoría subclínicas, pero puede causar abortos y enfermedad respiratoria. Si bien se ha descrito un solo serotipo de AVE, existen diferencias en cuanto a la antigenicidad, patogenicidad y patrones de neutralización en las cepas de campo. Los ORF5 y ORF6 del virus codifican las proteínas de envoltura GP5 y M; la interacción entre estas proteínas es crítica para la infectividad. Los cambios en las secuencias de aminoácidos en la proteína GP5, especialmente en la región V1, afectan el fenotipo neutralizante, sin tener en cuenta variaciones aminoacídicas de otras proteínas virales. En este estudio evaluamos los fenotipos neutralizantes de las 5 únicas cepas de arteritis viral equina aisladas en Argentina y los comparamos con los de la cepa de referencia EAV-UCD por virus neutralización cruzada y análisis de secuencias aminoacídicas de las proteínas M y GP5. Las cepas argentinas presentaron un patrón de neutralización similar cuando se utilizaron sueros positivos del banco de sueros, mientras que fueron neutralizadas en menor medida por los sueros policlonales de referencia anti-AVE. A excepción de la cepa LP01, las cepas argentinas tienen casi las mismas sustituciones aminoacídicas en la primera región variable V1 de la proteína GP5, específicamente en los sitios neutralizantes B y C, pero difieren en gran medida respecto de la cepa de referencia EAV-UCD. Las diferencias encontradas en los aislamientos LP02/R, LP02/C, LP02/P y LT-LP-ARG no se reflejaron en variaciones en el fenotipo neutralizante.
The evolution of iron white dwarf stars L. G. Althaus; O. G. Benvenuto; J. A. Panei
Revista mexicana de astronomía y astrofísica,
2001, Letnik:
11
Journal Article
Equine viral arteritis (EVA) is a contagious viral disease that frequently causes mild or subclinical infections in adult horses. Only one EAV serotype has been described. However, there are ...differences in antigenicity, pathogenicity and neutralization characteristics of virus field strains. The interaction of two viral proteins, GP5 and M, is critical for infectivity and amino acid changes in the GP5 sequences have an effect on the neutralizing phenotype, regardless the effects of other viral proteins. The objective of the present study was to evaluate the neutralization phenotypes of the 5 unique Argentine EAV strains reported and to compare them with the neutralization phenotypes of the EAV-UCD reference strain, with special emphasis on the analysis of M and GP5 proteins. The strains had a similar neutralization phenotype pattern when anti-EAV serum, derived from EAV seropositive horses, was used in the analysis. Meanwhile, low titers were observed when equine polyclonal anti-EAV reference sera were used in the assay. Argentine strains have almost the same amino acid substitutions, with the exception of LP01 strain, that mainly involves the first variable region V1, especially in neutralization sites B and C. However, they are fairly different from the EAV-UCD strain. Nevertheless, the nucleotide and amino acid differences observed among the Argentine strains LP02/R, LP02/C, LP02/P and LP-LT-ARG did not show any variations in the neutralization phenotype.
Motivated by the recent detection of single and binary He-core white dwarfs in metal-rich clusters, we present a full set of evolutionary calculations and colors appropriate for the study of such ...white dwarfs. The paper is also aimed at investigating whether stable hydrogen burning may constitute a main source of energy for massive He-core white dwarfs resulting from high-metallicity progenitors. White dwarf sequences are derived by taking into account the evolutionary history of progenitor stars with supersolar metallicities. We also incorporate a self-consistent, time-dependent treatment of gravitational settling and chemical diffusion, as well as of the residual nuclear burning. We find that the influence of residual nuclear burning during the late stages of white dwarf evolution is strongly dependent on the occurrence of chemical diffusion at the base of the hydrogen-rich envelope. When no diffusion is considered, residual hydrogen burning strongly influences the advanced stages of white dwarf cooling, introducing evolutionary delays of several Gyr. By contrast, when diffusion is taken into account the role of residual nuclear burning is strongly mitigated, and the evolution is dictated only by the thermal content stored in the ions. In addition, for all of our sequences, we provide accurate color and magnitudes on the basis of new and improved non gray model atmospheres which explicitly include Ly\(\alpha\) quasi-molecular opacity.
We present full evolutionary calculations appropriate for the study of hot hydrogen-deficent DO white dwarfs, PG 1159 stars, and DB white dwarfs. White dwarf sequences are computed for a wide range ...of stellar masses and helium envelopes on the basis of a complete treatment of the evolutionary history of progenitors stars, including the core hydrogen and helium burning phases, the thermally-pulsing AGB phase, and the born-again episode that is responsible for the hydrogen deficiency. We also provide colors and magnitudes for the new sequences for \(T_{\rm eff} < 40 000\) K, where the NLTE effects are not dominant. These new calculations provide an homogeneous set of evolutionary tracks appropriate for mass and age determinations for both PG 1159 stars and DO white dwarfs. The calculations are extended down to an effective temperature of 7 000 K. We applied these new tracks to redetermine stellar masses and ages of all known DO white dwarfs with spectroscopically-determined effective temperatures and gravities, and compare them with previous results. We also compare for the first time consistent mass determinations for both DO and PG 1159 stars, and find a considerably higher mean mass for the DO white dwarfs. We discuss as well the chemical profile expected in the envelope of variable DB white dwarfs from the consideration of the evolutionary history of progenitor stars. Finally, we present tentative evidence for a different evolutionary channel, other than that involving the PG 1159 stars, for the formation of hot, hydrogen-deficient white dwarfs.
Astron.Astrophys.449:313,2006 We present evolutionary calculations aimed at describing the born-again
scenario for post-AGB remnant stars of 0.5842 and 0.5885 \msun. Results are
based on a detailed ...treatment of the physical processes responsible for the
chemical abundance changes. We considered two theories of convection: the
standard mixing length theory (MLT) and the double-diffusive GNA convection
developed by Grossman et al. The latter accounts for the effect of the chemical
gradient ($\nabla\mu$) in the mixing processes and in the transport of energy.
We also explore the dependence of the born-again evolution on some physical
hypothesis, such as the effect of the existence of non-zero chemical gradients,
the prescription for the velocity of the convective elements and the size of
the overshooting zones. Attention is given to the behavior of the born-again
times and to the chemical evolution during the ingestion of protons. We find
that in our calculations born again times are dependent on time resolution. In
particular when the minimum allowed time step is below $5 \times 10^{-5}$ yr we
obtain, with the standard mixing length theory, born again times of 5-10 yr.
This is true without altering the prescription for the efficiency of convective
mixing during the proton ingestion. On the other hand we find that the
inclusion of the chemical gradients in the calculation of the mixing velocity
tend to increase the born again times by about a factor of two. In addition we
find that proton ingestion can be seriously altered if the occurrence of
overshooting is modified by the $\nabla\mu$-barrier at the H-He interface,
strongly altering born again times.
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