Models of stellar winds from X-ray bursts

The study of stellar winds (SW) in the context of X-ray bursts (XRB) performed in this thesis has two main motivating issues. The first is whether or not the heavy elements produced from nucleosynthesis in XRBs can escape the neutron star (NS) gravity through the SW and contribute significantly to Galactic abundances. The special interest is set on some light p-nuclei (92,94Mo, 96,98Ru) that are under-produced in every other astrophysical scenario, with respect to inferred abundances. The second relates to the determination of the equation of state (EoS) of neutron-degenerate matter. Independent measurements of NS radii and masses are required to constrain available EoS theoretical models. In this regard, predictions of observable features in NS envelopes during SW are important. A non-relativistic SW model was successfully implemented, with some improvements with respect to previous works, like the use of modern opacity tables and treatment of the critical point. Its study also required developing novel numerical methods (robust root-finding) and other useful algorithms (Battleship-like grid search). The SW model was first applied to a generic NS scenario, as a way to test its implementation, characterize possible solutions and explore the parameter space. For this, a rather flexible but sensible choice of inner boundary condition at the wind base was imposed. Even with such a generic choice of inner boundary conditions, the simulations showed some remarkable features and common patterns. Most notably, some photospheric magnitudes showed a high correlation, namely $1/r ~ T^2 ~ \rho$, independently of the NS radii at which the wind base condition was imposed. These correlations are independent from model parameters too, so they are expected to appear in every scenario. They seem to derive from the choice of boundary conditions at the photosphere, and the fact that photospheric luminosity takes on values very close to Eddington luminosity, for every choice of parameters. Another set of correlations found involves both wind parameters and photospheric magnitudes as well. Since wind parameters are determined by physical conditions at the wind base, these correlations effectively link observable magnitudes to the physics of the innermost parts of the envelope, close to its interface with the NS core. This could lead to a technique that allows to indirectly determine the radius of the NS, independently from its mass, from observable magnitudes. A study in a more realistic XRB scenario was also performed, by linking the SW model to a series of XRB hydrodynamic models. For this, we developed a technique that successfully matched different wind profiles to the conditions given during the evolution of each burst, with a quasi-stationary approach. This allowed us to construct a time evolution of wind profiles and to quantify the mass-loss of each isotope synthesized in the XRB. The ejected material contained a small fraction of our light p-nuclei of interest. However, an estimation of their significance regarding Galactic abundances showed that an unreasonable number of XRB sources like the one analyzed (corresponding to a typical XRB episode) was required to account for the expected abundances. Therefore, we concluded that XRB sources are unlikely to constitute the sole explanation of their origin. Nevertheless, given that the models analyzed showed a large difference in the ejected mass of these p-nuclei, we cannot assure that a future study, with overall larger metallicity, will not show a more significant contribution. Upon analyzing the observable magnitudes during the wind phase, the correlations previously discussed were found to hold. This is a promising result regarding the issue of NS radii determination. However, further study is required to determine whether these results are affected by the inclusion of relativistic corrections or detailed radiative transfer.El estudio de vientos estelares (SW) en el contexto de erupciones de rayos X (XRB) realizado en esta tesis tiene dos motivaciones. La primera es saber si los elementos pesados producidos por nucleosíntesis en XRBs pueden escapar de la gravedad de la estrella de neutrones (NS) a través del SW y contribuir significativamente a las abundancias Galácticas. El interés se centra en algunos núcleos-p ligeros (92,94Mo, 96,98Ru) que están subproducidos en los demás escenarios astrofísicos, con respecto a abundancias inferidas. La segunda se relaciona con la determinación de la ecuación de estado (EoS) de la materia neutrónica degenerada. Se requieren mediciones independientes de radios y masas de NS para restringir los modelos teóricos de EoS disponibles. En este sentido, las predicciones de características observables en NS durante los SW son importantes. Se implementó con éxito un modelo de SW no relativista, con algunas mejoras respecto a trabajos anteriores, como el uso de tablas de opacidad modernas y tratamiento del punto crítico. Esto además requirió el desarrollo de métodos numéricos novedosos y otros algoritmos útiles. El modelo de SW se aplicó primero a un escenario de NS genérico, para probar su implementación, caracterizar posibles soluciones y explorar el espacio de parámetros. Para esto, se impuso una condición de contorno bastante flexible pero sensata en la base del viento. Estas primeras simulaciones mostraron algunas características notables y patrones comunes. Algunas magnitudes fotosféricas mostraron una alta correlación, a saber, $1/r ~ T^2 ~ \rho$, independientemente del radio en que se impusiera la condición de base del viento o de los parámetros del modelo, por lo que se espera que aparezcan en todos los escenarios. Parecen derivar de las condiciones de contorno en la fotosfera y del hecho de que la luminosidad allí toma valores muy cercanos a la de Eddington. Otras correlaciones encontradas involucran tanto parámetros del viento como magnitudes fotosféricas. Como los parámetros del viento están determinados por las condiciones en la base del viento, estas correlaciones vinculan las magnitudes observables con la física de las partes más internas de la envoltura, cerca del núcleo de la NS. Esto daría lugar a una técnica que permita determinar el radio de la NS, independientemente de su masa, a partir de magnitudes observables. Se realizó también un estudio en un escenario de XRB más realista, vinculando el modelo de SW a una serie de modelos hidrodinámicos de XRB. Para ello, desarrollamos una técnica que empalma con éxito diferentes perfiles de viento con las condiciones dadas durante la evolución de cada XRB, en aproximación cuasi-estacionaria. Esto nos permitió construir una evolución temporal de los perfiles de viento y cuantificar la masa eyectada de cada isótopo sintetizado en el XRB. El material eyectado contenía una pequeña fracción de los núcleos-p ligeros de interés. Sin embargo, una estimación de su relevancia para las abundancias Galácticas mostró que se requería un número poco razonable de fuentes de XRB como la analizada (que corresponde a un caso típico) para obtener las abundancias esperadas. Por lo tanto, concluimos que es poco probable que los XRB constituyan la principal explicación de su origen. Sin embargo, dado que los modelos analizados mostraron una gran diferencia en la masa expulsada de estos núcleos-p, no podemos asegurar que un estudio futuro, con mayor metalicidad, no muestre una contribución más significativa. Al analizar las magnitudes observables durante la fase de viento, se encontró que las correlaciones discutidas anteriormente se mantenían. Este es un resultado prometedor con respecto a la determinación de radios de NS. Sin embargo, se requieren más estudios para determinar si estos resultados se ven afectados por la inclusión de correcciones relativistas o transferencia radiativa detallada.Postprint (published version

Aspects of electrostatics in BTZ geometries

In the present paper the electrostatics of charges in nonrotating BTZ black hole and wormhole spacetimes is studied. Our attention is focused on the self-force of a point charge in the geometry, for which a regularization prescription based on the Haddamard Green function is employed. The differences between the self-force in both cases is a theoretical experiment for distinguishing both geometries, which otherwise are locally indistinguishable. This idea was applied before to four and higher-dimensional black holes by the present and other authors. However, the particularities of the BTZ geometry makes the analysis considerable more complicated than those. First, the BTZ spacetimes are not asymptotically flat but instead asymptotically AdS. In addition, the relative distance d ( r , r + 1 ) between two particles located at a radius r and r + 1 in the geometry tends to zero when r → ∞ . This behavior, which is radically different in a flat geometry, changes the analysis of the asymptotic conditions for the electrostatic field. The other problem is that there exist several regularization methods other than the one we are employing, and there does not exist a proof in three dimensions that they are equivalent. However, we focus on the Haddamard method and obtain an expression for the hypothetical self-force in series, and the resulting expansion is convergent to the real solution. We suspect that the convergence is not uniform, and furthermore there are no summation formulas at our disposal. It appears, for points that are far away from the black hole the calculation of the Haddamard self-force requires higher-order summation. These subtleties are carefully analyzed in the paper, and it is shown that they lead to severe problems when calculating the Haddamard self-force for asymptotic points in the geometry.Fil: Herrera, Yago. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Hurovich, Valeria Laura. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Santillán, Osvaldo Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Investigaciones Matemáticas ; ArgentinaFil: Simeone, Claudio Mauricio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; Argentin

Simulations of stellar winds from X-ray bursts. Characterization of solutions and observable variables

Photospheric radius expansion during X-ray bursts can be used to measure neutron star radii and help constrain the equation of state of neutron star matter. Understanding the stellar wind dynamics is important for interpreting observations. Stellar wind models, though studied in past decades, have thus regained interest and need to be revisited with updated data and methods. In this work we study the radiative wind model in the context of XRBs, with modern techniques and physics input. We focus on characterization of the solutions and study of observable magnitudes as a function of free model parameters. We implement a spherically-symmetric non-relativistic wind model in a stationary regime, with updated opacity tables and modern numerical techniques. Total mass and energy outflows $(\dot M,\dot E)$ are treated as free parameters. A high resolution parameter space exploration was performed to allow better characterization of observable magnitudes. High correlation was found between different photospheric magnitudes and free parameters. For instance, the photospheric ratio of gravitational energy outflow to radiative luminosity is in direct proportion to the photospheric wind velocity. The correlations found could help determine the physical conditions of the inner layers, where nuclear reactions take place, by means of observable photospheric values. Further studies are needed to determine the range of physical conditions in which the correlations are valid.Comment: Accepted in Astronomy and Astrophysics. New version with corrected typo in eq. (36) and some minor changes after language editio

Mass-loss and composition of wind ejecta in type I X-ray bursts

Context. X-Ray bursts (XRBs) are powerful thermonuclear events on the surface of accreting neutron stars (NSs) where nucleosynthesis of intermediate-mass elements occurs. The high surface gravity of an NS prevents the ejection of material by the XRB thermonuclear explosion. However, the predicted and observed XRB luminosities sometimes exceed Eddington’s value, and some of the material may escape by means of stellar wind. Aims. This work aims to determine the mass-loss and chemical composition of the material ejected through radiation-driven winds and its significance for Galactic abundances. It also reports on the evolution of observational quantities during the wind phase, which can help constrain the mass-radius relation in NSs. Methods. A non-relativistic radiative wind model was implemented, with modern opacity tables and treatment of the critical point, and linked through a new technique to a series of XRB hydrodynamic simulations that include over 300 isotopes. This allowed us to construct a quasi-stationary time evolution of the wind during the XRB. Results. In the models we studied, the total mass ejected by the wind was about 6 × 10^19 g; the average ejected mass per burst represented 2.6% of the accreted mass between bursts, with 0.1% of the envelope mass ejected per burst; and approximately 90% of the ejecta was composed by 60Ni, 64Zn, 68Ge, and 58Ni. The ejected material also contained a small fraction (10^-4 - 10^-5) of some light p-nuclei, but not enough to account for their Galactic abundances. Additionally, the observable magnitudes during the wind phase showed remarkable correlations, partly due to the fact that photospheric luminosity stays close to the Eddington limit. Some of these correlations involve wind parameters, such as energy and mass outflows, that are determined by the conditions at the base of the wind envelope. Conclusions. The simulations resulted in the first realistic quantification of mass-loss for each isotope synthesized in the XRB. The photospheric correlations we found could be used to link observable magnitudes to the physics of the innermost parts of the envelope, close to its interface with the NS crust. This is a promising result regarding the issue of NS radius determination.Peer ReviewedPostprint (author's final draft

Idiopathic portal hypertension regarding thiopurine treatment in patients with inflammatory bowel disease

Introduction: The possibility of developing idiopathic portal hypertension has been described with thiopurine treatment despite compromises the prognosis of these patients, the fact its true prevalence is unknown. Material and methods: A cross-sectional study was conducted in a cohort of inflammatory bowel disease (IBD) patients followed at our unit, to determine the prevalence of diagnosis of idiopathic portal hypertension (IPH) and its relationship with thiopurine treatment. Results: At the time of the analysis, 927/1,419 patients were under treatment with thiopurine drugs (65%). A total of 4 patients with IBD type Crohn's disease with idiopathic portal hypertension probably related to the thiopurine treatment were identified (incidence of 4.3 cases per 1,000). Seventy-five percent of patients started with signs or symptoms of portal hypertension. Only one patient was asymptomatic but the diagnosis of IPH because of isolated thrombocytopenia is suspected. However, note that all patients had thrombocytopenia previously. Abdominal ultrasound with fibroscan, hepatic vein catheterization and liver biopsy were performed on all of them as part of the etiology of portal hypertension. In the abdominal ultrasound, indirect portal hypertension data were observed in all patients (as splenomegaly) cirrhosis was also ruled out. The fibroscan data showed significant liver fibrosis (F2-F3). Conclusion: Idiopathic portal hypertension following thiopurine treatment in IBD patients is a rare occurrence, but it must be borne in mind in the differential diagnosis for early diagnosis, especially in patients undergoing thiopurine treatment over a long period. The presence of thrombocytopenia is often the only predictor of its development in the preclinical stage

Prótesis sin sutura: ¿es posible reducir la tasa de bloqueos postoperatorios modificando la técnica de implante?

Resumen: Introducción: El recambio valvular aórtico con prótesis sin sutura Perceval S se asocia a un aumento en la tasa de bloqueo auriculoventricular postoperatorio que precisa implante de marcapasos definitivo, comparado con las bioprótesis convencionales. En nuestra serie hemos modificado la técnica de implante (mínimo baloneo < 5 segundos, decalcificación anular rigurosa, avance de prótesis plegada al tracto de salida del ventrículo izquierdo y reposicionamiento mediante tracción de puntos guía). Objetivos: Analizar el impacto de la modificación de la técnica de implante de Perceval en el número de bloqueo auriculoventricular postoperatorio que precisa implante de marcapasos definitivo. Material y métodos: De 438 pacientes sometidos a recambio valvular aórtico con prótesis Perceval, se excluyeron los correspondientes a la fase inicial del programa (6 meses, n = 14), cirugía concomitante mitral (n = 18) o tricuspídea (n = 11) y portadores de marcapasos prequirúrgico (n = 11). Se establecieron dos grupos de comparación: grupo estándar (octubre 2013-noviembre 2016, n = 209) con técnica de implante estándar, y grupo modificado (diciembre 2016-noviembre 2017, n = 184) con técnica de implante modificada. Se analizaron las tasas de implante de marcapasos definitivo (6 meses de seguimiento) y variables de interés entre grupos. Resultados: Tasa implante de marcapasos definitivo grupo estándar y modificado: 10,05% vs. 4,35%, p = 0,031, respectivamente. Edad (años) grupo estándar y modificado: media 78,15 ± 0,34 vs. media 74,90 ± 0,47, p < 0,01, respectivamente. Euroscore II grupo estándar y modificado: media 3,76 ± 0,24 vs. media 3,00 ± 0,25, p = 0,03, respectivamente. No existieron otras diferencias significativas entre variables de interés. Conclusiones: La modificación de la técnica de implante de Perceval se ha asociado a una reducción estadísticamente significativa de la tasa de bloqueo auriculoventricular postoperatorio que precisa implante de marcapasos definitivo. Abstract: Introduction: Aortic valve replacement with sutureless prosthesis Perceval S is associated with an increase in the rate of postoperative atrioventricular block that requires permanent pacemaker implantation compared to conventional bioprostheses. In our series, we modified the implant technique (minimum ballooning < 5 seconds, rigorous annular decalcification, advancement of the folded prosthesis to the left ventricle outflow tract and repositioning by traction of guide sutures). Objectives: To analyze the impact of the modification in the Perceval implant technique on the postoperative atrioventricular block rate which requires permanent pacemaker implantation. Material and methods: 438 patients underwent aortic valve replacement with Perceval prosthesis, excluding those corresponding to the initial phase of the program (6 months, n = 14), concomitant mitral surgery (n = 18) or tricuspid (n = 11) and pre-surgical pacemaker carriers (n = 11). Two comparison groups were established; standard group (October 2013-November 2016, n = 209) with standard implant technique. Modified group (December 2016-November 2017, n = 184) with modified implant technique. We analyzed permanent pacemaker implantation rates (6 months follow-up) and variables of interest between groups. Results: Implantation rate of permanent pacemaker, standard and modified group (10.05% vs. 4.35%, P = .031, respectively). Age, standard and modified group (mean 78.15 ± 0.34 vs. mean 74.90 ± 0.47, P < .01, respectively). Euroscore II, standard and modified group (mean 3.76 ± 0.24 vs. mean 3.00 ± 0.25, P = .03, respectively). There were no other significant differences between variables of interest. Conclusions: Modification of the Perceval implant technique has been associated with a statistically significant reduction in the postoperative atrioventricular block rate requiring implantation of permanent pacemaker. Palabras clave: Recambio valvular aórtico, Estenosis valvular aórtica, Complicaciones postoperatorias, Bloqueo auriculoventricular, Marcapasos permanente, Keywords: Aortic valve replacement, Aortic valve stenosis, Postoperative complications, Atrioventricular block, Permanent pacemake

Organ-Specific Mechanisms of Transendothelial Neutrophil Migration in the Lung, Liver, Kidney, and Aorta

Immune responses are dependent on the recruitment of leukocytes to the site of inflammation. The classical leukocyte recruitment cascade, consisting of capture, rolling, arrest, adhesion, crawling, and transendothelial migration, is thoroughly studied but mostly in model systems, such as the cremasteric microcirculation. This cascade paradigm, which is widely accepted, might be applicable to many tissues, however recruitment mechanisms might substantially vary in different organs. Over the last decade, several studies shed light on organ-specific mechanisms of leukocyte recruitment. An improved awareness of this matter opens new therapeutic windows and allows targeting inflammation in a tissue-specific manner. The aim of this review is to summarize the current understanding of the leukocyte recruitment in general and how this varies in different organs. In particular we focus on neutrophils, as these are the first circulating leukocytes to reach the site of inflammation. Specifically, the recruitment mechanism in large arteries, as well as vessels in the lungs, liver, and kidney will be addressed

Lower Graft-versus-Host Disease and Relapse Risk in Post-Transplant Cyclophosphamide-Based Haploidentical versus Matched Sibling Donor Reduced-Intensity Conditioning Transplant for Hodgkin Lymphoma.

Classic Hodgkin lymphoma (cHL) patients with relapsed or refractory disease may benefit from allogeneic hematopoietic cell transplantation (allo-HCT), but many lack a matched sibling donor (MSD). Herein, we compare outcomes of 2 reduced-intensity conditioning (RIC) HCT platforms in cHL: T cell-replete related donor haploidentical (haplo) HCT with a post-transplant cyclophosphamide (PTCy)-based approach versus an MSD/calcineurin inhibitor (CNI)-based approach. The study included 596 adult patients who underwent a first RIC allo-HCT for cHL between 2008 and 2016 using either a haplo-PTCy (n = 139) or MSD/CNI-based (n = 457) approach. Overall survival (OS) was the primary endpoint. Secondary endpoints included acute graft-versus-host disease (aGVHD) and chronic GVHD (cGVHD), nonrelapse mortality (NRM), relapse/progression, and progression-free survival (PFS). On multivariate analysis, there was no significant difference between haplo/PTCy and MDS/CNI-based approaches in terms of OS (hazard ratio [HR], 1.07; 95% confidence interval [CI], .79 to 1.45; P = .66) or PFS (HR, .86; 95% CI, .68 to 1.10; P = .22). Haplo/PTCy was associated with a significantly higher risk of grades II to IV aGVHD (odds ratio [OR], 1.73, 95% CI, 1.16 to 2.59; P = .007), but the risk of grades III to IV aGVHD was not significantly different between the 2 cohorts (OR, .61; 95% CI, .29 to 1.27; P = .19). The haplo/PTCy platform provided a significant reduction in cGVHD risk (HR, .45; 95% CI, .32 to .64; P < .001), and a significant reduction in relapse risk (HR, .74; 95% CI, .56 to .97; P = .03). There was a statistically nonsignificant trend toward higher NRM with a haplo/PTCy approach (HR, 1.65; 95% CI, .99 to 2.77; P = .06). Haplo/PTCy-based approaches are associated with lower incidences of cGVHD and relapse, with PFS and OS outcomes comparable with MSD/CNI-based approaches. There was a leaning toward higher NRM with a haplo/PTCy-based platform. These data show that haplo/PTCy allo-HCT in cHL results in survival comparable with MSD/CNI-based allo-HCT