Pulsating White Dwarfs

The Sloan Digital Sky Survey has allowed us to increase the number of known white dwarfs by a factor of five and consequently the number of known pulsating white dwarfs also by a factor of five. It has also led to the discovery of new types of variable white dwarfs, as the variable hot DQs, and the pulsating Extremely Low Mass white dwarfs. With the Kepler Mission, it has been possible to discover new phenomena, the outbursts present in a few pulsating white dwarfs.Comment: 10 pages, 2 figures, Wide-field variability surveys: a 21st-century perspective, 22nd Los Alamos Stellar Pulsation Conference Series meeting, San Pedro de Atacama, Chile, Nov. 28 - Dec. 2, 201

An independent constraint on the secular rate of variation of the gravitational constant from pulsating white dwarfs

A secular variation of the gravitational constant modifies the structure and evolutionary time scales of white dwarfs. Using an state-of-the-art stellar evolutionary code and an up-to-date pulsational code we compute the effects of a secularly varying $G$ on the pulsational properties of variable white dwarfs. Comparing the the theoretical results obtained taking into account the effects of a running $G$ with the observed periods and measured rates of change of the periods of two well studied pulsating white dwarfs, G117--B15A and R548, we place constraints on the rate of variation of Newton's constant. We derive an upper bound $\dot G/G\sim -1.8\times 10^{-10}$ yr$^{-1}$ using the variable white dwarf G117--B15A, and $\dot G/G\sim -1.3\times 10^{-10}$ yr$^{-1}$ using R548. Although these upper limits are currently less restrictive than those obtained using other techniques, they can be improved in a future measuring the rate of change of the period of massive white dwarfs.Comment: 13 pages, 4 tables, 3 figures. To be published in the Journal of Cosmology and Astroparticle Physic

Asteroseismology of ZZ Ceti stars with fully evolutionary white dwarf models: I. The impact of the uncertainties from prior evolution on the period spectrum

ZZ Ceti stars are pulsating white dwarfs with a carbon-oxygen core build up during the core helium burning and thermally pulsing Asymptotic Giant Branch phases. Through the interpretation of their pulsation periods by means of asteroseismology, details about their origin and evolution can be inferred. The whole pulsation spectrum exhibited by ZZ Ceti stars strongly depends on the inner chemical structure. At present, there are several processes affecting the chemical profiles that are still not accurately determined. We present a study of the impact of the current uncertainties of the white dwarf formation and evolution on the expected pulsation properties of ZZ Ceti stars. Our analysis is based on a set of carbon-oxygen core white dwarf models with masses $0.548$ and 0.837 M_{\sun} derived from full evolutionary computations from the ZAMS to the ZZ Ceti domain. We have considered models in which we varied the number of thermal pulses, the amount of overshooting, and the $^{12}$C$(\alpha,\gamma)^{16}$O reaction rate within their uncertainties. We explore the impact of these major uncertainties in prior evolution on the chemical structure and the expected pulsation spectrum. We find that these uncertainties yield significant changes in the $g$-mode pulsation periods. We conclude that the uncertainties in the white dwarf progenitor evolution should be be taken into account in detailed asterseismological analysis of these pulsating stars.Comment: 7 pages, 8 figures. To be published in Astronomy and Astrophysic

White dwarf constraints on a varying GG

A secular variation of $G$ modifies the structure and evolutionary time scales of white dwarfs. Using an state-of-the-art stellar evolutionary code, an up-to-date pulsational code, and a detailed population synthesis code we demonstrate that the effects of a running $G$ are obvious both in the properties of individual white dwarfs, and in those of the white dwarf populations in clusters. Specifically, we show that the white dwarf evolutionary sequences depend on both the value of $\dot G/G$, and on the value of $G$ when the white dwarf was born. We show as well that the pulsational properties of variable white dwarfs can be used to constrain $\dot G/G$. Finally, we also show that the ensemble properties of of white dwarfs in clusters can also be used to set upper bounds to $\dot G/G$. Precisely, the tightest bound --- $\dot G/G \sim -1.8 10^{-12}$ yr$^{-1}$ --- is obtained studying the population of the old, metal-rich, well populated, open cluster NGC 6791. Less stringent upper limits can be obtained comparing the theoretical results obtained taking into account the effects of a running $G$ with the measured rates of change of the periods of two well studied pulsating white dwarfs, G117--B15A and R548. Using these white dwarfs we obtain $\dot G/G\sim -1.8\times 10^{-10}$ yr$^{-1}$, and $\dot G/G\sim -1.3\times 10^{-10}$ yr$^{-1}$, respectively, which although less restrictive than the previous bound, can be improved measuring the rate of change of the period of massive white dwarfs.Comment: 6 pages, 3 figures. To be published in the proceedings of the conference "Varying fundamental constants and dynamical dark energy" (8 - 13 July 2013, Sexten Center for Astrophysics

White dwarf and subdwarf stars in the Sloan Digital Sky Survey Data Release 14

White dwarfs carry information on the structure and evolution of the Galaxy, especially through their luminosity function and initial-to-final mass relation. Very cool white dwarfs provide insight into the early ages of each population. Examining the spectra of all stars with $3\sigma$ proper motion in the Sloan Digital Sky Survey Data Release 14, we report the classification for 20 088 spectroscopically confirmed white dwarfs, plus 415 hot subdwarfs, and 311 cataclysmic variables. We obtain Teff, log g and mass for hydrogen atmosphere white dwarf stars (DAs), warm helium atmosphere white dwarfs (DBs), hot subdwarfs (sdBs and sdOs), and estimate photometric Teff for white dwarf stars with continuum spectra (DCs). We find 15793 sdAs and 447 dCs between the white dwarf cooling sequence and the main sequence, especially below Teff= 10000 K; most are likely low-mass metal-poor main sequence stars, but some could be the result of interacting binary evolution.Comment: 18 pages, 13 figure

Probing the Structure of Kepler ZZ Ceti Stars with Full Evolutionary Models-based Asteroseismology

We present an asteroseismological analysis of four ZZ Ceti stars observed with the Kepler spacecraft: GD 1212, SDSS J113655.17+040952.6, KIC 11911480, and KIC 4552982, based on a grid of full evolutionary models of DA white dwarf (WD) stars. We employ a grid of carbon-oxygen core models, characterized by a detailed and consistent chemical inner profile for the core and the envelope. In addition to the observed periods, we take into account other information from the observational data, such as amplitudes, rotational splittings, and period spacing, as well as photometry and spectroscopy. For each star, we present an asteroseismological model that closely reproduces their observed properties. The asteroseismological stellar mass and effective temperature of the target stars are (0.632 ± 0.027 M, 10737 ± 73 K) for GD 1212, (0.745 ± 0.007 M, 11110 ± 69 K) for KIC 4552982, (05480 ± 0.01 M, 12,721 ± 228 K) for KIC11911480, and (0.570 ± 0.01 M, 12,060 ± 300 K) for SDSS J113655.17+040952.6. In general, the asteroseismological values are in good agreement with the spectroscopy. For KIC 11911480 and SDSS J113655.17+040952.6 we derive a similar seismological mass, but the hydrogen envelope is an order of magnitude thinner for SDSS J113655.17+040952.6, which is part of a binary system and went through a common envelope phase

Pulsation in the white dwarf HE 1017–1352: confirmation of the class of hot DAV stars

We report the detection of periodic variations on the Teff ≃ 32 000 K DA white dwarf star HE 1017–1352. We obtained time series photometry using the 4.1-m SOAR telescope on three separate nights for a total of 16.8 h. From the frequency analysis we found four periods of 605 s, 556 s, 508 s and 869 s with significant amplitudes above the 1/1000 false alarm probability detection limit. The detected modes are compatible with low harmonic degree g-mode non-radial pulsations with radial order higher than ∼9. This detection confirms the pulsation nature of HE 1017–1352 and thus the existence of the new pulsating class of hot DA white dwarf stars. In addition, we detect a long period of 1.52 h, compatible with a rotation period of DA white dwarf stars

S?ndrome de burnout en el personal de enfermer?a de un hospital de referencia Ibagu? 2014.

94 P?ginasRecurso Electr?nicoIntroducci?n: El S?ndrome de Burnout (SB) se define como la respuesta al estr?s laboral caracterizado por el cansancio emocional, la despersonalizaci?n y la baja realizaci?n personal, la desmotivaci?n, el desinter?s, el malestar interno o la insatisfacci?n laboral. Objetivo: Determinar la prevalencia del SB en el personal de enfermer?a de un hospital de referencia de una ciudad colombiana y su relaci?n con variables sociodemogr?ficas. Materiales y m?todos: Se llev? a cabo un estudio de corte transversal en una muestra aleatoria y representativa de 174 enfermeras(os), estratificada seg?n si la enfermera era profesional o auxiliar, en un hospital de referencia de una ciudad colombiana. Se utiliz? como instrumento para la determinaci?n del evento la escala validada en Colombia del MBI (Maslach Burnout Inventory). Para la obtenci?n de los resultados se utilizaron pruebas ji-cuadrado de independencia, t para diferencia de promedios en muestras independientes y an?lisis de la varianza de una v?a o de Kruskal Wal?s seg?n si las variables en los grupos de comparaci?n proven?an de una poblaci?n con distribuci?n normal. En an?lisis multivariado, se seleccionaron como variables candidatas a ingresar al modelo de regresi?n log?stica, aquellas que cumplieran con el criterio de Hosmer Lemeshow. En la construcci?n del modelo se tom? como medida de la asociaci?n el OR acompa?ado de su respectivo intervalo de confianza del 95%. Resultados: La prevalencia de Burnout fue del 20.1% (IC 95%: 13,9 26,4) y adem?s el 52,3% est?n a riesgo de padecerlo. Quienes afirmaron ser solteros/viudos/separados, las profesionales de enfermer?a, los que al momento de la encuesta ten?an una vinculaci?n temporal o de supernumerario, quienes laboraban en servicios administrativos/oncolog?a/camillero/esterilizaci?n y los 11 hombres y aquellos que afirmaron tener m?s de un contrato, fueron quienes presentaron indicadores de la proporci?n de Burnout mayores del 20,1%.En el an?lisis multivariado, los factores conjuntos que probablemente tienen mayor incidencia en la presencia del Burnout son el n?mero de hijos y ser hombre. Conclusiones: Con respecto a otros estudios, este estudio revela que la prevalencia del s?ndrome de Burnout en el hospital de referencia es mayor.Introduction: Burnout Syndrome (BS) is defined as the response to occupational stress characterized by emotional exhaustion, depersonalization and reduced personal accomplishment, discouragement, disinterest, internal discomfort or dissatisfaction labor. Objective: To determine the prevalence of BS nurses in a hospital reference a Colombian city and its relationship with sociodemographic variables. Materials and methods: A cross sectional study was conducted in a random and representative sample of 174 nurses, stratified according to whether they were professional or nurse assistant in a referral hospital of a Colombian city, was used as an instrument for determining the scale of the event in Colombia validated MBI (Maslach Burnout Inventory). To obtain the results chi- square test of independence, t-tests for mean differences in independent samples and analysis of variance or one-way Kruskal Wallis were used depending on whether the variables in the comparison groups were drawn from a population with normal distribution. In multivariate analysis, were selected as candidate variables to enter the logistic regression model those that met the criteria of Hosmer-Lemeshow. In building the model was taken as the measure of association OR accompanied by its respective confidence interval 95 %. Results: The prevalence of burnout was 201.1 % (95 % CI: 13.9 26.4) and also the 52.3 % are at risk for suffering. Who claimed to be single / widowed / separated, nursing professionals, which at the time of the survey had a temporary or temporary bonding, who worked in administrative / oncology / orderly / sterilization services and those men who reported having more than a contract, who presented were indicators of burnout higher proportion of 20.1%. In the multivariate analysis, the factors that sets probably have a greater incidence in the presence of burnout are the number of children and be a man. 13 Conclusions: With respect to other studies, this study reveals that the prevalence of burnout syndrome in the referral hospital is greater.RESUMEN 10 ABSTRACT 12 INTRODUCCI?N 14 1. PLANTEAMIENTO DEL PROBLEMAS Y JUSTIFICACION 16 2. MARCO TE?RICO 19 2.1 ESTR?S LABORAL 19 2.2 CONCEPTUALIZACI?N DEL S?NDROME DE BURNOUT 20 2.2.1 Caracter?sticas del s?ndrome de Burnout 22 2.2.2 Consecuencias del s?ndrome de Burnout 23 2.2.3 Instrumento de medici?n del s?ndrome de Burnout 25 2.2.4 Prevenci?n del s?ndrome de Burnout 27 2.2.5 Tratamiento del s?ndrome de Burnout 30 2.3 DEFINICI?N DE ENFERMER?A 35 2.4 GENERALIDADES DEL HOSPITAL DE REFERENCIA 39 2.5 LEGISLACI?N LABORAL EN COLOMBIA 40 3. OBJETIVOS 43 3.1 OBJETIVO GENERAL 43 3.2 OBJETIVOS ESPEC?FICOS 43 4. METODOLOG?A 44 4.1 TIPO DE ESTUDIO 44 4.2 POBLACI?N DE ESTUDIO 44 4.3 MUESTREO 44 5 4.4 CRITERIOS DE INCLUSI?N Y EXCLUSI?N 47 4.5. INSTRUMENTO DE RECOLECCI?N DE INFORMACI?N 47 4.6 CONTROL DE SESGOS 48 4.7 CONSIDERACIONES ?TICAS 49 5. RESULTADOS 50 5.1 CARACTERISTICAS SOCIODEMOGRAFICAS DEL 50 PERSONAL ENCUESTADO 5.1.1 Variables cualitativas 50 5.1.2 Variables cuantitativas 51 5.2 MASLASCH BURNOUT INVENTORY (MBI) 52 5.2.1 An?lisis de los ?tems 53 5.2.2 Grados del Burnout 55 5.2.3 An?lisis por patrones: Niveles del Burnout 56 5.2.4 Prevalencia del Burnout 59 5.2.5 Descripci?n de las dimensiones del MBI 62 5.3 ANALISIS BIVARIADO 65 5.4 ANALISIS MULTIVARIADO 69 6. DISCUSI?N 72 7. CONCLUSIONES 77 8. RECOMENDACIONES 78 9. LIMITACIONES 79 REFERENCIAS 8