Study of cool white dwarf stars

White dwarfs stars are the evolutionary endpoint for at least 97% of all stars in the Milky Way. Being the most common stellar fossil, they could be studied as a proxy for Galactic formation and evolution. White dwarfs also have information of the evolutionary path of their progenitors, which could be used to understand the physics of stellar evolution. The evolution of white dwarfs is practically a simple cooling, making them reliable cosmic clock to infer the age of stellar populations such as globular and open clusters and to the age of individual stars. The white dwarfs colder than 10 000K provide us information of the oldest stars of the Milky Way. In this work, we calculated parameters such as photometric effective temperature, mass and distance for a sample of more than 20 000 spectroscopically confirmed white dwarfs. We present the mass distribution for DAs, DBs and DCs, the photometric effective temperature distribution for DAs, DBs, DCs, DZs and DQs and the distance distribution for DAs and non-DAs. We also present our calculation of the helium to hydrogen atmosphere white dwarf number ratio and compare with previous works. We discuss the consequence of a non-uniform distribution for this ratio, which lead us to information about the formation and evolutionary path of white dwarf stars.Anãs brancas são o final da vida evolutiva de pelo menos 97% de todas as estrelas na Via Láctea. Sendo o fóssil estelar mais comum, elas podem ser estudadas como traçadores da formação e evolução da Galáxia. Anãs Brancas também possuem informação sobre caminho evolutivo de suas progenitoras, o que pode ser usado para compreender a física da evolução estelar. A evolução das anãs brancas é praticamente um simples resfriamento, fazendo delas relógios cósmicos confiáveis para se inferir a idade de populações estelares como aglomeradores abertos e globulares e da idade de estrelas individuais. As anãs brancas mais frias que 10 000K nos fornecem informação sobre as estrelas mais velhas da Via Láctea. Neste trabalho, nós calculamos parâmetros como a temperatura efetiva fotométrica, massa e a distância para uma amostra com mais de 20 000 anãs brancas espectroscopicamente confirmadas. Nós apresentamos a distribuição de massa para as DAs, DBs e DCs, a distribuição de temperatura efetiva fotométrica para DAs, DBs, DCs, DZs e DQs e a distribuição de distância para as DAs e não-DAs. Nós também apresentamos o nosso cálculo da razão entre o número de anãs brancas com a atmosfera composta por hélio e o número de anãs brancas com a atmosfera composta por hidrogênio em função da temperatura efetiva e o comparamos com trabalhos publicados anteriormente. Nós discutimos sobre as consequências de uma distribuição não uniforme para essa razão, o que pode nos levar a informação sobre a formação e o caminho evolutivo das anãs brancas

Evidence of spectral evolution on the white dwarf sample from the Gaia mission

Since the Gaia data release 2, several works have been published describing a bifurcation in the observed white dwarf colour−magnitude diagram for GBP−GRP>0. Some possible explanations in the literature include the existence of a double population with different initial mass functions or two distinct populations, one formed by hydrogen-envelope and one formed by helium-envelope white dwarfs. We propose instead spectral evolution to explain the bifurcation. From a population synthesis approach, we find that spectral evolution occurs for effective temperatures below ≃11000K and masses mainly between 0.64M⊙ and 0.74M⊙, which correspond to around 16 per cent of all DA white dwarfs. We also find that the Gaia white dwarf colour–magnitude diagram indicates a star formation history that decreases abruptly for objects younger than 1.4Gyr and a top-heavy initial mass function for the white dwarf progenitors

White dwarf and subdwarf stars in the Sloan Digital Sky Survey Data Release 16

White dwarfs are the end state of the evolution of more than 97 per cent of all stars, and therefore carry information on the structure and evolution of the Galaxy through their luminosity function and initial-to-final mass relation. Examining the new spectra of all white or blue stars in the Sloan Digital Sky Survey Data Release 16, we report the spectral classification of 2410 stars, down to our identification cut-off of signal-to-noise ratio equal to three. We newly identify 1404 DAs, 189 DZs, 103 DCs, 12 DBs, and nine CVs. The remaining objects are a mix of carbon or L stars (dC/L), narrow-lined hydrogen-dominated stars (sdA), dwarf F stars, and P Cyg objects. As white dwarf stars were not targeted by SDSS DR16, the number of new discoveries is much smaller than in previous releases. We also report atmospheric parameters and masses for a subset consisting of 555 new DAs, 10 new DBs, and 85 DZs for spectra with signal-to-noise ratio larger than 10

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

White dwarf and subdwarf stars in the Sloan Digital Sky Survey Data Release 16

White dwarfs are the end state of the evolution of more than 97 per cent of all stars, and therefore carry information on the structure and evolution of the Galaxy through their luminosity function and initial-to-final mass relation. Examining the new spectra of all white or blue stars in the Sloan Digital Sky Survey Data Release 16, we report the spectral classification of 2410 stars, down to our identification cut-off of signal-to-noise ratio equal to three. We newly identify 1404 DAs, 189 DZs, 103 DCs, 12 DBs, and nine CVs. The remaining objects are a mix of carbon or L stars (dC/L), narrow-lined hydrogen-dominated stars (sdA), dwarf F stars, and P Cyg objects. As white dwarf stars were not targeted by SDSS DR16, the number of new discoveries is much smaller than in previous releases. We also report atmospheric parameters and masses for a subset consisting of 555 new DAs, 10 new DBs, and 85 DZs for spectra with signal-to-noise ratio larger than 10

Strategic positioning of soybean cultivars in the state of Rio Grande do Sul

This work aims to highlight the best soybean genotypes for specific environments in the Northwest Region of the State of Rio Grande do Sul. The experiment was carried out in the 2018/19 crop season in fifteen cultivation environments in the Northwest region of the state of Rio Grande do Sul, using 52 soybean genotypes in 15 growing environments. The experimental design used was lattice with treatments (growing environments) arranged in three replications. In each useful area of ​​the experimental unit, the grain productivity of the genotypes was evaluated. Then, the Restricted Maximum Likelihood (REML) method was applied to estimate the variance components and genetic parameters. The following variance components were estimated: Genetic variation (Vg) and phenotypic variation (Vp). The genetic parameters estimated were: broad sense heritability (H²), coefficient of genotypic variation (CVg), coefficient of residual variation (CVe), ratio between genetic and residual coefficient (CVr) and selective accuracy (Ac). The phenotypic expression of grain yield is determined by 17% due to genetic effects and 83% by the environment. The NS 6909 RR IPRO, NS 5445 IPRO, DM 5958 IPRO and DM 6563 IPRO genotypes showed greater genetic gains for grain yield. The environments Doutor Maurício Cardoso (RS), Nova Ramada (RS) and Independência (RS) are characterized as favorable environments

Ground-based observation of ZZ Ceti stars and the discovery of four new variables

We perform ground-based photometric observations of 22 DA white dwarf stars, 10 already known ZZ Cetis and 12 candidates with atmospheric parameters inside the classical instability strip. We report on the discovery of four new variable DA white dwarf stars. Two objects are near the middle of the instability strip, SDSS J082804.63+094956.6 and SDSS J094929.09+101918.8, and two red edge pulsators, GD 195 and L495−82. In addition, we classified four objects as possible variables, since evidence of variability was detected in the light curve, but the signal-to-noise ratio was not sufficient to establish a definite detection. Follow-up observations were performed for 10 known ZZ Ceti stars to verify period stability and search for new periodicities. For each confirmed variable, we perform a detailed asteroseismological fit and compare the structural parameters obtained from the best-fitting models with those obtained from spectroscopy and photometry from Gaia. Finally we present a study of the asteroseismological properties of a sample of 91 ZZ Ceti stars

Prevalência do Diagnóstico de DPOC em Pacientes internados com Cardiopatia Isquêmica em um Hospital Universitário no interior do Estado do Rio Grande do Sul

Background and objectives: the Chronic Obstructive Pulmonary Disease (COPD) appears as a public health problem and has received increasing attention in recent years. We sought to evaluate the proportion of patients who were hospitalized for ischemic heart disease (IHD), had a history of exposure to risk factors and / or had been diagnosed with COPD. Methods: Cross-sectional, observational study prospectively. We selected all patients over 40 years admitted from September 2014 to June 2015, with the diagnosis of IC. Data were analyzed using SPSS 22.0 program. Results: The study included 69 patients who were hospitalized with a diagnosis of IC in the years 2014 and 2015. The average age of patients was 65 years and of these, 35 (50.7%) were male. The mean duration of hospitalization of these patients was 3 days. Patients who were diagnosed with COPD and were treated were six (8.69%), and those who had undergone previous spirometry totaled 5 (7.24%). As for respiratory symptoms in patients with IC, 25 patients (64.1%) had cough, sputum or dyspnea. There was a 8.7% of patients reported have been previously diagnosed with COPD. Conclusions: Despite the high prevalence of respiratory symptoms and exposure to risk factors, patients with COPD have more events and increased mortality from ischemic heart disease, our study suggests that there is a high percentage of underdiagnosis of COPD patients hospitalized for ischemic heart disease in our midst. KEYWORDS: Pulmonary Disease, Chronic Obstructive. Myocardial Ischemia. Risk Factors.Antecedentes y objetivos: La Enfermedad Pulmonar Obstructiva Crónica (EPOC) constituye un problema de salud pública y ha recibido creciente atención en los últimos años. Se buscó evaluar cuál era la proporción de pacientes hospitalizados por cardiopatía isquémica (CI) que contaba con historia de exposición a factores de riesgo y/o habían sido diagnosticados con EPOC. Métodos: Estudio transversal, observacional, del tipo prospectivo. Se seleccionaron todos los pacientes mayores de 18 años, lúcidos, que aceptaran participar del estudio, ingresados desde septiembre 2014 a junio 2015 con diagnóstico de CI. Datos analizados mediante programa SPSS 22.0. Resultados: Fueron incluidos 69 pacientes hospitalizados con diagnóstico de CI en 2014 y 2015. La media etaria fue de 65 años; de estos, 35 (50,7%) eran de sexo masculino. El promedio de duración de la internación de los pacientes fue de 3 días. Los pacientes con diagnóstico de EPOC que estaban en tratamiento fueron 6 (8,69%), y los que habían realizado espirometría anterior totalizaron 5 (7,24%). En cuanto a los síntomas respiratorios en pacientes con CI, 25 pacientes (64,1%) tenían tos, expectoración o disnea. Hubo reporte de que el 8,7% de los pacientes ya había sido diagnosticado previamente con EPOC. Conclusiones: A pesar de que la alta prevalencia de síntomas respiratorios y exposición a factores de riesgo hace que los pacientes con EPOC sufran mayor número de eventos y mayor mortalidad por cardiopatía isquémica, nuestro estudio sugiere que existe un alto porcentaje de subdiagnóstico de EPOC en pacientes internados por cardiopatía isquémica en nuestro medio. Palabras clave: Enfermedad pulmonar obstructiva crónica. La cardiopatía isquémica. Factores de riesgo.Justificativa e objetivos: A Doença Pulmonar Obstrutiva Crônica (DPOC) é um problema de saúde pública e tem recebido crescente atenção nos últimos anos. Buscouse avaliar qual a proporção dos pacientes que internaram por cardiopatia isquêmica (CI) tinham história de exposição a fatores de risco e/ou haviam sido diagnosticados como portadores de DPOC. Métodos: estudo transversal, observacional, do tipo prospectivo. Foram selecionados todos os pacientes, acima de 18 anos, lúcidos e que concordaram em participar do estudo, internados no período de setembro de 2014 a junho de 2015, com o diagnóstico de CI. Os dados analisados foram analisados no programa SPSS 22.0. Resultados: foram incluídos 69 pacientes que internaram com diagnóstico de CI nos anos de 2014 e 2015. A média de idade dos pacientes foi de 65 anos e destes, 35 (50,7%) eram do sexo masculino. A média da duração de internação desses pacientes foi de 3 dias. Os pacientes que apresentavam diagnóstico de DPOC e estavam em tratamento eram 6 (8,69%), e os que haviam realizado espirometria prévia totalizavam 5 (7,24%). Quanto às manifestações respiratórias nos pacientes com CI, 25 pacientes (64,1%) apresentavam tosse, expectoração ou dispneia. Houve um relato de 8,7% dos pacientes já terem sido diagnosticados previamente como portadores de DPOC. Conclusões: Apesar da alta prevalência de sintomas respiratórios e exposição a fatores de risco, pacientes com DPOC tem maior número de eventos e maior mortalidade por cardiopatia isquêmica, nosso estudo sugere que existe uma alta porcentagem de subdiagnóstico de DPOC em pacientes internados por cardiopatia isquêmica em nosso meio.portadores de DPOC. Conclusões: Apesar da alta prevalência de sintomas respiratórios e exposição a fatores de risco, pacientes com DPOC tem maior número de eventos e maior mortalidade por cardiopatia isquêmica, nosso estudo sugere que existe uma alta porcentagem de subdiagnóstico de DPOC em pacientes internados por cardiopatia isquêmica em nosso meio. DESCRITORES: Doença Pulmonar Obstrutiva Crônica. Cardiopatia Isquêmica. Fatores de risco