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High energy astrophysics

Abstract

An exciting unsolved problem in the study of high energy processes of early type stars is the physical mechanism for producing hard-thermal X-rays of moderate luminosity near the Be star gamma Cassiopeiae (gCas). The nature of such emission is currently a matter of controversy, but the two proposed interpretations imply in a breakthrough in the physics of massive stars: (i) a single-Be star with unusually strong magnetic activity, or (ii) a Be + compact object system, where the companion could be a white dwarf. Systems Be + white dwarf are predicted by the evolutionary models of massive binaries, though they still have not been identified. Recently, 6 similar Be stars - and 41 candidates - were identified, and thus a new class of X-ray emitters emerged: the gCas-like stars. The main objective of this project is investigate gCas-like stars and candidates from X-ray and optical observations to better determine the space of parameters and correlations among them: temperature, luminosity and variability in X-rays, photoelectric absorption of the X-rays, structure and variability of the circumstellar disk, binary status and spectral type. Such investigations are crucial to understand the true nature of these objects. This project also includes two other ongoing sub-projects in the X-ray domain. The first one is investigating a poor populated and relatively old group of stars for the first time in X-rays. Models predict a large fraction of binaries in such a group that include interacting binaries. X-rays observations are needed to identify them and validate or rule out the models. Finally, the second sub-project is aimed at the investigation of supernova remnants applying the Principal Components Analysis to X-ray observations in order to distinguish the spatial regions responsible for the thermal and nonthermal X-rays, faint structures, and tentatively the site of acceleration of cosmic rays. (AU)

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Scientific publications (4)
(References retrieved automatically from Web of Science and SciELO through information on FAPESP grants and their corresponding numbers as mentioned in the publications by the authors)
PROCTOR, ROBERT N.; DE OLIVEIRA, CLAUDIA MENDES; DUPKE, RENATO; DE OLIVEIRA, RAIMUNDO LOPES; CYPRIANO, EDUARDO S.; MILLER, ERIC D.; RYKOFF, ELI. On the mass-to-light ratios of fossil groups. Are they simply dark clusters?. Monthly Notices of the Royal Astronomical Society, v. 418, n. 3, p. 2054-2073, . (09/06295-7, 09/07154-8, 08/57331-0, 10/08341-3)
SMITH, M. A.; LOPES DE OLIVEIRA, R.; MOTCH, C.; HENRY, G. W.; RICHARDSON, N. D.; BJORKMAN, K. S.; STEE, PH.; MOURARD, D.; MONNIER, J. D.; CHE, X.; et al. The relationship between gamma Cassiopeiae's X-ray emission and its circumstellar environment. Astronomy & Astrophysics, v. 540, . (09/06295-7, 10/08341-3)
LOPES DE OLIVEIRA, R.; MOTCH, C.. A HARD AND VARIABLE X-RAY EMISSION FROM THE MASSIVE EMISSION-LINE STAR HD 157832. Astrophysical Journal Letters, v. 731, n. 1, . (09/06295-7, 10/08341-3)
MILLER, ERIC D.; RYKOFF, ELI S.; DUPKE, RENATO A.; DE OLIVEIRA, CLAUDIA MENDES; DE OLIVEIRA, RAIMUNDO LOPES; PROCTOR, ROBERT N.; GARMIRE, GORDON P.; KOESTER, BENJAMIN P.; MCKAY, TIMOTHY A.. FINDING FOSSIL GROUPS: OPTICAL IDENTIFICATION AND X-RAY CONFIRMATION. ASTROPHYSICAL JOURNAL, v. 747, n. 2, . (09/06295-7, 10/08341-3)

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