Relatamos neste artigo o desenvolvimento e a aplicação de um CD-ROM deóptica para o ensino médio, cobrindo todos os conteúdos usualmente vistos nessa disciplina. O material contém, além de textos didáticos escritos em linguagem html, 77 animações e 64 imagens geradas por nós, assim como 13 simuladores (Java Applets) disponíveis na internet. Comentamos sobre a aplicação e boa recepção do material por 40 alunos de duas turmas de 3 a série do ensino médio. Palavras-chave: ensino de física, ensino deóptica, novas tecnologias, hipermídia. In this article we report the development and use of a CD of optics for high-school teaching, covering all topics for this level. The material contains didactic texts in HTML language, 77 animations and 64 images generated by ourselves, as well as 13 simulators (Java Applets) available in the internet. We comment about the application and reception of the Hypermedia by a group of 40 high school seniors.
We report the discovery of fourteen new ZZ Cetis with the 4.1 m Southern Astrophysical Research telescope, at Cerro Pachon, in Chile. The candidates were selected from the SDSS (Sloan Digital Sky Survey) DA white dwarf stars with T eff obtained from the optical spectra fit, inside the ZZ Ceti instability strip. Considering these stars are multi-periodic pulsators and the pulsations propagate to the nucleus of the star, they carry information on the structure of the star and evolution of the progenitors. The ZZ Cetis discovered till 2003 are mainly within 100 pc from the Sun, and probe only the solar vicinity. The recently discovered ones, and those reported here, may sample a distinct population as they were selected mainly perpendicular to the galactic disk and cover a distance up to ≈400 pc.
We present a detailed investigation of the incidence of circumnuclear dust structure in a large, well-matched sample of early-type galaxies with and without active galactic nuclei (AGNs). All 34 early-type AGN hosts in our sample have circumnuclear dust, while dust is only observed in 26% (9) of a pair-matched sample of 34 early-type, inactive galaxies. This result demonstrates a strong correlation between the presence of circumnuclear dust and accretion onto the central, supermassive black hole in elliptical and lenticular galaxies. This correlation is not present at later Hubble types, where a sample of 31 active and 31 inactive galaxies all contain circumnuclear dust. These archival, Hubble Space Telescope observations reveal a wide range of mostly chaotic dust morphologies. Current estimates suggest the dust settling or destruction time is on order of 10 8 yr, and therefore the presence of dust in $50% of early-type galaxies requires frequent replenishment and similarly frequent fueling of their central supermassive black holes. The observed dust could be internally produced (via stellar winds) or externally accreted, although there are observational challenges for both of these scenarios. Our analysis also reveals that approximately one-third of the early-type galaxies without circumnuclear dust have nuclear stellar disks. These nuclear stellar disks may provide a preferred kinematic axis to externally accreted material, and this material may in turn form new stars in these disks. The observed incidence of nuclear stellar disks and circumnuclear dust suggests that episodic replenishment of nuclear stellar disks occurs and is approximately concurrent with the fueling of the central AGN.
Abstract. Optical spectra were used to study the stellar population and gas emission, when present, in the central parts of the elliptical galaxies NGC 6958, NGC 6851 and ESO 185-G54, and the spiral galaxies NGC 5757, NGC 7412 and IC 4214. Stellar population properties were derived by comparing the equivalent widths of the absorption lines with those of galaxy templates built from star clusters, as well as by applying a method of stellar population synthesis based on the same star clusters. For the galaxies with emission lines, the underlying stellar population was subtracted to obtain the pure emission spectrum, and the resulting emission line intensities were measured to determine the mechanism responsible for the gas excitation. From this analysis we concluded that the galaxies have solar metallicity except the elliptical ESO 185-G54 that reached metallicity slightly above solar. The three ellipticals and the Sa galaxy IC 4214 have their nuclei dominated by old stellar populations, although IC 4214 appears to have some contribution from the young generation stars. Recent star formation (t < 500 Myr) is prominent in the nucleus of the SBb galaxy NGC 5757, and is also present to a lesser degree in the Sbc NGC 7412. In these two galaxies, the recent star formation is responsible for the observed H ii type emission lines, while IC 4214 has LINER emission. Among the ellipticals, only in NGC 6958 did we detect ionized gas, whose spectra is typical of LINERs.
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