RCAAP - Repositório Científico de Acesso Aberto de Portugal
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Evidence for a precessing accretion disk in the nucleus of NGC 1097
No full textWe present new spectroscopic observations of the LINER (and now Seyfert 1) nucleus of NGC 1097, and discuss the evolution of its broad, double-peaked Balmer lines. When originally discovered in 1991, the red peak of the double-peaked Hα line was stronger than the blue, while by 1994 the Ha profile had become almost symmetric and the integrated line flux had decreased to half its original value. Our new spectrum, taken in 1996, shows that the broad, double-peaked lines have returned to almost their original strengths, the profiles of Hβ and Hα are identical to within errors, and the broad-line emitting region is unreddened. However, the proÐle of the Balmer lines is now such that the blue peak is stronger than the red, opposite to the asymmetry observed in 1991. Various models are considered for the observed behavior, all assuming that the emission lines originate in an accretion disk. We present a refined version of the precessing, planar, elliptical accretion-ring model proposed by Storchi-Bergmann et al. and Eracleous et al. This model provides an acceptable fit to the line profiles. We also consider the possibility that the line-profile evolution results from a precessing warp in the disk, induced by irradiation from the center, and show that the range of radii and precession timescales expected in this model are consistent with the observations. The sudden appearance of the “disklike" broad-line profiles in NGC 1097 could have resulted from the formation of a new accretion disk due, for example, to the tidal disruption of a star or the illumination of a preexisting disk by a transient ionizing source at the center of the disk
Efeito da fenilalanina sobre a atividade da enzima hexoquinase de córtex cerebral de ratos jovens
No full textEfeito in vivo e in vitro do HgCl2 e do 2,3-dimercaprol (BAL) sobre a atividade da ALA-D de cérebro, fígado e rim de camundongos adultos
No full textThe light curve of the ZZ ceti star G226-29
No full textG226-29 is a pulsating DA white dwarf, or ZZ Ceti star. Using 65 hr of high-speed photometry accumulated from 1980 to 1982, we have decomposed the light curve of G226-29 into its component pulsations. There are three pulsations in the light curve, ali of which have periods dose to 109.3 s. Their fractional semiamplitudes and periods are 0.0031 and 109.08684 s, 0.0011 and 109.27929 s, and 0.0031 and 109.47242 s. The pulsations are evenly spaced in frequency, and those with the longest and shortest periods have nearly equal amplitudes. We propose that the pulsations are g-mode pulsations with the same values of I and k, but with different values of m, whose periods have been split by slow rotation of the white dwarf. Depending on the specific value of I we assign to the pulsations, the equatorial rotational velocity of G226-29 is between I and 2 km s-ˡ
Efeito da administração de adrenalina em doses amnésicas sobre a memória de animais alimentados e em jejum
No full textSteps toward determination of the size and structure of the broad-line region in active galactic nuclei. VII. Variability of the optical spectrum of NGC 5548 over 4 years
No full textWe report on the results of a continuation of a large monitoring program of optical spectroscopy of the Seyfert 1 galaxy NGC 5548. The new observations presented here were obtained between 1990 December and 1992 October, and extend the existing database to nearly 1400 days, dating back to 1988 December. The continuum variations are generally smooth and well-resolved, except during the third year of this 4 year project, when the variations were apparently more rapid and of lower amplitude than observed at other times. The broad Hβ emission line is found to vary in response to the continuum variations with a lag of about 18 days, but with some changes from year to year. The Hβ transfer functions for each of the 4 yr and for the entire 4 yr database are derived by using a maximum entropy method
Determinação da atividade de glicogênio fosforilase em culturas de células de Sertoli de ratos de diferentes idades
No full textDust obscuration in starburst galaxies from near-infrared spectroscopy
No full textWe present new observations of the near-infrared hydrogen recombination lines Paβ and Bry in the central starburst regions of 13 galaxies. The near-infrared data are supplemented with data on the optical Balmer line emission and are used to study the geometrical distribution of the dust associated with the massive stars. We find that the reddening toward the starburst regions can be explained by the presence of foreground dust, either homogeneous or clumpy. The result suggests that there is little internal dust in the star-forming site. Mechanisms like shock waves and outflows produced by supernova explosions and hot star winds can be effective at destroying and removing the dust from inside the region
