On the size of the Fe II emitting region in the AGN Akn 120

We present a reverberation analysis of the strong, variable optical Fe II emission bands in the spectrum of Akn 120, a low-redshift AGN which is one of the best candidates for such a study. On time scales of several years the Fe II line strengths follow the variations in the continuum strength. However, we are unable to measure a clear reverberation lag time for these Fe II lines on any time scale. This is due to the very broad and flat-topped nature of the Fe II cross correlation functions, as compared to the H-beta response which is much more sharply localized in time. Although there is some suggestion in the light curve of a 300-day response time, our statistical analysis does not pick up such a feature. We conclude that the optical Fe II emission does not come from a photoionization-powered region similar in size to the H-beta emitting region, but we cannot say for sure where it does come from. Our results are generally consistent either with emission from a photoionized region several times larger than the H-beta zone, or with emission from gas heated by some other means, perhaps responding only indirectly to the continuum variations.Comment: Accepted for publication in the Ap

Spectroscopy of Close Companions to QSOs and the Ages of Interaction-Induced Starbursts

We present low-resolution absorption-line spectra of three candidate close ( < 3 arcsec) companions to the low redshift QSOs 3CR 323.1, PG 1700+518, and PKS 2135-147. The spectra were obtained with LRIS on the Keck telescopes and with the Faint Object Spectrograph on the University of Hawaii 2.2 m telescope. For 3CR 323.1 and PG 1700+518, we measure relative velocities that are consistent with an association between the QSOs and their companion galaxies. The spectral features of the companion galaxy to 3CR 323.1 indicate a stellar population of intermediate age (approx. 2.3 Gyr). In contrast, the spectrum of the companion object to PG 1700+518 shows strong Balmer absorption lines from a relatively young stellar population, along with the Mg Ib absorption feature and the 4000 A break from an older population. By modeling the two stellar components of this spectrum, it is possible to estimate the time that has elapsed since the end of the most recent major starburst event: we obtain approx. 0.1 Gyr. This event may have coincided with an interaction that triggered the QSO activity. Finally, our spectroscopy shows conclusively that the supposed companion to PKS 2135-147 is actually a projected Galactic G star.Comment: 10 pages, 5 Postscript figures. Latex (AASTEX). To appear in ApJ. Letters, Volume 480 (1997

Nonlinear optics in Xe-filled hollow-core PCF in high pressure and supercritical regimes

Supercritical Xe at 293 K offers a Kerr nonlinearity that can exceed that of fused silica while being free of Raman scattering. It also has a much higher optical damage threshold and a transparency window that extends from the UV to the infrared. We report the observation of nonlinear phenomena, such as self-phase modulation, in hollow-core photonic crystal fiber filled with supercritical Xe. In the subcritical regime, intermodal four-wave-mixing resulted in the generation of UV light in the HE12 mode. The normal dispersion of the fiber at high pressures means that spectral broadening can clearly obtained without influence from soliton effects or material damage

Host galaxies of AGN

The relationship of an AGN to its host galaxy is a crucial question in the study of galaxy evolution. We perform stellar population synthesis in the central regions of galaxies of different activity levels. A large number of stellar features are measured both in the optical and near-infrared. We find the nuclear stellar population to be related to the level of activity. These differences are no more conspicuous further away in the bulge of the galaxy

The Impact of New Technologies on the Environment

One of the objectives of IIASA's Study "Future Environments for Europe: Some Implications of Alternative Development Paths" is to characterize the large-scale and long-term environmental transformations that could be associated with plausible scenarios of Europe's socio-economic development over the next century. The purpose of this task is to help foresee potentially serious environmental problems before they actually occur. This Working Paper is an important contribution toward that goal. It is becoming increasingly clear that the linkages between technologies and their long-term effects on the environment require more careful attention and forethought than has been the case in the past. The socio-economic benefits of technologies are usually proportional to their scale of application, and the rewards are reaped almost instantaneously. The problem, however, is that the "disbenefits", in terms of ecological degradation, often very nonlinearly with the scale of application, and are manifested on relatively slow time scales. The danger of this syndrome is that the technology may tend to become entrenched over time, making it difficult for adjustment or change by the time the disbenefits become manifest. Therefore, this timely paper should be of interest to all those who ponder the long-term trade-offs between technological development and environmental degradation

Methicillin-resistant Staphylococcus aureus (MRSA) in the institutionalized older patient

SummaryNursing homes and long-term care facilities are usually considered as reservoirs for methicillin-resistant Staphylococcus aureus (MRSA) carriers. Actually, there are major differences in MRSA carriage between institutions, with variations from 1% to more than 30%. Overall there is a low incidence of MRSA infection in these institutions, even though carriage is associated with a higher risk of subsequent MRSA infection, with high mortality rates. The main risk factors for carriage are well known: recent hospitalization in an acute-care ward, skin wounds and recent antimicrobial therapy. Age over 75 years is also a risk factor. Residents of nursing homes and long-term care facilities pose a risk of MRSA transfer to acute-care wards, with potential consequences in terms of infection control strategy or surgical antibiotic prophylaxis. No well-designed study has identified the best strategy for MRSA control in institutions for older people and strategies that have been proposed are controversial. Studies to elucidate this would be useful, as well as studies specifically designed to identify the relative importance of different ways of MRSA transmission in these institutions (cross-transmission via healthcare workers or the environment, or direct transmission from one resident to another). Finally, a first important step towards MRSA control is a strict application of standard precautions, particularly good compliance with hand hygiene

On Quasar Masses and Quasar Host Galaxies

The mass of massive black holes in quasar cores can be deduced using the typical velocities of Hb-emitting clouds in the Broad Line Region (BLR) and the size of this region. However, this estimate depends on various assumptions and is susceptible to large systematic errors. The Hb-deduced black hole mass in a sample of 14 bright quasars is found here to correlate with the quasar host galaxy luminosity, as determined with the Hubble Space Telescope (HST). This correlation is similar to the black hole mass vs. bulge luminosity correlation found by Magorrian et al. in a sample of 32 nearby normal galaxies. The similarity of the two correlations is remarkable since the two samples involve apparently different types of objects and since the black hole mass estimates in quasars and in nearby galaxies are based on very different methods. This similarity provides a ``calibration'' of the Hb-deduced black hole mass estimate, suggesting it is accurate to +-0.5 on log scale. The similarity of the two correlations also suggests that quasars reside in otherwise normal galaxies, and that the luminosity of quasar hosts can be estimated to +-0.5 mag based on the quasar continuum luminosity and the Hb line width. Future imaging observations of additional broad-line active galaxies with the HST are required in order to explore the extent, slope, and scatter of the black hole mass vs. host bulge luminosity correlation in active galaxies.Comment: Accepted for publication in ApJ Letters, 7 pages, aas2pp4.st