A b s tra c t. -We present an atlas of very high resolution (R ~ 50000) Hα line profiles of 63 pre-main sequence stars, divided among 43 T Tauri stars, 18 Herbig Ae/Be stars, and 2 FU Orionis objects. Ha emission is the most common and prominent spectroscopic feature of pre-main sequence stars, and although it is optically very thick it is still the most frequently modelled emission line in young stars. In T Tauri stars the principal models involve magnetically driven winds, and more recently the role of infalling magnetospheric material has been explored. For Herbig Ae/Be stars a variety of models have been proposed, current emphasis is directed towards obscuration by clumpy circumstellar disk structures. In order to provide constraints on such models, we have made a statistical analysis of the 63 high resolution profiles. We here ignore the considerable variability of the Ha emission, which is discussed in detail in a second paper. Most of our observed lines show complex profiles due to an interplay between emission and absorption features, and we suggest a two-dimensional classification scheme to describe these line profiles, based on the relative height of a secondary peak to the primary peak, as well as whether the absorption is blue-or red-shifted. Among T Tauri stars, 25% have symmetric profiles, 49% have blueshifted absorption dips, and 5% have P Cygni profiles; the remaining 21% show a variety of redshifted absorptions. For Herbig Ae/Be stars symmetric lines are quite rare (11%), indeed almost all of these stars have deep and prominent central absorptions. We have measured the extent of the line wings for all of our stars at the I max/40 level, and find that almost all have very extended wings, with typical extents of ±350 km/s, but in high S /N spectra the wings can be traced to lower intensities, and velocities as high as ±900 km/s have been observed. Pronounced asymmetries of these extended wings are found for many stars, suggesting the possibility that the highest velocity material could be non-uniformly distributed. The equivalent widths of the Ha emission in our sample of stars span two orders of magnitude, with a distribution that increases with decreasing equivalent width.

A B S T R A C TWe present contemporaneous optical and infrared (IR) photometric observations of the Type IIn SN 1998S covering the period between 11 and 146 d after discovery. The IR data constitute the first ever IR light curves of a Type IIn supernova. We use blackbody and spline fits to the photometry to examine the luminosity evolution. During the first 2±3 months, the luminosity is dominated by the release of shock-deposited energy in the ejecta. After ,100 d the luminosity is powered mostly by the deposition of radioactive decay energy from 0X150X05 M ( of 56 Ni which was produced in the explosion. We also report the discovery of an astonishingly high IR excess, K 2 L H 2X5Y that was present at day 130. We interpret this as being due to thermal emission from dust grains in the vicinity of the supernova. We argue that to produce such a high IR luminosity so soon after the explosion, the dust must be preexisting and so is located in the circumstellar medium of the progenitor. The dust could be heated either by the UV/optical flash (IR echo) or by the X-rays from the interaction of the ejecta with the circumstellar material.

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A navegação consulta e descarregamento dos títulos inseridos nas Bibliotecas Digitais UC Digitalis, UC Pombalina e UC Impactum, pressupõem a aceitação plena e sem reservas dos Termos e Condições de Uso destas Bibliotecas Digitais, disponíveis em https://digitalis.uc.pt/pt-pt/termos.Conforme exposto nos referidos Termos e Condições de Uso, o descarregamento de títulos de acesso restrito requer uma licença válida de autorização devendo o utilizador aceder ao(s) documento(s) a partir de um endereço de IP da instituição detentora da supramencionada licença.Ao utilizador é apenas permitido o descarregamento para uso pessoal, pelo que o emprego do(s) título(s) descarregado(s) para outro fim, designadamente comercial, carece de autorização do respetivo autor ou editor da obra.Na medida em que todas as obras da UC Digitalis se encontram protegidas pelo Código do Direito de Autor e Direitos Conexos e demais legislação aplicável, toda a cópia, parcial ou total, deste documento, nos casos em que é legalmente admitida, deverá conter ou fazer-se acompanhar por este aviso. As actividades humanas e os processos morfogenéticos: o exemplo da Serra do Marão Autor(es):Pedrosa, António de Sousa Résumé:A veccet article nous prétendonscontribuer à 1' étudedes processus morphogénétiques responsables par l' évolution géomorphologique actuelle de la Serra doMarão (Nord du Portugal). La histoire ancienne du reliefn'a pas été oubliée, mais le travail de l'homme sur les versants a été envisagé par son action morphogénétique et ses conséquences dans l'environnement en créant des risques. Ces risques ne pourrontjamais être méconnus; au contraíre, ils devront être assumés par l'homme. Mots clés: Serra doMarão, Nord du Portugal, Géomorphologie, processus morphogénétiques, action humaine, risques. Abstract:Theaim ofthis articledeals with the study of geomorphic processeson Serra doMarão (Northem Portugal)present day geomorphological evolution. The old history oflandforms is notforgotten, but man' s work on the slopes is shown with its consequences on the environment making some risks appear. This risks must be known and assumed by man.

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Localized in the north of Portugal, Serra do Marão is part of a mountainous range that separates the mountains of Entre Douro e Minho from the plateaux of Trás-os-Montes. Weather characteristics of Quaternary coldest times were very important in terms of morphogenetic processes, which acted on its slopes, creating deposits that, nowadays, are conditioning the present dynamics.

When a catastrophic landslide occurred in a small river basin on the left bank of the Tamega valley, in the Northeast of Portugal, which involved the sudden sliding of several tons of arable land and rocks and caused the destruction of a house and the death of fifteen people, the authors decided to carry out a careful investigation of this geomorphological phenomenon. After having formulated a number of hypotheses, they did a lot of field workin the area and carried out measurements to determine, as accurately as possible, both the real extension and the causes of the occurrence of such a phenomenon in that particular place and at that particular time of the year. A series of studies enabled the authors to come the conclusion that the natural and human-induced causes had been responsible for the disaster. Disasters like this don't unfortunately constitute isolated incidents. Therefore, the authors think it is very important to study the local geomorphology carefully before any houses or the setting up of any human activity within the territory it is responsible for.