Towards the main sequence: detailed analysis of weak line and post-T Tauri stars

A detailed study was performed for a sample of low-mass pre-main-sequence (PMS) stars, previously identified as weak-line T Tauri stars, which are compared to members of the Tucanae and Horologium Associations. Aiming to verify if there is any pattern of abundances when comparing the young stars at different phases, we selected objects in the range from 1 to 100 Myr, which covers most of PMS evolution. High-resolution optical spectra were acquired at European Southern Observatory and Observatorio do Pico dos Dias. The stellar fundamental parameters effective temperature and gravity were calculated by excitation and ionization equilibria of iron absorption lines. Chemical abundances were obtained via equivalent width calculations and spectral synthesis for 44 per cent of the sample, which shows metallicities within 0.5 dex solar. A classification was developed based on equivalent width of Li I 6708 angstrom and Ha lines and spectral types of the studied stars. This classification allowed a separation of the sample into categories that correspond to different evolutive stages in the PMS. The position of these stars in the Hertzsprung-Russell diagram was also inspected in order to estimate their ages and masses. Among the studied objects, it was verified that our sample actually contains seven weak-line T Tauri stars, three are Classical T Tauri, 12 are Fe/Ge PMS stars and 21 are post-T Tauri or young main-sequence stars. An estimation of circumstellar luminosity was obtained using a disc model to reproduce the observed spectral energy distribution. Most of the stars show low levels of circumstellar emission, corresponding to less than 30 per cent of the total emission.

2060 Chiron back to a minimum of brightness

The results of photometric observations of comet/steroid 2060 Chiron at the Observatorio do Pico dos Dias (Brazil - OPD) and the Observatoire de Haute-Provence (France - OHP) during 1994 and 1995 are presented. The analysis of the data shows a decrease of 2060. Chiron brightness from its peak values of 1988-1991. The absolute magnitude, H-V, varies from a maximum of 6.6 in February 1994 up to a minimum of 6.8 in June 1995. Therefore 2060 Chiron is back to a minimum of activity close to that of 1983-1985. The slope parameter G is found to be G = 0.71 +/- 0.15. It is suggested that the H-G magnitude system, generally adopted to present 2060 Chiron brightness, is not the most appropriate due to the cometary activity of this object. Copyright (C) 1996 Elsevier B.V. Ltd.

Strengthening biregional cooperation between Latin America and Asia-Pacific: the role of FEALAC

Includes bibliography

Fortalecimiento de la cooperación birregional entre América Latina y Asia y el Pacífico El papel del FOCALAE

Incluye bibliografía

Políticas para el perfeccionamiento de la institucionalidad laboral en Costa Rica

Incluye Bibliografía

El monitoreo de los resultados de políticas agrícolas y rurales

Includes bibliography

Compendio de prácticas sobre implementación de preguntas de TIC en encuestas de hogares y en encuestas de empresas en América Latina y el Caribe: revisión 2010

Incluye Bibliografía

Mujeres indígenas en América Latina: dinámicas demográficas y sociales en el marco de los derechos humanos

Incluye bibliografía

Propuesta de indicadores complementarios para el monitoreo de los ODM: indicadores de acceso a las tecnologías de la información y las comunicaciones

Incluye Bibliografía

La paridad política en América Latina y el Caribe: percepciones y opiniones de los líderes de la región

Incluye Bibliografía

Una mirada analítica a la legislación sobre interrupción del embarazo en países de Iberoamérica y el Caribe

Incluye Bibliografía

Inventario de la información estadística, indicadores y explotación de fuentes sobre etnia, raza y género en los países de América Latina y el Caribe

Incluye Bibliografía

Medición de los ingresos monetarios individuales: una mirada desde la perspectiva de género

Incluye Bibliografía

Buenas prácticas para el acceso de mujeres a espacios de poder público

Incluye bibliografía

Hacia políticas de igualdad que promuevan la autonomía económica de las mujeres

Incluye bibliografía