On the nature of sn stars. I. A detailed abundance study

The sn stars present sharp Balmer lines, sharp metallic lines and broad coreless He I lines. Initially Abt & Levato proposed a shell-like nature to explain the sn stars, although this scenario was subsequently questioned. We aim to derive abundances for a sample of 9 stars, including sn and non-sn stars, to determine the possible relation between sn and CP stars. We analysed the photospheric chemical composition of sn stars and show that approximately 40% of them display chemical peculiarities (such as He-weak and HgMn stars) within a range of temperature of 10300 - 14500 K. We have studied the possible contribution of different processes to the broad He I lines present in the sn stars. Although NLTE effects could not be completely ruled out, it seems that NLTE is not directly related to the broad He I profiles observed in the sn stars. The broad-line He I 4026 is the clearest example of the sn characteristics in our sample. We succesfully fit this line in 4 out of 7 sn stars by using the appropriate Stark broadening tables, while small differences appear in the other 3 stars. Studying the plots of abundance vs depth for the He I lines resulted in some sn stars probably being stratified in He. However, a further study of variability in the He I lines would help for determining whether a possible non-uniform He superficial distribution could also play a role in these sn stars. We conclude that the broad He I lines that characterize the sn class could be modelled (at least in some of these stars) by the usual radiative transfer process with Stark broadening, without needing another broadening mechanism. The observed line broadening in sn stars seems to be related to the "normal" He line formation that originates in these atmospheres. (abridged)Comment: 18 pages, 11 figures, Astronomy & Astrophysics accepte

Rotational velocities of B stars

The rotational velocities of 87 B stars were obtained. The method used is based on the half widths of the HeI 4471 and MgII 4481 lines calibrated on a series of standard stars. Finally the present results were compared with Buscombe’s and Slettebak’s with the following results: V sin i ( Bu ) = 1.42 V sin i (SI) ± 46 km/sec. V sin i ( Bu ) = 1.56 V sin i (Ma-Le) ± 55 km/sec. The complete paper will be published elsewhere.Asociación Argentina de Astronomí

Rotational velocities of B stars

The rotational velocities of 87 B stars were obtained. The method used is based on the half widths of the HeI 4471 and MgII 4481 lines calibrated on a series of standard stars. Finally the present results were compared with Buscombe’s and Slettebak’s with the following results: V sin i ( Bu ) = 1.42 V sin i (SI) ± 46 km/sec. V sin i ( Bu ) = 1.56 V sin i (Ma-Le) ± 55 km/sec. The complete paper will be published elsewhere.Asociación Argentina de Astronomí

Rotational velocities of B stars

The rotational velocities of 87 B stars were obtained. The method used is based on the half widths of the HeI 4471 and MgII 4481 lines calibrated on a series of standard stars. Finally the present results were compared with Buscombe’s and Slettebak’s with the following results: V sin i ( Bu ) = 1.42 V sin i (SI) ± 46 km/sec. V sin i ( Bu ) = 1.56 V sin i (Ma-Le) ± 55 km/sec. The complete paper will be published elsewhere.Asociación Argentina de Astronomí

Avances en la puesta a punto del bHROS

A fin de poner en funcionamiento un colector de luz de 50cm de diámetro para alimentar a través de fibra el espectrógrafo bHROS en el laboratorio en la ciudad de San Juan, y poner a punto la capacidad de adquisición y guiado de objetos celestes para espectroscopía, en esta primera etapa se instaló en el telescopio un espectrógrafo LHIRES de Sheilak Instruments. Se reporta el estado de avance del proyecto BHROS.www.astronomiaargentina.orgpublishedVersionÓptica (incluida Óptica Láser y Óptica Cuántica), Acústic

El complejo astronómico El Leóncito

We describe the main characteristics of the new National facility build in Argentina for ground -based astronomical observations. Located at the Argentinien side of the Andes and at a southern latitude of -31̣°, the Complejo Astronómico El Leóncito, operates a 2.15 m reflector. The site has almost 270 useful nights per year. We describe the present auxiliary instrumentation and the plans for the near future. The total budget for the operation of the observatory is u$s 250.000.Asociación Argentina de Astronomí

Report of IAU Commission 30 on Radial Velocities (2006-2009)

Brief summaries are given on the following subjects: Radial velocities and exoplanets (Toward Earth-mass planets; Retired A stars and their planets; Current status and prospects); Toward higher radial velocity precision; Radial velocities and asteroseismology; Radial velocities in Galactic and extragalactic clusters; Radial velocities for field giants; Galactic structure -- Large surveys (The Geneva-Copenhagen Survey; Sloan Digital Sky Survey; RAVE); Working groups (WG on radial velocity standards; WG on stellar radial velocity bibliography; WG on the catalogue of orbital elements of spectroscopic binaries [SB9]).Comment: 11 pages, to appear in the IAU Transactions Vol. XXVIIA, Reports on Astronomy 2006-2009, ed. Karel van der Hucht. Editor: G. Torre

Polarización en sistemas binarios

El programa consiste en la detección de la variación temporal de la polarización en sistemas binarios. Determinar la curva de polarización (si existe) y en los casos posibles determinar la inclinación orbital. Finalmente obtener la dependencia de la polarización con la longitud de onda. Las observaciones de los sistemas seleccionados de los catálogos de Batten, Kukarkin y la "Finding List" de binarias eclipsantes, se realizan con el polarímetro del Observatorio de La Plata y su reflector de 83 cm.Asociación Argentina de Astronomí

Photoelectric results of the total lunar eclipse of April 12-13, 1968

According to an observational program of all lunar eclipses visible from La Plata it was photo-electrically measured an area of the Mare Crisium during the total eclipse of April 12-13,1968.Asociación Argentina de Astronomí