Study of two binary systems with O type components

We determined periods and orbital parameters for two binary systems with O-type components, namely Tr 16 Nº1 and HD 64315. Tr 16 Nº1 has a period p=1.5 days, components O9+O9 and minimum masses M₁ sen³i=17 M⊙ and M₂ sen³i=19 M⊙. HD 64315 has a period p=1.34 days, components O6+O6 and minimum masses M₁ sen³i=3.8 M⊙ and M₂ sen³i=3.3 M⊙.Asociación Argentina de Astronomí

Estudio espectroscópico de dos sistemas binarios masivos

Presentamos el estudio de dos sistemas binarios masivos con componentes de tipo espectral "O", EM Car y AB Cru. Determinamos los parámetros orbitales y estimamos las masas de las componentes en base a observaciones espectrográficas realizadas en el Observatorio Interamericano de Cerro Tololo.Asociación Argentina de Astronomí

The Vela-Puppis open clusters Pismis 8 and Pismis 13

CCD UBVI imaging photometry was carried out in the fields of the open clusters Pismis 8 and Pismis 13, located in the Vela-Puppis region in our Galaxy. MK spectral types have also been determined for a number of stars located in the fields of these two clusters which were used to secure membership among the brightest stars. Since our photometry goes to a fainter limit than previous studies we could provide better reddening, distance and age determinations. Both clusters are located close to the edge of the local arm in the third quadrant. Pismis 8 is a cluster about 5-7 My old located at 2000 pc from the Sun, while Pismis 13 was found at 2750 pc with a probable age of about 100 My. The estimate of the slopes of the mass functions in both cases yielded x ≈ 1.7 and x ≈ 2.1 for Pismis 8 and 13 respectively.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat

The Vela-Puppis open clusters Pismis 8 and Pismis 13

CCD UBVI imaging photometry was carried out in the fields of the open clusters Pismis 8 and Pismis 13, located in the Vela-Puppis region in our Galaxy. MK spectral types have also been determined for a number of stars located in the fields of these two clusters which were used to secure membership among the brightest stars. Since our photometry goes to a fainter limit than previous studies we could provide better reddening, distance and age determinations. Both clusters are located close to the edge of the local arm in the third quadrant. Pismis 8 is a cluster about 5-7 My old located at 2000 pc from the Sun, while Pismis 13 was found at 2750 pc with a probable age of about 100 My. The estimate of the slopes of the mass functions in both cases yielded x ≈ 1.7 and x ≈ 2.1 for Pismis 8 and 13 respectively.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat

Early-type stars in the open cluster NGC 4852

The southern open cluster NGC 4852 was re-observed in the UBVRI passbands to refine its intrinsic fundamental parameters. An extended spectral coverage was also undertaken aimed at obtaining a clear picture of the kind of stars inhabiting the cluster upper main sequence. We detected an unusual number of B-type stars including a new weak-emission Be star that raises to three the number of confirmed emission objects known in the cluster area. Our analysis, however, is conclusive in that none of them belongs to the cluster. With the new data set, we improved the fundamental parameters of NGC 4852: it is little bit farther than formerly assumed; the reddening, which increases smoothly with the distance, is lower than early estimates; and more importantly, it is really a young object of nearly 40-60Myr, contrary to the age of 200 Myr stated before. By means of spectroscopic parallaxes we secured the star distances, finding a good agreement between spectroscopic and zero-age main-sequence fitting distances, within the errors. The spatial distribution of the stars allows us to infer that NGC 4852 is the final, closer to the Sun, structure of a star-forming region and that a distant group of early-B-type stars, located immediately beyond the cluster, seems to be part of an extended OB association. The three emission stars detected in the region are related to this farther group. Finally, two extremely faint and blue stars were also found in the cluster zone. They have no connection with NGC 4852 but seem to be white-dwarf candidates.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat

Radial velocities and axial rotation for a sample of chemically peculiar stars

As part of a systematic project we have determined radial velocities and projected rotational velocities for a sample of 186 chemically peculiar stars which have been observed by the Hipparcos' satellite. The purpose is to provide necessary data to study the space velocities of peculiar stars.Facultad de Ciencias Astronómicas y Geofísica

NGC 2401: A template of the young population of the Norma-Cygnus arm in the Third Galactic Quadrant

Based on a deep optical CCD [UBV(RI)C] photometric survey and on the Two-Micron All Sky Survey (2MASS) data, we derived the main parameters of the open cluster NGC 2401. We found that this cluster is placed at 6.3 ± 0.5 kpc (Vo - Mv = 14.0 ± 0.2) from the Sun and is 25 Myr old, which allows us to identify NGC 2401 as a member of the young population belonging to the innermost side of the extension of the Norma-Cygnus spiral arm in the Third Galactic Quadrant. A spectroscopic study of the emission star LSS 440 that lies in the cluster area revealed that it is a B0Ve star; however, we could not confirm that it is a cluster member. We also constructed the cluster luminosity function (LF) down to V ∼ 22 and the cluster initial mass function (IMF) for all stars with masses above M ∼ 1-2 M ⊙. It was found that the slope of the cluster IMF is x ≈ 1.8 ± 0.2. The presence of a probable pre-main-sequence (PMS) star population associated with the cluster is weakly revealed.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat

Estudio de estrellas más tempranas que O7

Presentamos los primeros resultados, principalmente de estudios de velocidades radiales, de un grupo de estrellas O tempranas. Las estrellas fueron seleccionadas para su estudio en base a anterior detección de espectro con posibles líneas dobles, o de velocidad radial anómala, para descubrir nuevos sistemas binarios. El fin último es llegar a determinar la relación masa-luminosidad que actualmente no se conoce.Asociación Argentina de Astronomí

Multiplicidad en la asociación de Escorpio-Centauro

Hemos determinado velocidades radiales para 90 miembros de la asociación de Sco-Cen, tratando de descubrir estrellas de velocidad radial variable, mediante un test de análisis de varianza. Para esto, se obtuvieron alrededor de 600 espectrogramas en dispersiones que van desde los 16,9 Å/mm hasta 42 Å/mm, con los telescopios de Kitt Peak y Cerro Tololo. Para 10 de las binarias espectroscópicas así descubiertas determinamos elementos orbitales, y mejoramos los correspondientes a otros sistemas, usando observaciones publicadas en la literatura. Discutimos también la rotación axial de los miembros de la Asociación (diferenciando los dos subgrupos que la componen Upper Scorpius y Centaurus-Lupus-Crux) para incluirla en la correlación propuesta por Abt y colaboradores, que vincula el porcentaje de binarias espectroscópicas de corto período más estrellas peculiares magnéticas, con la velocidad de rotación axial proyectada promedio relativa a la velocidad de rotación axial proyectada de las estrellas de campo de los mismos tipos espectrales. También analizamos las diferencias entre la multiplicidad total observada en ambos subgrupos, a saber: 1,28 componentes por sistema, para Cen-Lup-Crux, con 19 miembros estudiados y 14 primarias normales, y 1,79 componentes por sistema para Upper-Sco, con 52 estrellas estudiadas y 47 estrellas primarias normales entre las mismas. A partir de estos datos, se intentó obtener la multiplicidad real de la Asociación, aplicando factores de completitud, según el método desarrollado por Abt y Levy (1976, 1978).Asociación Argentina de Astronomí

The Vela-Puppis open clusters Pismis 8 and Pismis 13

CCD UBVI imaging photometry was carried out in the fields of the open clusters Pismis 8 and Pismis 13, located in the Vela-Puppis region in our Galaxy. MK spectral types have also been determined for a number of stars located in the fields of these two clusters which were used to secure membership among the brightest stars. Since our photometry goes to a fainter limit than previous studies we could provide better reddening, distance and age determinations. Both clusters are located close to the edge of the local arm in the third quadrant. Pismis 8 is a cluster about 5-7 My old located at 2000 pc from the Sun, while Pismis 13 was found at 2750 pc with a probable age of about 100 My. The estimate of the slopes of the mass functions in both cases yielded x ≈ 1.7 and x ≈ 2.1 for Pismis 8 and 13 respectively.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat