Estadística de binarias en la asociación de Orion

Se obtuvieron espectros para determinación de velocidad radial de los 96 posibles miembros más brillantes de la Asociación OB 1, a razón de aproximadamente 10 espectros por estrella. Todo el material fue reducido en el Observatorio Astronómico de La Plata, así como numerosas placas de estrellas standard de velocidad radial correspondientes a cada turno de observación. Se utilizaron criterios estadísticos para la detección de variabilidad (test E/I análisis de varianza) de los cuales se desprende un porcentaje de 36 % de binarias espectroscópicas. Diez de las variables ya eran conocidas y cuenta con órbita publicada en el 7mo. Catálogo de Elementos Orbitales de Batten. En los otros publicados en la literatura por los diferentes observadores, obtener una solución que proveyera parámetros orbitales provisorios, lo cual se ha logrado para unos 15 sistemas. Discutimos también la incidencia de binarias de corto período y de estrellas peculiares magnéticas en relación con la velocidad de rotación axial proyectada de la Asociación comparada con la de las estrellas de campo de los mismos tipos espectrales, en la perspectiva de la correlación propuesta por Abt y colaboradores.Asociación Argentina de Astronomí

Cinemática de estrellas en cúmulos abiertos y asociaciones OB

The impact of the new observing techniques on radial velocity measurements is summarized here, along with some current efforts on proper motion studies. For stars with spectral types later than F5, results from CORAVEL and coudé-CCD spectroscopy achieve precision better than 0.5 km/sec (works by Mermilliod, Mayor, Latham, Mathieu, among others). Recently, Andersen et ai, 1990, showed how new radial velocity observations of stars in intermediate age open clusters (namely: IC 4651 and NGC 3680) changed dramatically the current ideas about the extent and shape of each cluster's Main Sequence. Regarding early-type stars, we face a quite different situation. Spectral features are often broad and few in number, making hard to get accurate radial velocities. The highest accuracy obtained so far is around 2 km/sec., with coudé-CCD spectroscopy and high S/N (see, for example, works by Fekel, Morse, etc.). As an example of the improvements obtained, we review different studies on the binary frequency of IC 4665 (Abt and Snowden, 1969; Abt et al., 1972; Crampton et al., 1976; Morrell and Abt, 1991) where the higher accuracy achieved led to a binary frequency lower than the one observed previously. However, proper motions determined by Prosser, 1992, cast some doubt about the membership in the cluster of 2 of the 4 binaries, in a sample of 15 probable members. The need of radial velocity work in OB associations is obvious if we are interested in knowing the Present Date Mass Function for that groups, based on empirical data.Asociación Argentina de Astronomí

Investigation of the Magellanic eclipsing binary HV 2241

We present a CCD V light curve of HV 2241, together with some observations in the B band. We analysed our photometric data jointly with previously published radial velocities by means of the Wilson-Devinney code, and derived new values for the physical parameters of this massive eclipsing binary system. We confirm that this system is semi-detached, with the secondary (less massive and less luminous component) filling its Roche-lobe. From our analysis, we estimate the following masses and radii for the components of HV 2241: M1 = 36.2 ± 0.7 M⊙, R1 = 14.9 ± 0.4 R⊙, M2 = 18.4 ± 0.7 M⊙ and R2 = 13.7 ± 0.4 R⊙. We review the spectral classification analysing HST and IUE data and discuss the temperature and the reddening for this star.Facultad de Ciencias Astronómicas y Geofísica

New giant H II regions in the southern sky

We present results of a search for giant H II regions in southern galaxies. Using high-resolution spectra, obtained with the Magellan Inamori Kyocera Echelle (MIKE) at the Las Campanas Magellan II telescope, we were able to resolve the emission-line profiles and determine the intrinsic velocity dispersion of the ionized gas. Out of four observed regions, selected from previous CCD narrow-band photometry, we detected three H II regions showing supersonic velocity dispersion, characteristic of giant H II regions, and their location in diagnostic diagrams suggests that a powerful starburst is the source of ionization energy.Facultad de Ciencias Astronómicas y Geofísica

Investigation of the Magellanic eclipsing binary HV 2241

We present a CCD V light curve of HV 2241, together with some observations in the B band. We analysed our photometric data jointly with previously published radial velocities by means of the Wilson-Devinney code, and derived new values for the physical parameters of this massive eclipsing binary system. We confirm that this system is semi-detached, with the secondary (less massive and less luminous component) filling its Roche-lobe. From our analysis, we estimate the following masses and radii for the components of HV 2241: M1 = 36.2 ± 0.7 M⊙, R1 = 14.9 ± 0.4 R⊙, M2 = 18.4 ± 0.7 M⊙ and R2 = 13.7 ± 0.4 R⊙. We review the spectral classification analysing HST and IUE data and discuss the temperature and the reddening for this star.Facultad de Ciencias Astronómicas y Geofísica

Pre-main-sequence stars in the Lagoon Nebula (M8)

We report the discovery of new pre-main-sequence (PMS) stars in the Lagoon Nebula (M8) at a distance of 1.25 kpc, based on intermediate-resolution spectra obtained with the Boiler & Chivens spectrograph at the 6.5-m Magellan I Telescope (Las Campanas Observatory, Chile). According to the spectral types, the presence of emission lines and the lithium λ 6708 absorption line, we are able to identify 27 classical T Tauri stars, seven weak-lined T Tauri stars and three PMS emission objects with spectral type G, which we include in a separate stellar class denominated 'PMS Fe/Ge class'. Using near-infrared photometry either from the Two-Micron All-Sky Survey or from our own previous work, we derive effective temperatures and luminosities for these stars and locate them in the Hertzsprung-Russell diagram, in order to estimate their masses and ages. We find that almost all of our sample stars are younger than 3 × 106 yr and span over a range of masses between 0.8 and 2.5 M⊙. A cross-correlation between our spectroscopic data and the X-ray sources detected with the Chandra ACIS instrument is also presented.Facultad de Ciencias Astronómicas y Geofísica

XMM-Newton X-ray observations of the Carina nebula

We use new XMM-Newton observations to perform a detailed X-ray analysis of the Carina nebula region in the 0.3-12 keV energy range. Our source detection yields 80 discrete X-ray sources, from which about 20 per cent seem not to have optical counterparts. To get an idea of the energy spectrum of these sources, we construct an X-ray.colour-colour diagram using the energy bands 0.3-2, 2-4.5 and 4.5-12 keV. We analyse the spectra of the most intense X-ray sources associated with early-type stars, including the luminous blue variable η Carina and WR25. We show that the X-ray emission from these sources is well fitted by multitemperature model spectra. We detect surprisingly intense X-ray emission at energies above 4 keV for some of the observed early-type stars, especially from CPD-59 2629 (Tr16-22) which presents particularly hard X-ray emission. We detect intense soft X-ray emission, below <2 keV, in HDE 303311, which presents an X-ray excess of about 100 times higher than has been observed in other 05V stars. We use these data to construct the L x/Lbol relation for the 0.3-12 and 3.0-12 keV energy ranges, for all the observed O-type stars, plus η Carina and WR25. Most of the bright stars seem to agree with low metallicity spectral models. The L x/Lbol ratio for O-type stars in the 0.3-12 keV range is well fitted by a constant ≈6.04.87.5 × 10 -7, in fair agreement with the canonical expression L x/Lbol ∼ 2 × 10-7 formerly estimated for the 0.3-2.4 keV energy band. In contrast, the Lx/Lbol relation for the 3.0-12 keV range presents a strong deviation from the canonical relation, with a high dispersion of about four orders of magnitude. We also detect intrinsic X-ray time variability in seven sources, over the time-scale of about 50 h covered by the observations. This includes an X-ray flare of about 2-h duration detected in DETWC Tr16 J104429.2-594143, a source probably not physically associated with the Carina nebula. We discuss the different underlying physical mechanisms that can be responsible for the X-ray emission from early-type stars.Facultad de Ciencias Astronómicas y Geofísica

A survey of N IV and O IV features near 3400 Å in O2-O5 spectra

We have conducted a survey of little-known N IV and O IV multiplets near 3400 Å in an extensive sample of well-classified, very early O-type spectra. The initial motivation was to search for additional useful classification criteria for these types, but an unexpected result is the high sensitivity of these features to evolutionary CNO processing. We have found a useful discriminant between O2 and later types in the relative strengths of the O IV multiplets, one of which is subject to selective emission in the hottest spectra; the overall strengths of these lines also decrease between spectral types O4 and O5. More remarkable, however, are the variations in the N/O ratios among both individual stars and clusters. For instance, several O4 If + spectra have very large ratios, while main-sequence stars in the Carina Nebula generally have smaller values than others of the same spectral types in other regions. These effects correspond to different degrees of mixing of processed material as a function of evolutionary age and initial rotational velocities; the second effect provides significant further evidence that very massive stars mix while still on the main sequence. Thus, further analysis of these features will likely provide valuable diagnostics of important evolutionary parameters.Facultad de Ciencias Astronómicas y Geofísica

Long Term Optical Spectroscopy of HD86161 (WR 16)

We present results of optical spectroscopy of the emission line star HD 86161=WR 16, the central star of an ejecta ring nebula, obtained between 1971 and 2000 in the wavelength domain 3200-7300 Á. The spectrum of type WN8 is rich in He and N lines, in particular Hell 5-n series emission lines are observed up to high quantum numbers. We analyze possible radial velocity variations observed between different epochs, and find stochastic variations with possible superimposed epoch to epoch variations. These last variations could be due to the orbital motion of an eccentric long period binary system.Facultad de Ciencias Astronómicas y Geofísica

Long Term Optical Spectroscopy of HD86161 (WR 16)

We present results of optical spectroscopy of the emission line star HD 86161=WR 16, the central star of an ejecta ring nebula, obtained between 1971 and 2000 in the wavelength domain 3200-7300 Á. The spectrum of type WN8 is rich in He and N lines, in particular Hell 5-n series emission lines are observed up to high quantum numbers. We analyze possible radial velocity variations observed between different epochs, and find stochastic variations with possible superimposed epoch to epoch variations. These last variations could be due to the orbital motion of an eccentric long period binary system.Facultad de Ciencias Astronómicas y Geofísica