VLT/NACO near-infrared imaging and spectroscopy of N88A in the SMC

We present near-infrared imaging and spectroscopic high spatial resolution observations of the SMC region N88 containing the bright, excited, extincted and compact H II region N88A of size ~ 1 pc. To investigate its stellar content and reddening, N88 was observed using spectroscopy and imagery in the JHKs- and L'-band at a spatial resolution of ~ 0.1-0.3", using the VLT UT4 equipped with the NAOS adaptive optics system. In order to attempt to establish if the origin of the infra-red (IR) excess is due to bright nebulosity, circumstellar material and/or local dust, we used Ks vs J-K colour-magnitude (CM) and JHK colour-colour (CC) diagrams, as well as L' imagery.Our IR-data reveal in the N88 area an IR-excess fraction of geq 30 per cent of the detected stars,as well as an unprecedently detailed morphology of N88A. It consists of an embedded cluster of ~3.5" (~ 1 pc) in diameter, of at least thirteen resolved stars superposed with an unusual bright continuum centered on a very bright star. The four brightest stars in this cluster lie red-ward of H-K geq 0.45 mag, and could be classified as young stellar object (YSO) candidates. Four other probable YSO candidates are also detected in N88 along a south-north bow-shaped thin H2 filament at ~ 7" east of the young central bright star. At 0.2" east of this star, a heavily embedded core is detected that could be a massive class I protostar candidate. The 2.12 mu H2 image of N88A resembles a shell of diameter ~ 3" ~ 0.9 pc) centered on the bright star. The line ratios of H2 2-1 S(1) and 1-0 S(0) relative to 1-0 S(1), as well as the presence of high v lines, are indicative of photodissociation regions, rather than shocks.Comment: 15 pages, 14 figures, accepted by Astronomy and Astrophysics, uses pdflatex, aa.cl

Stellar abundances and molecular hydrogen in high-redshift galaxies -the far-ultraviolet view

FUSE spectra of star-forming regions in nearby galaxies are compared to composite spectra of Lyman-break galaxies (LBGs), binned by strength of Lyman alpha emission and by mid-UV luminosity. Several far-UV spectral features, including lines dominated by stellar wind and by photospheric components, are very sensitive to stellar abundances. Their measurement in Lyman-break galaxies is compromised by the strong interstellar absorption features, allowing in some cases only upper limits. The derived C and N abundances in the LBGs are no higher than half solar (scaled to oxygen abundance for comparison with emission-line analyses), independent of the strength of Lyman alpha emission. P V absorption indicates abundances as low as 0.1 solar, with an upper limit near 0.4 solar in the reddest and weakest-emission galaxies. Unresolved interstellar absorption components would further lower the derived abundances. Trends of line strength, and derived abundances, are stronger with mid-UV luminosity than with Lyman-alpha strength. H2 absorption in the Lyman and Werner bands is very weak in the LBGs. Template H2 absorption spectra convolved to appropriate resolution show that strict upper limits N(H2)< 10^18 cm^-2 apply in all cases, with more stringent values appropriate for the stronger-emission composites and for mixes of H2 level populations like those on Milky Way sight lines. Since the UV-bright regions are likely to be widespread in these galaxies, these results rule out massive diffuse reservoirs of H2, and suggest that the dust/gas ratio is already fairly large at z~3.Comment: Astron J., in press (June 2006

The Massive Wolf-Rayet Binary SMC WR7

We present a study of optical spectra of the Wolf--Rayet star AzV 336a (= SMC WR7) in the Small Magellanic Cloud. Our study is based on data obtained at several Observatories between 1988 and 2001. We find SMC WR7 to be a double lined WN+O6 spectroscopic binary with an orbital period of 19.56 days. The radial velocities of the He absorption lines of the O6 component and the strong He{\sc ii} emission at $\lambda$4686\AA of the WN component describe antiphased orbital motions. However, they show a small phase shift of $\sim$ 1 day. We discuss possible explanations for this phase shift. The amplitude of the radial velocity variations of He {\sc ii} emission is twice that of the absorption lines. The binary components have fairly high minimum masses, $\sim$ 18 \modot and 34 \modot for the WN and O6 components, respectively.Comment: Accepted by MNRA

The massive Wolf-Rayet binary SMC WR7

We present a study of optical spectra of the Wolf-Rayet star AzV 336a (= SMC WR7) in the Small Magellanic Cloud. Our study is based on data obtained at several Observatories between 1988 and 2001. We find SMC WR7 to be a double-lined WN+O6 spectroscopic binary with an orbital period of 19.56 d. The radial velocities of the He absorption lines of the O6 component and the strong He II emission at λ4686 Å of the WN component describe anti-phased orbital motions. However, they show a small phase shift of ∼ 1 d. We discuss possible explanations for this phase shift. The amplitude of the radial velocity variations of He II emission is twice that of the absorption lines. The binary components have fairly high minimum masses, ∼ 18 and 34 M⊙ for the WN and O6 components, respectively.Facultad de Ciencias Astronómicas y Geofísica

The OB associations LH 101 and LH 104 in the HII region N158 of the LMC

We present photometric and spectroscopic ob- servations of stars in the Large Magellanic Cloud OB as- sociations LH 101 and LH 104, located in the HII region N158, which we have also imaged. From our observations we have constructed upper H R diagrams for these OB associations, which we nd to consist mainly of three pop- ulations, one of 2 6 Myr for the stars inside the northern bubble (LH 104), and two populations in the southern HII region (LH 101), one of 2 Myr and the other one aged 3 6 Myr. We have obtained for LH 101 a normal IMF, with a slope of = 1:29 0.20 whereas for LH 104 the IMF is flatter with a slope of = 1:05 0.12. These IMF slopes are consistent with that of other OB associa- tions in the LMC. Our observations reveal in the region of LH 101 the presence of both unevolved and evolved very massive stars, whose ionizing flux is in excess of that derived from our H images of the HII region. The north- west nebulosity in the region of LH 101 thus appears to be matter bound.Facultad de Ciencias Astronómicas y Geofísica

El contenido estelar de la asociación LH 47 en la nube mayor de magallanes

Hemos determinado tipos espectrales y magnitudes para estrellas en la asociación LH 47 en la Nube Mayor de Magallanes. Esta asociación esta embebida en la región HII N 44, la cual es un anillo gigante donde también se observa radiación X difusa. Nuestras observaciones muestran la presencia de muchas estrellas masivas del tipo O y supergigantes B en LH 47. Las estrellas O se encuentran en la zona de mayor densidad de gas ionizado, mientras las supergigantes B se ven en la zona de baja densidad de gas, indicando que la formación estelar en LH 47 no ha sido coeval, sino secuencial.Asociación Argentina de Astronomí

Integration of ARGO trajectories in the Mediterranean Forecasting System and impact on the regional analysis of the Western Mediterranean circulation

The impact of ARGO trajectory assimilation on the quality of ocean analyses is studied by means of an operational oceanographic model implemented in the Mediterranean Sea and a 3D-var assimilation scheme. For the first time, both ARGO trajectories and vertical profiles together with satellite data are assimilated to produce analyses for short term forecasts. The study period covers three months during winter 2005 when four ARGO trajectories were present in the northwestern Mediterranean Sea. It is shown that their integration is consistent with the other components of the assimilation system, and it contributes to refine the model error structure with new information on horizontal pressure gradients. So the analysis benefits of a more accurate description of the boundary currents and their instabilities that drive the mesoscale activity of regional circulations. As a consequence, the trajectory assimilation remotely and significantly influences the basin scale circulation. Changes can be depicted by intermediate water mass redistributions, mesoscale eddy relocations or net transports modulations. These impacts are detailed and assessed considering historical and contemporary datasets. The obtained qualitative and quantitative agreements motivate the integration of ARGO trajectories in the operational Mediterranean Forecasting System

The massive Wolf-Rayet binary SMC WR7

We present a study of optical spectra of the Wolf-Rayet star AzV 336a (= SMC WR7) in the Small Magellanic Cloud. Our study is based on data obtained at several Observatories between 1988 and 2001. We find SMC WR7 to be a double-lined WN+O6 spectroscopic binary with an orbital period of 19.56 d. The radial velocities of the He absorption lines of the O6 component and the strong He II emission at λ4686 Å of the WN component describe anti-phased orbital motions. However, they show a small phase shift of ∼ 1 d. We discuss possible explanations for this phase shift. The amplitude of the radial velocity variations of He II emission is twice that of the absorption lines. The binary components have fairly high minimum masses, ∼ 18 and 34 M⊙ for the WN and O6 components, respectively.Facultad de Ciencias Astronómicas y Geofísica

A mid-infrared study of HII regions in the Magellanic Clouds: N88A and N160A

To show the importance of high-spatial resolution observations of HII regions when compared with observations obtained with larger apertures such as ISO, we present mid-infrared spectra of two Magellanic Cloud HII regions, N88A and N160A. We obtained mid-infrared (8-13 um), long-slit spectra with TIMMI2 on the ESO 3.6m telescope. These are combined with archival spectra obtained with the Infrared Spectrograph (IRS) onboard the Spitzer Space Telescope, and are compared with the low-spatial resolution ISO-SWS data. An inventory of the spectra in terms of atomic fine-structure lines and molecular bands is presented. Concerning N88A, an isolated HII region with no adjacent infrared sources, the observations indicate that the line fluxes observed by ISO-SWS and Spitzer-IRS come exclusively from the compact HII region of about 3 arcsec in diameter. This is not the case for N160A, which has a more complex morphology. We have spectroscopically isolated for the first time the individual contributions of the three components of N160A, two high-excitation blobs, A1 and A2, and the young stellar object N160A-IR. In addition, extended [SIV] emission is observed with TIMMI2 and is most likely associated with the central star cluster located between A1 and A2. We show the value of these high-spatial resolution data in determining source characteristics, such as the degree of ionization of each high-excitation blob or the bolometric luminosity of the YSO. This luminosity is about one order of magnitude lower than previously estimated. For each high-excitation blob, we also determine the electron density and the elemental abundances of Ne, S, and Ar.Comment: 13 pages, 8 figures, accepted for publication in A&