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Torres-Flores S.,University of La Serena | Scarano S.,University of Sao Paulo | Scarano S.,Southern Astrophysical Research Telescope SOAR | Scarano S.,Federal University of Sergipe | And 4 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2014

We present new Gemini/GMOS spectroscopic and archival imaging data of the interacting galaxy NGC 92, which is part of a compact group and displays an extended tidal tail.We have studied the physical properties of 20 star-forming complexes in this system. We found that the star-forming regions located in the tidal tail of NGC 92 have ages younger than ̃8Myr, which suggests that these objects were formed in situ. The spectroscopic data reveal that these regions have slightly sub-solar metallicities, suggesting that they were formed from pre-enriched material. Using the oxygen abundances derived for each system, we found that the extended tidal tail of NGC 92 has a flat metallicity distribution. Although this scenario is consistent with N-body simulations of interacting systems, where there is gas mixing triggered by the interaction, archival Hα Fabry-Perot data cubes of NGC 92 have not shown a velocity gradient along the tail of this galaxy, which under certain assumptions could be interpreted as a lack of gas flow in the tail. Our results suggest that a fraction of the enriched gas that was originally located in the centre of the galaxy was expelled into the tidal tail when the interacting process that formed the tail happened. However, we cannot exclude the scenario in which the star formation in the tail has increased its original oxygen abundance. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Roman-Lopes A.,University of La Serena | Franco G.A.P.,Federal University of Minas Gerais | Sanmartim D.,Southern Astrophysical Research Telescope SOAR
Astrophysical Journal | Year: 2016

In this work, we present the results of a spectroscopic study of very massive stars (VMSs) found outside the center of the massive stellar cluster NGC 3603. From the analysis of the associated Southern Astrophysical Research (SOAR) Telescope spectroscopic data and related optical-near-IR (NIR) photometry, we confirm the existence of several VMSs in the periphery of NGC 3603. The first group of objects (MTT58, WR42e, and RF7) is composed of three new Galactic exemplars of the OIf∗/WN type, all of them with probable initial masses well above 100 and estimated ages of about 1 Myr. Based on our Goodman blue-optical spectrum of another source in our sample (MTT68), we can confirm the previous finding in the NIR of the only other Galactic exemplar (besides HD 93129A) of the O2If∗ type known to date. Based on its position relative to a set of theoretical isochrones in a Hertzprung-Russel (H-R) diagram, we concluded that the new O2If∗ star could be one of the most massive (150 ) and luminous (M V =-7.3) O-stars in the Galaxy. Also, another remarkable result is the discovery of a new O2v star (MTT31), which is the first exemplar of that class so far identified in the Milk Way. From its position in the H-R diagram it is found that this new star probably had an initial mass of 80 , as well as an absolute magnitude of M V =-6.0, corresponding to a luminosity similar to other known O2v stars in the Large Magellanic Cloud. Finally, we also communicate the discovery of a new Galactic O3.5If∗ star (RFS8) that is quite an intriguing case. Indeed, it is located far to the south of the NGC 3603 center, in apparent isolation at a large radial projected linear distance of ∼62 pc. Its derived luminosity is similar to that of the other O3.5If∗ (Sh18) found in NGC 3603's innermost region, and the fact that a such high mass star is observed so isolated in the field led us to speculate that perhaps it could have been expelled from the innermost parts of the complex by a close fly-by dynamical encounter with a very massive hard binary system. © 2016. The American Astronomical Society. All rights reserved.

Scarano S.,University of Sao Paulo | Scarano S.,Southern Astrophysical Research Telescope SOAR | Scarano S.,Federal University of Sergipe | Lepine J.R.D.,University of Sao Paulo
Monthly Notices of the Royal Astronomical Society | Year: 2013

We analysed the relation between the corotation radii and the galactic radii at which breaks or changes of slope of the metallicity gradients occur in spiral galaxies. With this purpose we compiledthe results from the literature on rotation curves, corotation radii and radial metallicity distributions of 27 galaxies, of which 16 were considered qualified to be studied in the context of this work. We rescaled all references of each galaxy to the same framework in order to compare the results and to identify the radii where breaks and changes of slopes are found, when non-linear models fit the radial metallicities better than a linear model. In most galaxies we have found minima and breaks in radial metallicity near the corotation radius, revealing a significant correlation between these two radii, as it occurs in our Galaxy. The results are interpreted as a consequence of long-lived spiral structures, in which the star formation rate depends on the distance to the corotation radius, producing secular effects in the observed radial metallicity distributions.©2012 The Authors.

De Oliveira C.M.,University of Sao Paulo | Taylor K.,University of Sao Paulo | Quint B.,University of Sao Paulo | Andrade D.,University of Sao Paulo | And 21 more authors.
Publications of the Astronomical Society of the Pacific | Year: 2013

This article presents a description of a new Tunable Filter Instrument for the SOAR telescope. The Brazilian Tunable Filter Imager (BTFI) is a highly versatile new technology to be used both in seeing-limited mode and at higher spatial fidelity using the SAM Ground-Layer Adaptive Optics facility (SOAR Adaptive Module) which is being deployed at the SOAR telescope. Such an instrument presents important new science capabilities for the SOAR astronomical community, from studies of the centers of nearby galaxies and the insterstellar medium to statistical cosmological investigations. The BTFI concept takes advantage of three new technologies. The imaging Bragg Tunable Filter (iBTF) concept utilizes Volume Phase Holographic Gratings in a double-pass configuration as a tunable filter, while a new Fabry-Perot (FP) concept involves the use of commercially available technologies which allow a single FP etalon to act over a very large range of interference orders and hence spectral resolutions. Both of these filter technologies will be used in the same instrument. The combination allows for highly versatile capabilities. Spectral resolutions spanning the range between 25 and 30,000 can be achieved in the same instrument through the use of iBTF at low resolution and scanning FPs beyond R ~ 2; 000 with some overlap in the mid-range. The third component of the new technologies deployed in BTFI is the use of EMCCDs, which allow for rapid and cyclical wavelength scanning thus mitigating the damaging effect of atmospheric variability through the acquisition of the data cube. An additional important feature of the instrument is that it has two optical channels which allow for the simultaneous recording of the narrow-band, filtered image with the remaining (complementary) broadband light. This avoids the otherwise inevitable uncertainties inherent in tunable filter imaging using a single detector, which is subject to temporal variability of the atmospheric conditions. The system was designed to supply tunable filter imaging with a field-of-view of 3′ on a side, sampled at 0.12″ for direct Nasmyth seeing-limited area spectroscopy and for SAM's visitor instrument port for GLAO-fed area spectroscopy. The instrument has seen first light, mounted on the SOAR telescope, as a visitor instrument. It is now in commissioning phase.

Scarano Jr S.,University of Sao Paulo | Scarano Jr S.,Southern Astrophysical Research Telescope SOAR | Lepine J.R.D.,University of Sao Paulo | Marcon-Uchida M.M.,University of Sao Paulo
Monthly Notices of the Royal Astronomical Society | Year: 2011

The correlation between the breaks in the metallicity distribution and the corotation radius of spiral galaxies has been already advocated in the past and is predicted by a chemodynamical model of our Galaxy that effectively introduces the role of spiral arms in the star formation rate. In this work, we present photometric and spectroscopic observations made with the Gemini Telescope for three of the best candidates of spiral galaxies to have the corotation inside the optical disc: IC 0167, NGC 1042 and NGC 6907. We observed the most intense and well-distributed Hii regions of these galaxies, deriving reliable galactocentric distances and oxygen abundances by applying different statistical methods. From these results, we confirm the presence of variations in the gradients of metallicity of these galaxies that are possibly correlated with the corotation resonance. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.

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