Time filter

Source Type

Sartori M.J.,Laboratorio Nacional Of Astrofisica Mct | Gregorio-Hetem J.,University of Sao Paulo | Rodrigues C.V.,National Institute for Space Research | Annibal Hetem,Fundaco Santo Andre | Batalha C.,Evergreen Valley College
Astronomical Journal | Year: 2010

A large sample of Herbig Ae/Be (HAeBe) candidates, distributed in different Galactic regions south to declination +30°, were identified by the Pico dos Dias Survey (a search for young stellar objects based on IRAS colors). Most of the candidates are nearby or associated with star-forming clouds, but several others are considered isolated objects. Aiming to verify the young nature of 93 HAeBe candidates, we searched for additional information that could be useful to confirm if they are pre-main-sequence (PMS) stars or evolved objects, which coincidentally show similar IRAS colors. By adopting a spectral index that is related to the amount of infrared excess and the shape of the spectral energy distribution, we have classified the sample according to three groups, which are analyzed on the basis of (1) circumstellar luminosity; (2) spatial distribution; (3) optical polarization; (4) near-infrared colors; (5) stellar parameters (mass, age, effective temperature); and (5) intensity of emission lines. Our analysis indicates that only 76% of the studied sample, mainly the group with intermediate to low levels of circumstellar emission, can be more confidently considered PMS stars. The nature of the remaining stars, which are in the other group that contains the highest levels of infrared excess, remains to be confirmed. They share the same characteristics of evolved objects, requiring complementary studies in order to correctly classify them. At least seven objects show characteristics typical of post-asymptotic giant branch or proto-planetary nebulae. © 2010. The American Astronomical Society. All rights reserved.

De Silva G.M.,Australian Astronomical Observatory | D'Orazi V.,Macquarie University | D'Orazi V.,Monash University | Melo C.,European Southern Observatory | And 5 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2013

We explore the possible connection between the open cluster IC 2391 and the unbound Argus association identified by the search for associations containing young stars survey. In addition to common kinematics and ages between these two systems, here we explore their chemical abundance patterns to confirm if the two substructures shared a common origin. We carry out a homogenous high-resolution elemental abundance study of eight confirmed members of IC 2391 as well as six members of the Argus association using UVES spectra. We derive spectroscopic stellar parameters and abundances for Fe, Na, Mg, Al, Si, Ca, Ti, Cr, Ni and Ba. All stars in the open cluster and Argus association were found to share similar abundances with the scatter well within the uncertainties, where [Fe/H] = -0.04 ± 0.03 for cluster stars and [Fe/H] = -0.06 ± 0.05 for Argus stars. Effects of overionization/excitation were seen for stars cooler than roughly 5200 K as previously noted in the literature. Also, enhanced Ba abundances of around 0.6 dex were observed in both systems. The common ages, kinematics and chemical abundances strongly support the fact that the Argus association stars originated from the open cluster IC 2391. Simple modelling of this system finds this dissolution to be consistent with two-body interactions. © 2013 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.

Torres C.A.O.,Laboratorio Nacional Of Astrofisica Mct | Quast G.R.,Laboratorio Nacional Of Astrofisica Mct | Montes D.,Complutense University of Madrid
Proceedings of the International Astronomical Union | Year: 2015

To analyze the SACY (Search for Associations Containing Young stars) survey we developed a method to find young associations and to define their high probability members. These bona fide members enable to obtain the kinematical and the physical properties of each association in a proper way. Recently we noted a concentration in the UV plane and we found a new association we are calling ASYA (All Sky Young Association) for its overall distribution in the sky with a total of 38 bonafide members and an estimated age of 110 Myr, the oldest young association found in the SACY survey. We present here its kinematical, space and Li distributions and its HR diagram. © 2016 International Astronomical Union.

Sales D.A.,Federal University of Rio Grande do Sul | Pastoriza M.G.,Federal University of Rio Grande do Sul | Riffel R.,Federal University of Rio Grande do Sul | Winge C.,Gemini Observatory | And 2 more authors.
Astrophysical Journal | Year: 2011

We present mid-infrared (mid-IR) spectra of the Compton-thick Seyfert 2 galaxy NGC3281, obtained with the Thermal-Region Camera Spectrograph at the Gemini-South telescope. The spectra present a very deep silicate absorption at 9.7 μm, and [S IV] 10.5 μm and [Ne II] 12.7 μm ionic lines, but no evidence of polycyclic aromatic hydrocarbon emission. We find that the nuclear optical extinction is in the range 24mag ≤ AV ≤ 83mag. A temperature T = 300K was found for the blackbody dust continuum component of the unresolved 65pc nucleus and the region at 130pc SE, while the region at 130pc NW reveals a colder temperature (200K). We describe the nuclear spectrum of NGC3281 using a clumpy torus model that suggests that the nucleus of this galaxy hosts a dusty toroidal structure. According to this model, the ratio between the inner and outer radius of the torus in NGC3281 is R 0/R d = 20, with 14 clouds in the equatorial radius with optical depth of τV = 40mag. We would be looking in the direction of the torus equatorial radius (i = 60°), which has outer radius of R 0 11pc. The column density is N H 1.2 × 1024 cm-2 and the iron Kα equivalent width (0.5-1.2keV) is used to check the torus geometry. Our findings indicate that the X-ray absorbing column density, which classifies NGC3281 as a Compton-thick source, may also be responsible for the absorption at 9.7 μm providing strong evidence that the silicate dust responsible for this absorption can be located in the active galactic nucleus torus. © 2011. The American Astronomical Society. All rights reserved.

Martins L.P.,Southern Cross University of Brazil | Rodriguez-Ardila A.,Laboratorio Nacional Of Astrofisica Mct | de Souza R.,University of Sao Paulo | Gruenwald R.,University of Sao Paulo
Monthly Notices of the Royal Astronomical Society | Year: 2010

We report the first simultaneous zJHK spectroscopy on the archetypical Seyfert 2 galaxy NGC 1068 covering the wavelength region 0.9-2.4 μm. The slit, aligned in the north-south direction and centred in the optical nucleus, maps a region 300 pc in radius at subarcsec resolution, with a spectral resolving power of 360 km s-1. This configuration allows us to study the physical properties of the nuclear gas including that of the north side of the ionization cone, map the strong excess of continuum emission in the K band and attributed to dust and study the variations, both in flux and profile, in the emission lines. Our results show the following. (1) Mid- to low-ionization emission lines are split into two components, whose relative strengths vary with the position along the slit and seem to be correlated with the jet. (2) The coronal lines are single-peaked and are detected only in the central few hundred of pc from the nucleus. (3) The absorption lines indicate the presence of intermediate age stellar population, which might be a significant contributor to the continuum in the near-IR spectra. (4) Through some simple photoionization models we find photoionization as the main mechanism powering the emitting gas. (5) Calculations using stellar features point to a mass concentration inside the 100-200 pc of about 1010 M⊙. © 2010 The Authors. Journal compilation © 2010 RAS.

Martins L.P.,Southern Cross University of Brazil | Riffel R.,Federal University of Rio Grande do Sul | Rodriguez-Ardila A.,Laboratorio Nacional Of Astrofisica Mct | Gruenwald R.,University of Sao Paulo | de Souza R.,University of Sao Paulo
Monthly Notices of the Royal Astronomical Society | Year: 2010

We performed stellar population synthesis on the nuclear and extended regions of NGC 1068 by means of near-infrared spectroscopy to disentangle their spectral energy distribution components. This is the first time that such a technique is applied to the whole 0.8-2.4 μm wavelength interval in this galaxy. NGC 1068 is one of the nearest and probably the most studied Seyfert 2 galaxy, becoming an excellent laboratory to study the interaction between black holes, the jets that they can produce and the medium in which they propagate. Our main result is that traces of young stellar population are found at ∼100 pc south of the nucleus. The contribution of a power-law continuum in the centre is about 25 per cent, which is expected if the light is scattered from a Seyfert 1 nucleus. We find peaks in the contribution of the featureless continuum about 100-150 pc from the nucleus on both sides. They might be associated with regions where the jet encounters dense clouds. Further support to this scenario is given by the peaks of hot dust distribution found around these same regions and the H2 emission-line profile, leading us to propose that the peaks might be associated to regions where stars are being formed. Hot dust also has an important contribution to the nuclear region, reinforcing the idea of the presence of a dense, circumnuclear torus in this galaxy. Cold dust appears mostly in the south direction, which supports the view that the south-west emission is behind the plane of the galaxy and is extinguished very likely by dust in the plane. Intermediate-age stellar population contributes significantly to the continuum, especially in the inner 200 pc. © 2010 The Authors. Journal compilation © 2010 RAS.

Ramirez I.,University of Texas at Austin | Michel R.,National Autonomous University of Mexico | Sefako R.,South African Astronomical Observatory | Tucci Maia M.,Federal University of Itajubá | And 6 more authors.
Astrophysical Journal | Year: 2012

Photometric data in the UBV(RI)C system have been acquired for 80 solar analog stars for which we have previously derived highly precise atmospheric parameters T eff, log g, and [Fe/H] using high-resolution, high signal-to-noise ratio spectra. UBV and (RI)C data for 46 and 76 of these stars, respectively, are published for the first time. Combining our data with those from the literature, colors in the UBV(RI)C system, with ≃ 0.01mag precision, are now available for 112 solar analogs. Multiple linear regression is used to derive the solar colors from these photometric data and the spectroscopically derived T eff, log g, and [Fe/H] values. To minimize the impact of systematic errors in the model-dependent atmospheric parameters, we use only the data for the 10 stars that most closely resemble our Sun, i.e., the solar twins, and derive the following solar colors: (B - V) = 0.653 ± 0.005, (U - B) = 0.166 ± 0.022, (V - R) = 0.352 ± 0.007, and (V - I) = 0.702 ± 0.010. These colors are consistent, within the 1σ errors, with those derived using the entire sample of 112 solar analogs. We also derive the solar colors using the relation between spectral-line-depth ratios and observed stellar colors, i.e., with a completely model-independent approach, and without restricting the analysis to solar twins. We find (B - V) = 0.653 ± 0.003, (U - B) = 0.158 ± 0.009, (V - R) = 0.356 ± 0.003, and (V - I) = 0.701 ± 0.003, in excellent agreement with the model-dependent analysis. © 2012. The American Astronomical Society. All rights reserved..

Rodriguez-Ardila A.,Laboratorio Nacional Of Astrofisica Mct | Prieto M.A.,Institute of Astrophysics of Canarias | Portilla J.G.,National University of Colombia | Tejeiro J.M.,National University of Colombia
Astrophysical Journal | Year: 2011

The relationship between the emission of coronal lines (CLs) and nuclear activity in 36 Type 1 and 18 Type 2 active galactic nuclei (AGNs) is analyzed, for the first time, based on near-infrared (0.8-2.4 μm) spectra. The eight CLs studied, of Si, S, Fe, Al, and Ca elements and corresponding to ionization potentials (IPs) in the range 125-450eV, are detected (3σ) in 67% (36 AGNs) of the sample. Our analysis shows that the four most frequent CLs [Si VI]1.963 μm, [S VIII]0.9913 μm, [S IX]1.252 μm, and [Si X]1.430 μm display a narrow range in luminosity, with most lines located in the interval log L 39-40 ergs-1. We found that the non-detection is largely associated with either loss of spatial resolution or increasing object distance: CLs are essentially nuclear and easily lose contrast in the continuum stellar light for nearby sources or get diluted by the strong AGN continuum as the redshift increases. Yet, there are AGNs where the lack of coronal emission, i.e., lines with IP ≥ 100eV, may be genuine. The absence of these lines reflects a non-standard AGN ionizing continuum, namely, a very hard spectrum lacking photons below a few Kev. The analysis of the line profiles points out a trend of increasing FWHM with increasing IPs up to energies around 300eV, where a maximum in the FWHM is reached. For higher IP lines, the FWHM remains nearly constant or decreases with increasing IPs. We ascribe this effect to an increasing density environment as we approach the innermost regions of these AGNs, where densities above the critical density of the CLs with IPs larger than 300eV are reached. This sets a strict range limit for the density in the boundary region between the narrow and the broad region of 10 8-109cm-3. A relationship between the luminosity of the CLs and that of the soft and hard X-ray emission and the soft X-ray photon index is observed: the coronal emission becomes stronger with both increasing X-ray emission (soft and hard) and steeper X-ray photon index, i.e., softer X-ray spectra. Thus, photoionization appears as the dominant excitation mechanism. These trends hold when considering Type 1 sources only; they get weaker or vanish when including Type 2 sources, very likely because the X-ray emission measured in the latter is not the intrinsic ionizing continuum. © 2011 The American Astronomical Society. All rights reserved.

Riffel R.A.,Federal University of Santa Maria | Storchi-Bergmann T.,Federal University of Rio Grande do Sul | Riffel R.,Federal University of Rio Grande do Sul | Pastoriza M.G.,Federal University of Rio Grande do Sul | And 7 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2013

We use near-infrared (near-IR) spectroscopic data from the inner few hundred parsecs of a sample of 47 active galaxies to investigate possible correlations between the stellar velocity dispersion (σ*), obtained from the fit of the K-band CO stellar absorption bands, and the gas velocity dispersion (σ), obtained from the fit of the emission-line profiles of [S III] λ0.953 μm, [Fe II] λ1.257 μm, [Fe II] λ1.644 μm and H2 λ2.122 μm. While no correlations with s were found for H2 and [S III], a good correlation was found for the two [Fe II] emission lines, expressed by the linear fit σz.ast; = 95.4 ± 16.1 + (0.25 ± 0.08) × σ[Fe II]. Excluding barred objects from the sample, a better correlation is found between σz.ast; and σ[Fe II], with a correlation coefficient of R = 0.80 and fitted by the following relation: σz.ast; = 57.9 ± 23.5 + (0.42 ± 0.10) × σ[Fe II]. This correlation can be used to estimate σz.ast; in cases where it cannot be directly measured and the [Fe II] emission lines are present in the spectra, allowing us to obtain the mass of the supermassive black hole (SMBH) from the Mbull.-σz.ast; relation. The scatter from a one-to-one relationship between σz.ast; and its value derived from σ[Fe II] using the equation above for our sample is 0.07 dex, which is smaller than that obtained in previous studies which use σ[O III] in the optical as a proxy for σz.ast;. The use of σ[Fe II] in the near-IR instead of σ[O III] in the optical is a valuable option for cases in which optical spectra are not available or are obscured, as in the case of many active galactic nuclei. The comparison between the SMBH masses obtained using the Mbull.-σz.ast; relation in which σz.ast; was directly measured with those derived from σ[Fe II] reveals only a small average difference of Δ logMbull = 0.02 with a scatter of 0.32 dex for the complete sample and Δ logMbull = 0.00 with a scatter of 0.28 dex for a subsample excluding barred galaxies. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Elliott P.,European Southern Observatory | Elliott P.,University of Exeter | Bayo A.,European Southern Observatory | Bayo A.,Max Planck Institute for Astronomy | And 5 more authors.
Astronomy and Astrophysics | Year: 2014

Context. Dynamically undisrupted, young populations of stars are crucial in studying the role of multiplicity in relation to star formation. Loose nearby associations provide us with a great sample of close (<150 pc) pre-main sequence (PMS) stars across the very important age range (≈5-70 Myr) to conduct such research. Aims. We characterize the short period multiplicity fraction of the search for associations containing young stars (SACY) sample, accounting for any identifiable bias in our techniques and present the role of multiplicity fractions of the SACY sample in the context of star formation. Methods. Using the cross-correlation technique we identified double-lined and triple-lined spectroscopic systems (SB2/SB3s), in addition to this we computed radial velocity (RV) values for our subsample of SACY targets using several epochs of Fiber-fed Extended Range Optical Spectrograph (FEROS) and Ultraviolet and Visual Echelle Spectrograph (UVES) data. These values were used to revise the membership of each association that was then combined with archival data to determine significant RV variations across different data epochs characteristic of multiplicity; single-lined multiple systems (SB1). Results. We identified seven new multiple systems (SB1s: 5, SB2s: 2). We find no significant difference between the short period multiplicity fraction (Fm) of the SACY sample and that of close star-forming regions (≈1-2 Myr) and the field (Fm ≤ 10%). These are seen both as a function of age and as a function of primary mass, M 1, in the ranges P [1:200 day] and M2 [0.08 M⊗-M1], respectively. Conclusions. Our results are consistent with the picture of universal star formation, when compared to the field and close star-forming regions (SFRs). We comment on the implications of the relationship between increasing multiplicity fraction with the primary mass within the close companion range in relation to star formation. © 2014 ESO.

Loading Laboratorio Nacional Of Astrofisica Mct collaborators
Loading Laboratorio Nacional Of Astrofisica Mct collaborators