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Leiva A.M.,Observatorio Astronomico de Cordoba | Leiva A.M.,CONICET | Briozzo C.B.,CONICET
Monthly Notices of the Royal Astronomical Society

We put forward a dynamical model for the distribution of dust falling on the surface of Iapetus. Theoretical distributions are obtained by solving the Saturn-Iapetus circular restricted threebody problem for low- and intermediate-energy particles entering the system and colliding with Iapetus. Comparison of the resulting impact densities with photometric data gives an empirical model for the boundary of the heavily impacted regions, which reproduces some, but not all, relevant features of the observed dark region. Comparison with the dust deposition rate assumed to trigger the thermal segregation process proposed by Spencer & Denk (2010) gives instead qualitatively good agreement. The relevant features are best reproduced for a uniform density of incoming particleswithin a relatively narrowrange of intermediate energies. The corresponding incoming trajectories are direct and originate in a close external neighbourhood of Iapetus' orbit, at no more than 1.33 times the Saturn-Iapetus distance. The features of the population originating this flux, as shaped by the influence of Solar gravity, are briefly discussed. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. Source

Lagos P.,University of Porto | Papaderos P.,University of Porto | Gomes J.M.,University of Porto | Smith Castelli A.V.,CONICET | And 2 more authors.
Astronomy and Astrophysics

Aims. The main goal of this study is to carry out a spatially resolved investigation of the warm interstellar medium (ISM) in the extremely metal-poor blue compact dwarf (BCD) galaxy HS 2236+1344. Special emphasis is laid on analysis of the spatial distribution of chemical abundances, emission-line ratios, and the kinematics of the ISM, and to the recent star-forming (SF) activity in this galaxy. Methods. This study is based on optical integral field unit spectroscopy data from Gemini Multi-Object Spectrograph (GMOS) at the Gemini North telescope and archival Sloan Digital Sky Survey (SDSS) images. The galaxy was observed at medium spectral resolution over the spectral range from ∼4300 Å to 7300 Å. The data were obtained in two different positions across the galaxy, obtaining a total 4″ × 8″ field that encompasses most of its ISM. Results. Emission-line maps and broad-band images obtained in this study indicate that HS 2236+1344 hosts three giant H'ii regions (GH'iiRs). Our data also reveal some faint curved features in the BCD periphery that might be due to tidal perturbations or expanding ionized-gas shells. The ISM velocity field shows systematic gradients along the major axis of the BCD, with its southeastern and northwestern half differing by ∼80 km's-1in their recessional velocity over the field of view. The Hα and Hβ equivalent-width distribution in the central part of HS 2236+1344 is consistent with a very young (∼3 Myr) burst. Our surface photometry analysis reveals an underlying low surface brightness component with moderately red colors, which suggest that the galaxy has undergone previous star formation. We derive an integrated oxygen abundance of 12 + log'(O / H) = 7.53 ± 0.06 and a nitrogen-to-oxygen ratio of log'(N / O) = -1.57 ± 0.19. Our results are consistent, within the uncertainties, with a homogeneous distribution of oxygen and nitrogen within the ISM of the galaxy. The high-ionization He'ii λ4686 emission line is detected only in the central part of HS 2236+1344. Similar to many BCDs with He'ii λ4686 emission, HS 2236+1344 shows no Wolf-Rayet (WR) bump. © ESO, 2014. Source

De La Reza R.,Observatorio Nacional | Chavero C.,Observatorio Astronomico de Cordoba
Proceedings of the International Astronomical Union

Using a collection of 40 debris disks (DD) around dwarf A-type stars (from which 17 are spatially resolved) having well determined stellar ages (Vican 2012), we found that for a collisional self-stirring model of flux distributions (Kenyon & Bromley, 2008, 2010) dusty DD occupy for a large part the terminal age positions corresponding the end of the MS phase. This situation does not necessarily mean that the dust generation in these DD is finished at this stage. Dusty DD can continue their lives in the next Post-MS stages, as is the case of the recent first resolved dusty DD with planets around the K-type subgiant star κ CrB. This star is considered a retired A star (Bonsor et al. 2013). In order to explain the apparent lack of dusty DD in the giant phase, we propose here that this could be due, in part, to a dilution of any planetesimal belt existing around these stars, with the corresponding diminishing of collisions and subsequent dust generation. This dilution is provoked by the dynamical expansion of this belt produced by the important stellar mass loss during the RGB phase. This scenario is being studied by means of numerical simulations by de la Reza, Roig & Chavero 2013 (in preparation). Copyright © 2013, International Astronomical Union. Source

Alvarez G.E.,Georgia Institute of Technology | Sowell J.R.,Georgia Institute of Technology | Williamon R.M.,Emory University | Lapasset E.,Observatorio Astronomico de Cordoba
Publications of the Astronomical Society of the Pacific

We present differential UBV photoelectric photometry obtained by Williamon of the short-period A-type W UMa binary MW Pav. With the Wilson–Devinney analysis program, we obtained a simultaneous solution of these observations with the UBV photometry of Lapasset, the V measurements by the ASAS program, and the double-lined radial velocity measurements of Rucinski and Duerbeck. Our solution indicates that MW Pav is in an overcontact state, where both components exceed their critical Roche lobes. We derive masses of M1 = 1.514 ± 0.063 M⊙ and M2 = 0.327 ± 0.014 M⊙, and equal-volume radii of R1 = 2.412 ± 0.034 R⊙ and R2 = 1.277 ± 0.019 R⊙ for the primary and secondary, respectively. The system is assumed to have a circular orbit and is seen at an inclination of 86.39° ± 0.63°. The effective temperature of the primary was held fixed at 6900 K, whereas the secondary’s temperature was found to be 6969 ± 10 K. The asymmetry of the light curves requires a large, single star spot on the smaller, less massive secondary component. A consistent base solution, with different spot characteristics for the Williamon, Lapasset, and ASAS data, was found. The modeled spot varied little during the 40-year range of photometric observations. The combined solution utilized a third light component and found that the period is changing at a rate of dP/dt = (6.50 ± 0.19) × 10-10. © 2015, The Astronomical Society of the Pacific. All rights reserved. Source

Persi P.,Istituto di Astrofisica Spaziale e Fisica Cosmica | Tapia M.,National Autonomous University of Mexico | Gomez M.,Observatorio Astronomico de Cordoba
Astronomy and Astrophysics

Context. The infrared cluster CBJC 8 is associated with a 6.7 GHz methanol maser and a compact radio-continuum source, G85.40-0.00. It is located at a distance of about 8 kpc. Aims. The aim is to study the characteristics of this distant and compact embedded cluster and derive the properties of its stellar population. Methods. We present new ground-based near- and mid-infrared imaging observations of this region. The calibrated images were analysed together with archive Spitzer IRAC images. Results. Based on the discovery of a considerable fraction of embedded sources with infrared excess emission that are concentrated within a radius around 16" centred near the position of the compact HII region G85.40-0.00, we were able to confirm the presence of a very young embedded cluster. It was found to contain more than 58 members brighter than MK = 2.6, two-thirds of which showing significant near- or mid-IR excess emission. We present spectral energy distributions and extrapolated total luminosities for nine sources with large mid-infrared excesses that were measured in all four IRAC bands. For the brightest of these, G8540A, which is associated with a methanol maser and a compact HII region, we fitted a model of an infalling envelope plus disc plus central star to its observed 1.6 to 850 μm fluxes to get an idea of its physical properties. We also report a single 2.12 μm molecular hydrogen line emission knot near the centre of the cluster, which support the idea about an outflow activity. © 2010 ESO. Source

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