Spectroscopic characterization of X-ray emitting young stars associated with the Sh 2-296 nebula

We studied a sample of stars associated with the Sh 2-296 nebula, part of the reflection nebulae complex in the region of Canis Major (CMa R1). Our sample corresponds to optical counterparts of X-ray sources detected from observations with the XMM-Newton satellite, which revealed dozens of possible low-mass young stars not yet known in this region. A sample of 58 young star candidates were selected based on optical spectral features, mainly H{\alpha} and lithium lines, observed with multi-objects spectroscopy performed by the Gemini South telescope. Among the candidates, we find 41 confirmed T Tauri and 15 very likely young stars. Based on the H{\alpha} emission, the T Tauri stars were distinguished between classical (17%) and weak-lined (83%), but no significant difference was found in the age and mass distribution of these two classes. The characterization of the sample was complemented by near- and mid-infrared data, providing an estimate of ages and masses from the comparison with pre-main-sequence evolutionary models. While half of the young stars have an age of 1-2 Myrs or less, only a small fraction (~25%) shows evidence of IR excess revealing the presence of circumstellar discs. This low fraction is quite rare compared to most young star-forming regions, suggesting that some external factor has accelerated the disc dissipation

On the spatial distributions of stars and gas in numerical simulations of molecular clouds

This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society. © 2015 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.We compare the spatial distribution of stars which form in hydrodynamical simulations to the spatial distribution of the gas, using the Q -parameter. The Q-parameter enables a self-consistent comparison between the stars and gas because it uses a pixelated image of the gas as a distribution of points, in the same way that the stars (sink particles in the simulations) are a distribution of points. We find that, whereas the stars have a substructured, or hierarchical spatial distribution (Q∼0.4−0.7), the gas is dominated by a smooth, concentrated component and typically has Q∼0.9. We also find no statistical difference between the structure of the gas in simulations that form with feedback, and those that form without, despite these two processes producing visually different distributions. These results suggest that the link between the spatial distributions of gas, and the stars which form from them, is non-trivial.Peer reviewe

Star formation history of Canis Major OB1 - II. A bimodal X-ray population revealed by XMM-Newton

The Canis Major OB1 Association has an intriguing scenario of star formation, especially in the Canis Major R1 (CMa R1) region traditionally assigned to a reflection nebula, but in reality an ionized region. This work is focused on the young stellar population associated to CMa R1, for which our previous results from ROSAT, optical and near-infrared data had revealed two stellar groups with different ages, suggesting a possible mixing of populations originated from distinct star-formation episodes. The X-ray data allow the detected sources to be characterized according to hardness ratios, light curves and spectra. Estimates of mass and age were obtained from the 2MASS catalogue, and used to define a complete subsample of stellar counterparts, for statistical purposes. A catalogue of 387 XMM-Newton sources is provided, 78% being confirmed as members or probable members of the CMa R1 association. Flares were observed for 13 sources, and the spectra of 21 bright sources could be fitted by a thermal plasma model. Mean values of fits parameters were used to estimate X-ray luminosities. We found a minimum value of log(L$_X$[erg/s]) = 29.43, indicating that our sample of low-mass stars (M$_\star$ $\leq$ 0.5 M$_\odot$), being faint X-ray emitters, is incomplete. Among the 250 objects selected as our complete subsample (defining our best sample), 171 are found to the East of the cloud, near Z CMa and dense molecular gas, 50% of them being young ( 10 Myr). The opposite happens to the West, near GU CMa, in areas lacking molecular gas: among 79 objects, 30% are young and 50% are older. These findings confirm that a first episode of distributed star formation occurred in the whole studied region ~10 Myr ago and dispersed the molecular gas, while a second, localized episode (< 5 Myr) took place in the regions where molecular gas is still present.Comment: 38 pages, 21 figures, accepted for A&

Animação e rock'n'roll usados para facilitar ensino de astronomia e química

Por sua característica multidisciplinar, a astronomia tem sido amplamente utilizada na aplicação da pesquisa científica no ensino de ciências naturais. As chamadas por projetos de ensino e divulgação científica, visando a produção de materiais didáticos, configuram-se em excelentes oportunidade de aliar o fascínio da população pelos astros e a informação que estes podem trazer sobre conceitos básicos das ciências fundamentais. No presente trabalho descrevemos a experiência em criar materiais didáticos em linguagem atrativa aos jovens (livros de história em quadrinhos; filmes de animação) com o objetivo de ampliar a cultura cientifica entre o público em geral. Para os estudantes da graduação, nossos projetos fazem parte das açoes afirmativas que buscam diminuir a evasão e estimular a conclusão no tempo ideal. Esse artigo é dedicado à descrição da metodologia adotada e apresentação de alguns exemplos dos resultados alcançados, nesse tipo de atuação “antes” e “depois” do ingresso do estudante na graduação.Due to its multidisciplinary character, astronomy has been subject of educational projects that use scientific research to improve the learning of natural sciences. The financial support in the form of Announcements of Opportunities, devoted to the production of teaching and outreach material, are the best way to combine the fascination that people have about the stars, with the information that these objects can bring concerning the basic concepts related to fundamental sciences. In the present work, we describe the experience in developing educational resources by adopting modern communication language (comics, animations) that is attractive among young people. Our goal is to enlarge the scientific culture of the citizens. For undergraduate students, our projects aim to diminish the evasion, as well as to promote the course conclusion in the ideal period. The paper is dedicated to describe the adopted methodology and to report the partial results of acting “before “and “after” the student entrance in the undergraduate course

Three Li-rich K giants: IRAS 12327-6523, IRAS 13539-4153, and IRAS 17596-3952

We report on spectroscopic analyses of three K giants previously suggested to be Li-rich: IRAS 12327-6523, IRAS 13539-4153, and IRAS 17596-3952. High-resolution optical spectra and the LTE model atmospheres are used to derive the stellar parameters: ($T_{\rm eff}$, log $g$, [Fe/H]), elemental abundances, and the isotopic ratio $^{12}$C/$^{13}$C. IRAS 13539-4153 shows an extremely high Li abundance of $\log\epsilon$(Li) $\approx$ 4.2, a value ten times more than the present Li abundance in the local interstellar medium. This is the third highest Li abundance yet reported for a K giant. IRAS 12327-6523 shows a Li abundances of $\log\epsilon$(Li)$\approx$ 1.4. IRAS 17596-3952 is a rapidly rotating ($V{\sin i}$ $\approx$ 35 km s$^{-1}$) K giant with $\log\epsilon$(Li) $\approx$ 2.2. Infrared photometry which shows the presence of an IR excess suggesting mass-loss. A comparison is made between these three stars and previously recognized Li-rich giants.Comment: 17 pages, 6 figures, accepted for A

Finding new sub-stellar co-moving companion candidates - the case of CT Cha

We have searched for close and faint companions around T Tauri stars in the Chamaeleon star forming region. Two epochs of direct imaging data were taken with the VLT Adaptive Optics instrument NaCo in February 2006 and March 2007 in Ks band for the classical T Tauri star CT Cha together with a Hipparcos binary for astrometric calibration. Moreover a J band image was taken in March 2007 to get color information. We found CT Cha to have a very faint companion (Ks{0} = 14.6 mag) of ~ 2.67" separation corresponding to ~ 440 AU. We show that CT Cha A and the faint object form a common proper motion pair and that the companion is not a non-moving background object (with 4 sigma significance).Comment: 5 pages, 2 figures, Proceedings of the IAU Symposium 249: Exoplanets: Detection, Formation and Dynamics, Suzhou - China, 22-26 October 200

The Molecular Hydrogen Deficit in Gamma-Ray Burst Afterglows

Recent analysis of five gamma-ray burst (GRB) afterglow spectra reveal the absence of molecular hydrogen absorption lines, a surprising result in light of their large neutral hydrogen column densities and the detection of H$_2$ in similar, more local star-forming regions like 30 Doradus in the Large Magellanic Cloud (LMC). Observational evidence further indicates that the bulk of the neutral hydrogen column in these sight lines lies 100 pc beyond the progenitor and that H$_2$ was absent prior to the burst, suggesting that direct flux from the star, FUV background fields, or both suppressed its formation. We present one-dimensional radiation hydrodynamical models of GRB host galaxy environments, including self-consistent radiative transfer of both ionizing and Lyman-Werner photons, nine-species primordial chemistry with dust formation of H$_2$, and dust extinction of UV photons. We find that a single GRB progenitor is sufficient to ionize neutral hydrogen to distances of 50 - 100 pc but that a galactic Lyman-Werner background is required to dissociate the molecular hydrogen in the ambient ISM. Intensities of 0.1 - 100 times the Galactic mean are necessary to destroy H$_2$ in the cloud, depending on its density and metallicity. The minimum radii at which neutral hydrogen will be found in afterglow spectra is insensitive to the mass of the progenitor or the initial mass function (IMF) of its cluster, if present.Comment: 12 pages, 7 figures, accepted for Ap