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Teste tuberculínico: pesquisa operacional no Mato Grosso do Sul; Tuberculin skin test: operational research in the state of Mato Grosso do Sul, Brazil

OLIVEIRA, Sandra Maria do Valle Leone de; RUFFINO-NETTO, Antônio; PANIAGO, Anamaria Mello Miranda; OLIVEIRA, Olcinei Alves de; MARQUES, Marli; CUNHA, Rivaldo Venâncio da; ANDREOTTI, Renato
Fonte: Sociedade Brasileira de Pneumologia e Tisiologia Publicador: Sociedade Brasileira de Pneumologia e Tisiologia
Tipo: Artigo de Revista Científica
Português
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OBJETIVO: Investigar a operacionalização da utilização do teste tuberculínico (TT) em programas de controle de tuberculose e em serviços de assistência especializada do Programa Nacional de Doenças Sexualmente Transmissíveis/AIDS e Hepatites Virais em municípios prioritários para o controle da tuberculose no estado de Mato Grosso do Sul. MÉTODOS: Estudo epidemiológico descritivo, transversal, do tipo inquérito. A formação profissional dos responsáveis pela realização do TT, existência de treinamentos, período de realização dos TTs, conduta em caso de perda de leitura, insumos disponíveis e sua conservação foram levantados por meio de entrevistas e visitas técnicas. O número de inquéritos em populações vulneráveis, número de TTs realizados e número de pacientes em tratamento de tuberculose latente entre 2008 e 2009 foram também levantados. RESULTADOS: Foram entrevistados 12 gestores de seis municípios. Alguns programas/serviços não realizavam o TT. A equipe de enfermagem realizava os TTs, não havia leitores especialistas, e treinamentos eram raros. A conservação dos frascos de PPD RT23 (5 mL) era adequada. Frequentemente utilizava-se a seringa de insulina. A realização de TT ocorria no horário comercial...

Towards the development of a two-time scale CUEP/BCU method

Theodoro, Edson Aparecido Rozas; Alberto, Luís Fernando Costa; Hsiao-Dong, Chiang
Fonte: IEEE; Manhattan Publicador: IEEE; Manhattan
Tipo: Conferência ou Objeto de Conferência
Português
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This paper proposes a new Two-Time Scale (TTS) BCU method, and reports the first ever known use of the TTSCUEP method in a multi-machine power system. The proposed TTS-BCU method is a numerical algorithm to correctly compute the slow and fast CUEPs of the TTS-CUEP method. It also provides a more robust algorithm to compute the CUEP of the original system.; FAPESP

The nature of X-ray sources associated to young clusters around SH2-296

Hetem, Jane Cristina Gregorio; Fernandes, B.; Montmerle, T.
Fonte: International Astronomical Union; Florianópolis Publicador: International Astronomical Union; Florianópolis
Tipo: Conferência ou Objeto de Conferência
Português
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Aiming to unravel the star formation activity in the Canis Major R1 (CMaR1), we have studied the young (< 5 Myr) clusters associated to the arcshaped ionized nebula Sh2-296. Based on our Xray data complemented by optical and near-IR data, we discovered, near to GU CMa, a stellar cluster that is older by at least a few Myr than the previously known cluster, around Z CMa, where star formation is still very active. Multi-object optical spectroscopy of our X-ray sources nearby Z CMa was performed with Gemini telescopes to confirm the existence of a mixed population from both older and younger clusters around the edge of Sh2-296. In the present work we show the results for optical counterparts candidates of 45 X-ray sources. Spectral type determination was based on comparison with standard spectra library and fitting the continuum and TiO bands. Typical features of young stars were inspected to confirm the nature of the sample that is mainly classified as T Tauri stars (TTs), since their spectra show the Li I line, one of the indicators of youth. The equivalent width of Hα measured at 10% of the total flux was used to separate Classical TTs (CTTs) from weak-line TTs (WTTs). Among 51 optical counterparts candidates...

Avaliação de clearance nasal, propriedades físicas do muco, celularidade e citocinas em lavado nasal de trabalhadores cortadores de cana-de-açúcar queimada no Estado de São Paulo; Evaluation of nasal mucociliary clearance, mucus physical properties, cellularity and cytokines in nasal lavage of sugarcane workers in São Paulo State

Goto, Danielle Miyuki
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 09/03/2012 Português
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A queima de biomassa produz gases tóxicos e partículas suspensas que contribuem para a poluição atmosférica. Este estudo avaliou os efeitos da colheita de cana-de-açúcar queimada sobre o transporte mucociliar (TMC) nasal, as propriedades físicas do muco nasal e celularidade e concentrações de citocinas em lavado nasal (LN) de cortadores de cana-de-açúcar e residentes de região urbana próxima aos canaviais (Mendonça, São Paulo). Métodos: Avaliamos 154 jovens não tabagistas (idade entre 18 e 43 anos) sendo 73 residentes e 81 cortadores na: (a) Pré-safra: 4 meses sem exposição à queimada de biomassa (fevereiro e março), e na (b) Pós-safra: aproximadamente 7 a 8 meses de exposição (outubro e novembro). Avaliamos: o TMC nasal por meio do teste da sacarina (TTS), as propriedades físicas do muco por meio da transportabilidade por alto fluxo e ângulo de contato, a expressão de fator de necrose tumoral (TNF)-, interleucinas (IL)-4, IL-6, IL-8 e IL-10 em LN, celularidade total e diferencial em LNsinais vitais e ocorrência de eventos respiratórios. Resultados: Na Pré-safra, comparados com os residentes, cortadores apresentaram menor pressão arterial média (95,5±9,1 e 88,7±9,4 mmHg, respectivamente; p<0,001)...

Transporte mucociliar e atividade física na vida diária de fumantes saudáveis

Proença, Mahara-Daian Garcia Lemes
Fonte: Universidade Estadual Paulista (UNESP) Publicador: Universidade Estadual Paulista (UNESP)
Tipo: Dissertação de Mestrado Formato: 77 f. : il.
Português
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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); Pós-graduação em Fisioterapia - FCT; A eficiência do transporte mucociliar pode variar em diferentes condições, como na exposição a partículas nocivas da fumaça do cigarro. O presente estudo avaliou os efeitos do cigarro, tanto imediato quanto a curto prazo, no transporte mucociliar nasal de fumantes por meio da quantificação do tempo de trânsito da sacarina (TTS), e os correlacionou com a intensidade de consumo tabagístico. Métodos: Dezenove fumantes ativos (11 homens; 51±16 anos; IMC 23±9 kg/m2; 27±11 cigarros/dia; 44±25 anos/maço), participantes de programa de intervenção antitabagismo, responderam a um questionário referente ao histórico tabagístico e foram submetidos à avaliação da função pulmonar (espirometria) e transporte mucociliar (pelo TTS), este imediatamente e após 8 horas do ato de fumar. Para comparação, um grupo pareado composto por 19 indivíduos saudáveis não-fumantes foi avaliado por meio dos mesmos testes. Resultados: Quando comparados ao TTS de não-fumantes (10±4 min; média±desvio padrão), os fumantes apresentaram tempo de transporte similar imediatamente após fumar (11±6 min; p=0,87) e significativamente mais lento 8 horas após fumar (16±6 min; p=0...

Análise comparativa dos métodos de sintetização de voz

Albuquerque, Almir dos Santos
Fonte: Florianópolis, SC Publicador: Florianópolis, SC
Tipo: Dissertação de Mestrado
Português
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Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico. Programa de Pós-Graduação em Ciência da Computação.; Na síntese de voz text-to-speech (TTS), o computador recebe como entrada, um texto digitado ou em memória e devolve, por meio de alto-falantes a leitura em voz alta do mesmo texto. As técnicas utilizadas para a síntese TTS são: concatenação, formantes, LPC e articulatória, sendo as duas primeiras as mais utilizadas. Esta dissertação tem como meta principal realizar uma análise comparativa destes dois métodos, por meio de análises teóricas e comparação de resultados de softwares TTS que seguem estas duas técnicas.

Teste tuberculínico: pesquisa operacional no Mato Grosso do Sul

Oliveira,Sandra Maria do Valle Leone de; Ruffino-Netto,Antônio; Paniago,Anamaria Mello Miranda; Oliveira,Olcinei Alves de; Marques,Marli; Cunha,Rivaldo Venâncio da; Andreotti,Renato
Fonte: Sociedade Brasileira de Pneumologia e Tisiologia Publicador: Sociedade Brasileira de Pneumologia e Tisiologia
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/10/2011 Português
Relevância na Pesquisa
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OBJETIVO: Investigar a operacionalização da utilização do teste tuberculínico (TT) em programas de controle de tuberculose e em serviços de assistência especializada do Programa Nacional de Doenças Sexualmente Transmissíveis/AIDS e Hepatites Virais em municípios prioritários para o controle da tuberculose no estado de Mato Grosso do Sul. MÉTODOS: Estudo epidemiológico descritivo, transversal, do tipo inquérito. A formação profissional dos responsáveis pela realização do TT, existência de treinamentos, período de realização dos TTs, conduta em caso de perda de leitura, insumos disponíveis e sua conservação foram levantados por meio de entrevistas e visitas técnicas. O número de inquéritos em populações vulneráveis, número de TTs realizados e número de pacientes em tratamento de tuberculose latente entre 2008 e 2009 foram também levantados. RESULTADOS: Foram entrevistados 12 gestores de seis municípios. Alguns programas/serviços não realizavam o TT. A equipe de enfermagem realizava os TTs, não havia leitores especialistas, e treinamentos eram raros. A conservação dos frascos de PPD RT23 (5 mL) era adequada. Frequentemente utilizava-se a seringa de insulina. A realização de TT ocorria no horário comercial...

Presence of Type III Secretion Genes in Burkholderia pseudomallei Correlates with Ara− Phenotypes

Winstanley, Craig; Hart, C. Anthony
Fonte: American Society for Microbiology Publicador: American Society for Microbiology
Tipo: Artigo de Revista Científica
Publicado em /02/2000 Português
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Dot blot hybridization and PCR amplification of 14 Ara+ and 8 Ara− Burkholderia pseudomallei strains showed that type III secretion (TTS) genes were present in all the Ara− strains but absent from all but one of the Ara+ strains. The link between TTS genes and an Ara− phenotype suggests a role for TTS in virulence.

An experimental study of the physiological effects of chain saw operation.

Miyakita, T; Miura, H; Futatsuka, M
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /01/1987 Português
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This experimental study was designed to determine whether a combination of noise and vibration produced more pronounced changes in temporary shifts of finger skin temperature and temporary threshold shift (TTS) of hearing than those resulting from exposure to either stress alone. Nineteen healthy subjects were exposed to six different combinations of vibration, noise, and handle holding by using a chain saw for a pre-determined time. The mean value of normalised finger skin temperature decreased much more when the subjects operated a chain saw at high speed (exposure 1) than when they operated the chain saw with the noise isolated by double hearing protection (exposure 2). In five of the 14 subjects significantly larger TTS values at 4 kHz were observed in the former condition (exposure 1) compared with the values obtained when they stood beside someone else operating a chain saw (exposure 3). The results of this study suggest that noise may play a part in inducing the constriction of the peripheral vessels seen with local exposure to vibration, and that hand-arm vibration may produce an additive effect on the noise induced TTS.

Factors influencing vibration sense thresholds used to assess occupational exposures to hand transmitted vibration.

Harada, N; Griffin, M J
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /03/1991 Português
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The effects of various conditions, including temporary threshold shifts (TTS) induced by exposure to vibration on vibration sense thresholds, have been investigated. The vibration sense thresholds of five subjects were measured on the middle fingertip of the left hand. A contactor with a diameter of 7 mm was surrounded by three alternative plates with holes of different sizes. The contact force was controlled at either 1 N, 2 N, or 3 N. For the TTS test, the left hand was exposed to vibration at 20 ms-2 rms for five minutes. The frequencies of both the exposure to vibration and the vibration threshold test were in the range 16 Hz to 500 Hz. Using a surround around the contactor greatly reduced the vibration sense threshold at 16 Hz and 31.5 Hz but increased the threshold at 125 Hz, 250 Hz, and 500 Hz. An effect of contact force was seen only at the higher frequencies; larger contact forces led to lower thresholds at 125 Hz, 250 Hz, and 500 Hz. As temperature of the finger skin decreased, the vibration thresholds increased, with the changes at higher frequencies greater than those at lower frequencies. The TTS at 16 Hz and 31.5 Hz measured 0.5 minutes after exposure to vibration (TTS0.5) were highest after exposures to vibration at lower frequencies. The TTS0.5 at 63 Hz was similar after exposure to all frequencies. The TTS0.5 values at 125 Hz...

Domain Structure of HrpE, the Hrp Pilus Subunit of Xanthomonas campestris pv. vesicatoria

Weber, Ernst; Koebnik, Ralf
Fonte: American Society for Microbiology Publicador: American Society for Microbiology
Tipo: Artigo de Revista Científica
Publicado em /09/2005 Português
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The plant-pathogenic bacterium Xanthomonas campestris pv. vesicatoria possesses a type III secretion (TTS) system necessary for pathogenicity in susceptible hosts and induction of the hypersensitive response in resistant plants. This specialized protein transport system is encoded by a 23-kb hrp (hypersensitive response and pathogenicity) gene cluster. X. campestris pv. vesicatoria produces filamentous structures, Hrp pili, at the cell surface under hrp-inducing conditions. The Hrp pilus acts as a cell surface appendage of the TTS system and serves as a conduit for the transfer of bacterial effector proteins into the plant cell cytosol. The major pilus component, the HrpE pilin, is unique to xanthomonads and is encoded within the hrp gene cluster. In this study, functional domains of HrpE were mapped by linker-scanning mutagenesis and by reporter protein fusions to an N-terminally truncated avirulence protein (AvrBs3Δ2). Thirteen five-amino-acid peptide insertion mutants were obtained and could be grouped into six phenotypic classes. Three permissive mutations were mapped in the N-terminal half of HrpE, which is weakly conserved within the HrpE protein family. Four dominant-negative peptide insertions in the strongly conserved C-terminal region suggest that this domain is critical for oligomerization of the pilus subunits. Reporter protein fusions revealed that the N-terminal 17 amino acid residues act as an efficient TTS signal. From these results...

Structure of Spa15, a type III secretion chaperone from Shigella flexneri with broad specificity

van Eerde, André; Hamiaux, Cyril; Pérez, Javier; Parsot, Claude; Dijkstra, Bauke W
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Português
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Type III secretion (TTS) systems are used by many Gram-negative pathogens to inject virulence proteins into the cells of their hosts. Several of these virulence effectors require TTS chaperones that maintain them in a secretion-competent state. Whereas most chaperones bind only one effector, Spa15 from the human pathogen Shigella flexneri and homologous chaperones bind several seemingly unrelated effectors, and were proposed to form a special subgroup. Its 1.8 Å crystal structure confirms this specific classification, showing that Spa15 has the same fold as other TTS effector chaperones, but forms a different dimer. The presence of hydrophobic sites on the Spa15 surface suggests that the different Spa15 effectors all possess similar structural elements that can bind these sites. Furthermore, the Spa15 structure reveals larger structural differences between class I chaperones than previously anticipated, which does not support the hypothesis that chaperone–effector complexes are structurally conserved and function as three-dimensional secretion signals.

Numerical analysis of Ca2+ depletion in the transverse tubular system of mammalian muscle.

Friedrich, O; Ehmer, T; Uttenweiler, D; Vogel, M; Barry, P H; Fink, R H
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /05/2001 Português
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Calcium currents were recorded in contracting and actively shortening mammalian muscle fibers. In order to characterize the influence of extracellular calcium concentration changes in the small unstirred lumina of the transverse tubular system (TTS) on the time course of the slow L-type calcium current (I(Ca)), we have combined experimental measurements of I(Ca) with quantitative numerical simulations of Ca2+ depletion. I(Ca) was recorded both in calcium-buffered and unbuffered external solutions using the two-microelectrode voltage clamp technique (2-MVC) on short murine toe muscle fibers. A simulation program based on a distributed TTS model was used to calculate the effect of ion depletion in the TTS. The experimental data obtained in a solution where ion depletion is suppressed by a high amount of a calcium buffering agent were used as input data for the simulation. The simulation output was then compared with experimental data from the same fiber obtained in unbuffered solution. Taking this approach, we could quantitatively show that the calculated Ca2+ depletion in the transverse tubular system of contracting mammalian muscle fibers significantly affects the time-dependent decline of Ca2+ currents. From our findings, we conclude that ion depletion in the tubular system may be one of the major effects for the I(Ca) decline measured in isotonic physiological solution under voltage clamp conditions.

Determination of Atmospheric Parameters of T Tauri Stars

Schiavon, R. Piorno; Batalha, C.; Barbuy, B.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
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The inferred effective temperatures (T$_{\rm eff}$) and surface gravities of T Tauri stars (TTS) are usually contaminated by the presence of a non stellar continuum emission (veiling) and the strong chromospheric activity characteristic of these objects. In this work, we develop a method to determine T$_{\rm eff}$'s and surface gravities (log$\,g$) of a group of TTS. This method is based on the comparison between observed and theoretical molecular and atomic line depth ratios being therefore insensitive to the influence of veiling. We show the strong dependence of our line depth ratios upon gravity and temperature. The resulting gravities, as expected for TTS, average between the values of dwarf and giant stars. Previously published gravities for each of our stars vary widely due in part to the differences in the adopted visual extinction, veiling (if ever considered) and methods of assessing the stellar luminosity. Our values of T$_{\rm eff}$ and log$\,g$ have the uniqueness of being entirely derived from high resolution data and are not affected by circumstellar extinction or veiling when line ratios are used. They therefore serve as more reliable input parameters for future spectral synthesis analyses of T Tauri Stars requiring model atmospheres. We provide a table relating theoretical line depth ratio with T$_{\rm eff}$ and log $\...

Polarimetry of DG Tau at 350 microns

Krejny, M.; Matthews, T.; Novak, G.; Cho, J.; Li, H.; Shinnaga, H.; Vaillancourt, J. E.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 06/03/2009 Português
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We present the first 350 micron polarization measurement for the disk of the T Tauri star (TTS) DG Tau. The data were obtained using the SHARP polarimeter at the Caltech Submillimeter Observatory. We did not detect polarization but we provide constraints on the normalized Stokes parameters q and u. We derive information about the polarization spectrum by comparing our 350 micron result with an 850 micron polarization detection previously published for this source. This empirical information concerning the polarization spectrum disagrees with the predictions of a recent model for TTS disk polarization. We conclude, however, that adding more mass to the model disk would probably result in model polarization spectra that agree much better with the 350 and 850 micron polarimetric observations. We suggest that multiwavelength polarimetry of TTS disk emission may provide a promising method for probing the opacity of TTS disks.; Comment: 20 pages, 2 figures, one table

ROSAT PSPC observations of T Tauri stars in MBM12

Hearty, T.; Neuhauser, R.; Stelzer, B.; Fernandez, M.; Alcala, J. M.; Covino, E.; Hambaryan, V.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 14/11/1999 Português
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We present the ROSAT PSPC pointed and ROSAT All-Sky Survey (RASS) observations and the results of our low and high spectral resolution optical follow-up observations of the T Tauri stars (TTS) and X-ray selected T Tauri star candidates in the region of the high galactic latitude dark cloud MBM12 (L1453-L1454, L1457, L1458). Previous observations have revealed 3 "classical" T Tauri stars and 1 "weak-line" T Tauri star along the line of sight to the cloud. Because of the proximity of the cloud to the sun, all of the previously known TTS along this line of sight were detected in the 25 ks ROSAT PSPC pointed observation of the cloud. We conducted follow-up optical spectroscopy at the 2.2-meter telescope at Calar Alto to look for signatures of youth in additional X-ray selected T Tauri star candidates. These observations allowed us to confirm the existence of 4 additional TTS associated with the cloud and at least 2 young main sequence stars that are not associated with the cloud and place an upper limit on the age of the TTS in MBM12 ~ 10 Myr. The distance to MBM12 has been revised from the previous estimate of 65+-5 pc to 65+-35 pc based on results of the Hipparcos satellite. At this distance MBM12 is the nearest known molecular cloud to the sun with recent star formation. We estimate a star-formation efficiency for the cloud of 2-24%. We have also identified a reddened G9 star behind the cloud with Av ~ 8.4-8.9 mag. Therefore...

Improved kinematics for brown dwarfs and very low-mass stars in ChaI and a discussion of brown dwarf formation

Joergens, V.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
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We present a precise kinematic study of very young brown dwarfs (BDs) in the ChaI cloud based on radial velocities (RVs) measured with UVES / VLT. This is compared to the kinematics of T Tauri stars (TTS) in the same field, based on both own measurements and on RVs from the literature. More UVES spectra were taken compared with a former paper (Joergens & Guenther 2001), and the reduction of the spectra was improved, while studying the literature for RVs of T Tauri stars in ChaI led to a cleaned and enlarged sample of T Tauri stars. The result is an improved empirical RV distribution of BDs as well as of TTS in ChaI. We found that nine BDs/VLMSs (M6-M8) in ChaI have a RV dispersion of 0.9 km/s measured in terms of a standard deviation. This is consistent with the dispersion measured earlier in terms of fwhm of 2.1 km/s. The studied sample of 25 TTS (G2-M5) has a dispersion of 1.3 km/s (standard deviation). The RV dispersion of the BDs is consistent within the errors with that of TTS, which is in line with the finding of no mass dependence in some theoretical models of the ejection-scenario for the formation of brown dwarfs. In contrast to current N-body simulations, we did not find a high-velocity tail for the BDs RVs. We found hints suggesting different kinematics for binaries compared to predominantly single objects in ChaI. The global RV dispersion for ChaI members (1.24 km/s) is significantly lower than for Taurus members (2.0 km/s)...

Mid-Infrared Observations of Class I/Flat-Spectrum Systems in Six Nearby Molecular Clouds

Haisch Jr., Karl E.; Barsony, Mary; Ressler, Michael E.; Greene, Thomas P.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 08/09/2006 Português
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We have obtained new mid-infrared observations of 65 Class I/Flat-Spectrum (F.S.) objects in the Perseus, Taurus, Chamaeleon I/II, Rho Ophiuchi, and Serpens dark clouds. We detected 45/48 (94%) of the single sources, 16/16 (100%) of the primary components, and 12/16 (75%) of the secondary/triple components of the binary/multiple objects surveyed. The composite spectral energy distributions (SEDs) for all of our sample sources are either Class I or F.S., and, in 15/16 multiple systems, at least one of the individual components displays a Class I or F.S. spectral index. However, the occurrence of mixed pairings, such as F.S. with Class I, F.S. with Class II, and, in one case, F.S. with Class III, is surprisingly frequent. Such behaviour is not consistent with that of multiple systems among T Tauri stars (TTS), where the companion of a classical TTS also tends to be a classical TTS, although other mixed pairings have been previously observed among Class II objects. Based on an analysis of the spectral indices of the individual binary components, there appears to be a higher proportion of mixed Class I/F.S. systems (65-80%) than that of mixed Classical/Weak-Lined TTS (25-40%), demonstrating that the envelopes of Class I/ F.S. systems are rapidly evolving during this evolutionary phase. We report the discovery of a steep spectral index secondary companion to ISO-ChaI 97...

MN Lup: X-rays from a weakly accreting T Tauri star

Guenther, H. M.; Wolter, U.; Robrade, J.; Wolk, S. J.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 14/05/2013 Português
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Young T Tauri stars (TTS) are surrounded by an accretion disk, which over time disperses due to photoevaporation, accretion, and possibly planet formation. The accretion shock on the central star produces an UV/optical veiling continuum, line emission, and X-ray signatures. As the accretion rate decreases, the impact on the central star must change. In this article we study MN Lup, a young star where no indications of a disk are seen in IR observations. We present XMM-Newton and VLT/UVES observations, some of them taken simultaneously. The X-ray data show that MN Lup is an active star with L_X/L_bol close to the saturation limit. However, we find high densities (n_e > 3e10 /cm^3) in the X-ray grating spectrum. This can be well fitted using an accretion shock model with an accretion rate of 2e-11 M_sun/yr. Despite the simple Halpha line profile which has a broad component, but no absorption signatures as typically seen on accreting TTS, we find rotational modulation in Ca II K and in photospheric absorption lines. In the Halpha line we see a prominence in absorption about 2R_* above the stellar surface - the first of its kind on a TTS. MN Lup is also the only TTS where accretion is seen, but no dust disk is detected that could fuel it. We suggest that MN Lup presents a unique and short-lived state in the disk evolution. It may have lost its dust disk only recently and is now accreting the remaining gas at a very low rate.; Comment: 13 pages...

Polarimetry of DG TAU at 350 μm

Krejny, M.; Matthews, T. G.; Novak, G.; Chow, J.; Li, H.; Shinnaga, H.; Vaillancourt, J. E.
Fonte: American Astronomical Society Publicador: American Astronomical Society
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em 01/11/2009 Português
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We present the first 350 μm polarization measurement for the disk of the T Tauri star (TTS) DG Tau. The data were obtained using the SHARP polarimeter at the Caltech Submillimeter Observatory. We measured normalized Stokes parameters q= –0.0086 ± 0.0060 and u = –0.0012 ± 0.0061, which gives a 2σ upper limit for the percent polarization of 1.7%. We obtain information about the polarization spectrum by comparing our 350 μm measurement with an 850 μm polarization detection previously published for this source. Comparing the two measurements in Stokes space (not in percent polarization) shows that the two data points are not consistent, i.e., either the degree of polarization or the angle of polarization (or both) must change significantly as one moves from 850 μm to 350 μm. This conclusion concerning the polarization spectrum disagrees with the predictions of a recent model for TTS disk polarization. We show that this discrepancy can be explained by optical depth effects. Specifically, we demonstrate that if one were to add more mass to the model disk, one would expect to obtain a model polarization spectrum in which the polarization degree falls sharply with increasing frequency, consistent with the observations at the two wavelengths. We suggest that multiwavelength polarimetry of TTS disk emission may provide a promising method for probing the opacity of TTS disks.