637 research outputs found
Line-dependent veiling in very active T Tauri Stars
The T Tauri stars with active accretion disks show veiled photospheric
spectra. This is supposedly due to non-photospheric continuum radiated by hot
spots beneath the accretion shocks at stellar surface and/or chromospheric
emission lines radiated by the post-shocked gas. The amount of veiling is often
considered as a measure of the mass-accretion rate. We analysed high-resolution
photospheric spectra of accreting T Tauri stars LkHa 321, V1331 Cyg, and AS 353
A with the aim of clarifying the nature of the line-dependent veiling. Each of
these objects shows a highly veiled, strong emission line spectrum and powerful
wind features indicating high rates of accretion and mass loss. Equivalent
widths of hundreds of weak photospheric lines were measured in the observed
spectra and compared with those in synthetic spectra with the same spectral
type. We found that the veiling is strongly line-dependent: larger in stronger
photospheric lines and weak or absent in the weakest ones. No dependence of
veiling on excitation potential within 0 to 5 eV was found. Different physical
processes responsible for these unusual veiling effects are discussed in the
framework of the magnetospheric accretion model. The observed veiling has two
origins: 1) an abnormal structure of stellar atmosphere heated up by the
accreting matter, and 2) a non-photospheric continuum radiated by a hot spot
with temperature lower than 10000 K. The true level of the veiling continuum
can be derived by measuring the weakest photospheric lines with equivalent
widths down to 10 m\AA. A limited spectral resolution and/or low
signal-to-noise ratio results in overestimation of the veiling continuum. In
the three very active stars, the veiling continuum is a minor contributor to
the observed veiling, while the major contribution comes from the
line-dependent veiling.Comment: 10 pages, 10 figures. Accepted for publication in Astronomy and
Astrophysic
Deterministic and random phase synchronizers
This work study two groups of synchronizers, namely
the Deterministic Phase Synchronizer and the Random
Phase Synchronizer. The difference between them is only
inside of the phase comparator.
In the first group, the VCO (Voltage Controlled
Oscillator) synchronizes with the input deterministic
phase of an expected periodic transition. In the second
group the VCO synchronizes with the input random
phase of an unexpected no periodic transition.
Each group is studied under four topologies (analog,
hybrid, combinational and sequential).
The objective is to evaluate the two synchronizers
groups with the four topologies and to observe their jitter
behaviors with the noise
Facing the wind of the pre-FUor V1331 Cyg
The mass outflows in T Tauri stars (TTS) are thought to be an effective
mechanism to remove angular momentum during the pre-main-sequence contraction
of a low-mass star. The most powerful winds are observed at the FUor stage of
stellar evolution. V1331 Cyg has been considered as a TTS at the pre-FUor
stage. We analyse high-resolution spectra of V1331 Cyg collected in 1998-2007
and 20-d series of spectra taken in 2012. For the first time the photospheric
spectrum of the star is detected and stellar parameters are derived: spectral
type G7-K0 IV, mass 2.8 Msun, radius 5 Rsun, vsini < 6 km/s. The photospheric
spectrum is highly veiled, but the amount of veiling is not the same in
different spectral lines, being lower in weak transitions and much higher in
strong transitions. The Fe II 5018, Mg I 5183, K I 7699 and some other lines of
metals are accompanied by a `shell' absorption at radial velocity of about -240
km/s. We show that these absorptions form in the post-shock gas in the jet,
i.e. the star is seen though its jet. The P Cyg profiles of H-alpha and H-beta
indicate the terminal wind velocity of about 500 km/s, which vary on
time-scales from several days to years. A model of the stellar wind is
developed to interpret the observations. The model is based on calculation of
hydrogen spectral lines using the radiative transfer code TORUS. The observed
H-alpha and H-beta line profiles and their variability can be well reproduced
with a stellar wind model, where the mass-loss rate and collimation (opening
angle) of the wind are variable. The changes of the opening angle may be
induced by small variability in magetization of the inner disc wind. The
mass-loss rate is found to vary within (6-11)x10^{-8} Msun/yr, with the
accretion rate of 2.0x10^{-6} Msun/yr.Comment: 11 pages, 12 figures; accepted for publication in MNRAS.
Typographical errors have been corrected after the proof stag
CaII Infrared triplet line models in Classical T Tauri stars
We study the formation of the calcium II infrared triplet lines 8498\AA,
8542\AA and 8662\AA, in the accreting magnetospheric flows of Classical T Tauri
stars (CTTS), and present a grid of models for a large range of magnetospheric
conditions. We apply our models to the interpretation of multi epoch
observations of the CTTS DI Cep. We find that these lines form in the
magnetospheric infall and that the variability of the CaII triplet lines in DI
Cep can be explained in the context of changes in the mass accretion
rate/temperature of the accretion column gas
Megapróteses revestidas a prata
As endomegapróteses representam cada vez mais uma solução cirúrgica em situações de perdas ósseas significativas no contexto da cirurgia oncológica, em cirurgia reconstrutiva traumática e em cirurgia de recolocações de próteses articulares. Todavia, estão sujeitas a diferentes tipos de complicações que podem levar, a curto ou a longo prazo, à sua falência mecânica.
A principal e mais devastadora é a infeção periprotética (IPP). Esta complicação desenvolve-se, uma vez que a alargada superfície da prótese permite a colonização bacteriana, com produção de biofilme, tornando a infeção difícil de erradicar.
A prata, aliando a sua ação antibacteriana à baixa toxicidade, tem sido utilizada para revestir estas MP com o intuito de prevenir e tratar esta complicação. Apesar disso, efeitos adversos relacionados com a prata, como a argiria local, já foram descritos.
A implantação de megapróteses revestidas a prata (MPR) é uma opção cirúrgica relativamente recente, no entanto a sua utilização parece estar associada a uma menor incidência da IPP, bem como a um tratamento mais eficaz e menos agressivo desta complicação, quando comparada com o uso de megapróteses não revestidas (MPNR). A implantação de MP tem demonstrado bons resultados funcionais e não parece haver diferença entre doentes com MPR e doentes com MPNR.
Quanto à argiria, o desenvolvimento desta complicação parece ser idiossincrático, uma vez que não foi encontrada relação com a massa de prata da prótese utilizada, nem com os níveis séricos de prata iónica (Ag+).
No entanto, são precisos mais estudos, preferencialmente prospetivos, controlados e randomizados, com grupos de doentes mais numerosos, com maiores períodos de recuo clínico, sobretudo na área da cirurgia de trauma e revisão de prótese para confirmar estes resultados, para que no futuro as MPR sejam a escolha de eleição sempre que as MP estejam indicadas.info:eu-repo/semantics/publishedVersio
Transformation of a Cutaneous Follicle Center Lymphoma to a Diffuse Large B-Cell Lymphoma—An Unusual Presentation
Primary cutaneous follicle center lymphoma (PCFCL) is characterized by a proliferation of follicle center cells in the skin. A definitive diagnosis is frequently delayed because of difficulties in interpretation of the histopathologic findings. It has an excellent prognosis with a 5-year survival over 95% and its risk of transformation has not been established. We describe a case report of man with a gastric diffuse large B-cell lymphoma (DLBCL) referred to our clinic because of nodules in the back that had gradually developed over a period of 10 years. A biopsy performed 3 years before was interpreted as reactive follicular hyperplasia. A new skin biopsy revealed a diffuse large B-cell lymphoma and immunoglobulin heavy chain gene rearrangements from the initial skin biopsy (PCBCL) and the DLBCL gastric biopsy were studied by polymerase chain reaction and an identical clonal rearrangement was detected which was highly suggestive of a transformation lymphoma
A Paraneoplastic Syndrome to Remember: A Case of Disseminated Intravascular Coagulation in Lung Cancer
Disseminated intravascular coagulation (DIC) is an acquired syndrome characterized by the widespread activation of coagulation. It can
present as an acute life-threatening emergency or as a chronic process. Mortality is highly dependent on the reversibility of the aetiology
and degree of coagulation impairment, so treatment of the underlying cause is vital. The authors present the case of a 57-year-old man
whose inaugural presentation of lung cancer was chronic DIC, characterized by three thrombotic events, followed by acute DIC, culminating
in death. Metastatic lung cancer was diagnosed only after death
Unveiling extremely veiled T Tauri stars
Photospheric absorption lines in classical T Tauri stars (CTTS) are weak
compared to normal stars. This so-called veiling is normally identified with an
excess continuous emission formed in shock-heated gas at the stellar surface
below the accretion streams. We have selected four stars (RW Aur A, RU Lup, S
CrA NW and S CrA SE) with unusually strong veiling to make a detailed
investigation of veiling versus stellar brightness and emission line strengths
for comparisons to standard accretion models. We have monitored the stars
photometrically and spectroscopically at several epochs. In standard accretion
models a variable accretion rate will lead to a variable excess emission.
Consequently, the stellar brightness should vary accordingly. We find that the
veiling of absorption lines in these stars is strongly variable and usually so
large that it would require the release of several stellar luminosities of
potential energy. At states of very large line dilution, the correspondingly
large veiling factors derived correlate only weakly with brightness. Moreover,
the emission line strengths violate the expected trend of veiling versus line
strength. The veiling can change dramatically in one night, and is not
correlated with the phase of the rotation periods found for two stars. We show
that in at least three of the stars, when the veiling becomes high, the
photospheric lines become filled-in by line emission, which produces large
veiling factors unrelated to changes in any continuous emission from shocked
regions. We also consider to what extent extinction by dust and electron
scattering in the accretion stream may affect veiling measures in CTTS. We
conclude that the degree of veiling cannot be used as a measure of accretion
rates in CTTS with rich emission line spectra.Comment: Accepted for publication in A&A Letters. New language-edited version.
(4 pages, 3 figures
Non-axisymmetric accretion on the classical TTS RW Aur A
(Abridged) High-resolution spectroscopic monitoring of RW Aur A was carried out in 1996, 1998 and 1999 with simultaneous B, V photometry. A multicomponent spectrum is revealed with a veiled photospheric spectrum, broad emissions, narrow emission lines of helium, and accretion, wind and shell features. Periodic modulations in many spectral features were found. The photospheric absorption lines show sinusoidal variations in radial velocity with an amplitude of +-6 km/s and a period of about 2.77 days. The radial velocities of the narrow emission lines of He vary with the same period but in anti-phase to the photospheric lines. The equivalent widths of the narrow emissions vary with a phase-shift with respect to the velocity curve. The strength of the red-shifted accretion components of Na D and other lines is also modulated with the same period. The broad emission lines of metals vary mostly with the double period of about 5.5 days. One unexpected result is that no correlation was found between the veiling and the brightness, although both varied in wide ranges. This is partly due to a contribution of the shell absorption to the photospheric line profiles, which make them vary in width and depth thus simulating lower veiling. Most of the observed features can be interpreted in the framework of non-axisymmetric magnetospheric accretion. We consider two possible models. In the first the asymmetry is induced by orbital motion of an invisible, low mass secondary, which also influences the gasflows around the star, the second considers rotational modulation of a single star with an inclined or asymmetric magnetosphere
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