191 research outputs found
Caracterização das plantas daninhas em áreas de sistemas de preparo de solo de longa duração.
bitstream/item/211242/1/Cot-241.pd
Accreting Protoplanets in the LkCa 15 Transition Disk
Exoplanet detections have revolutionized astronomy, offering new insights
into solar system architecture and planet demographics. While nearly 1900
exoplanets have now been discovered and confirmed, none are still in the
process of formation. Transition discs, protoplanetary disks with inner
clearings best explained by the influence of accreting planets, are natural
laboratories for the study of planet formation. Some transition discs show
evidence for the presence of young planets in the form of disc asymmetries or
infrared sources detected within their clearings, as in the case of LkCa 15.
Attempts to observe directly signatures of accretion onto protoplanets have
hitherto proven unsuccessful. Here we report adaptive optics observations of
LkCa 15 that probe within the disc clearing. With accurate source positions
over multiple epochs spanning 2009 - 2015, we infer the presence of multiple
companions on Keplerian orbits. We directly detect H{\alpha} emission from the
innermost companion, LkCa 15 b, evincing hot (~10,000 K) gas falling deep into
the potential well of an accreting protoplanet.Comment: 35 pages, 3 figures, 1 table, 9 extended data item
The brightest gamma-ray flaring blazar in the sky: AGILE and multi-wavelength observations of 3C 454.3 during November 2010
Since 2005, the blazar 3C 454.3 has shown remarkable flaring activity at all
frequencies, and during the last four years it has exhibited more than one
gamma-ray flare per year, becoming the most active gamma-ray blazar in the sky.
We present for the first time the multi-wavelength AGILE, SWIFT, INTEGRAL, and
GASP-WEBT data collected in order to explain the extraordinary gamma-ray flare
of 3C 454.3 which occurred in November 2010. On 2010 November 20 (MJD 55520),
3C 454.3 reached a peak flux (E>100 MeV) of F_gamma(p) = (6.8+-1.0)E-5 ph/cm2/s
on a time scale of about 12 hours, more than a factor of 6 higher than the flux
of the brightest steady gamma-ray source, the Vela pulsar, and more than a
factor of 3 brighter than its previous super-flare on 2009 December 2-3. The
multi-wavelength data make a thorough study of the present event possible: the
comparison with the previous outbursts indicates a close similarity to the one
that occurred in 2009. By comparing the broadband emission before, during, and
after the gamma-ray flare, we find that the radio, optical and X-ray emission
varies within a factor 2-3, whereas the gamma-ray flux by a factor of 10. This
remarkable behavior is modeled by an external Compton component driven by a
substantial local enhancement of soft seed photons.Comment: Accepted for publication in ApJ Letters. 18 Pages, 4 Figures, 1 Tabl
Accreting protoplanets: Spectral signatures and magnitude of gas and dust extinction at H α
Context. Accreting planetary-mass objects have been detected at H α, but targeted searches have mainly resulted in non-detections. Accretion tracers in the planetary-mass regime could originate from the shock itself, making them particularly susceptible to extinction by the accreting material. High-resolution (R > 50 000) spectrographs operating at H α should soon enable one to study how the incoming material shapes the line profile.
Aims. We calculate how much the gas and dust accreting onto a planet reduce the H α flux from the shock at the planetary surface and how they affect the line shape. We also study the absorption-modified relationship between the H α luminosity and accretion rate.
Methods. We computed the high-resolution radiative transfer of the H α line using a one-dimensional velocity–density–temperature structure for the inflowing matter in three representative accretion geometries: spherical symmetry, polar inflow, and magnetospheric accretion. For each, we explored the wide relevant ranges of the accretion rate and planet mass. We used detailed gas opacities and carefully estimated possible dust opacities.
Results. At accretion rates of Ṁ ≲ 3 × 10−6 MJ yr−1, gas extinction is negligible for spherical or polar inflow and at most AH α ≲ 0.5 mag for magnetospheric accretion. Up to Ṁ ≈ 3 × 10−4 MJ yr−1, the gas contributes AH α ≲ 4 mag. This contribution decreases with mass. We estimate realistic dust opacities at H α to be κ ~ 0.01–10 cm2 g−1, which is 10–104 times lower than in the interstellar medium. Extinction flattens the LH α –Ṁ relationship, which becomes non-monotonic with a maximum luminosity LH α ~ 10−4 L⊙ towards Ṁ ≈ 10−4 MJ yr−1 for a planet mass ~10 MJ. In magnetospheric accretion, the gas can introduce features in the line profile, while the velocity gradient smears them out in other geometries.
Conclusions. For a wide part of parameter space, extinction by the accreting matter should be negligible, simplifying the interpretation of observations, especially for planets in gaps. At high Ṁ, strong absorption reduces the H α flux, and some measurements can be interpreted as two Ṁ values. Highly resolved line profiles (R ~ 105) can provide (complex) constraints on the thermal and dynamical structure of the accretion flow
Circumstellar discs: What will be next?
This prospective chapter gives our view on the evolution of the study of
circumstellar discs within the next 20 years from both observational and
theoretical sides. We first present the expected improvements in our knowledge
of protoplanetary discs as for their masses, sizes, chemistry, the presence of
planets as well as the evolutionary processes shaping these discs. We then
explore the older debris disc stage and explain what will be learnt concerning
their birth, the intrinsic links between these discs and planets, the hot dust
and the gas detected around main sequence stars as well as discs around white
dwarfs.Comment: invited review; comments welcome (32 pages
Planetary population synthesis
In stellar astrophysics, the technique of population synthesis has been
successfully used for several decades. For planets, it is in contrast still a
young method which only became important in recent years because of the rapid
increase of the number of known extrasolar planets, and the associated growth
of statistical observational constraints. With planetary population synthesis,
the theory of planet formation and evolution can be put to the test against
these constraints. In this review of planetary population synthesis, we first
briefly list key observational constraints. Then, the work flow in the method
and its two main components are presented, namely global end-to-end models that
predict planetary system properties directly from protoplanetary disk
properties and probability distributions for these initial conditions. An
overview of various population synthesis models in the literature is given. The
sub-models for the physical processes considered in global models are
described: the evolution of the protoplanetary disk, the planets' accretion of
solids and gas, orbital migration, and N-body interactions among concurrently
growing protoplanets. Next, typical population synthesis results are
illustrated in the form of new syntheses obtained with the latest generation of
the Bern model. Planetary formation tracks, the distribution of planets in the
mass-distance and radius-distance plane, the planetary mass function, and the
distributions of planetary radii, semimajor axes, and luminosities are shown,
linked to underlying physical processes, and compared with their observational
counterparts. We finish by highlighting the most important predictions made by
population synthesis models and discuss the lessons learned from these
predictions - both those later observationally confirmed and those rejected.Comment: 47 pages, 12 figures. Invited review accepted for publication in the
'Handbook of Exoplanets', planet formation section, section editor: Ralph
Pudritz, Springer reference works, Juan Antonio Belmonte and Hans Deeg, Ed
A Large Double-ring Disk around the Taurus M Dwarf J04124068+2438157
Planet formation imprints signatures on the physical structures of disks. In
this paper, we present high-resolution (50 mas, 8 au) Atacama Large
Millimeter/submillimeter Array (ALMA) observations of 1.3 mm dust continuum and
CO line emission toward the disk around the M3.5 star 2MASS J04124068+2438157.
The dust disk consists only of two narrow rings at radial distances of 0.47 and
0.78 arcsec (70 and 116 au), with Gaussian widths of 5.6 and 8.5
au, respectively. The width of the outer ring is smaller than the estimated
pressure scale height by , suggesting dust trapping in a radial
pressure bump. The dust disk size, set by the location of the outermost ring,
is significantly larger (by ) than other disks with similar millimeter
luminosity, which can be explained by an early formation of local pressure bump
to stop radial drift of millimeter dust grains. After considering the disk's
physical structure and accretion properties, we prefer planet--disk interaction
over dead zone or photoevaporation models to explain the observed dust disk
morphology. We carry out high-contrast imaging at band using Keck/NIRC2 to
search for potential young planets, but do not identify any source above
. Within the dust gap between the two rings, we reach a contrast level
of 7 mag, constraining the possible planet below 2--4 . Analyses of the gap/ring properties suggest a Saturn mass planet
at 90 au is likely responsible for the formation of the outer ring, which
can be potentially revealed with JWST.Comment: 15 pages, 5 figures. Accepted for publication in Ap
Evaluation of gene amplification and protein expression of HER-2/neu in esophageal squamous cell carcinoma using Fluorescence in situ Hybridization (FISH) and immunohistochemistry
<p>Abstract</p> <p>Background</p> <p>Esophageal squamous cell carcinoma (ESCC) is the sixth most frequent neoplasia in Brazil. It is usually associated with a poor prognosis because it is often at an advanced stage when diagnosed and there is a high frequency of lymph node metastases. It is important to know what prognostic factors can facilitate diagnosis, optimize therapeutic decisions, and improve the survival of these patients. A member of the epidermal growth factor receptor (EGFR) family, c-erbB-2, has received much attention because of its therapeutic implications; however, few studies involving fluorescence <it>in situ </it>hybridization (FISH) analysis of HER-2/neu gene amplification and protein expression in ESCC have been conducted. The aim of this study was to verify the presence of HER-2/neu gene amplification using FISH, and to correlate the results with immunohistochemical expression and clinical-pathological findings.</p> <p>Methods</p> <p>One hundred and ninety-nine ESCC cases were evaluated using the Tissue Microarray (TMA) technique. A polyclonal antibody against c-erbB-2 was used for immunohistochemistry. Analyses were based on the membrane staining pattern. The results were classified according to the Herceptest criteria (DAKO): negative (0/1+), potential positive (2+) and positive (3+). The FISH reactions were performed according to the FISH HER2 PharmDx (DAKO) protocol. In each case, 100 tumor nuclei were evaluated. Cases showing a gene/CEN17 fluorescence ratio ≥ 2 were considered positive for gene amplification.</p> <p>Results</p> <p>The c-erbB-2 expression was negative in 117/185 cases (63.2%) and positive in 68 (36.8%), of which 56 (30.3%) were 2+ and 12 (6.5%) were 3+. No significant associations were found among protein expression, clinicopathological data and overall survival. Among the 47 cases analyzed, 38 (80.9%) showed no gene amplification while 9 (19.1%) showed amplification, as demonstrated by FISH. Cases that were negative (0/1+) and potential positive (2+) for c-erbB-2 expression by immunohistochemistry showed no gene amplification. However, all cases with gene amplification were positive (3+) by immunohistochemistry. According to univariate analysis, there was a significant difference (p = 0.003) in survival rates when cases with and without HER-2/neu amplification were compared.</p> <p>Conclusion</p> <p>Our data demonstrate the correspondence between gene amplification and protein expression of HER-2/neu. Gene amplification is an indicator of poor prognosis in ESCC.</p
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