249 research outputs found
The circumstellar environment of HD50138 revealed by VLTI/AMBER at high angular resolution
HD50138 is a Herbig B[e] star with a circumstellar disc detected at IR and mm
wavelength. Its brightness makes it a good candidate for NIR interferometry
observations. We aim to resolve, spatially and spectrally, the continuum and
hydrogen emission lines in the 2.12-2.47 micron region, to shed light on the
immediate circumstellar environment of the star. VLTI/AMBER K-band observations
provide spectra, visibilities, differential phases, and closure phases along
three long baselines for the continuum, and HI emission in Br and five
high-n Pfund lines. By computing the pure-line visibilities, we derive the
angular size of the different line-emitting regions. A simple LTE model was
created to constrain the physical conditions of HI emitting region. The
continuum region cannot be reproduced by a geometrical 2D elongated Gaussian
fitting model. We estimate the size of the region to be 1 au. We find the
Br and Pfund lines come from a more compact region of size 0.4 au. The
Br line exhibits an S-shaped differential phase, indicative of
rotation. The continuum and Br line closure phase show offsets of
-255 and 2010, respectively. This is evidence of an
asymmetry in their origin, but with opposing directions. We find that we cannot
converge on constraints for the HI physical parameters without a more detailed
model. Our analysis reveals that HD50138 hosts a complex circumstellar
environment. Its continuum emission cannot be reproduced by a simple disc
brightness distribution. Similarly, several components must be evoked to
reproduce the interferometric observables within the Br, line.
Combining the spectroscopic and interferometric data of the Br and
Pfund lines favours an origin in a wind region with a large opening angle.
Finally, our results point to an evolved source.Comment: accepted for publication in A&
Exploring the dimming event of RW Aur A through multi-epoch VLT/X-Shooter spectroscopy
RW Aur A is a CTTS that has suddenly undergone three major dimming events
since 2010. We aim to understand the dimming properties, examine accretion
variability, and derive the physical properties of the inner disc traced by the
CO ro-vibrational emission at NIR wavelengths (2.3 mic).
We compared two epochs of X-Shooter observations, during and after the
dimming. We modelled the rarely detected CO bandhead emission in both epochs to
examine whether the inner disc properties had changed. The SED was used to
derive the extinction properties of the dimmed spectrum and compare the
infrared excess between the two epochs. Lines tracing accretion were used to
derive the mass accretion rate in both states. The CO originates from a region
with physical properties of T=3000 K, N=1x10 cm and
vsini=113 km/s. The extinction properties of the dimming layer were derived
with the effective optical depth ranging from teff 2.5-1.5 from the UV to the
NIR. The inferred mass accretion rate Macc is Msun/yr and Msun/yr after and during the dimming respectively. By fitting the
SED, additional emission is observed in the IR during the dimming event from
dust grains with temperatures of 500-700K. The physical conditions traced by
the CO are similar for both epochs, indicating that the inner gaseous disc
properties do not change during the dimming events. The extinction curve is
flatter than that of the ISM, and large grains of a few hundred microns are
thus required. When we correct for the observed extinction, Macc is constant in
the two epochs, suggesting that the accretion is stable and therefore does not
cause the dimming. The additional hot emission in the NIR is located at about
0.5 au from the star. The dimming events could be due to a dust-laden wind, a
severe puffing-up of the inner rim, or a perturbation caused by the recent
star-disc encounter.Comment: Accepted by Astronomy & Astrophysic
Floristic composition of weeds in different winter and summer covers.
The usage of cover crops is an adopted cultural measure that shows positive effects when associated with the no-till system and weed management. During the cycle of the plants there might be competition within them for water, solar radiation and nutrients and effects of allelopathic substances released by leaching, volatilization and/or root exudation in the environment might also coexist. The study aimed to quantify the floristic composition of weed species in an cultivated area with cover crops during winter and summer, for two years, 2011/12 and 2012/13, in an experimental area of UFSM, Campus of Frederico Westphalen ? RS state, Brazil. The treatments consisted of Italian ryegrass, wild radish, black oat, vetch, wheat and uncultivated, in winter, and, sorghum, sunflower, black velvet bean, dwarf velvet bean, gray velvet bean and green velvet bean in the summer. In the first year of the experiment, a diversity of weeds in winter was observed, especially occuring Stellaria media and Bowlesia incana. In summer, the weeds of higher importance were Ipomoea spp. and Bidens spp., both of utter importance in agricultural systems. Winter cover crops of wild radish and Italian ryegrass and summer cover crops of sorghum and sunflower provided a lower weed infestatio
Corrections to Einstein's relation for Brownian motion in a tilted periodic potential
In this paper we revisit the problem of Brownian motion in a tilted periodic
potential. We use homogenization theory to derive general formulas for the
effective velocity and the effective diffusion tensor that are valid for
arbitrary tilts. Furthermore, we obtain power series expansions for the
velocity and the diffusion coefficient as functions of the external forcing.
Thus, we provide systematic corrections to Einstein's formula and to linear
response theory. Our theoretical results are supported by extensive numerical
simulations. For our numerical experiments we use a novel spectral numerical
method that leads to a very efficient and accurate calculation of the effective
velocity and the effective diffusion tensor.Comment: 29 pages, 7 figures, submitted to the Journal of Statistical Physic
AMBER/VLTI high spectral resolution observations of the Br emitting region in HD 98922. A compact disc wind launched from the inner disc region
We analyse the main physical parameters and the circumstellar environment of
the young Herbig Be star HD 98922. We present AMBER/VLTI high spectral
resolution (R =12000) interferometric observations across the Br line,
accompanied by UVES high-resolution spectroscopy and SINFONI-AO assisted
near-infrared integral field spectroscopic data. To interpret our observations,
we develop a magneto-centrifugally driven disc-wind model. Our analysis of the
UVES spectrum shows that HD 98922 is a young (~5x10^5 yr) Herbig Be star
(SpT=B9V), located at a distance of 440(+60-50) pc, with a mass accretion rate
of ~9+/-3x10^(-7) M_sun yr^(-1). SINFONI K-band AO-assisted imaging shows a
spatially resolved circumstellar disc-like region (~140 AU in diameter) with
asymmetric brightness distribution. Our AMBER/VLTI UT observations indicate
that the Br emitting region (radius ~0.31+/-0.04 AU) is smaller than
the continuum emitting region (inner dust radius ~0.7+/-0.2 AU), showing
significant non-zero V-shaped differential phases (i.e. non S-shaped, as
expected for a rotating disc). The value of the continuum-corrected pure
Br line visibility at the longest baseline (89 m) is ~0.8+/-0.1, i.e.
the Br emitting region is partially resolved. Our modelling suggests
that the observed Br line-emitting region mainly originates from a disc
wind with a half opening angle of 30deg, and with a mass-loss rate of ~2x10(-7)
M_sun yr^(-1). The observed V-shaped differential phases are reliably
reproduced by combining a simple asymmetric continuum disc model with our
Br disc-wind model. The Br emission of HD 98922 can be modelled
with a disc wind that is able to approximately reproduce all interferometric
observations if we assume that the intensity distribution of the dust continuum
disc is asymmetric.Comment: Accepted for publication on Astronomy \& Astrophysics. High
resolution figures published on the main journal (see Astronomy &
Astrophysics: Forthcoming) or at
www.researchgate.net/profile/Alessio_Caratti_o_Garatti/publication
Relative yield of wheat in coexistence with concurrent plants as indicator of competitiveness.
One of the factors that limit the yield of wheat is the weed competition, being the competitive potential of plants affected by their morphophysiological characteristics. The objective of this study was to determine the competitiveness of wheat when in coexistence with Italian ryegrass (Lolium multiflorum) and radish (Raphanus sativus) competitive plants or with wheat as simulator competition plant. There were realized four experiments in the greenhouse of the Agricultural Department of Environmental Sciences of the UFSM, Campus of Frederico Westphalen ? RS, during July to September, 2012. The treatments were arranged in a replacement series, in the proportions of 100:00 (wheat monoculture), 75:25, 50:50, 25:75 and 100:00 (competitor plant monoculture) for wheat plants (cv. Fundacep Cristalino) and for Italian ryegrass, radish and wheat (cv. BRS Guamirim) as competitor plants. The wheat is more competitive than Italian ryegrass in initial coexistence, even in the smallest proportion of plants. The radish when intercropped with wheat demonstrates similar competitive potential for environmental resources to the crop. There is mutual beneficial effect when wheat cultivars Fundacep Cristalino and BRS Guamirim coexisted, and each cultivar seems to have mechanism to avoid competition
Ocorrência de capim-annoni no banco de sementes do solo de áreas infestadas.
O objetivo do trabalho foi caracterizar e comparar o banco de sementes do solo de campo nativo infestado por capim-annoni, após anos de adoção do Método Integrado de Recuperação de Pastagens - MIRAPASTO e de sistema de Integração Lavoura-Pecuária ? ILP, através da avaliação da distribuição vertical de sementes da planta indesejável no perfil do solo.bitstream/item/218527/1/BPD-46-online.pd
Investigating episodic accretion in a very low-mass young stellar object
Very low-mass Class I protostars have been investigated very little thus far.
Variability of these young stellar objects (YSOs) and whether or not they are
capable of strong episodic accretion is also left relatively unstudied. We
investigate accretion variability in IRS54, a Class I very low-mass protostar
with a mass of M ~ 0.1 - 0.2 M. We obtained spectroscopic
and photometric data with VLT/ISAAC and VLT/SINFONI in the near-infrared (,
, and bands) across four epochs (2005, 2010, 2013, and 2014). We used
accretion-tracing lines (Pa and Br) and outflow-tracing lines
(H and [FeII] to examine physical properties and kinematics of the object.
A large increase in luminosity was found between the 2005 and 2013 epochs of
more than 1 magnitude in the band, followed in 2014 by a steep decrease.
Consistently, the mass accretion rate () rose by an order of
magnitude from ~ 10 M yr to ~ M
yr between the two early epochs. The visual extinction () has also
increased from ~ 15 mag in 2005 to ~ 24 mag in 2013. This rise in in
tandem with the increase in is explained by the lifting up of a
large amount of dust from the disc of IRS54, following the augmented accretion
and ejection activity in the YSO, which intersects our line of sight due to the
almost edge-on geometry of the disc. Because of the strength and timescales
involved in this dramatic increase, this event is believed to have been an
accretion burst possibly similar to bursts of EXor-type objects. IRS54 is the
lowest mass Class I source observed to have an accretion burst of this type,
and therefore potentially one of the lowest mass EXor-type objects known so
far
LBT/LUCIFER near-infrared spectroscopy of PV Cephei. An outbursting young stellar object with an asymmetric jet
We present a detailed spectroscopic investigation of the young eruptive star
PV Cep, to improve our understanding of its nature and characterise its
circumstellar environment after its last outburst in 2004. The analysis of our
medium-resolution spectroscopy in the near-IR (0.9-2.35 um), collected in 2012
at the Large Binocular Telescope with the IR spectrograph LUCIFER, allows us to
infer the main stellar parameters (visual extinction, accretion luminosity,
mass accretion and ejection rates), and model the inner disc, jet, and wind.
The NIR spectrum displays several strong emission lines associated with
accretion/ejection activity and circumstellar environment. Our analysis shows
that the brightness of PV Cep is fading, as well as the mass accretion rate
(2x10^-7 Msun/yr^-1 in 2012 vs ~5x10^-6 Msun/yr^-1 in 2004), which is more than
one order of magnitude lower than in the outburst phase. Among the several
emission lines, only the [FeII] intensity increased after the outburst. The
observed [FeII] emission delineates blue- and red-shifted lobes, both with
high- and low-velocity components, which trace an asymmetric jet and wind,
respectively. The observed emission in the jet has a dynamical age of ~8 years,
indicating that it was produced during the last outburst. The mass ejection
rate in both lobes is 1.5x10^-7 Msun/yr^-1, approximately matching the high
accretion rate observed during and immediately after the outburst . The
observed jet/outflow asymmetries are consistent with an inhomogeneous medium.
Our modelling of the CO emission hints at a small-scale gaseous disc ring,
extending from ~0.2-0.4 AU to ~3 AU from the source, with an inner temperature
of ~3000 K. Our HI lines modelling indicates that most of the observed emission
comes from an expanding disc wind at Te=10000 K. The line profiles are strongly
affected by scattering, disc screening, and outflow self-absorption.Comment: To be published in A&
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