1,273 research outputs found
Magnetism, rotation and accretion in Herbig Ae-Be stars
Studies of stellar magnetism at the pre-main sequence phase can provide
important new insights into the detailed physics of the late stages of star
formation, and into the observed properties of main sequence stars. This is
especially true at intermediate stellar masses, where magnetic fields are
strong and globally organised, and therefore most amenable to direct study.
This talk reviews recent high-precision ESPaDOnS observations of pre-main
sequence Herbig Ae-Be stars, which are yielding qualitatively new information
about intermediate-mass stars: the origin and evolution of their magnetic
fields, the role of magnetic fields in generating their spectroscopic activity
and in mediating accretion in their late formative stages, and the factors
influencing their rotational angular momentum.Comment: 8 page
Charged-Current Neutral Pion production at SciBooNE
SciBooNE, located in the Booster Neutrino Beam at Fermilab, collected data
from June 2007 to August 2008 to accurately measure muon neutrino and
anti-neutrino cross sections on carbon below 1 GeV neutrino energy. SciBooNE is
studying charged current interactions. Among them, neutral pion production
interactions will be the focus of this poster. The experimental signature of
neutrino-induced neutral pion production is constituted by two electromagnetic
cascades initiated by the conversion of the neutral pion decay photons, with an
additional muon in the final state for CC processes.
In this poster, I will present how we reconstruct and select charged-current
muon neutrino interactions producing neutral pions in SciBooNE.Comment: NuInt09 poster proceedings, 4 page
Characterisation of the magnetic field of the Herbig Be star HD 200775
After our recent discovery of four magnetic Herbig stars, we have decided to
study in detail one of them, HD 200775, to determine if its magnetic topology
is similar to that of the main sequence magnetic stars. With this aim, we
monitored this star in Stokes I and V over more than two years, using the new
spectropolarimeters ESPaDOnS at CFHT, and Narval at TBL. Using our data, we
find that HD 200775 is a double-lined spectroscopic binary system, whose
secondary seems similar, in temperature, to the primary. We determine the
luminosity ratio of the system, and using the luminosity of the system found in
literature, we derive the luminosity of both stars. From our measurements of
the radial velocities of both stars we determine the ephemeris and the orbital
parameters of the system. We have fitted 30 Stokes V profiles simultaneously,
using a chi2 minimisation method, with a decentered-dipole model. The best-fit
model provides a rotation period of 4.3281 d an inclination angle of 60
degrees, and a magnetic obliquity angle of 125 degrees. The polar strength of
the magnetic dipole field is 1000 G, which is decentered by 0.05 R* from the
center of the star. The derived magnetic field model is qualitatively identical
to those commonly observed in the Ap/Bp stars, which bring strong argument in
favour of the fossil field hypothesis, to explain the origin of the magnetic
fields in the main sequence Ap/Bp stars. Our determination of the inclination
of the rotation axis leads to a radius of the primary which is smaller than
that derived from the HR diagram position. This can be explained by a larger
intrinsic luminosity of the secondary relative to the primary, due to a larger
circumstellar extinction of the secondary relative to the primary.Comment: Accepted for publication in MNRAS, 14 pages, 10 figure
Patterns of antenal sensilla of Panstrongylus megistus from three Brazilian states
The objective of the present study was to analyze and describe the phenotype of the antennal sensilla of Panstrongylus megistus, one of the epidemiologically most important species of triatomines in Brazil. Specimens from the Brazilian states of Goiás (GO), Minas Gerais (MG), and Rio Grande do Sul (RS) were compared, based on studies of four types of sensilla on three antennal segments: thick-walled trichoid (TK), thin-walled trichoid (TH), bristles (BR), and basiconica (BA). Discriminant analysis allowed the separation of the RS specimens from those of GO and MG. Multivariate discriminant analysis demonstrated that the sensilla of males differed from those of females, the variables with greatest weight being the BA of all three segments and the TK of flagellum 1. The basiconica sensilla were significantly more abundant in females, on all three segments. Antennal sensilla patterns also demonstrated significant differences among P. megistus specimens.Fil: Villela, M. M.. Fundación Oswaldo Cruz; BrasilFil: Catala, Silvia Susana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Universidad Nacional de La Rioja. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Universidad Nacional de Catamarca. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Secretaría de Industria y Minería. Servicio Geológico Minero Argentino. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Provincia de La Rioja. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja; ArgentinaFil: Juberg, J.. Instituto Oswaldo Cruz; Brasil. Fundación Oswaldo Cruz; BrasilFil: Silva, I. G.. Universidade Federal de Goiás; BrasilFil: Dias, J. C. P.. Fundación Oswaldo Cruz; Brasi
Size dependence of the photoinduced magnetism and long-range ordering in Prussian blue analog nanoparticles of rubidium cobalt hexacyanoferrate
Nanoparticles of rubidium cobalt hexacyanoferrate
(RbCo[Fe(CN)]HO) were synthesized using different
concentrations of the polyvinylpyrrolidone (PVP) to produce four different
batches of particles with characteristic diameters ranging from 3 to 13 nm.
Upon illumination with white light at 5 K, the magnetization of these particles
increases. The long-range ferrimagnetic ordering temperatures and the coercive
fields evolve with nanoparticle size. At 2 K, particles with diameters less
than approximately 10 nm provide a Curie-like magnetic signal.Comment: 10 pages, 6 figures in text, expanded text and dat
Spectropolarimetry of the H-alpha line in Herbig Ae/Be stars
Using the HiVIS spectropolarimeter built for the Haleakala 3.7m AEOS
telescope, we have obtained a large number of high precision spectropolarimetrc
observations (284) of Herbig AeBe stars collected over 53 nights totaling more
than 300 hours of observing. Our sample of five HAeBe stars: AB Aurigae,
MWC480, MWC120, MWC158 and HD58647, all show systematic variations in the
linear polarization amplitude and direction as a function of time and
wavelength near the H-alpha line. In all our stars, the H-alpha line profiles
show evidence of an intervening disk or outflowing wind, evidenced by strong
emission with an absorptive component. The linear polarization varies by 0.2%
to 1.5% with the change typically centered in the absorptive part of the line
profile. These observations are inconsistent with a simple disk-scattering
model or a depolarization model which produce polarization changes centered on
the emmissive core. We speculate that polarized absorption via optical pumping
of the intervening gas may be the cause.Comment: Accepted for publication in ApJ Letter
Polarization dOTF: on-sky focal plane wavefront sensing
The differential Optical Transfer Function (dOTF) is a focal plane wavefront
sensing method that uses a diversity in the pupil plane to generate two
different focal plane images. The difference of their Fourier transforms
recovers the complex amplitude of the pupil down to the spatial scale of the
diversity. We produce two simultaneous PSF images with diversity using a
polarizing filter at the edge of the telescope pupil, and a polarization camera
to simultaneously record the two images. Here we present the first on-sky
demonstration of polarization dOTF at the 1.0m South African Astronomical
Observatory telescope in Sutherland, and our attempt to validate it with
simultaneous Shack-Hartmann wavefront sensor images.Comment: 11 pages, 9 figures, Proc. SPIE Vol. 991
The PLATO End-to-End CCD Simulator -- Modelling space-based ultra-high precision CCD photometry for the assessment study of the PLATO Mission
The PLATO satellite mission project is a next generation ESA Cosmic Vision
satellite project dedicated to the detection of exo-planets and to
asteroseismology of their host-stars using ultra-high precision photometry. The
main goal of the PLATO mission is to provide a full statistical analysis of
exo-planetary systems around stars that are bright and close enough for
detailed follow-up studies. Many aspects concerning the design trade-off of a
space-based instrument and its performance can best be tackled through
realistic simulations of the expected observations. The complex interplay of
various noise sources in the course of the observations made such simulations
an indispensable part of the assessment study of the PLATO Payload Consortium.
We created an end-to-end CCD simulation software-tool, dubbed PLATOSim, which
simulates photometric time-series of CCD images by including realistic models
of the CCD and its electronics, the telescope optics, the stellar field, the
pointing uncertainty of the satellite (or Attitude Control System [ACS]
jitter), and all important natural noise sources. The main questions that were
addressed with this simulator were the noise properties of different
photometric algorithms, the selection of the optical design, the allowable
jitter amplitude, and the expected noise budget of light-curves as a function
of the stellar magnitude for different parameter conditions. The results of our
simulations showed that the proposed multi-telescope concept of PLATO can
fulfil the defined scientific goal of measuring more than 20000 cool dwarfs
brighter than mV =11 with a precision better than 27 ppm/h which is essential
for the study of earth-like exo-planetary systems using the transit method.Comment: 5 pages, submitted for the Proceedings of the 4th HELAS International
Conference: Seismological Challenges for Stellar Structur
The dramatic change of the fossil magnetic field of HD 190073: evidence of the birth of the convective core in a Herbig star ?
In the context of the ESPaDOnS and Narval spectropolarimetric surveys of
Herbig Ae/Be stars, we discovered and then monitored the magnetic field of HD
190073 over more than four years, from 2004 to 2009. Our observations all
displayed similar Zeeman signatures in the Stokes V spectra, indicating that HD
190073 hosted an aligned dipole, stable over many years, consistent with a
fossil origin. We obtained new observations of the star in 2011 and 2012 and
detected clear variations of the Zeeman signature on timescales of days to
weeks, indicating that the configuration of its field has changed between 2009
and 2011. Such a sudden change of external structure of a fossil field has
never previously been observed in any intermediate or high-mass star. HD 190073
is an almost entirely radiative pre-main sequence star, probably hosting a
growing convective core. We propose that this dramatic change is the result of
the interaction between the fossil field and the ignition of a dynamo field
generated in the newly-born convective core.Comment: 4 pages, 5 figures, accepted for publication in A&
Asymptotic and measured large frequency separations
With the space-borne missions CoRoT and Kepler, a large amount of
asteroseismic data is now available. So-called global oscillation parameters
are inferred to characterize the large sets of stars, to perform ensemble
asteroseismology, and to derive scaling relations. The mean large separation is
such a key parameter. It is therefore crucial to measure it with the highest
accuracy. As the conditions of measurement of the large separation do not
coincide with its theoretical definition, we revisit the asymptotic expressions
used for analysing the observed oscillation spectra. Then, we examine the
consequence of the difference between the observed and asymptotic values of the
mean large separation. The analysis is focused on radial modes. We use series
of radial-mode frequencies to compare the asymptotic and observational values
of the large separation. We propose a simple formulation to correct the
observed value of the large separation and then derive its asymptotic
counterpart. We prove that, apart from glitches due to stellar structure
discontinuities, the asymptotic expansion is valid from main-sequence stars to
red giants. Our model shows that the asymptotic offset is close to 1/4, as in
the theoretical development. High-quality solar-like oscillation spectra
derived from precise photometric measurements are definitely better described
with the second-order asymptotic expansion. The second-order term is
responsible for the curvature observed in the \'echelle diagrams used for
analysing the oscillation spectra and this curvature is responsible for the
difference between the observed and asymptotic values of the large separation.
Taking it into account yields a revision of the scaling relations providing
more accurate asteroseismic estimates of the stellar mass and radius.Comment: accepted in A&
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