764 research outputs found
HST Scattered Light Imaging and Modeling of the Edge-on Protoplanetary Disk ESO-H 569
We present new HST ACS observations and detailed models for a recently
discovered edge-on protoplanetary disk around ESO H 569 (a low-mass T
Tauri star in the Cha I star forming region). Using radiative transfer models
we probe the distribution of the grains and overall shape of the disk
(inclination, scale height, dust mass, flaring exponent and surface/volume
density exponent) by model fitting to multiwavelength (F606W and F814W) HST
observations together with a literature compiled spectral energy distribution.
A new tool set was developed for finding optimal fits of MCFOST radiative
transfer models using the MCMC code emcee to efficiently explore the high
dimensional parameter space. It is able to self-consistently and simultaneously
fit a wide variety of observables in order to place constraints on the physical
properties of a given disk, while also rigorously assessing the uncertainties
in those derived properties. We confirm that ESO H 569 is an optically
thick nearly edge-on protoplanetary disk. The shape of the disk is well
described by a flared disk model with an exponentially tapered outer edge,
consistent with models previously advocated on theoretical grounds and
supported by millimeter interferometry. The scattered light images and spectral
energy distribution are best fit by an unusually high total disk mass (gas+dust
assuming a ratio of 100:1) with a disk-to-star mass ratio of 0.16.Comment: Accepted for publication in Ap
High-spin structures of 88Kr and 89Rb: Evolution from collective to single-particle behaviors
The high-spin states of the two neutron-rich nuclei, 88Kr and 89R have been
studied from the 18O + 208Pb fusion-fission reaction. Their level schemes were
built from triple gamma-ray coincidence data and gamma-gamma angular
correlations were analyzed in order to assign spin and parity values to most of
the observed states. The two levels schemes evolve from collective structures
to single-particle excitations as a function of the excitation energy.
Comparison with results of shell-model calculations gives the specific proton
and neutron configurations which are involved to generate the angular momentum
along the yrast lines.Comment: 12 pages, 9 figures, Physical Review C (2013) in pres
HST/ACS Images of the GG Tauri Circumbinary Disk
Hubble Space Telescope Advanced Camera for Surveys images of the young binary
GG Tauri and its circumbinary disk in V and I bandpasses were obtained in 2002
and are the most detailed of this system to date. The confirm features
previously seen in the disk including: a "gap" apparently caused by shadowing
from circumstellar material; an asymmetrical distribution of light about the
line of sight on the near edge of the disk; enhanced brightness along the near
edge of the disk due to forward scattering; and a compact reflection nebula
near the secondary star. New features are seen in the ACS images: two short
filaments along the disk; localized but strong variations in disk intensity
("gaplets"); and a "spur" or filament extending from the reflection nebulosity
near the secondary. The back side of the disk is detected in the V band for the
first time. The disk appears redder than the combined light from the stars,
which may be explained by a varied distribution of grain sizes. The brightness
asymmetries along the disk suggest that it is asymmetrically illuminated by the
stars due to extinction by nonuniform circumstellar material or the illuminated
surface of the disk is warped by tidal effects (or perhaps both). Localized,
time-dependent brightness variations in the disk are also seen.Comment: 28 pages, 7 figures, accepted for publication in the Astronomical
Journa
Probing stellar accretion with mid-infrared hydrogen lines
In this paper we investigate the origin of the mid-infrared (IR) hydrogen
recombination lines for a sample of 114 disks in different evolutionary stages
(full, transitional and debris disks) collected from the {\it Spitzer} archive.
We focus on the two brighter {H~{\sc i}} lines observed in the {\it Spitzer}
spectra, the {H~{\sc i}}(7-6) at 12.37m and the {H~{\sc i}}(9-7) at
11.32m. We detect the {H~{\sc i}}(7-6) line in 46 objects, and the {H~{\sc
i}}(9-7) in 11. We compare these lines with the other most common gas line
detected in {\it Spitzer} spectra, the {[Ne~{\sc iii}]} at 12.81m. We
argue that it is unlikely that the {H~{\sc i}} emission originates from the
photoevaporating upper surface layers of the disk, as has been found for the
{[Ne~{\sc iii}]} lines toward low-accreting stars. Using the {H~{\sc
i}}(9-7)/{H~{\sc i}}(7-6) line ratios we find these gas lines are likely
probing gas with hydrogen column densities of 10-10~cm.
The subsample of objects surrounded by full and transitional disks show a
positive correlation between the accretion luminosity and the {H~{\sc i}} line
luminosity. These two results suggest that the observed mid-IR {H~{\sc i}}
lines trace gas accreting onto the star in the same way as other hydrogen
recombination lines at shorter wavelengths. A pure chromospheric origin of
these lines can be excluded for the vast majority of full and transitional
disks.We report for the first time the detection of the {H~{\sc i}}(7-6) line
in eight young (< 20~Myr) debris disks. A pure chromospheric origin cannot be
ruled out in these objects. If the {H~{\sc i}}(7-6) line traces accretion in
these older systems, as in the case of full and transitional disks, the
strength of the emission implies accretion rates lower than
10M/yr. We discuss some advantages of extending accretion
indicators to longer wavelengths
Contact binaries with additional components. III. The adaptive optics detections
We present results of the CFHT adaptive optics search for companions of a
homogeneous group of contact binary stars, as a contribution to our attempts to
prove a hypothesis that these binaries require a third star to become so close
as observed. In addition to companions directly discovered at separations of
>=1", we introduced a new method of AO image analysis utilizing distortions of
the AO diffraction ring pattern at separations of 0.07"-1". Very close
companions, with separations in the latter range were discovered in systems HV
Aqr, OO Aql, CK Boo, XY Leo, BE Scl, and RZ Tau. More distant companions were
detected in V402 Aur, AO Cam, V2082 Cyg. Our results provide a contribution to
the mounting evidence that the presence of close companions is a very common
phenomenon for very close binaries with orbital periods <1 day.Comment: Full Figs.4 and 5 are in
http://www.astro.utoronto.ca/~rucinski/Triples3
Sélection de segments pertinents dans des enregistrements SEMG en conditions expérimentales perturbées
L'objet de cet article est de proposer une mĂ©thode d'extraction de segments pertinents dans des enregistrements Ă©lectromyographiques de surface (SEMG) en conditions expĂ©rimentales perturbĂ©es. Nous montrons l'intĂ©rĂȘt de l'algorithme CEM pour segmenter les SEMG en classes de bruit de grande amplitude, bouffĂ©es d'activitĂ© et activitĂ© posturale de base. Nous utilisons la modĂ©lisation AR afin de classifier les activitĂ©s EMG exploitables. Un taux de succĂšs de 96% montre l'efficacitĂ© de la mĂ©thode pour des signaux SEMG enregistrĂ©s sur des passagers soumis Ă des accĂ©lĂ©rations latĂ©rales
Medium-separation binaries do not affect the first steps of planet formation
The first steps of planet formation are marked by the growth and
crystallization of sub-micrometer-sized dust grains accompanied by dust
settling toward the disk midplane. In this paper we explore whether the first
steps of planet formation are affected by the presence of medium-separation
stellar companions. We selected two large samples of disks around single and
binary T Tauri stars in Taurus that are thought to have only a modest age
spread of a few Myr. The companions of our binary sample are at projected
separations between 10 and 450 AU with masses down to about 0.1 solar masses.
We used the strength and shape of the 10 micron silicate emission feature as a
proxy for grain growth and for crystallization respectively. The degree of dust
settling was evaluated from the ratio of fluxes at two different mid-infrared
wavelengths. We find no statistically significant difference between the
distribution of 10 micron silicate emission features from single and binary
systems. In addition, the distribution of disk flaring is indistinguishable
between the single and binary system samples. These results show that the first
steps of planet formation are not affected by the presence of a companion at
tens of AU.Comment: To appear in the Astrophysical Journa
Panchromatic observations and modeling of the HV Tau C edge-on disk
We present new high spatial resolution (<~ 0.1") 1-5 micron adaptive optics
images, interferometric 1.3 mm continuum and 12CO 2-1 maps, and 350 micron, 2.8
and 3.3 mm fluxes measurements of the HV Tau system. Our adaptive optics images
reveal an unusually slow orbital motion within the tight HV Tau AB pair that
suggests a highly eccentric orbit and/or a large deprojected physical
separation. Scattered light images of the HV Tau C edge-on protoplanetary disk
suggest that the anisotropy of the dust scattering phase function is almost
independent of wavelength from 0.8 to 5 micron, whereas the dust opacity
decreases significantly over the same range. The images further reveal a marked
lateral asymmetry in the disk that does not vary over a timescale of 2 years.
We further detect a radial velocity gradient in the disk in our 12CO map that
lies along the same position angle as the elongation of the continuum emission,
which is consistent with Keplerian rotation around an 0.5-1 Msun central star,
suggesting that it could be the most massive component in the triple system. We
use a powerful radiative transfer model to compute synthetic disk observations
and use a Bayesian inference method to extract constraints on the disk
properties. Each individual image, as well as the spectral energy distribution,
of HV Tau C can be well reproduced by our models with fully mixed dust provided
grain growth has already produced larger-than-interstellar dust grains.
However, no single model can satisfactorily simultaneously account for all
observations. We suggest that future attempts to model this source include more
complex dust properties and possibly vertical stratification. (Abridged)Comment: 26 pages, 11 figures, editorially accepted for publication in Ap
High-spin structures of 136Cs
Odd-odd 136Cs nuclei have been produced in the 18O + 208Pb and 12C + 238U
fusion-fission reactions and their gamma rays studied with the Euroball array.
The high-spin level scheme has been built up to ~ 4.7 MeV excitation energy and
spin I ~ 16 hbar from the triple gamma-ray coincidence data. The configurations
of the three structures observed above ~ 2 MeV excitation energy are first
discussed by analogy with the proton excitations identified in the semi-magic
137Cs nucleus, which involve the three high-j orbits lying above the Z=50 gap,
pi g_{7/2}, pi d_{5/2} and pi h_{11/2}. This is confirmed by the results of
shell-model calculations performed in this work.Comment: 6 pages, 4 figures, 3 table
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