2,038 research outputs found
Sub-millimeter images of a dusty Kuiper belt around eta Corvi
We present sub-millimeter and mid-infrared images of the circumstellar disk
around the nearby F2V star eta Corvi. The disk is resolved at 850um with a size
of ~100AU. At 450um the emission is found to be extended at all position
angles, with significant elongation along a position angle of 130+-10deg; at
the highest resolution (9.3") this emission is resolved into two peaks which
are to within the uncertainties offset symmetrically from the star at 100AU
projected separation. Modeling the appearance of emission from a narrow ring in
the sub-mm images shows the observed structure cannot be caused by an edge-on
or face-on axisymmetric ring; the observations are consistent with a ring of
radius 150+-20AU seen at 45+-25deg inclination. More face-on orientations are
possible if the dust distribution includes two clumps similar to Vega; we show
how such a clumpy structure could arise from the migration over 25Myr of a
Neptune mass planet from 80-105AU. The inner 100AU of the system appears
relatively empty of sub-mm emitting dust, indicating that this region may have
been cleared by the formation of planets, but the disk emission spectrum shows
that IRAS detected an additional hot component with a characteristic
temperature of 370+-60K (implying a distance of 1-2AU). At 11.9um we found the
emission to be unresolved with no background sources which could be
contaminating the fluxes measured by IRAS. The age of this star is estimated to
be ~1Gyr. It is very unusual for such an old main sequence star to exhibit
significant mid-IR emission. The proximity of this source makes it a perfect
candidate for further study from optical to mm wavelengths to determine the
distribution of its dust.Comment: 22 pages, 4 figures. Scheduled for publication in ApJ 10 February
2005 issu
Energy dependence on fractional charge for strongly interacting subsystems
The energies of a pair of strongly-interacting subsystems with arbitrary
noninteger charges are examined from closed and open system perspectives. An
ensemble representation of the charge dependence is derived, valid at all
interaction strengths. Transforming from resonance-state ionicity to ensemble
charge dependence imposes physical constraints on the occupation numbers in the
strong-interaction limit. For open systems, the chemical potential is evaluated
using microscopic and thermodynamic models, leading to a novel correlation
between ground-state charge and an electronic temperature.Comment: 4 pages, 3 figs.; as accepted (Phys. Rev. Lett.
Exploring the multidimensional assessment of interoceptive awareness in youth aged 7–17 years
Objective
This study aimed to adapt the Multidimensional Assessment of Interoceptive Awareness (MAIA) questionnaire for younger respondents.
Method
The language of the MAIA was revised and children aged 7–10 years (n = 212) and adolescents aged 11–17 years (n = 217) completed the questionnaire.
Results
The original eight‐factor model was tested for fit using confirmatory factor analysis. The model had an acceptable fit in the total sample and younger subsample and overall fit in the older subsample was adequate following modification. Internal consistency was good, except for the Noticing, Not‐Distracting and Not‐Worrying scales. Results also demonstrated a negative linear relationship between the trusting scale and age, suggesting that youths may lose trust in their body as they age.
Conclusion
The adapted MAIA can be used with a younger population and, depending on the research question, individual MAIA scales may be selected. The survey is available at https://osher.ucsf.edu/maia
CO emission from discs around isolated HAeBe and Vega-excess stars
We describe results from a survey for J=3-2 12CO emission from visible stars
with an infrared excess. The line is clearly detected in 21 objects, with
molecular gas (>10^-3 Jupiter masses) common in targets with infrared excesses
>0.01 (>56% of objects). Such high excesses indicate the presence of a disc of
opening angle >12 degrees; within this, the optically thick disc prevents CO
photodissociation. Two or three stars with associated CO have an excess <0.01,
implying a disc opening angle <1 degree. Most line profiles are double-peaked
or relatively broad. Model fits, assuming a Keplerian disc, indicate outer
radii, R_out, of ~20-300 au. As many as 5 discs have outer radii smaller than
the Solar System (50 au), and a further 4 have gas at radii <20 au. R_out is
independent of the stellar spectral type (from K through to B9), but is
correlated with total dust mass. R_out appears to decrease with time: discs
around stars of age 3-7 Myr have a mean radius of ~210 au, whereas discs of age
7-20 Myr are a factor of 3 smaller. The only bona fide debris disc with
detected CO is HD9672; this has a double peaked line profile and is the most
compact gas disc observed, with a modelled radius 17 au). A fit to HD141569
suggests the gas lies in two rings of radii 90 and 250 au, similar to the
scattered light structure. In both AB Aur and HD163296 the sizes of the
molecular and dust scattering discs are also similar, suggesting that the gas
and small dust grains are co-located.Comment: 16 pages, 5 figures MNRAS - accepte
Charge Transfer in Partition Theory
The recently proposed Partition Theory (PT) [J.Phys.Chem.A 111, 2229 (2007)]
is illustrated on a simple one-dimensional model of a heteronuclear diatomic
molecule. It is shown that a sharp definition for the charge of molecular
fragments emerges from PT, and that the ensuing population analysis can be used
to study how charge redistributes during dissociation and the implications of
that redistribution for the dipole moment. Interpreting small differences
between the isolated parts' ionization potentials as due to environmental
inhomogeneities, we gain insight into how electron localization takes place in
H2+ as the molecule dissociates. Furthermore, by studying the preservation of
the shapes of the parts as different parameters of the model are varied, we
address the issue of transferability of the parts. We find good transferability
within the chemically meaningful parameter regime, raising hopes that PT will
prove useful in chemical applications.Comment: 12 pages, 16 figure
Spectropolarimetric observations of Herbig Ae/Be Stars I: HiVIS spectropolarimetric calibration and reduction techniques
Using the HiVIS spectropolarimeter built for the Haleakala 3.7m AEOS
telescope in Hawaii, we are collecting a large number of high precision
spectropolarimetrc observations of stars. In order to precisely measure very
small polarization changes, we have performed a number of polarization
calibration techniques on the AEOS telescope and HiVIS spectrograph. We have
extended our dedicated IDL reduction package and have performed some hardware
upgrades to the instrument. We have also used the ESPaDOnS spectropolarimeter
on CFHT to verify the HiVIS results with back-to-back observations of MWC 361
and HD163296. Comparision of this and other HiVIS data with stellar
observations from the ISIS and WW spectropolarimeters in the literature further
shows the usefulness of this instrument.Comment: 35 pages, 44 figures, Accepted by PAS
Polarization of the Microwave Background in Defect Models
We compute the polarization power spectra for global strings, monopoles,
textures and nontopological textures, and compare them to inflationary models.
We find that topological defect models predict a significant (1 microK)
contribution to magnetic type polarization on degree angular scales, which is
produced by the large vector component of the defect source. We also
investigate the effect of decoherence on polarization. It leads to a smoothing
of acoustic oscillations both in temperature and polarization power spectra and
strongly suppresses the cross-correlation between temperature and polarization
relative to inflationary models. Presence or absence of magnetic polarization
or cross-correlation would be a strong discriminator between the two theories
of structure formation and will be testable with the next generation of CMB
satellites.Comment: 4 pages, 3 figures, RevTeX fil
Heterotropic co-operative effects between amino acid substrates of phenylalanine hydroxylase
Doppler peaks from active perturbations
We examine how the qualitative structure of the Doppler peaks in the angular
power spectrum of the cosmic microwave anisotropy depends on the fundamental
nature of the perturbations which produced them. The formalism of Hu and
Sugiyama is extended to treat models with cosmic defects. We discuss how
perturbations can be ``active'' or ``passive'' and ``incoherent'' or
``coherent'', and show how causality and scale invariance play rather different
roles in these various cases. We find that the existence of secondary Doppler
peaks and the rough placing of the primary peak unambiguously reflect these
basic properties.Comment: uufile, 8pages, 3 figures. Now available at
http://euclid.tp.ph/Papers/index.html; Changes: URL added, Eqn. (8) expanded,
grant numbers include
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