54,357 research outputs found
Are Stars with Planets Polluted?
We compare the metallicities of stars with radial velocity planets to the
metallicity of a sample of field dwarfs. We confirm recent work indicating that
the stars-with-planet sample as a whole is iron rich. However, the lowest mass
stars tend to be iron poor, with several having [Fe/H]<-0.2, demonstrating that
high metallicity is not required for the formation of short period Jupiter-mass
planets. We show that the average [Fe/H] increases with increasing stellar mass
(for masses below 1.25 solar masses) in both samples, but that the increase is
much more rapid in the stars-with-planet sample. The variation of metallicity
with stellar age also differs between the two samples. We examine possible
selection effects related to variations in the sensitivity of radial velocity
surveys with stellar mass and metallicity, and identify a color cutoff
(B-V>0.48) that contributes to but does not explain the mass-metallicity trend
in the stars-with-planets sample. We use Monte Carlo models to show that adding
an average of 6.5 Earth masses of iron to each star can explain both the
mass-metallicity and the age-metallicity relations of the stars-with-planets
sample. However, for at least one star, HD 38529, there is good evidence that
the bulk metallicity is high. We conclude that the observed metallicities and
metallicity trends are the result of the interaction of three effects;
accretion of about 6 Earth masses of iron rich material, selection effects, and
in some cases, high intrinsic metallicity.Comment: 19 pages 11 figure
R-Band Imaging of Fields Around 1<z<2 Radiogalaxies
We have taken deep -band images of fields around five radiogalaxies:
0956+47, 1217+36, 3C256, 3C324 and 3C294 with . 0956+47 is found to
show a double nucleus. Our data on 1217+36 suggest the revision of its
classification as a radiogalaxy. We found a statistically significant excess of
bright () galaxies on scales of 2 arcmin around the radiogalaxies
(which have ) in our sample. The excess has been determined
empirically to be at level. It is remarkable that this excess
is not present for galaxies within the same area, suggesting that
the excess is not physically associated to the galaxies but due to intervening
groups and then related to gravitational lensing.Comment: 20 pages, uuencoded compressed PostScript including tables. Figures
available upon request. To appear in the March 1995 issue of The Astronomical
Journa
Are optically-selected QSO catalogs biased ?
A thorough study of QSO-galaxy correlations has been done on a region close
to the North Galactic Pole using a complete subsample of the optically selected
CFHT/MMT QSO survey and the galaxy catalog of Odewahn and Aldering (1995).
Although a positive correlation between bright QSOs and galaxies is expected
because of the magnification bias effect, none is detected. On the contrary,
there is a significant (>99.6%) anticorrelation between z<1.6 QSOs and red
galaxies on rather large angular distances. This anticorrelation is much less
pronounced for high redshift z>1.6 QSOs, which seems to exclude dust as a cause
of the QSO underdensity. This result suggests that the selection process
employed in the CFHT/MMT QSO survey is losing up to 50% of low redshift z<1.6
QSOs in regions of high galaxy density. The incompleteness in the whole z<1.6
QSO sample may reach 10% and have important consequences in the estimation of
QSO evolution and the QSO autocorrelation function.Comment: 17 pages LaTeX (aasms4), plus 6 EPS figures. To be published in the
Astronomical Journa
Global analysis of the negative parity non-strange baryons in the 1/Nc expansion
A global study of the negative parity non-strange baryon observables is
performed in the frame- work of the 1/Nc expansion. Masses, partial decay
widths and photo-couplings are simultaneously analyzed. A main objective is to
determine the composition of the spin 1/2 and 3/2 nucleon states, which come in
pairs and involve two mixing angles which can be determined and tested for
consistency by the mentioned observables. The issue of the assignment of those
nucleon states to the broken SU(4) x O(3) mixed-symmetry multiplet is studied
in detail, with the conclusion that the assignment made in the old studies
based on the non-relativistic quark model is the preferred one. In addition,
the analysis involves an update of the input data with respect to previous
works.Comment: 30 pages, 3 figure
N electrons in a quantum dot: Two-point Pade approximants
We present analytic estimates for the energy levels of N electrons (N = 2 -
5) in a two-dimensional parabolic quantum dot. A magnetic field is applied
perpendicularly to the confinement plane. The relevant scaled energy is shown
to be a smooth function of the parameter \beta=(effective Rydberg/effective dot
energy)^{1/6}. Two-point Pade approximants are obtained from the series
expansions of the energy near the oscillator () and Wigner
() limits. The approximants are expected to work with an error
not greater than 2.5% in the entire interval .Comment: 27 pages. LaTeX. 6 figures not include
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