47,943 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
Quantum Levy flights and multifractality of dipolar excitations in a random system
We consider dipolar excitations propagating via dipole-induced exchange among
immobile molecules randomly spaced in a lattice. The character of the
propagation is determined by long-range hops (Levy flights). We analyze the
eigen-energy spectra and the multifractal structure of the wavefunctions. In 1D
and 2D all states are localized, although in 2D the localization length can be
extremely large leading to an effective localization-delocalization crossover
in realistic systems. In 3D all eigenstates are extended but not always
ergodic, and we identify the energy intervals of ergodic and non-ergodic
states. The reduction of the lattice filling induces an ergodic to non-ergodic
transition, and the excitations are mostly non-ergodic at low filling.Comment: 5 pages, 6 figure
Cosmology with intensity mapping techniques using atomic and molecular lines
We present a systematic study of the intensity mapping technique using
updated models for the different emission lines from galaxies and identify
which ones are more promising for cosmological studies of the post reionization
epoch. We consider the emission of , , H,
optical and infrared oxygen lines, nitrogen lines, CII and the CO rotational
lines. We then identify that , , OII, CII and
the lowest rotational CO lines are the best candidates to be used as IM probes.
These lines form a complementary set of probes of the galaxies emission
spectra. We then use reasonable experimental setups from current, planned or
proposed experiments to access the detectability of the power spectrum of each
emission line. Intensity mapping of emission from to 3
will be possible in the near future with HETDEX, while far-infrared lines
require new dedicated experiments. We also show that the proposed SPHEREx
satellite can use OII and IM to study the large-scale
distribution of matter in intermediate redshifts of 1 to 4. We found that
submilimeter experiments with bolometers can have similar performances at
intermediate redshifts using CII and CO(3-2).Comment: 18 pages, 21 figures, 5 tables, published in MNRAS, typos correcte
High resolution imaging of the early-type galaxy NGC 1380: an insight into the nature of extended extragalactic star clusters
NGC 1380 is a lenticular galaxy located near the centre of the Fornax Cluster
northeast of NGC 1399. The globular cluster system of this galaxy was
previously studied only from the ground. Recent studies of similar early-type
galaxies, specially lenticular ones, reveal the existence of star clusters that
apparently break up the traditional open/globular cluster dichotomy. With
higher quality photometry from HST/WFPC2 we study the star clusters in NGC
1380, measuring their magnitudes, colours, sizes and projected distances from
the centre of the galaxy. We used deep archival HST/WFPC2 in the B and V bands.
We built colour magnitude diagrams from which we selected a sample of cluster
candidates. We also analysed their colour distribution and measured their
sizes. Based on their location in the luminosity-size diagram we estimated
probabilities of them being typical globular clusters as those found in the
Galaxy. A total of about 570 cluster candidates were found down to V=26.5. We
measured sizes for approximately 200 of them. The observed colour distribution
has three apparent peaks. Likewise for the size distribution. We identified the
smaller population as being mainly typical globular clusters, while the more
extended objects have small probabilities of being such objects. Different
correlations between absolute magnitudes, sizes, colours and location were
inferred for these cluster sub-populations. Most extended clusters (Reff > 4
pc) share similar properties to the diffuse star clusters reported to inhabit
luminous early-type galaxies in the Virgo galaxy cluster such as being of low
surface brightness and fainter than MV ~ -8. We also report on a small group of
(Reff ~ 10 pc), -8< MV < -6, red clusters located near the centre of NGC 1380,
which may be interpreted as faint fuzzies.Comment: accepted for publication in A&
When is the Haar measure a Pietsch measure for nonlinear mappings?
We show that, as in the linear case, the normalized Haar measure on a compact
topological group is a Pietsch measure for nonlinear summing mappings on
closed translation invariant subspaces of . This answers a question posed
to the authors by J. Diestel. We also show that our result applies to several
well-studied classes of nonlinear summing mappings. In the final section some
problems are proposed
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