15,153 research outputs found
The possibility of determining open-cluster parameters from BVRI photometry
In the last decades we witnessed an increase in studies of open clusters of
the Galaxy, especially because of the good determination for a wide range of
values of parameters such as age, distance, reddening, and proper motion. The
reliable determination of the parameters strongly depends on the photometry
available and especially on the U filter, which is used to obtain the color
excess E(B-V) through the color-color diagram (U-B) by (B-V) by fitting a zero
age main-sequence. Owing to the difficulty of performing photometry in the U
band, many authors have tried to obtain E(B-V) without the filter. But because
of the near linearity of the color-color diagrams that use the other bands,
combined with the fact that most fitting procedures are highly subjective (many
done "by eye") the reliability of those results has always been questioned. Our
group has recently developed, a tool that performs isochrone fitting in
open-cluster photometric data with a global optimization algorithm, which
removes the need to visually perform the fits and thus removes most of the
related subjectivity. Here we apply our method to a set of synthetic clusters
and two observed open clusters (Trumpler 1 and Melotte 105) using only
photometry for the BVRI bands. Our results show that, considering the cluster
structural variance caused only by photometric and Poisson sampling errors, our
method is able to recover the synthetic cluster parameters with errors of less
than 10% for a wide range of ages, distances, and reddening, which clearly
demonstrates its potential. The results obtained for Trumpler 1 and Melotte 105
also agree well with previous literature values.Comment: 5 pages, 5 figures, accepted for publication in
Astronomy&Astrophysic
Tuning the Mott transition in a Bose-Einstein condensate by multi-photon absorption
We study the time-dependent dynamics of a Bose-Einstein condensate trapped in
an optical lattice. Modeling the system as a Bose-Hubbard model, we show how
applying a periodic driving field can induce coherent destruction of tunneling.
In the low-frequency regime, we obtain the novel result that the destruction of
tunneling displays extremely sharp peaks when the driving frequency is resonant
with the depth of the trapping potential (``multi-photon resonances''), which
allows the quantum phase transition between the Mott insulator and the
superfluid state to be controlled with high precision. We further show how the
waveform of the field can be chosen to maximize this effect.Comment: Minor changes, this version to be published in Phys. Rev. Let
- …