42,504 research outputs found
Object DUO 2: A New Binary Lens Candidate
We present the light curve of an unusual variable object, DUO 2, detected
during the search for microlensing events by the DUO project. The star remained
stable for more than 150 days before it brightened by more than two magnitudes
in 6 days in the B and R bands. The light curves are achromatic during the
variability. We consider possible explanations of the photometric behavior,
with particular emphasis on the binary lens interpretation of the event. The
masses of the lenses are quite small, with the companion possibly in the range
of a brown dwarf or even a few times of Jupiter. We report evidence of blending
of the source by a companion through the first detection of shift in the light
centroid among all the microlensing experiments. This shift sets a lower limit
of on the separation between the stars. The best lens
model obtained requires moderate blending, which was what motivated us to check
the centroid shift that was subsequently found. The best lens model predicts a
separation of between the two blended stars. This prediction
was recently tested using two CCD images taken under good seeing conditions.
Both images show two components. Their separation and position angle are in
good agreement with our model.Comment: uuencoded, compressed PostScript, 4 pages, 4 figures (in text).
Accepted for publication in Astronomy and Astrophysics Letter
A New Photometric Model of the Galactic Bar using Red Clump Giants
We present a study of the luminosity density distribution of the Galactic bar
using number counts of red clump giants (RCGs) from the OGLE-III survey. The
data were recently published by Nataf et al. (2013) for 9019 fields towards the
bulge and have RC stars over a viewing area of . The data include the number counts, mean distance modulus
(), dispersion in and full error matrix, from which we fit the data
with several tri-axial parametric models. We use the Markov Chain Monte Carlo
(MCMC) method to explore the parameter space and find that the best-fit model
is the model, with the distance to the GC is 8.13 kpc, the ratio of
semi-major and semi-minor bar axis scale lengths in the Galactic plane
, and vertical bar scale length , is (close to being prolate). The scale length of the stellar
density profile along the bar's major axis is 0.67 kpc and has an angle
of , slightly larger than the value obtained from a similar study
based on OGLE-II data. The number of estimated RC stars within the field of
view is , which is systematically lower than the observed
value. We subtract the smooth parametric model from the observed counts and
find that the residuals are consistent with the presence of an X-shaped
structure in the Galactic centre, the excess to the estimated mass content is
. We estimate the total mass of the bar is . Our results can be used as a key ingredient to construct new density
models of the Milky Way and will have implications on the predictions of the
optical depth to gravitational microlensing and the patterns of hydrodynamical
gas flow in the Milky Way.Comment: 15 pages, 6 figures, 4 tables. MNRAS accepte
Radiative and leptonic decays of the pseudoscalar charmonium state
The radiative and leptonic decays of and are studied. For decay, the second-order
electromagnetic tree-level diagram gives the leading contribution. The decay
rate of is calculated, the prediction is in good
agreement with the experimental data. For \eta_c\to l^+\l^-, both the tree
and loop diagrams are calculated. The analysis shows that the loop contribution
dominates, the contribution of tree diagram with intermediate state can
only modifies the decay rate by less than 1%. The prediction of the branching
ratios of and are very tiny within the standard
model. The smallness of these predictions within the standard model makes the
leptonic decays of sensitive to physics beyond the standard model.
Measurement of the leptonic decay may give information of new physics.Comment: 9 pages, 4 figures, RevTex, small change, version to appear in Phys.
Rev.
- …