3,397 research outputs found
Predicting Stellar Angular Sizes
Reliable prediction of stellar diameters, particularly angular diameters, is
a useful and necessary tool for the increasing number of milliarcsecond
resolution studies being carried out in the astronomical community. A new and
accurate technique of predicting angular sizes is presented for main sequence
stars, giant and supergiant stars, and for more evolved sources such as carbon
stars and Mira variables. This technique uses observed and either or
broad-band photometry to predict V=0 or B=0 zero magnitude angular sizes,
which are then readily scaled to the apparent angular sizes with the or
photometry. The spread in the relationship is 2.2% for main sequence stars; for
giant and supergiant stars, 11-12%; and for evolved sources, results are at the
20-26% level. Compared to other simple predictions of angular size, such as
linear radius-distance methods or black-body estimates, zero magnitude angular
size predictions can provide apparent angular sizes with errors that are 2 to 5
times smaller.Comment: 28 pages, 4 figures, accepted by PAS
New Particles from Belle
I report recent results on hidden charm spectroscopy from Belle. These
include: observation of a near-threshold enhancement in the omega-J/psi
invariant mass distribution for exclusive B-->K omega J/psi decays; evidence
for the decay X(3872)-->pi+pi-pi0 J/psi, where the pi+pi-pi0 invariant mass
distribution has a strong peak between 750 MeV and the kinematic limit of 775
MeV, suggesting that the process is dominated by the sub-threshold decay
X-->omega J/psi; and the observation of a peak near 3940 MeV in the J/psi
recoil mass spectrum for the inclusive continuum process e+e- --> J/psi X. The
results are based on a study of a 287 fb-1 sample of e+e- annihilation data
collected at center- of-mass energies around the Upsilon(4S) in the Belle
detector at the KEKB collider.Comment: 10 pages 12 figures. Invited talk at the 1st meeting of the APS
Topical Group on Hadronic Physics, Fermilab, October 24-26, 2004; revised to
correct some reference
Supersymmetric Contributions to Bs->K+K-
Inspired by the existing calculation of B->piK decays in supersymmetry
(SUSY), we evaluate the dominant SUSY contributions to Bs->K+K-. We show that
the observables of this process can be significantly modified in the presence
of SUSY. In particular, the branching ratio can be increased considerably
compared to the prediction of the standard model (SM). The effect is even more
dramatic for the CP-violating asymmetries A_dir and A_mix. These asymmetries,
expected to be small in the SM (A_dir is predicted to take only positive
values), change drastically with SUSY contributions. The measurement of these
observables can therefore be used to detect the presence of physics beyond the
SM, and put constraints on its parameters.Comment: 17 pages, 2 figures. This new version contains one added reference
and some minor style change
Precision Flavour Physics with and
We show that a combined analysis of and
allows for new physics tests practically free of form factor uncertainties.
Residual theory errors are at the level of several percent. Our study
underlines the excellent motivation for measuring these modes at a Super
Flavour Factory.Comment: 26 pages, 2 figure
Dynamical mass of the O-type supergiant in Zeta Orionis A
A close companion of Zeta Orionis A was found in 2000 with the Navy Precision
Optical Interferometer (NPOI), and shown to be a physical companion. Because
the primary is a supergiant of type O, for which dynamical mass measurements
are very rare, the companion was observed with NPOI over the full 7-year orbit.
Our aim was to determine the dynamical mass of a supergiant that, due to the
physical separation of more than 10 AU between the components, cannot have
undergone mass exchange with the companion. The interferometric observations
allow measuring the relative positions of the binary components and their
relative brightness. The data collected over the full orbital period allows all
seven orbital elements to be determined. In addition to the interferometric
observations, we analyzed archival spectra obtained at the Calar Alto, Haute
Provence, Cerro Armazones, and La Silla observatories, as well as new spectra
obtained at the VLT on Cerro Paranal. In the high-resolution spectra we
identified a few lines that can be associated exclusively to one or the other
component for the measurement of the radial velocities of both. The combination
of astrometry and spectroscopy then yields the stellar masses and the distance
to the binary star. The resulting masses for components Aa of 14.0 solar masses
and Ab of 7.4 solar masses are low compared to theoretical expectations, with a
distance of 294 pc which is smaller than a photometric distance estimate of 387
pc based on the spectral type B0III of the B component. If the latter (because
it is also consistent with the distance to the Orion OB1 association) is
adopted, the mass of the secondary component Ab of 14 solar masses would agree
with classifying a star of type B0.5IV. It is fainter than the primary by about
2.2 magnitudes in the visual. The primary mass is then determined to be 33
solar masses
Establishing Visible Interferometer System Responses: Resolved and Unresolved Calibrators
The propagation of errors through the uniform disk visibility function is
examined. Implications of those errors upon measures of absolute visibility
through optical and near-infrared interferometers are considered within the
context of using calibration stars to establish system visibilities for these
instruments. We suggest a simple ratio test to establish empirically whether or
not the measured visibilities produced by such an instrument are relative
(errors dominated by calibrator angular size prediction error) or absolute
(errors dominated by measurement error).Comment: 20 pages, 7 figures, to be published in the PAS
- …