4,819 research outputs found
The Optical Gravitational Lensing Experiment. Variable Stars in Globular Clusters - IV. Fields 104A-E in 47 Tuc
Five fields located close to the center of the globular cluster NGC 104=47
Tuc were surveyed in a search for variable stars. We present V-band light
curves for 42 variables. This sample includes 13 RR Lyr stars -- 12 of them
belong to the Small Magellanic Cloud (SMC) and 1 is a background object from
the galactic halo. Twelve eclipsing binaries were identified -- 9 contact
systems and 3 detached/semi-detached systems. Seven eclipsing binaries are
located in the blue straggler region on the cluster color-magnitude diagram
(CMD) and four binaries can be considered main-sequence systems. One binary is
probably a member of the SMC. Eight contact binaries are likely members of the
cluster and one is most probably a foreground star. We show that for the
surveyed region of 47 Tuc, the relative frequency of contact binaries is very
low as compared with other recently surveyed globular clusters. The sample of
identified variables also includes 15 red variables with periods ranging from
about 2 days to several weeks. A large fraction of these 15 variables probably
belong to the SMC but a few stars are likely to be red giants in 47 Tuc. VI
photometry for about 50 000 stars from the cluster fields was obtained as a by
product of our survey.Comment: Latex file, l-aa style, 10 pages, 7 ps figures included. Submitted to
A&A. Figure 8 available from
ftp://sirius.astrouw.edu.pl/pub/jka/47Tuc/fig8.ps.
Desorption Dynamics of Heavy Alkali Metal Atoms (Rb, Cs) off the Surface of Helium Nanodroplets
We present a combined ion imaging and density functional theory study of the
dynamics of the desorption process of rubidium and cesium atoms off the surface
of helium nanodroplets upon excitation of the perturbed and states,
respectively. Both experimental and theoretical results are well represented by
the pseudodiatomic model for effective masses of the helium droplet in the
desorption reaction of m_eff/m_He~10 (Rb) and 13 (Cs). Deviations from this
model are found for Rb excited to the 6p state. Photoelectron spectra indicate
that the dopant-droplet interaction induces relaxation into low-lying
electronic states of the desorbed atoms in the course of the ejection process.Comment: in press, J. Phys. Chem. A (2014
Ca impurity in small mixed He-He clusters
The structure of small mixed helium clusters doped with one calcium atom has
been determined within the diffusion Monte Carlo framework. The results show
that the calcium atom sits at the He-He interface. This is in agreement
with previous studies, both experimental and theoretical, performed for large
clusters. A comparison between the results obtained for the largest cluster we
have considered for each isotope shows a clear tendency of the Ca atom to
reside in a deep dimple at the surface of the cluster for He clusters, and
to become fully solvated for He clusters. We have calculated the absorption
spectrum of Ca around the transition and have found that
it is blue-shifted from that of the free-atom transition by an amount that
depends on the size and composition of the cluster.Comment: 24 pages, 11 figures. Accepted on Journal of Chemical Physic
Are the Ogle Microlenses in the Galactic Bar?
The analysis of the first two years of OGLE data revealed 9 microlensing
events of the galactic bulge stars, with the characteristic time scales in the
range days, where . The optical depth to
microlensing is larger than , in excess of
current theoretical estimates, indicating a much higher efficiency for
microlensing by either bulge or disk lenses. We argue that the lenses are
likely to be ordinary stars in the galactic bar, which has its long axis
elongated towards us. A relation between and the lens masses remains
unknown until a quantitative model of bar microlensing becomes available. At
this time we have no evidence that the OGLE events are related to dark matter.
The geometry of lens distribution can be determined observationally when the
microlensing rate is measured over a larger range of galactic longitudes, like
, and the relative proper motions of the galactic bulge
(bar) stars are measured with the HST.Comment: 10 pages, 2 figures, revised version accepted for the publication in
ApJL, uses AAS LaTeX aaspp.sty macro, PostScript figures and PostScript
version of the paper available through anonymous ftp from
astro.princeton.edu, directory stanek/tau, or on reques
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