5,567 research outputs found
New RR Lyrae variables in binary systems
Despite their importance, very few RR Lyrae (RRL) stars have been known to
reside in binary systems. We report on a search for binary RRL in the OGLE-III
Galactic bulge data. Our approach consists in the search for evidence of the
light-travel time effect in so-called observed minus calculated ()
diagrams. Analysis of 1952 well-observed fundamental-mode RRL in the OGLE-III
data revealed an initial sample of 29 candidates. We used the recently released
OGLE-IV data to extend the baselines up to 17 years, leading to a final sample
of 12 firm binary candidates. We provide diagrams and binary parameters
for this final sample, and also discuss the properties of 8 additional
candidate binaries whose parameters cannot be firmly determined at present. We
also estimate that per cent of the RRL reside in binary systems.Comment: MNRAS Letters, in pres
Two-photon E1M1 decay of 2 3P0 states in heavy heliumlike ions
Two-photon E1M1 transition rates are evaluated for heliumlike ions with
nuclear charges in the range Z = 50-94. The two-photon rates modify previously
published lifetimes/transition rates of 2 3P0 states. For isotopes with nuclear
spin I not equal 0, where hyperfine quenching dominates the 2 3P0 decay,
two-photon contributions are significant; for example, in heliumlike 187 Os the
two-photon correction is 3% of the total rate. For isotopes with I= 0, where
the 2 3P0 decay is unquenched, the E1M1 corrections are even more important
reaching 60% for Z=94. Therefore, to aid in the interpretation of experiments
on hyperfine quenching in heliumlike ions and to provide a more complete
database for unquenched transitions, a knowledge of E1M1 rates is important.Comment: 6 pages, 3 figures, 3 table
Highly accurate calculations of the rotationally excited bound states in three-body systems
An effective optimization strategy has been developed to construct highly
accurate bound state wave functions in various three-body systems. Our
procedure appears to be very effective for computations of weakly bound states
and various excited states, including rotationally excited states, i.e. states
with . The efficiency of our procedure is illustrated by computations
of the excited states in the and muonic
molecular ions, states in the non-symmetric and
ions and and states in He atom(s)
The Interaction of Venus-like, M-dwarf Planets with the Stellar Wind of Their Host Star
We study the interaction between the atmospheres of Venus-like,
non-magnetized exoplanets orbiting an M-dwarf star, and the stellar wind using
a multi-species Magnetohydrodynaic (MHD) model. We focus our investigation on
the effect of enhanced stellar wind and enhanced EUV flux as the planetary
distance from the star decreases. Our simulations reveal different topologies
of the planetary space environment for sub- and super-Alfvenic stellar wind
conditions, which could lead to dynamic energy deposition in to the atmosphere
during the transition along the planetary orbit. We find that the stellar wind
penetration for non-magnetized planets is very deep, up to a few hundreds of
kilometers. We estimate a lower limit for the atmospheric mass-loss rate and
find that it is insignificant over the lifetime of the planet. However, we
predict that when accounting for atmospheric ion acceleration, a significant
amount of the planetary atmosphere could be eroded over the course of a billion
years.Comment: 13 pages, 7 figures, accepted to Ap
Abundance analysis, spectral variability, and search for the presence of a magnetic field in the typical PGa star HD19400
The aim of this study is to carry out an abundance determination, to search
for spectral variability and for the presence of a weak magnetic field in the
typical PGa star HD19400. High-resolution, high signal-to-noise HARPS
spectropolarimetric observations of HD19400 were obtained at three different
epochs in 2011 and 2013. For the first time, we present abundances of various
elements determined using an ATLAS12 model, including the abundances of a
number of elements not analysed by previous studies, such as Ne I, Ga II, and
Xe II. Several lines of As II are also present in the spectra of HD19400. To
study the variability, we compared the behaviour of the line profiles of
various elements. We report on the first detection of anomalous shapes of line
profiles belonging to Mn and Hg, and the variability of the line profiles
belonging to the elements Hg, P, Mn, Fe, and Ga. We suggest that the
variability of the line profiles of these elements is caused by their
non-uniform surface distribution, similar to the presence of chemical spots
detected in HgMn stars. The search for the presence of a magnetic field was
carried out using the moment technique and the SVD method. Our measurements of
the magnetic field with the moment technique using 22 Mn II lines indicate the
potential existence of a weak variable longitudinal magnetic field on the first
epoch. The SVD method applied to the Mn II lines indicates =-76+-25G on
the first epoch, and at the same epoch the SVD analysis of the observations
using the Fe II lines shows =-91+-35G. The calculated false alarm
probability values, 0.008 and 0.003, respectively, are above the value 10^{-3},
indicating no detection.Comment: 13+6 pages, 14 figures, 6+1 tables, including the online-only
material, accepted for publication in MNRA
Modeling the Low State Spectrum of the X-Ray Nova XTE J1118+480
Based on recent multiwavelength observations of the new X-ray nova XTE
J1118+480, we can place strong constraints on the geometry of the accretion
flow in which a low/hard state spectrum, characteristic of an accreting black
hole binary, is produced. We argue that the absence of any soft blackbody-like
component in the X-ray band implies the existence of an extended hot
optically-thin region, with the optically-thick cool disk truncated at some
radius R_{tr} > 55 R_{Schw}. We show that such a model can indeed reproduce the
main features of the observed spectrum: the relatively high optical to X-ray
ratio, the sharp downturn in the far UV band and the hard X-ray spectrum. The
absence of the disk blackbody component also underscores the requirement that
the seed photons for thermal Comptonization be produced locally in the hot
flow, e.g. via synchrotron radiation. We attribute the observed spectral break
at 2 keV to absorption in a warm, partially ionized gas.Comment: 6 pages, including 1 figure; LaTeX (emulateapj5.sty), to appear in
Ap
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