34,175 research outputs found
OGLE-2018-BLG-0584 and KMT-2018-BLG-2119: two microlensing events with two lens masses and two source stars
We conduct a systematic investigation of the microlensing data collected
during the previous observation seasons for the purpose of reanalyzing
anomalous lensing events with no suggested plausible models. We find that two
anomalous lensing events OGLE-2018-BLG-0584 and KMT-2018-BLG-2119 cannot be
explained with the usual models based on either a binary-lens single-source
(2L1S) or a single-lens binary-source (1L2S) interpretation. We test the
feasibility of explaining the light curves with more sophisticated models by
adding an extra lens (3L1S model) or a source (2L2S model) component to the
2L1S lens-system configuration. We find that a 2L2S interpretation well
explains the light curves of both events, for each of which there are a pair of
solutions resulting from the close and wide degeneracy. For the event
OGLE-2018-BLG-0584, the source is a binary composed of two K-type stars, and
the lens is a binary composed of two M dwarfs. For KMT-2018-BLG-2119, the
source is a binary composed of two dwarfs of G and K spectral types, and the
lens is a binary composed of a low-mass M dwarf and a brown dwarf.Comment: 9 pages, 9 figure
V1135 Herculis: a double-lined eclipsing binary with an Anomalous Cepheid
BVR light curves and radial velocities for the double-lined eclipsing binary
V1135\,Her were obtained. The brighter component of V1135\,Her is a Cepheid
variable with a pulsation period of 4.224330.00026 days. The orbital
period of the system is about 39.997820.00233 days, which is the shortest
value among the known Type\,II Cepheid binaries. The observed B, V, and R
magnitudes were cleaned for the intrinsic variations of the primary star. The
remaining light curves, consisting of eclipses and proximity effects, are
obtained. Our analyses of the multi-colour light curves and radial velocities
led to the determination of fundamental stellar properties of both components
of the interesting system V1135\,Her. The system consists of two evolved stars,
G1+K3 between giants and supergiants, with masses of M=1.4610.054
\Msun ~and M=0.5040.040 {\Msun} and radii of R=27.10.4
{\Rsun} and R=10.40.2 {\Rsun}. The pulsating star is almost filling
its corresponding Roche lobe which indicates the possibility of mass loss or
transfer having taken place. We find an average distance of d=7500450 pc
using the BVR magnitudes and also the V-band extinction. Location in the Galaxy
and the distance to the galactic plane with an amount of 1300 pc indicate that
it probably belongs to the thick-disk population. Most of the observed and
calculated parameters of the V1135\,Her and its location on the color-magnitude
and period-luminosity diagrams lead to a classification of an Anomalous
Cepheid.Comment: 25 pages, 9 Tables, 9 Figures, Accepted Revista Mexicana de
Astronom\'ia y Astrof\'isica. arXiv admin note: substantial text overlap with
arXiv:1211.120
Mass and p-factor of the type II Cepheid OGLE-LMC-T2CEP-098 in a binary system
We present the results of a study of the type II Cepheid () in the eclipsing binary system OGLE-LMC-T2CEP-098 ().
The Cepheid belongs to the peculiar W Vir group, for which the evolutionary
status is virtually unknown. It is the first single-lined system with a
pulsating component analyzed using the method developed by Pilecki et al.
(2013). We show that the presence of a pulsator makes it possible to derive
accurate physical parameters of the stars even if radial velocities can be
measured for only one of the components. We have used four different methods to
limit and estimate the physical parameters, eventually obtaining precise
results by combining pulsation theory with the spectroscopic and photometric
solutions. The Cepheid radius, mass and temperature are ,
and , respectively, while its companion
has similar size (), but is more massive () and
hotter (). Our best estimate for the p-factor of the Cepheid is . The mass, position on the period-luminosity diagram, and pulsation
amplitude indicate that the pulsating component is very similar to the
Anomalous Cepheids, although it has a much longer period and is redder in
color. The very unusual combination of the components suggest that the system
has passed through a mass transfer phase in its evolution. More complicated
internal structure would then explain its peculiarity.Comment: 23 pages, 17 figures, accepted for publication in Ap
Detectability of extrasolar moons as gravitational microlenses
We evaluate gravitational lensing as a technique for the detection of
extrasolar moons. Since 2004 gravitational microlensing has been successfully
applied as a detection method for extrasolar planets. In principle, the method
is sensitive to masses as low as an Earth mass or even a fraction of it. Hence
it seems natural to investigate the microlensing effects of moons around
extrasolar planets. We explore the simplest conceivable triple lens system,
containing one star, one planet and one moon. From a microlensing point of
view, this system can be modelled as a particular triple with hierarchical mass
ratios very different from unity. Since the moon orbits the planet, the
planet-moon separation will be small compared to the distance between planet
and star. Such a configuration can lead to a complex interference of caustics.
We present detectability and detection limits by comparing triple-lens light
curves to best-fit binary light curves as caused by a double-lens system
consisting of host star and planet -- without moon. We simulate magnification
patterns covering a range of mass and separation values using the inverse ray
shooting technique. These patterns are processed by analysing a large number of
light curves and fitting a binary case to each of them. A chi-squared criterion
is used to quantify the detectability of the moon in a number of selected
triple-lens scenarios. The results of our simulations indicate that it is
feasible to discover extrasolar moons via gravitational microlensing through
frequent and highly precise monitoring of anomalous Galactic microlensing
events with dwarf source stars.Comment: 14 pages, 11 figures. Updated to A&A published version: updated
references, 1 additional illustration (Fig. 10), further analogies to solar
system and extended discussio
RXTE highlights of 34.85-day cycle of Her X-1
An analysis of the publically available RXTE archive on Her X-1 including
data on 23 34.85-day cycles is performed. The turn-on times for these cycles
are determined. The number of cycles with a duration of 20.5 orbits has been
found exceedingly larger than of shorter (20 orbits) or longer (21 orbits). A
correlation between the duration of a cycle and its mean X-ray flux is noted.
The mean X-ray light curve shows a very distinct short-on state. The anomalous
X-ray absorption dip is found during the first orbit after the turn-on in the
main-on state for the cycles starting near the binary phase 0.25, while is
present during two successive orbits in the low-on state. The post-eclipse
recovery feature have not been found in the main-on state but appears at least
for two orbits during the low-on state. The pre-eclipse dips are present both
in main-on and low-on state and demonstrate the behaviour as in early
observations. The comparison of durations of the main-on and short-on states
enabled us to constrain the accretion disk semi-thickness and its inclination
to the orbital plane.Comment: 7 pages with 4 eps figures (large figures 1, 4a,b, 5a,b are available
at ftp://xray.sai.msu.su/pub/preprints/Prokhorov/rxte/ or at
ftp://xray.sai.msu.ru/pub/preprints/Prokhorov/rxte/), LaTeX, uses mn.sty.
Submitted to MNRA
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