419 research outputs found
Astrometric Detection of Double Gravitational Microlensing Events
If a gravitational microlensing event is caused by a widely separated binary
lens and the source approaches both lens components, the source flux is
successively magnified by the individual lenses: double microlensing events. If
events are observed astrometrically, double lensing events are expected to
occur with an increased frequency due to the long range astrometric effect of
the companion. We find that although the trajectory of the source star image
centroid shifts of an astrometric double lensing event has a distorted shape
from both of the elliptical ones induced by the individual single lens
components, event duplication can be readily identified by the characteristic
loop in the trajectory formed during the source's passage close to the
companion. We determine and compare the probabilities of detecting double
lensing events from both photometric and astrometric lensing observations by
deriving analytic expressions for the relations between binary lensing
parameters to become double lensing events. From this determination, we find
that for a given set of the binary separation and the mass ratio the
astrometric probability is roughly an order higher than the photometric
probability. Therefore, we predict that a significant fraction of events that
will be followed up by using future high precision interferometeric instruments
will be identified as double lensing events.Comment: total 6 pages, including 4 figures and no table, ApJ, submitte
Benthic invertebrate fauna in the islets of Namuseom and Bukhyeongjeseom off Busan
AbstractThis study was conducted to examine the benthic invertebrate fauna inhabiting in the subtidal zone in and around the islets of Namuseom and Bukhyeongjeseom off the coast of Busan by SCUBA diving in September 2013. As a consequence, it was confirmed that a total of 6 phyla, 14 classes, 20 orders, 46 families, and 73 species of zoobenthos inhabit in and around those islets. The total number of species surveyed by taxon during the study is 22 species of Arthropoda (30%), 20 species of Mollusca (27%), 15 species of Cnidaria (21%), 10 species of Echinodermata (14%), four species of Poridera (5%), and two species of Chordata
Probing the Spatial Distribution of Extrasolar Planets with Gravitational Microlensing
Under the current microlensing planet search strategy of monitoring events
caused by stellar-mass lenses, only planets located within a narrow region of
separations from central stars can be effectively detected. However, with the
dramatic increase of the monitoring frequency, two additional populations of
free-floating and wide-orbit planets can be detected. In this paper, we
investigate the lensing properties of events caused by wide-orbit planets and
find that the light curves of a significant fraction of these events will
exhibit signatures of central stars, enabling one to distinguish them from
those caused by free-floating planets. Due to the large primary/planet mass
ratio, the effect of the central star endures to considerable separations. We
find that for a Jupiter-mass planet the signatures of the central star can be
detected with fractional deviations of > 5% from the best-fitting single-lens
light curves for > 80% of events caused by bound planets with separations < 10
AU and the probability is still substantial for planets with separations up to
20 AU. Therefore, detecting a large sample of these events will provide useful
information about the distribution of extrasolar planets around their central
stars. Proper estimation of the probability of distinguishing events caused by
wide-orbit planets from those caused by free-floating planets will be important
for the correct determination of the frequency of free-floating planets, whose
microlensing sample will be contaminated by wide-orbits planets.Comment: total 7 pages, including 4 figures, ApJ, submitte
TOWARD A BETTER UNDERSTANDING OF THE DISTANCE SCALE FROM RR LYRAE VARIABLE STARS: A CASE STUDY FOR THE INNER HALO GLOBULAR CLUSTER NGC 6723
We present BV photometry for 54 variables in the metal-rich inner halo globular cluster NGC 6723. With the discovery of new RR Lyrae variables (RRLs), we obtain P ab = 0.541 ± 0.066 and P c = 0.292 ± 0.030 day, n(c)/n(ab+c) = 0.167, and V(RR)int = 15.459 ± 0.055. We carry out the Fourier decomposition analysis and obtain [Fe/H]ZW = â1.23 ± 0.11 and E(B â V) = 0.063 ± 0.015 for NGC 6723. By calibrating the zero point from the recent absolute trigonometric parallax measurements for RR Lyr, we derive the revised MV(RR)-[Fe/H] relation, providing MV(RR) = 0.52 at [Fe/H] = â1.50 and (m â M)0 = 18.54 for the Large Magellanic Cloud, in excellent agreement with others. We obtain (m â M)0 = 14.65 ± 0.05, equivalent to a distance from the Sun of 8.47 ± 0.17 kpc, for NGC 6723 from various distance measurement methods using RRLs. We find that RRLs in NGC 6723 do not have magnitude dependency on the radial distance because there is not a severe degree of apparent crowdedness. Finally, we show that a relation exists between the degree of photometric contamination and the apparent crowdedness of the central region of globular cluster systems, . The use of this relation can play a significant role in mitigating the discrepancy in establishing a cosmic distance scale using RRLs in resolved stellar populations in near-field cosmology
Raman Scattered He II 6545 Line in the Symbiotic Star V1016 Cygni
We present a spectrum of the symbiotic star V1016 Cyg observed with the 3.6 m
Canada-France-Hawaii Telescope, in order to illustrate a method to measure the
covering factor of the neutral scattering region around the giant component
with respect to the hot emission region around the white dwarf component. In
the spectrum, we find broad wings around H and a broad emission feature
around 6545 that is blended with the [N II] 6548 line.
These two features are proposed to be formed by Raman scattering by atomic
hydrogen, where the incident radiation is proposed to be UV continuum radiation
around Ly in the former case and He II 1025 emission line
arising from transitions for the latter feature. We remove the
H wings by a template Raman scattering wing profile and subtract the [N
II] 6548 line using the 3 times stronger [N II] 6583
feature in order to isolate the He II Raman scattered 6545 \AA line. We obtain
the flux ratio of the He II 6560 emission
line and the 6545 \AA feature for V1016 Cyg. Under the assumption that the He
II emission from this object is isotropic, this ratio is converted to the ratio
of the number of the incident photons and that
of the scattered photons. This implies that the scattering region with H I
column density covers 17 per cent of the
emission region. By combining the presumed binary period yrs of this
system we infer that a significant fraction of the slow stellar wind from the
Mira component is ionized and that the scattering region around the Mira
extends a few tens of AU, which is closely associated with the mass loss
process of the Mira component.Comment: 12 pages, 6 figures, accepted for publication in Ap
Hepatocellular Carcinoma Arising in a Huge Hepatocellular Adenoma with Bone Marrow Metaplasia
Hepatocellular adenoma (HCA) is the most common type of benign liver tumor, and its major complication is malignant transformation to hepatocellular carcinoma (HCC). Here, we report a case of HCC arising in HCA with bone marrow metaplasia in a 24-year-old Korean woman who presented with abdominal discomfort. A huge liver mass was found on abdominal ultrasonography. She underwent surgical hepatic resection, and the resected specimen was entirely involved by a 20-cm-sized tumor. Histological review revealed a well differentiated HCC arising from inflammatory HCA with ÎČ-catenin nuclear positivity and bone marrow metaplasia that contained hematopoietic cells. This case was unique because malignant transformation, inflammatory type HCA, ÎČ-catenin nuclear staining, and bone marrow metaplasia were simultaneously observed. Additionally, it should be noted that a large HCA with ÎČ-catenin activation can undergo malignant transformation and should be surgically resected in a timely manner
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