71 research outputs found
Clump Distance to the Magellanic Clouds and Anomalous Colors in the Galactic Bulge
I demonstrate that the two unexpected results in the local Universe: 1)
anomalous intrinsic (V-I)_0 colors of the clump giants and RR Lyrae stars in
the Galactic center, and 2) very short distances to the Magellanic Clouds (LMC,
SMC) as inferred from clump giants, are connected with each other. The (V-I)_0
anomaly is partially resolved by using the photometry from the phase-II of the
Optical Gravitational Lensing Experiment (OGLE) rather than phase-I. The need
for V- or I-magnitude-based change in the bulge (V-I)_0 is one option to
explain the remaining color discrepancy. Such change may originate in a
coefficient of selective extinction A_V/E(V-I) smaller than typically assumed.
Application of the (V-I)_0 correction (independent of its source) doubles the
slope of the absolute magnitude - metallicity relation for clump giants, so
that M_I(RC) = -0.23 + 0.19[Fe/H]. Consequently, the estimates of the clump
distances to the LMC and SMC are affected. Udalski's (1998c) distance modulus
of mu_{LMC} = 18.18 +/- 0.06 increases to mu_{LMC} = 18.27 +/- 0.07. The
distance modulus to the SMC increases by 0.12 to mu_{SMC} = 18.77 +/- 0.08. I
argue that a more comprehensive assessment of the metallicity effect on M_I(RC)
is needed.Comment: accepted by ApJ Letters, brief review of the short distance scale
dropped, discussion of the absolute magnitude - metallicity relation for
clump giants shortened and made more qualitative, results basically unchange
Can CCM law properly represent all extinction curves?
We present the analysis of a large sample of lines of sight with extinction
curves covering wavelength range from near-infrared (NIR) to ultraviolet (UV).
We derive total to selective extinction ratios based on the Cardelli, Clayton
and Mathis (1989, CCM) law, which is typically used to fit the extinction data
both for diffuse and dense interstellar medium. We conclude that the CCM law is
able to fit most of the extinction curves in our sample. We divide the
remaining lines of sight with peculiar extinction into two groups according to
two main behaviors: a) the optical/IR or/and UV wavelength region cannot be
reproduced by the CCM formula; b) the optical/NIR and UV extinction data are
best fit by the CCM law with different values of R_V. We present examples of
such curves. The study of both types of peculiar cases can help us to learn
about the physical processes that affect dust in the interstellar medium, e.g.,
formation of mantles on the surface of grains, evaporation, growing or
shattering.Comment: 6 pages, 4 figures, in "Light, dust and chemical evolution", Journal
of Physics: Conference Serie
Real-Time Treatment Planning Optimisation for Brachytherapy
In this paper, we present an integrated system for real-time dose distribution calculation and treatment planning optimisation for brachytherapy of prostate cancer, with a special emphasis on the visual integration of the dosimetry and target images obtained from the open magnetic resonance system. This system involves a fast method to calculate dose distributions of multiple concurrent radioactive sources, based on the combination of elements from a database of pre-calculated dose distribution maps for single sources, combined linearly to provide the final dose distribution map. Simulated annealing, in conjunction with the inverse planning method, is used to determine the source dwell times at pre-selected locations in order to optimally irradiate thetumour while preserving the surrounding healthy tissues. This algorithm, implemented in FORTRAN, is integrated into a computer-assisted treatment planning tool, written in JAVA, using the runtime class and RMI API of Java. The whole system is now under clinical testing at the Geneva University Hospital
The Angstrom Project: a microlensing survey of the structure and composition of the bulge of the Andromeda galaxy
The Andromeda Galaxy Stellar Robotic Microlensing Project (The Angstrom
Project) aims to use stellar microlensing events to trace the structure and
composition of the inner regions of the Andromeda Galaxy (M31). We present
microlensing rate and timescale predictions and spatial distributions for
stellar and sub-stellar lens populations in combined disk and barred bulge
models of M31. We show that at least half of the stellar microlenses in and
around the bulge are expected to have characteristic durations between 1 and 10
days, rising to as much as 80% for brown-dwarf dominated mass functions. These
short-duration events are mostly missed by current microlensing surveys that
are looking for Macho candidates in the M31 dark matter halo. Our models
predict that an intensive monitoring survey programme such as Angstrom, which
will be able to detect events of durations upwards of a day, could detect
around 30 events per season within ~5 arcminutes of the M31 centre, due to
ordinary low-mass stars and remnants. This yield increases to more than 60
events for brown-dwarf dominated mass functions. The overall number of events
and their average duration are sensitive diagnostics of the bulge mass, in
particular the contribution of low-mass stars and brown dwarfs. The combination
of an inclined disk, an offset bar-like bulge, and differences in the bulge and
disk luminosity functions results in a four-way asymmetry in the number of
events expected in each quadrant defined by the M31 disk axes. The asymmetry is
sensitive to the bar prolongation, orientation and mass.Comment: 9 pages, submitted to MNRA
Decreased expression of breast cancer resistance protein in the duodenum in patients with obstructive cholestasis
Background/Aims: The expression of transporters involved in bile acid homeostasis is differentially regulated during obstructive cholestasis. Since the drug efflux transporter breast cancer resistance protein (BCRP) is known to transport bile acids, we investigated whether duodenal BCRP expression could be altered during cholestasis. Methods: Using real-time RT-PCR analysis we determined mRNA expression levels in duodenal tissue of 19 cholestatic patients. Expression levels were compared to 14 healthy subjects. BCRP protein staining was determined in biopsies of 6 cholestatic and 6 healthy subjects by immunohistochemistry. Results: We found that in patients with obstructive cholestasis mean duodenal BCRP mRNA levels were significantly reduced to 53% and mean protein staining was reduced to 57%. Conclusions: BCRP, a transporter for bile acids and numerous drugs, appears to be down-regulated in the human duodenum during cholestasis. The clinical impact of these results has to be investigated in further studies. Copyright (c) 2006 S. Karger AG, Basel
Endoluminal beta-radiation therapy for the prevention of coronary restenosis after balloon angioplasty.
BACKGROUND: Beta radiation is effective in reducing vascular neointimal proliferation in animals after injury caused by balloon angioplasty. However, the lowest dose that can prevent restenosis after coronary angioplasty has yet to be determined. METHODS: After successful balloon angioplasty of a previously untreated coronary stenosis, 181 patients were randomly assigned to receive 9, 12, 15, or 18 Gy of radiation delivered by a centered yttrium-90 source. Adjunctive stenting was required in 28 percent of the patients. The primary end point was the minimal luminal diameter six months after treatment, as a function of the delivered dose of radiation. RESULTS: At the time of follow-up coronary angiography, the mean minimal luminal diameter was 1.67 mm in the 9-Gy group, 1.76 mm in the 12-Gy group, 1.83 mm in the 15-Gy group, and 1.97 mm in the 18-Gy group (P=0.06 for the comparison of 9 Gy with 18 Gy), resulting in restenosis rates of 29 percent, 21 percent, 16 percent, and 15 percent, respectively (P=0.14 for the comparison of 9 Gy with 18 Gy). At that time, 86 percent of the patients had had no serious cardiac events. In 130 patients treated with balloon angioplasty alone, restenosis rates were 28 percent, 17 percent, 16 percent, and 4 percent, respectively (P=0.02 for the comparison of 9 Gy with 18 Gy). Among these patients, there was a dose-dependent enlargement of the lumen in 28 percent, 50 percent, 45 percent, and 74 percent of patients, respectively (P<0.001 for the comparison of 9 Gy with 18 Gy). The rate of repeated revascularization was 18 percent with 9 Gy and 6 percent with 18 Gy (P=0.26). CONCLUSIONS: Intracoronary beta radiation therapy produces a significant dose-dependent decrease in the rate of restenosis after angioplasty. An 18-Gy dose not only prevents the renarrowing of the lumen typically observed after successful balloon angioplasty, but actually induces luminal enlargement
Evidence for dark matter in the inner Milky Way
The ubiquitous presence of dark matter in the universe is today a central
tenet in modern cosmology and astrophysics. Ranging from the smallest galaxies
to the observable universe, the evidence for dark matter is compelling in
dwarfs, spiral galaxies, galaxy clusters as well as at cosmological scales.
However, it has been historically difficult to pin down the dark matter
contribution to the total mass density in the Milky Way, particularly in the
innermost regions of the Galaxy and in the solar neighbourhood. Here we present
an up-to-date compilation of Milky Way rotation curve measurements, and compare
it with state-of-the-art baryonic mass distribution models. We show that
current data strongly disfavour baryons as the sole contribution to the
galactic mass budget, even inside the solar circle. Our findings demonstrate
the existence of dark matter in the inner Galaxy while making no assumptions on
its distribution. We anticipate that this result will compel new
model-independent constraints on the dark matter local density and profile,
thus reducing uncertainties on direct and indirect dark matter searches, and
will shed new light on the structure and evolution of the Galaxy.Comment: First submitted version of letter published in Nature Physics on
Febuary 9, 2015:
http://www.nature.com/nphys/journal/vaop/ncurrent/full/nphys3237.htm
Planetary and Other Short Binary Microlensing Events from the MOA Short Event Analysis
We present the analysis of four candidate short duration binary microlensing
events from the 2006-2007 MOA Project short event analysis. These events were
discovered as a byproduct of an analysis designed to find short timescale
single lens events that may be due to free-floating planets. Three of these
events are determined to be microlensing events, while the fourth is most
likely caused by stellar variability. For each of the three microlensing
events, the signal is almost entirely due to a brief caustic feature with
little or no lensing attributable mainly to the lens primary. One of these
events, MOA-bin-1, is due to a planet, and it is the first example of a
planetary event in which stellar host is only detected through binary
microlensing effects. The mass ratio and separation are q = 4.9 +- 1.4 x
10^{-3} and s = 2.10 +- 0.05, respectively. A Bayesian analysis based on a
standard Galactic model indicates that the planet, MOA-bin-1Lb, has a mass of
m_p = 3.7 +- 2.1 M_{Jup}, and orbits a star of M_* = 0.75{+0.33 -0.41} M_solar
at a semi-major axis of a = 8.3 {+4.5 -2.7} AU. This is one of the most massive
and widest separation planets found by microlensing. The scarcity of such wide
separation planets also has implications for interpretation of the isolated
planetary mass objects found by this analysis. If we assume that we have been
able to detect wide separation planets with a efficiency at least as high as
that for isolated planets, then we can set limits on the distribution on
planets in wide orbits. In particular, if the entire isolated planet sample
found by Sumi et al. (2011) consists of planets bound in wide orbits around
stars, we find that it is likely that the median orbital semi-major axis is >
30 AU.Comment: 47 pages with 14 figure
The EROS2 search for microlensing events towards the spiral arms: the complete seven season results
The EROS-2 project has been designed to search for microlensing events
towards any dense stellar field. The densest parts of the Galactic spiral arms
have been monitored to maximize the microlensing signal expected from the stars
of the Galactic disk and bulge. 12.9 million stars have been monitored during 7
seasons towards 4 directions in the Galactic plane, away from the Galactic
center. A total of 27 microlensing event candidates have been found. Estimates
of the optical depths from the 22 best events are provided. A first order
interpretation shows that simple Galactic models with a standard disk and an
elongated bulge are in agreement with our observations. We find that the
average microlensing optical depth towards the complete EROS-cataloged stars of
the spiral arms is , a number that is
stable when the selection criteria are moderately varied. As the EROS catalog
is almost complete up to , the optical depth estimated for the
sub-sample of bright target stars with () is easier to interpret. The set of microlensing events
that we have observed is consistent with a simple Galactic model. A more
precise interpretation would require either a better knowledge of the distance
distribution of the target stars, or a simulation based on a Galactic model.
For this purpose, we define and discuss the concept of optical depth for a
given catalog or for a limiting magnitude.Comment: 22 pages submitted to Astronomy & Astrophysic
The MACHO Project 9 Million Star Color-Magnitude Diagram of the Large Magellanic Cloud
We present a 9 million star color-magnitude diagram (9M CMD) of the LMC bar.
The 9M CMD reveals a complex superposition of different age and metallicity
stellar populations, with important stellar evolutionary phases occurring over
3 orders of magnitude in number density. First, we count the non-variable
supergiants, the associated Cepheids, and measure the effective temperatures
defining the instability strip. Lifetime predictions of stellar evolution
theory are tested, with implications for the origin of low-luminosity Cepheids.
The highly-evolved AGB stars have a bimodal distribution in brightness, which
we interpret as discrete old populations (>1 Gyr). The faint AGB may be
metal-poor and very old. We identify the clusters NGC 411 and M3 as templates
for the admixture of old stellar populations. However, there are indications
that the old and metal-poor field population has a red HB morphology: the RR
Lyraes lie on the red edge of the instability strip, the AGB-bump is very red,
and the ratio of AGB-bump stars to RR Lyraes is quite large. If the HB second
parameter is age, the old and metal-poor field population likely formed after
the oldest clusters. Lifetime predictions of stellar evolution theory lead us
to associate a significant fraction of the red HB clump giants with the same
old and metal-poor population producing the RR Lyraes and the AGB-bump. In this
case, compared to the age-dependent luminosity predictions of stellar evolution
theory, the red HB clump is too bright relative to the RR Lyraes and AGB-bump.
Last, the surface density profile of RR Lyraes is fit by an exponential,
favoring a disk-like rather than spheroidal distribution. We conclude that the
age of the LMC disk is probably similar to the age of the Galactic disk.
(ABRIDGED)Comment: to appear in the Astronomical Journal, 49 pages, 12 figures,
aaspp4.st
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