67 research outputs found
Limb-darkening measurements for a cool red giant in microlensing event OGLE 2004-BLG-482
Aims: We present a detailed analysis of OGLE 2004-BLG-482, a relatively
high-magnification single-lens microlensing event which exhibits clear
extended-source effects. These events are relatively rare, but they potentially
contain unique information on the stellar atmosphere properties of their source
star, as shown in this study. Methods: Our dense photometric coverage of the
overall light curve and a proper microlensing modelling allow us to derive
measurements of the OGLE 2004-BLG-482 source star's linear limb-darkening
coefficients in three bands, including standard Johnson-Cousins I and R, as
well as in a broad clear filter. In particular, we discuss in detail the
problems of multi-band and multi-site modelling on the expected precision of
our results. We also obtained high-resolution UVES spectra as part of a ToO
programme at ESO VLT from which we derive the source star's precise fundamental
parameters. Results: From the high-resolution UVES spectra, we find that OGLE
2004-BLG-482's source star is a red giant of MK type a bit later than M3, with
Teff = 3667 +/- 150 K, log g = 2.1 +/- 1.0 and an assumed solar metallicity.
This is confirmed by an OGLE calibrated colour-magnitude diagram. We then
obtain from a detailed microlensing modelling of the light curve linear
limb-darkening coefficients that we compare to model-atmosphere predictions
available in the literature, and find a very good agreement for the I and R
bands. In addition, we perform a similar analysis using an alternative
description of limb darkening based on a principal component analysis of ATLAS
limb-darkening profiles, and also find a very good agreement between
measurements and model predictions.Comment: Accepted in A&
A comparative study of the electrochemical properties of vitamin B-6 related compounds at physiological pH
A comparative study of vitamin B6 group and related compounds in buffered solutions using electrochemical techniques has been performed at neutral pH. Irreversible bi- or tetra-electronic processes are observed for these substances, and the electron transfer coefficient (αn) calculated. It was concluded that either the first or second electron transfer were the rate determining step of the electrode process. The diffusion coefficient of these substances was calculated and the values given follow an inverse tendency to the molecular size. For aldehydes the values obtained were corrected of the hydration reaction.
It is important to remark that catalytic waves were reported for the first time for these compounds. Using a model involving the nitrogen of the basic structure the kinetic constants were calculated for most of them
MOA-2010-BLG-477Lb: constraining the mass of a microlensing planet from microlensing parallax, orbital motion and detection of blended light
Microlensing detections of cool planets are important for the construction of
an unbiased sample to estimate the frequency of planets beyond the snow line,
which is where giant planets are thought to form according to the core
accretion theory of planet formation. In this paper, we report the discovery of
a giant planet detected from the analysis of the light curve of a
high-magnification microlensing event MOA-2010-BLG-477. The measured
planet-star mass ratio is and the projected
separation is in units of the Einstein radius. The angular
Einstein radius is unusually large mas. Combining
this measurement with constraints on the "microlens parallax" and the lens
flux, we can only limit the host mass to the range . In
this particular case, the strong degeneracy between microlensing parallax and
planet orbital motion prevents us from measuring more accurate host and planet
masses. However, we find that adding Bayesian priors from two effects (Galactic
model and Keplerian orbit) each independently favors the upper end of this mass
range, yielding star and planet masses of
and at a distance of kpc,
and with a semi-major axis of AU. Finally, we show that the
lens mass can be determined from future high-resolution near-IR adaptive optics
observations independently from two effects, photometric and astrometric.Comment: 3 Tables, 12 Figures, accepted in Ap
Gravitational Lensing
Gravitational lensing has developed into one of the most powerful tools for
the analysis of the dark universe. This review summarises the theory of
gravitational lensing, its main current applications and representative results
achieved so far. It has two parts. In the first, starting from the equation of
geodesic deviation, the equations of thin and extended gravitational lensing
are derived. In the second, gravitational lensing by stars and planets,
galaxies, galaxy clusters and large-scale structures is discussed and
summarised.Comment: Invited review article to appear in Classical and Quantum Gravity, 85
pages, 15 figure
Characterizing Lenses and Lensed Stars of High-Magnification Single-lens Gravitational Microlensing Events With Lenses Passing Over Source Stars
We present the analysis of the light curves of 9 high-magnification
single-lens gravitational microlensing events with lenses passing over source
stars, including OGLE-2004-BLG-254, MOA-2007-BLG-176,
MOA-2007-BLG-233/OGLE-2007-BLG-302, MOA-2009-BLG-174, MOA-2010-BLG-436,
MOA-2011-BLG-093, MOA-2011-BLG-274, OGLE-2011-BLG-0990/MOA-2011-BLG-300, and
OGLE-2011-BLG-1101/MOA-2011-BLG-325. For all events, we measure the linear
limb-darkening coefficients of the surface brightness profile of source stars
by measuring the deviation of the light curves near the peak affected by the
finite-source effect. For 7 events, we measure the Einstein radii and the
lens-source relative proper motions. Among them, 5 events are found to have
Einstein radii less than 0.2 mas, making the lenses candidates of very low-mass
stars or brown dwarfs. For MOA-2011-BLG-274, especially, the small Einstein
radius of mas combined with the short time scale of
days suggests the possibility that the lens is a
free-floating planet. For MOA-2009-BLG-174, we measure the lens parallax and
thus uniquely determine the physical parameters of the lens. We also find that
the measured lens mass of is consistent with that of a
star blended with the source, suggesting that the blend is likely to be the
lens. Although we find planetary signals for none of events, we provide
exclusion diagrams showing the confidence levels excluding the existence of a
planet as a function of the separation and mass ratio.Comment: 14 pages, 12 figures, 5 table
Photometric Constraints on Microlens Spectroscopy of EROS-BLG-2000-5
We apply EROS photometric data to interpret previously published Keck and VLT
spectra of the binary-microlens caustic-crossing event EROS-BLG-2000-5. We show
that the VLT data imply that the outer 4 % of the limb of the K3-giant source
is strongly in emission in Halpha, in contradiction to available models of the
photosphere. This conflict could be resolved if the integrated Halpha emission
from the chromosphere were equal to 8 % of the integrated Halpha absorption
from the source as a whole. These conclusions regarding the extreme limb are
almost completely model-independent. We also present a general method for using
the photometric data to facilitate direct comparison between the atmospheric
model and the spectroscopic data. While this method has some model-dependent
features, it is fairly robust and can serve to guide the analysis of spectra
while more detailed models of the lens geometry are being developed. In
addition, we find that the color of the limb of the source (outer 5.5 % by
radius) is Delta(V-I) = 0.37 redder than the source as a whole, so that it has
the color of a M0 giant.Comment: 7 figures, 1 tabl
Discovery and Mass Measurements of a Cold, 10-Earth Mass Planet and Its Host Star
We present the discovery and mass measurement of the cold, low-mass planet
MOA-2009-BLG-266Lb, made with the gravitational microlensing method. This
planet has a mass of m_p = 10.4 +- 1.7 Earth masses and orbits a star of mass
M_* = 0.56 +- 0.09 Solar masses at a semi-major axis of a = 3.2 (+1.9 -0.5) AU
and an orbital period of P = 7.6 (+7.7 -1.5} yrs. The planet and host star mass
measurements are enabled by the measurement of the microlensing parallax
effect, which is seen primarily in the light curve distortion due to the
orbital motion of the Earth. But, the analysis also demonstrates the capability
to measure microlensing parallax with the Deep Impact (or EPOXI) spacecraft in
a Heliocentric orbit. The planet mass and orbital distance are similar to
predictions for the critical core mass needed to accrete a substantial gaseous
envelope, and thus may indicate that this planet is a "failed" gas giant. This
and future microlensing detections will test planet formation theory
predictions regarding the prevalence and masses of such planets.Comment: 38 pages with 7 figure
Demography and Dispersal Ability of a Threatened Saproxylic Beetle: A Mark-Recapture Study of the Rosalia Longicorn (Rosalia alpina)
The Rosalia longicorn or Alpine longhorn (Coleoptera: Cerambycidae) is an endangered and strictly protected icon of European saproxylic biodiversity. Despite its popularity, lack of information on its demography and mobility may compromise adoption of suitable conservation strategies. The beetle experienced marked retreat from NW part of its range; its single population survives N of the Alps and W of the Carpathians. The population inhabits several small patches of old beech forest on hill-tops of the Ralska Upland, Czech Republic. We performed mark-recapture study of the population and assessed its distribution pattern. Our results demonstrate the high mobility of the beetle, including dispersal between hills (up to 1.6 km). The system is thus interconnected; it contained ∼2000 adult beetles in 2008. Estimated population densities were high, ranging between 42 and 84 adult beetles/hectare a year. The population survives at a former military-training ground despite long-term isolation and low cover of mature beech forest (∼1%). Its survival could be attributed to lack of forestry activities between the 1950s and 1990s, slow succession preventing canopy closure and undergrowth expansion, and probably also to the distribution of habitat patches on conspicuous hill-tops. In order to increase chances of the population for long term survival, we propose to stop clear-cuts of old beech forests, increase semi-open beech woodlands in areas currently covered by conifer plantations and active habitat management at inhabited sites and their wider environs
Polarographic Behavior of Manganese(II) in the Presence of Oxalate Ions in Perchlorate and Sulfate Solutions
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