94 research outputs found
Center-to-limb variation of the continuum intensity and linear polarization of stars with transiting exoplanets
The limb darkening and center-to-limb variation of the continuum polarization is calculated for a grid of one-dimensional stellar model atmospheres and for a wavelength range between 300 and 950 nm. Model parameters match those of the transiting stars taken from the NASA exoplanet archive. The limb darkening of the continuum radiation for these stars is shown to decrease with the rise in their effective temperature. For the lambda = 370 nm wavelength, which corresponds to the maximum of the Johnson-Cousins UX filter, the limb darkening values of the planet transiting stars lie in a range between 0.03 and 0.3. The continuum linear polarization depends not only on the effective temperature of the star but also on its gravity and metallicity. Its value decreases for increasing values of these parameters. In the UX band, the maximum linear polarization of stars with transiting planets amounts to 4%, while the minimum value is approximately 0.3%. The continuum limb darkening and the linear polarization decrease rapidly with wavelength. At the R band maximum (lambda = 700 nm), the linear polarization close to the limb is in fact two orders of magnitude smaller than in the UX band. The center- to-limb variation of the continuum intensity and the linear polarization of the stars with transiting planets can be approximated, respectively, by polynomials of the fourth and the sixth degree. The coefficients of the polynomials, as well as the IDL procedures for reading them, are available in electronic form. It is shown that there are two classes of stars with high linear polarization at the limb. The first one consists of cold dwarfs. Their typical representatives are HATS-6, Kepler-45, as well as all the stars with similar parameters. The second class of stars includes hotter giants and subgiants. Among them we have CoRoT-28, Kepler-91, and the group of stars with effective temperatures and gravities of approximately 5000 K and 3.5, respectively
The impact of non-LTE effects and granulation inhomogeneities on the derived iron and oxygen abundances in metal-poor halo stars
This paper presents the results of a detailed theoretical investigation of
the impact of non-LTE effects and of granulation inhomogeneities on the derived
iron and oxygen abundances in the metal-poor halo subgiant HD140283. Our
analysis is based on both the `classical' one-dimensional (1D) stellar
atmosphere models and on the new generation of three-dimensional (3D)
hydrodynamical models. We find that the non-LTE effects on the iron abundance
derived from Fe {\sc i} lines are very important, amounting to dex
and to dex in the 3D and 1D cases, respectively. On the other hand,
we find that non-LTE and 3D effects have to be taken into account for a
reliable determination of the iron abundance from weak Fe {\sc ii} lines,
because the significant overexcitation of their upper levels in the granular
regions tend to produce emission features. As a result such Fe {\sc ii} lines
are weaker than in LTE and the abundance correction amounts to dex
for the 3D case. We derive also the oxygen-to-iron abundance ratio in the
metal-poor star HD140283 by using the O {\sc i} triplet at 7772--5 \AA and the
forbidden [O {\sc i}] line at 6300 \AA. Interestingly, when both non-LTE and 3D
effects are taken into account there still remains significant discrepancies in
the iron abundances derived from Fe {\sc i} and Fe {\sc ii} lines, as well as
in the oxygen abundances inferred from the O {\sc i} and [O {\sc i}] lines. We
conclude that the metalicity of this type of metal-poor stars could be
significantly larger than previously thought, which may have far-reaching
implications in stellar astrophysics.Comment: The Astrophysical Journal (in press). (35 pages, 5 figures and 4
tables
Oxygen and Magnesium Abundance in the Ultra-Metal-Poor Giants CS22949-037 and CS29498-043: Challenges in Models of Atmospheres
We report the results of a non-LTE Fe, O and Mg abundance analysis of the
carbon-nitrogen-rich ultra-metal-poor giants CS29498--043 and CS22949--037. The
abundance of oxygen has been derived from measurements of the oxygen triplet at
7771-5 A in high resolution spectra obtained with KeckI/HIRES and the forbidden
line [OI] 6300 A detected in the TNG/SARG spectra of CS29498-043. Detailed
non-LTE analysis of Fe lines has provided reliable stellar parameters which,
however, do not resolve the oxygen abundance conflict as derived from the OI
7771-5 A triplet and the [OI] 6300 A forbidden lines. We obtained the following
oxygen abundance: for CS22949-037 [O/Fe] =3.13, 1.95; and for CS29498-043;
[O/Fe]=3.02, 2.49, based on the OI 7771-5 A triplet and the [OI] 6300 A
forbidden line, respectively. A similar conflict appears to exist between the
forbidden resonance line MgI 4571 A and several subordinate lines, such as MgI
5172 and 5183 A. Our analysis demonstrates the failure of standard
plane--parallel atmosphere models to describe the physical conditions in the
line-forming regions of these ultra-metal-poor giants.Comment: 16 pages, 15 figures, accepted by Astronomy and Astrophysic
Редокс-реакции у Hydrocharis morsus-ranae L. в условиях техногенной нагрузки
Aquatic ecosystems are very sensitive to industrial impacts, and, therefore, it is increasingly important to study the mechanisms underlying the tolerance of aquatic organisms to water pollution. Heavy metals (HMs) are among the most common and toxic pollutants of aquatic ecosystems. They have a particularly strong effect on macrophytes, which are in close contact with the aquatic environment and can accumulate metals in considerable quantities. Hydrocharis morsus-ranae L. is a floating macrophyte (pleistophyte) with a high capacity for accumulation of HMs. The aim of the present study was to assess the effect of industrial pollution on the redox reactions in H. morsus-ranae and to identify the role of low molecular weight antioxidants in adaptation of this macrophyte to unfavorable conditions. A comparative analysis of the physiological and biochemical characteristics of H. morsus-ranae from two (reference and impacted) water bodies was carried out. The study revealed an increased level of lipid peroxidation products in the leaves of H. morsus-ranae under industrial impact, which indicates oxidative stress. Nevertheless, this floating plant demonstrated fairly high resistance to adverse conditions, due to the synthesis of non-enzymatic antioxidants such as proline and soluble protein thiols. Revealing the response of macrophytes to pollution of water bodies will help predict the state of aquatic ecosystems with an increase in anthropogenic pressure. © Siberian Federal University. All rights reserved.Acknowledgements. The reported study was partly funded by RFBR and the Government of the Sverdlovsk Region, project number 20–45–660014. The authors are grateful to the reviewer, Prof., D. Sc. Golovko T. K. (Institute of Biology of Komi Scientific Centre of the Ural Branch of RAS, Syktyvkar) for valuable comments that helped improve this paper and to Dr. Tripti (Ural Federal University, Ekaterinburg, Russia) for editing the English language
DYNAMICS OF BIOCHEMICAL INDICES OF BLOOD SERUM IN RABBITS UNDER THE INFLUENCE OF PHOTOTHERAPY AFTER LOCAL SKIN THERMAL BURN
The article presents data on the dynamics of some biochemical indices in blood serum of rabbits (total protein, alanine aminotransferase, ureal, creatinine, total cholesterol, glucose) during phototherapy of local skin thermal injury using "Bioprone", "Rikta", "Azor", OKN-11M, BOP-4 devices in 5-15 days after wounding. Obtained data testifies to the development of the response of an organism in the form of metabolic processes aimed at the maintenance of constant internal environment but expressed less that at vast burns. Course of phototherapy quite effectively but without distinct differentiation by the method of therapy has positive effect on the normalization of biochemical indices of blood serum
Solar BaII 4554 A line as Doppler diagnostics: NLTE analysis in 3D hydrodynamical model
The aim of this paper is to analyse the validity of the Dopplergram and
lambda-meter techniques for the Doppler diagnostics of solar photospheric
velocities using the BaII 4554 A line. Both techniques are evaluated by means
of NLTE radiative transfer calculations of the BaII 4554 A line in a
three-dimensional hydrodynamical model of solar convection. We consider the
cases of spatially unsmeared profiles and the profiles smeared to the
resolution of ground-based observations. We find that: (i)
Speckle-reconstructed Dopplergram velocities reproduce the ``true'' velocities
well at heights around 300 km, except for intergranular lanes with strong
downflows where the velocity can be overestimated. (ii) The lambda-meter
velocities give a good representation of the ``true'' velocities through the
whole photosphere, both under the original and reduced spatial resolutions. The
velocities derived from the inner wing of smeared BaII 4554 A line profiles are
more reliable than those for the outer wing. Only under high spatial resolution
does the inner wing velocities calculated in intergranular regions give an
underestimate (or even a sign reversal) compared with the model velocities.
(iii) NLTE effects should be taken into account in modelling the BaII 4554 A
line profiles. Such effects are more pronounced in intergranular regions. Our
analysis supports the opinion that the Dopplergram technique applied to the
BaII 4554 A line is a valuable tool for the Doppler diagnostics of the middle
photosphere around 300 km. The \lambda-meter technique applied to this line
gives us a good opportunity to ``trace'' the non-thermal motions along the
whole photosphere up to the temperature minimum and lower chromosphere.Comment: accepted by Astronomy and Astrophysic
Oxygen abundances in planet-harbouring stars. Comparison of different abundance indicators
We present a detailed and uniform study of oxygen abundances in 155 solar
type stars, 96 of which are planet hosts and 59 of which form part of a
volume-limited comparison sample with no known planets. EW measurements were
carried out for the [O I] 6300 \AA line and the O I triplet, and spectral
synthesis was performed for several OH lines. NLTE corrections were calculated
and applied to the LTE abundance results derived from the O I 7771-5 \AA\
triplet. Abundances from [O I], the O I triplet and near-UV OH were obtained in
103, 87 and 77 dwarfs, respectively. We present the first detailed and uniform
comparison of these three oxygen indicators in a large sample of solar-type
stars. There is good agreement between the [O/H] ratios from forbidden and OH
lines, while the NLTE triplet shows a systematically lower abundance. We found
that discrepancies between OH, [O I] and the O I triplet do not exceed 0.2 dex
in most cases. We have studied abundance trends in planet host and comparison
sample stars, and no obvious anomalies related to the presence of planets have
been detected. All three indicators show that, on average, [O/Fe] decreases
with [Fe/H] in the metallicity range -0.8<[Fe/H]<0.5. The planet host stars
present an average oxygen overabundance of 0.1-0.2dex with respect to the
comparison sample.Comment: 19 pages, 11 figures (low resolution), accepted for publication in
A&
An overview of early investigational drugs for the treatment of human papilloma virus infection and associated dysplasia
Introduction: High-risk HPV (HR-HPV) related invasive cervical cancer (ICC) causes >270,000 deaths per annum world-wide with over 85% of these occurring in low-resource countries. Ablative and excisional treatment modalities are restricted for use with high-grade pre-cancerous cervical disease with HPV infection and low-grade dysplasia mostly managed by a watch-and-wait policy.Areas Covered: Various pharmacological approaches have been investigated as non-destructive alternatives for the treatment of HR-HPV infection and associated dysplasia. These are discussed dealing with efficacy, ease-of-use (physician or self-applied), systemic or locally applied, side-effects, cost and risks. The main focus is the perceived impact on current clinical practice of a self-applied, effective and safe pharmacological anti-HPV treatment.Expert opinion: Current prophylactic HPV vaccines are expensive, HPV type restricted and have little effect in already infected women. Therapeutic vaccines are under development but are also HPV type-restricted. At present, the developed nations use national cytology screening and surgical procedures to treat only women identified with HPV-related high-grade dysplastic disease. However, since HPV testing is rapidly replacing cytology as the test-of-choice, a suitable topically-applied and low-cost antiviral treatment could be an ideal solution for treatment of HPV infection per se with test-of-cure carried out by repeat HPV testing. Cytology would only then be necessary for women who remained HPV positive. Although of significant benefit in the developed countries, combining such a treatment with self-sampled HPV testing could revolutionise the management of this disease in the developing world which lack both the infrastructure and resources to establish national cytology screening programs
Oxygen in the Very Early Galaxy
Oxygen abundances in a sample of ultra-metal-poor subdwarfs have been derived
from measurements of the oxygen triplet at 7771--5 A and OH lines in the near
UV performed in high-resolution and high signal-to-noise spectra obtained with
WHT/UES, KeckI/HIRES, and VLT/UVES. Our Fe abundances were derived in LTE and
then corrected for NLTE effects following Thevenin and Idiart (1999). The new
oxygen abundances confirm previous findings for a progressive linear rise in
the oxygen-to-iron ratio with a slope -0.33+-0.02 from solar metallicity to
[Fe/H] -3. A slightly higher slope would be obtained if the Fe NLTE corrections
were not considered. Below [Fe/H]= -2.5 our stars show [O/Fe] ratios as high as
~ 1.17 (G64-12), which can be interpreted as evidence for oxygen overproduction
in the very early epoch of the formation of the halo, possibly associated with
supernova events with very massive progenitor stars. We show that the arguments
against this linear trend given by Fulbright and Kraft (1999), based on the LTE
Fe analysis of two metal-poor stars cannot be sustained when an NLTE analysis
is performed. Using 1-D models our analysis of three oxygen indicators
available for BD +23 3130 gives consistent abundances within 0.16 dex and
average [O/Fe] ratio of 0.91.Comment: 45 pages, 11 figures, accepted for publication in The Astrophysical
Journa
Eclipses observed by LYRA - a sensitive tool to test the models for the solar irradiance
We analyze the light curves of the recent solar eclipses measured by the
Herzberg channel (200-220 nm) of the Large Yield RAdiometer (LYRA) onboard
PROBA-2. The measurements allow us to accurately retrieve the center- to-limb
variations (CLV) of the solar brightness. The formation height of the radiation
depends on the observing angle so the examination of the CLV provide
information about a broad range of heights in the solar atmosphere. We employ
the 1D NLTE radiative transfer COde for Solar Irradiance (COSI) to model the
measured light curves and corresponding CLV dependencies. The modeling is used
to test and constrain the existing 1D models of the solar atmosphere, e.g. the
temperature structure of the photosphere and the treatment of the pseudo-
continuum opacities in the Herzberg continuum range. We show that COSI can
accurately reproduce not only the irradiance from the entire solar disk, but
also the measured CLV. It hence can be used as a reliable tool for modeling the
variability of the spectral solar irradiance.Comment: 19 pages, 9 figures, Solar Physic
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