2,359 research outputs found
Identification of Absorption Features in an Extrasolar Planet Atmosphere
Water absorption is identified in the atmosphere of HD209458b by comparing
models for the planet's transmitted spectrum to recent, multi-wavelength,
eclipse-depth measurements (from 0.3 to 1 microns) published by Knutson et al.
(2007). A cloud-free model which includes solar abundances, rainout of
condensates, and photoionization of sodium and potassium is in good agreement
with the entire set of eclipse-depth measurements from the ultraviolet to
near-infrared. Constraints are placed on condensate removal by gravitational
settling, the bulk metallicity, and the redistribution of absorbed stellar
flux. Comparisons are also made to the Charbonneau et al. (2002) sodium
measurements.Comment: Accepted for publication in ApJL., in emulate ApJ forma
Characterization of the hot Neptune GJ 436b with Spitzer and ground-based observations
We present Spitzer Space Telescope infrared photometry of a secondary eclipse
of the hot Neptune GJ436b. The observations were obtained using the 8-micron
band of the InfraRed Array Camera (IRAC). The data spanning the predicted time
of secondary eclipse show a clear flux decrement with the expected shape and
duration. The observed eclipse depth of 0.58 mmag allows us to estimate a
blackbody brightness temperature of T_p = 717 +- 35 K at 8 microns. We compare
this infrared flux measurement to a model of the planetary thermal emission,
and show that this model reproduces properly the observed flux decrement. The
timing of the secondary eclipse confirms the non-zero orbital eccentricity of
the planet, while also increasing its precision (e = 0.14 +- 0.01). Additional
new spectroscopic and photometric observations allow us to estimate the
rotational period of the star and to assess the potential presence of another
planet.Comment: Accepted for publication in A&A on 11/09/2007; 7 pages, 6 figure
Astrometric Monitoring of the HR 8799 Planets: Orbit Constraints from Self-Consistent Measurements
We present new astrometric measurements from our ongoing monitoring campaign
of the HR 8799 directly imaged planetary system. These new data points were
obtained with NIRC2 on the W.M. Keck II 10 meter telescope between 2009 and
2014. In addition, we present updated astrometry from previously published
observations in 2007 and 2008. All data were reduced using the SOSIE algorithm,
which accounts for systematic biases present in previously published
observations. This allows us to construct a self-consistent data set derived
entirely from NIRC2 data alone. From this dataset, we detect acceleration for
two of the planets (HR 8799b and e) at 3. We also assess possible
orbital parameters for each of the four planets independently. We find no
statistically significant difference in the allowed inclinations of the
planets. Fitting the astrometry while forcing coplanarity also returns
consistent to within 1 of the best fit values, suggesting that if
inclination offsets of 20 are present, they are not detectable
with current data. Our orbital fits also favor low eccentricities, consistent
with predictions from dynamical modeling. We also find period distributions
consistent to within 1 with a 1:2:4:8 resonance between all planets.
This analysis demonstrates the importance of minimizing astrometric systematics
when fitting for solutions to highly undersampled orbits.Comment: 18 pages, 11 figures. Accepted for publication in A
Accurate Spitzer infrared radius measurement for the hot Neptune GJ 436b
We present Spitzer Space Telescope infrared photometry of a primary transit
of the hot Neptune GJ 436b. The observations were obtained using the 8 microns
band of the InfraRed Array Camera (IRAC). The high accuracy of the transit data
and the weak limb-darkening in the 8 microns IRAC band allow us to derive
(assuming M = 0.44 +- 0.04 Msun for the primary) a precise value for the
planetary radius (4.19 +0.21-0.16 Rearth), the stellar radius (0.463
+0.022-0.017 Rsun), the orbital inclination (85.90 +0.19-0.18 degrees) and
transit timing (2454280.78186 +0.00015-0.00008 HJD). Assuming current planet
models, an internal structure similar to that of Neptune with a small H/He
envelope is necessary to account for the measured radius of GJ 436b.Comment: Accepted for publication in A&A on 21/07/2007; 5 pages, 3 figure
Quantitative and qualitative assessment of plankton: some ecological aspect and water quality parameters of the river Meghna, Bangladesh
Investigation on the seasonal distribution and abundance of various major taxa of phyto and zooplankton and the corresponding physico-chemical characteristics were carried out in four selected stations between the latitude 22°35.494N N-23°23.987 N and longitude 90°35.793 E- 90°49.061 E of the Meghna river system, Bangladesh. Drop count method was followed for the qualitative and quantitative analysis of both phyto- and zooplankton. A total of 41 phytoplankton genera belonging to 17 families and 13 zooplankton genera belonging to 11 families were recorded. Zooplankton growth cycle was noticeably less (3.0%) than the phytoplankton abundance almost throughout the study period. Quantity of plankton registered to increase chronologically from the upper to lower stretches of the river. During summer investigation the load of phytoplankton was recorded maximum (11,300-51,850 No/1). Ratio-wise quantitative difference between zoo- and phytoplankton in composition of the total standing crop fluctuated between 1.0:5.5 and 1:1037. Among the phytoplanktonic groups, Chlorophyceae was found to be dominating (95.0%) in all sampling stations. Protococcus, a single genus of Chlorophyceae played a unique role during summer, contributing the highest density of about 74.0%. The pattern of qualitative and quantitative difference of plankton standing crop in different sampling sites can be attributed to the existing physico-chemical characteristics, mainly water temperature, pH and hardness
VV Pup in a low state: secondary-star irradiation or stellar activity?
Aims. Emission lines in polars show complex profiles with multiple components
that are typically ascribed to the accretion stream, threading region,
accretion spot, and the irradiated secondary-star. In low-state polars the
fractional contribution by the accretion stream, and the accretion spot is
greatly reduced offering an opportunity to study the effect of the
secondary-star irradiation or stellar activity. We observed VV Pup during an
exceptional low-state to study and constrain the properties of the line-forming
regions and to search for evidence of chromospheric activity and/or
irradiation. Methods. We obtained phase-resolved optical spectra at the ESO
VLT+FORS1 with the aim of analyzing the emission line profile and radial
velocity as a function of the orbital period. We also tailored irradiated
secondary-star models to compare the predicted and the observed emission lines
and to establish the nature of the line-forming regions. Results. Our
observations and data analysis, when combined with models of the irradiated
secondary-star, show that, while the weak low ionization metal lines (FeI and
MgI) may be consistent with irradiation processes, the dominant Balmer H
emission lines, as well as NaI and HeI, cannot be reproduced by the irradiated
secondary-star models. We favor the secondary-star chromospheric activity as
the main forming region and cause of the observed H, NaI, and He emission
lines, though a threading region very close to the L1 point cannot be excluded.Comment: 10 pages, 9 figures, in press on A&
The automated detection of proliferative diabetic retinopathy using dual ensemble classification
Objective: Diabetic retinopathy (DR) is a retinal vascular disease that is caused by complications of diabetes. Proliferative diabetic retinopathy (PDR) is the advanced stage of the disease which carries a high risk of severe visual impairment. This stage is characterized by the growth of abnormal new vessels. We aim to develop a method for the automated detection of new vessels from retinal images.
Methods: This method is based on a dual classification approach. Two vessel segmentation approaches are applied to create two separate binary vessel maps which each hold vital information. Local morphology, gradient and intensity features are measured using each binary vessel map to produce two separate 21-D feature vectors. Independent classification is performed for each feature vector using an ensemble system of bagged decision trees. These two independent outcomes are then combined to a produce a final decision.
Results: Sensitivity and specificity results using a dataset of 60 images are 1.0000 and 0.9500 on a per image basis.
Conclusions: The described automated system is capable of detecting the presence of new vessels
Emerging giant resonant exciton induced by Ta-substitution in anatase TiO: a tunable correlation effect
Titanium dioxide (TiO) has rich physical properties with potential
implications in both fundamental physics and new applications. Up-to-date, the
main focus of applied research is to tune its optical properties, which is
usually done via doping and/or nano-engineering. However, understanding the
role of -electrons in materials and possible functionalization of
-electron properties are still major challenges. Herewith, within a
combination of an innovative experimental technique, high energy optical
conductivity, and of the state-of-the-art {\it ab initio} electronic structure
calculations, we report an emerging, novel resonant exciton in the deep
ultraviolet region of the optical response. The resonant exciton evolves upon
low concentration Ta-substitution in anatase TiO films. It is
surprisingly robust and related to strong electron-electron and electron-hole
interactions. The - and - orbitals localization, due to Ta-substitution,
plays an unexpected role, activating strong electronic correlations and
dominating the optical response under photoexcitation. Our results shed light
on a new optical phenomenon in anatase TiO films and on the possibility
of tuning electronic properties by Ta substitution
- …