221 research outputs found
High-precision analysis of binary stars with planets. I. Searching for condensation temperature trends in the HD 106515 system
We explore the probable chemical signature of planet formation in the
remarkable binary system HD 106515. The A star hosts a massive long-period
planet with 9 MJup detected by radial velocity. We also refine stellar and
planetary parameters by using non-solar-scaled opacities when modeling the
stars. Methods. We carried out a simultaneous determination of stellar
parameters and abundances, by applying for the first time non-solar-scaled
opacities in this binary system, in order to reach the highest possible
precision. Results. The stars A and B in the binary system HD 106515 do not
seem to be depleted in refractory elements, which is different when comparing
the Sun with solar-twins. Then, the terrestrial planet formation would have
been less efficient in the stars of this binary system. Together with HD
80606/7, this is the second binary system which does not seem to present a
(terrestrial) signature of planet formation, and hosting both systems an
eccentric giant planet. This is in agreement with numerical simulations, where
the early dynamical evolution of eccentric giant planets clear out most of the
possible terrestrial planets in the inner zone. We refined the stellar mass,
radius and age for both stars and found a notable difference of 78% in R
compared to previous works. We also refined the planet mass to mp sini = 9.08
+/- 0.20 MJup, which differs by 6% compared with literature. In addition, we
showed that the non-solar-scaled solution is not compatible with the classical
solar-scaled method, and some abundance differences are comparable to NLTE or
GCE effects specially when using the Sun as reference. Then, we encourage the
use of non-solar-scaled opacities in high-precision studies such as the
detection of Tc trends.[abridged]Comment: 9 pages, 10 figures, A&A accepted. arXiv admin note: text overlap
with arXiv:1507.0812
Absorption efficiency of gold nanorods determined by quantum dot fluorescence thermometry
In this work quantum dot fluorescence thermometry, in combination with double-beam confocal microscopy, has been applied to determine the thermal loading of gold nanorods when subjected to an optical excitation at the longitudinal surface plasmon resonance. The absorbing/heating efficiency of low (≈3) aspect ratio gold nanorods has been experimentally determined to be close to 100%, in excellent agreement with theoretical simulations of the extinction, absorption, and scattering spectra based on the discrete dipole approximation
KELT-17: a chemically peculiar Am star and a hot-Jupiter planet
Context. The detection of planets orbiting chemically peculiar stars is very
scarcely known in the literature. Aims. To determine the detailed chemical
composition of the remarkable planet host star KELT-17. This object hosts a
hot-Jupiter planet with 1.31 MJup detected by transits, being one of the more
massive and rapidly rotating planet hosts to date. We aimed to derive a
complete chemical pattern for this star, in order to compare it with those of
chemically peculiar stars. Methods. We carried out a detailed abundance
determination in the planet host star KELT-17 via spectral synthesis. Stellar
parameters were estimated iteratively by fitting Balmer line profiles and
imposing the Fe ionization balance, using the program SYNTHE together with
plane-parallel ATLAS12 model atmospheres. Specific opacities for an arbitrary
composition and microturbulence velocity vmicro were calculated through the
Opacity Sampling (OS) method. The abundances were determined iteratively by
fitting synthetic spectra to metallic lines of 16 different chemical species
using the program SYNTHE. The complete chemical pattern of KELT-17 was compared
to the recently published average pattern of Am stars. We estimated the stellar
radius by two methods: a) comparing the synthetic spectral energy distribution
with the available photometric data and the Gaia parallax, and b) using a
Bayesian estimation of stellar parameters using stellar isochrones. Results. We
found overabundances of Ti, Cr, Mn, Fe, Ni, Zn, Sr, Y, Zr, and Ba, together
with subsolar values of Ca and Sc. Notably, the chemical pattern agrees with
those recently published of Am stars, being then KELT-17 the first exoplanet
host whose complete chemical pattern is unambiguously identified with this
class. The stellar radius derived by two different methods agrees to each other
and with those previously obtained in the literature.Comment: 5 pages, 8 figures, 2 tables, A&A accepte
SNOM characterization of a potential low cost thin gold coated micro-structured grating using a commercial CD substrate
In this work near-field optical measurements of a corrugated grating coated with a 30 nm thick gold film are presented. The grating was made using the polycarbonate corrugated substrate of a commercially available recordable CD as template. This has been proved to be a versatile and low cost technique in producing large 1.6 μm period gratings. The study was carried out using a Scanning Near-Field Optical Microscope (SNOM) working in both collection and reflection modes at two different wavelengths, 532 nm and 633 nm. The results illustrate that the intensity patterns of near-field images are strongly polarization-dependent, even showing different periodicity of the localized fields for orthogonal polarization states. When electric field of the light is polarized parallel to the grooves, the periodicity of the SNOM images is coincident with the grating period, whereas when the light is polarized perpendicular to the grooves the SNOM pattern shows a periodicity twice that of the corresponding topography of the grating. Numerical simulations of the SNOM data based on a two-dimensional Finite Difference Time-Domain (2D-FDTD) model have been realized. The results of the simulations are in good agreement with the experimental data, emphasizing the need of performing numerical simulation for the correct interpretation of SNOM data
Order in driven vortex lattices in superconducting Nb films with nanostructured pinning potentials
Driven vortex lattices have been studied in a material with strong pinning,
such as Nb films. Samples in which natural random pinning coexists with
artificial ordered arrays of defects (submicrometric Ni dots) have been
fabricated with different geometries (square, triangular and rectangular).
Three different dynamic regimes are found: for low vortex velocities, there is
a plastic regime in which random defects frustrate the effect of the ordered
array; then, for vortex velocities in the range 1-100 m/s, there is a sudden
increase in the interaction between the vortex lattice and the ordered dot
array, independent on the geometry. This effect is associated to the onset of
quasi long range order in the vortex lattice leading to an increase in the
overlap between the vortex lattice and the magnetic dots array. Finally, at
larger velocities the ordered array-vortex lattice interaction is suppresed
again, in agreement with the behavior found in numerical simulations.Comment: 8 text pages + 4 figure
A generalized approach to photon avalanche upconversion in luminescent nanocrystals
Photon avalanching nanoparticles (ANPs) exhibit extremely nonlinear
upconverted emission valuable for sub-diffraction imaging, nanoscale sensing,
and optical computing. Avalanching has been demonstrated with Tm3+, Nd3+ or
Pr3+-doped nanocrystals, but their emission is limited to 600 and 800 nm,
restricting applications. Here, we utilize Gd3+-assisted energy migration to
tune the emission wavelengths of Tm3+-sensitized ANPs and generate highly
nonlinear emission of Eu3+, Tb3+, Ho3+, and Er3+ ions. The upconversion
intensities of these spectrally discrete ANPs scale with the nonlinearity
factor s = 10-17 under 1064 nm excitation at power densities as low as 6
kW/cm2. This strategy for imprinting avalanche behavior on remote emitters can
be extended to fluorophores adjacent to ANPs, as we demonstrate with
CdS/CdSe/CdS core/shell/shell quantum dots. ANPs with rationally designed
energy transfer networks provide the means to transform conventional linear
emitters into a highly nonlinear ones, expanding the use of photon avalanching
in biological, chemical, and photonic applications.Comment: 13 pages, 5 figure
Evaluation of rare earth doped silica sub-micrometric spheres as optically controlled temperature sensors
We report on the evaluation of rare earth (Er3þ, Eu3þ, and Tb3þ ions) SiO2 sub-micrometric
spheres as potential optically controllable temperature sensors. Details about fabrication, optical
manipulation and spectroscopic characterization of the sub-micrometric spheres are presented.
The fluorescence properties of the micros-spheres in the biological range (25–60 C) have been
systematically investigated. From this systematic study, the thermal resolution potentially
achieved in each case has been determined and compared to previous works
Optical second harmonic generation in Yttrium Aluminum Borate single crystals (theoretical simulation and experiment)
Experimental measurements of the second order susceptibilities for the second
harmonic generation are reported for YAl3(BO3)4 (YAB) single crystals for the
two principal tensor components xyz and yyy. First principles calculation of
the linear and nonlinear optical susceptibilities for Yttrium Aluminum Borate
YAl3(BO3)4 (YAB) crystal have been carried out within a framework of the
full-potential linear augmented plane wave (FP-LAPW) method. Our calculations
show a large anisotropy of the linear and nonlinear optical susceptibilities.
The observed dependences of the second order susceptibilities for the static
frequency limit and for the frequency may be a consequence of different
contribution of electron-phonon interactions. The imaginary parts of the second
order SHG susceptibility chi_{123}^{(2)}(omega), chi_{112}^{(2)}(omega),
chi_{222}^{(2)}(omega), and chi_{213}^{(2)}(omega) are evaluated. We find that
the 2(omega) inter-band and intra-band contributions to the real and imaginary
parts of chi_{ijk}^{(2)}\l(omega) show opposite signs. The calculated second
order susceptibilities are in reasonably good agreement with the experimental
measurements.Comment: 16 pages, 11 figure
Ethnic differences in ovulatory function in nulliparous women
African-American women have a long-standing approximately 20% higher breast cancer incidence rate than USA White women under age 40 while rates among Latinas are lower than those of Whites. The reasons for this are not clear, however they may be due to ethnic differences in circulating oestradiol and progesterone levels. In a cross-sectional study, we investigated whether anovulation frequency and circulating serum oestradiol and/or progesterone levels vary among normally cycling nulliparous African-American (n=60), Latina (n=112) and non-Latina White (n=69) women. Blood and urine specimens were collected over two menstrual cycles among healthy 17- to 34-year-old women. Frequency of anovulation was greater among White women (nine out of 63, 14.3%) than African-American women (four out of 56, 7.1%) or Latina women (seven out of 102, 6.9%), although these differences were not statistically significant. African-American women had 9.9% (P=0.26) higher follicular phase oestradiol concentrations than Latina women and 17.4% (P=0.13) higher levels than White women. African-American women also had considerably higher levels of luteal phase oestradiol (vs Latinas, +9.4%, P=0.14; vs Whites, +25.3%, P=0.003) and progesterone (vs Latinas, +15.4%, P=0.07; vs Whites, +36.4%, P=0.002). Latina women were also observed to have higher follicular oestradiol, and luteal oestradiol and progesterone levels than White women (follicular oestradiol: +6.8%, P=0.48; luteal oestradiol: +14.6%, P=0.04; luteal progesterone: +18.2%, P=0.06). These results suggest that exposure to endogenous steroid hormones may be greater for young African-American and Latina women than for Whites
A Compact Multiphoton 3D Imaging System for Recording Fast Neuronal Activity
We constructed a simple and compact imaging system designed specifically for the recording of fast neuronal activity in a 3D volume. The system uses an Yb:KYW femtosecond laser we designed for use with acousto-optic deflection. An integrated two-axis acousto-optic deflector, driven by digitally synthesized signals, can target locations in three dimensions. Data acquisition and the control of scanning are performed by a LeCroy digital oscilloscope. The total cost of construction was one order of magnitude lower than that of a typical Ti:sapphire system. The entire imaging apparatus, including the laser, fits comfortably onto a small rig for electrophysiology. Despite the low cost and simplicity, the convergence of several new technologies allowed us to achieve the following capabilities: i) full-frame acquisition at video rates suitable for patch clamping; ii) random access in under ten microseconds with dwelling ability in the nominal focal plane; iii) three-dimensional random access with the ability to perform fast volume sweeps at kilohertz rates; and iv) fluorescence lifetime imaging. We demonstrate the ability to record action potentials with high temporal resolution using intracellularly loaded potentiometric dye di-2-ANEPEQ. Our design proffers easy integration with electrophysiology and promises a more widespread adoption of functional two-photon imaging as a tool for the study of neuronal activity. The software and firmware we developed is available for download at http://neurospy.org/ under an open source license
- …