408 research outputs found
Search for cool giant exoplanets around young and nearby stars - VLT/NaCo near-infrared phase-coronagraphic and differential imaging
[Abridged] Context. Spectral differential imaging (SDI) is part of the
observing strategy of current and future high-contrast imaging instruments. It
aims to reduce the stellar speckles that prevent the detection of cool planets
by using in/out methane-band images. It attenuates the signature of off-axis
companions to the star, such as angular differential imaging (ADI). However,
this attenuation depends on the spectral properties of the low-mass companions
we are searching for. The implications of this particularity on estimating the
detection limits have been poorly explored so far. Aims. We perform an imaging
survey to search for cool (Teff<1000-1300 K) giant planets at separations as
close as 5-10 AU. We also aim to assess the sensitivity limits in SDI data
taking the photometric bias into account. This will lead to a better view of
the SDI performance. Methods. We observed a selected sample of 16 stars (age <
200 Myr, d < 25 pc) with the phase-mask coronagraph, SDI, and ADI modes of
VLT/NaCo. Results. We do not detect any companions. As for the sensitivity
limits, we argue that the SDI residual noise cannot be converted into mass
limits because it represents a differential flux, unlike the case of
single-band images. This results in degeneracies for the mass limits, which may
be removed with the use of single-band constraints. We instead employ a method
of directly determining the mass limits. The survey is sensitive to cool giant
planets beyond 10 AU for 65% and 30 AU for 100% of the sample. Conclusions. For
close-in separations, the optimal regime for SDI corresponds to SDI flux ratios
>2. According to the BT-Settl model, this translates into Teff<800 K. The
methods described here can be applied to the data interpretation of SPHERE. We
expect better performance with the dual-band imager IRDIS, thanks to more
suitable filter characteristics and better image quality.Comment: 19 pages, 16 figures, accepted for publication in A&A, version
including language editin
Search for cool extrasolar giant planets combining coronagraphy, spectral and angular differential imaging
Spectral differential imaging (SDI) is part of the observing strategy of
current and on-going high-contrast imaging instruments on ground-based
telescopes. Although it improves the star light rejection, SDI attenuates the
signature of off-axis companions to the star, just like angular differential
imaging (ADI). However, the attenuation due to SDI has the peculiarity of being
dependent on the spectral properties of the companions. To date, no study has
investigated these effects. Our team is addressing this problem based on data
from a direct imaging survey of 16 stars combining the phase-mask coronagraph,
the SDI and the ADI modes of VLT/NaCo. The objective of the survey is to search
for cool (Teff<1000-1300 K) giant planets at separations of 5-10 AU orbiting
young, nearby stars (<200 Myr, <25 pc). The data analysis did not yield any
detections. As for the estimation of the sensitivity limits of SDI-processed
images, we show that it requires a different analysis than that used in
ADI-based surveys. Based on a method using the flux predictions of evolutionary
models and avoiding the estimation of contrast, we determine directly the mass
sensitivity limits of the survey for the ADI processing alone and with the
combination of SDI and ADI. We show that SDI does not systematically improve
the sensitivity due to the spectral properties and self-subtraction of point
sources.Comment: 5 pages, 2 figure
Discovery of a Low-Mass Companion to the F7V star HD 984
We report the discovery of a low-mass companion to the nearby (d = 47 pc) F7V
star HD 984. The companion is detected 0.19" away from its host star in the L'
band with the Apodizing Phase Plate on NaCo/VLT and was recovered by L'-band
non-coronagraphic imaging data taken a few days later. We confirm the companion
is co-moving with the star with SINFONI integral field spectrograph H+K data.
We present the first published data obtained with SINFONI in pupil-tracking
mode. HD 984 has been argued to be a kinematic member of the 30 Myr-old Columba
group, and its HR diagram position is not altogether inconsistent with being a
ZAMS star of this age. By consolidating different age indicators, including
isochronal age, coronal X-ray emission, and stellar rotation, we independently
estimate a main sequence age of 11585 Myr (95% CL) which does not rely on
this kinematic association. The mass of directly imaged companions are usually
inferred from theoretical evolutionary tracks, which are highly dependent on
the age of the star. Based on the age extrema, we demonstrate that with our
photometric data alone, the companion's mass is highly uncertain: between 33
and 96 M (0.03-0.09 M) using the COND evolutionary
models. We compare the companion's SINFONI spectrum with field dwarf spectra to
break this degeneracy. Based on the slope and shape of the spectrum in the
H-band, we conclude that the companion is an M dwarf. The age of the
system is not further constrained by the companion, as M dwarfs are poorly fit
on low-mass evolutionary tracks. This discovery emphasizes the importance of
obtaining a spectrum to spectral type companions around F-stars.Comment: Accepted for publication in MNRAS, 10 pages, 5 figure
Characterization of an ETREMA MP 50/6 Magnetostrictive Actuator
This report presents the Displacement (Strain)-Current characteristic of an ETREMA MP 50/6 magnetostrictive actuator. This actuator is made of TERFENOL-D and displays giant magnetostriction. The displacement-current characteristic shows significant hysteresis behavior that depends on the rate at which the input is applied. Another important property of ferromagnetic hysteresis - the wiping out property, was also observed in the experiments
Orbits for the Impatient: A Bayesian Rejection Sampling Method for Quickly Fitting the Orbits of Long-Period Exoplanets
We describe a Bayesian rejection sampling algorithm designed to efficiently
compute posterior distributions of orbital elements for data covering short
fractions of long-period exoplanet orbits. Our implementation of this method,
Orbits for the Impatient (OFTI), converges up to several orders of magnitude
faster than two implementations of MCMC in this regime. We illustrate the
efficiency of our approach by showing that OFTI calculates accurate posteriors
for all existing astrometry of the exoplanet 51 Eri b up to 100 times faster
than a Metropolis-Hastings MCMC. We demonstrate the accuracy of OFTI by
comparing our results for several orbiting systems with those of various MCMC
implementations, finding the output posteriors to be identical within shot
noise. We also describe how our algorithm was used to successfully predict the
location of 51 Eri b six months in the future based on less than three months
of astrometry. Finally, we apply OFTI to ten long-period exoplanets and brown
dwarfs, all but one of which have been monitored over less than 3% of their
orbits, producing fits to their orbits from astrometric records in the
literature.Comment: 32 pages, 28 figures, Accepted to A
Energy dissipation in the time domain governed by bosons in a correlated material
In complex materials various interactions play important roles in determining
the material properties. Angle Resolved Photoelectron Spectroscopy (ARPES) has
been used to study these processes by resolving the complex single particle
self energy and quantifying how quantum interactions modify bare
electronic states. However, ambiguities in the measurement of the real part of
the self energy and an intrinsic inability to disentangle various contributions
to the imaginary part of the self energy often leave the implications of such
measurements open to debate. Here we employ a combined theoretical and
experimental treatment of femtosecond time-resolved ARPES (tr-ARPES) and show
how measuring the population dynamics using tr-ARPES can be used to separate
electron-boson interactions from electron-electron interactions. We demonstrate
the analysis of a well-defined electron-boson interaction in the unoccupied
spectrum of the cuprate BiSrCaCuO characterized by an
excited population decay time constant that maps directly to a
discrete component of the equilibrium self energy not readily isolated by
static ARPES experiments.Comment: 19 pages with 6 figure
High-contrast imaging constraints on gas giant planet formation - The Herbig Ae/Be star opportunity
Planet formation studies are often focused on solar-type stars, implicitly
considering our Sun as reference point. This approach overlooks, however, that
Herbig Ae/Be stars are in some sense much better targets to study planet
formation processes empirically, with their disks generally being larger,
brighter and simply easier to observe across a large wavelength range. In
addition, massive gas giant planets have been found on wide orbits around early
type stars, triggering the question if these objects did indeed form there and,
if so, by what process. In the following I briefly review what we currently
know about the occurrence rate of planets around intermediate mass stars,
before discussing recent results from Herbig Ae/Be stars in the context of
planet formation. The main emphasis is put on spatially resolved polarized
light images of potentially planet forming disks and how these images - in
combination with other data - can be used to empirically constrain (parts of)
the planet formation process. Of particular interest are two objects, HD100546
and HD169142, where, in addition to intriguing morphological structures in the
disks, direct observational evidence for (very) young planets has been
reported. I conclude with an outlook, what further progress we can expect in
the very near future with the next generation of high-contrast imagers at 8-m
class telescopes and their synergies with ALMA.Comment: Accepted by Astrophysics and Space Science as invited short review in
special issue about Herbig Ae/Be stars; 12 pages incl. 5 figures, 2 tables
and reference
Discovery of a low-mass companion to the F7V star HD 984
We report the discovery of a low-mass companion to the nearby (d = 47pc) F7V star HD 984. The companion is detected 0.19 arcsec away from its host star in the L′ band with the Apodized Phase Plate on NaCo/Very Large Telescope and was recovered by L′-band non-coronagraphic imaging data taken a few days later. We confirm the companion is comoving with the star with SINFONI integral field spectrograph H + K data. We present the first published data obtained with SINFONI in pupil-tracking mode. HD 984 has been argued to be a kinematic member of the 30Myr-old Columba group, and its HR diagram position is not altogether inconsistent with being a zero-age main sequence star of this age. By consolidating different age indicators, including isochronal age, coronal X-ray emission, and stellar rotation, we independently estimate a main-sequence age of 115±85Myr (95 per cent CL) which does not rely on this kinematic association. The mass of directly imaged companions are usually inferred from theoretical evolutionary tracks, which are highly dependent on the age of the star. Based on the age extrema, we demonstrate that with our photometric data alone, the companion's mass is highly uncertain: between 33 and 96 MJup (0.03-0.09M⊙) using the COND evolutionary models. We compare the companion's SINFONI spectrum with field dwarf spectra to break this degeneracy. Based on the slope and shape of the spectrum in the H band, we conclude that the companion is an M6.0 ± 0.5 dwarf. The age of the system is not further constrained by the companion, as M dwarfs are poorly fit on low-mass evolutionary tracks. This discovery emphasizes the importance of obtaining a spectrum to spectral type companions around F-star
Identification and expression pattern of a new carotenoid cleavage dioxygenase gene member from Bixa orellana
Carotenoid cleavage dioxygenases (CCDs) are a class of enzymes involved in the biosynthesis of a broad diversity of secondary metabolites known as apocarotenoids. In plants, CCDs are part of a genetic family with members which cleave specific double bonds of carotenoid molecules. CCDs are involved in the production of diverse and important metabolites such as vitamin A and abscisic acid (ABA). Bixa orellana L. is the main source of the natural pigment annatto or bixin, an apocarotenoid accumulated in large quantities in its seeds. Bixin biosynthesis has been studied and the involvement of a CCD has been confirmed in vitro. However, the CCD genes involved in the biosynthesis of the wide variety of apocarotenoids found in this plant have not been well documented. In this study, a new CCD1 gene member (BoCCD1) was identified and its expression was charaterized in different plant tissues of B. orellana plantlets and adult plants. The BoCCD1 sequence showed high homology with plant CCD1s involved mainly in the cleavage of carotenoids in several sites to generate multiple apocarotenoid products. Here, the expression profiles of the BoCCD1 gene were analysed and discussed in relation to total carotenoids and other important apocarotenoids such as bixin
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