57 research outputs found
Binaries among low-mass stars in nearby young moving groups
The solar galactic neighbourhood contains a number of young co-moving
associations of stars (so-called `young moving groups') with ages of ~10--150
Myr, which are prime targets for a range of scientific studies, including
direct imaging planet searches. The late-type stellar population of such groups
still remain in their pre-main sequence phase, and are thus well suited for
purposes such as isochronal dating. Close binaries are particularly useful in
this regard, since they allow for a model-independent dynamical mass
determination. Here we present a dedicated effort to identify new close
binaries in nearby young moving groups, through high-resolution imaging with
the AstraLux Sur Lucky Imaging camera. We surveyed 181 targets, resulting in
the detection of 61 companions or candidates, of which 38 are new discoveries.
An interesting example of such a case is 2MASS J00302572-6236015 AB, which is a
high-probability member of the Tucana-Horologium moving group, and has an
estimated orbital period of less than 10 years. Among the previously known
objects is a serendipitous detection of the deuterium burning boundary
circumbinary companion 2MASS J01033563-5515561 (AB)b in the z'-band, thereby
extending the spectral coverage for this object down to near-visible
wavelengths.Comment: 12 pages, 3 figures, accepted for publication in A&
Near-Infrared Detection and Characterization of the Exoplanet HD 95086 b with the Gemini Planet Imager
HD 95086 is an intermediate-mass debris-disk-bearing star. VLT/NaCo observations revealed it hosts a companion (HD
95086 b) at AU. Follow-up observations at 1.66 and 2.18
yielded a null detection, suggesting extremely red colors for the planet and
the need for deeper direct-imaging data. In this Letter, we report H- () and - () band detections of HD 95086 b from
Gemini Planet Imager (GPI) commissioning observations taken by the GPI team.
The planet position in both spectral channels is consistent with the NaCo
measurements and we confirm it to be comoving. Our photometry yields colors of
H-L'= mag and K-L'= mag, consistent with
previously reported 5- upper limits in H and Ks. The photometry of HD
95086 b best matches that of 2M 1207 b and HR 8799 cde. Comparing its spectral
energy distribution with the BT-SETTL and LESIA planet atmospheric models
yields T600-1500 K and log g2.1-4.5. Hot-start
evolutionary models yield M= M. Warm-start models reproduce the
combined absolute fluxes of the object for M=4-14 M for a wide range of
plausible initial conditions (S=8-13 k/baryon). The
color-magnitude diagram location of HD 95086 b and its estimated
T and log g suggest that the planet is a peculiar L-T
transition object with an enhanced amount of photospheric dust.Comment: 4 pages, 4 figures, 3 tables, accepted on April, 15th, 201
High-Cadence, High-Contrast Imaging for Exoplanet Mapping: Observations of the HR 8799 Planets with VLT/SPHERE Satellite Spot-Corrected Relative Photometry
Time-resolved photometry is an important new probe of the physics of
condensate clouds in extrasolar planets and brown dwarfs. Extreme adaptive
optics systems can directly image planets, but precise brightness measurements
are challenging. We present VLT/SPHERE high-contrast, time-resolved broad
H-band near-infrared photometry for four exoplanets in the HR 8799 system,
sampling changes from night to night over five nights with relatively short
integrations. The photospheres of these four planets are often modeled by
patchy clouds and may show large-amplitude rotational brightness modulations.
Our observations provide high-quality images of the system. We present a
detailed performance analysis of different data analysis approaches to
accurately measure the relative brightnesses of the four exoplanets. We explore
the information in satellite spots and demonstrate their use as a proxy for
image quality. While the brightness variations of the satellite spots are
strongly correlated, we also identify a second-order anti-correlation pattern
between the different spots. Our study finds that PCA-based KLIP reduction with
satellite spot-modulated artificial planet-injection based photometry (SMAP)
leads to a significant (~3x) gain in photometric accuracy over standard
aperture-based photometry and reaches 0.1 mag per point accuracy for our
dataset, the signal-to-noise of which is limited by small field rotation.
Relative planet-to-planet photometry can be compared be- tween nights, enabling
observations spanning multiple nights to probe variability. Recent high-quality
relative H-band photometry of the b-c planet pair agree to about 1%.Comment: Astrophysical Journal, in pres
The 2008-2009 outburst of the young binary system Z CMa unraveled by interferometry with high spectral resolution
Z CMa is a young binary system consisting of an Herbig primary and a FU Ori
companion. Both components seem to be surrounded by active accretion disks and
a jet was associated to the Herbig B0. In Nov. 2008, K. Grankin discovered that
Z CMa was exhibiting an outburst with an amplitude larger than any photometric
variations recorded in the last 25 years. To study the innermost regions in
which the outburst occurs and understand its origin, we have observed both
binary components with AMBER/VLTI across the Br{\gamma} emission line in Dec.
2009 in medium and high spectral resolution modes. Our observations show that
the Herbig Be, responsible for the increase of luminosity, also produces a
strong Br{\gamma} emission, and they allow us to disentangle from various
origins by locating the emission at each velocities through the line.
Considering a model of a Keplerian disk alone fails at reproducing the
asymmetric spectro-astrometric measurements, suggesting a major contribution
from an outflow.Comment: To be published in the proceedings of the SPIE'2010 conference on
"Optical and Infrared Interferometry II
An upper limit on the mass of the circumplanetary disk for DH Tau b
DH Tau is a young (1 Myr) classical T Tauri star. It is one of the few
young PMS stars known to be associated with a planetary mass companion, DH Tau
b, orbiting at large separation and detected by direct imaging. DH Tau b is
thought to be accreting based on copious H emission and exhibits
variable Paschen Beta emission. NOEMA observations at 230 GHz allow us to place
constraints on the disk dust mass for both DH Tau b and the primary in a regime
where the disks will appear optically thin. We estimate a disk dust mass for
the primary, DH Tau A of , which gives a disk-to-star
mass ratio of 0.014 (assuming the usual Gas-to-Dust mass ratio of 100 in the
disk). We find a conservative disk dust mass upper limit of 0.42
for DH Tau b, assuming that the disk temperature is dominated by irradiation
from DH Tau b itself. Given the environment of the circumplanetary disk,
variable illumination from the primary or the equilibrium temperature of the
surrounding cloud would lead to even lower disk mass estimates. A MCFOST
radiative transfer model including heating of the circumplanetary disk by DH
Tau b and DH Tau A suggests that a mass averaged disk temperature of 22 K is
more realistic, resulting in a dust disk mass upper limit of 0.09
for DH Tau b. We place DH Tau b in context with similar objects and discuss the
consequences for planet formation models.Comment: accepted for publication in A
Precise radial velocities of giant stars IX. HD 59686 Ab: a massive circumstellar planet orbiting a giant star in a ~13.6 au eccentric binary system
Context: For over 12 yr, we have carried out a precise radial velocity survey
of a sample of 373 G and K giant stars using the Hamilton \'Echelle
Spectrograph at Lick Observatory. There are, among others, a number of multiple
planetary systems in our sample as well as several planetary candidates in
stellar binaries. Aims: We aim at detecting and characterizing
substellar+stellar companions to the giant star HD 59686 A (HR 2877, HIP
36616). Methods: We obtained high precision radial velocity (RV) measurements
of the star HD 59686 A. By fitting a Keplerian model to the periodic changes in
the RVs, we can assess the nature of companions in the system. In order to
discriminate between RV variations due to non-radial pulsation or stellar spots
we used infrared RVs taken with the CRIRES spectrograph at the Very Large
Telescope. Additionally, to further characterize the system, we obtain
high-resolution images with LMIRCam at the Large Binocular Telescope. Results:
We report the likely discovery of a giant planet with a mass of orbiting at
au from the giant star HD 59686 A. Besides the planetary signal, we discover an
eccentric () binary companion with a mass of
orbiting at a semi-major axis
of just au. Conclusions: The existence of the
planet HD 59686 Ab in a tight eccentric binary system severely challenges
standard giant planet formation theories and requires substantial improvements
to such theories in tight binaries. Otherwise, alternative planet formation
scenarios such as second generation planets or dynamical interactions in an
early phase of the system's lifetime should be seriously considered in order to
better understand the origin of this enigmatic planet.Comment: 14 pages, 11 figures, 2 tables. Accepted for publication in A&A.
Updated version to match the published pape
Direct Imaging and Spectroscopy of Extrasolar Planets
Direct imaging and spectroscopy is the likely means by which we will someday
identify, confirm, and characterize an Earth-like planet around a nearby
Sun-like star. This Chapter summarizes the current state of knowledge regarding
discovering and characterizing exoplanets by direct imaging and spectroscopy.
We detail instruments and software needed for direct imaging detections and
summarize the current inventory of confirmed and candidate directly-imaged
exoplanets. Direct imaging and spectroscopy in the past decade has provided key
insights into jovian planet atmospheres, probed the demographics of the
outskirts of planetary systems, and shed light on gas giant planet formation.
We forecast the new tools and future facilities on the ground and in space that
will enhance our capabilities for exoplanet imaging and will likely image
habitable zone rocky planets around the nearest stars.Comment: 34 pages; 19 figures; Review of the Direct Imaging field in
Protostars and Planets VII; in pres
Can the evaluation of marker placement confidence be used as an indicator of gait kinematic variability?
IntroductionThree-dimensional gait analysis is widely used for the clinical assessment of movement disorders. However, measurement error reduces the reliability of kinematic data and consequently assessment of gait deviations. The identification of high variability is associated with low reliability and those parameters should be ignored or excluded from gait data interpretation. Moreover, marker placement error has been demonstrated to be the biggest source of variability in gait analysis and may be affected by factors intrinsic to the evaluators such as the evaluator's expertise which could be appraised through his/her experience and confidence in marker placement.ObjectivesIn the present study, we hypothesized that confidence in marker placement is correlated with kinematic variability and could potentially be used as part of a score of reliability. Therefore, we have proposed a questionnaire to evaluate qualitatively the confidence of evaluators in lower-limb marker placement. The primary aim of this study was to evaluate the reliability and validity of the presented questionnaire. The secondary objective was to test a possible relationship between marker placement confidence and kinematics variability.MethodsTo do so, test-retest gait data were acquired from two different experimental protocols. One protocol included data from a cohort of 32 pathological and 24 asymptomatic subjects where gait analysis was repeated three times, involving two evaluators. A second protocol included data from a cohort of 8 asymptomatic adults with gait analysis repeated 12 times, per participant, and involving four evaluators with a wider range of experience.ResultsResults demonstrated that the questionnaire proposed is valid and reliable to evaluate qualitatively the confidence of evaluators in placing markers. Indeed, confidence scores were correlated with the actual variability of marker placement and revealed the evaluator's experience and the subjects' characteristics. However, no correlation was observed between confidence scores and kinematic variability and the formulated hypothesis was not supported
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