413 research outputs found
Possible detection of phase changes from the non-transiting planet HD 46375b by CoRoT
The present work deals with the detection of phase changes in an exoplanetary
system. HD 46375 is a solar analog known to host a non-transiting Saturn-mass
exoplanet with a 3.0236 day period. It was observed by the CoRoT satellite for
34 days during the fall of 2008. We attempt to identify at optical wavelengths,
the changing phases of the planet as it orbits its star. We then try to improve
the star model by means of a seismic analysis of the same light curve and the
use of ground-based spectropolarimetric observations. The data analysis relies
on the Fourier spectrum and the folding of the time series. We find evidence of
a sinusoidal signal compatible in terms of both amplitude and phase with light
reflected by the planet. Its relative amplitude is Delta Fp/F* = [13.0, 26.8]
ppm, implying an albedo A=[0.16, 0.33] or a dayside visible brightness
temperature Tb ~ [1880,2030] K by assuming a radius R=1.1 R_Jup and an
inclination i=45 deg. Its orbital phase differs from that of the
radial-velocity signal by at most 2 sigma_RV. However, the tiny planetary
signal is strongly blended by another signal, which we attribute to a telluric
signal with a 1 day period. We show that this signal is suppressed, but not
eliminated, when using the time series for HD 46179 from the same CoRoT run as
a reference. This detection of reflected light from a non-transiting planet
should be confirmable with a longer CoRoT observation of the same field. In any
case, it demonstrates that non-transiting planets can be characterized using
ultra-precise photometric lightcurves with present-day observations by CoRoT
and Kepler. The combined detection of solar-type oscillations on the same
targets (Gaulme et al. 2010a) highlights the overlap between exoplanetary
science and asteroseismology and shows the high potential of a mission such as
Plato.Comment: 4 pages, 6 figure
Oxygen as a Driver of Early Arthropod Micro-Benthos Evolution
BACKGROUND: We examine the physiological and lifestyle adaptations which facilitated the emergence of ostracods as the numerically dominant Phanerozoic bivalve arthropod micro-benthos. METHODOLOGY/PRINCIPAL FINDINGS: The PO(2) of modern normoxic seawater is 21 kPa (air-equilibrated water), a level that would cause cellular damage if found in the tissues of ostracods and much other marine fauna. The PO(2) of most aquatic breathers at the cellular level is much lower, between 1 and 3 kPa. Ostracods avoid oxygen toxicity by migrating to waters which are hypoxic, or by developing metabolisms which generate high consumption of O(2). Interrogation of the Cambrian record of bivalve arthropod micro-benthos suggests a strong control on ecosystem evolution exerted by changing seawater O(2) levels. The PO(2) of air-equilibrated Cambrian-seawater is predicted to have varied between 10 and 30 kPa. Three groups of marine shelf-dwelling bivalve arthropods adopted different responses to Cambrian seawater O(2). Bradoriida evolved cardiovascular systems that favoured colonization of oxygenated marine waters. Their biodiversity declined during intervals associated with black shale deposition and marine shelf anoxia and their diversity may also have been curtailed by elevated late Cambrian (Furongian) oxygen-levels that increased the PO(2) gradient between seawater and bradoriid tissues. Phosphatocopida responded to Cambrian anoxia differently, reaching their peak during widespread seabed dysoxia of the SPICE event. They lacked a cardiovascular system and appear to have been adapted to seawater hypoxia. As latest Cambrian marine shelf waters became well oxygenated, phosphatocopids went extinct. Changing seawater oxygen-levels and the demise of much of the seabed bradoriid micro-benthos favoured a third group of arthropod micro-benthos, the ostracods. These animals adopted lifestyles that made them tolerant of changes in seawater O(2). Ostracods became the numerically dominant arthropod micro-benthos of the Phanerozoic. CONCLUSIONS/SIGNIFICANCE: Our work has implications from an evolutionary context for understanding how oxygen-level in marine ecosystems drives behaviour
HD 46375: seismic and spectropolarimetric analysis of a young Sun hosting a Saturn-like planet
HD 46375 is known to host a Saturn-like exoplanet orbiting at 0.04 AU from
its host star. Stellar light reflected by the planet was tentatively identified
in the 34-day CoRoT run acquired in October-November 2008. We constrain the
properties of the magnetic field of HD 46375 based on spectropolarimetric
observations with the NARVAL spectrograph at the Pic du Midi observatory. In
addition, we use a high-resolution NARVAL flux spectrum to contrain the
atmospheric parameters. With these constraints, we perform an asteroseismic
analysis and modelling of HD 46375 using the frequencies extracted from the
CoRoT light curve. We used Zeeman Doppler imaging to reconstruct the magnetic
map of the stellar surface. In the spectroscopic analysis we fitted isolated
lines using 1D LTE atmosphere models. This analysis was used to constrain the
effective temperature, surface gravity, and chemical composition of the star.
To extract information about the p-mode oscillations, we used a technique based
on the envelope autocorrelation function (EACF). From the Zeeman Doppler
imaging observations, we observe a magnetic field of ~5 gauss. From the
spectral analysis, HD 46375 is inferred to be an unevolved K0 type star with
high metallicity [Fe/H]=+0.39. Owing to the relative faintness of the star
(m_hip=8.05), the signal-to-noise ratio is too low to identify individual
modes. However, we measure the p-mode excess power and large separation Delta
nu_0=153.0 +/- 0.7 muHz. We are able do constrain the fundamental parameters of
the star thanks to spectrometric and seismic analyses. We conclude that HD
46375 is similar to a young version of Alpha-CenB. This work is of special
interest because of its combination of exoplanetary science and
asteroseismology, which are the subjects of the current Kepler mission and the
proposed PLATO mission.Comment: Accepted in Astronomy & Astrophysics. 8 pages, 9 figure
ImageParser: a tool for finite element generation from three-dimensional medical images
BACKGROUND: The finite element method (FEM) is a powerful mathematical tool to simulate and visualize the mechanical deformation of tissues and organs during medical examinations or interventions. It is yet a challenge to build up an FEM mesh directly from a volumetric image partially because the regions (or structures) of interest (ROIs) may be irregular and fuzzy. METHODS: A software package, ImageParser, is developed to generate an FEM mesh from 3-D tomographic medical images. This software uses a semi-automatic method to detect ROIs from the context of image including neighboring tissues and organs, completes segmentation of different tissues, and meshes the organ into elements. RESULTS: The ImageParser is shown to build up an FEM model for simulating the mechanical responses of the breast based on 3-D CT images. The breast is compressed by two plate paddles under an overall displacement as large as 20% of the initial distance between the paddles. The strain and tangential Young's modulus distributions are specified for the biomechanical analysis of breast tissues. CONCLUSION: The ImageParser can successfully exact the geometry of ROIs from a complex medical image and generate the FEM mesh with customer-defined segmentation information
An overview of the mid-infrared spectro-interferometer MATISSE: science, concept, and current status
MATISSE is the second-generation mid-infrared spectrograph and imager for the
Very Large Telescope Interferometer (VLTI) at Paranal. This new interferometric
instrument will allow significant advances by opening new avenues in various
fundamental research fields: studying the planet-forming region of disks around
young stellar objects, understanding the surface structures and mass loss
phenomena affecting evolved stars, and probing the environments of black holes
in active galactic nuclei. As a first breakthrough, MATISSE will enlarge the
spectral domain of current optical interferometers by offering the L and M
bands in addition to the N band. This will open a wide wavelength domain,
ranging from 2.8 to 13 um, exploring angular scales as small as 3 mas (L band)
/ 10 mas (N band). As a second breakthrough, MATISSE will allow mid-infrared
imaging - closure-phase aperture-synthesis imaging - with up to four Unit
Telescopes (UT) or Auxiliary Telescopes (AT) of the VLTI. Moreover, MATISSE
will offer a spectral resolution range from R ~ 30 to R ~ 5000. Here, we
present one of the main science objectives, the study of protoplanetary disks,
that has driven the instrument design and motivated several VLTI upgrades
(GRA4MAT and NAOMI). We introduce the physical concept of MATISSE including a
description of the signal on the detectors and an evaluation of the expected
performances. We also discuss the current status of the MATISSE instrument,
which is entering its testing phase, and the foreseen schedule for the next two
years that will lead to the first light at Paranal.Comment: SPIE Astronomical Telescopes and Instrumentation conference, June
2016, 11 pages, 6 Figure
Direct constraint on the distance of y2 Velorum from AMBER/VLTI observations
In this work, we present the first AMBER observations, of the Wolf-Rayet and
O (WR+O) star binary system y2 Velorum. The AMBER instrument was used with the
telescopes UT2, UT3, and UT4 on baselines ranging from 46m to 85m. It delivered
spectrally dispersed visibilities, as well as differential and closure phases,
with a resolution R = 1500 in the spectral band 1.95-2.17 micron. We interpret
these data in the context of a binary system with unresolved components,
neglecting in a first approximation the wind-wind collision zone flux
contribution. We show that the AMBER observables result primarily from the
contribution of the individual components of the WR+O binary system. We discuss
several interpretations of the residuals, and speculate on the detection of an
additional continuum component, originating from the free-free emission
associated with the wind-wind collision zone (WWCZ), and contributing at most
to the observed K-band flux at the 5% level. The expected absolute separation
and position angle at the time of observations were 5.1±0.9mas and
66±15° respectively. However, we infer a separation of
3.62+0.11-0.30 mas and a position angle of 73+9-11°. Our analysis thus
implies that the binary system lies at a distance of 368+38-13 pc, in agreement
with recent spectrophotometric estimates, but significantly larger than the
Hipparcos value of 258+41-31 pc
Near-Infrared interferometry of Eta Carinae with high spatial and spectral resolution using the VLTI and the AMBER instrument
We present the first NIR spectro-interferometry of the LBV Eta Carinae. The K
band observations were performed with the AMBER instrument of the ESO Very
Large Telescope Interferometer using three 8.2m Unit Telescopes with baselines
from 42 to 89m. The aim of this work is to study the wavelength dependence of
Eta Car's optically thick wind region with a high spatial resolution of 5 mas
(11 AU) and high spectral resolution. The medium spectral resolution
observations (R=1,500) were performed in the wavelength range around both the
HeI 2.059 micron and the Br gamma 2.166 micron emission lines, the high
spectral resolution observations (R=12,000) only in the Br gamma line region.
In the K-band continuum, a diameter of 4.0 +/-0.2 mas (Gaussian FWHM, fit range
28-89m) was measured for Eta Car's optically thick wind region. If we fit
Hillier et al. (2001) model visibilities to the observed AMBER visibilities, we
obtain 50 % encircled-energy diameters of 4.2, 6.5 and 9.6mas in the 2.17
micron continuum, the HeI, and the Br gamma emission lines, respectively. In
the continuum near the Br gamma line, an elongation along a position angle of
120+/-15 degrees was found, consistent with previous VLTI/VINCI measurements by
van Boekel et al. (2003). We compare the measured visibilities with predictions
of the radiative transfer model of Hillier et al. (2001), finding good
agreement. Furthermore, we discuss the detectability of the hypothetical hot
binary companion. For the interpretation of the non-zero differential and
closure phases measured within the Br gamma line, we present a simple geometric
model of an inclined, latitude-dependent wind zone. Our observations support
theoretical models of anisotropic winds from fast-rotating, luminous hot stars
with enhanced high-velocity mass loss near the polar regions.Comment: 22 pages, 14 figures, 2 tables; A&A in pres
A multiwavelength look at the GJ 9827 system: No evidence of extended atmospheres in GJ 9827b and d from HST and CARMENES data
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