46 research outputs found
Structure and evolution of the first CoRoT exoplanets: Probing the Brown Dwarf/Planet overlapping mass regime
We present detailed structure and evolution calculations for the first
transiting extrasolar planets discovered by the space-based CoRoT mission.
Comparisons between theoretical and observed radii provide information on the
internal composition of the CoRoT objects. We distinguish three different
categories of planets emerging from these discoveries and from previous
ground-based surveys: (i) planets explained by standard planetary models
including irradiation, (ii) abnormally bloated planets and (iii) massive
objects belonging to the overlapping mass regime between planets and brown
dwarfs. For the second category, we show that tidal heating can explain the
relevant CoRoT objects, providing non-zero eccentricities. We stress that the
usual assumption of a quick circularization of the orbit by tides, as usually
done in transit light curve analysis, is not justified a priori, as suggested
recently by Levrard et al. (2009), and that eccentricity analysis should be
carefully redone for some observations. Finally, special attention is devoted
to CoRoT-3b and to the identification of its very nature: giant planet or brown
dwarf ? The radius determination of this object confirms the theoretical
mass-radius predictions for gaseous bodies in the substellar regime but, given
the present observational uncertainties, does not allow an unambiguous
identification of its very nature. This opens the avenue, however, to an
observational identification of these two distinct astrophysical populations,
brown dwarfs and giant planets, in their overlapping mass range, as done for
the case of the 8 Jupiter-mass object Hat-P-2b. (abridged)Comment: 6 pages, 5 figures, accepted for publication in Astronomy and
Astrophysic
Skin vascular resistance in the standing position increases significantly after 7 days of dry immersion
Actual and simulated microgravity induces hypovolemia and cardiovascular deconditioning, associated with vascular dysfunction. We hypothesized that vasoconstriction of skin microcirculatory bed should be altered following 7 days of simulated microgravity in order to maintain cardiovascular homeostasis during active standing. Eight healthy men were studied before and after 7 days of simulated microgravity modeled by dry immersion (DI). Changes of plasma volume and orthostatic tolerance were evaluated. Calf skin blood flow (laser-Doppler flowmetry), ECG and blood pressure signal during a 10-min stand test were recorded, and skin vascular resistance, central hemodynamics, baroreflex sensitivity and heart rate variability were estimated. After DI we observed increased calf skin vascular resistance in the standing position (12.0 +/- 1.0 AU-after- vs. 6.8 +/- 1.4 AU-before), while supine it was unchanged. Cardiovascular deconditioning was confirmed by greater tachycardia on standing and by hypovolemia (-16 +/- 3% at day 7 of DI). Total peripheral resistance and indices of cardiovascular autonomic control were not modified. In conclusion, unchanged autonomic control and total peripheral resistance suggest that increased skin vasoconstriction to standing involves rather local mechanisms-as venoarteriolar reflex-and might compensate insufficient vasoconstriction of other vascular beds
Detection of brown dwarf-like objects in the core of NGC3603
We use near-infrared data obtained with the Wide Field Camera 3 (WFC3) on the
Hubble Space Telescope to identify objects having the colors of brown dwarfs
(BDs) in the field of the massive galactic cluster NGC 3603. These are
identified through use of a combination of narrow and medium band filters
spanning the J and H bands, and which are particularly sensitive to the
presence of the 1.3-1.5{\mu}m H2O molecular band - unique to BDs. We provide a
calibration of the relationship between effective temperature and color for
both field stars and for BDs. This photometric method provides effective
temperatures for BDs to an accuracy of {\pm}350K relative to spectroscopic
techniques. This accuracy is shown to be not significantly affected by either
stellar surface gravity or uncertainties in the interstellar extinction. We
identify nine objects having effective temperature between 1700 and 2200 K,
typical of BDs, observed J-band magnitudes in the range 19.5-21.5, and that are
strongly clustered towards the luminous core of NGC 3603. However, if these are
located at the distance of the cluster, they are far too luminous to be normal
BDs. We argue that it is unlikely that these objects are either artifacts of
our dataset, normal field BDs/M-type giants or extra-galactic contaminants and,
therefore, might represent a new class of stars having the effective
temperatures of BDs but with luminosities of more massive stars. We explore the
interesting scenario in which these objects would be normal stars that have
recently tidally ingested a Hot Jupiter, the remnants of which are providing a
short-lived extended photosphere to the central star. In this case, we would
expect them to show the signature of fast rotation.Comment: 26 Pages, 8 Figures, Accepted for publication on Ap
Transiting exoplanets from the CoRoT space mission. XV. CoRoT-15b: a brown dwarf transiting companion
We report the discovery by the CoRoT space mission of a transiting brown
dwarf orbiting a F7V star with an orbital period of 3.06 days. CoRoT-15b has a
radius of 1.12 +0.30 -0.15 Rjup, a mass of 63.3 +- 4.1 Mjup, and is thus the
second transiting companion lying in the theoretical mass domain of brown
dwarfs. CoRoT-15b is either very young or inflated compared to standard
evolution models, a situation similar to that of M-dwarfs stars orbiting close
to solar-type stars. Spectroscopic constraints and an analysis of the
lightcurve favors a spin period between 2.9 and 3.1 days for the central star,
compatible with a double-synchronisation of the system.Comment: 7 pages, 6 figures, accepted in A&
Low-magnitude whole body vibration with resistive exercise as a countermeasure against cardiovascular deconditioning after 60 days of head-down bed rest
Whole body vibration with resistive exercise is a promising countermeasure against some weightlessness-induced dysfunctions. Our objective was to study whether the combination of low-magnitude whole body vibration with a resistive exercise can prevent the cardiovascular deconditioning induced by a nonstrict 60-day head-down bed rest (Earth Star International Bed Rest Experiment Project). Fourteen healthy men participated in this study. We recorded electrocardiograms and blood pressure waves by means of a noninvasive beat-by-beat measurement system (Cardiospace, integrated by Centre National d\u27Etudes Spatiales and Astronaut Center of China) during an orthostatic test (20 min of 75-degree head-up tilt test) before and immediately after bed rest. We estimated heart rate, blood pressure, cardiac output, stroke volume, total peripheral resistance, baroreflex sensitivity, and heart rate variability. Low-magnitude whole body vibration with resistive exercise prevented an increase of the sympathetic index (reflecting the sympathovagal balance of cardiac autonomic control) and limited the decrease of the spontaneous baroreflex sensitivity induced by 60 days of head-down bed rest. However, this countermeasure had very little effect on cardiac hemodynamics and did not improve the orthostatic tolerance. This combined countermeasure did not efficiently prevent orthostatic intolerance but prevents changes in the autonomic nervous system associated with cardiovascular deconditioning. The underlying mechanisms remain hypothetical but might involve cutaneous and muscular mechanoreceptors
Rotation of planet-harbouring stars
The rotation rate of a star has important implications for the detectability,
characterisation and stability of any planets that may be orbiting it. This
chapter gives a brief overview of stellar rotation before describing the
methods used to measure the rotation periods of planet host stars, the factors
affecting the evolution of a star's rotation rate, stellar age estimates based
on rotation, and an overview of the observed trends in the rotation properties
of stars with planets.Comment: 16 pages, 4 figures: Invited review to appear in 'Handbook of
Exoplanets', Springer Reference Works, edited by Hans J. Deeg and Juan
Antonio Belmont
Interpreting and predicting the yield of transit surveys: Giant planets in the OGLE fields
Transiting extrasolar planets are now discovered jointly by photometric
surveys and by radial velocimetry. We want to determine whether the different
data sets are compatible between themselves and with models of the evolution of
extrasolar planets. We simulate directly a population of stars corresponding to
the OGLE transit survey and assign them planetary companions based on radial
velocimetry discoveries. We use a model of the evolution and structure of giant
planets assuming a variable fraction of heavy elements. The output list of
detectable planets of the simulations is compared to the real detections. We
confirm that the radial velocimetry and photometric survey data sets are
compatible within the statistical errors, assuming that planets with periods
between 1 and 2 days are approximately 5 times less frequent than planets with
periods between 2 and 5 days. We show that evolution models fitting present
observational constraints predict a lack of small giant planets with large
masses. We also identify distinct populations of planets: those with short
periods (P
-0.07. We further confirm the relative absence of low-mass giant planets at
small orbital distances.Comment: article in press in A&A, 21 pages, 18 figure
Introduction to special section on the Phoenix Mission: Landing Site Characterization Experiments, Mission Overviews, and Expected Science
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94752/1/jgre2486.pd
Observational Evidence for Tidal Interaction in Close Binary Systems
This paper reviews the rich corpus of observational evidence for tidal
effects in short-period binaries. We review the evidence for ellipsoidal
variability and for the observational manifestation of apsidal motion in
eclipsing binaries. Among the long-term effects, circularization was studied
the most, and a transition period between circular and eccentric orbits has
been derived for eight coeval samples of binaries. As binaries are supposed to
reach synchronization before circularization, one can expect finding eccentric
binaries in pseudo-synchronization state, the evidence for which is reviewed.
The paper reviews the Rossiter-McLaughlin effect and its potential to study
spin-orbit alignment. We discuss the tidal interaction in close binaries that
are orbited by a third distant companion, and review the effect of pumping the
binary eccentricity by the third star. We then discuss the idea that the tidal
interaction induced by the eccentricity modulation can shrink the binary
separation.
The paper discusses the extrasolar planets and the observational evidence for
tidal interaction with their parent stars which can induce radial drift of
short-period planets and circularization of planetary orbits. The paper reviews
the revolution of the study of binaries that is currently taking place, driven
by large-scaled photometric surveys that are detecting many thousands of new
binaries and tens of extrasolar planets. In particular, we review several
studies that have been used already thousands of lightcurves of eclipsing
binaries to study tidal circularization of early-type stars in the LMC.Comment: 67 pages. Review Paper. To appear in "Tidal effects in stars, planets
and disks", M.-J. Goupil and J.-P. Zahn (eds.), EAS Publications Serie