984 research outputs found
Prospects for near-infrared characterisation of hot Jupiters with VSI
In this paper, we study the feasibility of obtaining near-infrared spectra of
bright extrasolar planets with the 2nd generation VLTI Spectro-Imager
instrument (VSI), which has the required angular resolution to resolve nearby
hot Extrasolar Giant Planets (EGPs) from their host stars. Taking into account
fundamental noises, we simulate closure phase measurements of several
extrasolar systems using four 8-m telescopes at the VLT and a low spectral
resolution (R = 100). Synthetic planetary spectra from T. Barman are used as an
input. Standard chi2-fitting methods are then used to reconstruct planetary
spectra from the simulated data. These simulations show that low-resolution
spectra in the H and K bands can be retrieved with a good fidelity for half a
dozen targets in a reasonable observing time (about 10 hours, spread over a few
nights). Such observations would strongly constrain the planetary temperature
and albedo, the energy redistribution mechanisms, as well as the chemical
composition of their atmospheres. Systematic errors, not included in our
simulations, could be a serious limitation to these performance estimations.
The use of integrated optics is however expected to provide the required
instrumental stability (around 10^-4 on the closure phase) to enable the first
thorough characterisation of extrasolar planetary emission spectra in the
near-infrared.Comment: 10 pages, 8 figures, Proc. SPIE conference 7013 "Optical and Infrared
Interferometry" (Marseille 2008
L'irrigation d'acide lactique : traitement des fistules cutanéo-digestives avec sécrétion tryptique et auto-digestion pariétale
The HARPS search for southern extra-solar planets XIX. Characterization and dynamics of the GJ876 planetary system
Precise radial-velocity measurements for data acquired with the HARPS
spectrograph infer that three planets orbit the M4 dwarf star GJ876. In
particular, we confirm the existence of planet "d", which orbits every 1.93785
days. We find that its orbit may have significant eccentricity (e=0.14), and
deduce a more accurate estimate of its minimum mass of 6.3 Earth masses.
Dynamical modeling of the HARPS measurements combined with literature
velocities from the Keck Observatory strongly constrain the orbital
inclinations of the "b" and "c" planets. We find that i_b = 48.9 degrees and
i_c = 48.1 degrees, which infers the true planet masses of M_b = 2.64 Jupiter
masses and M_c = 0.83 Jupiter masses, respectively. Radial velocities alone, in
this favorable case, can therefore fully determine the orbital architecture of
a multi-planet system, without the input from astrometry or transits.
The orbits of the two giant planets are nearly coplanar, and their 2:1 mean
motion resonance ensures stability over at least 5 Gyr. The libration amplitude
is smaller than 2 degrees, suggesting that it was damped by some dissipative
process during planet formation. The system has space for a stable fourth
planet in a 4:1 mean motion resonance with planet "b", with a period around 15
days. The radial velocity measurements constrain the mass of this possible
additional planet to be at most that of the Earth.Comment: 10 pages, 10 figures, accepted for publication in Astronomy &
Astrophysic
The HARPS search for southern extra-solar planets. VI. A Neptune-mass planet around the nearby M dwarf Gl 581
We report the discovery of a Neptune-mass planet around Gl 581 (M3V, M = 0.31
Msol), based on precise Doppler measurements with the HARPS spectrograph at La
Silla Observatory. The radial velocities reveal a circular orbit of period P =
5.366 days and semi-amplitude K1 = 13.2 m/s. The resulting minimum mass of the
planet (m2 sin i) is only 0.052 Mjup = 0.97 Mnep = 16.6 Mearth making Gl 581b
one of the lightest extra-solar planet known to date. The Gl 581 planetary
system is only the third centered on an M dwarf, joining the Gl 876
three-planet system and the lone planet around Gl 436. Its discovery reinforces
the emerging tendency of such planets to be of low mass, and found at short
orbital periods. The statistical properties of the planets orbiting M dwarfs do
not seem to match a simple mass scaling of their counterparts around solar-type
stars.Comment: letter submitted to A&
Long-term magnetic activity of a sample of M-dwarf stars from the HARPS program II. Activity and radial velocity
Due to their low mass and luminosity, M dwarfs are ideal targets if one hopes
to find low-mass planets similar to Earth by using the radial velocity (RV)
method. However, stellar magnetic cycles could add noise or even mimic the RV
signal of a long-period companion. Following our previous work that studied the
correlation between activity cycles and long-term RV variations for K dwarfs we
now expand that research to the lower-end of the main sequence. Our objective
is to detect any correlations between long-term activity variations and the
observed RV of a sample of M dwarfs. We used a sample of 27 M-dwarfs with a
median observational timespan of 5.9 years. The cross-correlation function
(CCF) with its parameters RV, bisector inverse slope (BIS), full-width-at-half-
maximum (FWHM) and contrast have been computed from the HARPS spectrum. The
activity index have been derived using the Na I D doublet. These parameters
were compared with the activity level of the stars to search for correlations.
We detected RV variations up to ~5 m/s that we can attribute to activity cycle
effects. However, only 36% of the stars with long-term activity variability
appear to have their RV affected by magnetic cycles, on the typical timescale
of ~6 years. Therefore, we suggest a careful analysis of activity data when
searching for extrasolar planets using long-timespan RV data.Comment: 20 pages, 12 figures, 3 tables, accepted for publication in Astronomy
and Astophysic
Interfacial waves in the presence of wind and current: an asymptotic study
We use asymptotic methods to study the evolution of short wavelength
interfacial waves driven by the combined action of wind and current. We solve
the Rayleigh equation for the stability of the shear flow, and construct a
uniformly valid approximation for the perturbed streamfunction, or
eigenfunction. We then expand the real part of the eigenvalue, the phase speed,
in a power series of the inverse wavenumber and show that the imaginary part is
exponentially small. We give expressions for the growth rates of the Miles
(1957) and rippling (e.g., Young & Wolfe 2013) instabilities that are valid for
an arbitrary shear flow. The accuracy of the results is demonstrated by a
comparison with the exact solution of the eigenvalue problem in the case when
both the wind and the current have an exponential profile
M dwarf stars in the light of (future) exoplanet searches
We present a brief overview of a splinter session on M dwarf stars as planet
hosts that was organized as part of the Cool Stars 17 conference. The session
was devoted to reviewing our current knowledge of M dwarf stars and exoplanets
in order to prepare for current and future exoplanet searches focusing in low
mass stars. We review the observational and theoretical challenges to
characterize M dwarf stars and the importance of accurate fundamental
parameters for the proper characterization of their exoplanets and our
understanding on planet formation.Comment: 4 pages, 1 figure. Summary of the splinter session "M dwarf stars in
the light of (future) exoplanet searches" held at the 17th Cambridge Workshop
on Cool Stars, Stellar Systems, and the Sun, June 28th 2012, Barcelona,
Spain. Submitted for publication in Astronomische Nachrichten - Astronomical
Notes (AN) 334, Issue 1-2, Eds Klaus Strassmeier and Mercedes L\'opez-Morale
On the equilibrium rotation of Earth-like extra-solar planets
The equilibrium rotation of tidally evolved "Earth-like" extra-solar planets
is often assumed to be synchronous with their orbital mean motion. The same
assumption persisted for Mercury and Venus until radar observations revealed
their true spin rates. As many of these planets follow eccentric orbits and are
believed to host dense atmospheres, we expect the equilibrium rotation to
differ from the synchronous motion. Here we provide a general description of
the allowed final equilibrium rotation states of these planets, and apply this
to already discovered cases in which the mass is lower than twelve
Earth-masses. At low obliquity and moderate eccentricity, it is shown that
there are at most four distinct equilibrium possibilities, one of which can be
retrograde. Because most presently known "Earth-like" planets present eccentric
orbits, their equilibrium rotation is unlikely to be synchronous.Comment: 4 pages, 2 figures. accepted for publication in Astronomy and
Astrophysics. to be published in Astronomy and Astrophysic
A global analysis of Spitzer and new HARPS data confirms the loneliness and metal-richness of GJ 436 b
Context. GJ 436b is one of the few transiting warm Neptunes for which a
detailed characterisation of the atmosphere is possible, whereas its
non-negligible orbital eccentricity calls for further investigation.
Independent analyses of several individual datasets obtained with Spitzer have
led to contradicting results attributed to the different techniques used to
treat the instrumental effects. Aims. We aim at investigating these previous
controversial results and developing our knowledge of the system based on the
full Spitzer photometry dataset combined with new Doppler measurements obtained
with the HARPS spectrograph. We also want to search for additional planets.
Methods. We optimise aperture photometry techniques and the photometric
deconvolution algorithm DECPHOT to improve the data reduction of the Spitzer
photometry spanning wavelengths from 3-24 {\mu}m. Adding the high precision
HARPS radial velocity data, we undertake a Bayesian global analysis of the
system considering both instrumental and stellar effects on the flux variation.
Results. We present a refined radius estimate of RP=4.10 +/- 0.16 R_Earth, mass
MP=25.4 +/- 2.1 M_Earth and eccentricity e= 0.162 +/- 0.004 for GJ 436b. Our
measured transit depths remain constant in time and wavelength, in disagreement
with the results of previous studies. In addition, we find that the
post-occultation flare-like structure at 3.6 {\mu}m that led to divergent
results on the occultation depth measurement is spurious. We obtain occultation
depths at 3.6, 5.8, and 8.0 {\mu}m that are shallower than in previous works,
in particular at 3.6 {\mu}m. However, these depths still appear consistent with
a metal-rich atmosphere depleted in methane and enhanced in CO/CO2, although
perhaps less than previously thought. We find no evidence for a potential
planetary companion, stellar activity, nor for a stellar spin-orbit
misalignment. [ABRIDGED]Comment: 25 pages, 26 figures, 8 tables, accepted for publication in A&
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