1,138 research outputs found
CoRoT's first seven planets: An overview
The up to 150 day uninterrupted high-precision photometry of about 100000
stars - provided so far by the exoplanet channel of the CoRoT space telescope -
gave a new perspective on the planet population of our galactic neighbourhood.
The seven planets with very accurate parameters widen the range of known planet
properties in almost any respect. Giant planets have been detected at low
metallicity, rapidly rotating and active, spotted stars. CoRoT-3 populated the
brown dwarf desert and closed the gap of measured physical properties between
standard giant planets and very low mass stars. CoRoT extended the known range
of planet masses down to 5 Earth masses and up to 21 Jupiter masses, the radii
to less than 2 Earth radii and up to the most inflated hot Jupiter found so
far, and the periods of planets discovered by transits to 9 days. Two CoRoT
planets have host stars with the lowest content of heavy elements known to show
a transit hinting towards a different planet-host-star-metallicity relation
then the one found by radial-velocity search programs. Finally the properties
of the CoRoT-7b prove that terrestrial planets with a density close to Earth
exist outside the Solar System. The detection of the secondary transit of
CoRoT-1 at the -level and the very clear detection of the 1.7 Earth
radii of CoRoT-7b at relative flux are promising evidence of
CoRoT being able to detect even smaller, Earth sized planets.Comment: 8 pages, 19 figures and 3 table
- A tool for multiband light curve modeling of planetary transits and stellar spots
Several studies have shown that stellar activity features, such as occulted
and non-occulted starspots, can affect the measurement of transit parameters
biasing studies of transit timing variations and transmission spectra. We
present , which we designed to model multiband transit
light curves showing starspot anomalies, inferring both transit and spot
parameters. The code follows a pixellation approach to model the star with its
corresponding limb darkening, spots, and transiting planet on a two dimensional
Cartesian coordinate grid. We combine with an MCMC
framework to study and derive exoplanet transmission spectra, which provides
statistically robust values for the physical properties and uncertainties of a
transiting star-planet system. We validate 's performance
by analyzing eleven synthetic light curves of four different star-planet
systems and 20 transit light curves of the well-studied WASP-41b system. We
also investigate the impact of starspots on transit parameters and derive
wavelength dependent transit depth values for WASP-41b covering a range of
6200-9200 , indicating a flat transmission spectrum.Comment: 17 pages, 22 figures; accepted for publication in Astronomy &
Astrophysic
Coronal properties of planet-bearing stars
Do extrasolar planets affect the activity of their host stars? Indications
for chromospheric activity enhancement have been found for a handful of
targets, but in the X-ray regime, conclusive observational evidence is still
missing. We want to establish a sound observational basis to confirm or reject
major effects of Star-Planet Interactions (SPI) in stellar X-ray emissions. We
therefore conduct a statistical analysis of stellar X-ray activity of all known
planet-bearing stars within 30pc distance for dependencies on planetary
parameters such as mass and semimajor axis. We find that in our sample, there
are no significant correlations of X-ray luminosity or the activity indicator
L_X/L_bol with planetary parameters which cannot be explained by selection
effects. Coronal SPI seems to be a phenomenon which might only manifest itself
as a strong effect for a few individual targets, but not to have a major effect
on planet-bearing stars in general.Comment: accepted by A&
On the protection of extrasolar Earth-like planets around K/M stars against galactic cosmic rays
Previous studies have shown that extrasolar Earth-like planets in close-in
habitable zones around M-stars are weakly protected against galactic cosmic
rays (GCRs), leading to a strongly increased particle flux to the top of the
planetary atmosphere. Two main effects were held responsible for the weak
shielding of such an exoplanet: (a) For a close-in planet, the planetary
magnetic moment is strongly reduced by tidal locking. Therefore, such a
close-in extrasolar planet is not protected by an extended magnetosphere. (b)
The small orbital distance of the planet exposes it to a much denser stellar
wind than that prevailing at larger orbital distances. This dense stellar wind
leads to additional compression of the magnetosphere, which can further reduce
the shielding efficiency against GCRs. In this work, we analyse and compare the
effect of (a) and (b), showing that the stellar wind variation with orbital
distance has little influence on the cosmic ray shielding. Instead, the weak
shielding of M star planets can be attributed to their small magnetic moment.
We further analyse how the planetary mass and composition influence the
planetary magnetic moment, and thus modify the cosmic ray shielding efficiency.
We show that more massive planets are not necessarily better protected against
galactic cosmic rays, but that the planetary bulk composition can play an
important role.Comment: 7 figure
Escaping Particle fluxes in the atmospheres of close-in exoplanets: I. model of hydrogen
A multi-fluid model for an atomic hydrogen-proton mixture in the upper
atmosphere of extrosolar planet is presented when the continuity and momentum
equations of each component have been already solved with an energy equation.
The particle number density, the temperature distribution and the structure of
velocity can be found by means of the model. We chose two special objects, HD
209458b and HD 189733b, as discussion samples and the conclusion is that their
mass loss rates predicted by the model are in accordance with those of
observation. The most important physical process in coupling each component is
charge exchange which tightly couples atomic hydrogen with protons. Most of the
hydrogen escaping from hot Jupiters is protons, especially in young star-planet
system. We found that the single-fluid model can describe the escape of
particles when the mass loss rate is higher than a few times g/s while
below g/s the multi-fluid model is more suitable for it due to the
decoupling of particles. We found that the predicted mass loss rates of HD
189733b with the assumption of energy-limit are a factor of 10 larger than that
calculated by our models due to the high ionization degree. For the ionized
wind which is almost compose of protons, the assumption of energy-limit is no
longer effective. We fitted the mass loss rates of the ionized wind as a
function of by calculating the variation of the mass loss rates with
UV fluxes.Comment: 35 pages, 6 figures, submitted to Ap
The high-energy environment in the super-earth system CoRoT-7
High-energy irradiation of exoplanets has been identified to be a key
influence on the stability of these planets' atmospheres. So far,
irradiation-driven mass-loss has been observed only in two Hot Jupiters, and
the observational data remain even more sparse in the super-earth regime. We
present an investigation of the high-energy emission in the CoRoT-7 system,
which hosts the first known transiting super-earth. To characterize the
high-energy XUV radiation field into which the rocky planets CoRoT-7b and
CoRoT-7c are immersed, we analyzed a 25 ks XMM-Newton observation of the host
star. Our analysis yields the first clear (3.5 sigma) X-ray detection of
CoRoT-7. We determine a coronal temperature of ca. 3 MK and an X-ray luminosity
of 3*10^28 erg/s. The level of XUV irradiation on CoRoT-7b amounts to ca. 37000
erg/cm^2/s. Current theories for planetary evaporation can only provide an
order-of-magnitude estimate for the planetary mass loss; assuming that CoRoT-7b
has formed as a rocky planet, we estimate that CoRoT-7b evaporates at a rate of
about 1.3*10^11 g/s and has lost ca. 4-10 earth masses in total.Comment: 5 pages, accepted for publication by Astronomy & Astrophysic
Seasonal and diurnal variations in Martian surface ultraviolet irradiation: biological and chemical implications for the Martian regolith
The issue of the variation of the surface ultraviolet (UV) environment on Mars was investigated with particular emphasis being placed on the interpretation of data in a biological context. A UV model has been developed to yield the surface UV irradiance at any time and place over the Martian year. Seasonal and diurnal variations were calculated and dose rates evaluated. Biological interpretation of UV doses is performed through the calculation of DNA damage effects upon phage T7 and Uracil, used as examples for biological dosimeters. A solar UV 'hotspot' was revealed towards perihelion in the southern hemisphere, with a significant damaging effect upon these species. Diurnal profiles of UV irradiance are also seen to vary markedly between aphelion and perihelion. The effect of UV dose is also discussed in terms of the chemical environment of the Martian regolith, since UV irradiance can reach high enough levels so as to have a significant effect upon the soil chemistry. We show, by assuming that H2O is the main source of hydrogen in the Martian atmosphere, that the stoichiometrically desirable ratio of 2:1 for atmospheric H and O loss rates to space are not maintained and at present the ratio is about 20:1. A large planetary oxygen surface sink is therefore necessary, in contrast with escape to space. This surface oxygen sink has important implications for the oxidation potential and the toxicology of the Martian soil. UV-induced adsorption of {\rm O}_{2}^{-} super-radicals plays an important role in the oxidative environment of the Martian surface, and the biologically damaging areas found in this study are also shown to be regions of high subsurface oxidation. Furthermore, we briefly cover the astrobiological implications for landing sites that are planned for future Mars missions
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