3,258 research outputs found
Transit observations of the Hot Jupiter HD 189733b at X-ray wavelengths
We present new X-ray observations obtained with Chandra ACIS-S of the HD
189733 system, consisting of a K-type star orbited by a transiting Hot Jupiter
and an M-type stellar companion. We report a detection of the planetary transit
in soft X-rays with a significantly larger transit depth than observed in the
optical. The X-ray data favor a transit depth of 6-8%, versus a broadband
optical transit depth of 2.41%. While we are able to exclude several possible
stellar origins for this deep transit, additional observations will be
necessary to fully exclude the possibility that coronal inhomogeneities
influence the result. From the available data, we interpret the deep X-ray
transit to be caused by a thin outer planetary atmosphere which is transparent
at optical wavelengths, but dense enough to be opaque to X-rays. The X-ray
radius appears to be larger than the radius observed at far-UV wavelengths,
most likely due to high temperatures in the outer atmosphere at which hydrogen
is mostly ionized. We furthermore detect the stellar companion HD 189733B in
X-rays for the first time with an X-ray luminosity of log LX = 26.67 erg/s. We
show that the magnetic activity level of the companion is at odds with the
activity level observed for the planet-hosting primary. The discrepancy may be
caused by tidal interaction between the Hot Jupiter and its host star.Comment: 15 pages, accepted for publication in The Astrophysical Journa
Evolution of hierarchical clustering in the CFHTLS-Wide since z~1
We present measurements of higher order clustering of galaxies from the
latest release of the Canada-France-Hawaii-Telescope Legacy Survey (CFHTLS)
Wide. We construct a volume-limited sample of galaxies that contains more than
one million galaxies in the redshift range 0.2<z<1 distributed over the four
independent fields of the CFHTLS. We use a counts in cells technique to measure
the variance and the hierarchical moments S_n = /^(n-1)
(3<n<5) as a function of redshift and angular scale.The robustness of our
measurements if thoroughly tested, and the field-to-field scatter is in very
good agreement with analytical predictions. At small scales, corresponding to
the highly non-linear regime, we find a suggestion that the hierarchical
moments increase with redshift. At large scales, corresponding to the weakly
non-linear regime, measurements are fully consistent with perturbation theory
predictions for standard LambdaCDM cosmology with a simple linear bias.Comment: 17 pages, 11 figures, submitted to MNRA
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