41 research outputs found
Estimation of the XUV radiation onto close planets and their evaporation
Context: The current distribution of planet mass vs. incident stellar X-ray
flux supports the idea that photoevaporation of the atmosphere may take place
in close-in planets. Integrated effects have to be accounted for. A proper
calculation of the mass loss rate due to photoevaporation requires to estimate
the total irradiation from the whole XUV range. Aims: The purpose of this paper
is to extend the analysis of the photoevaporation in planetary atmospheres from
the accessible X-rays to the mostly unobserved EUV range by using the coronal
models of stars to calculate the EUV contribution to the stellar spectra. The
mass evolution of planets can be traced assuming that thermal losses dominate
the mass loss of their atmospheres. Methods: We determine coronal models for 82
stars with exoplanets that have X-ray observations available. Then a synthetic
spectrum is produced for the whole XUV range (~1-912 {\AA}). The determination
of the EUV stellar flux, calibrated with real EUV data, allows us to calculate
the accumulated effects of the XUV irradiation on the planet atmosphere with
time, as well as the mass evolution for planets with known density. Results: We
calibrate for the first time a relation of the EUV luminosity with stellar age
valid for late-type stars. In a sample of 109 exoplanets, few planets with
masses larger than ~1.5 Mj receive high XUV flux, suggesting that intense
photoevaporation takes place in a short period of time, as previously found in
X-rays. The scenario is also consistent with the observed distribution of
planet masses with density. The accumulated effects of photoevaporation over
time indicate that HD 209458b may have lost 0.2 Mj since an age of 20 Myr.
Conclusions: Coronal radiation produces rapid photoevaporation of the
atmospheres of planets close to young late-type stars. More complex models are
needed to explain fully the observations.Comment: Accepted by A&A. 10 pages, 8 figures, 7 Tables (2 online). Additional
online material includes 7 pages, 6 figures and 6 tables, all include
Non-parametric modeling of the intra-cluster gas using APEX-SZ bolometer imaging data
We demonstrate the usability of mm-wavelength imaging data obtained from the
APEX-SZ bolometer array to derive the radial temperature profile of the hot
intra-cluster gas out to radius r_500 and beyond. The goal is to study the
physical properties of the intra-cluster gas by using a non-parametric
de-projection method that is, aside from the assumption of spherical symmetry,
free from modeling bias. We use publicly available X-ray imaging data from the
XMM-Newton observatory and our Sunyaev-Zel'dovich Effect (SZE) imaging data
from the APEX-SZ experiment at 150 GHz to de-project the density and
temperature profiles for the relaxed cluster Abell 2204. We derive the gas
density, temperature and entropy profiles assuming spherical symmetry, and
obtain the total mass profile under the assumption of hydrostatic equilibrium.
For comparison with X-ray spectroscopic temperature models, a re-analysis of
the recent Chandra observation is done with the latest calibration updates.
Using the non-parametric modeling we demonstrate a decrease of gas temperature
in the cluster outskirts, and also measure the gas entropy profile. These
results are obtained for the first time independently of X-ray spectroscopy,
using SZE and X-ray imaging data. The contribution of the SZE systematic
uncertainties in measuring T_e at large radii is shown to be small compared to
the Chandra systematic spectroscopic errors. The upper limit on M_200 derived
from the non-parametric method is consistent with the NFW model prediction from
weak lensing analysis.Comment: Replaced with the published version; A&A 519, A29 (2010
Exploring the role of sphingolipid machinery during the epithelial to mesenchymal transition program using an integrative approach
10.18632/oncotarget.7947Oncotarget71622295-2232