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Several transiting hot Jupiters orbit relatively inactive main-sequence stars. For some of those, the logRHK activity parameter lies below the basal level (-5.1). Two explanations have been proposed so far: (i) the planet affects the stellar dynamo, (ii) the logRHK measurements are biased by extrinsic absorption, either by the interstellar medium (ISM) or by material local to the system. We present here Hubble Space Telescope/COS far-UV spectra of WASP-13, which hosts an inflated hot Jupiter and has a measured logRHK value (-5.26), well below the basal level. From the stars spectral energy distribution we obtain an extinction E(B-V) = 0.045+/-0.025 mag and a distance d = 232+/-8 pc. We detect at >4 sigma lines belonging to three different ionization states of carbon (C1, C2, and C4) and the Si4 doublet at ~3 sigma. Using far-UV spectra of nearby early G-type stars of known age, we derive a C4/C1 flux ratio-age relation, from which we estimate WASP-13s age to be 5.1+/-2.0 Gyr. We rescale the solar irradiance reference spectrum to match the flux of the C4 1548 doublet. By integrating the rescaled solar spectrum, we obtain an XUV flux at 1 AU of 5.4 erg s^-1 cm^-2. We use a detailed model of the planets upper atmosphere, deriving a mass-loss rate of 1.5x10^11 g s^-1. Despite the low logRHK value, the star shows a far-UV spectrum typical of middle-aged solar-type stars, pointing toward the presence of significant extrinsic absorption. The analysis of a high-resolution spectrum of the Ca2H&K lines indicates that the ISM absorption could be the origin of the low logRHK value. Nevertheless, the large uncertainty in the Ca2 ISM abundance does not allow us to firmly exclude the presence of circumstellar gas.
WASP-18 hosts a massive, very close-in Jupiter-like planet. Despite its young age ($<$1 Gyr), the star presents an anomalously low stellar activity level: the measured logR$_{rm HK}$ activity parameter lies slightly below the basal level; there is no
We measured the chromospheric activity of the four hot Jupiter hosts WASP-43, WASP-51/HAT-P-30, WASP-72 & WASP-103 to search for anomalous values caused by the close-in companions. The Mount Wilson Ca II H&K S-index was calculated for each star using
The space experiment CoRoT has recently detected a transiting hot Jupiter in orbit around a moderately active F-type main-sequence star (CoRoT-Exo-4a). This planetary system is of particular interest because it has an orbital period of 9.202 days, th
HD189733 is an active K dwarf that is, with its transiting hot Jupiter, among the most studied exoplanetary systems. In this first paper of the Multiwavelength Observations of an eVaporating Exoplanet and its Star (MOVES) program, we present a 2-year
The study of planet occurrence as a function of stellar mass is important for a better understanding of planet formation. Estimating stellar mass, especially in the red giant regime, is difficult. In particular, stellar masses of a sample of evolved