Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userLarger Planet Radii Inferred from Stellar Flicker Brightness Variations of Bright Planet Host Stars
138
0
0.0
(
0
)
Authors
Fabienne A. Bastien
Ask ChatGPT about the research
No Arabic abstract
Most extrasolar planets have been detected by their influence on their parent star, typically either gravitationally (the Doppler method) or by the small dip in brightness as the planet blocks a portion of the star (the transit method). Therefore, the accuracy with which we know the masses and radii of extrasolar planets depends directly on how well we know those of the stars, the latter usually determined from the measured stellar surface gravity, logg. Recent work has demonstrated that the short-timescale brightness variations (flicker) of stars can be used to measure logg to a high accuracy of ~0.1-0.2 dex (Bastien et al. 2013). Here, we use flicker measurements of 289 bright (Kepmag<13) candidate planet-hosting stars with Teff=4500-6650 K to re-assess the stellar parameters and determine the resulting impact on derived planet properties. This re-assessment reveals that for the brightest planet-host stars, an astrophysical bias exists that contaminates the stellar sample with evolved stars: nearly 50% of the bright planet-host stars are subgiants. As a result, the stellar radii, and hence the radii of the planets orbiting these stars, are on average 20-30% larger than previous measurements had suggested.
rate research
Read More
We obtained high-resolution, high-contrast optical imaging in the SDSS $i$ band with the LuckyCam camera mounted on the 2.56m Nordic Optical Telescope, to search for faint stellar companions to 16 stars harbouring transiting exoplanets. The Lucky Imaging technique uses very short exposures to obtain near diffraction-limited images yielding sub-arcsecond sensitivity, allowing us to search for faint stellar companions within the seeing disc of the primary planet host. Here we report the detection of two candidate stellar companions to the planet host TrES-1 at separations $<6.5arcsec$ and we confirm stellar companions to CoRoT-2, CoRoT-3, TrES-2, TrES-4, and HAT-P-7 already known in the literature. We do not confirm the candidate companions to HAT-P-8 found via Lucky Imaging by citet{Bergfors2013}, however, most probably because HAT-P-8 was observed in poor seeing conditions. Our detection sensitivity limits allow us to place constraints on the spectral types and masses of the putative bound companions to the planet host stars in our sample. If bound, the stellar companions identified in this work would provide stringent observational constraints to models of planet formation and evolution. In addition these companions could affect the derived physical properties of the exoplanets in these systems.
The Sun is the only star whose surface can be directly resolved at high resolution, and therefore constitutes an excellent test case to explore the physical origin of stellar radial-velocity (RV) variability. We present HARPS observations of sunlight scattered off the bright asteroid 4/Vesta, from which we deduced the Suns activity-driven RV variations. In parallel, the HMI instrument onboard the Solar Dynamics Observatory provided us with simultaneous high spatial resolution magnetograms, Dopplergrams, and continuum images of the Sun in the Fe I 6173A line. We determine the RV modulation arising from the suppression of granular blueshift in magnetised regions and the flux imbalance induced by dark spots and bright faculae. The rms velocity amplitudes of these contributions are 2.40 m/s and 0.41 m/s, respectively, which confirms that the inhibition of convection is the dominant source of activity-induced RV variations at play, in accordance with previous studies. We find the Doppler imbalances of spot and plage regions to be only weakly anticorrelated. Lightcurves can thus only give incomplete predictions of convective blueshift suppression. We must instead seek proxies that track the plage coverage on the visible stellar hemisphere directly. The chromospheric flux index R_HK derived from the HARPS spectra performs poorly in this respect, possibly because of the differences in limb brightening/darkening in the chromosphere and photosphere. We also find that the activity-driven RV variations of the Sun are strongly correlated with its full-disc magnetic flux density, which may become a useful proxy for activity-related RV noise.
Aims. In this work we derive new precise and homogeneous parameters for 37 stars with planets. For this purpose, we analyze high resolution spectra obtained by the NARVAL spectrograph for a sample composed of bright planet host stars in the northern hemisphere. The new parameters are included in the SWEET-Cat online catalogue. Methods. To ensure that the catalogue is homogeneous, we use our standard spectroscopic analysis procedure, ARES+MOOG, to derive effective temperatures, surface gravities, and metallicities. These spectroscopic stellar parameters are then used as input to compute the stellar mass and radius, which are fundamental for the derivation of the planetary mass and radius. Results. We show that the spectroscopic parameters, masses, and radii are generally in good agreement with the values available in online databases of exoplanets. There are some exceptions, especially for the evolved stars. These are analyzed in detail focusing on the effect of the stellar mass on the derived planetary mass. Conclusions. We conclude that the stellar mass estimations for giant stars should be managed with extreme caution when using them to compute the planetary masses. We report examples within this sample where the differences in planetary mass can be as high as 100% in the most extreme cases.
Some highly irradiated close-in exoplanets orbit stars showing anomalously low stellar chromospheric emission. We attribute this to absorption by circumstellar gas replenished by mass loss from ablating planets. Here we report statistics validating this hypothesis. Among ~3000 nearby, bright, main sequence stars ~40 show depressed chromospheric emission indicative of undiscovered mass-losing planets. The Dispersed Matter Planet Project uses high precision, high cadence radial velocity measurements to detect these planets. We summarise results for two planetary systems (DMPP-1 and DMPP-3) and fully present observations revealing a Mp sin i = 0.469 M$_{rm J}$ planet in a 5.207 d orbit around the $gamma$-Doradus pulsator HD 11231 (DMPP-2). We have detected short period planets wherever we have made more than 60 RV measurements, demonstrating that we have originated a very efficient method for detecting nearby compact planetary systems. Our shrouded, ablating planetary systems may be a short-lived phase related to the Neptunian desert: i.e. the dearth of intermediate-mass planets at short orbital periods. The circumstellar gas facilitates compositional analysis; allowing empirical exogeology in the cases of sublimating rocky planets. Dispersed Matter Planet Project discoveries will be important for establishing the empirical mass-radius-composition relationship(s) for low mass planets.
It has been suggested that planetary radii increase with the stellar mass, for planets below 6 R$_{oplus}$ and host below 1 M$_odot$. In this study, we explore whether this inferred relation between planetary size and the host stars mass can be explained by a larger planetary mass among planets orbiting more massive stars, inflation of the planetary radius due to the difference in stellar irradiation, or different planetary compositions and structures. Using exoplanetary data of planets with measured masses and radii, we investigate the relations between stellar mass and various planetary properties for G- and K- stars, and confirm that more massive stars host larger planets and more massive. We find that the differences in the planetary masses and temperatures are insufficient to explain the measured differences in radii between planets surrounding different stellar types. We show that the larger planetary radii can be explained by a larger fraction of volatile material (H-He atmospheres) among planets surrounding more massive stars. We conclude that planets around more massive stars are larger most probably as a result of larger H-He atmospheres. Our findings imply that planets forming around more massive stars tend to accrete H-He atmospheres more efficiently.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
