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the dragon s gaze the dragon s gaze friday december 8 2017 a self consistent cloud model for brown dwarfs and young giant exoplanets comparison with photometric and spectroscopic observations a self consistent cloud model for brown dwarfs and young giant exoplanets comparison with photometric and spectroscopic observations authors charnay et al abstract we developed a simple physical and self consistent cloud model for brown dwarfs and young giant exoplanets we compared different parametrisations for the cloud particle size by either fixing particle radii or fixing the mixing efficiency parameter fsed or estimating particle radii from simple microphysics the cloud scheme with simple microphysics appears as the best parametrisation by successfully reproducing the observed photometry and spectra of brown dwarfs and young giant exoplanets in particular it reproduces the l t transition due to the condensation of silicate and iron clouds below the visible near ir photosphere it also reproduces the reddening observed for low gravity objects due to an increase of cloud optical depth for low gravity in addition we found that the cloud greenhouse effect shifts chemical equilibriums increasing the abundances of species stable at high temperature this effect should significantly contribute to the strong variation of methane abundance at the l t transition and to the methane depletion observed on young exoplanets finally we predict the existence of a continuum of brown dwarfs and exoplanets for absolute j magnitude 15 18 and j k color 0 3 due to the evolution of the l t transition with gravity this self consistent model therefore provides a general framework to understand the effects of clouds and appears well suited for atmospheric retrievals posted by will baird at 8 00 am no comments email this blogthis share to x share to facebook share to pinterest labels brown dwarf clouds exoatmosphere simulation thursday december 7 2017 hot jupiters driven by high eccentricity migration in globular clusters hot jupiters driven by high eccentricity migration in globular clusters authors hammers et al abstract hot jupiters hjs are short period giant planets that are observed around sim 1 of solar type field stars one possible formation scenario for hjs is high eccentricity high e migration in which the planet forms at much larger radii is excited to high eccentricity by some mechanism and migrates to its current orbit due to tidal dissipation occurring near periapsis we consider high e migration in dense stellar systems such as the cores of globular clusters gcs in which encounters with passing stars can excite planets to the high eccentricities needed to initiate migration we study this process via monte carlo simulations of encounters with a star planet system including the effects of tidal dissipation using an efficient regularized restricted three body code hjs are produced in our simulations over a significant range of the stellar number density n _ star assuming the planet is initially on a low eccentricity orbit with semimajor axis 1 au for n _ star lesssim 10 3 mathrm pc 3 the encounter rate is too low to induce orbital migration whereas for n _ star gtrsim 10 6 mathrm pc 3 hj formation is suppressed because the planet is more likely ejected from its host star tidally disrupted or transferred to a perturbing star the fraction of planets that are converted to hjs peaks at approx 2 for intermediate number densities of approx 4 times 10 4 mathrm pc 3 warm jupiters giant planets with periods between 10 and 100 days are produced in our simulations with an efficiency of up to approx 0 5 our results suggest that hjs can form through high e migration induced by stellar encounters in the centers of of dense gcs but not in their outskirts where the densities are lower posted by will baird at 4 00 pm no comments email this blogthis share to x share to facebook share to pinterest labels exoplanet migration gas giants giant planets globular clusters hot jupiters stellar clusters the most eccentric planet orbiting a giant star the pan pacific planet search vii the most eccentric planet orbiting a giant star authors wittenmyer et al abstract radial velocity observations from three instruments reveal the presence of a 4 m jup planet candidate orbiting the k giant hd 76920 hd 76920b has an orbital eccentricity of 0 856 0 009 making it the most eccentric planet known to orbit an evolved star there is no indication that hd 76920 has an unseen binary companion suggesting a scattering event rather than kozai oscillations as a probable culprit for the observed eccentricity the candidate planet currently approaches to about four stellar radii from its host star and is predicted to be engulfed on a 100 myr timescale due to the combined effects of stellar evolution and tidal interactions posted by will baird at 12 00 pm no comments email this blogthis share to x share to facebook share to pinterest labels eccentric orbit gas giants giant planets k giant exoplanets kozai lidov oscillations possible detection of a bimodal cloud distribution in the atmosphere of hat p 32ab possible detection of a bimodal cloud distribution in the atmosphere of hat p 32ab from multi band photometry authors tregloan reed et al abstract we present high precision photometry of eight separate transit events in the hat p 32 planetary system one transit event was observed simultaneously by two telescopes of which one obtained a simultaneous multi band light curve in three optical bands giving a total of 11 transit light curves due to the filter selection and in conjunction with using the defocussed photometry technique we were able to obtain an extremely high precision ground based transit in the textit u band 350 nm with an rms scatter of 1 mmag all 11 transits were modelled using textsc prism and textsc gemc and the physical properties of the system calculated we find the mass and radius of the host star to be 1 182 pm 0 041 msun and 1 225 pm0 015 rsun respectively for the planet we find a mass of 0 80 pm 0 14 mjup a radius of 1 807 pm0 022 rjup and a density of 0 126 pm0 023 pjup these values are consistent with those found in the literature we also obtain a new orbital ephemeris for the system t0 bjd tdb2454420 447187 96 2 15000800 10 e we measured the transmission spectrum of hat p 32 a b and compared it to theoretical transmission spectra our results indicate a bimodal cloud particle distribution consisting of rayleigh like haze and grey absorbing cloud particles within the atmosphere of hat p 32 a b posted by will baird at 8 00 am no comments email this blogthis share to x share to facebook share to pinterest labels clouds exoatmosphere gas giants giant planets hat p 32ab hot jupiters wednesday december 6 2017 sdb pulsating star v391 peg s giant planet not detected the sdb pulsating star v391 peg and its putative giant planet revisited after 13 years of time series photometric data authors silvotti et al abstract v391 peg alias hs2201 2610 is a subdwarf b sdb pulsating star that shows both p and g modes by studying the arrival times of the p mode maxima and minima through the o c method in a previous article the presence of a planet was inferred with an orbital period of 3 2 yr and a minimum mass of 3 2 m_jup here we present an updated o c analysis using a larger data set of 1066 hours of photometric time series 2 5x larger in terms of the number of data points which covers the period between 1999 and 2012 compared with 1999 2006 of the previous analysis up to the end of 2008 the new o c diagram of the main pulsation frequency f1 is compatible with and improves the previous two component solution representing the long term variation of the pulsation period parabolic component and the giant planet sine wave component since 2009 the o c trend of f1 changes and the time derivative of the pulsation period p_dot passes from positive to negative the reason of this change of regime is not clear and could be related to nonlinear interactions between different pulsation modes with the new data the o c diagram of the secondary pulsation frequency f2 continues to show two components parabola and sine wave like in the previous analysis various solutions are proposed to fit the o c diagrams of f1 and f2 but in all of them the sinusoidal components of f1 and f2 differ or at least agree less well than before the nice agreement found previously was a coincidence due to various small effects that are carefully analysed now with a larger dataset the presence of a planet is more uncertain and would require confirmation with an independent method the new data allow us to improve the measurement of p_dot for f1 and f2 using only the data up to the end of 2008 we obtain p_dot_1 1 34 0 04 x10 12 and p_dot_2 1 62 0 22 x10 12 posted by will baird at 4 00 pm no comments email this blogthis share to x share to facebook share to pinterest labels false positive gas giants giant planets host stars v391 peg ogle 2016 blg 0613labb a microlensing planet in a binary system ogle 2016 blg 0613labb a microlensing planet in a binary system authors han et al abstract we present the analysis of ogle 2016 blg 0613 for which the lensing light curve appears to be that of a typical binary lens event with two caustic spikes but with a discontinuous feature on the trough between the spikes we find that the discontinuous feature was produced by a planetary companion to the binary lens we find four degenerate triple lens solution classes each composed of a pair of solutions according to the well known wide close planetary degeneracy one of these solution classes is excluded due to its relatively poor fit for the remaining three pairs of solutions the most likely primary mass is about m _ 1 sim 0 7 m _ odot while the planet is a super jupiter in all cases the system lies in the galactic disk about halfway toward the galactic bulge however in one of these three solution classes the secondary of the binary system is a low mass brown dwarf with relative mass ratios 1 0 03 0 003 while in the two others the masses of the binary components are comparable these two possibilities can be distinguished in about 2024 when the measured lens source relative proper motion will permit separate resolution of the lens and source posted by will baird at 12 00 pm no comments email this blogthis share to x share to facebook share to pinterest labels binary star systems brown dwarf gas giants giant planets micro lensing ogle 2016 blg 0613labb on the cavity of a debris disc carved by a giant planet on the cavity of a debris disc carved by a giant planet authors regály et al abstract one possible explanation of the cavity in debris discs is the gravitational perturbation of an embedded giant planet planetesimals passing close to a massive body are dynamically stirred resulting in a cleared region known as the chaotic zone theory of overlapping mean motion resonances predicts the width of this cavity to test whether this cavity is identical to the chaotic zone we investigate the formation of cavities by means of collisionless n body simulations assuming a 1 25 10 jupiter mass planet with eccentricities of 0 0 9 synthetic images at millimetre wavelengths are calculated to determine the cavity properties by fitting an ellipse to 14 per cent contour level depending on the planetary eccentricity epl the elliptic cavity wall rotates as the planet orbits with the same epl less than 0 2 or half epl greater than 0 2 period that of the planet the cavity centre is offset from the star along the semimajor axis of the planet with a distance of d 0 1q 0 17e0 5pl d 0 1q 0 17epl0 5 in units of cavity size towards the planet s orbital apocentre where q is the planet to star mass ratio pericentre apocentre glow develops for epl less than 0 05 epl greater than 0 1 while both are present for 0 05 epl 0 1 empirical formulae are derived for the sizes of the cavities δacav 2 35q0 36 and δacav 7 87q0 37e0 38pl δacav 7 87q0 37epl0 38 for epl 0 05 and epl greater 0 05 respectively the cavity eccentricity ecav equals to that of the planet only for 0 3 epl 0 6 a new method based on atacama large millimeter submillimeter array observations for estimating the orbital parameters and mass of the planet carving the cavity is also given posted by will baird at 8 00 am no comments email this blogthis share to x share to facebook share to pinterest labels gapped disk giant planets protoplanetary disks older posts home subscribe to posts atom an exoplanet blog my projects the dragon s tales xenopermian exoplanet links exoplanet transit database extrasolar planets encyclopaedia habitable exoplanets catalog open exoplanet catalogue exoplanets org exoplanet blog roll universe today mars has a warm region inside 14 hours ago systemic ember 1 week ago centauri dreams disrupted systems implications for life 1 week ago blog archive 2017 537 december 13 a self consistent cloud model for brown dwarfs and hot jupiters driven by high eccentricity migration the most eccentric planet orbiting a giant star possible detection of a bimodal cloud distribution sdb pulsating star v391 peg s giant planet not det ogle 2016 blg 0613labb a microlensing planet in a on the cavity of a debris disc carved by a giant p linking the climate and thermal phase curve of sup the discovery and mass measurement of a new ultra epic 246393474 b a 5 earth mass super earth trans whole planet coupling between climate mantle and hunting for a proxima centauri b transit ross 128b a temperate exo earth around a quiet m november 72 october 99 september 93 august 75 july 11 june 20 february 61 january 93 2016 1217 december 101 november 102 october 98 september 101 august 95 july 101 june 103 may 112 april 101 march 105 february 99 january 99 2015 1187 december 115 november 107 october 100 september 96 august 96 july 99 june 92 may 98 april 93 march 99 february 90 january 102 2014 1082 december 98 november 97 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