294 research outputs found
On the tidal evolution of Hot Jupiters on inclined orbits
Tidal friction is thought to be important in determining the long-term
spin-orbit evolution of short-period extrasolar planetary systems. Using a
simple model of the orbit-averaged effects of tidal friction, we study the
evolution of close-in planets on inclined orbits, due to tides. We analyse the
effects of the inclusion of stellar magnetic braking by performing a
phase-plane analysis of a simplified system of equations, including the braking
torque. The inclusion of magnetic braking is found to be important, and its
neglect can result in a very different system history. We then present the
results of numerical integrations of the tidal evolution equations, where we
find that it is essential to consider coupled evolution of the orbital and
rotational elements, including dissipation in both the star and planet, to
accurately model the evolution. The main result of our integrations is that for
typical Hot Jupiters, tidal friction aligns the stellar spin with the orbit on
a similar time as it causes the orbit to decay. This means that if a planet is
observed to be aligned, then it probably formed coplanar. This reinforces the
importance of Rossiter-McLaughlin effect observations in determining the degree
of spin-orbit alignment in transiting systems. We apply these results to the
XO-3 system, and constrain the tidal quality factors Q' in both the star and
planet in this system. Using a model in which inertial waves are excited by
tidal forcing in the outer convective envelope and dissipated by turbulent
viscosity, we calculate Q' for a range of F-star models, and find it to vary
considerably within this class of stars. This means that assuming a single Q'
applies to all stars is probably incorrect. We propose an explanation for the
survival of WASP-12 b & OGLE-TR-56 b, in terms of weak dissipation in the star.Comment: 19 pages, 8 figures, accepted in MNRA
A simple model of the reflection effect for the interacting binaries and extrasolar planets
Extrasolar planets are a natural extension of the interacting binaries
towards the companions with very small masses and similar tools might be used
to study them. Unfortunately, the generally accepted treatment of the
reflection effect in interacting binaries is not very suitable to study cold
objects irradiated by hot objects or extrasolar planets. Our simple model of
the reflection effect takes into account the reflection (scattering), heating
and heat redistribution over the surface of the irradiated object. The shape of
the objects is described by the Roche potential and limb and gravity darkening
can be taken into account. The orbital revolution and rotation of the planet
with proper Doppler shifts for the scattered and thermal radiation are also
accounted for. Subsequently, light-curves and/or spectra of exoplanets were
modeled and the effects of the heat redistribution, limb darkening/brightening,
(non-)grey albedo, and non-spherical shape were studied. Recent observations of
HD189733b, WASP12b, and Wasp-19b were reproduced reasonably well. HD189733b has
low Bond albedo and intense heat redistribution. Wasp-19b has low Bond albedo
and low heat redistribution. We also calculate the exact Roche shapes and
temperature distribution over the surface of all 78 transiting extrasolar
planets known so far. It is found that the departures from the sphere vary
considerably within the sample. Departures of about 1% are common. In some
cases: WASP-12b, WASP-19b, WASP-33b departures can reach about 14, 12, and 8%,
respectively. The mean temperatures of these planets also vary considerably
from 300 K to 2600 K. The extreme cases are WASP-33b, WASP-12b, and WASP-18b
with mean temperatures of about 2600, 2430, and 2330 K, respectively.Comment: Any comments or suggestions will be appreciate
Tidal Evolution of Close-in Planets
Recent discoveries of several transiting planets with clearly non-zero
eccentricities and some large inclinations started changing the simple picture
of close-in planets having circular and well-aligned orbits. Two major
scenarios to form such planets are planet migration in a disk, and
planet--planet interactions combined with tidal dissipation. The former
scenario can naturally produce a circular and low-obliquity orbit, while the
latter implicitly assumes an initially highly eccentric and possibly
high-obliquity orbit, which are then circularized and aligned via tidal
dissipation. We investigate the tidal evolution of transiting planets on
eccentric orbits. We show that the current and future orbital evolution of
these systems is likely dominated by tidal dissipation, and not by a more
distant companion. Although most of these close-in planets experience orbital
decay all the way to the Roche limit, there are two characteristic evolution
paths for them, depending on the relative efficiency of tidal dissipation
inside the star and the planet. We point out that the current observations may
be consistent with one of them. Our results suggest that at least some of the
close-in planets with non-zero orbital eccentricity may have been formed by
tidally circularizing an initially eccentric orbit. We also find that even when
the stellar spin-orbit misalignment is observed to be small at present, some
systems could have had a highly misaligned orbit in the past. Finally, we also
re-examine the recent claim by Levrard et. al., who found that all orbital and
spin parameters evolve on a similar timescale to orbital decay.Comment: Accepted for publication in ApJ, 22 pages, 19 figures, 2 tables,
Corrupted figures are fixe
Measurement of the Boson Mass
A measurement of the mass of the boson is presented based on a sample of
5982 decays observed in collisions at
= 1.8~TeV with the D\O\ detector during the 1992--1993 run. From a
fit to the transverse mass spectrum, combined with measurements of the
boson mass, the boson mass is measured to be .Comment: 12 pages, LaTex, style Revtex, including 3 postscript figures
(submitted to PRL
Search for Production via Trilepton Final States in collisions at TeV
We have searched for associated production of the lightest chargino,
, and next-to-lightest neutralino, , of the
Minimal Supersymmetric Standard Model in collisions at
\mbox{ = 1.8 TeV} using the \D0 detector at the Fermilab Tevatron
collider. Data corresponding to an integrated luminosity of 12.5 \ipb
were examined for events containing three isolated leptons. No evidence for
pair production was found. Limits on
BrBr are
presented.Comment: 17 pages (13 + 1 page table + 3 pages figures). 3 PostScript figures
will follow in a UUEncoded, gzip'd, tar file. Text in LaTex format. Submitted
to Physical Review Letters. Replace comments - Had to resumbmit version with
EPSF directive
The Azimuthal Decorrelation of Jets Widely Separated in Rapidity
This study reports the first measurement of the azimuthal decorrelation
between jets with pseudorapidity separation up to five units. The data were
accumulated using the D{\O}detector during the 1992--1993 collider run of the
Fermilab Tevatron at 1.8 TeV. These results are compared to
next--to--leading order (NLO) QCD predictions and to two leading--log
approximations (LLA) where the leading--log terms are resummed to all orders in
. The final state jets as predicted by NLO QCD
show less azimuthal decorrelation than the data. The parton showering LLA Monte
Carlo {\small HERWIG} describes the data well; an analytical LLA prediction
based on BFKL resummation shows more decorrelation than the data.Comment: 6 pages with 4 figures, all uuencoded and gzippe
Second Generation Leptoquark Search in p\bar{p} Collisions at = 1.8 TeV
We report on a search for second generation leptoquarks with the D\O\
detector at the Fermilab Tevatron collider at = 1.8 TeV.
This search is based on 12.7 pb of data. Second generation leptoquarks
are assumed to be produced in pairs and to decay into a muon and quark with
branching ratio or to neutrino and quark with branching ratio
. We obtain cross section times branching ratio limits as a function
of leptoquark mass and set a lower limit on the leptoquark mass of 111
GeV/c for and 89 GeV/c for at the 95%\
confidence level.Comment: 18 pages, FERMILAB-PUB-95/185-
Jet Production via Strongly-Interacting Color-Singlet Exchange in Collisions
A study of the particle multiplicity between jets with large rapidity
separation has been performed using the D{\O}detector at the Fermilab Tevatron
Collider operating at TeV. A significant excess of
low-multiplicity events is observed above the expectation for color-exchange
processes. The measured fractional excess is , which is consistent with a strongly-interacting
color-singlet (colorless) exchange process and cannot be explained by
electroweak exchange alone. A lower limit of 0.80% (95% C.L.) is obtained on
the fraction of dijet events with color-singlet exchange, independent of the
rapidity gap survival probability.Comment: 15 pages (REVTeX), 3 PS figs (uuencoded/tar compressed, epsf.sty)
Complete postscript available at http://d0sgi0.fnal.gov/d0pubs/journals.html
Submitted to Physical Review Letter
Measurements of fiducial and differential cross sections for Higgs boson production in the diphoton decay channel at s√=8 TeV with ATLAS
Measurements of fiducial and differential cross sections are presented for Higgs boson production in proton-proton collisions at a centre-of-mass energy of s√=8 TeV. The analysis is performed in the H → γγ decay channel using 20.3 fb−1 of data recorded by the ATLAS experiment at the CERN Large Hadron Collider. The signal is extracted using a fit to the diphoton invariant mass spectrum assuming that the width of the resonance is much smaller than the experimental resolution. The signal yields are corrected for the effects of detector inefficiency and resolution. The pp → H → γγ fiducial cross section is measured to be 43.2 ±9.4(stat.) − 2.9 + 3.2 (syst.) ±1.2(lumi)fb for a Higgs boson of mass 125.4GeV decaying to two isolated photons that have transverse momentum greater than 35% and 25% of the diphoton invariant mass and each with absolute pseudorapidity less than 2.37. Four additional fiducial cross sections and two cross-section limits are presented in phase space regions that test the theoretical modelling of different Higgs boson production mechanisms, or are sensitive to physics beyond the Standard Model. Differential cross sections are also presented, as a function of variables related to the diphoton kinematics and the jet activity produced in the Higgs boson events. The observed spectra are statistically limited but broadly in line with the theoretical expectations
Transiting exoplanets from the CoRoT space mission. IV. CoRoT-Exo-4b: a transiting planet in a 9.2 day synchronous orbit
Copyright © The European Southern Observatory (ESO)CoRoT, the first space-based transit search, provides ultra-high-precision light curves with continuous time-sampling over periods of up to 5 months. This allows the detection of transiting planets with relatively long periods, and the simultaneous study of the host star’s photometric variability. In this Letter, we report the discovery of the transiting giant planet CoRoT-Exo-4b and use the CoRoT light curve to perform a detailed analysis of the transit and determine the stellar rotation period. The CoRoT light curve was pre-processed to remove outliers and correct for orbital residuals and artefacts due to hot pixels on the detector. After removing stellar variability about each transit, the transit light curve was
analysed to determine the transit parameters. A discrete autocorrelation function method was used to derive the rotation period of the star from the out-of-transit light curve. We determine the periods of the planetary orbit and star’s rotation of 9.20205 ± 0.00037 and 8.87 ± 1.12 days respectively, which is consistent with this being a synchronised system. We also derive the inclination, i = 90.00+0.000
−0.085 in degrees, the ratio of the
orbital distance to the stellar radius, a/Rs = 17.36+0.05−0.25, and the planet-to-star radius ratio Rp/Rs = 0.1047+0.0041−0.0022.We discuss briefly the coincidence between the orbital period of the planet and the stellar rotation period and its possible implications for the system’s migration and star-planet interaction history
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