The negligible eccentricity of all extrasolar planets with periods less than 6 days can be accounted for by dissipation of tidal disturbances within their envelopes that are induced by their host ...stars. In the period range of 7-21 days, planets with circular orbits coexist with planets with eccentric orbits. These are referred to as the borderline planets. We propose that this discrepancy can be attributed to the variation in spin-down rates of young stars. In particular, prior to spin-down, dissipation of a planet's tidal disturbance within the envelope of a sufficiently rapidly spinning star can excite eccentricity growth and, for a more slowly spinning star, at least reduce the eccentricity-damping rate. In contrast, tidal dissipation within the envelope of a slowly spinning low-mass mature star can enhance the eccentricity- damping process. On the basis of these results, we suggest that short-period planets around relatively young stars may have a much larger dispersion in eccentricity than those around mature stars. We also suggest that because the rate of angular momentum loss from G and K dwarfs via stellar winds is much faster than the tidal transfer of angular momentum between themselves and their very short (3-4 days) period planets, they cannot establish a dynamical configuration in which the stellar and planetary spins are approximately parallel and synchronous with the orbital frequency. In principle, however, such configurations may be established for planets (around G and K dwarfs) with orbital periods of up to several weeks. In contrast to G and K dwarfs, the angular momentum loss due to stellar winds is much weaker in F dwarfs. It is therefore possible for synchronized short-period planets to exist around such stars. The planet around Tau Boo is one such example.
The currently feasible method of detecting Earth-mass planets is transit photometry, with detection probability decreasing with a planet's distance from the star. The existence or otherwise of ...short-period terrestrial planets will tell us much about the planet-formation process, and such planets are likely to be detected first, if they exist. Tidal forces are intense for short-period planets and result in decay of the orbit on a timescale that depends on properties of the star as long as the orbit is circular. However, if an eccentric companion planet exists, orbital eccentricity (e sub(i), where i is the inner orbit) is induced, and the decay timescale depends on properties of the short-period planet, reduced by a factor of the order of 10 super(5)e super(2) sub(i) if it is terrestrial. Here we examine the influence companion planets have on the tidal and dynamical evolution of short-period planets with terrestrial structure, and we show that the relativistic potential of the star is fundamental to their survival.
We present high-precision radial velocity observations of WASP-17 throughout the transit of its close-in giant planet, using the MIKE spectrograph on the 6.5 m Magellan Telescope at Las Campanas ...Observatory. By modeling the Rossiter-McLaughlin effect, we find the sky-projected spin-orbit angle to be Delta *l = 167.4 ? 11.2 deg. This independently confirms the previous finding that WASP-17b is on a retrograde orbit, suggesting it underwent migration via a mechanism other than just the gravitational interaction between the planet and the disk. Interestingly, our result for Delta *l differs by 45 ? 13 deg from the previously announced value, and we also find that the spectroscopic transit occurs 15 ? 5 minutes earlier than expected, based on the published ephemeris. The discrepancy in the ephemeris highlights the need for contemporaneous spectroscopic and photometric transit observations whenever possible.
The DI Herculis system has been extensively studied over the past few decades because its observed rate of apsidal advance is less than a quarter of that which is expected from its physical and ...orbital properties. Work by Khaliullin et al. (1991) proposed that this slow rate of apsidal advance is a result of the presence of a third (stellar mass) body orbiting the system, however, observations by Guinan et al. (1994) severely restrict the orbital properties of such a solution. We show that a planetary mass object in a highly inclined orbit relative to the binary is capable of producing the observed apsidal motion, while remaining within the bounds of the most recent set of observations. A wide range of stable solutions are possible.
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