* Astronomy

Title: A HET search for planets around evolved stars
Authors: Andrzej Niedzielski, Alex Wolszczan

 We present our ongoing survey of ~1000 GK-giants with the 9.2-m Hobby-Eberly Telescope in search for planets around evolved stars. The stars selected for this survey are brighter than 11 mag and are located in the section of the HR-diagram, which is approximately delimited by the main sequence, the instability strip, and the coronal dividing line. We use the High Resolution Spectrograph to obtain stellar spectra for radial velocity measurements with a 4-6 m/s precision. So far, the survey has discovered a planetary-mass companion to the K0-giant HD 17092, and it has produced a number of plausible planet candidates around other stars. Together with other similar efforts, our program provides information on planet formation around intermediate mass main sequence-progenitors and it will create the experimental basis with which to study dynamics of planetary systems around evolving stars.

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Rocky extrasolar planets thought to be half frozen and half scorched might instead rock back and forth, creating large swaths of twilight with temperatures suitable for life.
Because of gravitational tugs with the objects they orbit, rocky bodies often settle into trajectories in which they always show the same face to their hosts. Such 'tidally locked' exoplanets would thus seem like bad candidates for life, since the hemisphere facing their host stars would roast and the dark side would freeze.
But a new computer model by Anthony Dobrovolskis of NASA Ames Research Center in California, US, suggests this is not always so. He finds that such planets can rock to and fro if they travel on elongated, or eccentric orbits, creating a 'twilight zone' that could be hospitable to life.
The Moon experiences a similar rocking motion. It always shows the same face to Earth, taking the same amount of time to rotate around its axis as it does to circle our planet once. However, because the Moon's path around the Earth is not perfectly circular, its orbital speed is sometimes faster or slower than its rotational speed. The difference between the two motions causes the Moon to rock slightly.

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Title: Tidal friction in close-in satellites and exoplanets. The Darwin theory re-visited
Authors: Sylvio Ferraz-Mello (1), Adrián Rodríguez (1), Hauke Hussmann (2) ((1) Instituto de Astronomia Geofísica e Ciências Atmosféricas. Universidade de São Paulo, Brasil, (2) Institut für Planetenforschung, DLR, Berlin-Adlershof, Germany)

This report is a review of Darwin's classical theory of bodily tides in which are given the analytical expressions for the orbital and rotational evolution of the bodies and for the energy dissipation rates due to their tidal interaction. It is shown that almost all results found in the literature for the study of evolution due to tidal friction can be straightforwardly derived from Darwin's theory. General formulas are given which do not depend on any assumption linking the tidal lags to the frequencies of the corresponding tidal waves (except that equal frequency harmonics are assumed to span equal lags). The general formulas are applied to several physical scenarios including both fast and slow rotating central bodies as well as their companions. Emphasis is given on the case of companions having reached one of the two possible final states: capture into a 1:1 spin-orbit resonance (synchronisation) or the super-synchronous stationary rotation resulting from the vanishing of the average tidal torque. The true synchronisation with non-zero eccentricity is only possible if an extra torque exists opposite to the tidal torque. The theory is developed assuming that this additional torque is produced by an equatorial permanent asymmetry in the companion. The indirect tidal effects and some non-tidal effects due to that asymmetry are considered. The theory is developed only to the second degree in eccentricity and inclination (obliquity), but can easily be extended to higher orders.

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Gas giant planets can get twice as close to their stars as Mercury is to the Sun without evaporating, a new computer simulation suggests. The work suggests the 'hot Jupiters' discovered on tight orbits around their stars are in no immediate danger of boiling away into space.
Many gas giants have been found very close to their parent stars a handful even lie less than 6% of Mercury's distance from the Sun. But it has never been clear just how close planets could get without heating up so much that their atmospheres would start escaping or "evaporating" into space.
A new study suggests this threshold lies more than twice as close as Mercury's distance to the Sun (or about 0.15 astronomical units, where 1 AU is the distance between the Earth and the Sun). Tommi Koskinen of University College London, UK, led the team that carried out the study.
The outermost layer of a planet's atmosphere is where the action is as far as evaporation is concerned. The star blasts this layer with ultraviolet light and X-rays, which heat it up. The atmosphere can stay cool and avoid evaporating if it can radiate enough energy back into space in the form of infrared light.
To see how the balance between these two effects shifted with distance from the star, Koskinen's team created a 3D computer simulation of the upper atmosphere of a planet with the mass of Jupiter orbiting a Sun-like star. They found that evaporation did not occur until the planet was within about 40% of Mercury's distance from the Sun about twice as close as a previous estimate.

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