Secular Café: Astrobites - Stars and Planets

Secular Café Serious discussion of science, skepticism, evolution, pseudoscience, and the paranormal

Astrobites - Stars and Planets May 3rd 2012, 14:17 Courtney Dressing of Astrobites has recently blogged about some stuff related to stars and planets. Star Hoppers: Planets in Evolving Binary Star Systems | astrobites reporting on Star Hoppers and [1204.2014] Star Hoppers: Planet Instability and Capture in Evolving Binary Systems What happens to a planet when its primary becomes a red giant? The star may swallow the planet, but the star may also lose enough mass to push the planet's orbit outward. If it happens slowly enough, the orbit's eccentricity and orientation will be unaffected, but its major axis will increase in inverse proportion to the star's mass: a ~ 1/M But if the planet was orbiting one star of a binary system, it may get pushed out to the unstable region around the stars, halfway between orbiting one star and orbiting both of them. It may then run into one of the stars or enter a stable orbit around the second one. The latter case happens about 10% of the time. How to Build a Low-Density Super-Earth | astrobites reporting on [1204.5302] In-situ Accretion of Hydrogen-Rich Atmospheres on Short-Period Super-Earths: Implications for the Kepler-11 Planets It can collect hydrogen and helium from the surrounding nebula, thus giving it a super atmosphere, and thus explaining the large sizes of some of the planets observed by the Kepler spacecraft. In our Solar System, Uranus and Neptune may have done likewise. The Invisible Monster Has Two Faces | astrobites reporting on [1202.6643] The Invisible Monster Has Two Faces: Observations of Epsilon Aurigae with the Herschel Space Observatory The star Epsilon Aurigae dims from apparent magnitude +3 to +4 for about 2 years every 27.1 years. Quote: Today we know that the ε Aurigae binary star system is located 625 parsecs away and consists of a 2.2 solar mass post-asymptotic giant branch (evolved) F-star and a 5.9 solar mass main-sequence B dwarf with an orbital period of 27.1 years. The B dwarf is surrounded by a large dust disk, but astronomers are still working to constrain the disk properties. As the two stars orbit each other, astronomers on Earth are able to observe different regions of the dust disk surrounding the B dwarf. When the B dwarf passes in front of the F star during primary eclipse, astronomers are able to study the cool back side of the dust disk on the side of the B dwarf opposite the F star. Astronomers can study the warmer front side of the dust disk by observing the system at opposition when the B dwarf lies on the far side of the F star. Signposts of Planet Formation & Destruction | astrobites reporting on [1201.3622] Debris disks as signposts of terrestrial planet formation. II Dependence of exoplanet architectures on giant planet and disk properties and [1104.0007] Debris disks as signposts of terrestrial planet formation Or, Giant Planets vs. All the Others. Sean Raymond et al. did a lot of planetary-formation number crunching, and they showed that giant planets can give each other big eccentricities, and can even eject some of them. When they do that, they can clear out many or all of the smaller planets and much or all of the debris disks. So the authors propose that debris disks without giant planets are good places to look for Earthlike planets. This sort of orbital instability can explain why some exoplanets are observed to have very high eccentricities, sometimes close to 1. It may also explain the high eccentricities of the orbits of some binary stars. For planets, I've found the Exoplanet Orbit Database | Exoplanet Data Explorer. The champion eccentricity so far is about 0.93, for HD 80606 b and HD 20782 b. Both planets orbit stars that are much like the Sun, and scaling from 298 K at 1 AU, Planet Min M Per Min d Avg d Max d Max T Avg T Min T HD 80606 b 4 MJup 110 d 0.03 AU 0.45 AU 0.87 AU 710 K 360 K 310 K HD 20782 b 2 MJup 590 d 0.10 AU 1.36 AU 2.62 AU 540 K 280 K 230 K

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