SDSS-IV: Iron-Rich Stars Host Shorter-Period Planets

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SDSS-IV: Iron-Rich Stars Host Shorter-Period Planets

Postby bystander » Fri Jan 12, 2018 6:22 pm

The Long and Short of of It: Iron-Rich Stars Host Shorter-Period Planets
Sloan Digital Sky Survey | 2018 Jan 09

Astronomers with the Sloan Digital Sky Survey (SDSS) have learned that the chemical composition of a star can exert unexpected influence on its planetary system — a discovery made possible by an ongoing SDSS survey of stars seen by NASA’s Kepler spacecraft, and one that promises to expand our understanding of how extrasolar planets form and evolve.


The team presented their results today at the American Astronomical Society (AAS) meeting in National Harbor, Maryland. Using SDSS data, they found that stars with higher concentrations of iron tend to host planets that orbit quite close to their host star — often with orbital periods of less than about eight days — while stars with less iron tend to host planets with longer periods that are more distant from their host star. Further investigation of this effect may help us understand the full variety of extrasolar planetary systems in our Galaxy, and shed light on why planets are found where they are.

The story of planets around Sun-like stars began in 1995, when a team of astronomers discovered a single planet orbiting a Sun-like star 50 light years from Earth. The pace of discovery accelerated in 2009, when NASA launched the Kepler spacecraft, a space telescope designed to look for extrasolar planets. During its four-year primary mission, Kepler monitored thousands of stars at a time, watching for the tiny dimming of starlight that indicates a planet passing in front its host star. And because Kepler looked at the same stars for years, it saw their planets over and over again, and was thus able to measure the time the planet takes to orbit its star. This information reveals the distance to from star to planet, with closer planets orbiting faster than farther ones. Thanks to Kepler’s tireless monitoring, the number of exoplanets with known orbital periods increased dramatically, from about 400 in 2009 to more than 3,000 today.

Although Kepler was perfectly designed to spot extrasolar planets, it was not designed to learn about the chemical compositions of the stars around which those planets orbit. That knowledge comes from the SDSS’s Apache Point Observatory Galactic Evolution Experiment (APOGEE), which has studied hundreds of thousands of stars all over the Milky Way Galaxy. APOGEE works by collecting a spectrum for each star — a measurement of how much light the star gives off at different wavelengths (colors) of light. Because atoms of each chemical element interact with light in their own characteristic way, a spectrum allows astronomers to determine not only which elements a star contains, but also how much — for all elements including the key element iron. ...

Elemental Abundances of Kepler Objects of Interest in APOGEE. I. Two Distinct
Orbital Period Regimes Inferred from Host Star Iron Abundances
- Robert F. Wilson et al
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Re: SDSS-IV: Iron-Rich Stars Host Shorter-Period Planets

Postby BDanielMayfield » Sat Jan 13, 2018 2:01 pm

This study reports that only 25% more iron content than our Sun makes tight orbit (hot) planets much more common. Therefore this is yet another constraint on habitability.

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