[LINK] On using stellar spectra to find planets

[rfmcdonald]

Forbes' Bruce Dorminey describes an interesting new technique that may give astronomers a hint as to whether stars support planetary systems.

Ivan Ramirez, an astronomer at the University of Texas at Austin and colleagues [. . .] are testing a ground-based terrestrial planet-hunting shortcut. Using the Magellan Clay Telescope in Chile, the team has taken high-resolution stellar spectra from 88 solar twins that lie within 326 light years of Earth. The hope is that they can prove their hypothesis that these spectra contain signatures of depleted metals caused by the presence of unseen rocky planets in orbit around the parent star. In fact, Ramirez says the team has even found the signature of rocky planets in chemical spectra from the nearby star “Alpha Centauri A.”

In a forthcoming paper in Astronomy & Astrophysics, lead author Ramirez and colleagues note that their idea is that they would actually see less metals in a star that has planets. Ramirez points out that our own Sun also has a slightly lower presence of key “metals” necessary for terrestrial planet formation; which Ramirez ascribes to a depletion of elements that “like to stick together to form rocks.”

“That’s how this work started,” said Ramirez. “We saw this effect first in the Sun and we are extending it to these solar twin stars. Our idea is that these missing rocky elements are in the planets.”

Today, says Ramirez, it’s only possible to measure chemical composition with that kind of precision for stellar solar twins that are roughly the same age, mass and chemical makeup of our sun.

“So, instead of calculating how many atoms of titanium are in the target star,” said Ramirez, “we only care about how much more or less there is compared to the Sun. We look for a depletion of rocky elements relative to non-rocky elements.”

[. . .]

“Elements that cover a range of the ‘condensation sequence’,” said Ramirez, who explains that’s the temperature at which such elements change their “phase” from “gas to rock.” For example, Ramirez says our own Sun is depleted in specific elements that indicate that we have a planetary system; such as barium, aluminum, iron, magnesium, titanium, chromium, silicon, and yttrium.