Astrophysicist determines occurrence rate of giant planets around M-dwarfs

Jul 26, 2013

A study led by Notre Dame astrophysicist Justin Crepp has for the first time definitively determined how many of the lowest-mass stars in the galaxy host gas giant planets. The researchers' paper, "The Occurrence Rate of Giant Planets around M-dwarfs," was posted to arXiv this week and submitted for publication in the Astrophysical Journal.

The group used ground-based imaging observations in combination with the Doppler radial velocity method to determine that 6.5 percent of low-mass , the so-called "M-dwarfs," have planets located within 20 astronomical units, including the outer regions where researchers previously could not access.

"We have invented a new technique that allows us to peer beyond the orbits normally accessible to previous observations, thus taking a much-needed shortcut to the answer," Crepp said. "Our results show that low-mass stars form few planets similar to Jupiter, most likely because compared to Sun-like stars, low-mass stars have less material—circumstellar building blocks, if you will—to start with." Crepp, principal investigator for the NASA-funded high-contrast imaging program, co-authored the paper with Benjamin Montet, a graduate student at Caltech whom he co-advises, John Asher Johnson, Andrew W. Howard and Geoffrey W. Marcy.

Since the first extrasolar planet was discovered in 1995, researchers have identified planets located within 4 astronomical units of stars by carefully monitoring the gravitational "wobble" induced upon the star as the planet orbits. That movement typically creates a measurable periodic signal. In cases where the observations reveal a straight line, or systematic "trend," researchers suspect they are mapping only a fraction of the signal created by a more distant object with a much longer . Montet and Crepp obtained images to identify such planets using a sample of 111 M-stars. The results are consistent with the rates found by another technique, called , which detects orbiting planets when they pass between Earth and a background star. Such events are rare and not repeated, making follow-up observations challenging.

Three-fourths of all stars are M-dwarfs. The group plans to conduct a similar survey of stars at the next mass-level, the "K-dwarfs," just one below that of the Sun, in order to continue a methodical investigation that quantifies the occurrence rate of gas giant worlds around different types of stars. While the study showed that 1 in 16 of the lowest-mass stars have gas giants, Crepp expects to find more around more-massive targets. "We expect that number to increase," he said. "We think that bigger stars have a propensity to form more massive planets."

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More information: arxiv.org/abs/1307.5849

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User comments : 4

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philw1776
2.3 / 5 (3) Jul 27, 2013
Eagerly await the more habitat friendly K star data. I wonder if their technique yields a distance mass histogram for the M stars.
nkalanaga
not rated yet Jul 28, 2013
I don't know if they could. It's possible that all microlensing, like direct observation, would give is the observed separation, not the actual orbital distance. A distant planet, behind or in front of the star, would appear to be close to the star, throwing the distance/mass relationship off.

Looking at the paper itself, I didn't see (in a quick scan) anything that looked like such a table.
philw1776
1 / 5 (2) Jul 29, 2013
"The group used ground-based imaging observations in combination with the Doppler radial velocity method"

This group wasn't using microlensing
nkalanaga
not rated yet Jul 29, 2013
philw1776: Thank you. I read the abstract of their paper, where microlensing is discussed, and assumed they used it along with RV and imaging. Reading the entire paper it's clear that they didn't. But imaging has the same limitation, so the objection still stands, and they didn't include the data you wanted, if they have it.

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