July 30, 2013
Pulsating Star Observations Shed New Light On Planetary Systems
April Flowers for redOrbit.com - Your Universe Online
An international team of scientists, including physicists at New York University, Princeton University and the Max Planck Institute for Solar System Research, has devised a method for measuring the internal properties of a star that offers more accurate assessments of the star's orbiting planets.
The team examined a star approximately 92 light-years away and almost 20 percent more massive than our Sun, called HD 52265. Scientists identified an exoplanet in the star's orbit over a decade ago, making HD 52265 an ideal model for both measuring stars' properties and how such properties can shed light on planetary systems.
Prior studies have inferred stars' properties -- radius, mass and age, for example -- with observations of their color and brightness. However, the properties could not be inferred with sufficient accuracy to further characterize the nearby planets. For the current study, published in a recent issue of Proceedings of the National Academy of Sciences (PNAS), the team adopted a new approach to characterize star-planet systems. They used a technique known as asteroseismology, which identifies the internal properties of stars by measuring their surface oscillations. This approach has been compared to seismologists' use of earthquake oscillations to examine the earth's interior.
This technique allowed the team to make several assessments of the star's traits. These included the mass, radius, age and -- for the first time -- internal rotation. To detect tiny fluctuations in the intensity of starlight caused by starquakes, the scientists employed the COROT space telescope, part of a space mission led by the French Space Agency (CNES) in conjunction with the European Space Agency (ESA). The validity of these seismic results was confirmed by comparing them with independent measurements of related phenomena, including the motion of dark spots on the star's surface and the star's spectroscopic rotational velocity.
Asteroseismology, unlike other methods currently in use, returns both the rotation period of the star and the inclination of the rotation axis to the line of sight.
These findings could then be used to make a more definitive determination of an orbiting exoplanet. HD 52265 had previously been identified as an exoplanet by other scientists. However, some researchers suggested it could actually be a brown dwarf -- an object too small to be a star and too large to be a planet.
The precise calculations yielded by asteroseismology, however, allowed the current team to enhance the certainty of the earlier conclusion. Specifically, the researchers could infer the true mass of the latter -- which was calculated to be roughly twice that of our planet Jupiter and therefore too small to be a brown dwarf -- given the inclination of the rotation axis of HD 52265 and the minimum mass of the nearby exoplanet.