Collaboration Sharpens Planet-Finding Technology

November 13, 2009

Exoplanets, which are planets orbiting stars outside of our solar system, have been the subject of scientific investigation since the mid-nineteenth century. However, confirmation of their existence did not occur until the early 1990s when improved technology could provide adequate evidence for longstanding scientific speculation. Since then, more than 350 exoplanets have been detected. Subaru astronomer Olivier Guyon asserts, "As astronomers sharpen their planet-finding tools in the next few years, we can expect the number of known exoplanets to grow exponentially."

The development and adoption of scientific tools is not just a matter of technological expertise; it is also a process of cooperation among colleagues. Collaboration fosters the development of planet-finding technology, enabling a wider range of scientists to participate in this exciting frontier of astronomical research. Subaru Telescope has been involved in a variety of activities that demonstrate the fruits of pooling material and intellectual resources to identify exoplanets.

Subaru organized an international conference entitled "Exoplanets and Disks: Their Formation and Diversity", which took place in Kona, Hawaii from March 9-12, 2009. Conferences such as this provide an opportunity for astronomers to share their knowledge and creative ideas in presentations, workshops, and informal gatherings. They are one way to spark and finalize collaborations that advance the field.

During this conference, astronomers T. Usuda, S. Egner and Y. Hayano accompanied scientists M. Goto (Max Planck Institute of Astronomy, Germany) and A. Seifahrt (University of Goettingen, Germany / University of California Davis), to Mauna Kea's summit to check out their ideas for installing an IR-gas cell on the Subaru Telescope. They were able to view the telescope first-hand before the manufacture of the cell and determine the best location for its placement-inside the adaptive optics system.

Working together is a win/win for the collaborators. Subaru benefits from the U. of Goettingens's previous experience in manufacturing a similar gas cell for CRIRES (cryogenic high-resolution pre-dispersed infrared echelle spectrograph), a spectrograph at the Very Large Telescope in Chile; it can rely on its expertise to fabricate, test, and deliver a high quality cell. The U. of Goettingen enhances its reputation for international cooperation and development of a cell that will be part of exoplanet exploration from some of the world's largest optical-infrared telescopes. In addition, the collaboration is cost-effective; designation of roles and responsibilities makes the best use of time and resources, and building on past manufacturing expertise minimizes duplication of effort.

The collaboration that has yielded this relatively small addition to the Subaru Telescope will result in big advantages to planet-searchers. Here's why. The new IR(infrared)-gas cell will enable radial velocity measurements in the infrared (below visible light) and provide data about possible planets that could not be detected with present optical measurements.

Most exoplanets have been detected by radial velocity and other indirect measures rather than by direct imaging. Because planets are extremely faint light sources compared to their parent stars, the brightness of the parent star blots out light from the planet, making it difficult to detect. Subaru astronomer Dr. Olivier Guyon is leading an effort to develop an optical device that can remove starlight and retain planetary light so that exoplanets can be more directly observed. However, the development of this specialized coronagraph is a complex process that will not be complete for years. In the meantime, radial velocity measures will continue to occupy center stage in the search for exoplanets.

As a planet orbits a star, its gravitational pull creates a small, periodic movement of the star. Radial velocity is the speed with which the star moves towards or away from Earth, and measurements of changes in radial velocity are indirect indicators of a planet's presence. Like other telescopes, Subaru has measured RV (radial velocity) in optical wavelengths. However, optical RV observations are most sensitive to planets that are massive or have small orbits. Measurements with the new infrared gas cell will expand the range of objects that it can detect, especially low mass stars, which are faint in optical wavelengths. Since it appears that very low-mass planets are easier to find around low-mass stars, installation of Subaru's new infrared gas cell will provide observers with an excellent tool for increasing their chances of finding exoplanets. After the cell is tested, Subaru will make it available for open use by scientists in 2010.

As this example shows, collaboration transformed an idea for adding better tools for observations with the telescope into a workable plan that was implemented to produce a device from which the international astronomical community will benefit. The IR-gas cell has been manufactured and has been shipped to Subaru. Surely its use will lead to the discovery of more exoplanets and will contribute to laying the foundation for discoveries of planets around low-mass stars, which are most likely to support life.

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