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Na¯ Kilo Ho¯Ku¯ R a the ONES WHO LOOK to the STARS University of Hawai‘I Sity of H Imaging Other Worlds: NICI Planet-Finding Campaign by Michael C FOR A E ST T R U O No. 35 • 2010 T I N T O O S M M A Newsletter from the N N I I Y Y Institute for Astronomy U ‘ i n i i a ve w Na¯ Kilo Ho¯ku¯ University of Hawai‘i rsit f Ha THE ONES WHO LOOK TO THE STARS y o Imaging Other Worlds: NICI Planet-Finding Campaign by Michael C. Liu One of the most exciting developments in astronomy has been the discovery and characterization of exoplanets—planets orbiting stars other than our Sun. Our understanding of these objects has advanced by leaps and bounds over the past 15 years, since the discovery of the first exoplanet around the Sun-like star 51 Pegasi in 1995. We now are entering a rich and special time for such studies. The current exoplanet census now exceeds 400 objects, most of them with masses comparable to the gas-giant planet Jupiter, which has a mass of one-thousandth that of the Sun, or 300 times that of Earth. Most exoplanets have been identified by the very subtle gravitational tug they exert on their host stars. While these discoveries have been groundbreaking, such planets are studied only indirectly. Other planets have been found as they transit across the face of their host stars, thereby diminishing the amount of light we detect from them. Such planets can be studied in great detail, but they orbit very close to their stars, making them unlike any Gemini NICI Planet-Finding Campaign planets in our solar system. NICI image of a young star near Earth with a candidate The next major advance is direct imaging, that is, low-mass companion. The bright star in the center of the taking actual digital images of planets around other image is heavily dimmed by a barely transparent stars. Directly detecting light from exoplanets opens What’s Inside circular mask. The companion is at the 4 o'clock the door to a host of new information about their position. It would be undetectable by ordinary imagers, properties (temperature, composition, etc.) and their Humboldt Awards pg 3 but is easily detected by NICI. formation. Direct detection is Please see NICI, pg 2 Ma¯noa Open House & Hilo AstroDay pg 4 Planet Detected in Habitable Zone of Nearby Star Galaxy Collisions Create by Louise Good Large Black Holes, Quasars Sun’s Constant Size pg 6 A team led by IfA astronomer Nader Haghighipour has one gets for Earth for the same kind of calculation. discovered a planet with about the same mass as However, if the planet’s atmosphere holds in heat When, How Did Earth Saturn in the habitable zone of a star 36 light-years sufficiently, then the surface temperature will Become Friendly to Life? from Earth. Its detection is important because it certainly be warmer than minus 42 degrees. “indicates that observational techniques are on the Upcoming Events pg 7 The planet (HIP 57050b) circles its central star (HIP right track for finding habitable low-mass rocky 57050) every 41 days. The star, which is classified as From the Director pg 8 planets similar to Earth,” according to Haghighipour. an M dwarf, has a radius approximately 0.4 times that A planet is considered to be in the habitable zone if of the Sun, and has a mass about one-third of the its temperature is just right for having liquid water. Sun’s. “Because HIP 57050b is a giant planet, it is The approximate surface temperature of the above- unlikely that it is habitable,” Haghighipour notes. mentioned newly discovered planet is about minus 42 In the quest for potentially habitable planets, the degrees F, which was calculated by considering the nearest stars are of special importance. We know their surface temperature of the star, the planet’s size, the precise distances, as well as their masses, sizes, and The University of Hawai‘i proportion of the star’s light that the planet may temperatures, and they are the only stars for which is an Equal Opportunity/ reflect, and the time that it spends in close proximity follow-up by Please see Planet Detected, pg 2 Affirmative Action Institution. to the star. This temperature is colder than the value for the blurring of astronomical images caused by NICI from pg 1 Earth’s turbulent atmosphere. incredibly challenging. We see the planets in our own Since December 2008, we have been using NICI to solar system because they reflect light from the Sun. obtain very sensitive images of 300 nearby young Imaging the reflected light of exoplanets is currently stars (within about 200 light-years) to search for impossible because the light reflected by the planets gas-giant planets in emitted light. The campaign will take about three years and obtain a total of 50 nights is swamped by the glare of their host stars, which are of observations. This makes it the largest single about a billion times brighter. However, when gas- program ever carried out at the Gemini telescopes. By giant planets are young, they also emit their own light having a major campaign, it is possible to assemble a at infrared wavelengths, by releasing the heat stored large-scale coherent science program with a unified in their interiors at the time of formation. This makes set of goals, observing methods, and data analysis young planets much easier to detect, since they are techniques. While the observations are carried out in only(!) about one million times fainter than their Chile, the planning and analysis are done here at the parent star. In 2008, astronomers took the first direct IfA, with postdoctoral fellow Zahed Wahhaj and images of young gas-giant exoplanets, thereby opening Hubble Fellow Beth Biller being key contributors. the door to this new way of learning about them. The campaign is about halfway finished. We have My research group is leading an international effort imaged about 180 stars so far, already making NICI known as the Gemini NICI Planet-Finding Campaign the largest direct imaging search to date. However, in to expand the census of exoplanets detected by direct some sense, we are just getting started. Many of the imaging. NICI (the Near-Infrared Coronagraphic stars we have imaged have very faint companions Imager) is a powerful new instrument installed on the next to them, but we do not yet know what these are. Gemini South 8.1-meter telescope in Chile, the twin They could be gas-giant planets in orbit around these stars, or they could be ordinary background stars that of the Gemini North telescope on Mauna Kea. Most are much farther away but by chance are projected on astronomical instruments can do multiple kinds of the sky nearby. The way to check is to make a second observations, but NICI was designed to do only one set of observations about one year later to see if the thing very well, namely, image exoplanets directly. faint candidates move with the target star, thereby NICI was built by Doug Toomey of Mauna Kea proving that they are gravitationally bound together. Infrared in Hilo, with heavy involvement by IfA We are in the process of doing that right now. Once faculty members Christ Ftaclas and Mark Chun, and candidates are confirmed, we can learn a great deal funding from NASA. NICI is designed as a complete about the properties of young planets through end-to-end system for exoplanet imaging. It is based dedicated follow-up observations to measure their on an advanced adaptive optics system that corrects brightnesses, colors, atmospheres, and orbits. Planet Detected from pg 1 astrometry and direct imaging is possible. While the majority of the currently known extrasolar planets have been detected around larger nearby stars, more than 70 percent of the nearest stars are M dwarfs. As such, these stars have the special properties (distances and masses) that drive exoplanetary science, astrobiol- ogy, and the next generation of interferometry and direct imaging missions. The low surface temperatures of M dwarfs place their habitable zones at distances that are approxi- mately 10 to 20 percent of Earth’s distance from the Sun. These distances correspond to orbital periods of 20–50 days, another advantage of M dwarfs as poten- tial targets for detecting habitable planets—because of their small masses, these stars respond more notice- ably to the gravitational forces of close-in planets. Haghighipour adds that it is interesting to specu- late about the possible presence of a moon around HIP 57050b. While it is not out of the question that HIP 57050b could harbor a moon, and that moon would thus be in the habitable zone of the parent star, an object with only one-fifth the mass of Mars is probably not a particularly good prospect for habitabil- ity from various standpoints. Furthermore, direct Orbit of the planet HIP 57050b superimposed on our solar system. The orbits are to scale, but the detection of such a moon would be extremely challenging. 2 size of the Sun and the planets are not. The star HIP 57050 is much smaller than our Sun. IfA Astronomers Win 2010 Humboldt Awards Two IfA astronomers are the recipients of senior research awards from the Alexander von Humboldt Foundation in Germany. These research awards are intended to recognize the lifelong academic achievements of the awardees, are granted on the basis of nominations by eminent German scholars, and enable awardees to come to Germany to work on a research project with a German host. IfA Director Rolf-Peter Kudritzki, who will relin- quish the IfA directorship at the end of 2010, plans to use his Humboldt award during a 2011 sabbatical in Germany to investigate the physics of galaxies.
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