Title: Planet Searching at the Gemini Observatory
Podcaster: Main narration by Joy Pollard, with voice overs by Julian Cristou, Christian Marois, and Michael Liu
Organization: Gemini Observatory www.gemini.edu
Description: The Gemini Observatory consists of twin 8-meter optical/infrared telescopes built and operated by a consortium consisting of the United States, United Kingdom, Canada, Chile, Brazil, Argentina, and Australia. Scientists from around the world utilize the twin telescopes to explore the universe from both hemispheres of our planet.
Bio: Julian Cristou is the Adaptive Optics Scientist for Gemini he is located in Hilo, Hawai‘i.
Christian Marois is an astronomer at the Herzberg Institute of Astrophysics in Victoria Canada working in the field of exoplanets.
Michael Liu is an astronomer at the Institute for Astronomy at the University of Hawai‘i.
Today’s sponsor: This episode of “365 Days of Astronomy” is sponsored by the Physics Department at Eastern Illinois University: “Caring faculty guiding students through teaching and research” at www.eiu.edu/~physics/.
Welcome to the Gemini Observatory special podcast series, sharing our discoveries and the wonders of our Universe. This edition will feature astronomers who use Gemini to search for planets around other stars…
The search for worlds orbiting other stars has long been a mainstay of science fiction. Now, it is in the realm of science fact.
Directly imaging planet-sized worlds around other stars is a key scientific goal of our twin 8-meter telescopes at the Gemini Observatory — located in Hawaii and Chile. The instruments needed to show images of these “exoplanets” are advancing rapidly and the sophisticated techniques we now use are relatively new.
Until recently, evidence for planets around other stars has been limited to an indirect technique called radial velocity spectroscopy. This technique has revealed more than 300 planets around other stars over the past few decades.
Now, with high-resolution imaging at Gemini, and other observatories, we are able to directly image planets around other stars. According to Gemini scientist Julian Christou, “Gemini is using the NICI instrument, the Near Infrared Chronographic Imager, and, it is designed to reduce the amount of scattered light coming from the bright component star, in order to permit detection of faint sources such as extra-solar planets or very low mass stellar companions very close in to the parent star. ”
Recently the discovery of a planetary family around the young massive star called HR 8799, was a strong demonstration of the techniques and technologies that allow these discoveries. In late 2008, Christian Marois of the National Research Council of Canada’s Herzberg Institute of Astrophysics made an amazing discover with Gemini… “The Middle of last year we used the, the Gemini North Telescope with the NRC Altair Adaptive Optics systems, and the NIRI camera, to find that the first very faint objects orbiting the star HR 8799. So after further follow-ups we were able to confirm that these three very faint dots orbiting the star are actually real planets, the lights that we seen were in the infrared or near-infrared, at around one and five microns: and just to specify as well; that these three planets orbit at very wide separation compared to the planets of our solar system; they orbit between 25 and 80 astronomical unit from the star. So they are roughly equivalent at the outer planet of our own solar system.” (quote by Christian Marois)
Prior to that, David Lafreniere, also of Canada, discovered a single strange world around a sun-like star some 500 light years from our solar system. Both of these discoveries have shown the power of direct imaging of exoplanets and have inspired others as well.
Michael Liu, of the University of Hawaii’s Institute for Astronomy, is the Principal Investigator for the Gemini Planet Finding Campaign. “The Gemini Plant Finding Campaign is a new exciting major scientific project being carried out by a team of astronomers from around the world who are part of the Gemini partnership. And what we’re doing is, we’re taking the deepest most sensitive images ever obtained to date of about 300 of the nearest, youngest, stars to Earth. And the goals of the campaign are to systematically survey these stars to directly image planets around them. And then once we find those planets, to study their properties. Measure the kind of light coming from them, try to estimate their temperatures and their masses, and look at how they are distributed; both in terms of mass and also their orbital separations from the stars. We feel this will be an exciting opportunity to understand how planets form, and also to identify some of the very nearest solar systems closest to earth which will then be followed up by future even more exciting instruments in years to come. The way we are doing this is we are using a powerful new instrument known as NICI, that’s currently at Gemini South in Chile. And NICI combines a number of new technologies that have previously been used individually but puts them all together for the first time, and allows us to make very sensitive images to identify very, very faint things: planets. As seen in their emitted light next to their bright parent stars.”
[Voice over switch, Julian Christou continues.]
“Imagine you’re looking at the sun, and then you’re trying to find an extremely faint object within the glare of the sun; it’s so close to it from our apparent perception being so far away. So we’re looking for a faint object which is probably anywhere from a few million to almost a billion times fainter in the amount of light it’s emitting, compared to the star. So that’s, in a way, the ‘moth in a searchlight’ analogy. The searchlight, which is the star, is essentially blinding us with its glare; and we are trying to reduce that glare in order to see this very small, faint, object very close to it.”
“Now in order to determine if a blob in the structure surrounding the star, is actually a planet or not, there are two different techniques which are currently used. These are known as Angular Differential Imaging, or ADI, and Spectral Differential Imaging, SDI.”
Spectral Differential Imaging, you’re taking two simultaneous images of the star in two slightly different spectral bands. What happens is that the instrumental response changes slightly, and it changes at a spatial scale. An instrumental artifact will appear to shift, or change, its radial distance from the parent star. By comparison an astronomical source will always remain at the same fixed distance from the central star. Therefore we can distinguish between an instrumental source and an astronomical source by looking to see if there’s any apparent motion of these faint blobs between the two wave lengths.
When completed, the Gemini Planet Finding Campaign will be the first survey of its kind to systematically study a large collection of stars hunting for planets. It is likely that many new worlds will be revealed and ready for even more detailed studies.
All of the direct imaging techniques rely on adaptive optics technology, which is able to cancel out most of our own planet’s atmospheric turbulence that distorts astronomers’ views of fine details – like planets around other stars.
The next generation of planet finders will allow astronomers to get even closer to the host stars and see even smaller planetary bodies. Currently nearing completion at Gemini is the Gemini Planet Imager, which will combine all of the techniques; allowing us to see physical characteristics of planets even closer to its primary star.
The science of planet hunting is at the forefront of astronomical research. As strange new worlds are revealed through future surveys, the hunt is guaranteed to get even more exciting. Scientists will study them with sensors that past generations of astronomers could only dream about using. The next generation of instruments and observatories — including the planned Thirty-Meter Telescope on Mauna Kea, and the James Webb Space Telescope — will propel us even closer to ultimately finding worlds like Earth around other stars.
“So Gemini is now approaching very exciting, new discovery space in terms of extra-solar planets. Over the next year or so, we expect NICI to be actually producing results, which should be published and which you will be able to see on our Gemini Web pages, about brighter extra-solar planets which have not been previously discovered. And then, this level of discovery will be taken to the next step beginning approximately 2010 -2011, with the GPI instrument. So, the next 3, 4, 5 years we expect to be very interesting from the extra-solar planet perspective.”
We hope you enjoyed this podcast brought to you by the Gemini Observatory. Thank you for listening. For more information, current science results, images, and other podcasts go to: www.gemini.edu.
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365 Days of Astronomy
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