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dscn0495bDr. Jonathan Crass and PhD student Andrew Bechter install the enclosure of the iLocater demonstration system in the lab at Notre Dame.

Introduction

Each time a new star is born, so too are its planets. The points of light that we see in the constellations of the night sky each represent a distinct location, a specific address in the galaxy, where orbiting planets perform a rhythmic dance around their parent stars. Thanks to incredible recent discoveries from NASA's Kepler space mission, we now know the statistics of exoplanets. Other solar systems are common, and rocky worlds resembling the Earth may be innumerable.  

The Milky Way is teeming with terrestrial planets having conditions that might be conducive to the emergence of life. Which of the stars nearest to Earth are host to planets with temperate climates? What are their physical properties? Do they have an atmosphere with compositions that we might recognize?

At the University of Notre Dame, we are building a new instrument named "iLocater" to answer these very questions.

What is iLocater?

iLocater is an ultra-precise planet-finding spectrometer that operates at infrared wavelengths. It will be the world's first diffraction-limited Doppler radial velocity instrument. Currently being designed and built in the Department of Physics at the University of Notre Dame, we aim to install iLocater at the Large Binocular Telescope (LBT) at the same time that NASA's TESS space mission begins science operations in 2018.

iLocater was recently approved for construction by the LBT science steering committee, board, and observatory director.

Fighting to Explore our Universe

iLocater was also featured as part of the Notre Dame What Would You Fight For? series. The above video aired on NBC during halftime of the Sept. 6, 2014 Notre Dame vs. Michigan football game.

The following animation, courtesy of the European Southern Observatory (ESO) / L. Calçada, shows how spectrographs are used to identify exoplanets:

radial_velocity_method

The orbiting planet's gravitational pull causes its parent star to "wobble," i.e. change its radial velocity in a periodic fashion. This movement creates a tiny Doppler shift in the star's spectrum that can be detected using a spectrograph. 

Working at the Diffraction Limit

iLocater will receive a well-corrected beam of starlight from the LBT Interferometer (LBTI). With input images that achieve ~30 times higher spatial resolution than “seeing-limited” designs (i.e., all radial velocity predecessors), iLocater will simultaneously enable high spectral resolution (R=150,000), high throughput, and a compact optical design at low cost. Compared to present-day Doppler instruments, a diffraction-limited spectrometer will:

kepler186f_artistconcept_800x480Image credit: NASA Ames/SETI Institute/JPL-Caltech

  • be significantly easier to stabilize (temperature, pressure), thus leading to higher radial velocity precision;
  • receive three orders of magnitude less background contamination from sky-emission and the moon;
  • employ a single-mode optical fiber to eliminate modal noise, which is known to induce spurious Doppler shifts;
  • and reduce astrophysical jitter arising from spots that rotate with the surface of stars.

Further, iLocater will have the unique ability to monitor and ameliorate internal systematic errors by using two separate telescope dishes simultaneously, enabling the first RV measurement precisions well below 1 m/s at near-infrared wavelengths.

modal_noise_elimination1

Lab demonstration of the elimination of modal noise using a single-mode fiber (left). Multimode fibers (right) alter the illumination pattern of light as it enters the spectrograph limiting the precision of stellar velocity measurements. All existing spectrometers use multimode fibers; iLocater will become the first to circumvent this noise source.

Contact: PI Justin R. Crepp