This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).
There are at least four ways to detect a planet orbiting a star. By far the most successful means to date has been to very carefully monitor the velocity of the star. If the velocity tends to vary regularly about its average value, then it is possible that we are measuring the reflex velocity of the star as a planet moves around it in its orbit. This is a very exacting measurement to make and it relies on extremely accurate velocity measurements made with a spectrograph. Current technology has resulted in over 300 planet detections, but none of these is likely to support life; most of them are gas giants like Jupiter. To reach smaller earth-like planets it is necessary to increase the precision of the measurements. Dr. Andrew Szentgyorgyi of the Smithsonian Astrophysical Observatory is designing a very stable and accurate calibration mechanism to improve these radial velocity measurements. Dr. Szentgyorgyi's wavelength calibration scheme uses a very rapidly pulsed laser to imprint a regularly spaced calibration "comb" of lines of precisely known wavelengths onto the spectrum of the star. This new technique is expected to improve the velocity determination from the current standard enough to detect earth-like planets in the habitable zone. Funding for this work is being provided by NSF's Major Research Instrumentation program through the Division of Astronomical Sciences.
In this project we developed and tested a very-high-resolution Fourier Transform Spectrograph based on a scanning Michelson interferometer. We then used the Fourier Transform Spectrograph for detailed characterization of a new type of laser-based device intended for precise calibration of the spectral analysis capability of astronomical telescopes and spectrographs used for searches for planets around other stars ("exoplanets"). We refer to this laser calibration device as an "astro-comb," as it employs a laser frequency comb referenced to atomic clocks. We designed and fabricated the Fourier Transform Spectrograph to have the following properties: (i) a broad spectral bandwidth suitable for application to astro-comb characterization; (ii) ability to resolve individual astro-comb spectral lines; and (iii) sufficient sensitivity to detect all astro-comb spectral lines. Our measurements using the Fourier Transform Spectrograph allowed optimization of the visible wavelength astro-comb we had developed in parallel. This astro-comb was then successfully relocated for operation at the TNG telescope. As a broader impact, techniques and tools developed in this project, such as novel laser sources, broadband mirrors, and pulse characterization techniques, were transitioned to other research activities including frequency metrology and attosecond science. The laser characterization technology developed in this program thus contributes to the infrastructure for other research and education projects. Students and postdoctoral researchers were active participants in all phases of this research: design, construction, and execution of experiments; detailed calculations; analysis of data; presentation of results at scientific meetings; and writing scientific papers. In addition, the investigators on this NSF-supported project described the scientific process and results in a wide variety of presentations ranging from scientific conferences and seminars to public lectures.
