The NICI Planet-Finding Campaign

The Planet-Finding Campaign Team

From the Gemini Telescope's website:

"The NICI Campaign Science Team was selected January 2006.The Gemini Director, with input from the ITAC and a panel of independent experts, has chosen an international team led by Dr. Michael Liu of the Institute for Astronomy at the University of Hawaii to conduct a major campaign to directly image planets around nearby stars using NICI. The team includes members of the instrument team building NICI and a number of other collaborators from across the Gemini partnership. The NICI Campaign will be carried out over two to three years using 500 hours of observing time. With strong observational, technical, and theoretical expertise, Gemini expects that the NICI Campaign will significantly advance our understanding of the properties and frequencies of extrasolar planets using this exciting new instrument. "

The planet-finding campaign team includes the following individuals from international institutions:

Michael C. Liu, Zahed Wahhaj, Beth A. Biller, Eric L. Nielsen, Mark Chun, Laird M. Close, Christ Ftaclas, Markus Hartung, Thomas L. Hayward, Fraser Clarke, I. Neill Reid, Evgenya L. Shkolnik, Matthias Tecza, Niranjan Thatte, Silvia Alencar, Pawel Artymowicz, Alan Boss, Adam Burrows, Elisabethe de Gouveia Dal Pino, Jane Gregorio-Hetem, ShigeruIda, Marc J. Kuchner, Douglas Lin, Douglas Toomey

Introduction to the Campaign


NICI at the base of the Gemini South telescope. Image Source: Gemini Website
A science team, including UH's Mike Liu, Beth Biller, Zahed Wahaj, is carrying out a multi-year observing program to directly image and characterize young extrasolar planets using the Near-Infrared Coronagraphic Imager (NICI) on the Gemini-South 8.1-meter telescope. NICI is the first instrument on a large telescope designed from the outset for high-contrast imaging, comprising a high-performance curvature adaptive optics (AO) system with a simultaneous dual-channel coronagraphic imager. Combined with state-of-the-art AO observing methods and data processing, NICI typically achieves ≈ 2 magnitudes better contrast compared to previous ground-based or space-based planet-finding efforts, at separations inside of ≈ 2 ′′. As of the middle of 2010, the Planet-Finding Campaign is in its second year, with first-epoch imaging of 174 stars already obtained out of a total sample of 300 stars.

Planet-Finding Techniques and Approaches

Instrumentation

NICI combines a suite of capabilities to achieve high contrast imaging in one single intrument:

  1. an efficient natural guide star curvature AO system
  2. spectral differential imaging (SDI) mode
  3. angular differential imaging (ADI) mode
  4. Lyot-style coronograph

Read more about NICI's instrumentation on our NICI Instrument page.

Methane at 1.6 µm

Evolutionary models of young objects with ages less than 100 Myr and masses less than about 12 Jupiter masses predict the presence of methane in their atmospheres. This results in a signature absorption feature at the near-IR wavelengths at 1.6 µm. Comparing images inside and just blueward of this wavelength band will produce a unique photometric signature, strong emission in the blue band and little emission in the red one, that can be distinguished from the bright (methane-free) glare of the parent star.

H-band on- and off-methane filters were custom designed for the campaign to maximize imaging performance. The resulting filters are 4% wide, with central wavelengths of 1.578 µm (off-methane) and 1.652 µm (on-methane).


This set of images simulates the detection of a companion to a star. An artificial methane-bearing companion has been inserted next to a bright star. The companion appears fainter in the image to the right due to photospheric methane absorption. Image Source: The Gemini NICI Planet-Finding Campaign

Spectral Differential Imaging (SDI) and Angular Differential Imaging (ADI)

Both Spectral Differential Imaging (SDI) and Angular Differential Imaging (ADI) techniques seek to separate real objects from speckles. SDI achieves this by exploiting a spectral feature in the desired target (the 1.6 µm methane absorption feature). Images are taken simultaneously both within and outside the chosen absorption feature, resulting in largely identical coherent speckle patterns and star images in both filters. A faint companion will be bright in one filter and faint in the other. Subtracting the two images thus removes the starlight and speckle patterns while a real companion remains in the image. Using a specific sprectral feature, such as methane, greatly reduces the number of false positives detected (e.g. a background object, while real, will drop out of the SDI subtraction since it will not have methane absorption).

ADI employs a similar strategy to build a high quality reference PSF to remove speckles. Instead of observing at discrete roll angles, ADI leaves the rotator off and allows the telescope optics to rotate on the sky (this works best at Cassegrain focus). In a sequence of images taken at different parallactic angles, a real companion will track on the sky with the parallactic angle, while speckles will move randomly. From a series of images, a reference PSF can be constructed for and subtracted from each individual image, attenuating quasi-static speckle structure. Combining both SDI and ADI techniques thus allows an even greater degree of speckle supression.

SDI is the base mode of the NICI instrument. Whether SDI is combined with ADI or used at discrete roll angles is the choice of the observer.

Campaign Goals

The NICI Planet-Finding Campaign strives to address the following questions:

  1. What is the frequency of outer (> 5–10 AU) massive planets around other stars?
    Determining the incidence and properties of outer planetary companions will allow us to develop a complete picture of exoplanetary configurations. To this end, one major goal of the NICI Campaign is to probe the mass and separation distribution (dN/dM/da) of planets at distances as close as approximately ≥ 5 – 10 AU, as inferred from the complete set of NICI detections (discoveries) and non-detections. This distribution may have profound consequences for assessing the dominant formation mechanism of gas-giant planets.
  2. What is the dependence of planet frequency on the stellar host mass?
    The frequency of giant planets in the outer regions of low-mass stars (M dwarfs) is another key discriminant between the two competing theories of giant planet formation, namely core accretion and disk instability. By design, the Campaign is searching for planets around young stars over a wide range of masses, from spectral type B7 to M6. This is feasible thanks to the sensitivity of NICI’s curvature-based AO system to optically faint stars. Radial velocity surveys find few massive planets in the inner ≤ 1 AU regions around low-mass stars; the NICI Campaign will be a complementary study of the outer regions around these objects.
  3. What are the spectrophotometric properties of young extrasolar planets?
    Follow-up multi-band photometry and spectroscopy of directly imaged planets will test theoretical models, which are far from mature. The discovery space is large and unexplored. Cooling models may be incorrect or missing key opacity sources. Indeed, one of the early surprises from RV discoveries was the diversity of exoplanet orbits. Whether this diversity extends to their spectral energy distributions (SEDs) is an important open question. Initial studies of the SEDs of the HR 8799 planets point to unusually cloudy, non-equilibrium photospheres compared to field brown dwarfs, suggesting extreme physical properties in ultracool atmospheres at young ages. However, many more systems are needed for study.

To accomplish these goals, the targets for this campaign have been chosen to mazimize the likelihood of detecting planets. Combining simulations of host stars and companion objects with NICI sensitivity and performance characteristics has resulted in a carefully chosen target list. The final target list is composed primarily of stars with ages of approximately ≤ 300 Myr and distances of approximately ≤70 pc. The list does include stars with older ages or larger distances that are promising targets, especially if they have ancillary evidence for being hosts of planetary systems (e.g., the presence of circumstellar debris disks). Mass-wise, the final sample is split roughly equally between high-mass stars (AF spectral types), solar-type stars (GK types), and low-mass stars (M type).

Initial Campaign Results

(under construction)

 

 

The NICI Campaign in Popular Print and Web Media


Companion imaged around the sun-like star PZ Tel. Distributed by NICI team in press release to the public.
Imaging Giants and Dwarfs
by Paul Gilster on August 2, 2010
http://www.centauri-dreams.org/?p=13694

Brown dwarf found orbiting a young sun-like star
http://esciencenews.com/articles/2010/07/29/
brown.dwarf.found.orbiting.a.young.sun.star

Rare Find: Failed Star Circling Sun-Like Star
By Denise Chow, posted: 30 July 2010
http://www.space.com/scienceastronomy/brown-dwarf-orbiting-young-sun-like-star-100730.html

DISCOVER Magazine. Science, Technology and The Future
Found: Jupiter-sized Brown Dwarf, Hiding in a Tight Orbit Around a Young Sun
http://blogs.discovermagazine.com/80beats/2010/07/30/found-jupiter-sized-brown-dwarf-hiding-in-a-tight-orbit-around-a-young-sun/

Brown Dwarf Found Orbiting a Young Sun-Like Star
http://uanews.org/node/33014

Brown Dwarf Found Orbiting a Young Sun-Like Star
http://www.sciencedaily.com/releases/2010/07/100729172336.htm

Brown Dwarf Found Orbiting a Young Sun-Like Star
http://onorbit.com/node/2384

Brown dwarf found orbiting a young Sun-like star
http://www.astronomy.com/asy/default.aspx?c=a&id=10090

Brown Dwarf Found Orbiting A Young Sun-Like Star; The Discovery Is Expected To Shed Light On The Early Stages Of Solar System Formation
http://www.zimbio.com/NASA/articles/AeoBFO6zWRu/Brown+Dwarf+Found+Orbiting+Young+Sun+Like

“Failed star” orbits Sun look-alike
http://spaceinfo.com.au/2010/07/30/failed-star-orbits-sun-like-star

Brown dwarf in tight orbit around young Sun-like star
DR EMILY BALDWIN, ASTRONOMY NOW
http://www.astronomynow.com/news/n1007/30browndwarf/

Astronomers Discover Jupiter-Sized Brown Dwarf
http://www.cbsnews.com/8301-501465_162-20012235-501465.html

Brown Dwarf Found Orbiting Young Sun-like Star
http://www.techvert.com/brown-dwarf-orbiting-sun-like-star/

Found: Jupiter-sized Brown Dwarf, Hiding in a Tight Orbit Around a Young Sun
http://jetlib.com/news/tag/beth-biller/

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