Michael C. Cushing, Ph.D.


Ultracool Atmospheric Physics

Theoretical atmospheric models are fundamental tools used to understand and characterize brown dwarf and exoplanet atmospheres yet remain largely untested.  I use ground and spaced-based photometry and state of the art atmospheric models to not only derive atmospheric properties of brown dwarfs, but to also identify discrepancies that will eventually lead to improved model atmospheres.

LT Binaries and the L/T Transition

The study of binaries stars offers many advantages over isolated stars because they are presumably coeval and have the same metallicity.  Mike Liu (University of Hawai’i) and I have begun a study of binary systems composed of L and T dwarfs using the integral field spectrograph OSIRIS in combination with the laser guide star adaptive optics system on the Keck II telescope.  We hope to better understand the peculiar transition between the L and T dwarfs that is thought to be controlled by the redistribution of the condensate (i.e., dust) clouds.

Spectral libraries are important for both spectral classification of unknown sources and for population synthesis.  John Rayner, William Vacca, and myself are currently constructing a near-infrared spectral library using SpeX on the NASA IRTF.  The spectra, which sample the entire HR diagram (including WR stars and L and T dwarfs) have R=2000 and cover from 0.8 to 2.5 microns, with a large subset of the spectra extending to ~5 microns.

  1. The IRTF Spectral Library:  The Hot Stars
      (Vacca et al., in prep)

  2. The IRTF Spectral Library:  Cool Stars
       (Rayner et al. 2009)

  3. An Infrared Spectroscopic Sequence of M, L, and T Dwarfs
      (Cushing et al. 2005)

The IRTF Spectral Library

Data Reduction Algorithms

Spextool is an IDL-based data reduction package for SpeX, a medium resolution near-infrared spectrograph on the NASA IRTF.  It performs all of the steps necessary to produce spectra ready for analysis and publication. I am currently modifying Spextool to reduce data obtained with TripleSpec on the Palomar 200″, TripleSpec on the 3.5m APO, and FIRE on the 6.5m Magellan.

The Wide-field Infrared Survey Explorer (WISE)

There is currently a gap of some 400 K between the coolest brown dwarfs currently known and Jupiter.  The study of the brown dwarfs that inhabit this gap will allow us to measure the substellar mass function, determine the low-mass cut off for star formation, and provide insights into the atmospheric physics and chemistry of gas giant exoplanets.

  1. The First Ultra-Cool Brown Dwarf Discovered by the
       Wide-field Infrared Survey Explorer
    (Mainzer et al. 2011)

  2. The Discovery of Y dwarfs Using Data from the Wide-field
       Infrared Survey Explorer (WISE) (Cushing et al. 2011)

  3. The First Hundred Brown Dwarfs Discovered by the Wide-
       field Infrared Survey Explorer (WISE) (Kirkpatrick et al. 2011)


Last modified on: 

August 24, 2011

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