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STEPS
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STEPS performs the world's highest accuracy ground-based general-purpose astrometry. The custom-built instrument consists of a liquid nitrogen-cooled charge-coupled device (CCD) camera and a minimum number of optical surfaces. The noise floor is ~1 milliarcseconds and the current baseline is 9 years for many of the targets. The STEPS performance matches or exceeds that of the highest accuracy space-based astrometry instrument, Hubble Space Telescope's Fine Guidance Sensor.
STEPS has made the first astrometric discovery of an exoplanet. The planet is called VB 10b and the star, VB 10, is one of the smallest known, just above the
boundary separating low-mass stars and brown dwarfs. Read the preprint about this unique planet by following the links under 05.28.2009 on the right.
STEPS has discovered 5 low-mass companions to M-dwarfs that were previously believed to be single (see references). The companions are brown dwarfs or late M dwarfs. The dynamical measurements of the masses of all the components add to the currently scarce knowledge of such masses. Other candidate companions that are extrasolar giant planets (EGPs) can be confirmed with further STEPS observations. One of these would be the first astrometrically discovered EGP.
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The Orbit of VB 10b
The STEPS discovery VB 10b is the first astrometrically-discovered planet. The best-fit model has a mass 6 times that of Jupiter and an orbital period of 9 months.
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Derived Orbit
The STEPS discovery GJ 802b is believed to be a brown dwarf (BD). The derived model orbit is shown with the solid lines and the STEPS observations with the data points. The green circles depict an imaging observation that failed to detect the secondary providing further evidence that it is a BD.
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Mass Determination
The mass limits for the brown dwarf GJ 802b. The mass is between 0.04-0.08 Solar masses depending upon the poorly-determined eccentricity of the orbit.
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Hubble Space Telescope Image
The Hubble Space Telescope image that confirms the STEPS discovery of GJ 164B. GJ 164B is a late M dwarf or a brown dwarf.
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Keck Laser Guide Star Adaptive Optics Image
G 78-28AB binary was discovered with STEPS and confirmed with this laser guide star adative optics image from Pravdo et al. 2006, ApJ, v. 649, p. 389, also astro-ph/0605306. The separation between A and B is in milliarcseconds (mas).
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