Failed Stars and Super Planets A Report Based on the January 1998 Workshop on Substellar-Mass Objects (1998) / Chapter Skim
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1 Detection of Substellar-Mass Objects
1 Detection of Substellar-Mass Objects
Pages 6-18
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From page 6... ...
These discoveries, combined with the identification of the first bona fide brown dwarf, an object intermediate in mass between a star and a planet, have brought tile study of substellar-mass objects (SMOs) into a new phase of observational and theoretical investigation.
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From page 7... ...
Although it is generally assumed that the average planet v, ill be of lower mass than the average brown dwarf, the upper mass limit for planet formation and the lower mass limit for brown dwarf formation are not yet known. Indeeci, these mass limits may overlap, making it very difficult to know whether a particular object is a planet or a brown dwarf.
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From page 8... ...
Astrometric, Photometric, and Microlensing Techniques There are several alternative techniques for the indirect detection of SMOs. These include astrometry, which measures the change in position of a star in tile sky due to its reflex; orbit around the center of mass of the system, and photometry, which measures the dimming of the starlight when the companion object passes in its orbit between Earth and the star (for those systems with the orbital plane nearly along our line of sight to the star)
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From page 9... ...
Microlensing also stands out from the other techniques in that it can detect objects regardless of luminosity. DIRECT DETECTION OF SMOs In addition to the indirect methods discussed above, the intrinsic luminosity of SMOs particularly brown dwarfs, may be directly detected using, a number of different techniques.
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From page 10... ...
FIGURE 1.1 Brown dwarfs and giant extrasolar planets discovered to date (together with Jupiter and Saturn) are plotted as functions of their masses and their separation from their parent star.
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From page 11... ...
The main challenge is knowing, where in the sky to loom Using the second strategy, knowing where to look is obvious at nearby stars but the technical challenge is to resolve the faint brown dwarf against the bright glare of its companion star. Isolated Brown Dwarfs The 2-Micron All Sky Survey (2MASS)
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From page 12... ...
The second frame is an average of several images processed using the technique of methane difference imaging to remove the residual stellar halo seen in the first frame. This technique involves taking images in wavelengths correspondingto a methane absorption band and the continuum.
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From page 13... ...
will greatly increase the number of brown dwarf candidates available for study. Indeed, the new interferometers may allow sampling of several hundred nearby stars to a level sufficient to detect a Uranus-mass object 5 AU from its parent star (see presentation by R.W.
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From page 14... ...
The first two methods can succeed, but they require a large follow-up effort because purely optical colors do not discriminate well between low-mass stars and brown dwarfs. The third method, as employed by the Deep Infrared Survey of the Southern Sky (DENTS)
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From page 15... ...
By correcting their atmospheric wavefront errors to near-Hubble levels of accuracy, single telescopes such as the 6.5 m in the MMT and the MagelIan twins can be used to search the whole sky for Jupiter-size companions in reflected light, to distances of ~S parsecs. Sensitivity to the thermal emission from companion objects will be limited by the telescope emission, but will still be sufficient to allow direct detection with 8-m-class telescopes of S-Gy companions down to the brown-dwarf/superplanet boundary.
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From page 16... ...
The reflected light of giant extrasolar planets could be detected to 10 parsecs and analyzed spectroscopically for the strong features of methane and ice seen in Jupiter and Saturn. A robust search for terrestrial planets of ~ 100 nearby solar stars must await the TPF.
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From page 17... ...
Propulsion Laboratory, The long-term goal of NASA's Origins program is the detection and characterization of terrestrial planets. While the detection of the first Earthlike planet beyond our solar system lies many years and many daunting technical challenges in the future, the task of finding objects smaller titan stars, orbiting other stars as planets or floating freely in space as brown dwarfs, is already well under way using a combination of ~round- and space-based observatories.
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From page 18... ...
Ground- or space-based telescopes equipped with coronagraphs using sophisticated wavefront control to reduce scattered and diffracted light might image planets directly around the closest stars. Whether the Next Generation Space Telescope (NGST)
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