Planetary Sciences American and Soviet Research/Proceedings from the U.S.-U.S.S.R. Workshop on Planetary Sciences (1991) / Chapter Skim
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20. Progress in Extra-Solar Planet Detection
20. Progress in Extra-Solar Planet Detection
Pages 270-288
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From page 270... ...
Several observing programs have measured direct light from sub-stellar masses orbiting other stars. Those observations are helpful in understanding why planets have not been found by the same techniques: their visibility is very low as compared with more luminous bodies like brown dwarfs.
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From page 271... ...
The mass range for stars is customarily stated as M* > 0.08M~ >, where nuclear energy generation dominates gravitational contraction over the stellar lifetime (Bahcall 1986~.
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Van de Kamp (1986) uses a similar criterion to set Jupiter's mass as the upper limit to planets and the lower limit to brown dwarfs.
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From page 273... ...
Reflex motions are proportional to the planet/star mass ratio, and occultation effects vary with the planet/star radius ratio squared. Finally, the distance from the observer gives the planet orbit a small angular size, which is a problem for spatial techniques, either direct or indirect.
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From page 274... ...
reported the detection, via infrared speckle interferometry, of a cool (1360K) companion to the M dwarf star, VB 8.
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From page 275... ...
The imperfect optics in real telescopes also scatter starlight into the planet image, masking its signal to some additional degree. For ground-based telescopes, the atmosphere aggravates the problem by refracting a further amount of light from the image core into the wings; an effect called "seeing." For planet searches by direct imaging, the critical instrumental factor is the contrast in surface brightness, which is the ratio of the brightness of the planet's image core to the starlight in the same region of the telescope focal surface.
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From page 276... ...
lengthy integration times required by information theory, and the systematic problems they introduce, Brown and Burrows concluded that planet detection in reflected starlight is technically infeasible for HST. The following discussion of low-mass stars and brown dwarfs is not complete.
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From page 277... ...
Because the spectral characteristics of the cool emitting atmosphere are poorly understood, the reduction of the observed color temperature into an effective temperature is somewhat uncertain (Berriman and Reid 1984~. Cool companions to white dwarfs can also be directly detected by spectroscopy even when the image cannot be isolated.
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From page 278... ...
Figures 4 and 5 explain the basic geometry, physics, and parameterizations for the two types of planet search based on stellar reflex motion: the astrometric search and the radial velocity search. The radial velocity and astrometric techniques produce respectively one- and two-dimensional data records versus time.
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From page 279... ...
Because long periods are associated with wide orbits, these factors further impede drawing valid early results from planet searches. In practice, systematic rather than random errors may determine the 3Horne and Baliunas remark on page 761, "clear arrow signals with period slightly longer than T can sometimes be detected, but with poor resolution."
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From page 280... ...
When viewed from an inclined angle, a circular orbit is an apparent ellipse on the celestial sphere. In principle, the secular motion of the star along this elliptical path uniquely determines the true orbit, including the inclination angle.
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From page 281... ...
The authors report statistically significant, long-term accelerations for seven stars, and in one case, they claim the `'probable" detection of a period. The ~ Cephei observations, with a large quadratic drift subtracted, are shown in Figure 6.
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From page 282... ...
Van de Kamp (1986) claims the detection of two planets in his astrometric record of Barnard's star, which is shown in Figure 8.
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From page 283... ...
FIGURE 8 The data for the detection claimed by van de Kamp for two planetary companions to Ban~ard's Star. seconds, 12 years)
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From page 284... ...
b's radial velocity variations from a sine curve implies a non-circular orbit or a second orbiting body. ~ Cephei b and the companions to Barnard's Star are uncertain.
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From page 285... ...
Astrophysics of Brown Dwarfs. Cambridge University Press, Cambridge.
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From page 286... ...
Astrophysics of Brown Dwarfs. Cambridge University Press, Cambridge.
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From page 287... ...
van de Kamp, P
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