Strategy for the Detection and Study of Other Planetary Systems and Extrasolar Planetary Materials 1990-2000 (1990) / Chapter Skim
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5. Observational Requirements for Identification of Extrasolar-System Planets
5. Observational Requirements for Identification of Extrasolar-System Planets
Pages 44-56
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From page 44... ...
of binary stellar systems, is important to the theory of star formation. Many of the companion stars are unseen and can be detected only indirectly by measurement of stellar reflex motion.
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From page 45... ...
DIRECT DETECTION Any direct~etection system consists of a telescope coupled to ancillary instrumentation that analyzes and records the collected radiation. The efficiency with which a telescope performs its functions of gathering, relaying, and focusing radiation is crucial because of the very low intrinsic brightness of extrasolar planetary material The committee considers for illustration the challenge of observing Jupiter from a nearby star, using two space-borne telescopes in NASAs astrophysics program: the Hubble Space Telescope (MST)
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From page 46... ...
Dust, rocks, or planets gravitationally bound to a star and warmed by its radiation would emit thermal radiation in SIRTFs spectral range. Indeed, the dominant noise background for most SIRTE: observations would come from solar system zodiacal dust through which the telescope must view astronomical targets in deeper space.
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From page 47... ...
This light is not localized on the reimaged pupil; it passes the mask and forms the image wings after the pupil diffraction has been suppressed. HST has an anodization capability in the FOC, but the benefit of this feature is expected to be quite limited Hog to light scattering by the residual roughness of the Hers primary and secondary mirrors The committee concludes that if our solar system were to be observed by a HST or SIRTF at a nearby star, Jupiter would not be directly detected.
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From page 48... ...
In reflex response to a planet in circular orbit, a star will execute synchronized, coplanar circular motion of radius aMpM* ~ about the barycenter.
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From page 49... ...
For a nominal Uranus orbiting the same star at 1 AU, the apparent displacement would be only ~15 microarcsec. This orbital displacement must be distinguished from the displacement due to stellar proper motion, which for a velocity of 10 lan s~ ~ relative to the Sun amounts to 0.2 arcsec yr~ i.
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From page 50... ...
The reflex motion of a star in response to an orbiting planet also results in a periodic Doppler shift in stellar spectral features of amplitude AA/A = (V/c) sin i, where ~ is the wavelength, c is the speed of light, i is the angle between the orbit pole and the line of sight, and V is the stellar orbital speed.
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From page 51... ...
EVALUATION OF PROPOSED INDIRECT TECHNIQUES In this section, with the assistance of briefings by researchers expert in the principal search techniques discussed above, the committee evaluates the expected applicability of proposed and present instrumentation to the search for extrasolar planets. Astrometric Telescope Facility The committee has reviewed proposed plans for an astrometric telescope facility (ATF)
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From page 52... ...
. For an observing campaign with a duration of approximately 20 yr, the smallest planet detectable using this technique is of the order of 6 Me, about one-half to one-third the masses of Uranus, Neptune, and hypothetical giant planet cores.
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From page 53... ...
It is evident from the above discussion and from Figure 5.2 that an astrometnc accuracy approaching the 1 ~ design goal of the proposed spacebased ATE defines an accessible discovery space that includes a relatively broad and scientifically crucial range of planetary masses. For comparison, ground-based photoelectric measurement at a site with excellent seeing (assumed ~ = 10-3 arcsec)
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From page 54... ...
Photometric Planet Searches It is clear from the Jupiter transit example (under the heading Indirect Detection) that the photometric technique must deal with events that typically may be of short duration and low frequency, and are detectable only if the observer is in or very near the planet's orbital plane.
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From page 55... ...
Further, if dust contamination and residual surface roughness of the telescope optics can be suppressed, extraneous scattered light can be reduced, and innovative image tailoring by anodization can provide additionally enhanced contrast. Improved management of astronomical light within telescope systems would significantly augment the range, spatial specificity, and overall effectiveness of extrasolar planetary studies.
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From page 56... ...
COMPLEX encourages continued development of promising Earthbased and space-based instruments and techniques of this me for follow-on defiled study of 0arasolar planetary systems. · ~~ regard to unaging instruments, given Weir present importance in the study of preplanetary precursor systems and their ultimate potential for direct imaging of evolved planets, COMPLEX urges that the design of fixture telescopesincorporatediffrac~n controland techniques for the reduction of light scattering due to dust contamination and to residual errors in mirror figure.
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