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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 163 records · Page 9
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NASA NTRS1974

Interpretation of epsilon Aurigae. II - Infrared excess, secondary light variations, and plausible formation of a planetary system

Infrared excess based on the disk model proposed in a previous paper was computed. It was found that the disk alone will emit infrared radiation below the margin of detection. However, if individual condensations are present, the combined result of the disk proper and the condensations yields results of infrared excesses that are consistent with observations. The presence of condensations also makes the secondary light variation understandable. An elementary theory is developed that analyzes such light variations. The result of the analysis yields the size of the orbit of the condensation around the secondary component.

Huang, S.-S.↗
NASA NTRS1981

Solar nebula dispersal and the stability of the planetary system. I - Scanning secular resonance theory

Secular resonances in the early solar system are investigated with the aim of establishing constraints on the time scale and method of solar nebula dispersal. Simplified nebula models and dispersal routines are used to approximate changes in an assumed axisymmetric nebula potential. These changes drive an evolutionary sequence of Laplace-Lagrange solutions for the secular variations of the solar system. These sequences are characterized by a sweep of one or more giant planet resonances through the inner solar system. Their effect is rate-dependent; characteristic dispersal times of not greater than 10,000 to 100,000 years are required to avoid the generation of terrestrial eccentricities and inclinations in excess of observed values.

Ward, W. R.↗
NASA NTRS1985

IUE observations of Beta Pictoris - An IRAS candidate for a proto-planetary system

The results of a preliminary analysis of high-resolution and low-resolution UV spectra of the edge-on extended-disk shell star Beta Pic, obtained with the IUE SWP and LWR instruments on November 5-6, 1984, are reported and compared with IRAS and ground-based observations. No selective UV extinction is detected, and the fine structure of the Fe II and C I absorption lines and the presence of metastable Fe II lines are considered consistent with a circumstellar nebula or extended envelope of density greater than 1000/cu cm and electron density (1-10) x 10 to the 8th/cu cm or less at 1-2 AU from the central star. The possibility that the extended orbiting disk is clumpy, as observed by Smith and Terrile (1985), is discussed.

Kondo, Y.↗
NASA NTRS1988

Direct imaging of extra-solar planetary systems with the Circumstellar Imaging Telescope (CIT)

In a joint study conducted by the Jet Propulsion Laboratory and the Perkin-Elmer Corporation it was found that an earth orbital, 1.5 meter diameter low scattered light coronagraphic telescope can achieve a broad range of scientific objectives including the direct detection of Jupiter-sized planets around the nearby stars. Recent major advances in the understanding of coronagraphic performance and in the field of super smooth mirror fabrication allow such an instrument to be designed and built within current technology. Such a project, called the Circumstellar Imaging Telescope (CIT), is currently being proposed.

Terrile, Richard J.↗
NASA NTRS1988

Space Station Astrometric Telescope tracking for the detection of planetary systems

The paper presents a comprehensive star observation and tracking strategy, which uses a computer simulation of the Space Station orbital mechanics, system constraints, and Astrometric Telescope Facility (ATF) tracking maneuvers over a long observational period. This approach may be used to obtain data which may assist in the preliminary systems definition of the ATF. Results are given for an analysis which uses a restricted target set in order to demonstrate the disproportionate effect of the galactic-photon-rate index on the observation times for each star.

Mascy, Alfred C.↗
NASA NTRS1989

The impact of stellar evolution on planetary system development

The connection between stellar evolution and planet formation is investigated. Particular attention is given to the problem posed by the fact that the formation of Jupiter occurred before the formation of Mars and that the formation of the solid core of Saturn was completed before the dissipation of the gas in the nebula. Several possible solutions to this problem are suggested.

Bodenheimer, Peter↗
NASA NTRS1990

Imaging other planetary systems from the moon

This paper studies the problem of using a telescope like the HST, only larger and sensitive to a wider range of wavelengths, to image systems of planets like the solar system around other stars. Both reflected starlight and thermal radiation from the planets are treated. The instrumental effects of aperture diffraction, scattering due to the power spectral density of telescope mirror surface errors, and telescope thermal emission are included. The integration time required to achieve a signal-to-noise ratio is computed at 5 for photon-statistical random errors only, which is a necessary but not sufficient criterion for detection at a confidence level of five standard deviations. A cold telescope on the moon with 16m aperture and the optical quality of HST could detect and characterize planets around nearby stars.

Brown, Robert A.↗
NASA NTRS1992

A observational test for the existence of a planetary system orbiting PSR1257 + 12

It is pointed out that, because of the near commensurability of the orbital periods of the recently reported planets of the nearby millisecond pulsar PSR1257 + 12, the mutual gravitational perturbations of the two planets should produce not only small secular changes, but also larger periodic changes in their orbital elements. In particular, it is found that changes in the eccentricities and orbital periods should become measurable within a few years. Such a measurement would help determine the three masses in the system and the inclinations of the orbits. More important, a detection of these changes, if they agree with theoretical predictions presented here, should provide irrefutable confirmation that the periodic residuals are caused by orbiting planets rather than some other effect.

Rasio, F. A.↗
NASA NTRS1990

Space optics for studying extra-solar planetary systems

The sharp imaging of telescopes in space will improve the ability to see faint objects near bright ones. One exciting application is the search for planets around other stars. However, because a planet is, at best, 10 exp 9 times fainter than a star in visible light, specialized optical systems are required. Using apodization to remove diffracted light, the limiting source of noise is the intensity of starlight scattered by mirror figure errors. Based on the prelaunch metrology of the HST mirrors, and considering only photonstatistics, months of integration would be needed for HST to detect Jupiter next to the sun at a distance of 5 pc. The integration times will be shorter for future telescopes in space with smoother mirrors and/or larger apertures.

Brown, Robert A.↗
NASA NTRS1992

Dynamics of binary and planetary-system interaction with disks - Eccentricity changes

Protostellar and protoplanetary systems, as well as merging galactic nuclei, often interact tidally and resonantly with the astrophysical disks via gravity. Underlying our understanding of the formation processes of stars, planets, and some galaxies is a dynamical theory of such interactions. Its main goals are to determine the geometry of the binary-disk system and, through the torque calculations, the rate of change of orbital elements of the components. We present some recent developments in this field concentrating on eccentricity driving mechanisms in protoplanetary and protobinary systems. In those two types of systems the result of the interaction is opposite. A small body embedded in a disk suffers a decrease of orbital eccentricity, whereas newly formed binary stars surrounded by protostellar disks may undergo a significant orbital evolution increasing their eccentricities.

Atrymowicz, Pawel↗
NASA NTRS1993

Orbital evolution of the PSR1257+12 planetary system

The detection of orbital perturbation effects in the PSR1257+12 timing data would provide irrefutable confirmation that planets are indeed orbiting the pulsar. Here we give an overview of how perturbation effects are expected to affect the orbital elements of the two planets over the next few years. In particular, we give a simple calculation of resonant perturbations, including the nonlinear effects which could be important if sin i less than about 0.1. We also present a new analysis of the effects of close encounters between the two planets and we discuss their detectability.

Rasio, Frederic A.↗
NASA NTRS1992

The use of robotic telescopes for detecting planetary systems

It is argued that increases in the precision of photometric measurements and the development of fully automatic photometric telescopes (APTs) now make possible the detection of Jupiter-size objects around other stars. The two most promising approaches are to monitor binary stars that have their orbital plane nearly in our line of sight and to measure the rotation periods of stars that are known to have dark companions and have very accurate values for Vsini. Differential photometry with APTs, based on a rapid comparison among a group of stars, provides a precision of 2 parts in 1000. Transits of solar-type stars by planets or brown dwarfs the size of Jupiter or Saturn will produce brightness variations of about 10 parts per 1000.

Borucki, William J.↗
NASA NTRS1993

Detection of accreting gas toward HD 45677 - A newly recognized, Herbig Be proto-planetary system

We report the detection of high-velocity, accreting gas toward the BE(e) star with IR excess and bipolar nebula, HD 45677. High-velocity (+200 to +400 km/s), variable column density gas is visible in all IUE spectra from 1979 to 1992 in transitions of Si II, C II, Al III, Fe III, Si IV, and C IV. Low-velocity absorption profiles from low oscillator strength transitions of Si II, Fe II, and Zn II exhibit double-peaked absorption profiles similar to those previously reported in optical spectra of FU Orionis objects. The UV absorption data, together with previously reported analyses of the IR excess and polarization of this object, suggest that HD 45677 is a massive, Herbig Be star with an actively accreting circumstellar, protoplanetary disk.

Grady, C. A.↗
NASA NTRS1993

Working group for planetary system nomenclature

Most of the activity of the Working Group and Task Group of the IAU during these three years has been centered on the nomenclature of Neptune's satellites and rings as revealed by the Voyager spacecraft. The emphasis is now shifting to Venus, in preparation for the detailed radar mapping of that planet begun by the Magellan spacecraft in August 1990. Approval has been asked for nomenclature of the Earth's moon, Venus, Mars, and Triton features as well as 4 other Neptune satellites and three Neptune rings.

Source record↗
NASA NTRS1994

IUE observations of new A star candidate proto-planetary systems

As a result of the detection of accreting gas in the A5e PMS Herbig Ae star, HR 5999, most of the observations for this IUE program were devoted to Herbig Ae stars rather than to main sequence A stars. Mid-UV emission at optical minimum light was detected for UX Ori (A1e), BF Ori (A5e), and CQ Tau (F2e). The presence of accreting gas in HD 45677 and HD 50138 prompted reclassification of these stars as Herbig Be stars rather than as protoplanetary nebulae. Detailed results are discussed.

Grady, Carol A.↗
NASA NTRS1994

The expected morphology of the solar system planetary nebula

We examine the evolution of Jupiter's orbit as the Sun evolves to form a planetary nebula. We use an orbital synchronization mechanism, which was proposed by Tassoul (1987, ApJ, 322, 856), and find that Jupiter is likely to deposit a substantial fraction of its orbital angular momentum, in spinning-up the Sun, when the latter is on the upper Asymptotic Giant Branch (AGB). This amount of angular momentum is likely to cause some small degree of axisymmetric mass loss from the Sun. In this case, the Sun will form an elliptical planetary nebula. The formation of elliptical planetary nebulae with the influence of massive planets and brown dwarfs, may explain the large fraction of elliptical planetary nebulae among the total number of planetary nebulae known today.

Soker, Noam↗
NASA NTRS1994

Direct imaging of planetary systems with a ground-based radio telescope array

The National Radio Astronomy Observatory's proposed Millimeter Array (MMA) will bring unprecedented sensitivity, angular resolution, and image dynamic range to the millimeter wavelength region of the spectrum. An obvious question is whether such an instrument could be used to detect planets orbiting nearby stars. The techniques of aperture synthesis imaging developed for centimeter wavelength radio arrays are capable of producing images whose dynamic ranges greatly exceed the brightness ratio of a solar-type star and a Jupiter-like planet at sub-millimeter or millimeter wavelengths. The angular resolution required to separate a star and planet at a few pc distance can be obtained with baselines of several km. The greatest challenge is sensitivity. At the highest possible observing frequencies (approximately 300 GHz for typical high, dry sites, and approximately 900 GHz from the Antarctic plateau), the proposed MMA will be unable to detect the thermal emission from a Jupiter-like planet a few pc away. An upgraded MMA operating near 300 GHz with twice the currently proposed number of antennas, a 20% fractional bandwidth, and improved receivers could detect Jupiter at 4 pc in a few months. Building such an array on the Antarctic plateau and operating at approximately 900 GHz would allow Jupiter at 4 pc to be detected in approximately one day of observing time.

Jones, Dayton L.↗
NASA NTRS1996

A Road Map for the Exploration of Neighboring Planetary Systems (ExNPS)

A brown dwarf star having only 20-50 times the mass of Jupiter is located below and to the left of the bright star GL 229 in this image from the Hubble Space Telescope. At the 19 light year distance to GL 229, the 7.7-arcsec separation between the star and the brown dwarf corresponds to roughly the separation between Pluto and the Sun in our Solar System. The goal of the program described in this report is to detect and characterize Earth-like planets around nearby stars where conditions suitable for life might be found. For a star like the Sun located 30 light years away, the appropriate star-planet separation would be almost 100 times closer than seen here for GL 229B.

Elachi, Charles↗