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  • 1
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    The distribution of rotational velocities for low-mass stars in the Pleiades (1987)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: The available spectral type and color data for late-type Pleiades members have been reanalyzed, and new reddening estimates are obtained. New photometry for a small number of stars and a compilation of H-alpha equivalent widths for Pleiades dwarfs are presented. These data are used to examine the location of the rapid rotators in color-magnitude diagrams and the correlation between chromospheric activity and rotation. It is shown that the wide range of angular momenta exhibited by Pleiades K and M dwarfs is not necessarily produced by a combination of main-sequence spin-downs and a large age spread; it can also result from a plausible spread in initial angular momenta, coupled with initial main-sequence spin-down rates that are only weakly dependent on rotation. The new reddening estimates confirm Breger's (1985) finding of large extinctions confined to a small region in the southern portion of the Merope nebula.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 318; 337-355
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  • 2
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    Rotation and kinematics of the premain-sequence stars in Taurus-Auriga with Ca II emission (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Radial velocities and v sin i values for the stars in the Taurus-Auriga region that were found to have strong Ca II H and K emission by Herbig, Vrba, and Rydgren 'HVR', (1986) are reported. Most of the velocities are determined to better than 2 km/s precision. The kinematic properties of the Ca II emission stars with strong Li are found to be indistinguishable from conventional T Tauris in Taurus-Auriga, contrary to HVR. These Li-rich stars also rotate like T Tauris. Most of the stars that lack Li are probable or possible members of the Hyades, in the foreground, and are among the brightest and most active stars in that cluster for their spectral types. It is suggested following Jones and Herbig (1979), that the apparent absence of low-mass stars older than 10 Myr in Taurus-Auriga is real, and is due to the finite lifetime of the cloud.
    Keywords: ASTROPHYSICS
    Type: Astronomical Journal (ISSN 0004-6256); 93; 907-912
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  • 3
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    Further evidence for differential rotation in V1057 Cygni (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Further tests of the accretion disk hypothesis for FU Orionis objects are presented. High spectral resolution, high signal to noise, 5820-6830 A and 7500-9370 A spectra of V1057 Cyg reveal a correlation between linewidth and line transition lower excitation potential expected from this hypothesis. The magnitude of the effect compares favorably with that predicted by synthetic disk spectra. Additional evidence for previously documented spectral type and linewidth versus wavelength correlations is also presented. This kinematic evidence strongly supports the accretion disk hypothesis.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 349; 328-334
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  • 4
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    Rotational velocities of low-mass stars in the Hyades (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: High-resolution echelle spectra have been used to estimate rotational velocities for K and M dwarfs in the Hyades. All of the K dwarfs have rotational velocities less than the instrumental limit of 10 km/s. Most of the M dwarfs with (R - I)K larger than 1.0 have detectable rotational velocities, with v sin i between 10 and 20 km/s. Combining these data with results from the younger Pleiades and Alpha Persei clusters, it is found that G dwarfs spin down from about 100 km/s to about 10 km/s in less than 40 million yr, whereas M dwarfs take an order of magnitude longer to spin down.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters to the Editor (ISSN 0004-637X); 320; L51-L55
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  • 5
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    The rotational velocities of low-mass stars (1986)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The rotational velocities of stars provide important clues to how stars form and evolve. Yet until recently, studies of stellar rotation were limited to stars more massive than the sun. This is beginning to change, and an observational outline of the rotational velocity evolution of stars less massive than the sun can now be provided. Low-mass stars rotate slowly during the early stages of premain-sequence evolution, and spin up as they contract to the main sequence. This spin-up culminates in a brief period of very rapid rotation at an age of order 50 million years. Physical interpretation of this increase in rotation and the subsequent main-sequence spin-down are complicated by the possibility of differential internal rotation. The observed rapidity of spin-down among G dwarfs suggests that initially only the outer convective envelopes of these stars are slowed. The data suggest an intrinsic spread in angular momentum among young stars of the same mass and age, a spread which is apparently minimized by the angular-momentum loss mechanism in old low-mass stars.
    Keywords: ASTROPHYSICS
    Type: Astronomical Society of the Pacific, Publications (ISSN 0004-6280); 98; 1233-125
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  • 6
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    Time variation of ocean temperatures and its relation to internal waves and oceanic heat flow measurements. (1966)
    In:  Other Sources
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    Publication Date: 2019-05-30
    Description: Time variation of ocean temperatures and relation to internal waves and oceanic heat flow measurements from four stations
    Keywords: GEOPHYSICS
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  • 7
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    Heat-flow measurements in the north atlantic, caribbean, and mediterranean. (1964)
    In:  Other Sources
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    Publication Date: 2019-05-24
    Description: Heat flow measurement in North Atlantic, Caribbean and Mediterranean with independent data comparison
    Keywords: GEOPHYSICS
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  • 8
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    Optimal trajectories for the aeroassisted flight experiment (1989)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The optimal trajectories of the aeroassisted flight experiment (AFE) spacecraft are analyzed in a three-dimensional space using the full system of six ODEs describing the atmospheric pass. The optimal trajectories are computed for two possible transfers: indirect ascent to a 178 NM perigee via a 197 NM apogee and direct ascent to a 178 NM apogee. For each transfer, two cases are investigated: (1) the bank angle is continuously variable, and (2) the trajectory is divided into segments along which the bank angle is constant. It is shown that the optimal trajectories for both cases coalesce into a two subarc trajectory, with the bank angle constant in each subarc. It is also shown that, during the atmospheric pass, the peak values of the changes of the orbital inclination and the longitude of the ascending node are nearly zero.
    Keywords: ASTRODYNAMICS
    Type: IAF PAPER 89-361
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  • 9
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    Optimal trajectories for the Aeroassisted Flight Experiment. Part 2: Equations of motion in an inertial system (1989)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The determination of optimal trajectories for the aeroassisted flight experiment (AFE) is discussed. The AFE refers to the study of the free flight of an autonomous spacecraft, shuttle-launched and shuttle-recovered. Its purpose is to gather atmospheric entry environmental data for use in designing aeroassisted orbital transfer vehicles (AOTV). It is assumed that: (1) the spacecraft is a particle of constant mass; (2) the Earth is rotating with constant angular velocity; (3) the Earth is an oblate planet, and the gravitational potential depends on both the radial distance and the latitude (harmonics of order higher than four are ignored); and (4) the atmosphere is at rest with respect to the Earth. Under these assumptions, the equations of motion for hypervelocity atmospheric flight (which can be used not only for AFE problems, but also for AOT problems and space shuttle problems) are derived in an inertial system. Transformation relations are supplied which allow one to pass from quantities computed in an inertial system to quantities computed in an Earth-fixed system and vice versa.
    Keywords: ASTRODYNAMICS
    Type: NASA-CR-186135 , NAS 1.26:186135 , AAR-239-PT-2
    Format: application/pdf
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  • 10
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    Review of heat flow data. (1965)
    In:  Other Sources
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    Publication Date: 2019-05-24
    Description: Review and analysis of available data on heat flow through Earth crust
    Keywords: GEOPHYSICS
    Format: text
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