Search Results - (Author, Cooperation:J. N. Heasley)

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  1. 1
    Staff View
    Publication Date:
    2012-05-12
    Publisher:
    Nature Publishing Group (NPG)
    Print ISSN:
    0028-0836
    Electronic ISSN:
    1476-4687
    Topics:
    Biology
    Chemistry and Pharmacology
    Medicine
    Natural Sciences in General
    Physics
    Published by:
    http://www.nature.com/

    Latest Papers from Table of Contents or Articles in Press
  2. 2
    Christian, C. A. ; Heasley, J. N.
    Springer
    Published 1986
    Staff View
    ISSN:
    1572-946X
    Source:
    Springer Online Journal Archives 1860-2000
    Topics:
    Physics
    Notes:
    Abstract Color-magnitude diagrams are presented for the open cluster NGC 2158 and globular clusters Pal4 and NGC 1904.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1007/BF00651167

    Articles: DFG German National Licenses
  3. 3
    Heasley, J. N. ; Milkey, R. W. ; Engvold, Oddbjorn
    Springer
    Published 1977
    Staff View
    ISSN:
    1573-093X
    Source:
    Springer Online Journal Archives 1860-2000
    Topics:
    Physics
    Notes:
    Abstract Observations of the Ca ii H, K, and infrared triplet lines are compared with theoretical predictions from the slab models of Heasley and Milkey (1976). While the theoretical models describe the hydrogen and helium emission spectra of quiescent prominences satisfactorily the predicted Ca ii lines are systematically too bright. The most likely reason for the discrepancy is the inapplicability of the symmetric slab prominence model for lines which become even moderately optically thick in prominences.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1007/BF00216369

    Articles: DFG German National Licenses
  4. 4
    Auer, L. H. ; Heasley, J. N. ; House, L. L.
    Springer
    Published 1977
    Staff View
    ISSN:
    1573-093X
    Source:
    Springer Online Journal Archives 1860-2000
    Topics:
    Physics
    Notes:
    Abstract The application of Unno's (1956) solution of the transfer equation for polarized radiation to the determination of thevector magnetic field is investigated. An analysis procedure utilizing non-linear least squares techniques is developed that allows one to automate the reduction of measured spectral profiles of the Stokes parameters to determine the field angles, strength as well as other parameters. The method is applied to synthetic spectra generated using a model solar atmosphere and yields results of remarkably high accuracy. The influence of additional factors upon determination of the vector field are also considered. These factors include effects of asymmetric profiles, magneto-optical effects, magnetic field gradients, unresolved field elements, scattered light, and instrumental noise.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1007/BF00150873

    Articles: DFG German National Licenses
  5. 5
    Heasley, J. N. ; Kneer, F. ; Chapman, G. A.
    Springer
    Published 1977
    Staff View
    ISSN:
    1573-093X
    Source:
    Springer Online Journal Archives 1860-2000
    Topics:
    Physics
    Notes:
    Abstract We present theoretical Ca ii K-line profiles and filtergram contrasts for several recent models of solar faculae. The line profiles vary greatly between models and between complete and partial frequency redistribution non-LTE calculations for any given model. The filtergram contrasts are relatively insensitive to the line formation theory which greatly simplifies the calculation for comparison with observations. All of the models considered exhibit K-line contrasts smaller than the mean value observed by Mehltretter.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1007/BF00149647

    Articles: DFG German National Licenses
  6. 6
    Henry, J. Patrick ; Heasley, J. N.

    [s.l.] : Nature Publishing Group
    Published 1986
    Staff View
    ISSN:
    1476-4687
    Source:
    Nature Archives 1869 - 2009
    Topics:
    Biology
    Chemistry and Pharmacology
    Medicine
    Natural Sciences in General
    Physics
    Notes:
    [Auszug] Previous imaging of PG1115 + 08 has been either by direct photography or speckle interferometry2'6; in all cases components B and C have been unresolved. Component A is resolved into two subcomponents (termed At and A2, north and south, respectively) separated by 0.5 arc s at a position angle of ...
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1038/321139a0

    Articles: DFG German National Licenses
  7. 7
    Heasley, J. N.
    Springer
    Published 1975
    Staff View
    ISSN:
    1573-093X
    Source:
    Springer Online Journal Archives 1860-2000
    Topics:
    Physics
    Notes:
    Abstract A theoretical study of the influence of propagating acoustic pulses in the solar chromosphere upon the line profiles of the Ca ii resonance and infrared triplet lines has been made. The major objective has been to explain the observed asymmetries seen in the cores of the H and K lines and to predict the temporal behavior of the infrared lines caused by passing acoustic or shock pulses. The velocities in the pulses, calculated from weak shock theory, have been included consistently in the non-LTE calculations. The results of the calculations show that these lines are very sensitive to perturbations in the background atmosphere caused by the pulses. Only minor changes in the line shapes result from including the velocities consistently in the line source function calculations. The qualitative changes in the line profiles vary markedly with the strength of the shock pulses. The observed differences in the K line profiles seen on the quiet Sun can be explained in terms of a spectrum of pulses with different wave-lengths and initial amplitudes in the photosphere.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1007/BF00153208

    Articles: DFG German National Licenses