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  • Astronomy  (3)
  • Astrophysics  (1)
  • 1
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    Chandra Observations of Magnetic White Dwarfs and Their Theoretical Implications (2002)
    In:  Other Sources
    Details
    Publication Date: 2019-07-18
    Description: Observations of cool DA and DB white dwarfs have not yet been successful in detecting coronal X-ray emission but observations of late-type dwarfs and giants show that coronae are common for these stars. To produce coronal X-rays, a star must have dynamo-generated surface magnetic fields and a well-developed convection zone. There is strong observational evidence that the DA star LHS 1038 and the DB star GD 358 have weak and variable surface magnetic fields. Since these fields are likely to be generated by dynamo action and since both stars have well-developed convection zones, theory predicts detectable levels of coronal X-rays from these white dwarfs. However, we present analysis of Chandra observations of both stars showing no detectable X-ray emission. The derived upper limits for the X-ray fluxes provide strong constraints on theories of formation of coronae around magnetic white dwarfs.
    Keywords: Astronomy
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    Chandra Observations of Magnetic White Dwarfs and their Theoretical Implications (2003)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Observations of cool DA and DB white dwarfs have not yet been successful in detecting coronal X-ray emission, but observations of late-type dwarfs and giants show that coronae are common for these stars. To produce coronal X-rays, a star must have dynamo-generated surface magnetic fields and a well-developed convection zone. There is some observational evidence that the DA star LHS 1038 and the DB star GD 358 have weak and variable surface magnetic fields. It has been suggested that such fields can be generated by dynamo action, and since both stars have well-developed convection zones, theory predicts detectable levels of coronal X-rays from these white dwarfs. However, we present analysis of Chandra observations of both stars showing no detectable X-ray emission. The derived upper limits for the X-ray fluxes provide strong constraints on theories of formation of coronae around magnetic white dwarfs. Another important implication of our negative Chandra observations is the possibility that the magnetic fields of LHS 1038 and GD 358 are fossil fields.
    Keywords: Astrophysics
    Type: The Astrophysical Journal; 593; 481-485
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    NASA TECHNICAL REPORTS
  • 3
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    ROSAT Pointed Observations of Cool Magnetic White Dwarfs (1995)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Observational evidence for the existence of a chromosphere on the cool magnetic white dwarf GD 356 has been reported. In addition, there has been theoretical speculations that cool magnetic white dwarfs may be sources of coronal X-ray emission. This emission, if it exists, would be distinct from the two types of X-ray emission (deep photospheric and shocked wind) that have already been observed from hot white dwarfs. We have used the PSPC instrument on ROSAT to observe three of the most prominent DA white dwarf candidates for coronal X-ray emission: GD 356, KUV 2316+123, and GD 90. The data show no significant emission for these stars. The derived upper limits for the X-ray luminosities provide constraints for a revision of current theories of the generation of nonradiative energy in white dwarfs.
    Keywords: Astronomy
    Type: NASA-CR-203334 , NAS 1.26:203334 , The Astrophysical Journal; 453; L33-L35
    Format: application/pdf
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  • 4
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    Optical Characteristics of the Marshall Space Flight Center Solar Ultraviolet Magnetograph (2001)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: This paper will describe the scientific objectives of the Marshall Space Flight Center (MSFC) Solar Ultraviolet Magnetograph Investigation (SUMI) and the optical components that have been developed to meet those objectives. In order to test the scientific feasibility of measuring magnetic fields in the UV, a sounding rocket payload is being developed. This paper will discuss: (1) the scientific measurements that will be made by the SUMI sounding rocket program, (2) how the optics have been optimized for simultaneous measurements of two magnetic lines CIV (1550 Angstroms) and MgII (2800 Angstroms), and (3) the optical, reflectance, transmission and polarization measurements that have been made on the SUMI telescope mirror and polarimeter.
    Keywords: Astronomy
    Type: (ISSN 0277-786X)|Optical Characteristics of the Marshall Space Flight Center Solar Ultraviolet Magnetograph; Aug 01, 2001 - Aug 02, 2001; San Diego, CA; United States
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