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  • 1
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    Chromospheres of classical Cepheids (1982)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: The International Ultraviolet Explorer spectra of five classical Cepheids were obtained in the short and the long wavelength regions at low dispersion, curves and emission line strengths were obtained from the low resolution spectra. The amplitudes of the light curves increase with decreasing wavelength except around 1550 A where the amplitude is surprisingly small. The emission line fluxes behave differently in the various stars and it appears that bumps in the ultraviolet light curves are related to the behavior of the chromospheres. However, the strengths of the emission lines are roughly comparable to nonvariable stars of similar temperature and luminosity. The high resolution spectra were used to study the fluxes of the emission from the Mg II h and k lines. It is found that the emission components come and go during the cycles and the behavior differs from one star to another, with generally stronger and more persistent emission at longer periods. This is compared with the times of appearance of the Ca II H and K emission features and provides insight into the way in which the chromosphere reacts to shock waves generated by the pulsation of the star.
    Keywords: ASTRONOMY
    Type: Advan. in Ultraviolet Astron.; p 439-441
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    Simultaneous X-ray and optical observations of an Ursae Majoris during a low state (1981)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: In November 1975, AN UMa was detected as a soft X-ray source with a 0.1-0.4 keV flux which was modulated with the orbital cycle. In order to investigate further this orbital dependence and to correlate it with existing photometric and spectroscopic observations to aid in determining the geometry of the system, simultaneous X-ray and optical observations were made throughout several cycles of AN UMa. The system was in a low optical state during the observations. The X-ray observations were made with the Imaging Proportional Counter on the Einstein Observatory, yielding measurements over an available energy range of 0.1-4 keV. Attention is given to total X-ray flux, the X-ray light curve, optical and infrared data, and model implications.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal; vol. 246
    Format: text
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    NASA TECHNICAL REPORTS
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