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The onset of chromospheric activity among the A- and F- type starsIUE observations of C II lambda1335 and C IV lambda1549 and ground-based observations of He I lambda5876 have previously discovered intense levels of chromospheric activity among early F type stars. Virtually all F dwarfs show stronger chromospheric and transition region emission than do the cooler and more deeply convective dwarf stars like the Sun. The IUE spectra and those of He lambda5876 place the onset of stellar activity along the main sequence near a color B - V = 0.28, which corresponds approximately to spectral type FO and an effective temperature of 7300 K. However, existing X-ray observations of A and F stars suggest that coronal activity may reach a peak blueward of this high temperature boundary at B - V = 0.28 before vanishing among the early and mid A-type stars. Discussed are preliminary results of a new effort to refine the location of the high temperature boundary to chromospheric activity among A- and F- type stars, making use of low dispersion short-wavelength spectra from the IUE archives from which the strengths of C IV, C II, and Lyman alpha emission have been measured.
Document ID
Document Type
Conference Paper
Simon, Theodore
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Landsman, Wayne
(ST Systems Corp. Greenbelt, Md., United States)
Date Acquired
September 5, 2013
Publication Date
July 1, 1987
Publication Information
Publication: Colorado Univ., 5th Cambridge Workshop on Cool Stars, Stellar Systems and the Sun
Subject Category
Distribution Limits
Work of the US Gov. Public Use Permitted.
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