High-Excitation Emission Lines in the Far-Ultraviolet Spectrum of the Late-A Star Alpha Cephei

Details High-Excitation Emission Lines in the Far-Ultraviolet Spectrum of the Late-A Star Alpha Cephei High-Excitation Emission Lines in the Far-Ultraviolet Spectrum of the Late-A Star Alpha Cephei

Jun 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998apj...500l..37s&link_type=abstract

Astrophysical Journal Letters v.500, p.L37

Astronomy and Astrophysics

Astronomy

5

Stars: Activity, Stars: Individual Constellation Name: Alpha Cephei, Ultraviolet: Stars

Scientific paper

The A7 V star alpha Cephei lies in a region of the Hertzsprung-Russell diagram that is generally thought to be devoid of solar-like magnetic activity. The far-ultraviolet spectrum of this star was observed with the Berkeley spectrograph during the 1996 ORFEUS-SPAS II mission. We detected emission lines of Si III, C III, and O VI in the 900-1200 A interval, spanning formation temperatures of 2x104 - 3x105 K. The normalized strengths of these lines, RL=fL/f_{{bol}} , are within a factor of 2 of solar values. Lines of two C III multiplets in the ORFEUS spectrum yield an electron density estimate, ne~10^{9.4+/-0.3} , at a temperature of ~ 6x104 K. The corresponding electron pressure, p=neT~10^{14.2+/-0.3} , is similar to that of the average Sun, but several times smaller than previous estimates made for other late-type G-K stars. At higher temperatures, the normalized flux ratio for coronal soft X-rays is 20 times less for alpha Cep than it is for the Sun. This greatly reduced X-ray brightness suggests that the outer atmosphere of alpha Cep differs strikingly from that of the average Sun, being more akin to a low-density "coronal hole."

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