Accession Number:

ADA523269

Title:

Resolving the xi Boo Binary with Chandra, and Revealing the Spectral Type Dependence of the Coronal Fip Effect

Descriptive Note:

Journal article

Corporate Author:

NAVAL RESEARCH LAB WASHINGTON DC SPACE SCIENCE DIV

Personal Author(s):

Report Date:

2010-07-10

Pagination or Media Count:

14.0

Abstract:

On 2008 May 2, Chandra observed the X-ray spectrum of xi Boo G8 VK4 V, resolving the binary for the first time in X-rays and allowing the coronae of the two stars to be studied separately. With the contributions of 958 Boo A and B to the systems total X-ray emission now observationally established 88.5 and 11.5 respectively, consideration of mass loss measurements for GK dwarfs of various activity levels including one for xi Boo leads to the surprising conclusion that xi Boo B may dominate the wind from the binary, with xi Boo As wind being very weak despite its active corona. Emission measure EM distributions and coronal abundances are computed for both stars and compared with Chandra measurements of other moderately active stars with G8-K5 spectral types, all of which exhibit a narrow peak in EM near log T 6.6, indicating that the coronal heating process in these stars has a strong preference for this temperature. As is the case for the Sun and many other stars, our sample of stars shows coronal abundance anomalies dependent on the first ionization potential FIP of the element. We see no dependence of the degree of FIP effect on activity, but there is a dependence on spectral type, a correlation that becomes more convincing when moderately active main-sequence stars with a broader range of spectral types are considered. This clear dependence of coronal abundances on spectral type weakens if the stellar sample is allowed to be contaminated by evolved stars, interacting binaries or extremely active stars with logLX 29, explaining why this correlation has not been recognized in the past.

Subject Categories:

  • Astronomy
  • Numerical Mathematics
  • Electricity and Magnetism

Distribution Statement:

APPROVED FOR PUBLIC RELEASE