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Resolving the xi Boo Binary with Chandra, and Revealing the Spectral Type Dependence of the Coronal "Fip Effect"On 2008 May 2, Chandra observed the X-ray spectrum of xi Boo (G8 V+K4 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 ΞΎ Boo A and B to the system's 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 A's 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.
Document ID
20100027420
Acquisition Source
Headquarters
Document Type
Reprint (Version printed in journal)
Authors
Wood, Brian E.
(Naval Research Lab. Washington, DC, United States)
Linsky, Jeffrey L.
(Colorado Univ. Boulder, CO, United States)
Date Acquired
August 24, 2013
Publication Date
July 10, 2010
Publication Information
Publication: The Astrophysical Journal
Volume: 717
Issue: 2
Subject Category
Astronomy
Report/Patent Number
AD-A523269
Funding Number(s)
CONTRACT_GRANT: GO8-9003Z
CONTRACT_GRANT: NAS8-03060
Distribution Limits
Public
Copyright
Other
Keywords
CHANDRA
BOO BINARY
FIP (FIRST IONIZATION POTENTIAL)

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