FK COMAE BERENICES, KING OF SPIN: THE COCOA-PUFS PROJECT
Name
Ayres-2016-FK COMAE BERENICES.pdf
Size
4.57 MB
Format
Adobe PDF
Checksum (MD5)
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Author(s)
Ayres, Thomas R.
Kashyap, V.
Saar, S.
Korhonen, H.
Drake, J. J.
Cohen, O.
Garraffo, C.
Granzer, T.
Strassmeier, K.
Testa, Paola
Date Issued
March 2016
Journal
Astrophysical Journal. Supplement Series
Publisher
IOP Publishing
Citation
Ayres, Thomas R., V. Kashyap, S. Saar, D. Huenemoerder, H. Korhonen, J. J. Drake, P. Testa, et al. “FK COMAE BERENICES, KING OF SPIN: THE COCOA-PUFS PROJECT.” The Astrophysical Journal Supplement Series 223, no. 1 (March 17, 2016): 5. © 2016 The American Astronomical Society
Version
Final published version
Abstract
COCOA-PUFS is an energy-diverse, time-domain study of the ultra-fast spinning, heavily spotted, yellow giant FK Comae Berenices (FK Com: HD117555; G4 III). This single star is thought to be a recent binary merger, and is exceptionally active by measure of its intense ultraviolet (UV) and X-ray emissions, and proclivity to flare. COCOA-PUFS was carried out with the Hubble Space Telescope in the UV (1200–3000 Å), using mainly its high-performance Cosmic Origins Spectrograph, but also high precision Space Telescope Imaging Spectrograph; Chandra X-ray Observatory in the soft X-rays (0.5–10 keV), utilizing its High-Energy Transmission Grating Spectrometer; together with supporting photometry and spectropolarimetry in the visible from the ground. This is an introductory report on the project. FK Com displayed variability on a wide range of timescales over all wavelengths during the week-long main campaign, including a large X-ray flare; "super-rotational broadening" of the far-ultraviolet "hot lines" (e.g., Si iv 1393 Å; 8 × 10[superscript 4] K) together with chromospheric Mg ii 2800 Å and C ii 1335 Å (1–3 × 10[superscript 4] K); large Doppler swings suggestive of bright regions alternately on advancing and retreating limbs of the star; and substantial redshifts of the epoch-average emission profiles. These behaviors paint a picture of a highly extended, dynamic, hot (~10 MK) coronal magnetosphere around the star, threaded by cooler structures perhaps analogous to solar prominences and replenished continually by surface activity and flares. Suppression of angular momentum loss by the confining magnetosphere could temporarily postpone the inevitable stellar spindown, thereby lengthening this highly volatile stage of coronal evolution.
MIT Department
MIT Kavli Institute for Astrophysics and Space Research
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DOI of Published Version
https://doi.org/10.3847/0067-0049/223/1/5
