A1 Refereed original research article in a scientific journal
FK COMAE BERENICES, KING OF SPIN: THE COCOA-PUFS PROJECT
Authors: Ayres TR, Kashyap V, Saar S, Huenemoerder D, Korhonen H, Drake JJ, Testa P, Cohen O, Garraffo C, Granzer T, Strassmeier K
Publisher: IOP PUBLISHING LTD
Publication year: 2016
Journal: Astrophysical Journal Supplement
Journal name in source: ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES
Journal acronym: ASTROPHYS J SUPPL S
Article number: ARTN 5
Volume: 223
Issue: 1
Number of pages: 30
ISSN: 0067-0049
eISSN: 1538-4365
DOI: https://doi.org/10.3847/0067-0049/223/1/5(external)
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 angstrom), 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 angstrom; 8 x 10(4) K) together with chromospheric Mg II 2800 angstrom and C II 1335 angstrom (1-3. x. 10(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 (similar to 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.
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 angstrom), 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 angstrom; 8 x 10(4) K) together with chromospheric Mg II 2800 angstrom and C II 1335 angstrom (1-3. x. 10(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 (similar to 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.
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