FK Comae Berenices, King of Spin: The COCOA-PUFS Project
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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 ×
104 K) together with chromospheric Mg ii 2800 Å and C
ii 1335 Å (1-3 × 104 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.
COordinated Campaign of Observations and Analysis, Photosphere to Upper
Atmosphere, of a Fast-rotating Star.
Originalsprog | Engelsk |
---|---|
Artikelnummer | 5 |
Tidsskrift | Astrophysical Journal Supplement Series |
Vol/bind | 223 |
Udgave nummer | 1 |
ISSN | 0067-0049 |
DOI | |
Status | Udgivet - 1 mar. 2016 |
ID: 170453908