FK COMAE BERENICES, KING OF SPIN: THE COCOA-PUFS PROJECT

Journal Article · Tue Mar 15 04:00:00 EDT 2016 · Astrophysical Journal, Supplement Series

DOI:https://doi.org/10.3847/0067-0049/223/1/5· OSTI ID:22519970

Ayres, Thomas R. ^[1]; Kashyap, V.; Saar, S.; Drake, J. J.; Testa, P.; Cohen, O.; Garraffo, C. ^[2]; Huenemoerder, D. ^[3]; Korhonen, H. ^[4]; Granzer, T.

---

1. Center for Astrophysics and Space Astronomy, 389 UCB, University of Colorado, Boulder, CO 80309 (United States)
2. Harvard-Smithsonian Center for Astrophysics, Cambridge, MA (United States)
3. Massachusetts Institute of Technology, Cambridge, MA (United States)
4. Finnish Centre for Astronomy with ESO (FINCA), University of Turku, Väisäläntie 20, FI-21500 Piikkiö (Finland)

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{sup 4} K) together with chromospheric Mg ii 2800 Å and C ii 1335 Å (1–3 × 10{sup 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.

• OSTI ID: 22519970
• Journal Information: Astrophysical Journal, Supplement Series, Journal Name: Astrophysical Journal, Supplement Series Journal Issue: 1 Vol. 223; ISSN 0067-0049; ISSN APJSA2
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
FAR ULTRAVIOLET RADIATION
GIANT STARS
KEV RANGE
MAGNESIUM
PHOTOMETRY
POLARIMETRY
POWER TRANSMISSION
RED SHIFT
SOFT X RADIATION
SOLAR PROMINENCES
SPACE
SPIN
STELLAR CHROMOSPHERES
TELESCOPES
VOLATILITY