X‐Ray Spectroscopic Signatures of the Extended Corona of FK Comae

Drake, J. J.; Chung, Sun Mi; Kashyap, Vinay; Korhonen, H.; Ballegooijen, A. A. van; Elstner, D.

doi:10.1086/587443

Cited by 12 publications

(22 citation statements)

References 41 publications

(63 reference statements)

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“…Line broadening in YY Men at levels of 100-200 km s −1 could indicate a coronal source confined to about one pressure scale height or ≈3R * above the equator, but the extremely high coronal temperatures around 40 MK make Doppler thermal broadening equally important . Near-polar X-ray sources confined to a height of ≈1R * are indicated in the prototype FK Com, based on line shifts, line broadening, and comparison with surface Doppler images (Drake et al 2008). …”

Section: Rotation and Orbital Motionmentioning

confidence: 99%

Plasma Motion and Kinematics in Cool and Hot Stars

Güdel

Nazé

2010

Space Sci Rev

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The environments of both hot and cool stars are the sites of highly dynamic processes involving motion of gas and plasma in winds, flows across shocks, plasma motions in closed magnetic fields, or streams along magnetospheric accretion funnels. X-ray spectroscopy has opened new windows toward the study of these processes. Kinematics are evident in line shifts and line broadening, and also more indirectly through the analysis and interpretation of density-sensitive lines. In hot stellar winds, expanding-wind kinematics are directly seen in broadened lines although the broadening has turned out to often be smaller than anticipated, and some lines are so narrow that coronal models have been revived. Although X-ray spectra of cool stars have shown line shifts and broadening due to the kinematics of the entire corona, e.g., in binary systems, intrinsic mass motions are challenging to observe at the presently available resolution. Much indirect evidence for mass motion in magnetic coronae is nevertheless available. And finally, spectral diagnostics has also led to a new picture of X-ray production in accreting pre-main sequence stars where massive accretion flows collide with the photospheric gas, producing shocks in which gas is heated to high temperatures. We summarize evidence for the above mechanisms based on spectroscopic data from XMM-Newton and Chandra.

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Section: Rotation and Orbital Motionmentioning

confidence: 99%

Plasma Motion and Kinematics in Cool and Hot Stars

Güdel

Nazé

2010

Space Sci Rev

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“…The star shows signs of activity from photosphere to corona (Merrill 1948;Chugainov 1966;Ramsey et al 1981;Dorren et al 1984;Oliveira & Foing 1999;Ayres et al 2006;Drake et al 2008). FK Com was also the first object where the so-called flip-flop phenomenon was observed (Jetsu et al 1993(Jetsu et al , 1994: it shows active longitudes separated by ∼180…”

Section: Introductionmentioning

confidence: 99%

Study of FK Comae Berenices

Vida

Korhonen

Ilyin

et al. 2015

A&A

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Aims. We study the connection between the chromospheric and photospheric behaviour of the active late-type star FK Comae. Methods. We use spot temperature modelling, light curve inversion based on narrow-and wide-band photometric measurements, Hα observations from 1997−2010, and Doppler maps from 2004−2010 to compare the behaviour of chromospheric and photospheric features. Results. Investigating low-resolution Hα spectra, we find that the changes in the chromosphere seem to happen mainly on a time scale longer than a few hours, but shorter variations are also observed. According to the Hα measurements, prominences are often found in the chromosphere that reach to more than a stellar radius and are stable for weeks, and they seem to be often, but not always connected to dark photospheric spots. The rotational modulation of the Hα emission typically seems to be anticorrelated with the light curve, but we did not find convincing evidence of a clear connection in the long-term trends of the Hα emission and the brightness of the star. In addition, FK Com seems to be in an unusually quiet state in 2009−2010 with very little chromospheric activity and low spot contrast, which might indicate the long-term decrease in activity.

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“…Jetsu et al 1994a;Oláh et al 2006;Panov & Dimitrov 2007;Korhonen et al 2009a;Hughes & McLean 1987;Bopp & Stencel 1981;Ayres et al 2006;Drake et al 2008).…”

Section: Introductionmentioning

confidence: 99%

Flip-flops of FK Comae Berenices

Hackman

Pelt

Mantere

et al. 2013

A&A

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Context. FK Comae Berenices is a rapidly rotating magnetically active star, the light curve of which is modulated by cool spots on its surface. It was the first star where the "flip-flop" phenomenon was discovered. Since then, flip-flops in the spot activity have been reported in many other stars. Follow-up studies with increasing length have shown, however, that the phenomenon is more complex than was thought right after its discovery. Aims. Therefore, it is of interest to perform a more thorough study of the evolution of the spot activity in FK Com. In this study, we analyse 15 years of photometric observations with two different time series analysis methods, with a special emphasis on detecting flip-flop type events from the data. Methods. We apply the continuous period search and carrier fit methods on long-term standard Johnson-Cousins V-observations from the years 1995−2010. The observations were carried out with two automated photometric telescopes, Phoenix-10 and Amadeus T7 located in Arizona. Results. We identify complex phase behaviour in 6 of the 15 analysed data segments. We identify five flip-flop events and two cases of phase jumps, where the phase shift is Δφ < 0.4. In addition we see two mergers of spot regions and two cases where the apparent phase shifts are caused by spot regions drifting with respect to each other. Furthermore we detect variations in the rotation period corresponding to a differential rotation coefficient of |k| > 0.031. Conclusions. The flip-flop cannot be interpreted as a single phenomenon, where the main activity jumps from one active longitude to another. In some of our cases the phase shifts can be explained by differential rotation: two spot regions move with different angular velocity and even pass each other. Comparison between the methods show that the carrier fit utility is better in retrieving slow evolution especially from a low amplitude light curve, while the continuous period search is more sensitive in case of rapid changes.

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X‐Ray Spectroscopic Signatures of the Extended Corona of FK Comae

Cited by 12 publications

References 41 publications

Plasma Motion and Kinematics in Cool and Hot Stars

Plasma Motion and Kinematics in Cool and Hot Stars

Study of FK Comae Berenices

Flip-flops of FK Comae Berenices

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