scholarly journals Superflares on the late-type giant KIC 2852961

2020 ◽  
Vol 641 ◽  
pp. A83 ◽  
Author(s):  
Zs. Kővári ◽  
K. Oláh ◽  
M. N. Günther ◽  
K. Vida ◽  
L. Kriskovics ◽  
...  
Keyword(s):  
Magnetic Energy ◽  
Magnetic Activity ◽  
Linear Functions ◽  
Flare Activity ◽  
Late Type ◽  
Dynamo Action ◽  
Giant Stars ◽  
Flare Energy ◽  
Type Giant ◽  
Stellar Properties

Context. The most powerful superflares reaching 1039 erg bolometric energy are from giant stars. The mechanism behind flaring is thought to be the magnetic reconnection, which is closely related to magnetic activity (including starspots). However, it is poorly understood how the underlying magnetic dynamo works and how the flare activity is related to the stellar properties that eventually control the dynamo action. Aims. We analyze the flaring activity of KIC 2852961, a late-type giant star, in order to understand how its flare statistics are related to those of other stars with flares and superflares, and to understand the role of the observed stellar properties in generating flares. Methods. We searched for flares in the full Kepler dataset of KIC 2852961 using an automated technique together with visual inspection. We cross-matched the flare-like events detected by the two different approaches and set a final list of 59 verified flares during the observing term. We calculated flare energies for the sample and performed a statistical analysis. Results. The stellar properties of KIC 2852961 are revised and a more consistent set of parameters are proposed. The cumulative flare energy distribution can be characterized by a broken power law; that is to say, on the log-log representation the distribution function is fitted by two linear functions with different slopes, depending on the energy range fitted. We find that the total flare energy integrated over a few rotation periods correlates with the average amplitude of the rotational modulation due to starspots. Conclusions. Flares and superflares seem to be the result of the same physical mechanism at different energy levels, also implying that late-type stars in the main sequence and flaring giant stars have the same underlying physical process for emitting flares. There might be a scaling effect behind the generation of flares and superflares in the sense that the higher the magnetic activity, the higher the overall magnetic energy released by flares and/or superflares.

Magnesium emission variability among late-type giant stars

1982 ◽  
Vol 253 ◽  
pp. 716 ◽  
Author(s):  
D. J. Mullan ◽  
R. E. Stencel
Keyword(s):  
Late Type ◽  
Giant Stars ◽  
Type Giant

scholarly journals Stellar activity

1986 ◽  
Vol 118 ◽  
pp. 283-283
Author(s):  
D. K. Duncan
Keyword(s):  
Sunspot Cycle ◽  
Late Type ◽  
Stellar Activity ◽  
Giant Stars ◽  
Rotation Periods ◽  
Type Giant

We have been monitoring the CaII H and K emission in late-type giant stars using the Mt Wilson 60-inch telescope. It is a continuation of work that Olin Wilson began almost 20 years ago. As a result not only have starspot cycles been detected (equivalent to the solar sunspot cycle), but rotation periods have now been measured.

scholarly journals Surface magnetism of cool giant and supergiant stars

2013 ◽  
Vol 9 (S302) ◽  
pp. 350-358
Author(s):  
Heidi Korhonen
Keyword(s):  
Binary Systems ◽  
Magnetic Activity ◽  
Close Binary ◽  
Surface Magnetism ◽  
Giant Stars ◽  
The Past ◽  
Activity Cycles ◽  
Photometric Monitoring ◽  
Type Giant

AbstractThe existence of starspots on late-type giant stars in close binary systems, that exhibit rapid rotation due to tidal locking, has been known for more than five decades. Photometric monitoring spanning decades has allowed studying the long-term magnetic activity in these stars revealing complicated activity cycles. The development of observing and analysis techniques that has occurred during the past two decades has also enabled us to study the detailed starspot and magnetic field configurations on these active giants. In the recent years magnetic fields have also been detected on slowly rotating giants and supergiant stars. In this paper I review what is known of the surface magnetism in the cool giant and supergiant stars.

Luminosity and Temperature from Near-Infrared Spectra of Late-Type Giant Stars

1997 ◽  
Vol 113 ◽  
pp. 1411 ◽  
Author(s):  
S. V. Ramirez ◽  
D. L. Depoy ◽  
Jay A. Frogel ◽  
K. Sellgren ◽  
R. D. Blum
Keyword(s):  
Infrared Spectra ◽  
Near Infrared ◽  
Late Type ◽  
Giant Stars ◽  
Near Infrared Spectra ◽  
Type Giant

scholarly journals Absolute Measurements of Starspot Area and Temperature

1993 ◽  
Vol 137 ◽  
pp. 193-195
Author(s):  
James E. Neff ◽  
Douglas O’Neal ◽  
Steven H. Saar
Keyword(s):  
Magnetic Field ◽  
Magnetic Activity ◽  
Local Magnetic Field ◽  
The Sun ◽  
Late Type ◽  
Solar Observations ◽  
Absolute Measure ◽  
Standard Picture ◽  
Stellar Properties ◽  
Absolute Measurements

Photometric and spectroscopic variability of late-type stars frequently has been interpreted as evidence of magnetic activity. The standard picture of stellar activity – inherited from solar observations – includes cool, dark “spots” in the photosphere and hot, dense regions in the chromosphere and coronae. The immediate cause of each of these phenomena is a closed topology of the local magnetic field. Because stars appear as mere points of light, these localized phenomena have not been directly resolvable on stars other than the Sun. Most observed effects are produced by an asymmetric distribution of starspots. If the distribution is symmetric, it would escape detection by most current techniques of light-curve and line-profile modeling. Even more troubling, the stellar properties measured with these techniques describe only a difference between contrasting hemispheres, not an absolute measure.

scholarly journals Doppler Images of Spotted Late-Type Stars

1988 ◽  
Vol 132 ◽  
pp. 253-272 ◽  
Author(s):  
Steven S. Vogt
Keyword(s):  
Magnetic Activity ◽  
Doppler Imaging ◽  
Type Star ◽  
Quality Data ◽  
High Signal ◽  
Rotating Stars ◽  
Late Type ◽  
Dynamo Action ◽  
Type Boundary ◽  
Rapidly Rotating Stars

Doppler imaging is a technique for deriving resolved images of rapidly rotating stars from a detailed analysis of very high signal-to-noise high resolution spectral line profiles. An improved version of this technique is presented, which now uses principles of maximum entropy image reconstruction to invert the line profile information. The effects that noise, finite resolution, and uncertainties in the assumed stellar physics have on the resultant images were explored through various test simulations. The technique is found to be efficient, accurate, and robust at deriving images of certain classes of stars from realistic quality data. Doppler images are presented of two spotted late-type stars, the RS CVn-type star HR 1099, and the FK Com-type star HD 199178. Both stars show surprisingly similar spot distributions. In each case, there is a single large cool spot straddling the pole, and a number of small cool spots at low latitudes. We expect that the small low latitude spots on each star will migrate poleward to join the polar spot, and suspect that the observed long-lived polar spots are the result of the poleward migration and merging of many active region complexes. If true, the poleward migration of starspots suggests that magnetic activity on very rapidly rotating stars is qualitatively different than that seen on our Sun. We suggest that the observed rotational trigger velocity for the appearance of large spots on late-type stars marks the transition from solar-type boundary layer dynamos to distributed dynamos, which occur only in more rapidly rotating stars. The sizes, locations, and migrations of the spots, however, may be more a result of the convective flow patterns than of any dynamo action, since the spots are quite long-lived.

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