scholarly journals Gaia-ESO Survey: Role of magnetic activity and starspots on pre-main-sequence lithium evolution

2021 ◽  
Author(s):  
E. Franciosini ◽  
E. Tognelli ◽  
S. Degl'Innocenti ◽  
P. G. Prada Moroni ◽  
S. Randich ◽  
...  
Keyword(s):  
Main Sequence ◽  
Magnetic Activity

The Main Sequence of Human Optokinetic Afternystagmus (OKAN)

2009 ◽  
Vol 101 (6) ◽  
pp. 2889-2897 ◽  
Author(s):  
Andre Kaminiarz ◽  
Kerstin Königs ◽  
Frank Bremmer
Keyword(s):  
Neural Networks ◽  
Eye Movements ◽  
Main Sequence ◽  
Critical Role ◽  
Saccade Target ◽  
Control Mechanisms ◽  
Visually Guided ◽  
Background Characteristics ◽  
Optokinetic Afternystagmus

Different types of fast eye movements, including saccades and fast phases of optokinetic nystagmus (OKN) and optokinetic afternystagmus (OKAN), are coded by only partially overlapping neural networks. This is a likely cause for the differences that have been reported for the dynamic parameters of fast eye movements. The dependence of two of these parameters—peak velocity and duration—on saccadic amplitude has been termed “main sequence.” The main sequence of OKAN fast phases has not yet been analyzed. These eye movements are unique in that they are generated by purely subcortical control mechanisms and that they occur in complete darkness. In this study, we recorded fast phases of OKAN and OKN as well as visually guided and spontaneous saccades under identical background conditions because background characteristics have been reported to influence the main sequence of saccades. Our data clearly show that fast phases of OKAN and OKN differ with respect to their main sequence. OKAN fast phases were characterized by their lower peak velocities and longer durations compared with those of OKN fast phases. Furthermore we found that the main sequence of spontaneous saccades depends heavily on background characteristics, with saccades in darkness being slower and lasting longer. On the contrary, the main sequence of visually guided saccades depended on background characteristics only very slightly. This implies that the existence of a visual saccade target largely cancels out the effect of background luminance. Our data underline the critical role of environmental conditions (light vs. darkness), behavioral tasks (e.g., spontaneous vs. visually guided), and the underlying neural networks for the exact spatiotemporal characteristics of fast eye movements.

scholarly journals Extended main sequence turnoffs in open clusters as seen by Gaia – I. NGC 2818 and the role of stellar rotation

2018 ◽  
Vol 480 (3) ◽  
pp. 3739-3746 ◽  
Author(s):  
N Bastian ◽  
S Kamann ◽  
I Cabrera-Ziri ◽  
C Georgy ◽  
S Ekström ◽  
...  
Keyword(s):  
Main Sequence ◽  
Open Clusters ◽  
Stellar Rotation

scholarly journals Eclipsing spotted giant star with K2 and historical photometry

2018 ◽  
Vol 620 ◽  
pp. A189 ◽  
Author(s):  
K. Oláh ◽  
S. Rappaport ◽  
T. Borkovits ◽  
T. Jacobs ◽  
D. Latham ◽  
...  
Keyword(s):  
Binary System ◽  
Main Sequence ◽  
Rapid Evolution ◽  
Magnetic Activity ◽  
Primary Component ◽  
Physical Parameters ◽  
Giant Star ◽  
Eclipsing Binary ◽  
Giant Stars ◽  
Active Stars

Context. Stars can maintain their observable magnetic activity from the pre-main sequence (PMS) to the tip of the red giant branch. However, the number of known active giants is much lower than active stars on the main sequence (MS) since the stars spend only about 10% of their MS lifetime on the giant branch. Due to their rapid evolution it is difficult to estimate the stellar parameters of giant stars. A possibility for obtaining more reliable stellar parameters for an active giant arises when it is a member of an eclipsing binary system. Aims. We have discovered EPIC 211759736, an active spotted giant star in an eclipsing binary system during the Kepler K2 Campaign 5. The eclipsing nature allows us to much better constrain the stellar parameters than in most cases of active giant stars. Methods. We have combined the K2 data with archival HATNet, ASAS, and DASCH photometry, new spectroscopic radial velocity measurements, and a set of follow-up ground-based BVRCIC photometric observations, to find the binary system parameters as well as robust spot models for the giant at two different epochs. Results. We determined the physical parameters of both stellar components and provide a description of the rotational and long-term activity of the primary component. The temperatures and luminosities of both components were examined in the context of the Hertzsprung–Russell diagram. We find that both the primary and the secondary components deviate from the evolutionary tracks corresponding to their masses in the sense that the stars appear in the diagram at lower masses than their true masses. Conclusions. We further evaluate the proposition that traditional methods generally result in higher masses for active giants than what is indicated by stellar evolution tracks in the HR diagram. A possible reason for this discrepancy could be a strong magnetic field, since we see greater differences in more active stars.

Model and theoretical seismicity

1967 ◽  
Vol 57 (3) ◽  
pp. 341-371 ◽  
Author(s):  
R. Burridge ◽  
L. Knopoff
Keyword(s):  
Numerical Model ◽  
Potential Energy ◽  
Main Sequence ◽  
Magnitude Scale ◽  
Laboratory Model ◽  
Earthquake Mechanism

abstract A laboratory and a numerical model have been constructed to explore the role of friction along a fault as a factor in the earthquake mechanism. The laboratory model demonstrates that small shocks are necessary to the loading of potential energy into the focal structure; a large part, but not all, of the stored potential energy is later released in a major shock, at the end of a period of loading energy into the system. By the introduction of viscosity into the numerical model, aftershocks take place following a major shock. Both models have features which describe the statistics of shocks in the main sequence, the statistics of aftershocks and the energy-magnitude scale, among others.

scholarly journals The effects of rotation on the lithium depletion of G- and K-dwarfs in Messier 35

2020 ◽  
Vol 500 (1) ◽  
pp. 1158-1177
Author(s):  
R D Jeffries ◽  
R J Jackson ◽  
Qinghui Sun ◽  
Constantine P Deliyannis
Keyword(s):  
Rotation Rate ◽  
Binary Systems ◽  
Main Sequence ◽  
Strong Relationship ◽  
Magnetic Activity ◽  
Rich Cluster ◽  
Stellar Radius ◽  
Rotation Periods ◽  
Probability Zero ◽  
Lithium Depletion

ABSTRACT New fibre spectroscopy and radial velocities from the WIYN telescope are used to measure photospheric lithium in 242 high-probability, zero-age main-sequence F- to K-type members of the rich cluster M35. Combining these with published rotation periods, the connection between lithium depletion and rotation is studied in unprecedented detail. At Teff < 5500 K there is a strong relationship between faster rotation and less Li depletion, although with a dispersion larger than measurement uncertainties. Components of photometrically identified binary systems follow the same relationship. A correlation is also established between faster rotation rate (or smaller Rossby number), decreased Li depletion and larger stellar radius at a given Teff. These results support models where star-spots and interior magnetic fields lead to inflated radii and reduced Li depletion during the pre-main-sequence (PMS) phase for the fastest rotators. However, the data are also consistent with the idea that all stars suffered lower levels of Li depletion than predicted by standard PMS models, perhaps because of deficiencies in those models or because saturated levels of magnetic activity suppress Li depletion equally in PMS stars of similar Teff regardless of rotation rate, and that slower rotators subsequently experience more mixing and post-PMS Li depletion.

scholarly journals Activity and rotation of the X-ray emitting Kepler stars

2019 ◽  
Vol 628 ◽  
pp. A41 ◽  
Author(s):  
D. Pizzocaro ◽  
B. Stelzer ◽  
E. Poretti ◽  
S. Raetz ◽  
G. Micela ◽  
...  
Keyword(s):  
White Light ◽  
Main Sequence ◽  
Magnetic Activity ◽  
Light Curves ◽  
Late Type ◽  
Main Sequence Stars ◽  
Photometric Variability ◽  
X Ray ◽  
Rotation Periods ◽  
Flare Frequency

The relation between magnetic activity and rotation in late-type stars provides fundamental information on stellar dynamos and angular momentum evolution. Rotation-activity studies found in the literature suffer from inhomogeneity in the measurement of activity indexes and rotation periods. We overcome this limitation with a study of the X-ray emitting, late-type main-sequence stars observed by XMM-Newton and Kepler. We measured rotation periods from photometric variability in Kepler light curves. As activity indicators, we adopted the X-ray luminosity, the number frequency of white-light flares, the amplitude of the rotational photometric modulation, and the standard deviation in the Kepler light curves. The search for X-ray flares in the light curves provided by the EXTraS (Exploring the X-ray Transient and variable Sky) FP-7 project allows us to identify simultaneous X-ray and white-light flares. A careful selection of the X-ray sources in the Kepler field yields 102 main-sequence stars with spectral types from A to M. We find rotation periods for 74 X-ray emitting main-sequence stars, 20 of which do not have period reported in the previous literature. In the X-ray activity-rotation relation, we see evidence for the traditional distinction of a saturated and a correlated part, the latter presenting a continuous decrease in activity towards slower rotators. For the optical activity indicators the transition is abrupt and located at a period of ~10 d but it can be probed only marginally with this sample, which is biased towards fast rotators due to the X-ray selection. We observe seven bona-fide X-ray flares with evidence for a white-light counterpart in simultaneous Kepler data. We derive an X-ray flare frequency of ~0.15 d−1, consistent with the optical flare frequency obtained from the much longer Kepler time-series.

scholarly journals Chromospheric variation in cool supergiant stars

1996 ◽  
Vol 176 ◽  
pp. 415-422
Author(s):  
J. A. Eaton ◽  
G. W. Henry
Keyword(s):  
Main Sequence ◽  
Active Regions ◽  
Magnetic Activity ◽  
Hybrid Stars ◽  
Magnetic Phenomena ◽  
Dividing Line

Stars close to the main sequence, if they rotate rapidly enough, show magnetic activity in the form of spots, active regions, and strong chromospheres. With the exception of the hybrid stars, stars cooler and more luminous than the so-called Linsky-Haisch dividing line, in contrast, are not known to have any of these phenomena. In fact, it is not clear such stars, even though rotating and convective, show any magnetic phenomena at all. We discuss (1) photometry used to search for spots in the hybrid stars, which we have not found, and (2) evidence for chromospheric variation in K supergiants that takes the form of enhanced winds, but which may be analogous to the activity of stars closer to the main sequence.

scholarly journals Differential Rotation and Magnetic Activity of the Lower Main Sequence Stars

1980 ◽  
Vol 51 ◽  
pp. 296-297
Author(s):  
G. Belvedere ◽  
L. Paterno ◽  
M. Stix
Keyword(s):  
Spherical Shell ◽  
Differential Rotation ◽  
Main Sequence ◽  
Magnetic Activity ◽  
The Sun ◽  
Coupling Constant ◽  
Main Sequence Stars ◽  
Dynamo Theory ◽  
Magnetic Cycles ◽  
Surface Convection

AbstractWe extend to the lower main sequence stars the analysis of convection interacting with rotation in a compressible spherical shell, already applied to the solar case (Belvedere and Paterno, 1977; Belvedere et al. 1979a). We assume that the coupling constant ε between convection and rotation, does not depend on the spectral type. Therefore we take ε determined from the observed differential rotation of the Sun, and compute differential rotation and magnetic cycles for stars ranging from F5 to MO, namely for those stars which are supposed to possess surface convection zones (Belvedere et al. 1979b, c, d). The results show that the strength of differential rotation decreases from a maximum at F5 down to a minimum at G5 and then increases towards later spectral types. The computations of the magnetic cycles based on the αω-dynamo theory show that dynamo instability decreases from F5 to G5, and then increases towards the later spectral types reaching a maximum at MO. The period of the magnetic cycles increases from a few years at F5 to about 100 years at MO. Also the extension of the surface magnetic activity increases substantially towards the later spectral types. The results are discussed in the framework of Wilson’s (1978) observations.

scholarly journals Thermonuclear Burning in the Envelope of an Accreting Neutron Star

1980 ◽  
Vol 88 ◽  
pp. 329-334 ◽  
Author(s):  
E. Ergma ◽  
T. Tutukov
Keyword(s):  
Neutron Star ◽  
Analytical Method ◽  
Main Sequence ◽  
Radiative Cooling ◽  
Hydrogen Burning ◽  
Heating Source ◽  
Thermonuclear Burning ◽  
Evolutionary Scenario ◽  
Low Mass

A simple analytical method has been used to investigate thermonuclear flashes in a degenerate envelope of an accreting neutron star. The heating source is the compression of envelope and the cooling is due to the radiative cooling of the envelope. The role of hydrogen burning is discussed. A possible evolutionary scenario for formation of preburster binaries consisting of a neutron star and a low mass main sequence star is proposed.

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