scholarly journals Wavelet analysis of the long-term activity of V833 Tau

2020 ◽  
Vol 495 (4) ◽  
pp. 3788-3794 ◽  
Author(s):  
R Stepanov ◽  
N I Bondar’ ◽  
M M Katsova ◽  
D Sokoloff ◽  
P Frick
Keyword(s):  
Solar Activity ◽  
Wavelet Analysis ◽  
Time Scales ◽  
Best Practice ◽  
Dynamo Theory ◽  
Theoretical Understanding ◽  
Stellar Activity ◽  
Order Of Magnitude ◽  
Consistent Method ◽  
Photometric Monitoring

ABSTRACT The bulk of available stellar activity observations is frequently checked for the manifestation of signs in comparison with the known characteristic of solar magnetic modulation. The problem is that stellar activity records are usually an order of magnitude shorter than available observations of solar activity variation. Therefore, the resolved time-scales of stellar activity are insufficient to decide reliably that a cyclic variation for a particular star is similar to the well-known 11-yr sunspot cycles. As a result, recent studies report several stars with double or multiple cycles which serve to challenge the underlying theoretical understanding. This is why a consistent method to separate ‘true’ cycles from stochastic variations is required. In this paper, we suggest that a conservative method, based on the best practice of wavelet analysis previously applied to the study of solar activity, for studying and interpreting the longest available stellar activity record – photometric monitoring of V833 Tau for more than 100 yr. We find that the observed variations of V833 Tau with time-scales of 2–50 yr should be comparable with the known quasi-periodic solar mid-term variations, whereas the true cycle of V833 Tau, if it exists, should be of about a century or even longer. We argue that this conclusion does not contradict the expectations from the stellar dynamo theory.

scholarly journals The Geometrical Structure of Activity in the AR Lac System

1983 ◽  
Vol 6 ◽  
pp. 650-650
Author(s):  
Gibor Basri ◽  
David Gibson ◽  
Fredrick Walter
Keyword(s):  
Solar Activity ◽  
Time Scales ◽  
Geometrical Structure ◽  
Good Reason ◽  
Stellar Rotation ◽  
Stellar Activity ◽  
Reasonable Time ◽  
X Ray ◽  
Short Period

Although solar activity is seen to exhibit a very inhomogeneous and convoluted set of structures, and we have good reason to expect that stellar activity is also very structured, it is naturally quite difficult to resolve such structures on other stars. One of the best opportunities for doing so is afforded by an active eclipsing system of short period, in which both the eclipses and stellar rotation serve to cover and uncover features on reasonable time scales. AR Lac is the nearest and most suitable such system, it is an RSCVn system comprised of an active G dwarf and active K subgiant with a two day period. We report here on simultaneous X-ray and UV coverage of an eclipse in this system obtained with the Einstein and IUE observations. More details are given in reports in IAU Coll. No. 71 and IAU Symp. No. 102.

scholarly journals The application of a new laminitis scoring method to model the rate and pattern of improvement from equine endocrinopathic laminitis in a clinical setting

2021 ◽  
Vol 17 (1) ◽  
Author(s):  
A. Meier ◽  
J. McGree ◽  
R. Klee ◽  
J. Preuß ◽  
D. Reiche ◽  
...  
Keyword(s):  
Best Practice ◽  
Clinical Status ◽  
Clinical Signs ◽  
Scoring Method ◽  
Pain Medications ◽  
Exponential Decay Model ◽  
History Of ◽  
Consistent Method ◽  
Foot Disease ◽  
New Treatments

Abstract Background Endocrinopathic, or hyperinsulinaemia-associated laminitis (HAL) is a common and debilitating equine foot disease, and although no pharmacological treatments are registered, several are under development. To evaluate the effect of such treatments, an accurate and consistent method is needed to track the clinical signs of laminitis over time, and the natural history of the disease, in terms of a ‘normal’ pattern of improvement, needs to be understood. This study examined the improvement pattern in clinical cases of naturally-occurring HAL subjected to a range of best-practice interventions, using two different scoring methods. Eighty horses and ponies with suspected HAL were enrolled in a study conducted at 16 veterinary practices across Germany. The severity of laminitis was assessed by independent veterinarians using both the traditional Obel method and a modified Obel method developed by Meier and colleagues. Assessments were made on the day of diagnosis (d 0), then on days 4, 9, 14, 25 and 42 during the intervention period. Pain medications were withheld for 24 h prior to clinical examination in all cases. Results Time to marked improvement from laminitis varied between individuals, but was difficult to monitor accurately using the Obel method, with the median grade being 2/4 on days 0 and 4, then 0/4 from d 9 onwards. More subtle changes could be identified using the Meier method, however, and the median scores were seen to follow the form of an exponential decay model in most horses, improving from 8/12 on d 0, to 0/12 on d 25. Within this composite scoring method, considerable variation was observed in the rate of improvement of individual clinical signs, with the average time taken for each sign to reach a median score of 0 ranging from 4 days (foot lift and weight shifting) to 25 days (gait when turned in a circle) across all 80 horses. Conclusions The Meier method provides a reliable and consistent method for monitoring the clinical status of horses with HAL, and despite the variability, the pattern of improvement described here should provide a useful benchmark against which individual cases and new treatments can be assessed.

scholarly journals On the relation between solar activity and seismicity on different time-scales

2002 ◽  
Vol 22 (3) ◽  
pp. 291-300
Author(s):  
Katya Georgieva ◽  
Boian Kirov ◽  
Atanasov Dimitar
Keyword(s):  
Solar Activity ◽  
Time Scales ◽  
Different Time Scales

scholarly journals Turbulence and magnetic fields in molecular clouds

1991 ◽  
Vol 147 ◽  
pp. 83-92
Author(s):  
R. N. Henriksen
Keyword(s):  
Magnetic Fields ◽  
Wavelet Analysis ◽  
Molecular Clouds ◽  
Fractal Structure ◽  
Compressible Turbulence ◽  
Dynamo Theory ◽  
First Results ◽  
Self Similar

in this paper I first review some of the simple structural concepts associated with compressible turbulence. In particular the hierarchical or self-similar fractal structure to be expected is formulated in a manner readily compared to the observations, and to previous work. In the next section I present the first results of a wavelet analysis on molecular clouds, which seem to comfirm the hierarchical scaling. I conclude with an extention of the theory to include magnetic fields. This latter theory represents an alternative to the more conventional dynamo theory.

scholarly journals The Near-Synchronous Polar Candidate V4633 Sgr (Nova Sagittarii 1998)

2004 ◽  
Vol 190 ◽  
pp. 176-177
Author(s):  
Y. Lipkin ◽  
E. M. Leibowitz
Keyword(s):  
Angular Momentum ◽  
Momentum Transfer ◽  
White Dwarf ◽  
Moment Of Inertia ◽  
The Other ◽  
Angular Momentum Transfer ◽  
Classical Nova ◽  
Order Of Magnitude ◽  
Photometric Monitoring ◽  
The Moment

AbstractThe classical nova V4633 Sgr (1998) exhibits two photometric periodicities. The shorter period (P1=3.01 hr) is stable, while the other one, longer by ~2.5%, has decreased monotonically since shortly after the nova eruption, with Ṗ2 ≈ –10−6 (Lipkin et al. 2001).Here we report on results of photometric monitoring of the star in 2001 and 2002. During our observations, the longer period decreased more, and in 2002 it was only 1.8% longer than P1 The decrease rate (Ṗ2) in 2001-2002 was an order of magnitude smaller than in 1998-2000.These new results support the Near-Synchronous Polar classification which was suggested for V4633 Sgr (Lipkin et al. 2001). In this model, the longer period of V4633 Sgr is the spin of the white dwarf, and its variation since 1998 reflects changes in the moment of inertia of the white dwarf, and angular momentum transfer in the system following the nova eruption.

Stellar activity and winds shaping the atmospheres of Earth-like planets

2018 ◽  
Vol 14 (S345) ◽  
pp. 181-184
Author(s):  
Theresa Lueftinger ◽  
Manuel Güdel ◽  
Sudeshna Boro Saikia ◽  
Colin Johnstone ◽  
Beatrice Kulterer ◽  
...  
Keyword(s):  
Magnetic Fields ◽  
Extreme Environments ◽  
Doppler Imaging ◽  
Research Network ◽  
Theoretical Understanding ◽  
Stellar Activity ◽  
Active Stars ◽  
Earth Like Planets ◽  
Stellar Magnetic Fields ◽  
Host Stars

AbstractPlanets orbiting young, active stars are embedded in an environment that is far from being as calm as the present solar neighbourhood. They experience the extreme environments of their host stars, which cannot have been without consequences for young stellar systems and the evolution of Earth-like planets to habitable worlds. Stellar magnetism and the related stellar activity are crucial drivers of ionization, photodissociation, and chemistry. Stellar winds can compress planetary magnetospheres and even strip away the outer layers of their atmospheres, thus having an enormous impact on the atmospheres and the magnetospheres of surrounding exoplanets. Modelling of stellar magnetic fields and their winds is extremely challenging, both from the observational and the theoretical points of view, and only ground breaking advances in observational instrumentation and a deeper theoretical understanding of magnetohydrodynamic processes in stars enable us to model stellar magnetic fields and their winds – and the resulting influence on the atmospheres of surrounding exoplanets – in more and more detail. We have initiated a national and international research network (NFN): ‘Pathways to Habitability – From Disks to Active Stars, Planets to Life’, to address questions on the formation and habitability of environments in young, active stellar/planetary systems. We discuss the work we are carrying out within this project and focus on how stellar evolutionary aspects in relation to activity, magnetic fields and winds influence the erosion of planetary atmospheres in the habitable zone. We present recent results of our theoretical and observational studies based on Zeeman Doppler Imaging (ZDI), field extrapolation methods, wind simulations, and the modeling of planetary upper atmospheres.

Markov-modulated traffic with nearly complete decomposability characteristics and associated fluid queueing models

1995 ◽  
Vol 27 (04) ◽  
pp. 1144-1185
Author(s):  
Kimon P. Kontovasilis ◽  
Nikolas M. Mitrou
Keyword(s):  
State Space ◽  
Time Scales ◽  
Structural Characteristics ◽  
Queueing Systems ◽  
Queuing Models ◽  
Aggregation Techniques ◽  
Phase Perturbation ◽  
Order Of Magnitude ◽  
Markov Modulated ◽  
The Individual

This paper considers fluid queuing models of Markov-modulated traffic that, due to large differences in the time-scales of events, possess structural characteristics that yield a nearly completely decomposable (NCD) state-space. Extension of domain decomposition and aggregation techniques that apply to approximating the eigensystem of Markov chains permits the approximate subdivision of the full system to a number of small, independent subsystems (decomposition phase), plus an ‘aggregative' system featuring a state-space that distinguishes only one index per subsystem (aggregation phase). Perturbation analysis reveals that the error incurred by the approximation is of an order of magnitude equal to the weak coupling of the NCD Markov chain. The study in this paper is then extended to the structure of NCD fluid models describing source superposition (multiplexing). It is shown that efficient spectral factorization techniques that arise from the Kronecker sum form of the global matrices can be applied through and combined with the decomposition and aggregation procedures. All structural characteristics and system parameters are expressible in terms of the individual sources multiplexed together, rendering the construction of the global system unnecessary. Finally, besides providing efficient computational algorithms, the work in this paper can be recast as a conceptual framework for the better understanding of queueing systems under the presence of events happening in widely differing time-scales.

scholarly journals Cosmic-ray propagation around the Sun: investigating the influence of the solar magnetic field on the cosmic-ray Sun shadow

2020 ◽  
Vol 633 ◽  
pp. A83
Author(s):  
J. Becker Tjus ◽  
P. Desiati ◽  
N. Döpper ◽  
H. Fichtner ◽  
J. Kleimann ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solar Activity ◽  
Solar Cycle ◽  
Cosmic Rays ◽  
Solar Magnetic Field ◽  
Cosmic Ray ◽  
High Energy ◽  
High Solar Activity ◽  
The Sun ◽  
Theoretical Understanding

The cosmic-ray Sun shadow, which is caused by high-energy charged cosmic rays being blocked and deflected by the Sun and its magnetic field, has been observed by various experiments, such as Argo-YBJ, Tibet, HAWC, and IceCube. Most notably, the shadow’s size and depth was recently shown to correlate with the 11-year solar cycle. The interpretation of such measurements, which help to bridge the gap between solar physics and high-energy particle astrophysics, requires a solid theoretical understanding of cosmic-ray propagation in the coronal magnetic field. It is the aim of this paper to establish theoretical predictions for the cosmic-ray Sun shadow in order to identify observables that can be used to study this link in more detail. To determine the cosmic-ray Sun shadow, we numerically compute trajectories of charged cosmic rays in the energy range of 5−316 TeV for five different mass numbers. We present and analyze the resulting shadow images for protons and iron, as well as for typically measured cosmic-ray compositions. We confirm the observationally established correlation between the magnitude of the shadowing effect and both the mean sunspot number and the polarity of the magnetic field during the solar cycle. We also show that during low solar activity, the Sun’s shadow behaves similarly to that of a dipole, for which we find a non-monotonous dependence on energy. In particular, the shadow can become significantly more pronounced than the geometrical disk expected for a totally unmagnetized Sun. For times of high solar activity, we instead predict the shadow to depend monotonously on energy and to be generally weaker than the geometrical shadow for all tested energies. These effects should become visible in energy-resolved measurements of the Sun shadow, and may in the future become an independent measure for the level of disorder in the solar magnetic field.

Sign in / Sign up

Export Citation Format

Share Document