scholarly journals Pulsations of Be stars: time series analysis of He I λ4921

1994 ◽  
Vol 162 ◽  
pp. 100-101
Author(s):  
M. E. Hahula ◽  
D. R. Gies
Keyword(s):  
Time Series ◽  
Time Series Analysis ◽  
Mass Loss ◽  
Power Spectra ◽  
Phase Content ◽  
Be Stars ◽  
Optical Photometry ◽  
Multi Wavelength ◽  
Spectroscopy Optical ◽  
Nonradial Pulsation

We present the results of time series observations of He I λ4921 in the spectra of 10 Be stars. The spectra were obtained during multi-wavelength campaigns of IUE spectroscopy, optical photometry and polarimetry, and spectroscopy undertaken to study the connection (if any) between nonradial pulsation (NRP) and mass loss in Be stars. Power spectra have been calculated for the time series of intensity variations within the profiles. These were used to determine periodic variability and phase content to analyze the variations in the context of the NRP model. The observations were made at three observatories (Table 1). All the spectra record at least Hβ and He I λ4921 with a S/N > 200 per pixel and a resolution of ≈ 0.2 Å. We have concentrated the analysis on He I λ4921 as a probe of photospheric variability. This line is generally free of emission (unlike He I λ6678), but in some cases an Fe II λ4924 shell component appears in the red wing.

scholarly journals Mass-ejection events in Be stars triggered by coupled nonradial pulsation modes

2016 ◽  
Vol 12 (S329) ◽  
pp. 384-384
Author(s):  
D. Baade ◽  
Th. Rivinius ◽  
A. Pigulski ◽  
A. Carciofi ◽  
Keyword(s):  
Power Spectra ◽  
Unknown Origin ◽  
Circumstellar Matter ◽  
List Type ◽  
Be Stars ◽  
Aspect Angle ◽  
Stellar Pulsation ◽  
Mass Ejection ◽  
Nonradial Pulsation ◽  
High Cadence

AbstractBe stars (for an in-depth review see Rivinius, Carciofi & Martayan 2013) rotate at ⩾80% of the critical velocity and are multi-mode nonradial pulsators. Magnetic dipole fields are not detected, and binaries with periods less than 30 days are rare. The name-giving emission lines form in a Keplerian decretion disk, which is viscously re-accreted and also radiatively ablated unless replenished by outburts of unknown origin.Months-long, high-cadence space photometry with the BRITE-Constellation nanosatellites (Pablo et al. 2016) of about 10 early-type Be stars reveals the following (cf. Baade et al. 2016a, Baade et al. 2016b): ○Many Be stars exhibit 1 or 2 so-called Δ frequencies, which are differences between two nonradial-pulsation (NRP) frequencies and much lower (mostly less than 0.1 c/d) than the parent frequencies. The associated light curves are roughly sinusoidal. The amplitudes can exceed that of the sum of the parent amplitudes.○Conventional beat patterns also occur.○Amplitudes of both Δ and beat frequencies can temporarily be enhanced. Around phases of maximal amplitude the mean brightness is in- or decreased, and the scatter can be enhanced.○During high-activity phases (outbursts), broad and dense groups of numerous spikes arise in the power spectra. The two strongest groups often have a frequency ratio near 2. The phase coherence seems to be low.○Time coverage (less than half a year) is not yet sufficient to infer whether two Δ or beat frequencies can combine to cause long-lasting (years) superoutbursts (cf. Carciofi et al. 2012).From these observations it is concluded: •The variable mean brightness and the increased Δ-frequency amplitude and scatter trace the amount of near-circumstellar matter.•Increase or decrease of mean brightness is aspect-angle dependent (pole-on vs. equator-on).•Increased amounts of near-circumstellar matter are due to rotation-assisted mass ejections caused by coupled NRP modes.•Observations do not constrain the location of the coupling (atmosphere or stellar interior).•Broad frequency groups do not represent stellar pulsation modes but circumstellar variability.•Be stars later than B5 are less active and may in some cases even behave differently.

Dynamical Peculiarities of Concatenational Changes in Functional Cardiovascular Parameters

2018 ◽  
Vol 3 (82) ◽  
Author(s):  
Eurelija Venskaitytė ◽  
Jonas Poderys ◽  
Tadas Česnaitis
Keyword(s):  
Time Series ◽  
Time Series Analysis ◽  
Functional State ◽  
The Body ◽  
Functional Changes ◽  
High Intensity Training ◽  
Series Analysis ◽  
Greco Roman ◽  
St Segment ◽  
Standard Lead

Research  background  and  hypothesis.  Traditional  time  series  analysis  techniques,  which  are  also  used  for the analysis of cardiovascular signals, do not reveal the relationship between the  changes in the indices recorded associated with the multiscale and chaotic structure of the tested object, which allows establishing short-and long-term structural and functional changes.Research aim was to reveal the dynamical peculiarities of interactions of cardiovascular system indices while evaluating the functional state of track-and-field athletes and Greco-Roman wrestlers.Research methods. Twenty two subjects participated in the study, their average age of 23.5 ± 1.7 years. During the study standard 12 lead electrocardiograms (ECG) were recorded. The following ECG parameters were used in the study: duration of RR interval taken from the II standard lead, duration of QRS complex, duration of JT interval and amplitude of ST segment taken from the V standard lead.Research  results.  Significant  differences  were  found  between  inter-parametric  connections  of  ST  segment amplitude and JT interval duration at the pre and post-training testing. Observed changes at different hierarchical levels of the body systems revealed inadequate cardiac metabolic processes, leading to changes in the metabolic rate of the myocardium and reflected in the dynamics of all investigated interactions.Discussion and conclusions. It has been found that peculiarities of the interactions of ECG indices interactions show the exposure of the  functional changes in the body at the onset of the workload. The alterations of the functional state of the body and the signs of fatigue, after athletes performed two high intensity training sessions per day, can be assessed using the approach of the evaluation of interactions between functional variables. Therefore the evaluation of the interactions of physiological signals by using time series analysis methods is suitable for the observation of these processes and the functional state of the body.Keywords: electrocardiogram, time series, functional state.

The Contribution of Foreign Direct Investment for Economic Growth of Ethiopia: Time Series Analysis

2018 ◽  
Vol 9 (02) ◽  
Author(s):  
Addissie Melak
Keyword(s):  
Economic Growth ◽  
Time Series ◽  
Foreign Direct Investment ◽  
Time Series Analysis ◽  
Direct Investment ◽  
Policy Framework ◽  
Annual Growth Rate ◽  
African Countries ◽  
Series Analysis ◽  
Integration Test

Economic growth of countries is one of the fundamental questions in economics. Most African countries are opening their economies for welcoming of foreign investors. As such Ethiopia, like many African countries took measures to attract and improve foreign direct investment. The purpose of this study is to examine the contribution of foreign direct investment (FDI) for economic growth of Ethiopia over the period of 1981-2013. The study shows an overview of Ethiopian economy and investment environment by the help of descriptive and econometric methods of analysis to establish empirical investigation for the contribution of FDI on Ethiopian economy. OLS method of time series analysis is employed to analyse the data. The stationary of the variables have been checked by using Augmented Dickey Fuller (ADF) Unit Root test and hence they are stationery at first difference. The co- integration test also shows that there is a long run relationship between the dependent and independent variables. Accordingly, the finding of the study shows that FDI, GDP per capita, exchange rate, total investment as percentage of GDP, inflow of FDI stock, trade as percentage of GDP, annual growth rate of GDP and liberalization of the economy have positive impact on Ethiopian GDP. Whereas Gross fixed domestic investment, inflows of FDI and Gross capital formation influence economic growth of Ethiopia negatively. This finding suggests that there should be better policy framework to attract and improve the volume of FDI through creating conducive environment for investment.

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