scholarly journals Pulsational properties of ten new slowly pulsating B stars

2020 ◽  
Vol 633 ◽  
pp. A122 ◽  
Author(s):  
M. Fedurco ◽  
E. Paunzen ◽  
S. Hümmerich ◽  
K. Bernhard ◽  
Š. Parimucha
Keyword(s):  
Main Sequence ◽  
Time Series Data ◽  
Stellar Structure ◽  
Series Data ◽  
B Stars ◽  
Rotation Periods ◽  
Important Input ◽  
Stellar Models ◽  
Frequency Search ◽  
The Masses

Context. Slowly pulsating B (SPB) stars are upper main-sequence multi-periodic pulsators that show non-radial g-mode oscillations driven by the κ mechanism acting on the iron bump. These multi-periodic pulsators have great asteroseismic potential and can be employed for the calibration of stellar structure and evolution models of massive stars. Aims. We collected a sample of ten hitherto unidentified SPB stars with the aim of describing their pulsational properties and identifying pulsational modes. Methods. Photometric time series data from various surveys were collected and analyzed using diverse frequency search algorithms. We calculated astrophysical parameters and investigated the location of our sample stars in the log Teff vs. log L/L⊙ diagram. Current pulsational models were calculated and used for the identification of pulsational modes in our sample stars. An extensive grid of stellar models along with their g-mode eigenfrequencies was calculated and subsequently cross-matched with the observed pulsational frequencies. The best-fit models were then used in an attempt to constrain stellar parameters such as mass, age, metallicity, and convective overshoot. Results. We present detected frequencies, corresponding g-mode identifications, and the masses and ages of the stellar models producing the best frequency cross-matches. We partially succeeded in constraining stellar parameters, in particular concerning mass and age. Where applicable, rotation periods have been derived from the spacing of triplet component frequencies. No evolved SPB stars are present in our sample. We identify two candidate high-metallicity objects (HD 86424 and HD 163285), one young SPB star (HD 36999), and two candidate young SPB stars (HD 61712 and HD 61076). Conclusions. We demonstrate the feasibility of using ground-based observations to perform basic asteroseismological analyses of SPB stars. Our results significantly enlarge the sample of known SPB stars with reliable pulsational mode identifications, which provides important input parameters for modeling attempts aiming to investigate the internal processes at work in upper main-sequence stars.

scholarly journals Probing the size of a magnetosphere of a young solar-like star

2008 ◽  
Vol 4 (S259) ◽  
pp. 413-414
Author(s):  
Catrina M. Hamilton ◽  
C. M. Johns-Krull ◽  
R. Mundt ◽  
W. Herbst ◽  
J. N. Winn
Keyword(s):  
Time Series ◽  
High Resolution ◽  
Binary System ◽  
Line Profile ◽  
Main Sequence ◽  
Time Series Data ◽  
Young Stars ◽  
Series Data ◽  
Accretion Flows ◽  
Magnetospheric Accretion

AbstractWe have obtained high resolution spectra of the pre-main sequence binary system KH 15D (V582 Mon) while the star is fully visible, fully occulted, and during several ingress and egress events over the course of five contiguous observing seasons. The Hα line profile is a standard probe of the magnetospheric accretion flows on young stars such as KH 15D. We use these time series data to map out the size of the magnetosphere and find that it changes size from one observing season to the next.

scholarly journals Characterizing Sparse Asteroid Light Curves with Gaussian Processes

2021 ◽  
Vol 163 (1) ◽  
pp. 29
Author(s):  
Christina Willecke Lindberg ◽  
Daniela Huppenkothen ◽  
R. Lynne Jones ◽  
Bryce T. Bolin ◽  
Mario Jurić ◽  
...  
Keyword(s):  
Gaussian Processes ◽  
Time Series Data ◽  
Rotation Period ◽  
Light Curves ◽  
Series Data ◽  
Model Parameters ◽  
Wide Field ◽  
Pulse Profile ◽  
Rotation Periods ◽  
Period Detection

Abstract In the era of wide-field surveys like the Zwicky Transient Facility and the Rubin Observatory’s Legacy Survey of Space and Time, sparse photometric measurements constitute an increasing percentage of asteroid observations, particularly for asteroids newly discovered in these large surveys. Follow-up observations to supplement these sparse data may be prohibitively expensive in many cases, so to overcome these sampling limitations, we introduce a flexible model based on Gaussian processes to enable Bayesian parameter inference of asteroid time-series data. This model is designed to be flexible and extensible, and can model multiple asteroid properties such as the rotation period, light-curve amplitude, changing pulse profile, and magnitude changes due to the phase-angle evolution at the same time. Here, we focus on the inference of rotation periods. Based on both simulated light curves and real observations from the Zwicky Transient Facility, we show that the new model reliably infers rotational periods from sparsely sampled light curves and generally provides well-constrained posterior probability densities for the model parameters. We propose this framework as an intermediate method between fast but very limited-period detection algorithms and much more comprehensive but computationally expensive shape-modeling based on ray-tracing codes.

scholarly journals Stellar models of rotating, pre-main sequence low-mass stars with magnetic fields

2013 ◽  
Vol 9 (S302) ◽  
pp. 112-113 ◽  
Author(s):  
Luiz T. S. Mendes ◽  
Natália R. Landin ◽  
Luiz P. R. Vaz
Keyword(s):  
Magnetic Fields ◽  
Stellar Evolution ◽  
Large Scale ◽  
Main Sequence ◽  
Stellar Structure ◽  
Low Mass Stars ◽  
Large Scale Magnetic Field ◽  
Low Mass ◽  
Structure Equations ◽  
Stellar Models

AbstractWe report our present efforts for introducing magnetic fields in the ATON stellar evolution code code, which now evolved to truly modifying the stellar structure equations so that they can incorporate the effects of an imposed, large-scale magnetic field. Preliminary results of such an approach, as applied to low-mass stellar models, are presented and discussed.

scholarly journals Recent Theoretical Results for Cepheid Pulsation

1980 ◽  
Vol 5 ◽  
pp. 487-488
Author(s):  
Arthur N. Cox
Keyword(s):  
Main Sequence ◽  
Red Giants ◽  
Theoretical Studies ◽  
Reasonable Accuracy ◽  
Instability Strip ◽  
B Stars ◽  
Stellar Pulsation ◽  
Theoretical Investigations ◽  
The Masses ◽  
Theoretical Results

Detailed theoretical investigations of stellar pulsation need a mass and a composition before models can be constructed for study. Unfortunately, for the last ten years the masses of the Cepheids, which can be determined with reasonable accuracy by six different methods, have been in dispute. One possible way to resolve these various mass anomalies is to postulate an inhomogeneous composition envelope structure. Thus the principal problem in current theoretical studies is: What are both the masses and envelope compositions of Cepheids?Stellar evolution theory has indicated that main sequence B stars evolve to become red giants or supergiants and then loop blueward in the Hertzsprung-Russell diagram to cross again the pulsation instability strip the second and third (or even more) times. The second and third crossings are the slowest for models of evolutionary masses between 4 and 13 M⊙. Both below and above this mass the stars become Cepheids (or δ Scuti variables at the lowest masses) on their sole crossing to the red. Massive stars do not become cool enough to become Cepheids if the main sequence mass is above 18 M⊙.

scholarly journals Multiplicity in 5 M⊙ stars

2010 ◽  
Vol 6 (S272) ◽  
pp. 537-538
Author(s):  
Nancy Remage Evans
Keyword(s):  
Main Sequence ◽  
Mass Ratio ◽  
Subsequent Evolution ◽  
B Stars ◽  
X Ray ◽  
Triple Systems ◽  
High Fraction ◽  
Low Mass ◽  
M Stars ◽  
The Masses

AbstractBinary/multiple status can affect stars at all stages of their lifetimes: evolution onto the main sequence, properties on the main sequence, and subsequent evolution. 5 M⊙ stars have provided a wealth of information about the binary properties fairly massive stars. The combination of cool evolved primaries and hot secondaries in Cepheids (geriatric B stars) have yielded detailed information about the distribution of mass ratios. and have also provided a surprisingly high fraction of triple systems. Ground-based radial velocity orbits combined with satellite data from Hubble, FUSE, IUE, and Chandra are needed to provide full information about the systems, including the masses. As a recent example, X-ray observations can identify low mass companions which are young enough to be physical companions. Typically binary status and properties (separation, eccentricity, mass ratio) determine whether any stage of evolution takes an exotic form.

scholarly journals Earth’s albedo time series reveals low radiative energy input in December 2020

2021 ◽  
Author(s):  
Antti Penttilä ◽  
Karri Muinonen ◽  
Olli Ihalainen ◽  
Elizaveta Uvarova ◽  
Mikko Vuori ◽  
...  
Keyword(s):  
Time Series ◽  
Time Series Data ◽  
Radiative Energy ◽  
Series Data ◽  
Radiation Balance ◽  
The Sun ◽  
The Earth ◽  
Important Input ◽  
Low Earth Orbits ◽  
Earth Orbits

Abstract The Earth’s spherical albedo describes the ratio of light reflected from the Earth to that incident from the Sun, an important input variable for the Earth’s radiation balance. The spherical albedo has been previously estimated from satellites in low-Earth orbits, and from light reflected from the Moon. However, neither of these methods can produce continuous time series of the entire planet. We developed a global method to derive the Earth’s spherical albedo using the images from the Earth Polychromatic Imaging Camera (EPIC) on board NOAA’s Deep Space Climate Observatory (DSCOVR). The satellite is located in the Lagrange 1 point between the Earth and the Sun and observes the complete illuminated part of the Earth at once. The method allows us to provide continuously updated spherical albedo time series data starting from 2015. This time series shows a systematic seasonal variation with the mean annual albedo estimated as 0.295±0.008 and an exceptional albedo maximum in 2020, attributed to unusually abundant cloudiness over the Southern Oceans.

scholarly journals A SEARCH FOR PULSATION IN TWENTY-ONE WHITE DWARFS

2020 ◽  
Vol 56 (2) ◽  
pp. 193-199
Author(s):  
E. Paunzen ◽  
G. Handler ◽  
J. Janík ◽  
Z. Zemanová ◽  
M. Rode-Paunzen ◽  
...  
Keyword(s):  
Time Series ◽  
White Dwarfs ◽  
Time Series Data ◽  
Series Data ◽  
Upper Limits ◽  
Important Input

Well-defined astrophysical constraints of white dwarfs (WDs), such as on the presence or absence of pulsational variability, are very much needed to refine and develop current models. Because these stars are rather faint and variability periods are mostly below one hour, only a very limited amount of space-based data is currently available for these objects. We present about 68 hours of highquality ground-based photometric time-series data for twenty-one WDs acquired at five different observatories. No new pulsators were detected but the derived upper limits of variability, which are typically on the order of only a few mmags, provide important input for pulsation models.

scholarly journals X-Ray Binaries and Related Systems

1992 ◽  
Vol 151 ◽  
pp. 91-101
Author(s):  
Virginia Trimble
Keyword(s):  
Neutron Stars ◽  
Main Sequence ◽  
Gamma Ray ◽  
X Rays ◽  
X Ray ◽  
Ss 433 ◽  
Rotation Periods ◽  
Time Domains ◽  
The Masses ◽  
X Ray Binaries

Neutron stars and a few black holes in binaries reveal their presence by emitting X-rays when they accrete gas from their companions via a wind or disk. Related objects include SS 433, Geminga, gamma ray bursters, TeV/PeV sources, and the source in CTB 108. Systems with secondaries 8 Mo are the natural descendents of main sequence OB binaries. Those with secondaries ≤ 1 Mo arguably form some other way. These systems display a wealth of structure in both wavelength and time domains, much of which is reasonably well understood. Among the things we would like to know more about are the masses and rotation periods of the neutron stars in the two main kinds of systems.

Graphical Exploratory Data Analysis for Categorical Longitudinal and Time Series Data

2013 ◽  
Author(s):  
Stephen J. Tueller ◽  
Richard A. Van Dorn ◽  
Georgiy Bobashev ◽  
Barry Eggleston
Keyword(s):  
Time Series ◽  
Data Analysis ◽  
Exploratory Data Analysis ◽  
Time Series Data ◽  
Series Data ◽  
Exploratory Data

Some statistical and CI models to predict chaotic high-frequency financial data

2020 ◽  
Vol 39 (5) ◽  
pp. 6419-6430
Author(s):  
Dusan Marcek
Keyword(s):  
Time Series Data ◽  
Moving Average ◽  
Methodological Approach ◽  
Back Propagation ◽  
Large Data ◽  
Series Data ◽  
Data Set ◽  
Training Time ◽  
Optimal Population ◽  
Forecast Time

To forecast time series data, two methodological frameworks of statistical and computational intelligence modelling are considered. The statistical methodological approach is based on the theory of invertible ARIMA (Auto-Regressive Integrated Moving Average) models with Maximum Likelihood (ML) estimating method. As a competitive tool to statistical forecasting models, we use the popular classic neural network (NN) of perceptron type. To train NN, the Back-Propagation (BP) algorithm and heuristics like genetic and micro-genetic algorithm (GA and MGA) are implemented on the large data set. A comparative analysis of selected learning methods is performed and evaluated. From performed experiments we find that the optimal population size will likely be 20 with the lowest training time from all NN trained by the evolutionary algorithms, while the prediction accuracy level is lesser, but still acceptable by managers.

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