scholarly journals Predictions on the Number of Variable Stars for the GAIA Space Mission and for Surveys such as the Ground-Based International Liquid Mirror Telescope

2000 ◽  
Vol 176 ◽  
pp. 71-72 ◽  
Author(s):  
Laurent Eyer ◽  
Jan Cuypers
Keyword(s):  
Time Series ◽  
Space Mission ◽  
Variable Stars ◽  
Photometric Data ◽  
Huge Number ◽  
Future Space ◽  
Survey Instruments ◽  
Mirror Telescope ◽  
Stars Survey

AbstractFuture space and ground-based survey programmes will produce an impressive amount of photometric data. The GAIA space mission will map the complete sky down to V = 20m, and produce time series for about 1 billion stars. Survey instruments such as the International Liquid Mirror Telescope will observe slices of the sky down to V = 23m. In both experiments, the opportunity exists to discover a huge number of variable stars. Predictions of the expected total number of variable stars and the number of variables in specific subgroups are given.

scholarly journals Asteroseismology from Dome A, Antarctica

2013 ◽  
Vol 9 (S301) ◽  
pp. 409-410
Author(s):  
J. N. Fu ◽  
W. K. Zong ◽  
Y. Yang ◽  
A. Moore ◽  
M. C. B. Ashley ◽  
...  
Keyword(s):  
Time Series ◽  
Variable Stars ◽  
Photometric Data ◽  
Dome A ◽  
Pulsating Variable Stars ◽  
Scientific Potential

AbstractGattini and CSTAR have been installed at Dome A, Antarctica, which provide time-series photometric data for a large number of pulsating variable stars. We present the study for several variable stars with the data collected with the two facilities in 2009 to demonstrate the scientific potential of observations from Dome A for asteroseismology.

scholarly journals Nonlinear Time-Series Analysis of Pulsation of Post-AGB Stars by Genetic Algorithm/Neural Network Hybrid Systems

2000 ◽  
Vol 176 ◽  
pp. 135-136
Author(s):  
Toshiki Aikawa
Keyword(s):  
Neural Network ◽  
Genetic Algorithm ◽  
Neural Networks ◽  
Time Series ◽  
Artificial Neural Networks ◽  
Hybrid System ◽  
Nonlinear Time Series ◽  
Photometric Data ◽  
Nonlinear Time Series Analysis ◽  
Agb Stars

AbstractSome pulsating post-AGB stars have been observed with an Automatic Photometry Telescope (APT) and a considerable amount of precise photometric data has been accumulated for these stars. The datasets, however, are still sparse, and this is a problem for applying nonlinear time series: for instance, modeling of attractors by the artificial neural networks (NN) to the datasets. We propose the optimization of data interpolations with the genetic algorithm (GA) and the hybrid system combined with NN. We apply this system to the Mackey–Glass equation, and attempt an analysis of the photometric data of post-AGB variables.

scholarly journals An autoregressive model for irregular time series of variable stars

2016 ◽  
Vol 12 (S325) ◽  
pp. 259-262
Author(s):  
Susana Eyheramendy ◽  
Felipe Elorrieta ◽  
Wilfredo Palma
Keyword(s):  
Time Series ◽  
Gravitational Lensing ◽  
Autoregressive Model ◽  
Likelihood Estimation ◽  
Estimation Procedure ◽  
Variable Stars ◽  
Light Curves ◽  
Finite Sample ◽  
Harmonic Model ◽  
Dependency Structure

AbstractThis paper discusses an autoregressive model for the analysis of irregularly observed time series. The properties of this model are studied and a maximum likelihood estimation procedure is proposed. The finite sample performance of this estimator is assessed by Monte Carlo simulations, showing accurate estimators. We implement this model to the residuals after fitting an harmonic model to light-curves from periodic variable stars from the Optical Gravitational Lensing Experiment (OGLE) and Hipparcos surveys, showing that the model can identify time dependency structure that remains in the residuals when, for example, the period of the light-curves was not properly estimated.

scholarly journals Prospects of Variable Star Research by Future Space Missions

2000 ◽  
Vol 176 ◽  
pp. 41-45
Author(s):  
Laurent Eyer
Keyword(s):  
Time Series ◽  
Variable Star ◽  
Space Missions ◽  
Planet Detection ◽  
Pulsation Mode ◽  
National Space ◽  
Future Space ◽  
The Future

AbstractESA and NASA are studying projects having a tremendous return on variable star research. Other national space agencies are also studying or developing projects of smaller costs but with impressive returns. The projects range from global Galactic surveys like the ESA mission GAIA which will give photometric time series for about 1 billion stars, to detailed pulsation-mode studies like the CNES mission COROT which could reach a photometric precision lower than 1 ppm. The presentation will emphasize the future astrometric, asteroseismological and planet detection missions.

scholarly journals Discrete-time autoregressive model for unequally spaced time-series observations

2019 ◽  
Vol 627 ◽  
pp. A120 ◽  
Author(s):  
Felipe Elorrieta ◽  
Susana Eyheramendy ◽  
Wilfredo Palma
Keyword(s):  
Time Series ◽  
State Space ◽  
Discrete Time ◽  
Likelihood Estimation ◽  
Variable Stars ◽  
Space Representation ◽  
Finite Sample ◽  
Unequally Spaced ◽  
Astronomical Time ◽  
Astronomical Time Series

Most time-series models assume that the data come from observations that are equally spaced in time. However, this assumption does not hold in many diverse scientific fields, such as astronomy, finance, and climatology, among others. There are some techniques that fit unequally spaced time series, such as the continuous-time autoregressive moving average (CARMA) processes. These models are defined as the solution of a stochastic differential equation. It is not uncommon in astronomical time series, that the time gaps between observations are large. Therefore, an alternative suitable approach to modeling astronomical time series with large gaps between observations should be based on the solution of a difference equation of a discrete process. In this work we propose a novel model to fit irregular time series called the complex irregular autoregressive (CIAR) model that is represented directly as a discrete-time process. We show that the model is weakly stationary and that it can be represented as a state-space system, allowing efficient maximum likelihood estimation based on the Kalman recursions. Furthermore, we show via Monte Carlo simulations that the finite sample performance of the parameter estimation is accurate. The proposed methodology is applied to light curves from periodic variable stars, illustrating how the model can be implemented to detect poor adjustment of the harmonic model. This can occur when the period has not been accurately estimated or when the variable stars are multiperiodic. Last, we show how the CIAR model, through its state space representation, allows unobserved measurements to be forecast.

scholarly journals New results on OGLE Cepheids and PL relations in the LMC and SMC

2004 ◽  
Vol 193 ◽  
pp. 75-82
Author(s):  
A. Udalski
Keyword(s):  
Gravitational Lensing ◽  
Variable Stars ◽  
Magellanic Clouds ◽  
Photometric Data ◽  
Second Phase ◽  
Internet Archive ◽  
Pulsating Stars ◽  
Third Phase ◽  
Pulsating Variable Stars ◽  
Star Field

AbstractWe present results of the search for pulsating variable stars in the Magellanic Cloud fields covering central parts of these galaxies. The data were collected during the second phase of the Optical Gravitational Lensing Experiment survey (OGLE-II) from 1997 to 2000. In total, several thousand pulsating stars (Cepheids, RR Lyr) were found in both Magellanic Clouds. The photometric data of all objects are available to the astronomical community from the OGLE Internet archive. We present basic properties of pulsating stars in the Magellanic Clouds including Period–Luminosity relations for Cepheids. We also discuss observational prospects for the pulsating star field in the ongoing third phase of the OGLE project (OGLE-III) which started in 2001.

scholarly journals The Carina Dwarf Galaxy Variable Star Population

2002 ◽  
Vol 185 ◽  
pp. 134-135
Author(s):  
V. Ripepi ◽  
M. Dall’Ora ◽  
L. Pulone ◽  
M. Castellani ◽  
C. Corsi ◽  
...  
Keyword(s):  
Variable Star ◽  
Dwarf Galaxy ◽  
Variable Stars ◽  
Photometric Data ◽  
Wide Field ◽  
Preliminary Results

AbstractWe present some preliminary results based on new observations of the variable stars belonging to the Carina Dwarf Galaxy (DG). Photometric data were collected with the two wide field imagers available at ESO ([email protected].) and CTIO (4m prime focus).

scholarly journals An elastic model of Phobos’ libration

2020 ◽  
Vol 636 ◽  
pp. A27
Author(s):  
Yongzhang Yang ◽  
Jianguo Yan ◽  
Xi Guo ◽  
Qingbao He ◽  
Jean-Pierre Barriot
Keyword(s):  
Numerical Model ◽  
Gravity Field ◽  
Numerical Integration ◽  
Elastic Properties ◽  
Rotational Motion ◽  
Space Mission ◽  
Elastic Model ◽  
Shape Model ◽  
Future Space ◽  
Least Squares Fit

Context. Study the rotation of a celestial body is an efficient way to infer its interior structure, and then may give information of its origin and evolution. In this study, based on the latest shape model of Phobos from Mars Express (MEX) mission, the polyhedron approximation approach was used to simulate the gravity field of Phobos. Then, the gravity information was combined with the newest geophysical parameters such as GM and k2 to construct the numerical model of Phobos’ rotation. And with an appropriate angles transformation, we got the librational series respect to Martian mean equator of date. Aims. The purpose of this paper is to develop a numerical model of Phobos’ rotational motion that includes the elastic properties of Phobos. The frequencies analysis of the librational angles calculated from the numerical integration results emphasize the relationship between geophysical properties and dynamics of Phobos. This work will also be useful for a future space mission dedicated to Phobos. Methods. Based on the latest shape model of Phobos from MEX mission, we firstly modeled the gravity field of Phobos, then the gravity coefficients were combined with some of the newest geophysical parameters to simulate the rotational motion of Phobos. To investigate how the elastic properties of Phobos affect its librational motion, we adopted various k2 into our numerical integration. Then the analysis was performed by iterating a frequency analysis and linear least-squares fit of Phobos’ physical librations. From this analysis, we identified the influence of k2 on the largest librational amplitude and its phase. Results. We showed the first ten periods of the librational angles and found that they agree well with the previous numerical results which Phobos was treated as a perfectly rigid body. We also found that the maximum amplitudes of the three parameters of libration are also close to the results from a rigid model, which is mainly due to the inclination of Phobos and moments of inertia. The other amplitudes are slightly different, since the physics contained in our model is different to that of a previous study, specifically, the different low-degree gravity coefficients and ephemeris. The libration in longitude τ has the same quadratic term with previous numerical study, which is consistent with the secular acceleration of Phobos falling onto Mars. We investigated the influence of the tidal Love number k2 on Phobos’ rotation and found a detectable amplitude changes (0.0005°) expected in the future space mission on τ, which provided a potential possibility to constrain the k2 of Phobos by observing its rotation. We also studied the influence of Phobos’ orbit accuracy on its libration and suggested a simultaneous integration of orbit and rotation in future work.

scholarly journals Variability Survey of ω Centauri in the Near-IR: Period-Luminosity Relations

2015 ◽  
Vol 12 (S316) ◽  
pp. 351-352
Author(s):  
C. Navarrete ◽  
M. Catelan ◽  
R. Contreras Ramos ◽  
F. Gran ◽  
J. Alonso-García ◽  
...  
Keyword(s):  
Time Series ◽  
Milky Way ◽  
Dwarf Galaxy ◽  
Variable Stars ◽  
Star Cluster ◽  
Wide Field ◽  
Time Series Study ◽  
Near Ir ◽  
Series Study

Abstractω Centauri is by far the most massive globular star cluster in the Milky Way, and possibly the remnant of a dwarf galaxy. As such, it contains a large number of variable stars of different classes. Here we report on an extensive, wide-field time-series study of ω Cen in the J and KS bands, which has allowed us to study the near-IR period-luminosity relations for different variability classes, including the first such relations for the SX Phoenicis stars.

scholarly journals Transiting exocomets detected in broadband light by TESS in the β Pictoris system

2019 ◽  
Vol 625 ◽  
pp. L13 ◽  
Author(s):  
S. Zieba ◽  
K. Zwintz ◽  
M. A. Kenworthy ◽  
G. M. Kennedy
Keyword(s):  
Time Series ◽  
High Resolution ◽  
Light Curve ◽  
Frequency Analysis ◽  
Photometric Data ◽  
High Resolution Spectroscopy

Aims. We search for signs of falling evaporating bodies (FEBs, also known as exocomets) in photometric time series obtained for β Pictoris after fitting and removing its δ Scuti-type pulsation frequencies. Methods. Using photometric data obtained by the TESS satellite we determined the pulsational properties of the exoplanet host star β Pictoris through frequency analysis. We then pre-whitened the 54 identified δ Scuti p-modes and investigated the residual photometric time series for the presence of FEBs. Results. We identify three distinct dipping events in the light curve of β Pictoris over a 105-day period. These dips have depths from 0.5 to 2 millimagnitudes and durations of up to 2 days for the largest dip. These dips are asymmetric in nature and are consistent with a model of an evaporating comet with an extended tail crossing the disc of the star Conclusions. We present the first broadband detections of exocomets crossing the disc of β Pictoris, complementing the predictions made 20 years earlier by Lecavelier Des Etangs et al. (1999, A&A, 343, 916). No periodic transits are seen in this time series. These observations confirm the spectroscopic detection of exocomets in calcium H and K lines that have been seen in high resolution spectroscopy.

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