scholarly journals New Ways of Revealing Cepheid Binaries

1993 ◽  
Vol 139 ◽  
pp. 406-407
Author(s):  
L. Szabados
Keyword(s):  
Radial Velocity ◽  
Amplitude Ratio ◽  
Wavelength Dependence ◽  
Light Variation ◽  
Pulsation Period ◽  
Regular Pattern ◽  
Observable Effect ◽  
Velocity Amplitude ◽  
Slope Method ◽  
Classical Cepheids

AbstractTwo methods involving the observed amplitudes of radial velocity and UBVR light variations for classical Cepheids have been analysed, both being implicitly known: their principle is trivial but these methods had not yet been used systematically as indicators of duplicity.The slope method is based on the alteration of the wavelength dependence of the light variation amplitude if either a blue or a red companion is added to the light of the Cepheid. The amplitude ratio (AR) method makes use of the fact that the companion reduces the amplitude of the light variation without observable effect on the pulsational radial velocity amplitude. This means that the ratio of these two amplitudes (Arad.vel./AB) has a larger value for binary Cepheids as compared with the single pulsators.Each method has been applied to more than 100 Cepheids, thus allowing to study how the uncontaminated parameters (amplitude ratio and slope) depend on the pulsation period. Binary Cepheids deviate from the regular pattern in these diagrams, and a number of new binaries can be discovered in this way. The effect of duplicity is revealed by both methods independently for VZ CMa, FM Cas, CR Cep, V402 Cyg, VI154 Cyg, V440 Per and DR Vel.

scholarly journals Importance of Precise Radial Velocities for Cepheid Binaries

1999 ◽  
Vol 170 ◽  
pp. 211-217 ◽  
Author(s):  
L. Szabados
Keyword(s):  
Radial Velocity ◽  
Binary Systems ◽  
Velocity Variation ◽  
Pulsation Period ◽  
Radial Pulsation ◽  
Velocity Amplitude ◽  
Radial Velocity Variation ◽  
Classical Cepheids ◽  
Orbital Effect ◽  
Low Amplitude

AbstractIn view of the high incidence of duplicity among Cepheids, a large number of binary systems remain to be discovered because of the low amplitude of the orbital effect superimposed on the radial velocity variation due to radial pulsation. This fact is shown by simple statistics. The importance of combining astrometric data with radial velocity measurements is also emphasized. Finally the systematics of the radial velocity amplitude as a function of the pulsation period is considered for classical Cepheids.

Active Control of Passive and Active Particle Distribution at the Outlet of Double Y-Microchannel Using Pulsatile Flow

2020 ◽  
Vol 142 (8) ◽  
Author(s):  
Minh Chau Nguyen ◽  
Hassan Peerhossaini ◽  
Elnaz Pashmi ◽  
Mohammad Mehdi Salek ◽  
Mojtaba Jarrahi
Keyword(s):  
Phase Shift ◽  
Pulsatile Flow ◽  
Particle Distribution ◽  
Amplitude Ratio ◽  
Pulsation Period ◽  
Steady Flows ◽  
Control Parameters ◽  
Flow Conditions ◽  
Velocity Amplitude ◽  
Series Of Experiments

Abstract While a variety of active and passive techniques have been proposed for steady flows, pulsatile flow has received much less attention. Pulsation makes more control parameters available for passive methods and enables them to separate particles. The purpose of this work is to determine the effects of the phase shift between two entering flows (only one includes the particles) on particle separation inside a double Y-microchannel. Numerical simulations were carried out for both steady and pulsating flow conditions. The results showed that when the velocity amplitude ratio (β) is less than 2, the separation index increases with the phase shift (φ) and the highest efficiency occurs at φ = 180 deg. A similar trend can be observed for higher values of β only if the pulsation period is short enough. A series of experiments qualitatively validated the numerical results.

Control of Particle Distribution at the Outlet of a Double Y-Microchannel Using Pulsatile Flow

2019 ◽  
Author(s):  
Minh Chau Nguyen ◽  
Hassan Peerhossaini ◽  
Mohammad Mehdi Salek ◽  
Mojtaba Jarrahi
Keyword(s):  
Phase Shift ◽  
Pulsatile Flow ◽  
Particle Distribution ◽  
Amplitude Ratio ◽  
Pulsation Period ◽  
Steady Flows ◽  
Control Parameters ◽  
Flow Conditions ◽  
Velocity Amplitude ◽  
Series Of Experiments

Abstract While a variety of active and passive techniques have been proposed for steady flows, pulsatile flow has received much less attention. Pulsation makes more control parameters available for passive methods and enables them to separate particles. The purpose of this work is to determine the effects of phase shift between two entering flows (only one includes the particles) on particle separation inside a double Y-microchannel. Numerical simulations were carried out for both steady and pulsating flow conditions. The results showed that when the velocity amplitude ratio (β) is less than 2, the separation index increases with the phase shift (φ) and the highest efficiency occurs at φ = 180°. A similar trend can be observed for higher values of β only if the pulsation period is short enough. A series of experiments qualitatively validated the numerical results.

scholarly journals The relationship between photometric and spectroscopic oscillation amplitudes from 3D stellar atmosphere simulations

2021 ◽  
Author(s):  
Yixiao Zhou ◽  
Thomas Nordlander ◽  
Luca Casagrande ◽  
Meridith Joyce ◽  
Yaguang Li ◽  
...  
Keyword(s):  
Radial Velocity ◽  
Three Dimensional ◽  
Quantitative Relationship ◽  
Stellar Atmospheres ◽  
Spectral Lines ◽  
Wavelength Shift ◽  
The Sun ◽  
Theoretical Derivation ◽  
Velocity Amplitude ◽  
Good Agreement

Abstract We establish a quantitative relationship between photometric and spectroscopic detections of solar-like oscillations using ab initio, three-dimensional (3D), hydrodynamical numerical simulations of stellar atmospheres. We present a theoretical derivation as proof of concept for our method. We perform realistic spectral line formation calculations to quantify the ratio between luminosity and radial velocity amplitude for two case studies: the Sun and the red giant ε Tau. Luminosity amplitudes are computed based on the bolometric flux predicted by 3D simulations with granulation background modelled the same way as asteroseismic observations. Radial velocity amplitudes are determined from the wavelength shift of synthesized spectral lines with methods closely resembling those used in BiSON and SONG observations. Consequently, the theoretical luminosity to radial velocity amplitude ratios are directly comparable with corresponding observations. For the Sun, we predict theoretical ratios of 21.0 and 23.7 ppm/[m s−1] from BiSON and SONG respectively, in good agreement with observations 19.1 and 21.6 ppm/[m s−1]. For ε Tau, we predict K2 and SONG ratios of 48.4 ppm/[m s−1], again in good agreement with observations 42.2 ppm/[m s−1], and much improved over the result from conventional empirical scaling relations which gives 23.2 ppm/[m s−1]. This study thus opens the path towards a quantitative understanding of solar-like oscillations, via detailed modelling of 3D stellar atmospheres.

The Motion of a Flat-Plate Pendulum in a Viscous Fluid

1969 ◽  
Vol 91 (4) ◽  
pp. 1100-1104
Author(s):  
J. P. Ries ◽  
W. G. Harrach
Keyword(s):  
Viscous Fluid ◽  
Flat Plate ◽  
Amplitude Ratio ◽  
Harmonic Oscillation ◽  
Oscillation Period ◽  
Velocity Amplitude ◽  
Boundary Layer Equations ◽  
Light Oil ◽  
Damped Oscillation ◽  
Predicted Values

The motion of an infinite, flat plate undergoing free oscillations as a submerged pendulum in a viscous fluid is analyzed. An analytical solution has been obtained through a simultaneous solution of the equation of motion for the plate, the drag force relationship, and the boundary-layer equations for the case of laminar, incompressible, unsteady flow. Expressions for the displacement and velocity of the plate appear as the sum of a damped harmonic oscillation and a particular solution which decays asymptotically to zero with increasing time. The period and logarithmic decrement are expressed as functions of a single parameter which contains the physical properties of the fluid and dimensions of the system. Predicted values of plate displacement, plate velocity, amplitude ratio, and damped oscillation period are compared to the results of an experimental investigation performed in water and a light oil.

scholarly journals Radial Velocities of Classical Cepheids

1985 ◽  
Vol 82 ◽  
pp. 32-33
Author(s):  
T. G. Barnes ◽  
T. J. Moffett
Keyword(s):  
Radial Velocity ◽  
Photometric Data ◽  
Radial Velocities ◽  
Time Interval ◽  
Classical Cepheids ◽  
Homogeneous Set

Approximately 2000 radial velocities of 88 classical Cepheids have been observed using a photoelectric radial velocity meter. During the same time interval, these same Cepheids were intensively observed in the BVRI bandpasses, as reported elsewhere in these proceedings. This provides a homogeneous set of phase-locked radial velocity and photometric data which are useful in several contexts. We present here a sample of these results which will be published in their entirety elsewhere.

scholarly journals Observations of evolutionary changes in the pulsation period of cepheids

1984 ◽  
Vol 105 ◽  
pp. 445-448
Author(s):  
L. Szabados
Keyword(s):  
Detailed Analysis ◽  
Stellar Evolution ◽  
Time Scale ◽  
Theoretical Work ◽  
Pulsation Period ◽  
First Approximation ◽  
Evolutionary Changes ◽  
Classical Cepheids ◽  
Cepheid Variables

In spite of the fact that Cepheid variables pulsate quite regularly their pulsation period remains constant only in the first approximation. The pulsation period is subject to variations because of stellar evolution. The calculations made by Hofmeister (1965) predicted that the evolutionary period changes of classical Cepheids should be observed on a time scale of several decades or longer. No detailed analysis of the observed period changes has been made since Hofmeister's fundamental theoretical work.

scholarly journals Mode Discrimination in Nonradially Oscillating Stars From Light, Colour and Velocity Observations

1980 ◽  
Vol 58 ◽  
pp. 371-376
Author(s):  
L.A. Balona ◽  
R.S. Stobie
Keyword(s):  
Radial Velocity ◽  
Phase Difference ◽  
Spherical Harmonic ◽  
Amplitude Ratio ◽  
Harmonic Mode ◽  
Instability Strip ◽  
Nonradial Oscillation ◽  
Mode Discrimination ◽  
Velocity Variations

AbstractExpressions for the amplitudes and phases of the light, colour and radial velocity variations are derived for a star in nonradial oscillation. For stars in the cepheid instability strip the spherical harmonic mode of the oscillation can be obtained from the phase difference between the light and colour variations. For 3 Cep stars the mode can be estimated from the amplitude ratio of the light and colour variations.

scholarly journals Photospheric activity of the Sun with VIRGO and GOLF

2017 ◽  
Vol 608 ◽  
pp. A87 ◽  
Author(s):  
D. Salabert ◽  
R. A. García ◽  
A. Jiménez ◽  
L. Bertello ◽  
E. Corsaro ◽  
...  
Keyword(s):  
Solar Activity ◽  
Radial Velocity ◽  
Wavelength Dependence ◽  
Solar Photosphere ◽  
The Sun ◽  
Solar Cycles ◽  
Quasi Biennial Oscillation ◽  
Photometric Observations ◽  
Cycle 24 ◽  
Biennial Oscillation

We study the variability of solar activity using new photospheric proxies originally developed for the analysis of stellar magnetism with the CoRoT and Kepler photometric observations. These proxies were obtained by tracking the temporal modulations in the observations associated with the spots and magnetic features as the Sun rotates. We analyzed 21 yr of observations, spanning solar cycles 23 and 24, collected by the space-based photometric VIRGO and radial velocity GOLF instruments on board the SoHO satellite. We then calculated the photospheric activity proxy Sph is for each of the three VIRGO photometers and the associated Svel proxy from the radial velocity GOLF observations. Comparisons with several standard solar activity proxies sensitive to different layers of the Sun demonstrate that these new activity proxies, Sph and Svel, provide a new manner to monitor solar activity. We show that both the long- and short-term magnetic variabilities respectively associated with the 11-yr cycle and the quasi-biennial oscillation are well monitored, and that the magnetic field interaction between the subsurface, photosphere, and chromosphere of the Sun was modified between Cycle 24 and Cycle 23. Furthermore, the photometric proxies show a wavelength dependence of the response function of the solar photosphere among the three channels of the VIRGO photometers, providing inputs for the study of the stellar magnetism of Sun-like stars.

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