scholarly journals Recent Work on Beat Cepheids at Mount Stromlo Observatory

1980 ◽  
Vol 5 ◽  
pp. 483-485
Author(s):  
S. L. Barrell ◽  
B. C. Cogan ◽  
D. J. Faulkner ◽  
R. R. Shobbrook
Keyword(s):  
Fourier Analysis ◽  
Recent Work ◽  
Narrow Range ◽  
Fundamental Period ◽  
Frequency Change ◽  
Instability Strip ◽  
Period Ratio ◽  
Short Period ◽  
Period Estimate ◽  
Mode Energy

Beat Cepheids continue to pose a number of unanswered questions concerning the behaviour of stars near the short-period end of the Cepheid instability strip; in particular, why is it that such a high proportion of stars with fundamental period ≤ 5 days exhibit simultaneous pulsation in both the fundamental and first-overtone radial modes, and why is it that these stars exhibit such a narrow range of period ratio (P1/P0 ≃ 0.71)? A programme of observation and Fourier analysis of beat Cepheids is presently being undertaken at Mount Stromlo and Siding Spring in an effort to understand these phenomena.There is now evidence that, for the two best observed stars of this class - U TrA and TU Cas, both the period and the relative mode amplitudes are slowly changing with time. U TrA was observed in detail during the years 1953-59 by Oosterhoff (1957) and Jansen (1962), and a new series of 481 five colour observations of this star was obtained by Faulkner and Shobbrook (1979) in 1977. Using E = Σ(Amp × Freq)2 summed over all the Fourier terms for a given mode as a measure of the pulsational energy associated with that mode, we can use this 20 year timebase to calculate the change in relative mode energy. For U TrA the energy of the overtone is increasing (see Table I). Similarly we can compare the fundamental period derived for these 20 years with an earlier period estimate of Oosterhoff (1957) to obtain the rate of frequency change shown.

scholarly journals Ultra-Short Period Cepheids in the LMC

1980 ◽  
Vol 58 ◽  
pp. 443-448
Author(s):  
Leo Connolly
Keyword(s):  
Large Magellanic Cloud ◽  
Magellanic Cloud ◽  
Instability Strip ◽  
Additional Variable ◽  
Short Period

Six Cepheids in the Large Magellanic Cloud have been discovered with periods less than one day. They lie at the faint, blue end of the instability strip as would be expected but form a separate Period-Luminosity relation from that for normal Cepheids. Membership in the LMC is based upon the existence of the P-L relationship. Several of the variables have uncertain periods although all apparently have periods under one day. One additional variable has tentatively been identified as a bright Anomalous Cepheid.

Spectroscopic Studies and Atmospheric Parameters of ZZ Ceti Stars

1989 ◽  
Vol 114 ◽  
pp. 244-248
Author(s):  
D. Daou ◽  
F. Wesemael ◽  
P. Bergeron ◽  
G. Fontaine ◽  
J. B. Holberg
Keyword(s):  
Strong Evidence ◽  
White Dwarfs ◽  
Narrow Range ◽  
Spectroscopic Studies ◽  
Atmospheric Parameters ◽  
Instability Strip ◽  
Pulsating Stars ◽  
Evolutionary Phase ◽  
Effective Temperatures

The pulsating ZZ Ceti stars cover a narrow range of effective temperatures along the cooling sequence of DA white dwarfs (see, eg., Winget and Fontaine 1982). Fast-photometric searches for pulsating stars in that class have provided strong evidence that the ZZ Ceti phase is an evolutionary phase through which all cooling DA stars will eventually go through (Fontaine et al. 1982). Recent investigations, based on optical or ultraviolet photometry and spectrophotometry, have set the boundaries of the instability strip at temperatures near 10,000-11,000 K and 12,000-13,000 K, respectively (McGraw 1979; Greenstein 1982; Weidemann and Koester 1984; Fontaine et al. 1985; Wesemael, Lamontagne, and Fontaine 1986; Lamontagne, Wesemael, and Fontaine 1987, 1988).

scholarly journals Nematic liquid crystal alignment on subwavelength metal gratings

2018 ◽  
Vol 9 ◽  
pp. 42-47 ◽  
Author(s):  
Irina V Kasyanova ◽  
Artur R Geivandov ◽  
Vladimir V Artemov ◽  
Maxim V Gorkunov ◽  
Serguei P Palto
Keyword(s):  
Liquid Crystal ◽  
Fourier Analysis ◽  
Nematic Liquid Crystal ◽  
Slit Width ◽  
Homogeneous Surface ◽  
Period Ratio ◽  
Transmittance Spectra ◽  
Surface Alignment ◽  
Crystal Alignment ◽  
Metal Gratings

We have studied the alignment of a nematic liquid crystal (LC) material on aluminum subwavelength nanogratings as a function of the period, p, and the slit width to period ratio, w/p. A method, based on Fourier analysis of the transmittance spectra of the LC grating system, has been applied. We show that the gratings provide stable planar alignment only for shorter periods and narrower slits (p < 400 nm, w/p < 2/3). As these parameters increase, the homogeneous surface alignment changes to domains with different tilt angles or to spatially modulated alignment. We have also obtained a 90° twisted LC director distribution, implying sufficiently strong azimuthal LC anchoring at the grating surface.

scholarly journals Astrophysical Applications of Delta Scuti Stars

1995 ◽  
Vol 155 ◽  
pp. 70-80
Author(s):  
Michel Breger
Keyword(s):  
Main Sequence ◽  
Statistical Significance ◽  
Instability Strip ◽  
Short Period ◽  
Scuti Star ◽  
Systematic Behaviour ◽  
Delta Scuti ◽  
F Stars ◽  
Available Information ◽  
Scuti Stars

AbstractThe δ Scuti stars pulsate with a large number of low-order radial and nonradial p-modes. There also exists some evidence for the presence of g-modes.The pulsational variability outside the classical δ Scuti star instability strip (A1V - F0V on the main sequence) is examined. New measurements do not confirm the short-period variability of the hot B9p star ET And. However, a number of cool, early-F stars shows variability around one day: the γ Dor variables. An explanation involving nonradial g modes appears the most promising.An examination of available information on the multi-periodicity of δ Scuti stars shows no systematic behaviour in which pulsation modes axe excited to an observable level with luminosity and temperature. The asteroseismological potential of δ Scuti vaxiables is briefly examined.So far, the period changes of five luminous Pop. I δ Scuti variables have been studied. While stellar evolution predicts period increases, decreases have been observed and reported for all five stars. The statistical significance of this result and alternative explanations axe briefly examined.

scholarly journals Randomized Benchmarking as Convolution: Fourier Analysis of Gate Dependent Errors

Quantum ◽  
2021 ◽  
Vol 5 ◽  
pp. 581
Author(s):  
Seth T. Merkel ◽  
Emily J. Pritchett ◽  
Bryan H. Fong
Keyword(s):  
Fourier Analysis ◽  
Recent Work ◽  
Fourier Transforms ◽  
Decay Rates ◽  
Alternative Proof ◽  
Mathematical Framework ◽  
Fourier Space ◽  
Clifford Group ◽  
Depolarizing Channel ◽  
The Ideal

We show that the Randomized Benchmarking (RB) protocol is a convolution amenable to Fourier space analysis. By adopting the mathematical framework of Fourier transforms of matrix-valued functions on groups established in recent work from Gowers and Hatami \cite{GH15}, we provide an alternative proof of Wallman's \cite{Wallman2018} and Proctor's \cite{Proctor17} bounds on the effect of gate-dependent noise on randomized benchmarking. We show explicitly that as long as our faulty gate-set is close to the targeted representation of the Clifford group, an RB sequence is described by the exponential decay of a process that has exactly two eigenvalues close to one and the rest close to zero. This framework also allows us to construct a gauge in which the average gate-set error is a depolarizing channel parameterized by the RB decay rates, as well as a gauge which maximizes the fidelity with respect to the ideal gate-set.

scholarly journals A Theoretical Period-Luminosity Relation of Dwarf Cepheids

1993 ◽  
Vol 138 ◽  
pp. 437-438
Author(s):  
D.H. McNamara ◽  
John M. Powell
Keyword(s):  
Large Amplitude ◽  
High Accuracy ◽  
Fundamental Period ◽  
Instability Strip ◽  
Light Minimum ◽  
F Stars ◽  
Light Maximum ◽  
Very High

Dwarf Cepheids (large-amplitude δ Sct variables and SXPhe variables in the GCVS) are late A-type stars near light maximum and early-F stars near light minimum. In the lower part of the instability strip where these stars are found the pulsation constant Q varies only slightly. As pointed out by Andreasen, Hejlesen, and Petersen (1983) this makes it easy to transform a theoretical HR or alternatively a (logTe, logg) diagram to a theoretical logTe, logP0) diagram by the use of the relation. This follows from the equations:where P0 is the fundamental period of pulsation. The periods, of course, can be determined with very high accuracy.

scholarly journals Oscillations of HB Red Variable Stars

1998 ◽  
Vol 185 ◽  
pp. 401-402
Author(s):  
D.R. Xiong ◽  
Q. L. Cheng ◽  
L. Deng
Keyword(s):  
Globular Clusters ◽  
Turbulent Viscosity ◽  
Variable Stars ◽  
Instability Strip ◽  
Rr Lyrae ◽  
Short Period ◽  
Spatial Oscillations ◽  
The Right ◽  
Thermodynamic Coupling ◽  
Low Amplitude

Using a nonlocal time-dependent theory of convection, we have calculated the linear non-adiabatic oscillations of the Horizontal Branch (HB) stars, with both the dynamic and thermodynamic coupling between convection and oscillations been carefully treated. Turbulent pressure and turbulent viscosity have been included consistently in our equations of non-adiabatic pulsation. When the coupling between convection and oscillations is ignored, for all models with Te ≤ 7350K, the fundamental through the second overtone are pulsationally unstable; while for Te ≤ 6200K all the models are unstable up to (at least) the 9th overtone. When the coupling between convection and oscillations is included, the RR Lyrae instability strip is very well predicted. Within the strip most models are pulsationally unstable only for the fundamental and the first few overtones. Turbulent viscosity is an important damping mechanism. Being exclusively distinct from the luminous red variables (long period variables), the HB stars to the right of the RR Lyrae strip are pulsationally stable for the fundamental and low-order overtones, but become unstable for some of the high-order overtones. This may provide a valuable clue for the short period, low amplitude red variables found outside the red edge of the RR Lyrae strip on the H-R diagram of globular clusters. Moreover, we present a new radiation modulated excitation mechanism functioning in radiation flux gradient regions. The effects of nonlocal convection and the dynamic coupling between convection and oscillations are discussed. The spatial oscillations of the thermal variables in the pulsational calculations have been effectively suppressed.

scholarly journals Nuclei of Planetary Nebulae in the Pulsation Instability Strip

1977 ◽  
Vol 42 ◽  
pp. 342-345
Author(s):  
W. Dziembowski
Keyword(s):  
Planetary Nebulae ◽  
Instability Strip ◽  
Period Variability ◽  
Short Period ◽  
Stellar Models

Pulsation properties of relevant stellar models are investigated with the linear nonadiabatic method. Short-period variability of FG Sge is interpreted as a pulsation phenomenon.

scholarly journals Hd 24975: A New Delta Scuti Star? (Or A Mild Ap Star with Short Photometric Variations?)

1986 ◽  
Vol 90 ◽  
pp. 253-256
Author(s):  
C. Megessier ◽  
P. North ◽  
M. Burnet
Keyword(s):  
Clear Correlation ◽  
Comparison Star ◽  
Instability Strip ◽  
Precise Location ◽  
Short Period ◽  
Scuti Star ◽  
Delta Scuti Star ◽  
Delta Scuti ◽  
Ap Stars ◽  
Hr Diagram

Looking in the literature for short period variations of Ap stars, we found the puzzling case of HD 24975. Used as a comparison star by Weiss (1978), it had been found then to present variations with a peak-to-peak amplitude of 0.01 in U, B and V with a period of about 45mn, but with no clear correlation between the three passbands.HD 24975 has the same spectral type A2 as 21 Com which seems to present photometric variations with P ⋍ 31mn and Δ V < 0,02m (Percy, 1973, 1975). Both stars are near the blue edge of the δ Scuti instability strip in the HR diagram. The lack of photo metric data, however, prevented the precise location of HD 24975 from being found on the HR diagram.

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