The Cepheid Phase Lag Revisited

Szabo, Robert M.; Buchler, J. R.; Bartee, Justin

doi:10.1086/520917

Cited by 33 publications

(49 citation statements)

References 30 publications

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“…Turner et al (2006b) also doubt that V1726 Cyg pulsates in the first overtone: its carefully determined luminosity is consistent with that of a fundamental mode pulsator. The existence of fundamental mode Cepheids pulsating with small amplitude is also predicted by theoretical computations (Szabó et al 2007).…”

Section: Resultssupporting

confidence: 54%

“…Theoretical calculations modelling the pulsation of Cepheids have been unable to fully reproduce the P-A diagram delineated by observational data. Model calculations by Szabó et al (2007), however, confirm theoretically that the spread in photometric amplitude at a given pulsation period is partly caused by differences in the location of the datapoints within the instability strip (see their Fig. 7).…”

Section: Introductionmentioning

confidence: 77%

“…Szabó et al (2007) discussed how low pulsational amplitudes do not necessarily relate to oscillations in an overtone. Their nonlinear pulsation models indicate that fundamental mode Cepheids of periods longer than 10 days have small amplitude oscillations near both edges of the instability strip.…”

Section: Pulsation Modementioning

confidence: 99%

“…This behaviour implies that first overtone Cepheids can oscillate with any amplitude smaller than the largest possible value, while Cepheids pulsating in the fundamental mode prefer oscillating with a large amplitude, even though their physical properties do not place them in the middle of the instability strip. A remarkable exception is V440 Persei, which is classified as a fundamental mode Cepheid in spite of its extremely low amplitude (Szabó et al 2007).…”

Section: Period-amplitude Relationshipsmentioning

confidence: 99%

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Observational studies of Cepheid amplitudes

Klagyivik

Szabados

2009

A&A

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Context. The dependence of amplitude on the pulsation period differs from other Cepheid-related relationships. Aims. We attempt to revise the period-amplitude (P-A) relationship of Galactic Cepheids based on multi-colour photometric and radial velocity data. Reliable P-A graphs for Galactic Cepheids constructed for the U, B, V, R C , and I C photometric bands and pulsational radial velocity variations facilitate investigations of previously poorly studied interrelations between observable amplitudes. The effects of both binarity and metallicity on the observed amplitude, and the dichotomy between short-and long-period Cepheids can both be studied. Methods. A homogeneous data set was created that contains basic physical and phenomenological properties of 369 Galactic Cepheids. Pulsation periods were revised and amplitudes were determined by the Fourier method. P-A graphs were constructed and an upper envelope to the data points was determined in each graph. Correlations between various amplitudes and amplitude-related parameters were searched for, using Cepheids without known companions. Results. Large amplitude Cepheids with companions exhibit smaller photometric amplitudes on average than solitary ones, as expected, while s-Cepheids pulsate with an arbitrary (although small) amplitude. The ratio of the observed radial velocity to blue photometric amplitudes, A V RAD /A B , is not as good an indicator of the pulsation mode as predicted theoretically. This may be caused by an incorrect mode assignment to a number of small amplitude Cepheids, which are not necessarily first overtone pulsators. The dependence of the pulsation amplitudes on wavelength is used to identify duplicity of Cepheids. More than twenty stars previously classified as solitary Cepheids are now suspected to have a companion. The ratio of photometric amplitudes observed in various bands confirms the existence of a dichotomy among normal amplitude Cepheids. The limiting period separating short-and long-period Cepheids is 10.47 days. Conclusions. Interdependences of pulsational amplitudes, the period dependence of the amplitude parameters, and the dichotomy have to be taken into account as constraints in modelling the structure and pulsation of Cepheids. Studies of the P-L relationship must comply with the break at 10. d 47 instead of the currently used "convenient" value of 10 days.

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Section: Resultssupporting

confidence: 54%

Section: Introductionmentioning

confidence: 77%

Section: Pulsation Modementioning

confidence: 99%

Section: Period-amplitude Relationshipsmentioning

confidence: 99%

See 2 more Smart Citations

Observational studies of Cepheid amplitudes

Klagyivik

Szabados

2009

A&A

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“…One objective of these calculations must be to explain the origin of the phase lag of +0.15 cycles between maximum light and minimum radius in V652 Her. Phase lags exist in Cepheids but in the opposite sense (-0.25 cycles) and are understood in terms of linear (non-adiabatic) effects associated with the thin hydrogen ionization zone moving through mass layers almost as a discontinuity (Castor 1968;Szabó et al 2007). Since the hydrogen and first helium ionization zones play no role in V652 Her (too little hydrogen and too hot), it is suggested that an interaction between the second helium ionization zone and the nickel/iron opacity bump at 2 × 10 5 K will be important.…”

Section: Discussionmentioning

confidence: 99%

Subaru and Swift observations of V652 Herculis: resolving the photospheric pulsation★

Jeffery

Kurtz

Shibahashi

et al. 2015

Monthly Notices of the Royal Astronomical Society

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High resolution spectroscopy with the Subaru High Dispersion Spectrograph, and Swift ultraviolet photometry are presented for the pulsating extreme helium star V652 Her. Swift provides the best relative ultraviolet photometry obtained to date, but shows no direct evidence for a shock at ultraviolet or X-ray wavelengths. Subaru has provided high spectral and high temporal resolution spectroscopy over 6 pulsation cycles (and eight radius minima). These data have enabled a line-by-line analysis of the entire pulsation cycle and provided a description of the pulsating photosphere as a function of optical depth. They show that the photosphere is compressed radially by a factor of at least two at minimum radius, that the phase of radius minimum is a function of optical depth and the pulse speed through the photosphere is between 141 and 239 km s −1 (depending how measured) and at least ten times the local sound speed. The strong acceleration at minimum radius is demonstrated in individual line profiles; those formed deepest in the photosphere show a jump discontinuity of over 70 km s −1 on a timescale of 150 s. The pulse speed and line profile jumps imply a shock is present at minimum radius. These empirical results provide input for hydrodynamical modelling of the pulsation and hydrodynamical plus radiative transfer modelling of the dynamical spectra.

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Cepheids as distance indicators and stellar tracers

Bono,

Braga,

Pietrinferni

2024

Astron Astrophys Rev

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We review the phenomenology of classical Cepheids (CCs), Anomalous Cepheids (ACs) and type II Cepheids (TIICs) in the Milky Way (MW) and in the Magellanic Clouds (MCs). We also examine the Hertzsprung progression in different stellar systems by using the shape of I-band light curves (Fourier parameters) and observables based on the difference in magnitude and in phase between the bump and the minimum in luminosity. The distribution of Cepheids in optical and in optical–near infrared (NIR) color–magnitude diagrams is investigated to constrain the topology of the instability strip. The use of Cepheids as tracers of young (CCs), intermediate (ACs) and old (TIICs) stellar populations are brought forward by the comparison between observations (MCs) and cluster isochrones covering a broad range in stellar ages and in chemical compositions. The different diagnostics adopted to estimate individual distances (period–luminosity, period–Wesenheit, period–luminosity–color relations) are reviewed together with pros and cons in the use of fundamental and overtones, optical and NIR photometric bands, and reddening free pseudo magnitudes (Wesenheit). We also discuss the use of CCs as stellar tracers and the radial gradients among the different groups of elements (iron, $$\alpha $$ α , neutron-capture) together with their age-dependence. Finally, we briefly outline the role that near-future space and ground-based facilities will play in the astrophysical and cosmological use of Cepheids.

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The Cepheid Phase Lag Revisited

Cited by 33 publications

References 30 publications

Observational studies of Cepheid amplitudes

Observational studies of Cepheid amplitudes

Subaru and Swift observations of V652 Herculis: resolving the photospheric pulsation★

Cepheids as distance indicators and stellar tracers

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