Hydrodynamic and Radiative-Transfer Effects on an RR Lyrae Atmosphere

Hill, Stephen J.

doi:10.1086/151835

Cited by 49 publications

(32 citation statements)

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“…This mechanism has been previously detected in the theoretical hydrodynamic model of RR Lyrae (Hill 1972). This bump is interpreted as the consequence of a shock occurring simultaneously with the collision between the upper and lower layers of the atmosphere during the end of the ballistic movement.…”

Section: The Infalling Layers/shock Collisionsupporting

confidence: 64%

Neutral and ionized emission lines in the type II Cepheid W Virginis

Kovtyukh¹,

Wallerstein²,

Andrievsky³

et al. 2011

A&A

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Aims. The aim of this work was to perform a multiphase spectroscopic study of W Vir which represents stars of the class of population II Cepheids, in order to trace the behaviour of emission features in different lines, and to use the data to describe the dynamical processes in the atmosphere of this star associated with the shock wave propagation. Methods. Our spectroscopic study of W Vir involved 18 high-resolution spectra obtained with the help of 3.5-m telescope of Apache Point Observatory. These spectra cover W Vir's pulsational cycle with good phase resolution that enabled us to precisely fix the intervals of appearance, existence and disappearance of many anomalous spectral features, as well as to construct their radial velocity curves. Results. We detected and investigated the behaviour of emission and line doubling in many metallic lines (Na I, Fe I, Fe II, Ba II etc), as well as in hydrogen and helium lines. Analysis of the temporal characteristics of those emission features allowed us to make, in particular, the following conclusion. Conclusions. W Vir consists of two parts: the inner part, which is, in fact, a pulsating star itself with periodic shocks penetrating into the upper atmosphere, an outer one -a circumstellar envelope. The interaction of the main shock wave with the infalling envelope layers can explain the observed peculiarities of the spectral line variability.

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Section: The Infalling Layers/shock Collisionsupporting

confidence: 64%

Neutral and ionized emission lines in the type II Cepheid W Virginis

Kovtyukh¹,

Wallerstein²,

Andrievsky³

et al. 2011

A&A

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“…It is produced when outer atmospheric layers in ballistic infall collide with inner deep layers. The bump was interpreted by Hill (1972) as the consequence of a shock or collision, called "early shock".…”

Section: Shocks From Hydrogen Emission Lines: Observational Approachmentioning

confidence: 99%

“…However, their models do not have enough of an atmospheric extent to calculate fully developed shocks. For the first time, Hill (1972) calculated RRa models with a large enough extended atmosphere to allow a realistic shock-wave development. In the course of pulsation, the extension of the atmosphere increases by 21 times with respect to the static atmosphere.…”

Section: Shocks From Dynamical Models: Theoretical Approachmentioning

confidence: 99%

“…of Hα emission Hill (1972) showed that the early shock forms as the star is still contracting, although the shock is moving outward in mass. Because the intensity of shocks s4 and s3 are too low (Fokin & Gillet 1997) and the bump in the light curve is also observed in non-Blazhko stars, the shock s3' cannot be the cause of the "second apparition" of Hα emission.…”

Section: The Shock Associated To the "Second Apparition"mentioning

confidence: 99%

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Emission lines and shock waves in RR Lyrae stars

Gillet

Фокин

2014

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Context. Emission lines observed in radially pulsating stars are thought to be produced by atoms de-exciting after being excited by a shock wave that is traveling into and then compressing, heating, and accelerating the atmospheric gas. Aims. With the help of recent observations, we examine the origin of all the different types of emission lines of hydrogen and helium that appear during a pulsation cycle. Methods. To analyze the physical origin of emission lines, we used the different models of atmospheric dynamics of RR Lyrae stars that have been calculated so far. Results. In contrast to a recent explanation, we propose that the redshifted emission component of Hα, which occurs near the pulsation phase 0.3, is produced by the main shock. In this case, the emission is the natural consequence of the large extension of the expanding atmosphere. Therefore, this (weak) emission should only be observed in RR Lyrae stars for which the main shock will propagate far enough from the photosphere. It appears as a P-Cygni type profile. We estimate the shock front velocity during the shock propagation in the atmosphere and show that it decreases by 40% when the Hα emitting-shock passes from the photospheric level to the upper atmosphere. The Hα P-Cygni profile observed in long-period Cepheids also seems to be caused by the main shock wave. Although to date He II has only been detected in some Blazhko stars, a comprehensive survey of RR Lyrae stars is necessary to confirm this trend, so we can say that the most intense shocks will only be observed in Blazhko stars. Conclusions. The development of a model of atmospheric pulsation that takes the effects of 2D and 3D convection into account, seems to be a necessary step to fully quantify the effects of shock waves on the atmospheric dynamics of radially pulsating stars.

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“…Figure 1 shows the correlation radial velocity curve and its reverse light curve taking at the same time and over one pulsation period of S Arae. Both reveal very significant elbow and bump respectively consequence of the secondary shock, early shock, as interpreted by Hill (1972) and Gillet & Crowe (1988). We detected that the bump becomes more pronounced as the light curve amplitude decreases and vice versa.…”

Section: Discussionmentioning

confidence: 53%

First Antarctica light curve

Chadid

Vernin²,

Mékarnia³

et al. 2010

A&A

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Context. In the context of long and continuous time-series photometry and after the MOST, CoRoT, KEPLER space missions and large geographic longitude ground-based networks, a new method is offered by the polar location helping to cope with the problem associated with the Earth's day-night cycle. Aims. We present the first long time -series photometry from Dome Charlie in the heart of Antarctica and analyze ∼4400 photometric measurements of RR Lyrae star S Arae obtained in July and August 2007. Methods. The 40-cm telescope and Photometer AntarctIca eXtinction named PAIX were used for long photometric measurements with high time resolution and a duty cycle of 65%. The Fourier technique was used for the frequency analysis. New high-precision spectroscopic observations of S Arae were also collected using HARPS over one pulsation cycle of S Arae. Results. We confirm the known radial fundamental period of 0.452 day. The high order of its harmonics shows the nonlinear nature of the radial mode. The Blazhko modulation is directly detected in the spectrum and shows a value around 48 d. Together with the Blazhko frequency we also detected triplet structure components up to 15th order showing a nonlinear behavior of the Blazhko modulation. Thus, we conclude that S Arae is a bona fide Blazhko star. The data reveal that there are irregular changes in the S Arae atmosphere during the Blazhko cycle. A residual scatter phenomenon is detected and is more intense where the nonlinear effects are strongest. Therefore, the connection between temporal hydrodynamic phenomena and such modulation has to be taken into account in Blazhko models. Conclusions. High-precision CCD photometry with a very good time resolution can be undertaken at Dome Charlie in Antarctica, and it helps to complete astrophysical measurement time-series.

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Hydrodynamic and Radiative-Transfer Effects on an RR Lyrae Atmosphere

Cited by 49 publications

References 0 publications

Neutral and ionized emission lines in the type II Cepheid W Virginis

Neutral and ionized emission lines in the type II Cepheid W Virginis

Emission lines and shock waves in RR Lyrae stars

First Antarctica light curve

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