The moving bump in the light curves of SS For and RR Lyr

Guggenberger, E.; Kolenberg, K.

doi:10.1553/cia148s21

Cited by 9 publications

(10 citation statements)

References 4 publications

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“…Indeed, in Blazhko stars, the additional shock s3', which merges with the front s4+s3, must strongly affect the intensity and phase of the bump, as observed by Guggenberger & Kolenberg (2006. In some cases, the bump may even disappear temporarily.…”

Section: Moving Bumpmentioning

confidence: 87%

“…The variation of the parameters could be studied in many details and with unprecedented precision. First Guggenberger & Kolenberg (2006 showed that in the phase of the bump in the light curve of SS For and RR Lyr (RRab stars) is variable with a period equal to the Blazhko period. They conclude that there is a direct connection of the Blazhko effect and the "motion" of the bump.…”

Section: Variation Of the Pulsation Parameters During The Blazhko Cyclementioning

confidence: 99%

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Atmospheric dynamics in RR Lyrae stars

Gillet

2013

A&A

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Context. Discovered in 1907, the Blazhko effect is a modulation of the light variations of about half of the RR Lyr stars. It has remained unexplained for over 100 years, despite more than a dozen proposed explanations. Today it represents an ongoing challenge in variable-star research. Aims. We propose a new explanation. It is based on the observation that Blazhko stars seem to be located in the region of the instability strip where fundamental and first overtone modes are excited at the same time.Methods. An analysis of nonlinear and nonadiabatic pulsation models of RR Lyrae stars shows that a specific shock (called first overtone shock) may be generated by the perturbation of the fundamental mode by the transient first overtone. Results. The first overtone shock induces a sharp slowdown of the atmospheric layers during their infalling motion. This slowdown in turn affects the compression rate on the deep photospheric layers and the intensity of the κ-mechanism. After an amplification phase, the intensity of the main shock wave before the Blazhko maximum becomes high enough to provoke large radiative losses. These can be at least equal to 70% of the total energy flux of the shock, which induces a small decrease of the effective temperature at each pulsation cycle. In these conditions, when the intensity of the main shock reaches its highest critical value at the Blazhko maximum, it completely desynchronizes the motion of the phostospheric layers. At this point, the atmosphere relaxes and reaches a new synchronous state that occurs at the Blazhko minimum. Conclusions. The combined effects of these two shocks on the atmosphere cause the Blazhko effect. This effect can only exist if the first overtone mode is excited together with the fundamental mode. Because the involved physical mechanisms are essentially nonlinear (shocks, atmospheric dynamics, radiative losses, mode excitations), the Blazhko process is expected to be unstable and irregular. Consequently, the Blazhko process has a specific random nature that is in contrast with the pulsation of non-Blazhko stars.

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Section: Moving Bumpmentioning

confidence: 87%

Section: Variation Of the Pulsation Parameters During The Blazhko Cyclementioning

confidence: 99%

Atmospheric dynamics in RR Lyrae stars

Gillet

2013

A&A

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“…These bumps are probably connected with hypersonic shock waves (Chadid et al 2008), and the spreading of the residuals suggests a link between pulsation and atmosphere dynamics. More precisely, this could be the clue to an interaction between the Blazhko phenomenon and the atmosphere's dynamics (Guggenberger & Kolenberg 2006), since monoperiodic RR Lyrae stars also have very regular light curves in the presence of this bump (Poretti 2001).…”

Section: Discussionmentioning

confidence: 98%

CoRoT light curves of RR Lyrae stars

Poretti¹,

Paparó

Deleuil

et al. 2010

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Context. The CoRoT (Convection, Rotation and planetary Transits) space mission provides a valuable opportunity to monitor stars with uninterrupted time sampling for up to 150 days at a time. The study of RR Lyrae stars, performed in the framework of the Additional Programmes belonging to the exoplanetary field, will particularly benefit from such dense, long-duration monitoring. Aims. The Blazhko effect in RR Lyrae stars is a long-standing, unsolved problem of stellar astrophysics. We used the CoRoT data of the new RR Lyrae variable CoRoT 101128793 ( f 0 = 2.119 d −1 , P = 0.4719296 d) to provide us with more detailed observational facts to understand the physical process behind the phenomenon. Methods. The CoRoT data were corrected for one jump and the long-term drift. We applied different period-finding techniques to the corrected timeseries to investigate amplitude and phase modulation. We detected 79 frequencies in the light curve of CoRoT 101128793. They have been identified as the main frequency f 0 and its harmonics, two independent terms, the terms related to the Blazhko frequency f m , and to several combination terms. Results. A Blazhko frequency f m = 0.056 d −1 and a triplet structure around the fundamental radial mode and harmonics were detected, as were a long-term variability on the Blazhko modulation. Indeed, the amplitude of the main oscillation is decreasing along the CoRoT survey. The Blazhko modulation is one of the smallest observed in RR Lyrae stars. Moreover, the additional modes f 1 = 3.630 and f 2 = 3.159 d −1 are detected. Taking its ratio with the fundamental radial mode into account, the term f 1 could be the identified as the second radial overtone. Detecting of these modes in horizontal branch stars is a new result obtained by CoRoT.

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“…Moreover, it is well known that the light curve shape of RR Lyrae stars changes during the Blazhko cycle. Also, secondary features like the so-called bump are known to change during the modulation [6] resulting in changing amplitudes of the harmonics which describe the shape of the light curve. As mentioned earlier, 7 harmonics were included into the fit.…”

Section: Influence Of Nonlinearitiesmentioning

confidence: 99%