Through Spectroscopy, we aim to develop the field of pulsating stars, especially the atmospheric dynamics of high amplitude pulsators such as RR Lyr and R Scuti, in order to establish new models of ...the mechanical and thermal behavior of their atmospheres (shock waves, relaxation time, energy loss…). We used high-resolution spectra over a total of 81 nights from made with the spectrograph Eshell during years 2013 and 2015 runs from Oukaïmeden observatory in the High Atlas mountains (Morocco) completed with made with the spectrograph ELODIE (Haute Provence observatory, France) during years 1994–1997. A detailed analysis of line profile variations over the whole pulsation cycle is performed. Shock wave velocity and lines intensity were used as indicators of atmospheric dynamics activities. We have obtained and compared our results with those obtained by the large telescopes, we have obtained thanks to our site very satisfactory results, Indeed : For RR lyr: For the first time the second apparition of Helium (D3) was detected using our Telescope (0.35m) at Oukaïmeden Observatory. For the first time, during the phase of expansion of the star, the emission of the line D3 is visible on various phases Blazhko, including during the minimum of the cycle Blazhko. Also, we presented the results of a long- term, high-resolution spectroscopic study of the variable star R Sct. We analyzed the features of the optical spectra of this object and found RSct shows irregular behavior in its slight variations for much of the time that it was observed. Its average period is close to 142 d, but some- times the irregularities are so strong that it is not possible to define a periodic variation.
The stellar parameters of RR Lyrae stars vary considerably over a pulsation cycle, and their determination is crucial for stellar modelling. We present a detailed spectroscopic analysis of the ...pulsating star RR Lyr, the prototype of its class, over a complete pulsation cycle, based on high-resolution spectra collected at the 2.7-m telescope of McDonald Observatory. We used simultaneous photometry to determine the accurate pulsation phase of each spectrum and determined the effective temperature, the shape of the depth-dependent microturbulent velocity, and the abundance of several elements, for each phase. The surface gravity was fixed to 2.4. Element abundances resulting from our analysis are stable over the pulsation cycle. However, a variation in ionization equilibrium is observed around minimum radius. We attribute this mostly to a dynamical acceleration contributing to the surface gravity. Variable turbulent convection on time-scales longer than the pulsation cycle has been proposed as a cause for the Blazhko effect. We test this hypothesis to some extent by using the derived variable depth-dependent microturbulent velocity profiles to estimate their effect on the stellar magnitude. These effects turn out to be wavelength dependent and much smaller than the observed light variations over the Blazhko cycle: if variations in the turbulent motions are entirely responsible for the Blazhko effect, they must surpass the scales covered by the microturbulent velocity. This work demonstrates the possibility of a self-consistent spectroscopic analysis over an entire pulsation cycle using static atmosphere models, provided one takes into account certain features of a rapidly pulsating atmosphere.
We present an analysis of the COnvection, ROtation and planetary Transits (CoRoT) star 105288363, a new Blazhko RR Lyrae star of type RRab (f
0= 1.7623 d−1), observed with the CoRoT spacecraft during ...the second long run in the direction of the Galactic Centre (LRc02, time-base 145 d). The CoRoT data are characterized by an excellent time-sampling and a low noise amplitude of 0.07 mmag in the 2-12 d−1 range and allow us to study not only the fine details of the variability of the star, but also long-term changes in the pulsation behaviour and the stability of the Blazhko cycle. We use, among other methods, standard Fourier analysis techniques and O−C diagrams to investigate the pulsational behaviour of the Blazhko star 105288363. In addition to the frequency pattern expected for a Blazhko RR Lyrae star, we find an independent mode (f
1= 2.984 d−1) showing a f
0/f
1 ratio of 0.59 which is similar to that observed in other Blazhko RR Lyrae stars. The bump and hump phenomena are also analysed, with their variations over the Blazhko cycle. We carefully investigated the strong cycle-to-cycle changes in the Blazhko modulation (P
B= 35.6 d), which seem to happen independently and partly diametrically in the amplitude and phase modulations. Furthermore, the phasing between the two types of modulations is found to change during the course of the observations.
We present our analysis of the long-cadence Kepler data for the well-studied Blazhko star RR Lyr, gathered during the first two quarters of the satellite's observations and covering a total of 127 d. ...Besides being of great importance for our understanding of RR Lyrae stars in general, these RR Lyr data can be regarded as a case study for observations of bright stars with Kepler. Kepler can perform high-precision photometry on targets like RR Lyr, as the saturated flux is conserved to a very high degree. The Kepler data on RR Lyr are revolutionary in several respects. Even with long-cadence sampling (one measurement per 29.4 min), the unprecedented precision (< mmag) of the Kepler photometry allows the study of the star's extreme light-curve variations in detail. The multiplet structures at the main frequency and its harmonics, typical for Blazhko stars, are clearly detected up to the quintuplets. For the first time, photometric data of RR Lyr reveal the presence of half-integer frequencies, linked to a period-doubling effect. This phenomenon may be connected to the still unexplained Blazhko modulation. Moreover, with three observed Blazhko cycles at our disposal, we observe that there is no exact repetition in the light-curve changes from one modulation cycle to the next for RR Lyr. This may be due to additional periodicities in the star, or to transient or quasi-periodic changes.
Context.Multiplet structures are a common feature in pulsating stars, and can be the consequence of rotational splitting, mode interaction or sinusoidal amplitude variations. Aims.In this paper we ...examine the phenomenon of (nearly) equidistant triplets, which are unlikely to be caused by rotational splitting, in different types of pulsating stars: a δ Scuti variable (1 Mon), an RR Lyrae variable (RR Lyr) and a short-period Cepheid (V473 Lyr). We examine the hypothesis that one of the modes forming the triplet results from a combination of the other two modes. Methods.The analyses were carried out on recent data sets by using multiple-frequency analyses and statistics with the package PERIOD04. In particular, the small departures from equidistance were calculated for the three selected stars. Results.For the δ Scuti variable 1 Mon, the departure from equidistance is only 0.000079 ± 0.000001 cd-1 (or 0.91 ± 0.01 nHz). For 1 Mon the Combination Mode Hypothesis with a mode excited by resonance is the most probable explanation. For the star RR Lyr, the hypothesis of resonance through a combination of modes should be considered. The results for the best-studied cepheid with a Blazhko period (V473 Lyr) are inconclusive because of an unfavorable period of 1.49d and insufficient data.
The Blazhko effect of RR Lyrae in 2003-2004 Kolenberg, K.; Smith, H. A.; Gazeas, K. D. ...
Astronomy and astrophysics (Berlin),
11/2006, Letnik:
459, Številka:
2
Journal Article
Recenzirano
Odprti dostop
Aims.Extensive photometry of RR Lyr was obtained over a 421-day interval in 2003–2004, covering more than 10 Blazhko cycles in a multisite campaign. The length and density of this data set allow for ...a detailed analysis. Methods.We used Fourier techniques to study RR Lyr's behavior over the pulsation and the Blazhko cycle. We propose a two-frequency model for decomposing the frequency spectrum. Results.The light variations were fitted with the main radial frequency, its harmonics up to 11th order, and the detected triplet frequencies. No significant quintuplet components were found in the frequency spectrum. Given the total time span of the measurements, we can now unambiguously conclude that the Blazhko period has become notably shorter than the previously known value of 40.8 days, whereas the main pulsation period remained roughly the same. Changes in the modulation period have been reported for other well-studied Blazhko variables. They challenge the explanations for the Blazhko effect which link the modulation period directly to the rotation period. The new photometry reveals an interval in the pulsation cycle of RR Lyr during which the star's intensity barely changes over the Blazhko cycle. This interval occurs during the infalling motion and between the supposed phases of the early and the main shock. The data also permit a more detailed study of the light curve shape at different phases in the Blazhko period through Fourier parameters.
The amplitude and phase modulation observed in a significant fraction of the RR Lyrae variables - the Blazhko effect - represents a longstanding enigma in stellar pulsation theory. No satisfactory ...explanation for the Blazhko effect has been proposed so far. In this paper we focus on the Stothers idea, in which modulation is caused by changes in the structure of the outer convective zone, caused by a quasi-periodically changing magnetic field. However, up to this date no quantitative estimates were made to investigate whether such a mechanism can be operational and whether it is capable of reproducing the light variation we observe in Blazhko variables. We address the latter problem. We use a simplified model, in which the variation of turbulent convection is introduced into the non-linear hydrodynamic models in an ad hoc way, neglecting interaction with the magnetic field. We study the light-curve variation through the modulation cycle and properties of the resulting frequency spectra. Our results are compared with Kepler observations of RR Lyr. We find that reproducing the light-curve variation, as is observed in RR Lyr, requires a huge modulation of the mixing length, of the order of ±50 per cent, on a relatively short time-scale of less than 40 d. Even then, we are not able to reproduce all the observed relations between modulation components present in the frequency spectrum and the relations between Fourier parameters describing the shape of the instantaneous light curves.
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 (f0 = 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 f0 and its harmonics, two independent terms, the terms related to the Blazhko frequency fm, and to several combination terms. Results: A Blazhko frequency fm = 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 f1 = 3.630 and f2 = 3.159 d-1 are detected. Taking its ratio with the fundamental radial mode into account, the term f1 could be the identified as the second radial overtone. Detecting of these modes in horizontal branch stars is a new result obtained by CoRoT.
We have gathered and analysed multicolour Geneva photometry and high-resolution spectroscopy of the stars HD 121190 (B9V) and HD 106419 (B9III) whose short-term periodic variability had become ...evident from their HIPPARCOS data. We find three significant frequencies for HD 121190 in the Geneva data: 2.6831, 2.6199 and 2.4713 c d super(-1) and classify the star as a slowly pulsating B star, the coolest single star of that class known to date. Its amplitude ratios are compatible with low-degree gravity modes. The spectra reveal low-amplitude variability and v sin i = 118 km s super(-1) which implies that the star rotates at 26% of its critical velocity. For HD 106419 we are unable to confirm the period found from the HIPPARCOS photometry in our ground-based data; rather we find a marginally significant frequency of 0.8986 c d super(-1). This star is probably an evolved slowly pulsating B star with complex variations. HD 106409 is also a moderate rotator as the spectra reveal v sin i: 78 km s super(-1), which is also 26% of its critical velocity.
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