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| 2. |
- Fossati, L., et al.
(author)
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An in-depth spectroscopic analysis of RR Lyr Variations over the pulsation cycle
- 2014
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In: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 445:4, s. 4094-4104
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Journal article (peer-reviewed)abstract
- 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.
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| 3. |
- Kochukhov, Oleg, et al.
(author)
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Chemical stratification in the atmosphere of Ap star HD 133792. Regularized solution of the vertical inversion problem
- 2006
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 460:3, s. 831-842
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Journal article (peer-reviewed)abstract
- Context. High spectral resolution studies of cool Ap stars reveal conspicuous anomalies of the shape and strength of many absorption lines. This is a signature of large atmospheric chemical gradients ( chemical stratification) produced by the selective radiative levitation and gravitational settling of chemical species. Aims. Previous observational studies of the chemical stratification in Ap stars were limited to fitting simple parametrized chemical profiles. Here we present a new approach to mapping the vertical chemical structures in stellar atmospheres. Methods. We have developed a regularized chemical inversion procedure that uses all information available in high-resolution stellar spectra. The new technique for the first time allowed us to recover chemical profiles without making a priori assumptions about the shape of chemical distributions. We have derived average abundances and applied the vertical inversion procedure to the high-resolution VLT UVES spectra of the weakly magnetic, cool Ap star HD133792. Results. Our spectroscopic analysis yielded improved estimates of the atmospheric parameters of HD133792. We show that this star has negligible v(e) sin i and the mean magnetic field modulus < B > = 1.1 +/- 0.1 kG. We have derived average abundances for 43 ions and obtained vertical distributions of Ca, Si, Mg, Fe, Cr, and Sr. All these elements except Mg show high overabundance in the deep layers and solar or sub-solar composition in the upper atmosphere of HD133792. In contrast, the Mg abundance increases with height. Conclusions. We find that transition from the metal-enhanced to metal-depleted zones typically occurs in a rather narrow range of depths in the atmosphere of HD133792. Based on the derived photospheric abundances, we conclude that HD133792 belongs to the rare group of evolved cool Ap stars, which possesses very large Fe-peak enhancement, but lacks a prominent overabundance of the rare-earth elements.
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| 4. |
- Titarenko, A. P., et al.
(author)
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Chemical composition and evolutionary status of the Ap star HD 138633
- 2013
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In: Astronomy letters. - 1063-7737 .- 1562-6873. ; 39:5, s. 347-356
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Journal article (peer-reviewed)abstract
- We present the results of our study of the atmospheric chemical composition and evolutionary status for the chemically peculiar Ap star HD 138633. In contrast to ordinary Ap stars that exhibit strong lines of rare-earth elements in their spectra, these elements are represented very poorly in the spectrum of HD 138633. The magnetic field is estimated to be less than 700 G, which is also atypical of peculiar Ap stars. We have detected a stratification of such elements as Fe, Si, Ca, and Y in the atmosphere of HD 138633 whose pattern agrees qualitatively with the predictions of the theory of diffusive separation of elements under the joint action of gravity and radiation pressure forces. The nonuniform distribution obtained by assuming a stepwise distribution of elements in depth agrees qualitatively with the stratification distribution for beta CrB. The search for pulsations points to the possible existence of lowamplitude pulsations with a period of about 17 min.
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| 6. |
- Alentiev, D., et al.
(author)
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Discovery of the longest period rapidly oscillating Ap star HD177765
- 2012
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In: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966 .- 1745-3925. ; 421:1, s. L82-L86
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Journal article (peer-reviewed)abstract
- We present the discovery of a long-period, rapidly oscillating Ap (roAp) star, HD177765. Using high-resolution time-series observations obtained with the Ultraviolet and Visual Echelle Spectrograph at the European Southern Observatory Very Large Telescope, we found radial velocity variations with amplitudes 7-150 ms(-1) and a period of 23.6 min, exceeding that of any previously known roAp star. The largest pulsation amplitudes are observed for Eu III, Ce III and for the narrow core of H alpha. We derived the atmospheric parameters and chemical composition of HD177765, showing this star to be similar to other long-period roAp stars. Comparison with theoretical pulsational models indicates an advanced evolutionary state for HD177765. Abundance analyses of this and other roAp stars suggest a systematic variation with age of the rare-earth line anomalies seen in cool Ap stars.
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| 7. |
- Hareter, M., et al.
(author)
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MOST discovers a multimode delta Scuti star in a triple system : HD 61199
- 2008
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 492:1, s. 185-195
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Journal article (peer-reviewed)abstract
- Context. A field star, HD61199 (V approximate to 8), simultaneously observed with Procyon by the MOST (Microvariability & Oscillations of STars) satellite in continuous runs of 34, 17, and 34 days in 2004, 2005, and 2007, was found to pulsate in 11 frequencies in the delta Scuti range with amplitudes from 1.7 down to 0.09 mmag. The photometry also showed variations with a period of about four days. To investigate the nature of the longer period, 45 days of time-resolved spectroscopy was obtained at the Thuringer Landessternwarte Tautenburg in 2004. The radial velocity measurements indicate that HD61199 is a triple system. Aims. A delta Scuti pulsator with a rich eigenspectrum in a multiple system is promising for asteroseismology. Our objectives were to identify which of the stars in the system is the delta Scuti variable and to obtain the orbital elements of the system and the fundamental parameters of the individual components, which are constrained by the pulsation frequencies of the delta Scuti star.Methods. Classical Fourier techniques and least-squares multi-sinusoidal fits were applied to the MOST photometry to identify the pulsation frequencies. The groundbased spectroscopy was analysed with least-squares-deconvolution (LSD) techniques, and the orbital elements derived with the KOREL and ORBITX routines. Asteroseismic models were also generated. Results. The photometric and spectroscopic data are compatible with a triple system consisting of a close binary with an orbital period of 3.57 days and a d Scuti companion (HD61199 A) as the most luminous component. The d Scuti star is a rapid rotator with about v sin i = 130 km s(-1) and an upper mass limit of about 2.1 M-circle dot. For the close binary components, we find they are of nearly equal mass, with lower mass limits of about 0.7 M-circle dot. Comparisons to synthetic spectra indicate these stars have a late-F spectral type. The observed oscillation frequencies are compared to pulsation models to further constrain the evolutionary state and mass of HD61199 A. The orbit frequency of the close binary corresponds to the difference of the two d Scuti frequencies with the highest amplitudes a coincidence that is remarkable, but not explained.
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| 8. |
- Kochukhov, Oleg, et al.
(author)
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Discovery of new rapidly oscillating Ap pulsators in the UVES survey of cool magnetic Ap stars
- 2013
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In: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 431:3, s. 2808-2819
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Journal article (peer-reviewed)abstract
- We have carried out a survey of short-period pulsations among a sample of carefully chosen cool Ap stars using time-resolved observations with the Ultraviolet and Visual Echelle Spectrograph at the European Southern Observatory ESO 8 m Very Large Telescope. Here, we report the discovery of pulsations with amplitudes 50-100 m s(-1) and periods 7-12 min in HD 132205, HD 148593 and HD 151860. These objects are therefore established as new rapidly oscillating Ap (roAp) stars. In addition, we independently confirm the presence of pulsations in HD 69013, HD 96237 and HD 143487 and detect, for the first time, radial velocity oscillations in two previously known photometric roAp stars HD 119027 and HD 185256. At the same time, no pulsation variability is found for HD 5823, HD 178892 and HD 185204. All of the newly discovered roAp stars were previously classified as non-pulsating based on the low-precision ground-based photometric surveys. This shows that such observations cannot be used to reliably distinguish between pulsating and non-pulsating stars and that all cool Ap stars may harbour p-mode pulsations of different amplitudes.
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| 9. |
- Kolenberg, K., et al.
(author)
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An in-depth spectroscopic analysis of the Blazhko star RR Lyrae : I. Characterisation of the star: abundance analysis and fundamental parameters
- 2010
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 519, s. A64-
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Journal article (peer-reviewed)abstract
- Context. The knowledge of accurate stellar parameters is a keystone in several fields of stellar astrophysics, such as asteroseismology and stellar evolution. Although the fundamental parameters can be derived from both spectroscopy and multicolour photometry, the results obtained are sometimes affected by systematic uncertainties. Stellar pulsation reaches high amplitudes in RR Lyrae stars, and as a consequence the stellar parameters vary significantly over the pulsation cycle. The abundances of the star, however, are not expected to change. Aims. We present a self-consistent spectral analysis of the pulsating star RR Lyr, which is the primary target of our study of the Blazhko effect. Methods. We used high-resolution and high signal-to-noise ratio spectra to carry out a consistent parameter determination and abundance analysis for RR Lyr. The LLmodels code was employed for model atmosphere calculations, while the SYNTH3 and WIDTH9 codes were used for line profile calculations and LTE abundance analysis. We describe in detail the methodology adopted to derive the fundamental parameters and the abundances. From a set of available high-resolution spectra of RR Lyr, we selected the phase of maximum radius at which the spectra are least disturbed by the pulsation. Using the abundances determined at this phase as a starting point, we expect to be able to determine the fundamental parameters determined at other phases more accurately. Results. The set of fundamental parameters obtained in this work fits the observed spectrum accurately. From the abundance analysis, we find clear indications of a depth-dependent microturbulent velocity, that we quantify. Conclusions. We confirm the importance of a consistent analysis of relevant spectroscopic features, the application of advanced model atmospheres, and the use of up-to-date atomic line data for determining stellar parameters. These results are crucial for further studies, e. g., detailed theoretical modelling of the observed pulsations.
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