We present Kepler satellite photometry of KIC10661783, a short-period binary star system which shows total eclipses and multiperiodic delta Scuti pulsations. A frequency analysis of the ...eclipse-subtracted light curve reveals at least 68 frequencies, of which 55 or more can be attributed to pulsation modes. The main limitation on this analysis is the frequency resolution within the 27-d short-cadence light curve. Most of the variability signal lies in the frequency range 18-31 d-1, with amplitudes between 0.1 and 4 mmag. One harmonic term (2f) and a few combination frequencies (fi+fj) have been detected. From a plot of the residuals versus orbital phase, we assign the pulsations to the primary star in the system. The pulsations were removed from the short-cadence data and the light curve was modelled using the Wilson-Devinney code. We are unable to get a perfect fit due to the residual effects of pulsations and also to the treatment of reflection and reprocessing in the light-curve model. A model where the secondary star fills its Roche lobe is favoured, which means that KIC10661783 can be classified as an oEA system. Further photometric and spectroscopic observations will allow the masses and radii of the two stars to be measured to high precision and hundreds of delta Scuti pulsation frequencies to be resolved. This could lead to unique constraints on theoretical models of delta Scuti stars, if the evolutionary history of KIC10661783 can be accounted for.
Context. The influence of binarity on the late stages of stellar evolution remains an open issue. Aims. While the first binary post-AGB stars were serendipitously discovered, the distinct ...characteristics of their spectral energy distribution (SED) allowed us to launch a more systematic search for binaries. We selected post-AGB objects, which exhibit a broad dust excess starting either at H or K, pointing to the presence of a gravitationally bound dusty disc in the system. We initiated an extensive multiwavelength study of those systems and here report on our radial velocity and photometric monitoring results for six stars of early F type, which are pulsators of small amplitude. Methods. To determine the radial velocity of low signal-to-noise ratio time-series data, we constructed dedicated autocorrelation masks based on high signal-to-noise ratio spectra, used in our published chemical studies. The radial velocity variations were analysed in detail to differentiate between pulsational variability and variability caused by orbital motion. When available, the photometric monitoring data were used to complement the time series of radial velocity data and to establish the nature of the pulsation. Finally, orbital minimalisation was performed to constrain the orbital elements. Results. All of the six objects are binaries with orbital periods ranging from 120 to 1800 days. Five systems have non-circular orbits. The mass functions range from 0.004 to 0.57 $M_{\odot}$ and the companions are probably unevolved objects of (very) low initial mass. We argue that these binaries must have evolved through a phase of strong binary interaction when the primary was a cool supergiant. Although the origin of the circumstellar disc is not well understood, the disc is generally believed to have formed during this strong interaction phase. The eccentric orbits of these highly evolved objects remain poorly understood. In one object, the line-of-sight grazes the edge of the puffed-up inner rim of the disc. Conclusions. These results corroborate our earlier statement that evolved objects in binary stars create a Keplerian dusty circumbinary disc. With the measured orbits and mass functions, we conclude that the circumbinary discs seem to have a major impact on the evolution of a significant fraction of binary systems.
Context. Many aspects of the design trade-off of a space-based instrument and its performance can best be tackled through simulations of the expected observations. The complex interplay of various ...noise sources in the course of the observations make such simulations an indispensable part of the assessment and design study of any space-based mission. Aims. We present a formalism to model and simulate photometric time series of CCD images by including models of the CCD and its electronics, the telescope optics, the stellar field, the jitter movements of the spacecraft, and all of the important natural noise sources. Methods. This formalism has been implemented in a versatile end-to-end simulation software tool, specifically designed for the PLATO (Planetary Transists and Oscillations of Stars) space mission to be operated from L2, but easily adaptable to similar types of missions. We call this tool Plato Simulator. Results. We provide a detailed description of several noise sources and discuss their properties in connection with the optical design, the allowable level of jitter, the quantum efficiency of the detectors, etc. The expected overall noise budget of generated light curves is computed, as a function of the stellar magnitude, for different sets of input parameters describing the instrument properties. The simulator is offered to the scientific community for future use.
We present Kepler satellite photometry of KIC 10661783, a short-period binary star system which shows total eclipses and multiperiodic δ Scuti pulsations. A frequency analysis of the ...eclipse-subtracted light curve reveals at least 68 frequencies, of which 55 or more can be attributed to pulsation modes. The main limitation on this analysis is the frequency resolution within the 27-d short-cadence light curve. Most of the variability signal lies in the frequency range 18-31 d−1, with amplitudes between 0.1 and 4 mmag. One harmonic term (2f) and a few combination frequencies (fi
+fj
) have been detected. From a plot of the residuals versus orbital phase, we assign the pulsations to the primary star in the system. The pulsations were removed from the short-cadence data and the light curve was modelled using the Wilson-Devinney code. We are unable to get a perfect fit due to the residual effects of pulsations and also to the treatment of reflection and reprocessing in the light-curve model. A model where the secondary star fills its Roche lobe is favoured, which means that KIC 10661783 can be classified as an oEA system. Further photometric and spectroscopic observations will allow the masses and radii of the two stars to be measured to high precision and hundreds of δ Scuti pulsation frequencies to be resolved. This could lead to unique constraints on theoretical models of δ Scuti stars, if the evolutionary history of KIC 10661783 can be accounted for.
Abstract
This paper presents a numerical method to determine the proper rate of spray water mass flow to be supplied to an injection attemperator. The basic aim of this method is to keep the steam ...temperature of the superheater outlet at a constant (assumed) level, when the parameters of steam at the inlet to the attemperator and combustion gases at the inlet to the superheater vary. The presented method is suggested for digital control of superheated steam temperature. A crucial condition for correct control is setting up a precise numerical model of the superheater, which would provide fast and accurate determination of the cooling water mass flow supplied to the injection attemperator. For that purpose, a model of a superheater with distributed parameters was developed, which comprises solving equations describing the laws of mass, momentum, and energy conservation. The proposed method to determine the mass flowrate of spray water is based on computed steam temperatures at the inlet and outlet of the analysed superheater stage. The so formulated problem, being an inverse one, was solved using the Regula Falsi method. A computational test verifying the proposed solution is presented. A comparison of numerical calculation results and measurements, taken on the platen superheater of a steam boiler type OP-210 with 210 × 103 kg/h capacity, is also presented. In both cases, a fully satisfactory agreement of the computed steam temperature at the superheater outlet with the assumed value was achieved. The suggested solution to the inverse problem, combined with the proposed model of superheater dynamics, enables one to determine the proper mass flow of spray water in on-line mode and improve the control quality.
We have used high-speed spectroscopy of the rapidly oscillating Ap (roAp) star HD 99563 to study the pulsation amplitude and phase behaviour of elements in its stratified atmosphere over one 2.91-d ...rotation cycle. We identify spectral features related to patches in the surface distribution of chemical elements and study the pulsation amplitudes and phases as the patches move across the stellar disc. The variations are consistent with a distorted non-radial dipole pulsation mode. We measure a 1.6 km s−1 rotational variation in the mean radial velocities of Hα and argue that this is the first observation of Hα abundance spots caused by He settling through suppression of convection by the magnetic field on an oblique rotator, in support of a prime theory for the excitation mechanism of roAp star pulsation. We demonstrate that HD 99563 is the second roAp star to show aspect dependence of blue-to-red running wave line profile variations in Nd iii spots.
Context. S-type AGB stars are thought to be in the transitional phase between M-type and C-type AGB stars. Because the composition of the circumstellar environment reflects the photospheric ...abundances, one may expect a strong influence of the stellar C/O ratio on the molecular chemistry and the mineralogy of the circumstellar dust. Aims. In this paper, we present a large sample of 87 intrinsic galactic S-type AGB stars, observed at infrared wavelengths with the Spitzer Space Telescope, and supplemented with ground-based optical data. Methods. On the one hand, we derive the stellar parameters from the optical spectroscopy and photometry, using a grid of model atmospheres. On the other, we decompose the infrared spectra to quantify the flux-contributions from the different dust species. Finally, we compare the independently determined stellar parameters and dust properties. Results. For the stars without significant dust emission features, we detect a strict relation between the presence of SiS absorption in the Spitzer spectra and the C/O ratio of the stellar atmosphere. These absorption bands can thus be used as an additional diagnostic for the C/O ratio. For stars with significant dust emission, we define three distinct groups, based on the relative contribution of certain dust species to the infrared flux. We find a strong link between group-membership and C/O ratio. Furthermore, we show that these groups can be explained by assuming that the dust-condensation can be cut short before silicates are produced, while the remaining free atoms and molecules can then be used to form the observed magnesium sulfides or the carriers of the unidentified 13 μm and 20 μm features. Finally, we present the detection of emission features attributed to molecules and dust characteristic to C-type stars, such as molecular SiS, hydrocarbons and magnesium sulfide grains. We show that we often detect magnesium sulfides together with molecular SiS and we propose that it is formed by a reaction of SiS molecules with Mg.
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