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Frandsen S.,University of Aarhus | Lehmann H.,Thuringer Landessternwarte Tautenburg | Hekker S.,University of Amsterdam | Southworth J.,Keele University | And 13 more authors.
Astronomy and Astrophysics | Year: 2013

Context. Detached eclipsing binaries (dEBs) are ideal targets for accurately measuring the masses and radii of their component stars. If at least one of the stars has evolved off the main sequence (MS), the masses and radii give a strict constraint on the age of the stars. Several dEBs containing a bright K giant and a fainter MS star have been discovered by the Kepler satellite. The mass and radius of a red giant (RG) star can also be derived from its asteroseismic signal. The parameters determined in this way depend on stellar models and may contain systematic errors. It is important to validate the asteroseismically determined mass and radius with independent methods. This can be done when stars are members of stellar clusters or members of dEBs. Aims. This paper presents an analysis of the dEB system KIC 8410637, which consists of an RG and an MS star. The aim is to derive accurate masses and radii for both components and provide the foundation for a strong test of the asteroseismic method and the accuracy of the deduced mass, radius, and age. Methods. We analysed high-resolution, high-signal-to-noise spectra from three different spectrographs. We also calculated a fit to the Kepler light curve and used ground-based photometry to determine the flux ratios between the component stars in the BVRI passbands. Results. We measured the masses and radii of the stars in the dEB, and the classical parameters Teff, log g, and [Fe/H] from the spectra and ground-based photometry. The RG component of KIC 8410637 is most likely in the core helium-burning red clump phase of evolution and has an age and composition that are very similar to the stars in the open cluster NGC 6819. The mass of the RG in KIC 8410637 should therefore be similar to the mass of RGs in NGC 6819, thus lending support to the latest version of the asteroseismic scaling relations. This is the first direct measurement of both mass and radius for an RG to be compared with values for RGs from asteroseismic scaling relations thereby providing an accurate comparison. We find excellent agreement between log g values derived from the binary analysis and asteroseismic scaling relations. Conclusions. We have determined the masses and radii of the two stars in the binary accurately. A detailed asteroseismic analysis will be presented in a forthcoming paper, allowing an informative comparison between the parameters determined for the dEB and from asteroseismology. © ESO, 2013.

Garrido H.E.,Hemisphere | Garrido H.E.,University of Concepción | Mennickent R.E.,Hemisphere | Mennickent R.E.,University of Concepción | And 5 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2013

We analyse multicolour light curves and high-resolution optical spectroscopy of the eclipsing binary and double periodic variable (DPV) OGLE 05155332-6925581. According to Mennickent et al., this system shows a significant change in the long non-orbital photometric cycle, a loop in the colour-magnitude diagram during this cycle and discrete spectral absorption components that were interpreted as evidence of systemic mass loss. We find that the best fit to the multiband light curves requires a circumprimary optically thick disc with a radius about twice the radius of the more massive star. The spectroscopy indicates a mass ratio of 0.21 ± 0.02 and masses for the hot and cool stars of 9.1 ± 0.5 and 1.9 ± 0.2M(, respectively. A comparison with synthetic binary-star evolutionary models indicates that the system has an age of 4.76 × 107 yr, and is in the phase of rapid mass transfer, the second one in the life of this binary, in a Case-B mass-exchange stage. Donor-subtracted Hα profiles show the presence of double emission formed probably in an optically thin circumstellarmedium, while the variable He I profile and the Hβ absorption wings are probably formed in the optically thick circumprimary disc. The model that best fits the observations shows the system with a relatively large mass transfer rate of ̇ M = 3.1 × 10-6 M( yr-1. However, the orbital period remains relatively stable during almost 15 yr. This observation suggests that the hotspot mass-loss model proposed by other authors is not adequate in this case, and that some other mechanism is efficiently removing angular momentum from the binary. Furthermore, our observations suggest that the DPV phenomenon could have an important effect in the balance of mass and angular momentum in the system. © 2012 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Barria D.,University of Concepción | Barria D.,European Southern Observatory | Mennickent R.E.,University of Concepción | Schmidtobreick L.,European Southern Observatory | And 7 more authors.
Astronomy and Astrophysics | Year: 2013

Context. To add to the growing collection of well-studied double periodic variables (DPVs) we have carried out the first spectroscopic and photometric analysis of the eclipsing binary DQ Velorum to obtain its main physical stellar and orbital parameters. Aims. Combining spectroscopic and photometric observations that cover several orbital cycles allows us to estimate the stellar properties of the binary components and the orbital parameters. We also searched for circumstellar material around the more massive star. Methods. We separated DQ Velorum composite spectra and measured radial velocities with an iterative method for double spectroscopic binaries. We obtained the radial velocity curves and calculated the spectroscopic mass ratio. We compared our single-lined spectra with a grid of synthetic spectra and estimated the temperature of the stars. We modeled the V-band light curve with a fitting method based on the simplex algorithm, which includes an accretion disc. To constrain the main stellar parameters we fixed the mass ratio and donor temperature to the values obtained by our spectroscopic analysis. Results. We obtain a spectroscopic mass ratio q = 0.31 ± 0.03 together with donor and gainer masses Md = 2.2 ± 0.2 M⊙, M g = 7.3 ± 0.3 M⊙, the radii Rd = 8.4 ± 0.2 R⊙, Rg = 3.6 ± 0.2 R ⊙ and temperatures Td = 9400 ± 100 K, T g = 18 500 ± 500 K for the stellar components. We find that DQ Vel is a semi-detached system consisting of a B3V gainer and an A1III donor star plus an extended accretion disc around the gainer. The disc is filling 89% of the gainer Roche lobe with a temperature of 6580 ± 300 K at the outer radius. It has a concave shape that is thicker at its edge (de = 0.6 ± 0.1 R⊙) than at its centre (dc = 0.3 ± 0.1 R⊙). We find a significant sub-orbital frequency of 0.19 d-1 in the residuals of the V-band light curve, which we interpret as a pulsation of an slowly pulsating B-type (SPB) of a gainer star. We also estimate the distance to the binary (d ∼ 3.1 kpc) using the absolute radii, apparent magnitudes, and effective temperatures of the components found in our study. © ESO, 2013.

Molenda-Zakowicz J.,Instytut Astronomiczny Uniwersytetu Wroclawskiego | Sousa S.G.,University of Porto | Frasca A.,National institute for astrophysics | Uytterhoeven K.,Institute of Astrophysics of Canarias | And 16 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2013

The asteroseismic and planetary studies, like all research related to stars, need precise and accurate stellar atmospheric parameters as input. We aim at deriving the effective temperature (Teff), the surface gravity (log g), the metallicity ([Fe/H]), the projected rotational velocity (v sin i) and the MK type for 169 F-, G-, K- and M-type Kepler targets which were observed spectroscopically from the ground with five different instruments. We use two different spectroscopic methods to analyse 189 high-resolution, high-signal-to-noise spectra acquired for the 169 stars. For 67 stars, the spectroscopic atmospheric parameters are derived for the first time. KIC 9693187 and 11179629 are discovered to be double-lined spectroscopic binary systems. The results obtained for those stars for which independent determinations of the atmospheric parameters are available in the literature are used for a comparative analysis. As a result, we show that for solar-type stars the accuracy of present determinations of atmospheric parameters is ±150K in Teff, ±0.15 dex in [Fe/H] and ±0.3 dex in log g. Finally, we confirm that the curve-of-growth analysis and the method of spectral synthesis yield systematically different atmospheric parameters when they are applied to stars hotter than 6000 K. ©2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Benko J.M.,Konkoly Observatory | Kolenberg K.,University of Vienna | Szabo R.,Konkoly Observatory | Kurtz D.W.,University of Central Lancashire | And 17 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2010

We present our analysis of Kepler observations of 29-RR Lyrae stars, based on 138-d of observation. We report precise pulsation periods for all stars. Nine of these stars had incorrect or unknown periods in the literature. 14 of the stars exhibit both amplitude and phase Blazhko modulations, with Blazhko periods ranging from 27.7 to more than 200-d. For V445-Lyr, a longer secondary variation is also observed in addition to its 53.2-d Blazhko period. The unprecedented precision of the Kepler photometry has led to the discovery of the the smallest modulations detected so far. Moreover, additional frequencies beyond the well-known harmonics and Blazhko multiplets have been found. These frequencies are located around the half-integer multiples of the main pulsation frequency for at least three stars. In four stars, these frequencies are close to the first and/or second overtone modes. The amplitudes of these periodicities seem to vary over the Blazhko cycle. V350-Lyr, a non-Blazhko star in our sample, is the first example of a double-mode RR-Lyrae star that pulsates in its fundamental and second overtone modes. © 2010 The Authors. Journal compilation © 2010 RAS.

Kolenberg K.,University of Vienna | Szabo R.,Konkoly Observatory | Kurtz D.W.,University of Central Lancashire | Gilliland R.L.,US Space Telescope Science Institute | And 22 more authors.
Astrophysical Journal Letters | Year: 2010

We present the first results of our analyses of selected RRLyrae stars for which data have been obtained by the Kepler Mission. As expected, we find a significant fraction of the RRab stars to show the Blazhko effect, a still unexplained phenomenon that manifests itself as periodic amplitude and phase modulations of the light curve, on timescales of typically tens to hundreds of days. The long time span of the Kepler Mission of 3.5yr and the unprecedentedly high precision of its data provide a unique opportunity for the study of RRLyrae stars. Using data of a modulated star observed in the first roll as a showcase, we discuss the data, our analyses, findings, and their implications for our understanding of RRLyrae stars and the Blazhko effect. With at least 40% of the RR Lyrae stars in our sample showing modulation, we confirm the high incidence rate that was only found in recent high-precision studies. Moreover, we report the occurrence of additional frequencies, beyond the main pulsation mode and its modulation components. Their half-integer ratio to the main frequency is reminiscent of a period doubling effect caused by resonances, observed for the first time in RRLyrae stars. © 2010. The American Astronomical Society. All rights reserved.

Kolenberg K.,University of Vienna | Bryson S.,NASA | Szabo R.,Hungarian Academy of Sciences | Kurtz D.W.,University of Central Lancashire | And 18 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2011

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 127d. 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 29.4min), 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. © 2010 The Authors Monthly Notices of the Royal Astronomical Society © 2010 RAS.

Barria D.,University of Concepción | Mennickent R.E.,University of Concepción | Graczyk D.,University of Concepción | Kolaczkowski Z.,Instytut Astronomiczny Uniwersytetu Wroclawskiego
Astronomy and Astrophysics | Year: 2014

Aims. In order to better understand the double periodic variable (DPV) phenomenon, we analyse a series of optical spectra of the DPV system DQ Velorum during much of its long-term cycle. In addition, we investigate the evolutionary history of DQ Vel using theoretical evolutionary models to obtain the best representation for the current observed stellar and orbital parameters of the binary. We investigate the evolution of DQ Vel through theoretical evolutionary models to estimate the age and the mass transfer rate which are then compared with those of its twin V393 Scorpii. Methods. We subtracted the donor star contribution from the composite spectra of DQ Vel using a synthetic spectrum as a donor template. Donor-subtracted spectra covering around 60% of the long-term cycle allowed us to investigate time-modulated spectral variations of the gainer star plus the disc. We used Gaussian fits to measure the equivalent widths (EWs) of Balmer and helium lines in the separated spectra during the long-term cycle and thus analyse EW variabilities. We compared the observed stellar parameters of the system with a grid of theoretical evolutionary tracks computed under a conservative and a non-conservative evolution regime. Results. We have found that the EW of Balmer and helium lines in the donor-subtracted spectra are modulated with the long-term cycle. We observe a strengthening in the EWs in all analysed spectral features at the minimum of the long-term cycle which might be related to an extra line emission during the maximum of the long-term variability. Difference spectra obtained at the secondary eclipse support this scenario. We have found that a non-conservative evolutionary model where DQ Vel has lost mass at some stage of its binary history, is a better representation of the current observed properties of the system. The best evolutionary model suggests that DQ Vel has an age of 7.40 × 107 yr and is currently in a low mass transfer rate (-9.8 × 10-9 M ⊙/yr) stage, after a mass transfer burst episode. Comparing the evolutionary stages of DQ Vel and V393 Sco we observed that the former is an older system with a lower mass transfer rate. This might explain the differences observed in the physical parameters of their accretion discs. © 2014 ESO.

Drobek D.,Instytut Astronomiczny Uniwersytetu Wroclawskiego | Pigulski A.,Instytut Astronomiczny Uniwersytetu Wroclawskiego | Shobbrook R.R.,Australian National University | Narwid A.,Instytut Astronomiczny Uniwersytetu Wroclawskiego
Astronomische Nachrichten | Year: 2010

We present results of a photometric study of the young southern open cluster Stock 14. This cluster is known to contain two eclipsing systems with presumed β Cephei components, HD 101794 and HD 101838. We confirm variability due to pulsations and eclipses in both targets and announce the discovery of other variable stars in the observed field. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Brus P.,Instytut Astronomiczny Uniwersytetu Wroclawskiego | Kolaczkowski Z.,Instytut Astronomiczny Uniwersytetu Wroclawskiego
Proceedings of the International Astronomical Union | Year: 2014

We present a study of photometric properties of very crowded stellar fields toward the Galactic Bulge. We performed a search for pulsating stars among thousands of variable stars from the OGLE-II survey supplementing the variability study with photometric measurements in four Johnson-Cousins UBVIC passbands. Using these data, we analysed the properties of objects located at different distances and, whenever possible, classified them. Copyright © International Astronomical Union 2014.

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