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تسجيل مستخدم جديدPhotometry of Beta Lyrae in 2018 by the BRITE satellites
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Observations of Beta Lyr in four months of 2018 by three BRITE Constellation satellites (the red-filter BTr and BHr, and the blue-filter BLb) permitted a first, limited look into the light-curve variability in two spectral bands. The variations were found to be well correlated outside the innermost primary minima with the blue variations appearing to have smaller amplitudes than the red; this reduction may reflect their presumed origin in the cooler, outer parts of the accretion disk. This result must be confirmed with more extensive material as the current conclusions are based on observations spanning slightly less than three orbital cycles of the binary. The assumption of an instrumental problem and the applied corrections made to explain the unexpectedly large amplitude of the red-filter light-curve observed with the BTr satellite in 2016 are fully confirmed by the 2018 results.
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Photometric instabilities of $beta$ Lyr were observed in 2016 by two red-filter BRITE satellites over more than 10 revolutions of the binary, with $sim$100-minute sampling. Analysis of the time series shows that flares or fading events take place typ
ically 3 to 5 times per binary orbit. The amplitudes of the disturbances (relative to the mean light curve, in units of the maximum out-of-eclipse light-flux, f.u.) are characterized by a Gaussian distribution with $sigma=0.0130pm0.0004$ f.u. Most of the disturbances appear to be random, with a tendency to remain for one or a few orbital revolutions, sometimes changing from brightening to fading or the reverse. Phases just preceding the center of the deeper eclipse showed the most scatter while phases around secondary eclipse were the quietest. This implies that the invisible companion is the most likely source of the instabilities. Wavelet transform analysis showed domination of the variability scales at phase intervals $0.05-0.3$ (0.65--4 d), with the shorter (longer) scales dominating in numbers (variability power) in this range. The series can be well described as a stochastic Gaussian process with the signal at short timescales showing a slightly stronger correlation than red noise. The signal de-correlation timescale $tau=(0.068pm0.018)$ in phase or $(0.88pm0.23)$~d appears to follow the same dependence on the accretor mass as that observed for AGN and QSO masses 5--9 orders of magnitude larger than the $beta$~Lyr torus-hidden component.
The BTr and UBr satellites observed $beta$ Lyrae from May to October 2016 to continuously monitor light-curve instabilities with the time resolution of about 100 mins. An instrumental problem affecting localized patches on the BTr CCD detector has be
en discovered by comparison with partly simultaneous UBr observations; the origin of the problem is being investigated. A zero-point offset permits utilization of the BTr data for a time-series characterization of deviations from the mean light curve defined to $simeq 0.0025$ mag.
HD149404 is an evolved non-eclipsing O-star binary that has previously undergone a Roche lobe overflow interaction. Understanding some key properties of the system requires a determination of the orbital inclination and of the dimensions of the compo
nents. The BRITE-Heweliusz satellite was used to collect photometric data of HD149404. Additional photometry was retrieved from the SMEI archive. These data were analysed using a suite of period search tools. The orbital part of the lightcurve was modelled with the nightfall binary star code. The Gaia-DR2 parallax of HD149404 was used to provide additional constraints. The periodograms reveal a clear orbital modulation of the lightcurve with a peak-to-peak amplitude near 0.04 mag. The remaining non-orbital part of the variability is consistent with red noise. The lightcurve folded with the orbital period reveals ellipsoidal variations, but no eclipses. The minimum when the secondary star is in inferior conjunction is deeper than the other minimum due to mutual reflection effects between the stars. Combined with the Gaia-DR2 parallaxes, the photometric data indicate an orbital inclination in the range of 23{deg} to 31{deg} and a Roche lobe filling factor of the secondary larger than or equal to 0.96. The luminosity of the primary star is consistent with its present-day mass, whereas the more evolved secondary appears overluminous for its mass. We confirm that the primarys rotation period is about half the orbital period. Both features most probably stem from the past Roche lobe overflow episode.
BRITE-Constellation (where BRITE stands for BRIght Target Explorer) is an international nanosatellite mission to monitor photometrically, in two colours, brightness and temperature variations of stars brighter than V = 4. The current mission design c
onsists of three pairs of 7 kg nanosats from Austria, Canada and Poland carrying optical telescopes and CCDs. One instrument in each pair is equipped with a blue filter; the other, a red filter. The first two nanosats are UNIBRITE, designed and built by University of Toronto Institute for Aerospace Studies - Space Flight Laboratory and its twin, BRITE-Austria, built by the Technical University Graz with support of UTIAS-SFL. They were launched on 25 February 2013 by the Indian Space Agency under contract to the Canadian Space Agency into a low-Earth dusk-dawn polar orbit.
This paper aims to precisely determine the masses and detect pulsation modes in the two massive components of Beta Cen with BRITE-Constellation photometry. In addition, seismic models for the components are considered and the effects of fast rotation
are discussed. This is done to test the limitations of seismic modeling for this very difficult case. A simultaneous fit of visual and spectroscopic orbits is used to self-consistently derive the orbital parameters, and subsequently the masses, of the components. The derived masses are equal to 12.02 +/- 0.13 and 10.58 +/- 0.18 M_Sun. The parameters of the wider, A - B system, presently approaching periastron passage, are constrained. Analysis of the combined blue- and red-filter BRITE-Constellation photometric data of the system revealed the presence of 19 periodic terms, of which eight are likely g modes, nine are p modes, and the remaining two are combination terms. It cannot be excluded that one or two low-frequency terms are rotational frequencies. It is possible that both components of Beta Cen are Beta Cep/SPB hybrids. An attempt to use the apparent changes of frequency to distinguish which modes originate in which component did not succeed, but there is potential for using this method when more BRITE data become available. Agena seems to be one of very few rapidly rotating massive objects with rich p- and g-mode spectra, and precisely known masses. It can therefore be used to gain a better understanding of the excitation of pulsations in relatively rapidly rotating stars and their seismic modeling. Finally, this case illustrates the potential of BRITE-Constellation data for the detection of rich-frequency spectra of small-amplitude modes in massive pulsating stars.
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