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Register a new userStructural changes in the hot Algol OGLE-LMC-DPV-097 and its disk related to its long-cycle
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Added by
Ronald Mennickent Dr.
Publication date
2018
fields
Physics
and research's language is
English
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Double Periodic Variables (DPVs) are hot Algols showing a long photometric cycle of uncertain origin. We report the discovery of changes in the orbital light curve of OGLE-LMC-DPV-097 which depend on the phase of its long photometric cycle. During the ascending branch of the long-cycle the brightness at the first quadrature is larger than during the second quadrature, during the maximum of the long-cycle the brightness is basically the same at both quadratures, during the descending branch the brightness at the second quadrature is larger than during the first quadrature and during the minimum of the long-cycle the secondary minimum disappears. We model the light curve at different phases of the long-cycle and find that the data are consistent with changes in the properties of the accretion disk and two disk spots. The disks size and temperature change with the long-cycle period. We find a smaller and hotter disk at minimum and larger and cooler disk at maximum. The spot temperatures, locations and angular sizes also show variability during the long-cycle.
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OGLE-LMC-DPV-065 is an interacting binary whose double-hump long photometric cycle remains hitherto unexplained. We analyze photometric time series available in archive datasets spanning 124 years and present the analysis of new high-resolution spectra. A refined orbital period is found of 10fd0316267 $pm$ 0fd0000056 without any evidence of variability. In spite of this constancy, small but significant changes in timings of the secondary eclipse are detected. We show that the long period continuously decreases from 350 to 218 days during 13 years, then remains almost constant for about 10 years. Our study of radial velocities indicates a circular orbit for the binary and yields a mass ratio of 0.203 $pm$ 0.001. From the analysis of the orbital light curve we find that the system contains 13.8 and 2.81 msun stars of radii 8.8 and 12.6 rsun and absolute bolometric magnitudes -6.4 and -3.0, respectively. The orbit semi-major axis is 49.9 rsun and the stellar temperatures are 25460 K and 9825 K. We find evidence for an optically and geometrically thick disk around the hotter star. According to our model, the disk has a radius of 25 rsun, central and outer vertical thickness of 1.6 rsun and 3.5 rsun, and temperature of 9380 K at its outer edge. Two shock regions located at roughly opposite parts of the outer disk rim can explain the light curves asymmetries. The system is a member of the double periodic variables and its relatively high-mass and long photometric cycle make it similar in some aspects to $beta$ Lyrae.
V393 Scorpii is a member of the subclass of Algols dubbed Double Periodic Variables (DPVs). These are semidetached binaries with B-type primaries showing a long-photometric cycle lasting in average 33 times the orbital period. We describe the behavior of unreported metallic emission lines in the cool stellar component of this system. The emissions can be single or double for a same line and sometimes show velocity shifts regarding the velocity of the center of mass of the star. In addition, these lines are stronger during the high state. This behavior suggests the presence of active regions in the surface of the rapidly rotating A7 donor covering a fraction of the visible hemisphere, which have larger emissivity during the high state. Our finding supports the recently proposed dynamo model for the long cycle of DPVs proposed by Schleicher & Mennickent. The model predicts an increase of the dynamo number of the donor during epochs of mass transfer in this system, and a theoretical long/orbital period ratio very close to the observed one at the present system age.
The subtype of hot algol semidetached binaries dubbed Double Periodic Variables (DPVs) are characterized by a photometric cycle longer than the orbital one, whose nature has been related to a magnetic dynamo in the donor component controlling the mass transfer rate. We aim to understand the morphologic changes observed in the light curve of OGLE-BLG-ECL-157529 that are linked to the long cycle. In particular, we want to explain the changes in relative depth of primary and secondary eclipses. We analyze $I$ and $V$-band OGLE photometric times series spanning 18.5 years and model the orbital light curve. We find that OGLE-BLG-ECL-157529 is a new eclipsing Galactic DPV of orbital period 24fd8, and that its long cycle length decreases in amplitude and length during the time baseline. We show that the changes of the orbital light curve can be reproduced considering an accretion disk of variable thickness and radius, surrounding the hottest stellar component. Our models indicate changes in the temperatures of hot spot and bright spot during the long cycle, and also in the position of the bright spot. This, along with the changes in disk radius might indicate a variable mass transfer in this system.
This paper presents a detailed analysis of the light and radial velocity curves of the semi-detached eclipsing binary system OGLE-LMC-ECL-09937. The system is composed of a hot, massive and luminous primary star of a late-O spectral type, and a more evolved, but less massive and luminous secondary, implying an Algol-type system that underwent a mass transfer episode. We derive masses of 21.04 +/- 0.34 M_Sun and 7.61 +/- 0.09 M_Sun and radii of 9.93 +/- 0.06 R_Sun and 9.18 +/- 0.04 R_Sun, for the primary and the secondary component, respectively, which make it the most massive known Algol-type system with masses and radii of the components measured with <2% accuracy. Consequently, the parameters of OGLE-LMC-ECL-09937 provide an important contribution to the sparsely populated high-mass end of the stellar mass distribution, and an interesting object for stellar evolution studies, being a possible progenitor of a binary system composed of two neutron stars.
Helioseismic data for solar cycles 23 and 24 have shown unequivocally that solar dynamics changes with solar activity. Changes in solar structure have been more difficult to detect. Basu & Mandel (2004) had claimed that the then available data revealed changes in the HeII ionization zone of the Sun. The amount of change, however, indicated the need for larger than expected changes in the magnetic fields. Now that helioseismic data spanning two solar cycles are available, we have redone the analysis using improved fitting techniques. We find that there is indeed a change in the region around the HeII ionization zone that is correlated with activity. Since the data sets now cover two solar cycles, the time variation is easily discernible.
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