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Register a new userLong photometric cycle and disk evolution in the $beta$ Lyrae type binary OGLE-BLG-ECL-157529
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Added by
Ronald Mennickent Dr.
Publication date
2020
fields
Physics
and research's language is
English
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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.
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Some close binaries of the beta Lyrae type show photometric cycles longer than the orbital one, which are possibly related to changes in their accretion disks. We aim to understand the short- and long-scale changes observed in the light curve of the eclipsing system OGLE-BLG-ECL-157529. In particular, we want to shed light on the contribution of the disk to these changes, especially those related to the long cycle, occurring on timescales of hundreds of days. We studied I-band OGLE photometric times series spanning 18.5 years, constructing disk models by analyzing the orbital light curve at 52 consecutive epochs. An optimized simplex algorithm was used to solve the inverse problem by adjusting the light curve with the best stellar-orbital-disk parameters for the system. We applied principal components analysis to the parameters to evaluate their dependence and variability. We constructed a description of the mass transfer rate in terms of disk parameters. We find that the light variability can be understood in terms of a variable mass transfer rate and variable accretion disk. The system brightness at orbital phase 0.25 follows the long cycle and is correlated with the mass transfer rate and the disk thickness. The long-cycle brightness variations can be understood in terms of differential occultation of the hotter star by a disk of variable thickness. Our model fits the overall light curve during 18.5 years well, including epochs of reversal of main and secondary eclipse depths. The disk radius cyclically change around the tidal radius, decoupled from changes in the mass transfer rate or system brightness, suggesting that viscous delay might explain the non-immediate response. Although the disk is large and fills a large fraction of the hot star Roche lobe, Lindblad resonance are far beyond the disk, excluding viscous dissipation as a major source of photometric variability.
Aim: Our aim is to obtain high-accuracy measurements of the physical and orbital parameters of two evolved eclipsing binary systems, and to use these measurements to study their evolutionary status. We also aim to derive distances to the systems by using a surface brightness - colour relation and compare these distances with the measurements provided by GAIA. Methods: We measured the physical and orbital parameters on both systems based on V-band and I-band photometry from OGLE, near-infrared photometry obtained with the NTT telescope and the instrument SOFI, as well as high-resolution spectra obtained at ESO 3.6m/HARPS and Clay 6.5/MIKE spectrographs. The light curves and radial-velocity curves were analysed with the Wilson-Devinney code. Results: We analysed two double-lined eclipsing binary systems OGLE-BLG-ECL-23903 and OGLE-BLG-ECL-296596 from the Optical Gravitational Lensing Experiment (OGLE) catalogue. Both systems have a configuration of two well-detached giant stars. The masses of the components ofOGLE-BLG-ECL-123903 are M_1= 2.045 $pm$ 0.027 and M_2=2.074 $pm$ 0.023 $M_odot$ and the radii are R_1=9.540 $pm$ 0.049 and R_2=9.052 $pm$ 0.060 $R_odot$. For OGLE-BLG-ECL-296596, the masses are M_1=1.093 $pm$ 0.015 and M_2=1.125 $pm$ 0.014 $M_odot$, while the radii are R_1=18.06 $pm$ 0.28 and R_2=29.80 $pm$ 0.33 $R_odot$. Evolutionary status was discussed based on the isochrones and evolutionary tracks from PARSEC and MESA codes. The ages of the systems were establishes to be around 1.3 Gyr for the OGLE-BLG-ECL-123903 and 7.7 Gyr for the OGLE-BLG-ECL-296596. We also determined the distance to both systems. For OGLE-BLG-ECL-123903 this is equal to d=2.95 $pm$ 0.06 (stat.) $pm$ 0.07 (syst.) kpc, while for the OGLE-BLG-ECL-296596 it is d=5.68 $pm$ 0.07 (stat.) $pm$ 0.14 (syst.) kpc. This is the first analysis of its kind for these unique evolved eclipsing binary systems.
In this first paper of the series we describe our project to calibrate the distance determination method based on early-type binary systems. The final objective is to measure accurate, geometrical distances to galaxies beyond the Magellanic Clouds with a precision of 2%. We start with the analysis of two early-type systems for which we have collected all the required spectroscopic and photometric data. Apart from catalog publications, these systems have not been studied yet, and it is the first time the modeling of light and radial velocity curves is performed for them. From the analysis we obtained precise physical parameters of the components, including the masses measured with precision of 0.6-1% and radii with precision of 0.4-3%. For one system we determined the $(V-K)$ color and estimated the distance using the bolometric flux scaling method (DM=18.47 $pm$ 0.15 mag), which agrees well with our accurate determination of the distance to the LMC from late-type giants. For the same system we determined the surface brightness of individual stars using our model, and checked that it is consistent with a recent surface brightness -- color relation. We compared our results with evolution theory models of massive stars and found they agree in general, however, models with higher overshooting values give more consistent results. The age of the system was estimated to from 11.7 to 13.8 Myr, depending on the model.
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.
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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