The main aim of the present paper is the very first analysis of the binary-orbit precession out of our Galaxy. 559 binary is a detached system that is undergoing rapid orbit precession. The inclination 559 binary the orbit towards the observer has been changing, which has caused the eclipse depth to become lower over the past decade, and this is ongoing. The period of this effect was derived as only about 77 years, so it is the second fastest nodal motion known amongst such systems nowadays.
This is the first analysis of an extragalactic binary with nodal precession. This effect is probably caused by a distant third body 559 binary the pair, 559 binary could potentially be detected via spectroscopy. Some preliminary estimates of this body are presented.
However, even such 559 binary result can tell us something about the multiplicity fraction in other galaxies. Based on data collected with the Danish 1.
After more than a century of intensive study of eclipsing binaries EBsthey still represent the best method for deriving the masses, radii, and luminosities of stars. Thanks to modern ground- and 559 binary telescopes, we are able to also study these objects in other galaxies and to apply the same methods as used in our solar neighbourhood.
Clausen ; Ribas Studying other galaxies via detailed analysis of individual stars can provide some useful hints for answering these questions. However, one special group of EBs is still rather rare — those undergoing an orbit precession. If the orientation of the EB orbit is moving in space, then the depths of eclipse also change, and we can detect this orbit precession.
Observing the binary at 559 binary time epochs can help us to derive the inclination towards the observer as a function of time. However, 559 binary still know of only a few such systems, and detailed analysis has only been carried out for those located in our Galaxy at present. This is the first time such an effect has been studied in an extragalactic source. However, owing to the low 559 binary of LMC stars, there are still many 559 binary systems that lack detailed analysis.
The system is a detached eclipsing binary with its short orbital period of about 1. According to its photometric indices see belowit is probably a B2V-type system.
Therefore, we can make the first analysis of this interesting system ranging over two decades to 559 binary some long-term changes. For a complete 559 binary curve analysis, we need up-to-date ephemerides of the binary. These ephemerides are also suitable for 559 binary future observations. From the observations we determine that the orbit is circular i. The following 559 binary was used for the analysis.
First, the ephemerides and temperature of the primary 559 binary were fixed for the entire computational process. The temperature of the primary component was estimated from its photometric index. Owing to many different sources and a rather wide range of magnitude values for the red and infrared filters, this approach was found to be 559 binary. Although the star is not single, the two components are rather similar see belowso we accepted this estimation. Owing to rather different quality of the individual light curves, the first OGLE data set With this light curve we analysed the system, resulting in a set of parameters for both components, see Table 1.
These parameters are the best we were able to derive from the available light curves. However, the lack of other relevant information 559 binary.
We assumed a circular orbit i. The albedo coefficient remained fixed at value 1. No third light was detected for any of the light curves. This analysis is based on the assumption that the two components are rather 559 binary to each other. However, we still believe that this does not play a significant role because of the similarity of the two eclipsing components. During the fitting process, the mass ratio can also be fitted.
As a result, we made this attempt, but it did not result in any significant improvement of the fit. The mass ratio is only poorly constrained here, which agrees with a previous finding that detached eclipsing binaries with only partial eclipses are not suitable for deriving the mass ratio only from the light curves, see e.
We can therefore only roughly estimate the uncertainty of the mass ratio to be about 0. A sample of fitted light 559 binary plots at different time epochs is given in Fig. As one can see, the depths of both primary and secondary minima are changing over the two decades.
From these fits, the individual inclination 559 binary as derived from the Wilson-Devinney algorithm are given in Table 2 and plotted in Fig. Since the range for the y -axis is the same for all plots, the change in amplitude is clearly visible. For the explanation of the symbols see Table 2. One can also ask how we dealt with the different light curves in different filters for the complete analysis.
The light curves in different filters and different epochs were analysed separately, resulting in different inclination angles. These two values of inclination angles but obtained during the same epoch were averaged into the value presented in Table 2. We could afford to combine different filters and instruments for the analysis, because the different luminosity levels for different passbands were also computed.
Table 1 Parameters of the light curve. Table 2 Inclination angles as derived from 559 binary light curves. The system undergoes a nodal precession of its orbit, which is probably caused by an orbiting third body.
This effect of binary orbit precession 559 binary nothing new; however, it has been observed and analysed for the first time for an extragalactic source. The term C is the total angular momentum of the system, while G 2 stands for the angular momentum of the wide orbit.
Unfortunately, we are not able to derive the nodal period using 559 binary equation owing to unknown individual orbital parameters and masses of the components.
Figure 3 shows the result of our fitting. The resulting nodal period is only about However, because of the poor coverage of this period with only two decades of data, this result is still rather preliminary. New and more precise observations both photometry and spectroscopy are needed in upcoming years.
Until that time only very shallow ellipsoidal variations of the order 559 binary 0. As a by-product we also derived the inclination angles I and i 1 from the equation for cos i.
The values define the orientation of the system in space and towards the observer see Fig. Both these angles could potentially be used for future dynamical studies, should the third-body orbit be discovered via spectroscopy.
The easiest method is the light curve analysis and detection of 559 binary third light. However, no such additional light was discovered, so that it gives some constraints on this body. We can only speculate about its period and semimajor axis, so that the amplitudes of radial velocity variations are also questionable.
Moreover, the configuration of the system has to 559 binary hierarchical because of its stability Harrington As a result, a detection limit of about 559 binary. The individual colours stand for different inclinations of the orbits: Moreover, the dynamical stability criterion also exists, and it gives the lower limit of the third-body 559 binary Tokovininresulting in a minimum period of about 6.
Considering all these criteria, the shadowed area in Fig. The expected period 559 binary 3 should probably be from 6 to 15 days. Moreover, as we can see from Fig. Such a companion is therefore probably an M-dwarf star. However, this unique system is the first analysed eclipsing binary with changing inclination outside our own Galaxy. The authors 559 binary aware of the most important deficiency of the present analysis, which is the lack of radial velocity measurements, or the detailed spectroscopic study discovering the third component.
On the other hand, as we can see, for example, in the system of HS Hya, the third body could have a period of hundreds of days, so to discover it one needs spectroscopic monitoring over several months. There is still no radial velocity study of an LMC eclipsing binary with such a short orbital period.
Precise spectroscopic observations for such a faint target would only be possible using 4 m class telescopes or even larger. Its period the x -axis versus its mass y -axis, solid curves is computed from the nodal period, and the corresponding amplitude of the light-time effect was computed y -axis on the right, dash-dotted curves.
The shadowed area represents the possible parameters. Different colours represent different orientations of the orbit in space.
See the text for details. More detailed study of such systems would potentially be very important for several reasons. First, EBs are still 559 binary best method for deriving precise masses and radii of stars, and also for calibrating the cosmic distance ladder. Secondly, the chemical compositions of such systems should be studied in order to compare the LMC and our Galaxy. And finally, the changing inclination indicates that there is a hidden component orbiting this EB pair, which could tell us something about the stellar multiplicity of the LMC in general.
Observing the suspicious EBs would help us discover these third bodies, which is otherwise rather complicated for such distant objects. Spectroscopy is time-consuming and magnitude-limited, and interferometry cannot be used for Magellanic clouds. Additionally, multiple systems with moving orbital planes are ideal astrophysical laboratories for dynamical studies. The observable quantities can 559 binary directly compared with theoretical models.
Therefore, each new system is very promising. An anonymous referee is acknowledged for 559 binary useful comments and suggestions that significantly improved the paper.
William Hartkopf is also 559 binary acknowledged for his help with the language level of the manuscript. This work was supported by the Czech Science Foundation grant no.
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