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for contact binary stars. . . . Bartlomiej . Debski. Astronomical Observatory of the Jagiellonian University, Orla 171, 30-244 Krakow, Poland; email@example.com. Which minimum is the primary minimum?. ID: 549097Direct Link: Embed code:
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The Light Curve Morphology Analysis for contact binary stars Bartlomiej DebskiAstronomical Observatory of the Jagiellonian University, Orla 171, 30-244 Krakow, Poland; firstname.lastname@example.org
Which minimum is the primary minimum?Keywords: median maxima separation Separation of the brightness maxima in EW-type lightcurves produced by a (near) contact binary is affected mostly by the limb darkening and stellar activity. Our simulations show that if in the primary minimum the more massive star is beeing eclipsed by a less massive component, then the secondary maximum will occur more than 0.5 orbital phase after the primary maximum. The activity represented by the migrating star spots will produce a distinctive pattern in the evolving maxima separation. That is why the median of the separation should be measured, as it is almost unchanged and still larger than 0.5 orbital phase. This makes the median maxima separation a very good indicator, which minimum shall be called the primary, and which the secondary one. This is not trivial task as the minima may change their depths or shapes due to the ongoing stellar activity. Given the object is observed for many epochs, the median maxima separation serve as the objective tracer of which minimum is the primary one.Short version: choose your minima in such a way, that the median maxima separation will be larger than 0.5 ph.
Indicators of the starspot migrationKeywords: O'Connell effect, maxima separation A starspot that migrate along the stellar longitude will affect the height and position of the brightness maxima. During one migration cycle (360˚ around the star) the maxima will be varying up and down, one after another. Thus the evolution of maxima heights will be negatively correlated. In the same time, the separation of the maxima will be highest when spot reach the back of the star and smallest for a spot sitting just between the stars. The separation, however, will evolve with a relatively small amplitude. The diagram of the O'Connell effect vs maxima separation set with a similar scales on both axes shall display very flattened circle, resembling a horizontal line. In fact, we found that most of the objects in our sample manifest the signal attributable to the migrating starspot.Short version: Changes in the O'Connell effect and the evolution of the maxima separation allows to select binaries with the ongoing starspot migration.
Stationary, evolving starspots or not a contact binary at allKeywords: O'Connell effect, maxima separation, maxima height The confrontation between the evolution of the O’Connell effect and the maxima separiation may produce three results: 1) no correlation (no spot activity at all), 2) horizontally flattened circle (starspot migration) and 3) vertical distribution. The last one is particularly interesting, since it implies no changes in the O'Connell effect and fairly large variations in the maxima separation. In such situation, the spot model is constrained to just several possible locations of the evolving region: stellar pole, back or in front of the second star. Such a stationary starspot must produce a positive correlation between changes in the height of the light curve maxima. In our sample we found objects fulfilling these requirements, as shown in figures below. The problem is, all of those systems appear to have rather low inclination and fitting a model is rather troublesome. Apart of that, there are also objects with a positive correlation of brightness maxima changes, but having no variations in maxima separation and O'Connell effect whatsoever. These objects may experience radial pulsations of whole stars or not be contact binaries at all. One of the best examples is the dwarf nova J1621 (Zola et al. 2016), which in queiescence is mimicing a contact binary light curve.Short version: Some binaries manifest changes in the maxima height and location, which are allowed only in case of stationary spots, or exclude a contact binary model.
Direction of the starspot migrationKeywords: secondary minimum depth, secondary minimum location If a starspot is located on a primary star and migrates along the longitude, then the direction of the migration can be traced by comparing the signals of changes in the secondary minimum location and depth. This dependence is easy visible in case of a flat-bottom minima, because the amplitude of minima shifts are large due to the geometry of the light curve. We found the direction of a starspots migration in KIC 6118779 to be descending in the longitude (Debski, Zola, Baran 2014).Short version: the longitudal migration of a starspot is tracabe by comparing the evolution of the minimum depth and the changes in its location.
Summary: parameters of the system, parameters of the star spot The key to the understanding what happens on the surface of the close binary is hidden in the evolution of its light curve. The typical timescale of surface activity in short-period binaries last from several up to a few hundreds of orbital periods. Just because of that, it is crucial to conduct continuous observations lasting months or years and gather the information about a complete process. This is particularly aplicable to the ongoing and planned spaceborne missions of the orbital observatories, as the method presented here provides a very fast essesment for every potenetial object in the database. The analysis has been tested for contact binaries and can be extrapolated for the close, detached systems. In this poster we are showing some interesting correlations between the evolving parameters of the light curve. Reading such characteristics of the curve, like the O'Connell effect or maxima separation, allows to distinguish the binaries with different types of the surface activity manifestation. Moreover, the information about the median maxima separation can be used as the fast and universal determinant of which component is more massive, thus which minimum is the primary one. The choice of proper minimum is very important for further studies, as it, for example determines the geometry used in the WD code. This is extremely handy for making a preliminary catalogue with the light curve elements. In our other study we show the constraints on the sparspot parameters which enforces the starspots located asymmetrically on the stellar poles (Debski, Zola, Bara, 2015). This has a serious repercussions for most current contact binary models that place the modeled starspots on the stellar equator, as it influences the modeled system parametrs.
References Debski, B.; Baran, A.; Zola, S.: 2014, CoSka, 43, 427Debski, B., Zola, S., Baran, A., 2015, APSC, 496, 293Wilson, R.E.; Devinney, E.J.: 1971, AJ, 166, 605 Wilson R.E.: 1979, ApJ, 23, 1054Zola et al. 2016, ATel #9136
The histogram of median maxima separations in our sample taken directly from KEBC. The apparent bimodal distribution is caused by randomly attributed primary minima.
Figure 3: The histogram of median maxima separations after re-phasing the binaries. Now primary minima are chosen in such a way that the median maxima separation is larger than 0.5 ph.
Figure 4: Relation between the changes of the O’Connell effect and the variations of maxima separation can be explained with a migrating spot. Here a large spot moves closely around the pole.
Figure 5: The longitudal migration of such a starspot will affect the brightness maxima consecutively changing their heights. It is visible as the negative correlation in maxima heights diagram.
Figure 7 (left): Stationary, large region (radius r=45˚) located at the neck of the contact binary changing ith brightness from T=0.8 up to T=1.1 of the local surface tmeperature. No O’Connell effect changes occur , but the maxima separation is highly variable.
Figure 8 (right): The same „pulsating” region located at the neck is affecting both maxima simultaneously. Here the inclination is very low, therefore our model had to be rescaled, but the slope has been preserved.
Figure 6. The evolution of the secondary minimum of KIC 6118779 (black dots) superimposed with the changes of its depth in a timespan of almost three years. If the minimum gets deeper during the ascention in phase location, it implies that a dark staspot migrates in the direction of the descending longitude.
Morphology Analysis is a quick method for studying the general properties of the surface phenomena in close binary stars observed in a long-time base photometry
spaceborne missions like KEPLER, TESS, WFIRST, PLATO). Its application to the Kepler data allowed us to find the indicators for starspot migration, the direction of the starspot migration, constraints on the starspot co-latitude and size parameters and many other. One of the most promising prospects for this method is the determination of which component of the contact binary is the more massive one (which leads to the determination, which brightness minimum shall be called the primary one). In this work we present some applications of the Analysis to the 422 objects with the EW-type light curves from the Kepler Eclipsing Binary Catalogue. The method is based on the analysis of the evolution of the light curve extrema. The analysis takes into account the positions of the maxima (in orbital phase), their heights (in flux), the same for the minima (positions and depths) and cross-correlates their combinations. To examine the expected correlations and signals, we made a grid of simulations using a modified Wilson-Devinney code. The simulations covered a wide range od system parameters for contact binaries (mass ratio, fill-out factor, temperatures ratio, inclination) and their starspots (co-latitude, longitude, size and temperature).
Figure 1: naming convention in the analysis