Eclipse PredictionsZ Dra
The Observatory will post here predictions of times of primary and secondary minimum for selected eclipsing systems of interest to the observatory staff. These predictions may also include times for special or important phases for selected systems. Predictions are for the local time at the SSU Observatory (Pacific Standard Time), but the Universal Time is also listed. These predictions are based on a modified version of the Binary Star Ephemeris Program by Allen Joel Harris.
If you are not affiliated with the SSU Observatory and obtain data for any of the systems included in these predictions, contact us regarding possible collaboration with analysis and publication of results ( spear@sonoma.edu ).
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One of the SSUO research programs involves accumulating light curve data for some "interesting" eclipsing binary stars. An eclipsing binary is a binary star for which the solar system is very nearly in the orbital plane for the system. To see some examples of possible light curves, you can use the interactive Eclipsing Binary Lightcurve Simulator. This simulator allows the user to change key paramatersfor the system such as the sizes and temperatures for the stars, and the orbital inclination. This simulation is only for mainsequence stars. As it turns out, many "interesting" eclipsing systems contain non-mainsequence stars, and we even find that occasionally the more massive component appears not to be the most evolved component in the system. This situation has sometimes been termed the "Algol Problem." This can result from previous episodes of mass transfer in which the initially more massive component has transfered mass to the initially less massive component.
By obtaining data during primary and secondard eclipses we may determine times of minimum light and derive values for orbital periods. Changes in orbital periods can be associated with mass transfer events between the components, elliptical orbits, or third bodies in the system. Massive systems can even exhibit relativistic effects.
Complete light curves can be used for detailed analysis to infer important physical properties of the eclipsing systems.
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Z Dra is a poorly studied close binary system with a 1.3 day period. The primary visual eclipses are approximately 2.5 magnitudes deep and have been monitored by visual observers for many decades. Because of its high northern declination this system has a rather long observing season in mid-northern latitudes.
The system is apparently demonstrating interaction effects and has well documented period changes. The only known analysis of the light curve is based on visual observations from 1913. High quality photoelectric light curves have been obtained by Ed Devinney in the 1960s from Flower and Cook Observatory.
Coordinates for equator and equinox 2000.0:
RA ---> 11h 45m 29sDEC -> +72 deg 15'
A finding chart is available. This chart is 14 arcminutes on a side and centered on Z Dra. North is up and east is to the left in this image. This image is based on a red plate from POSS I. An obvious comparison star is located to the left (east) of Z Dra in this image.
Some eclipse predictions are available for Z Dra. Note that these predictions are for Pacific Standard Time (Local Time) at SSUO. Predictions are made for primary eclipse and secondary eclipse. Then follows a list of events sorted by local date.
With assistance from student Chris Trechter, we have obtained CCD observations through a primary minimum on April 29 PDT. Preliminary reductions to differential magnitude for the variable and comparison, and a check star and comparison are presented in the following plot. A preliminary analysis of the check and comparison star observations suggests a mean error for a single magnitude difference of approximately +/- 0.015 magnitude.
The following graph shows a preliminary analysis to determine the time of minimum light for this event.
Observations of this system are continuing.
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IU Aur is an 8.6 magnitude eclipsing system with a 1.8 day period. The primary eclipse depth is about 0.6 magnitude while the secondary eclipse depth is about 0.5 magnitude. Eclipses last approximately 6 hours. The system is semidetached and the light curve exhibits some variation even outside of eclipse. IU Aur is noteworthy in that the line of apsides and the orbital inclination are changing at a very high rate. The light curve appears noticeably different from one season to the next. The orbital inclination has increased to near 90 degrees and is about to begin decreasing. If the present trends continue, IU Aur will eventually stop eclipsing. The orbital changes are presumably due to the presence of an additional massive component in the system, although the confirmation of the existance of such a component has not yet been obtained.
Coordinates for equator and equinox 2000.0:
RA ---> 5h 27m 52sDEC -> +34 deg 47'
A finding chart is available. This chart is 14 arcminutes on a side and centered on IU Aur. North is up and east is to the left in this image. This image is based on a red plate from POSS I. An obvious comparison star is located to the lower right of IU Aur in this image.
Some eclipse predictions are available for IU Aur. Note that these predictions are for Pacific Standard Time (Local Time) at SSUO. Predictions are made for primary eclipse and secondary eclipse. Then follows a list of events sorted by local date. Unfortunately, the secondary eclipse predictions assume a phase of 0.5, which is not strictly correct for this eccentric binary. Predictions for the actual phase of secondary eclipse will be eventually be included here.
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