Vina Hing & Linh Thuy Nguyen
Astronomy Research Project
Eclipsing Binaries
Introduction
More than four-fifths of the single points of light in the sky are actually two or more stars orbiting
each other. This is called a binary system. An eclipsing binary system is a pair of stars at an angle
that, when observed from the Earth, appear to pass in front of each other, causing an eclipse. Eclipsing
binaries hold endless knowledge about the universe. They can be used to determine the distance of a
stellar object from the Earth, for example, the distance to the Large Magellanic Cloud (LMC) has
been discovered through the use of eight eclipsing binary systems found inside it. The change in
brightness of these systems combined with their orbital speeds can be used to determine their size and
mass (i.e. their physical properties) and their distance from the Earth, thus the distance of the LMC
from the Earth. Although they have not been closely observed, eclipsing binaries typically have short
periods, making them a convenient object to be studied and analysed. By doing this, we can obtain
additional information about the stellar environment.
Aim
The aims of this research task are to:





Produce a complete light curve of SZ Scl
Upload data to AAVSO
Determine the physical properties of the binary system using a binary maker (e.g. mass, size,
temperature)
Search for any period changes using previously collected data from other sources
Compare existing data on VSX of light curve and period to results
Hypothesis
SZ Scl, located in the constellation Sculptor, is classified as an EW/KW type binary system. As a
result, the components of this system are expected to be ellipsoidal and in contact, sharing material
between each other until they reach equilibrium (when they are about the same size). Because of this,
the depths of the primary and secondary eclipses are expected to be close to equal. EW/KW type
variables typically have periods shorter than one day.
Method
1. Receive funding from iTelescope.
2. Observations can be carried out immediately as the star is well placed for observations now.
3. Take photos on iTelescope.
 Use Telescope 9 located in Siding Spring, Australia (Southern Hemisphere), pictured below.
Vina Hing & Linh Thuy Nguyen
Astronomy Research Project




Observe the binary system over 7 days 10-15 times per day spread over the course of each
night. The objective is to create a complete folded light curve of the system using Excel, which
is a light curve that shows one period of the binary stars (i.e. when the curve repeats itself). This
period is called a ‘phase’. This will be done by plotting the ‘phase’ against the ‘flux’ (changes
in brightness) of the binary system. Each set of exposures will consist of photometric B and V
images.
The use of B and V Filters is so that colour index (B-V) and thus stellar temperatures can be
estimated. Determining stellar temperatures will help narrow down the possible solutions
determined by binary maker.
Field calibration will be performed in assistance with Mr Di Scala so that instrumental
magnitudes can be converted into standard magnitudes.
Appropriate comparison stars and check stars will be used during the image analysis process.
Data Collection and Analysis
4. Image reductions will be performed in VPHOT.
5. Upload the calibrated data to the AAVSO database for safe-keeping and so that other researchers
can access it.
Vina Hing & Linh Thuy Nguyen
Astronomy Research Project
6. Import data file into Binary Maker to perform the light curve analysis.
Results
The following graphs are the light curves of the binary system SZ Scl as viewed through a blue and
visual filter respectively.
B Magnitude Light Curve
0
0.2
0.4
0.6
0.8
1
12.4
12.5
12.6
12.7
12.8
B
12.9
13
13.1
13.2
13.3
13.4
Blue Filter (above)
V Magnitude Light Curve
0
0.2
0.4
0.6
0.8
1
11.7
11.8
11.9
12
V
12.1
12.2
12.3
12.4
12.5
Visual Filter (above)
Vina Hing & Linh Thuy Nguyen
Astronomy Research Project
The following image shows the light curve of the binary system SZ Scl as produced by our
measurements.
By inserting values into the ‘User Input’ window of the ‘Binary Maker’ software, we were able to
produce a light curve that closely matched with the one above. Our solution is displayed below (in
blue).
The software also produced a model of the binary system according to the values we inputted, shown
below.
Vina Hing & Linh Thuy Nguyen
Astronomy Research Project
Primary Eclipse – where the dimmer star passes in front of the brighter star (above)
Secondary Eclipse – where the brighter star passes in front of the dimmer star (above)
The values inputted to achieve this model are tabulated below:
Characteristic
Mass Ratio
Fillout 1
Fillout 2
Wavelength
Temperature 1
Temperature 2
G1
G2
X1
X2
Reflection 1
Reflection 2
L3
Inclination
Normalisation Phase
Normalisation Factor
Light Curve Residuals
Value
0.92
0.099998
0.099999
5500
5145
4800
0.59
0.74
0.49
0.71
0.1
0.1
0
78.1
0.25
1
0.122807
Vina Hing & Linh Thuy Nguyen
Astronomy Research Project
Conclusion
The light curve residuals is a measurement of the observed data minus the calculated data and from
the result of 0.122807, it is concluded that the solution above is relatively accurate, the perfect
solution giving a result of 0. From observation of the model created in binary maker viewed at an
inclination of 78.1, the fact that the components of the system are 5145 K and 4800 K,
approximately 400 K apart, concludes that SZ Scl is an overcontact binary system, where the smaller
star is continually stealing energy from its larger companion. To give an idea of the temperature of
these stars, they differ by a few hundred degrees from the Sun, which is approximately 5700 K at the
surface. Both stars appear to be reflecting the same amount of light off each other with no interference
from a third light source (L3). The components of the binary system are very similar in mass as the
mass ratio is close to 1. By analysing this model of the binary system, it is confirmed that SZ Scl is
classified correctly as an EW/KW type binary where the components are clearly in contact with each
other and are not perfectly spherical but slightly ellipsoidal.
Discussion
The period of the system was assumed for the construction of the folded light curve and it is
concluded that its period of 0.32082757 days is accurate as the curves produced (both B and V filters)
appear to be fairly continuous.
The information provided from AAVSO concerning SZ SCL (B Filter) magnitude range, however, do
not coincide with our findings. The B magnitude range provided by AVVSO was 12.98 – 13.68,
however from our obeservations and collated data, the magnitude range was 12.54 – 13.31. Our data
suggests that the binary system is brighter (lower values of magnitude mean a brighter system of
stars) where the magnitude differs by approximately 0.35. The weather should be taken into
consideration as the period we shot the photos in had a high percentage of moonlight interference.
Hence further obversations should be made to verify this information.
Acknowlegments:
We would like to acknowledge the following people and organisations for aiding us with this research
project.
Giorgio Di Scala: Supervisor and Mentor.
Johnathan Powles: Who observed SZ Scl prior to us and then published this data on AAVSO where it
was utilised to further expand the data we collected.
AAVSO: The data collected was all stored on AAVSO.
iTelescope: For providing us with funds and with a medium to take photos, making this project
possible.
Appendix
The funds (credit and time) received from iTelescope were in response to a proposal sent to the
iTelescope committee which included an introduction to the nature of binary stars and enlisted our
aims and our method. The funds came in the form of credit which in turn was used to pay for the time
spent using a telescope.
Vina Hing & Linh Thuy Nguyen
Astronomy Research Project