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Wildrik Botjes Planetarium
Physics & Astronomy Department

Astr384 Class Projects, Spring 2008

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Basic Properties of PPM 706067

We first set out merely to characterize PPM 706067. As mentioned above, eclipsing binary star systems are some of the few stars that can be characterized almost completely, without recourse to astronomical theory. In order to do this, we took optical data of PPM 706067 using the Calvin-Rehoboth telescope. We also received spectroscopic data from our collaborator David Latham, using the Whipple Observatory.

Optical Data

From 2005 to the end of May 2008, we have taken over 115 nights of optical data of PPM 706067, using the Calvin-Rehoboth telescope. This data has been taken in four filters: B, V, R, and I. We analyzed the data using differential photometry in which we compare the brightness of PPM 706067 to other stars in the fields of view to track changes in brightness to a 1% accuracy.

Lightcurve of PPM 706067 from June 2006

Shown is a typical lightcurve; this one is in B. This is from late May to early June of 2006. Here you can see two eclipses: one at a phase of 0.5 and the other at a phase of 1 wrapping around to 0. We see two eclipses because the first star passes in front of the second and the second star passes in front of the first.  The shallower eclipse, located at phase 0.5, occurs when the dimmer star is eclipsed by the brighter star. Thus, we lose some of the light because we can no longer see the dimmer star, but we still have the majority of the light because we still the brighter star. This eclipse is called the secondary eclipse. The deeper eclipse, the primary eclipse, is located at a phase of 1. This eclipse occurs when the dimmer star passes in front of the brighter. Since we lose the light from the brighter star, the system as a whole gets much dimmer.

Spectroscopic Data

Spectroscopy looks at the emission lines from elements in the star. We have 25 nights of data using the Whipple observatory. This data tells us is how fast our stars are moving around each other. This is found using the Doppler shift of the light coming from each of the stars. The Doppler shift is the changing of the wavelength of the light because the object that is emitting the light is moving. With that information we can do precise modeling of the stars’ orbits to determine the exact masses of the two stars and how far apart they are from each other. Spectral data also provided independent verification of the temperature that we calculated using the blackbody spectra of the stars. 

Radial Velocity Curve

This figure shows the radial velocity of the two stars, i.e. how radidly they are moving towardsa or away from us, as function of the orbital phase. The dots are the measured data while the curves are the calculated models. The stars have 0 radial velocity during the eclipses because there their motion is purely horizontal.


Mass Ratio




M1=1.09(8)MΘ    M2=0.73(3)MΘ


Fractional Radii

R1=0.14             R2=0.085

Photometry and Spectroscopy


T1=5500K          T2=4400K

Photometry and Spectroscopy


87° - 90°



8.6(2) RΘ



2.1502710(3) days





Further Study

X-Ray Data