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Physics & Astronomy Department

Astr384 Class Projects, Spring 2008

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X-Ray Data of PPM 706067

The highly variable star spots, as well as the knowledge that PPM 706067 is a strong x-ray source, prompted us to seek observing time on an x-ray telescope. In collaboration with Jurgen Schmitt, we received observing time on the XMM-Newton, an x-ray satellite run by the European Space Agency. We observed PPM 706067 over the course of a primary and a secondary eclipse in February 2008.

Sloan Digital Sky Survey Image pf PPM 706067
X-Ray Image of PPM 706067

These two images show the field of view surrounding PPM 706067 on similar scales. The first is in optical from the Sloan Digital Sky Survey, the second is in x-ray. They are on a similar scale. It is interesting to note that while there are bright sources in both wavelengths within the field of view, PPM 706067 is the only bright source in both fields. This is because most stars are not also strong x-ray sources.

The x-ray emission of PPM 706067 most likely comes from a few discrete locations. Using the procedure described above, we hoped to map the locations of the x-rays.

Within the corona, there are many highly energetic electrons. These electrons travel in spiral paths along the magnetic field lines. Because PPM 706067 has such a short rotational period, its magnetic fields are incredibly strong, and thus it is a bright x-ray source.

Most of the x-ray emission may come from the region of the star spots, where the magnetic fields lines bunch together as they enter and exit the surface of the star. This crowding of magnetic field lines would produce areas of relatively denser x-ray emission. Another possibility is that the electrons are bouncing back and forth on the magnetic field lines filling the space between the two stars. This would produce a bright x-ray source in the center of the system. We hoped to use the x-ray data to differentiate between these possibilities.

X-Ray Data

However, given the data, shown above, without extensive processing, the eclipses are not even visible. This is because the data is dominated by an extremely large flare. Ignoring the flare for a minute, we can draw conclusions about the possible depths of the x-ray eclipses. In optical, we see a variation of 38% for the primary eclipse. The variation in the x-ray for must be less than 30%. This suggests that the primary star is the x-ray source and that most of these x-rays originate in an extended photosphere that is never fully eclipsed by the secondary star.

While it is disappointing to not be able to easily study the x-ray eclipses, the flare itself is worth studying. We have observed flares in the optical, so we know the PPM 706067 does flare. However, flares are unpredictable events. We could never have planned to observe a flare. Thus, it is incredibly serendipitous that we caught one in x-ray.

Flares are generally produced by the magnetic field lines snapping, and then reforming, having released large amounts of energy. Since PPM 706067 has such strong magnetic fields, we would expect flares to be part of its repertoire.

Unanswered Questions

Given the ongoing nature of this project, it is only to be expected that we do not yet know everything about the system. There is possibility of a changing orbital period; the system needs to be observed for years more before anything conclusive can be said on that.

The star spots may be varying on short time scales (less than a month) or we may be observing a star spot cycle. Again, more thorough observations are needed to differentiate between these two explanations.

The x-ray data needs to be analyzed further. Then we will be able to both study the eclipses as well further study and understand the flare.

Even with all of these interesting twists in the story of PPM 706067, we have made substantial progress in being able to characterize the system. We have also taken and done preliminary analysis of data that will aid in answering these other questions.


A.D.F. Metanomski, L. Pasquini, J. Krautter, G. Cutispoto and T.A. Fleming. "F, G and K stars in the ROSAT all-sky survey." Astron. Astrophys. Suppl. Ser. 131, 197-208.

Sloan Digital Sky Survey. RA 14 43 12 Dec -0° 42' 15''

X-Ray Images from Jurgen Schmitt