Optical spectra from the millisecond pulsar triple system

Image may be NSFW.
Clik here to view.© Image copyright David Kaplan 2014

A group of researchers, at ASTRON and elsewhere, recently reported (daily image) the discovery and initial study of a pulsar with two white dwarf companions. This very unusual combination offers the possibility of some very interesting timing studies, including a test of Einstein's theory of gravity, but only if the system is "clean", that is, the companions really are white dwarfs. The paper this image is from studies the system in detail with optical spectroscopy to understand what the companions actually are.

The image above shows the results. The top panel shows a detailed optical spectrum of the system, with the Doppler effect of orbital motion removed. The black points are the measured spectrum, and the red line is the best-fit model; this fitting shows the white dwarf is at 15800 K and is able to estimate its surface gravity (which tells us about its size, and combined with brightness measurements, its distance, which is about 1300 parsecs). The blue points are the spectrum of a nearby quasar used for comparison.

The bottom panel shows the companion's velocity as measured from Doppler shifts, showing the inner companion moving around the pulsar. The inset shows that even in these velocities we can see the acceleration due to the outer companion's gravity. The amplitude of the velocity curve matches exactly that predicted from the pulsar timing. The fitting is also able to show that the system is moving away from us at 30 km/s.

This paper is accepted to the Astrophysical Journal (in press) and is available on the arXiv.