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Reflections from Stars

Stars reflect light as well as emitting it. Surprisingly this effect has been largely ignored by astronomers. We have been able to show, from observations and modelling of the bright binary system Spica, that the polarization we are seeing is due to reflection of light from one star off the other and vice-versa. We think this is likely to be an important effect in many binary systems and should enable us to determine fundamental properties such as masses and study binary frequency – an important clue to star formation mechanisms.

This work is described in a paper in Nature Astronomy published in Apr 2019.

The same effects have now been observed in the eclipsing binary system μ1 Sco for which variable polarization was discovered using the UNSW telescope. A paper on this system was published in MNRAS in Jul 2020.


Tracking a Martian Dust Storm

Every so often — when Mars is near perihelion — a global dust storm occurs with airborne dust being lifted high into the atmosphere and obscuring the surface. These dust storms are a major problem for solar-powered vehicles on the surface such as the Opportunity rover. One of these dust storms occurred during the recent 2018 perihelic opposition. We have been observing the whole-disk polarization of Mars using Mini-HIPPI on the UNSW telescope.

The variation of polarization with phase angle (angle between Sun and Earth at Mars) is sensitive to the properties and size of the dust grains.

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