What is optical timing and what are the most interesting recent discoveries in High Time Resolution Optical Astrophysics (HTROA)?

Although we can study the Universe at many different wavebands, the optical remains a key window where the largest telescopes are available. High time resolution optical astrophysics concerns the study of objects using visible light, but on timescales of minutes or faster. Even Sun-like stars show variability on short timescales and in recent years a particular highlight has been to be able to detect faint optical pulsations in starlight, which can then be used to study the interior structure of stars, similar to seismology methods used in geology. Rapid optical variability is also commonly seen around compact stellar remnants, similar to the complex variability such objects show at higher energies. We are now able to observe accreting black holes, neutron stars and white dwarfs simultaneously at different wavebands, linking fast optical observations with X-ray observations for example. Such multi-wavelength studies have proven to be particularly insightful as we try to understand the physics behind these spectacular variations.

How has High Time Resolution (HTR) modified the research in the optical? 

We now have the right detector technology that we can do fast optical observations with efficient detectors. Coupled with large optical telescopes such as the GTC (Gran Telescopio CANARIAS) or the VLT (Very Large Telescope), enables us to study rapid variability across a broad range of objects. This has made an impact on many areas of astrophysics, from solar system objects to extra-solar planets, stars and stellar binary systems and exotic objects such as pulsars and stellar mass black holes. 

How can we use optical timing to learn about stars and stellar systems? 

I have already mentioned the technique of asteroseismology. This is a very powerful tool, allowing us to determine detailed properties for large numbers of stars. Since the signals we detect are produced by waves travelling through the interior of these stars, we now for the first time can study the interior structure of a large number of stars and also a broad variety of stars. These different types (e.g. Sun-like, giant stars, evolved remnants) represent the different phases a star goes through as it evolves. Complimentary to that, we can determine very accurate basic parameters such as mass and size for stars in binaries. Thus optical timing observations are producing very strong observational constraints that we can use to test and improve our understanding of the structure and evolution of stars in general.

Annia Domènech