Following up HAT-South transiting planet candidates

Planets that transit their host stars offer us the unique opportunity to study individual planetary systems in great detail. Surveys to discover these transiting exoplanets, like HAT-South, depend on an extensive follow-up program to confirm and characterise their potential discoveries. As many astrophysical phenomena exist that mimic the transit signal of a 'hot-Jupiter', an exoplanet candidate has to be carefully scrutinised via a variety of observations before the discovery can be confirmed.

Reconnaissance spectroscopic observations are integral to the follow-up program. These observations are aimed at characterising the exoplanet candidates, and reject- ing those with properties inconsistent with 'hot-Jupiter' type planetary systems. Traditionally, reconnaissance observations have been conducted by way of high resolution (R > 10,000), low signal-to-noise spectroscopy on 1-2m class telescopes. In this work, we adopt a novel approach of following-up candidates with low and medium resolution (R = 3000/7000), high signal-to-noise spectroscopy. Following this approach, our observations with the ANU 2.3m telescope proved successful, with results that allowed the efficient prioritisation of HAT-South candidates.

We were able to reject up to 45% of candidates with these observations. Radial velocity measurements identified candidates with stellar mass companions that induce large reflex doppler motions on their host stars. Spectral classification observations measured the effective temperature and surface gravity of the candidates. From the stellar properties, we were able to reject candidate host stars that are giants, whose transiting companions have radii inconsistent with that of planets. Candidates with high rotational velocities or blended spectra were also identified and rejected.

High signal-to-noise transit lightcurves of promising candidates were obtained with the Faulkes Telescope South. Markov chain Monte Carlo fitting of the lightcurves were performed to test their consistency with the transiting 'hot-Jupiters' hypothesis.

We identified four very promising HAT-South candidates based on their photomet- ric and reconnaissance spectroscopic measurements. In addition, of the candidates followed-up by our spectroscopic observations, 26 have been passed on for high resolution radial velocity measurements. These promising candidates will be followed up with 4-8m class telescopes to be confirmed as true transiting planets.

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