Tag Archives: Amaury Triaud

A circumbinary planet transiting a WASP binary star

Circumbinary planets are planets that orbit a binary star, rather than a single star, in contrast to most planets known. Possibly they formed out of the same disk of material that formed the two stars. So long as the planet is sufficiently far from the binary, its orbit can be stable.

Several circumbinary planets were discovered by the Kepler mission, but the first such planet found using TESS has recently been announced by Veselin Kostov et al.

Here is the TESS lightcurve of “target of interest” TOI-1338:

Six-percent-deep eclipses recur every 14.6 days, when a small, M-dwarf star eclipses its Sun-like companion. But, when one looks more closely at portions of the lightcurve, one also sees:

Near Day 1483 is a deep eclipse (truncated in this plot). Near Day 1577 is a shallower secondary eclipse, when the Sun-like star eclipses the M-dwarf star. But, in addition, and highlighted by green bands, are two transits where a Saturn-like planet in a wide, 95-day orbit, transits the Sun-like star.

The interest, from the WASP point of view, is that the eclipsing binary had already been found by the WASP survey. The primary eclipses were too deep to be caused by a Jupiter-size planet, and were instead found to be caused by the M-dwarf, but such systems are interesting in their own right, and thus formed the “EBLM” programme offshoot from WASP, led by Amaury Triaud.

Since the eclipsing binary was already known to be an interesting system, this meant it could be observed with 2-min cadence in the TESS survey (instead of the default 30-min cadence data), and that made the detection of the circumbinary-planet transits much easier.

Above is an illustration of how the planet’s orbit precesses around the inner binary over time. The inner binary is illustrated in black and grey. The coloured dots show how the orbit of the planet changes over 2000 days. When the planet passes within the grey ellipses, transits can be seen.

Amaury Triaud wins the RAS Fowler Award

Congratulations to Dr Amaury Triaud, now at the University of Birmingham, recipient of the 2020 Fowler Award from the Royal Astronomical Society. The Fowler Award is for scientists making a “particularly noteworthy contribution to Astronomy & Geophysics at an early stage of their research career”.

Amaury Triaud

The citation reads: “Between 2007 and 2017, Dr Triaud led the radial-velocity follow-up of planet candidates south of declination −10 degrees from the Wide-Angle Search for Planets (WASP). His programme led to the discovery of over 130 planets from some 1000 candidates, making WASP the most successful of all ground-based transit searches.”

Amaury started looking for WASP exoplanets as a graduate student at the Geneva Observatory, under the direction of Didier Queloz (himself recipient of the 2019 Nobel Prize for Physics for his discoveries of exoplanets). Didier’s group at Geneva operated the CORALIE spectrograph on the 1.2-m Euler telescope at La Silla in Chile. Euler/CORALIE was the ideal follow-up instrument to vet the transiting exoplanet candidates coming from WASP-South, able to show which ones were genuinely the transits of planetary-mass bodies (only 1-in-10 of all candidates), and which were merely transit mimics. Amaury organised and ran the campaign, observing of order 1500 candidates and leading to the discovery of around 150 planets.

Euler telescope

The Euler 1.2-m telescope

While the citation mentions the campaign for Southern candidates south of declination −10 degrees, the Geneva group were also responsible for much of the follow-up in the equatorial strip from −10 to +10 degrees, where the candidates came jointly from data from WASP-South and from SuperWASP-North on La Palma.

Amaury’s work extended into studying the orbits of the WASP exoplanets, showing that many of the orbits were misaligned. He also developed programs identifying and studying the low-mass binary stars that also came from the WASP survey, and is now looking for circumbinary planets orbiting these low-mass binaries.

WASP thesis wins European Astronomical Society prize

Congratulations to Dr Amaury Triaud for winning the highly prestigious 2014 MERAC Prize, awarded by the European Astronomy Society for the Best Doctoral Thesis in Observational Astrophysics. Dr Triaud was a PhD student at the Geneva Observatory of the University of Geneva, supervised by Prof. Didier Queloz.

Amaury Triaud

Amaury Triaud took charge of the radial-velocity campaign following up WASP-South planet candidates, using the Coralie spectrograph on the Swiss/Euler 1.2-m telescope at La Silla, and has thus played a major part on the discovery of all WASP-South transiting exoplanets. The MERAC prize highights the success of the European collaboration between the British WASP-South transit search, the Swiss Euler/Coralie spectrograph, and the Belgian-led TRAPPIST robotic photometer.

Euler telescope

The Euler 1.2-m telescope

In addition to the planet discoveries, Amaury Triaud lead-authored a landmark paper on the dynamical origins of hot-Jupiter exoplanets, deduced by measuring the angle between the planet’s orbit and the host-star’s spin, which has already been cited 170 times. Amaury’s work provided strong evidence that hot Jupiters formed much further out than their current orbits, and were moved inwards by the Kozai mechanism.