Tag Archives: WASP-South

WASP-South detection of transits of HD 219666b

Transiting a bright star, the “Neptune desert” planet HD 219666b was one of the more important early discoveries from the TESS survey. With a depth of only 0.17 per cent, the transits would be a challenge for any ground-based transit survey.

Nevertheless, we think we’ve found them in WASP-South lightcurves dating back to 2010. Here they are:

The orange lines show times of transit, as found by the WASP transit-detection algorithms. The shallow dips seem to be real, since they align both in period and in phase with the dips seen in the TESS lightcurve. The output from the WASP search algorithm is not itself that convincing:

However, the period that it finds (6.03446 days) matches the TESS period to an accuracy of 0.03 per cent, and the WASP ephemeris then predicts the times of the TESS transits bang on (they occur at 420.99999 cycles on the WASP ephemeris), which together mean that the detection must be real. Here are the WASP data folded on a template of the TESS transit:

With a depth of 0.17 per cent, the transits of HD 219666b are the shallowest that WASP has detected.

The benefit of looking for such pre-detections of TESS planets is that we can then produce a transit ephemeris based on data spanning a baseline of 8 years, rather than the 20 days spanned by the TESS transits. This means we can predict future transits to an accuracy of minutes, instead of hours, which is highly useful for future observations. Hence this WASP-South detection of HD 219666b transits is well worth an AAS Research Note.

Nobel Prize for Michel Mayor and Didier Queloz


Naturally, we at WASP are chuffed at the award of the Nobel Prize in Physics to Michel Mayor and Didier Queloz for their discovery of 51 Peg b, the first extra-solar planet found orbiting a sun-like star. Congratulations to them both! The award is a welcome boost and recognition of the burgeoning field of exoplanets.

The WASP-South camera array

When, back in 2006, we built WASP-South in South Africa and started our Southern survey for transiting exoplanets, the Geneva Observatory team led by Mayor and Queloz were the obvious collaborators, given their world-leading track-record in the radial-velocity discovery of exoplanets, and their Euler telescope with its CORALIE spectrograph, situated at La Silla in Chile.

Prof Queloz, and his then-students Michaël Gillon and Amaury Triaud, started the radial-velocity observations of WASP-South transit candidates. Since many transit candidates turn out to be transit mimics, both the transit data and RV data are necessary to prove the discovery of a planet. That collaboration still continues, and has involved the Geneva Observatory team observing 1500 WASP candidates over many hundreds of clear nights with Euler/CORALIE.

Euler telescope

The Euler 1.2-m telescope

The result has been the discovery of over 150 exoplanets transiting bright stars, and many of them are among the most valuable exoplanets for further observation and study. So far the collaboration between Prof Queloz’s team and WASP-South has led to over 100 refereed papers in leading journals, that have so far been cited over 5000 times.

WASP-94: “cousin” planets around twin stars

Press release regarding our discovery of planets around binary stars WASP-94A and WASP-94B:

European astronomers have found two new Jupiter-sized extra-solar planets, each orbiting one star of a binary-star system. Most known extra-solar planets orbit stars that are alone, like our Sun. Yet many stars are part of binary systems, twin stars formed from the same gas cloud. Now, for the first time, two stars of a binary system are both found to host a “hot Jupiter” exoplanet.

The discoveries, around the stars WASP-94A and WASP-94B, were made by a team of British, Swiss and Belgian astronomers. The British WASP-South survey, operated by Keele University, found tiny dips in the light of WASP-94A, suggesting that a Jupiter-like planet was transiting the star; Swiss astronomers then showed the existence of planets around both WASP-94A and then its twin WASP-94B.

Marion Neveu-VanMalle (Geneva Observatory), who wrote the announcement paper, explains: “We observed the other star by accident, and then found a planet around that one also!”.

Hot Jupiter planets are much closer to their stars than our own Jupiter, with a “year” lasting only a few days. They are rare, so it would be unlikely to find two Hot Jupiters in the same star system by chance. Perhaps WASP-94 has just the right conditions for producing Hot Jupiters? If so WASP-94 could be an important system for understanding why Hot Jupiters are so close to the star they orbit.

The existence of huge, Jupiter-size planets so near to their stars is a long-standing puzzle, since they cannot form near to the star where it is far too hot. They must form much further out, where it is cool enough for ices to freeze out of the proto-planetary disk circling the young star, hence forming the core of a new planet. Something must then move the planet into a close orbit, and one likely mechanism is an interaction with another planet or star. Finding Hot-Jupiter planets in two stars of a binary pair might allow us to study the processes that move the planets inward.

Professor Coel Hellier, of Keele University, remarks: “WASP-94 could turn into one of the most important discoveries from WASP-South. The two stars are relatively bright, making it easy to study their planets, so WASP-94 could be used to discover the compositions of the atmospheres of exoplanets”.

The WASP survey is the world’s most successful search for hot-Jupiter planets that pass in front of (transit) their star. The WASP-South survey instrument scans the sky every clear night, searching hundreds of thousands of stars for transits. The Belgian team selects the best WASP candidates by obtaining high-quality data of transit lightcurves. Geneva Observatory astronomers then show that the transiting body is a planet by measuring its mass, which they do by detecting the planet’s gravitational tug on the host star.

The collaboration has now found over 100 hot-Jupiter planets, many of them around relatively bright stars that are easy to study, leading to strong interest in WASP planets from astronomers worldwide.

 An illustration of a planet orbiting one star of a binary system.  In WASP-94, the planet would transit the brighter star, causing a dip in the light that can be detected from Earth.  Another planet orbits the second star at lower-left. It does not transit and is not directly visible, but it can be detected by its gravitational tug on the second star.

An illustration of a planet orbiting one star of a binary system. In WASP-94, the planet would transit the brighter star, causing a dip in the light that can be detected from Earth. Another planet orbits the second star at lower-left. It does not transit and is not directly visible, but it can be detected by its gravitational tug on the second star. [ Image Credit: ESO/L. Calçada/Nick Risinger]

Update: This press release has resulted in articles in phys.org, sciencedaily.com, world-science.net, yahoo.news, Science World Report, and breakingnews.ie.