Edward Bryant
The Next Generation Transit Survey (NGTS) is a 12-telescope facility in Chile hunting for planets orbiting other stars (“exoplanets”). NGTS finds exoplanets by monitoring stars to search for periodic reductions in the star’s brightness, which occur when the planet passes in front of the star (“transits”). One of the keys to this is obtaining high photometric precision measurements of the star. NGTS is designed to obtain such high precision measurements.
We have pioneered a new method of using multiple NGTS telescopes to simultaneously monitor a single bright star. With this method we are achieving some of the best photometric precision ever achieved from the ground.
These bright star light curves are crucial for obtaining more accurate predictions of upcoming transits of the planet as well as accurate measurements of the depths of the transit events, from which the planet’s radius can be calculated. These measurements are crucial for future observations to study the atmospheres of these planets.
Using data obtained from a 9-NGTS-telescope simultaneous observation of the bright star WASP-166, I show that NGTS bright star light curves are free from time-correlated noise and the noise present is uncorrelated between the individual telescope systems. We achieved a precision of 150 parts-per-million, which is comparable to the precision obtained by the NASA TESS space telescope.
We are now using this method to contribute to some of the most exciting exoplanet discoveries from the ongoing TESS mission.
We will continue these efforts over the coming years, including obtaining ultra-high precision light curves for exoplanet discoveries from the third year of TESS observations (July 2020 - June 2021). This method of using multi-telescopes to observe bright stars is an important step towards ESA’s PLATO space mission of 2026, where almost every target star in the mission will be monitored simultaneously by multiple telescopes.
The Next Generation Transit Survey (NGTS) is a 12-telescope facility in Chile hunting for planets orbiting stars other than the Sun; these planets are called exoplanets. NGTS finds exoplanets by monitoring stars to search for periodic reductions in the star’s brightness, which occur when the planet passes in front of the star, known as transits. Obtaining observations of exoplanet transits from ground based facilities is a crucial part of confirming exoplanet discoveries. NGTS is designed to obtain high photometric precision observations of such stars.
In this poster, I present a new observing method we have pioneered where we use multiple NGTS telescopes to simultaneously monitor a single bright star. With this new method, we have successfully obtained some of the best photometric precision ever obtained from the ground. These ultra-high precision observations of exoplanet transits are crucial for accurately measuring the depth of the transit event, from which we can calculate the radius of the exoplanet, and accurately predicting the times of upcoming transit events. These measurements are vital for both confirming the exoplanet discovery and planning future observations to study the atmosphere of the planet.
Section 2 - NGTS vs TESS: A Transit of WASP-166b
To test the multi-telescope observing method we observed a transit of the exoplanet WASP-166b using 9 NGTS telescopes. The same transit of WASP-166b was also observed by the NASA space mission TESS. Figure 2 shows the light curves obtained from the two observations. We can compare our light curve to that from TESS, and both light curves are found to be of the same quality, and clearly display the transit event to have the same depth and to occur at the same time. We can also see that the NGTS and TESS data are of the same precision.
Section 3 - Multi-Telescope Precision
We used this same 9-telescope observation of the bright star WASP-166 to test the performance of the multi-telescope observing method. Figure 3 demonstrates the improvement in the photometric precision of the bright star light curves we achieve as we include additional NGTS telescopes in the simultaneous transit observation. It can be clearly seen that the improvement we achieve is very close to the best-case theoretical improvement that is expected for uncorrelated noise. The photometric precision of the combined 9-telescope light curve is just 150 parts-per-million. This is the same precision obtained by TESS for the same star, and some of the best photometric precision ever obtained from the ground.
Section 4 - Conclusions and Future
We have demonstrated that the noise in the NGTS bright star light curves does not correlate between the individual NGTS telescopes. By using multiple telescopes to observe the same exoplanet transit simultaneously, we can therefore greatly improve the photometric precision we achieve, reaching precisions of 150 parts-per-million, which rivals the performance of the NASA TESS space mission.
We have already used this new observing method to contribute ultra-high precision light curves to some of the most exciting exoplanet discoveries from the ongoing TESS mission. We will continue these observations over the next few years to contribute to many more exciting exoplanet discoveries!
This multi-telescope observing method is also an important step towards the ESA PLATO space mission, set to be launched in 2026. During the PLATO mission, every target star will be monitored simultaneously by multiple telescopes.