Shallow transit follow‑up from Next‑Generation Transit Survey: Simultaneous observations of HD 106315 with 11 identical telescopes

The Next Generation Transit Survey (NGTS) is a photometric survey for transiting exoplanets, consisting of 12 identical 0.2‑m telescopes. We report a measurement of the transit of HD 106315 c using a novel observing mode in which multiple NGTS telescopes observed the same target, with the aim of increasing the signal‑to‑noise ratio. Combining the data allows the robust detection of the transit, which has a depth less than 0.1%, rivaling the performance of much larger telescopes. We demonstrate the capability of NGTS to contribute to the follow‑up of K2 and Transiting Exoplanet Survey Satellite discoveries using this observing mode. In particular, NGTS is well‑suited to the measurement of shallow transits of bright targets. This is particularly important to improve orbital ephemerides of relatively long‑period planets, where only a small number of transits are observed from space.