VizieR Online Data Catalog: NGTS-4b A sub-Neptune transiting in the desert (West+, 2019)

NGTS-4 was observed using a single NGTS camera over a 272 night baseline between 2016 August 06 and 2017 May 05. The survey has operated at ESO's Paranal observatory since early 2016 and consists of an array of 12 roboticized 20cm telescopes. The facility is optimized for detecting small planets around K and early M stars (Chazelas et al. 2012SPIE.8444E..0EC; Wheatley et al. 2013EPJWC..4713002W; McCormac et al. 2017PASP..129b5002M; Wheatley et al. 2018MNRAS.475.4476W).

A total of 190696 images were obtained, each with an exposure time of 10s. The data were taken using the custom NGTS filter (550-927nm).

The complete data set was searched for transit-like signals and a ~0.2 per cent signal was detected at a period of 1.33734d. Confirming such a shallow transit signal from the ground is challenging, even given some of the best 1m-class telescopes available for precision time-series photometry. We therefore undertook a campaign of photometric follow-up using four different facilities (see Table 2).

Our first follow-up photometry of NGTS-4 was carried out at the South African Astronomical Observatory (SAAO) on 2017 November 27, with the 1.0m telescope and one of the three frame-transfer CCD Sutherland High-speed Optical Cameras (SHOC Coppejans et al. 2013PASP..125..976C). We monitored transit events of NGTS-4b using the Las Cumbres Observatory (LCO) 1m global telescope network (Brown et al. 2013PASP..125.1031B). All observations were taken using the Sinistro cameras. We also monitored a transit event using the SPECULOOS-South facility (Burdanov et al. 2018haex.bookE.130B; Delrez et al. 2018SPIE10700E..1ID) at Paranal Observatory in Chile on the night of 2018 April 15, taking advantage of the telescope commissioning period. SPECULOOS-South consists of four robotic 1m Ritchey-Chretien telescopes, and we were able to utilize two of these (Europa and Callisto) to observe the transit event. Two transits of NGTS-4 were observed with Eulercam on the 1.2m Euler Telescope at La Silla Observatory (Lendl et al. 2012A&A...544A..72L, Cat. J/A+A/544/A72). The observations took place on the nights beginning 2018 April 15 and 2018 April 19. Both transits were observed using the same broad NGTS filter that was used to obtain the discovery photometry.

Finally, we obtained multi-epoch spectroscopy for NGTS-4 with the HARPS spectrograph (Mayor et al. 2003Msngr.114...20M) on the ESO 3.6m telescope at La Silla Observatory, Chile, between 2017 December 01 and 2018 April 10 under programme ID 0101.C-0623(A). We used the standard HARPS data reduction software to measure the radial velocity of NGTS-4 at each epoch.

(12 data files).