Abstract
ABSTRACT Ground-based photometry of bright stars is expected to be limited by atmospheric scintillation, although in practice observations are often limited by other sources of systematic noise. We analyse 122 nights of bright star (Gmag ≲ 11.5) photometry using the 20-cm telescopes of the Next-Generation Transit Survey (NGTS) at the Paranal Observatory in Chile. We compare the noise properties to theoretical noise models and we demonstrate that NGTS photometry of bright stars is indeed limited by atmospheric scintillation. We determine a median scintillation coefficient at the Paranal Observatory of $C_{\scriptscriptstyle \text{Y}}= 1.54$, which is in good agreement with previous results derived from turbulence profiling measurements at the observatory. We find that separate NGTS telescopes make consistent measurements of scintillation when simultaneously monitoring the same field. Using contemporaneous meteorological data, we find that higher wind speeds at the tropopause correlate with a decrease in long-exposure (t = 10 s) scintillation. Hence, the winter months between June and August provide the best conditions for high-precision photometry of bright stars at the Paranal Observatory. This work demonstrates that NGTS photometric data, collected for searching for exoplanets, contains within it a record of the scintillation conditions at Paranal.
Highlights
M Ground-based photometry of bright stars is expected to be limited by atmospheric scintillation, in practice observations are often limited by other sources of systematic noise
D noise models and we demonstrate that Next-Generation Transit Survey (NGTS) photometry of bright stars is limited by atmospheric scintillation
U 4 CONCLUSIONS L We analyse the photometric precision of two years of NGTS bright A star observations from the Paranal Observatory
Summary
N observational astronomy, in particular for astereoseismology I (Brown & Gilliland 1994; Heasley et al 1996) and transiting exoplanet research (Winn 2010). Transiting exoplanet surveys such as WASP (Pollacco et al 2006), HATNet (Bakos et al 2004), and KELT (Pepper et al 2007) used small (∼510 cm) ground-based telescopes to survey large areas of sky These surveys were typically limited to detecting signals on the order of 1%. Larger telescopes (∼20 cm) were employed by the generation of ground-based transit surveys such as NGTS (Wheatley et al 2018) and HATSouth (Bakos et al 2013). ITtion 4 in Osborn et al (2015), it has the form was selected to match where the photometric noise is dominated by the scintillation effect for NGTS photometry (Wheatley et al 2018). We investigate whether there exists a seasonal correlation between wind speed and our long-exposure scintillation measurements, as expected based on the results presented in Kornilov et al (2012).
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