Ground-based optical transmission spectrum of the hot Jupiter HAT-P-1b

Abstract

Context. Time-series spectrophotometric studies of exoplanets during transit using ground-based facilities are a promising approach to characterize their atmospheric compositions. Aims. We aim to investigate the transit spectrum of the hot Jupiter HAT-P-1b. We compare our results to those obtained at similar wavelengths by previous space-based observations. Methods. We observed two transits of HAT-P-1b with the Gemini Multi-Object Spectrograph (GMOS) instrument on the Gemini North telescope using two instrument modes covering the 320 -800 nm and 520 -950 nm wavelength ranges. We used time-series spectrophotometry to construct transit light curves in individual wavelength bins and measure the transit depths in each bin. We accounted for systematic effects. We addressed potential photometric variability due to magnetic spots in the planet's host star with long-term photometric monitoring. Results. We find that the resulting transit spectrum is consistent with previous Hubble Space Telescope (HST) observations. We compare our observations to transit spectroscopy models that marginally favor a clear atmosphere. However, the observations are also consistent with a flat spectrum, indicating high-altitude clouds. We do not detect the Na resonance absorption line (589 nm), and our observations do not have sufficient precision to study the resonance line of K at 770 nm. Conclusions. We show that even a single Gemini/GMOS transit can provide constraining power on the properties of the atmosphere of HAT-P-1b to a level comparable to that of HST transit studies in the optical when the observing conditions and target and reference star combination are suitable. Our 520 -950 nm observations reach a precision comparable to that of HST transit spectra in a similar wavelength range of the same hot Jupiter, HAT-P-1b. However, our GMOS transit between 320 -800 nm suffers from strong systematic effects and yields larger uncertainties.

The GTC exoplanet transit spectroscopy survey

“…Lightcurves are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc. u-strasbg.fr/viz-bin/cat/J/A+A/641/A158 Casasayas-Barris et al 2018Seidel et al 2019;Chen et al 2020), studies at lower resolution can give us information about the continuum of the exoplanet spectrum (e.g., Rackham et al 2017;May et al 2018May et al , 2020Bixel et al 2019;Todorov et al 2019;Weaver et al 2020). Moreover, groundand space-based low-resolution transmission spectroscopy allows us to probe for potential broad absorption line wings and slopes caused by hazes in the atmosphere of Jovian-like transiting planets.…”

LBT transmission spectroscopy of HAT-P-12b

“…Ground-based observations have also proved to be successful in correcting for the telluric effects by applying the differential spectrophotometry method. These observations are mostly carried out with multi-object spectrographs mounted on large telescopes, for example, FORS2 on the Very Large Telescope (VLT; Lendl et al 2016;Nikolov et al 2016;Sedaghati et al 2016), OSIRIS on the Gran Telescopio Canarias (Chen et al 2017a;Murgas et al 2017), GMOS on the Gemini telescope (Gibson et al 2013;Todorov et al 2019), IMACS on the Magellan telescope (Rackham et al 2017;Espinoza et al 2019), and MODS on the Large Binocular Telescope (LBT; Mallonn & Strassmeier 2016). These ground-based observations provide transmission spectra in the optical wavelength range that cover features such as Na/K (Sing et al 2012;Lendl et al 2017;Chen et al 2018;Nikolov et al 2018;Pearson et al 2019), TiO/VO (Sedaghati et al 2017), and the Rayleigh-scattering slopes (Nikolov et al 2015;Parviainen et al 2016;Kirk et al 2017;Chen et al 2017b).…”

LRG-BEASTS: sodium absorption and Rayleigh scattering in the atmosphere of WASP-94A b using NTT/EFOSC2

“…Clouds and hazes are best characterised in the optical, where they are not degenerate with molecular abundances, and work with LRG-BEASTS and other surveys have shown that ground-based observations can provide optical transmission spectra with precision comparable to space-based telescopes (e.g. Todorov et al 2019;Alderson et al 2020;Carter et al 2020;Weaver et al 2021). With the upcoming launch of the James Webb Space Telescope (JWST), which will provide precise transmission spectra across the near-and mid-infrared, the measurement of optical transmission spectra will be crucial for combined analyses to break degeneracies due to clouds and hazes and measure accurate atmospheric abundances.…”