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We report 13 high-precision light curves of eight transits of the exoplanet WASP-52 b, obtained by using four medium-class telescopes, through different filters, and adopting the defocussing technique. One transit was recorded simultaneously from two different observatories and another one from the same site but with two different instruments, including a multi-band camera. Anomalies were clearly detected in five light curves and modelled as star-spots occulted by the planet during the transit events. We fitted the clean light curves with the jktebop code, and those with the anomalies with the prism+gemc codes in order to simultaneously model the photometric parameters of the transits and the position, size and contrast of each star-spot. We used these new light curves and some from the literature to revise the physical properties of the WASP-52 system. Star-spots with similar characteristics were detected in four transits over a period of 43 d. In the hypothesis that we are dealing with the same starspot, periodically occulted by the transiting planet, we estimated the projected orbital obliquity of WASP-52 b to be λ = 3 • .8 ± 8 • .4. We also determined the true orbital obliquity, ψ = 20 • ± 50 • , which is, although very uncertain, the first measurement of ψ purely from star-spot crossings. We finally assembled an optical transmission spectrum of the planet and searched for variations of its radius as a function of wavelength. Our analysis suggests a flat transmission spectrum within the experimental uncertainties.

Context. The measurement of the orbital obliquity of hot Jupiters with different physical characteristics can provide clues to the mechanisms of migration and orbital evolution of this particular class of giant exoplanets. Aims. We aim to derive the degree of alignment between planetary orbit and stellar spin angular momentum vectors and look for possible links with other orbital and fundamental physical parameters of the star-planet system. We focus on the characterisation of five transiting planetary systems (HAT-P-3, HAT-P-12, HAT-P-22, WASP-39, and WASP-60) and the determination of their sky-projected planet orbital obliquity through the measurement of the Rossiter–McLaughlin effect. Methods. We used HARPS-N high-precision radial velocity measurements, gathered during transit events, to measure the Rossiter–McLaughlin effect in the target systems and determine the sky-projected angle between the planetary orbital plane and stellar equator. The characterisation of stellar atmospheric parameters was performed by exploiting the HARPS-N spectra, using line equivalent width ratios and spectral synthesis methods. Photometric parameters of the five transiting exoplanets were re-analysed through 17 new light curves, obtained with an array of medium-class telescopes, and other light curves from the literature. Survey-time-series photometric data were analysed for determining the rotation periods of the five stars and their spin inclination. Results. From the analysis of the Rossiter–McLaughlin effect we derived a sky-projected obliquity of λ = 21.2° ± 8.7°, λ = −54°−13°+41°, λ = −2.1° ± 3.0°, λ = 0° ± 11°, and λ = −129° ± 17° for HAT-P-3 b, HAT-P-12 b, HAT-P-22 b, WASP-39 b, and WASP-60 b, respectively. The latter value indicates that WASP-60 b is moving on a retrograde orbit. These values represent the first measurements of λ for the five exoplanetary systems under study. The stellar activity of HAT-P-22 indicates a rotation period of 28.7 ± 0.4 days, which allowed us to estimate the true misalignment angle of HAT-P-22 b, ψ = 24° ± 18°. The revision of the physical parameters of the five exoplanetary systems returned values that are fully compatible with those existing in the literature. The exception to this is the WASP-60 system, for which, based on higher quality spectroscopic and photometric data, we found a more massive and younger star and a larger and hotter planet.

The radii of giant planets, as measured from transit observations, may vary with wavelength due to Rayleigh scattering or variations in opacity. Such an effect is predicted to be large enough to detect using ground‐based observations at multiple wavelengths. We present the defocused photometry of a transit in the HAT‐P‐5 system, obtained simultaneously through Strömgren u, Gunn g and r, and Johnson I filters. Two more transit events were observed through a Gunn r filter. We detect a substantially larger planetary radius in u, but the effect is greater than predicted using theoretical model atmospheres of gaseous planets. This phenomenon is most likely to be due to systematic errors present in the u‐band photometry, stemming from variations in the transparency of Earth’s atmosphere at these short wavelengths. We use our data to calculate an improved orbital ephemeris and to refine the measured physical properties of the system. The planet HAT‐P‐5 b has a mass of and a radius of (statistical and systematic errors, respectively), making it slightly larger than expected according to standard models of coreless gas‐giant planets. Its equilibrium temperature of 1517 ± 29 K is within 60 K of that of the extensively studied planet HD 209458 b.

We present seventeen high-precision light curves of five transits of the planet Qatar-2 b, obtained from four defocussed 2m-class telescopes. Three of the transits were observed simultaneously in the SDSS g ′ r ′ i ′ z ′ passbands using the seven-beam GROND imager on the MPG/ESO 2.2-m telescope. A fourth was observed simultaneously in Gunn grz using the CAHA 2.2-m telescope with BUSCA, and in r using the Cassini 1.52-m telescope. Every light curve shows small anomalies due to the passage of the planetary shadow over a cool spot on the surface of the host star. We fit the light curves with the prism+gemc model to obtain the photometric parameters of the system and the position, size and contrast of each spot. We use these photometric parameters and published spectroscopic measurements to obtain the physical properties of the system to high precision, finding a larger radius and lower density for both star and planet than previously thought. By tracking the change in position of one starspot between two transit observations we measure the orbital obliquity of Qatar-2 b to be λ = 4.3• ± 4.5• , strongly indicating an alignment of the stellar spin with the orbit of the planet. We calculate the rotation period and velocity of the cool host star to be 11.4 ± 0.5 d and 3.28 ± 0.13 km s −1 at a colatitude of 74• . We assemble the planet's transmission spectrum over the 386-976 nm wavelength range and search for variations of the measured radius of Qatar-2 b as a function of wavelength. Our analysis highlights a possible H 2 /He Rayleigh scattering in the blue.