The ultra-hot-Jupiter KELT-16 b: Dynamical Evolution and Atmospheric Properties.

We present broad-band photometry of 28 planetary transits of the transiting ultra-hot Jupiter KELT-16 b, using five medium-class telescopes and employing the telescope-defocusing technique. The transits were monitored through standard $B,V,R,I$ filters and four were simultaneously observed from different places, for a total of 34 new light curves. We used these new photometric data and those from the TESS space telescope to review the main physical properties of the KELT-16 planetary system. Our results agree with previous measurements but are more precise. We estimated the mid-transit times for each of these transits and combined them with others from the literature to obtain 69 epochs, with a time baseline extending over more than four years, and searched for transit time variations. We found no evidence for a period change, suggesting a lower limit for orbital decay at 2 Myr, with a lower limit on the reduced tidal quality factor of $Q^{\prime}_{\star}>(2.2 \pm 0.4) \times 10^5$ with $95\%$ confidence. We built up an observational, low-resolution transmission spectrum of the planet, finding evidence of the presence of optical absorbers, although with a low significance. Using TESS data, we reconstructed the phase curve finding that KELT-16 b has a phase offset of $ 25.25 \pm 14.03$ $^{\circ}$E, a day- and night-side brightness temperature of $3190 \pm 61$ K and $2668 \pm 56$ K, respectively. Finally, we compared the flux ratio of the planet over its star at the TESS and Spitzer wavelengths with theoretical emission spectra, finding evidence of a temperature inversion in the planet's atmosphere, the chemical composition of which is preferably oxygen-rich rather than carbon.