A low-density hot Jupiter in a near-aligned, 4.5-day orbit around a $V$ = 10.8, F5V star


Abstract in English

We report the independent discovery and characterisation of a hot Jupiter in a 4.5-d, transiting orbit around the star TYC 7282-1298-1 ($V$ = 10.8, F5V). The planet has been pursued by the NGTS team as NGTS-2b and by ourselves as WASP-179b. We characterised the system using a combination of photometry from WASP-South and TRAPPIST-South, and spectra from CORALIE (around the orbit) and HARPS (through the transit). We find the planets orbit to be nearly aligned with its stars spin. From a detection of the Rossiter-McLaughlin effect, we measure a projected stellar obliquity of $lambda = -19 pm 6^circ$. From line-profile tomography of the same spectra, we measure $lambda = -11 pm 5^circ$. We find the planet to have a low density ($M_{rm P}$ = 0.67 $pm$ 0.09 $M_{rm Jup}$, $R_{rm P}$ = 1.54 $pm$ 0.06 $R_{rm Jup}$), which, along with its moderately bright host star, makes it a good target for transmission spectroscopy. We find a lower stellar mass ($M_*$ = $1.30 pm 0.07$ $M_odot$) than reported by the NGTS team ($M_*$ = $1.64 pm 0.21$ $M_odot$), though the difference is only $1.5$ $sigma$.

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