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

TL;DR

This paper reports the discovery and detailed characterization of a low-density hot Jupiter orbiting a bright F5V star with a nearly aligned orbit, using multiple observational techniques including photometry and spectroscopy.

Contribution

It provides the first independent confirmation and detailed orbital and physical characterization of the hot Jupiter around TYC 7282-1298-1, including measurements of its orbit alignment and stellar properties.

Findings

The planet has a low density with mass 0.67 M_Jup and radius 1.54 R_Jup.

The orbit is nearly aligned with the star's spin, with a projected obliquity of about -19 degrees.

The host star's mass is estimated at 1.30 M_sun, slightly lower than previous reports.

Abstract

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 planet's orbit to be nearly aligned with its star's 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 $1.5$ $\sigma$.