A hot Jupiter transiting the m⁢v⁢=7.6 A-star HD 185603

In this paper we present MASCARA-2 b, a hot Jupiter transiting the m(v) = 7.6 A2 star HD 185603. Since early 2015, MASCARA has taken more than 1.6 million flux measurements of the star, corresponding to a total of almost 3000 h of observations, revealing a periodic dimming in the flux with a depth of 1.3%. Photometric follow-up observations were performed with the NITES and IAC80 telescopes and spectroscopic measurements were obtained with the Hertzsprung SONG telescope. We find MASCARA-2 b orbits HD 185603 with a period of 3.474119(-0.000006)(+0.000005) days at a distance of 0.057 +/- 0.006 au, has a radius of 1.83 +/- 0.07 R-J and place a 99% upper limit on the mass of <17 M-J. HD 185603 is a rapidly rotating early-type star with an effective temperature of 8980(-130)(+90) K and a mass and radius of 1.89(-0.05)(+0.06) M-circle dot, 1.60 +/- 0.06 R-circle dot, respectively. Contrary to most other hot Jupiters transiting early-type stars, the projected planet orbital axis and stellar spin axis are found to be aligned with lambda = 0.6 +/- 4 degrees. The brightness of the host star and the high equilibrium temperature, 2260 +/- 50 K, of MASCARA-2 b make it a suitable target for atmospheric studies from the ground and space. Of particular interest is the detection of TiO, which has recently been detected in the similarly hot planets WASP-33 b and WASP-19 b.