Beyond the Kepler/K2 bright limit: variability in the seven brightest members of the Pleiades

Abstract

The most powerful tests of stellar models come from the brightest stars in\nthe sky, for which complementary techniques, such as astrometry,\nasteroseismology, spectroscopy, and interferometry can be combined. The K2\nMission is providing a unique opportunity to obtain high-precision photometric\ntime series for bright stars along the ecliptic. However, bright targets\nrequire a large number of pixels to capture the entirety of the stellar flux,\nand bandwidth restrictions limit the number and brightness of stars that can be\nobserved. To overcome this, we have developed a new photometric technique, that\nwe call halo photometry, to observe very bright stars using a limited number of\npixels. Halo photometry is simple, fast and does not require extensive pixel\nallocation, and will allow us to use K2 and other photometric missions, such as\nTESS, to observe very bright stars for asteroseismology and to search for\ntransiting exoplanets. We apply this method to the seven brightest stars in the\nPleiades open cluster. Each star exhibits variability; six of the stars show\nwhat are most-likely slowly pulsating B-star (SPB) pulsations, with amplitudes\nranging from 20 to 2000 ppm. For the star Maia, we demonstrate the utility of\ncombining K2 photometry with spectroscopy and interferometry to show that it is\nnot a 'Maia variable', and to establish that its variability is caused by\nrotational modulation of a large chemical spot on a 10 d time scale.\n