Zodiacal Exoplanets in Time (ZEIT) XII: A Directly-Imaged Planetary-Mass
  Companion to a Young Taurus M Dwarf Star
  We report the discovery of a resolved (0".9) substellar companion to a member
of the 1-5 Myr Taurus star-forming region. The host star (2M0437) is a single
mid-M type ($T_{eff}\approx$3100K) dwarf with a position, space motion, and
color-magnitude that support Taurus membership, and possible affiliation with a
$\sim$2.5 Myr-old sub-group. A comparison with stellar models suggests a 2-5
Myr age and a mass of 0.15-0.18M$_{\odot}$. Although K2 detected quasi-periodic
dimming from close-in circumstellar dust, the star lacks detectable excess
infrared emission from a circumstellar disk and its H$\alpha$ emission is not
commensurate with accretion. Astrometry based on three years of AO imaging
shows that the companion (2M0437b) is co-moving, while photometry of two other
sources at larger separation indicates they are likely heavily-reddened
background stars. A comparison of the luminosity of 2M0437b with models
suggests a mass of 3-5$M_{\rm jup}$, well below the deuterium burning limit,
and an effective temperature of 1400-1500K, characteristic of a late L spectral
type. The $H$-$K$ color is redder than the typical L dwarf, but comparable to
other directly detected young planets, e.g. those around HR 8799. The discovery
of a super-Jupiter around a very young, very low mass star challenges models of
planet formation by either core accretion (which requires time) or disk
instability (which requires mass). We also detected a second, co-moving,
widely-separated (75") object which appears to be a heavily-extincted star.
This is certainly a fellow member of this Taurus sub-group and statistically
likely to be a bound companion.
