Confirmation and characterization of the protoplanet HD100546 b - Direct evidence for gas giant planet formation at 50 au

Abstract

We present the first multi-wavelength, high-contrast imaging study confirming the protoplanet embedded in the disk around the Herbig Ae/Be star HD100546. The object is detected at $L^{\prime }$ ($\sim 3.8\hat{I}¼m$) and $M^{\prime }$ ($\sim 4.8\hat{I}¼m$), but not at $K_s$ ($\sim 2.1\hat{I}¼m$), and the emission consists of a point source component surrounded by spatially resolved emission. For the point source component we derive apparent magnitudes of $L^{\prime }=13.92\pm 0.10$ mag, $M^{\prime }=13.33\pm 0.16$ mag, and $K_s>15.43\pm 0.11$ mag (3$\ddot{I}ƒ$ limit), and a separation and position angle of $(0.457\pm 0.014)"$ and $(8.4\pm 1.4{)}^{\circ }$, and $(0.472\pm 0.014)"$ and $(9.2\pm 1.4{)}^{\circ }$ in $L^{\prime }$ and $M^{\prime }$, respectively. We demonstrate that the object is co-moving with HD100546 and can reject any (sub-)stellar fore-/background object. Fitting a single temperature blackbody to the observed fluxes of the point source component yields an effective temperature of $T_{eff}=932_{-202}^{+193}$ K and a radius for the emitting area of $R=6.9_{-2.9}^{+2.7}$ R${}_{\mathrm{Jupiter}}$. The best-fit luminosity is $L=(2.3_{-0.4}^{+0.6})\cdot 10^{-4}{L}_{\mathrm{Sun}}$. We quantitatively compare our findings with predictions from evolutionary and atmospheric models for young, gas giant planets, discuss the possible existence of a warm, circumplanetary disk, and note that the de-projected physical separation from the host star of $(53\pm 2)$ au poses a challenge standard planet formation theories. Considering the suspected existence of an additional planet orbiting at $\sim$13--14 au, HD100546 appears to be an unprecedented laboratory to study the formation of multiple gas giant planets empirically.

Accepted for publication in ApJ; 13 pages incl. 9 figures, 2 tables and references in ApJ-style