Using the Spitzer Space Telescope , we observed a transit at 3.6 \mu m of KELT-11b ( 37 ) .
We also observed three partial planetary transits from the ground .
We simultaneously fit these observations , ground-based photometry from ( 37 ) , radial velocity data from ( 37 ) , and an SED model utilizing catalog magnitudes and the Hipparcos parallax to the system .
The only significant difference between our results and ( 37 ) is that we find the orbital period is shorter by 37 seconds , 4.73610 \pm 0.00003 vs . 4.73653 \pm 0.00006 days , and we measure a transit center time of { { BJD _ { TDB } } } 2457483.4310 \pm 0.0007 , which is 42 minutes earlier than predicted .
Using our new photometry , we precisely measure the density of the star KELT-11 to 4 % .
By combining the parallax and catalog magnitudes of the system , we are able to measure KELT-11b ’ s radius essentially empirically .
Coupled with the stellar density , this gives a parallactic mass and radius of 1.8 { M } _ { \sun } and 2.9 { R } _ { \sun } , which are each approximately 1 \sigma higher than the adopted model-estimated mass and radius .
If we conduct the same fit using the expected parallax uncertainty from the final Gaia data release , this difference increases to 4 \sigma .
The differences between the model and parallactic masses and radii for KELT-11 demonstrate the role that precise Gaia parallaxes , coupled with simultaneous photometric , RV , and SED fitting , can play in determining stellar and planetary parameters .
With high precision photometry of transiting planets and high precision Gaia parallaxes , the parallactic mass and radius uncertainties of stars become 1 % and 3 % , respectively .
TESS is expected to discover 60 to 80 systems where these measurements will be possible .
These parallactic mass and radius measurements have uncertainties small enough that they may provide observational input into the stellar models themselves .